EPA/600/R-97/066
July 1997
PHASE I
PILOT AIR CONVEYANCE SYSTEM DESIGN, CLEANING,
AND CHARACTERIZATION
by
Douglas W. VanOsdell and Karin K. Foarde
Center for Engineering and Environmental Technology
Research Triangle Institute
Research Triangle Park, NC 27709
EPA Cooperative Agreement CR822870-0-1 .
and
Roy Fortmann
Acurex Environmental Corporation
Research Triangle Park, NC 27709
EPA Contract 68-D4-0005 WA 2-030
EPA Project Officer: Russell N. Kulp
U. S. Environmental Protection Agency
National Risk Management Research Laboratory
Air Pollution Prevention and Control Division
Research Triangle Park, NC 27711
Prepared for:
U.S. Environmental Protection Agency
Office of Research and Development
Washington, DC 20460
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TECHNICAL REPORT DATA ... ......
(Please read Instructions on the reverse before compi II Ml 1 III 11 III 1II III
1. REPORT NO. 2.
EPA-600/R-97-066
3 iii mi ii man iiin linn 111
PB97-189682
4. TITLE AND SUBTITLE
Phase I Pilot Air Conveyance System Design, Clean-
ing, and Characterization
5. REPORT DATE
July 1997
6. PERFORMING ORGANIZATION CODE
7.author(s)D>w> Van0sdell andK.K.Foarde (RTI), and
R. F or tm ann (A cur ex)
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Research Triangle Institute, P. 0. Box 12194, Research
Triangle Park, NC 27709
Acurex Environmental Corporation, P. O. Box 13109,
Research Triangle Park, NC 27709
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
CR822870-0-1 (RTI)
68-D4-0005T2-303 (Acurex)
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Air Pollution Prevention and Control Division
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PERIOD COVERED
Final;
14. SPONSORING AGENCY CODE
EPA/600/13
15.supplementary notes APPCD project officer is Russell N.Kulp, Mail Drop 54, 919/541-
7980.
i6. abstractrep0rt gives results of a project to develop and refine surface and air-
borne contamination measurement techniques that can be used to evaluate air convey-
ance system (ACS) cleaning. (NOTE: ACS cleaning is advertized to homeowners as a
service having a number of benefits, including the improvement of indoor air quality.
Because ACS cleaning includes many procedures applied to many different duct sys-
tems, evaluation has been difficult, and the effectiveness of ACS cleaning has not
been adequately measured.) The research was in support of a field study to be con-
ducted later. To this end, a pilot air conveyance system (PACS), using full-size
residential heating and air-conditioning (HAC) equipment, was constructed and oper-
ated to provide a controlled, artificially soiled, ACS environment. The PACS consis-
ted of ducts, an HAC unit, a dust mixing room, and instrument room, and a dust
generation and injection system. Three types of duct systems were evaluated with the
proposed measurement methods under soiled and unsoiled conditions. Each duct sys-
tem was then cleaned by professional ACS cleaners and reevaluated. Asa result of
the pilot study, the surface contamination measurement methods were evaluated over
a range of conditions and improved. The significance of acquired results in an actual
residence was not determined.
17. KEY WORDS AND DOCUMENT ANALYSIS
a. DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Pollution Particles
Measurement
Ducts
Heating Equipment
Air Conditioning Equipment
Dust
Pollution Control
Stationary Sources
Air Conveyance Systems
Indoor Air Quality
Heating and Air-Condi-
tioning (HAC) Systems
13 B
14G
13K
13 A
UG
T8. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS (ThisReport)
Unclassified
21. NO. OF PAGFS
82
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
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NOTICE
This document has been reviewed in accordance with U.S.
Environmental Protection Agency policy and approved for publication.
Mention of trade names or commercial products does not constitute
endorsement or recommendation for use.
ii
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FOREWORD
The U. S. Environmental Protection Agency is charged by Congress with pro-
tecting the Nation's land, air, and water resources. Under a mandate of national
environmental laws, the Agency strives to formulate and implement actions lead-
ing to a compatible balance between human activities and the ability of natural
systems to support and nurture life. To meet this mandate, EPA's research
program is providing data and technical support for solving environmental pro-
blems today and building a science knowledge base necessary to manage our eco-
logical resources wisely, understand how pollutants affect our health, and pre-
vent or reduce environmental risks in the future.
The National Risk Management Research Laboratory is the Agency's center for
investigation of technological and management approaches for reducing risks
from threats to human health and the environment. The focus of the Laboratory's
research program is on methods for the prevention and control of pollution to air,
land, water, and subsurface resources; protection of water quality in public water
systems; remediation of contaminated sites and groundwater; and prevention and
control of indoor air pollution. The goal of this research effort is to catalyze
development and implementation of innovative, cost-effective environmental
technologies; develop scientific and engineering information needed by EPA to
support regulatory and policy decisions; and provide technical support and infor-
mation transfer to ensure effective implementation of environmental regulations
and strategies.
This publication has been produced as part of the Laboratory's strategic long-
term research plan. It is published and made available by EPA's Office of Re-
search and Development to assist the user community and to link researchers
with their clients.
E. Timothy Oppelt, Director
National Risk Management Research Laboratory
i i i
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ABSTRACT
Air conveyance system (ACS) cleaning is advertised to home owners as a service having
a number of benefits, including the improvement of indoor air quality. Because ACS cleaning
includes many procedures applied to many different duct systems, evaluation of these claims has
been difficult and the effectiveness of ACS cleaning has not been adequately measured.
The objective of this project was to develop and refine surface and airborne
contamination measurement techniques that could be used to evaluate ACS cleaning. The
research was in support of a field study to be conducted later. To this end, a pilot air conveyance
system (PACS) using full-size residential heating and air conditioning (HAC) equipment was
constructed and operated to provide a controlled, artificially-soiled, ACS environment. The
PACS consisted of ducts, an HAC unit, a dust/mixing room, an instrument room, and a dust
generation and injection system. Each of three types of duct systems was evaluated with the
proposed measurement methods when new, soiled by injecting previously collected duct dust,
cleaned by professional ACS cleaners, then evaluated again.
As a result of the pilot study, the ACS cleaning evaluation measurement methods were
applied over a range of conditions and improved. Surface contamination (microbial and total
dust) measurement methods and visual inspection showed that the pilot unit was effectively
cleaned by the ACS cleaning methods applied during this study. Submicron and larger particle
counts were reduced following ACS cleaning and respirable particle mass was reduced for two of
the three duct systems. The significance of these results in an actual residence was not
determined.
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Table of Contents
Section Page
1.0 INTRODUCTION 1
1.1 Background and Overview 1
1.2 Objectives 3
1.3 Phase I Project Activities 3
2.0 SUMMARY AND CONCLUSIONS 5
3.0 RECOMMENDATIONS 9
4.0 APPARATUS AND METHODS 11
4.1 System Design, Specification, and Construction 11
4.1.1 Pilot Air Conveyance System Design Concept 11
4.1.2 Duct Systems 13
4.1.3 Air Handling Unit 15
4.1.4 Dust Mixing Room 16
4.1.5 Instrument Room 17
4.1.6 Dust Generation System 18
4.1.7 HVAC Instrumentation 20
4.2 PACS Checkout 21
4.3 PACS Operation 22
5.0 EXPERIMENTAL PROCEDURES 23
5.1 Overview 23
5.2 Sampling and Measurement Procedures 23
5.2.1 Duct Dust Surface Mass Sampling 25
5.2.2 PM10 and PM25 Particle Mass Measurements 27
5.2.3 Particle Concentration Measurements - Laser Particle Counter 28
5.2.4 Particle Concentration Measurements - Laser Aerosol Spectrometer ... 28
5.2.5 Fiber Monitoring and Sampling Methods 29
5.2.6 Microbial Surface Sampling 30
5.2.7 Bioaerosol Sampling 31
5.3 Test Protocol 31
5.3.1 Dust Injection and Deposition 32
5.3.2 Application of the Test Methods in the PACS 33
5.4 Air Conveyance System Cleaning Operations Applied in the PACS 34
5.4.1 Operations Applied to All Systems 34
5.4.2 Galvanized Steel Duct 35
5.4.3 Fibrous Glass Lined Duct 36
5.4.4 Fiberglass Duct Board System 36
6. RESULTS AND DISCUSSION 37
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6.1 Pilot Ventilation System Operation 37
6.2 Surface Deposit Measurements 37
6.2.1 Gravimetric Duct Dust Measurement Results 37
6.2.2 Microbiological Surface Samples 51
6.3 Aerosol Measurements 55
6.3.1 PM10 and PM2 5 Particle Mass Measurements 55
6.3.2 Particle Concentrations - Optical Particle Counter 56
6.3.3 Particle Concentrations - Multi-Channel Spectrometer 65
6.3.4 Fiber Concentrations 66
6.3.5 Bioaerosols 67
7.0 QUALITY ASSURANCE/QUALITY CONTROL 70
7.1 Quality Control 70
7.1.1 Environmental Instrumentation 70
7.1.2 Dust Mass Sample QC 71
7.1.3 Microbiological Duct Sample QC 72
7.1.4 Microbial Aerosol QC 72
7.1.5 Aerosol Measurement QC 73
7.2 Method Performance 73
7.3 Data Completeness 74
8. REFERENCES 75
List of Tables
Caption Page
Table 1. PACS Design Parameters 13
Table 2. Measurement Parameters and Methods 24
Table 3. Test Matrix 31
Table 4. Measurement Schedule 34
Table 5. Dust Levels in the Galvanized Duct System Prior to Cleaning 39
Table 6. Dust Levels in the Galvanized Duct System After Cleaning 40
Table 7. Background Dust Levels from the Surfaces in the FDL System Prior to Soiling
43
Table 8. Dust Levels in the Fibrous Glass Duct Liner System Prior to Cleaning 44
Table 9. Dust Levels in the FDL System After Cleaning 45
Table 10. Dust Levels in the FDB System Prior to Cleaning 47
Table 11. Dust Levels in the FDB System After Cleaning 48
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Table 12. Microbial Results for Galvanized Steel in cfu/cm2 52
Table 13. Microbial Results for FDL in cfu/cm2 53
Table 14. Microbial Results for FDB in cfu/cm2 54
Table 15. Comparison of PM10 and PM25 Integrated Air Samples and Concurrent Optical
Particle Measurements in the Instrument Room 55
Table 16. Average Particle Concentrations (particles X 106/m3) Measured with Climet
During Pre- and Post-Cleaning Periods in the Three Tests 64
Table 17. Average Particle Concentrations Measured With the LAS-X in the
Instrumentation Room (Particles X 106/m3) 66
Table 18. Airborne Fungal Concentrations for Galvanized Steel Duct in cfu/m3 68
Table 19. Airborne Fungal Data for FDL and FDB Systems, cfu/m3 68
Table 20. Data Quality Indicator Goals 71
List of Figures
Caption Page
Figure 1. Schematic showing PACS operational modes 12
Figure 2. Elevation of PACS showing features of duct systems 14
Figure 3. Interior elevation of PACS showing construction detail 17
Figure 4. Airborne particle concentrations in the > 0.5 |im size fraction during the test with
the galvanized steel duct system 58
Figure 5. Airborne particle concentrations in the >5.0 (am size fraction during the test with
the galvanized duct system 59
Figure 6. Airborne particle concentrations in the > 0.5 |um size fraction during the test with
the fibrous duct liner system 60
Figure 7. Airborne particle concentrations in the > 5.0 |im size fraction during the test with
the fibrous duct liner system 61
Figure 8. Airborne particle concentrations in the > 0.5 |im size fraction during the test with
the FDB system 62
Figure 9. Airborne particle concentrations in the > 5.0 |im size fraction during the test with
the FDB system 63
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1.0 INTRODUCTION
1.1 Background and Overview
Commonly referred to as "duct cleaning", ACS cleaning is advertised to homeowners as a
service capable of preventing and possibly mitigating indoor air quality (IAQ) problems as well
as improving system efficiency. It is a broadly defined service, with a wide range of cleaning
apparatus used by different contractors and different parts of the system cleaned using different
equipment. ACS cleaning includes the cleaning of all air-side components of a ventilation
system: air handler, heat exchanger, humidifier, blower, and duct system (NADCA, 1992).
Many combinations of cleaning procedures could be used on any given system and there are
many types of systems. In general, residential ACS cleaning is intended to remove solid material
and is not specifically directed at condensed or adsorbed gases. Following cleaning, ACS
cleaning contractors may also coat the internal surfaces of damaged or biocontaminated fibrous
insulation with aftermarket polymeric coatings as part of their service, and may also treat the
ACS with biocides. Because the use of coatings and biocides on biocontaminated duct materials
has not been tested and is not recommended (EPA, 1991), neither were evaluated during this
research project.
The effectiveness of ACS cleaning could be evaluated in a number of ways: visually by
inspection, measurement of residual dust using various measures, measurement of indoor air
quality improvement following ACS cleaning, and measurement of improvements in air flow and
energy efficiency. Visual inspection has shown that ACS cleaning generally removes substantial
fractions of the dust in an ACS. The only published residual dust measurement method is that of
NADCA Standard 1992-01, used to evaluate nonporous surfaces. By this definition, an
adequately cleaned surface is visibly clean and when sampled following Standard 1992-01, is
found to retain less than < 1 mg debris collected/100 cm2 (0.1 g/m2). There is no analogous
standard for porous surfaces. Initial development of the surface sampling methods included a
literature review and the development of several alternative sampling techniques, only the best of
which were tested and further developed during the pilot unit research.
Adequate published research data are not available to support the IAQ improvement
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claims sometimes attributed to ACS cleaning contractors, and the data that are available are
difficult to interpret. Ahmad, Tansel, and Mitrani (1994) found a reduction in total super-
micrometer particles (measured with an optical particle counter) and in bioaerosol concentrations
following ACS cleaning, but no change in submicrometer particle concentrations. Particle
concentrations in the homes were found to be higher during cleaning than before or after. The
authors felt that their study was not general enough to justify broadly applicable conclusions, and
recommended that their results be considered as case studies. Fugler and Auger (1994) found
that cleaning did not impact the levels of circulating dust in residences and, in at least one
instance, a dust cloud was liberated after cleaning.
ACS cleaning, at least for relatively dirty ventilation systems, is thought to improve the
energy efficiency of HVAC systems (Carl and Smilie, 1991). Again, few data are available and
some conflicting reports have been published. Fugler and Auger (1994) reported finding no
improvement in fan pressure drop or duct flow rate. Fellman (1994) points out some limitations
of the work reported by Fugler and Auger.
A research program was undertaken by the U.S. EPA to investigate the application of
ACS cleaning to residences. The overall research program included separate, coordinated
projects conducted by the Research Triangle Institute (RTI) and Acurex Environmental
Corporation (Acurex), with ACS cleaning support being provided by the National Air Duct
Cleaners Association (NADCA). In addition, program review and comments were provided by
the North American Insulation Manufacturers Association (NAIMA) and the American Society
for Cleaning and Restoration (ASCR). The overall research program includes the following:
Phase I: Pilot Air Conveyance System Design, Characterization, and Operation to
develop test methods for field evaluation of ACS cleaning with respect to both
cleanliness on the ducts and ventilation surfaces and the IAQ in the building being
studied; and
Phase n. Field Investigation of ACS Cleaning in 9 local residences as a pilot study to
evaluate ACS cleaning and its effect on residential IAQ, and energy usage.
This report covers Phase I, PACS development, characterization, and operation, and the results of
Phase II of the research are reported by Fortmann et al. (1996).
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1.2 Objectives
The overall objectives of the Air Pollution Prevention and Control Division's (APPCD)
Air Duct Cleaning Program are to determine when and how to clean ACS, evaluate how effective
such cleaning is, and determine the impact of ACS cleaning on indoor air quality. A two-phase
research program was undertaken to develop evaluation methods to achieve these objectives.
First, a pilot study (Phase I) was used to develop the measurement methods. The specific
objectives of Phase I were to develop and operate a PACS as a test bed suitable for the
application of ACS cleaning to allow:
• Development and testing of proposed ACS cleaning evaluation methods, and
• Comparison of indoor air quality (IAQ) instrumentation, intended for use in the
field, under controlled conditions that were also as realistic as possible.
Data obtained in the pilot system were used to develop ACS cleaning field evaluation
methods and helped the interpretation of the results obtained during a field study (Phase II),
which was undertaken as a pilot study to evaluate ACS cleaning in actual field use.
1.3 Phase I Project Activities
The Phase I research was a cooperative effort, led by RTI, with participation by personnel
from APPCD/EPA, Acurex, and air duct cleaning professional organizations (NADCA and
ASCR.) The initial project activity was review of a conceptual design by all participant at
several workshops. This process resulted in the selection of 3 duct materials and associated
construction techniques that were to be studied during Phase I: bare galvanized sheet metal,
sheet metal with fibrous glass duct liner (FDL), and fiberglass duct board (FDB). In the opinion
of the participants, these are the 3 principal duct materials used in the United States.
The PACS was constructed at RTI and checked-out in early December 1995. The
workplan contemplated conducting the research over several months, while the actual research
period was only about 1 month from beginning the first duct cleaning operation to completion of
the third duct system test. This occurred because the research was a cooperative effort that
included contributions from EPA, Acurex, and NADCA as well as RTI, and the EPA furloughs
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that occurred in late 1995 and early 1996 delayed the project start and compressed the schedule.
In the end, all measurements and duct cleaning were conducted on the PACS between April 22,
1996 and May 24, 1996. This schedule compression did not adversely affect the overall research
program, but did prevent some non-critical measurements from being taken as the duct systems
were changed-out, soiled, and conditioned over short time spans.
The Phase I project described in this report included the following activities:
• Work/QA Plan Preparation
• PACS Design
• Design Review
• Equipment Specification
• Construction
• Checkout, and
• PACS Operation
• Field Method Development
The research results are summarized and conclusions drawn in Section 2 of this report.
Recommendations are given in Section 3. Section 4 provides a description of the experimental
apparatus and methods, and Section 5 describes the experimental procedures used to conduct the
research. Section 6 contains a presentation and detailed discussion of the results, and Section 7 a
discussion of project data quality assurance. References are provided in Section 8.
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2.0 SUMMARY AND CONCLUSIONS
Overall, the PACS was successful as a test bed for sampling method development. That
is, dust could be injected, conditioned, and the system cleaned such that the PACS was a
reasonable laboratory surrogate for a residential ACS. Operated for only short periods, as was
true of this work, it was not suitable for biocontaminant studies because active growth was not
present. Specific conclusions from this research are summarized below:
1. Previously collected duct dust can be mechanically dispersed into a duct system and
conditioned at high humidity to provide a realistic challenge to conventional ACS
cleaning techniques. The dust deposit was clearly artificial, but, in the opinion of
experienced ACS cleaning practitioners, had a reasonable distribution in the duct system
and adhesion to the duct walls.
2. A pilot ventilation system can be used to investigate some aspects of ACS cleaning under
controlled conditions and provide results that may be applicable to field ACS cleaning.
3. The medium volume dust sampler (MVDS), when fitted with a brush on the nozzle, was
shown to be suitable for collection of dust from bare galvanized steel, FDL, and foil liner
surfaces of ACS components. Conditioned dust could not be effectively removed with
the nozzle only. Collection efficiency of the MVDS with the brush was higher than the
MVDS with a slotted nozzle or the NADCA Vacuum Test Method.
4. Neither the MVDS with the slotted nozzle nor with the brush were suitable for collection
of dust from FDB. The brush dislodged a substantial amount of fibrous material from
new FDB. The nozzle did not effectively remove dust deposited on the fibrous surface.
Accurate measurements of dust on FDB surfaces can not be made with the vacuum
methods used in this study.
5. Dust loading on bare galvanized steel duct surfaces that were cleaned were less than 0.02
g/m2 (0.2 mg/100 cm2) when measured with the NADCA Vacuum Test Method, meeting
the NADCA Standard 1992-01 criterion for verifying cleaning effectiveness. Collocated
measurements with the MVDS-brush were 0.26, 0.37, and 0.36 g/m2 at the three
locations. The mass loadings were 26, 37, and 18 times higher than the NADCA results,
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demonstrating the low collection efficiency of the NADCA Vacuum Test method.
Overall, microbial contamination was low in the PACS because no active growth was
taking place. For microbial sampling of dust deposited on the surface of various fibrous
glass and galvanized metal surfaces, the vacuum method provided more consistently
reliable results that the surface swab technique. It was particularly superior on the fibrous
materials.
Measurements of dust levels on surfaces of various ACS components at multiple
locations demonstrated that the deposition of dust in the system was highly variable.
Deposition patterns varied between the three systems. The highest deposits in the supply
ducts occurred in the bare galvanized duct system.
The amount of dust measured on new ACS components prior to soiling in the PACS was
comparable to post-cleaning measurement results. That is, background dust levels on
"clean" FDL, flexible duct surfaces, the foil liner in the air handler, and the cooling coil
were similar to the amount of residual dust that could be collected after ACS cleaning.
The amount of residual dust collected with the MVDS-brush from galvanized steel duct,
FDL, flexible duct, foil liner, and cooling coil surfaces after cleaning ranged from 0.14 to
0.49 g/m2 (1.4 to 4.9 mg/100 cm2). Visually, this level of dust deposit on the surface
appeared as a thin film of dust. These results suggest that the criterion for determining
that surfaces have been effectively cleaned (in a manner comparable to NADCA 1992-01)
should be about 0.5 g/m2 when an efficient sampling method is used.
Both the results of the post-cleaning dust sampling and visual inspection indicated that
the ACS components could be cleaned effectively by the methods used in this study.
Concentrations of airborne particles in the > 0.5 (am size fraction measured with a laser
particle monitor were lower in the instrumentation room after ACS cleaning for all 3
systems tested. This may have been caused by the ACS cleaning, but may also have been
caused by changes in the particle concentrations of the infiltrating air from outside the
PACS. The decrease was not large, in any case.
Average PM2 5 and PM10 mass levels in 24-hr integrated samples ranged from 1.7 to 11.8
|jg/m3 in the instrumentation room during these tests. In the tests with the galvanized
steel duct and FDB systems, PM2 5 and PMI0 concentrations were lower after ACS
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cleaning. Because of a large variation in the particle concentrations in the
instrumentation room prior to cleaning of the FDL system, collection of a single
integrated sample prior to cleaning would likely result in an incorrect assessment of the
impact of ACS cleaning on indoor air quality. The tests demonstrated the importance of
collecting multiple integrated samples and the need to measure particle concentrations for
extended pre- and post-cleaning periods.
13. Fibers were not detected at levels greater than 0.001 fiber/cm3 in air samples collected in
the instrumentation room during tests with bare galvanized steel duct, FDL, or FDB.
Fibers also were not detected with a Fibrous Aerosol Monitor operated during the first
two tests.
14. A brief pulse of particles was released when the galvanized ACS was brought back in
service following cleaning. This phenomenon was detected by both the bioaerosol and
optical particle samplers. For the bioaerosol sampler in the galvanized ACS, about 80%
of the total bioaerosol was sampled in the first 15 minutes of the hour-long test and about
2% in the final 15 minutes. The optical particle counters detected an hours-long pulse of
particles. The other duct systems did not produce a clear pulse when restarted after
cleaning.
15. Results from the tests in the PACS identified problems with the LAS-X Aerosol
Spectrometer data logging hardware that were corrected prior to the field study.
Information was collected during the tests that was used to refine methods and protocols
that were used in the field study.
16. While not a focus of the study, as the research progressed it became apparent that ACS
construction quality was an important variable in both PACS operation and in the
"cleanability" of an ACS. While poor construction practices did not interfere with this
study, which focused on methods development and not measurements, they did affect the
performance of the ACS and the ease and thoroughness with which it could be cleaned.
With regard to the duct itself, the unlined galvanized duct installed in the PACS
had no apparent construction flaws. The butt-joints between sections in the FDL system
had been sprayed with duct liner adhesive but were not sealed with a mastic. A small
piece of liner near the return air inlet was found to be loose when inspected prior to
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cleaning. The cut edges in the FDB system did not appear to be sealed and were not
coated. These construction details, while not in accordance with applicable construction
standards, were flaws that the duct cleaning professionals considered to be very common.
In addition to duct quality shortcomings, the air handler, though it was in "as
received" condition, was not perfectly sealed and coil bypass and leaks occurred at
several points.
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3.0 RECOMMENDATIONS
The following recommendations arise as a result of the research described in this report:
1. The MVDS with brush should be used to sample dust mass deposited on surfaces during
the Phase II field study.
2. Surface microbial contamination on porous materials should be sampled with a vacuum
method rather than a swab method to ensure collection of sample in depth from the
material.
3. If fiberglass duct board ACS cleaning is to be evaluated, a suitable surface sampling
method will need to be developed.
4. NADCA Standard 1992-01 should only be used as intended. For research purposes, a
sampling method comparable to the MVDS with brush should be used with a clean
surface dust mass target of approximately 0.5 g/m2 to verify cleaning effectiveness.
5. Additional research is needed to understand all the parameters involved in obtaining a
suitable ACS dust deposit. This would include both studies of dust in ACS and dust
generation techniques. In this study, dust adhesion was found to be increased through
exposure to high relative humidity (>90%), but the phenomena was not investigated
quantitatively. The dust dispersion technique used during this research should have
provided a reasonable large particle dust source but may have provided fewer small
particles in the challenge than are normally present. However, little information is
available concerning the size and character of the dust circulating in an ACS. In addition,
the amount and distribution of the dust in a residential ACS must be evaluated through a
field study to allow the formation of realistic ACS dust deposits in pilot units.
6. ACS dust properties must be investigated and an more reliable dust source found before
research can be conducted over an extended period. The present work utilized duct dust
from a single area of the country, but the amount available was relatively small and of
unknown variability. Collection and mixing of a very large quantity of duct dust would be
one approach. However, an artificial dust would have many advantages for such a
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research program.
For continued research, the lessons learned from this work should be incorporated into
the study protocols of future field research.
The study of biocontamination in an ACS must be conducted over longer time periods
than were available to the present research so that active microbial growth can become
established in the ACS. Accomplishing this would present some risk of exposure for
those working in the vicinity unless the PACS was redesigned for containment to prevent
exposure, and may be impractical. Such studies are needed, and use of smaller
biocontamination study apparatus is thus recommended.
Biocides, encapsulants, and sealants are all used in residential ACS cleaning in attempts
to control biocontamination without replacing duct work. The usefulness of these
practices and their potential threats to residents have not been determined and should be
investigated.
The instrument room appeared to have potential for indoor air particle instrument
comparison. However, opening the door compromised the fine particle data through
contamination from the laboratory. More useful data could be obtained through remote
data logging and instrument servicing.
Additional study is required to determine whether FDB sheds fibers into the ACS such
that the fibers increase the airborne fiber concentrations indoors. The scope of this
research was too limited to draw conclusions.
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4.0 APPARATUS AND METHODS
4.1 System Design, Specification, and Construction
4.1.1 Pilot Air Conveyance System Design Concept.
4.1.1.1 Overview. To accomplish the project goals, a PACS was developed to allow
artificial soiling of ACS components using a reasonable (defined later) test aerosol. The pilot
system included commercially available components expected to accumulate dust in varying
degrees (e.g. bends, diffusers, registers, grills, blowers, heat exchangers, expansions,
contractions, regions of surface irregularity, and dampers) and was designed to allow application
of all aspects of the proposed evaluation method with the exception of evaluation of IAQ in the
residences, including pre- and post-cleaning inspections and evaluations. The equipment was all
scaled for a small residential air handler at 5.28 kW (1.5 tons) of refrigeration capacity.
To the extent practical, the PACS was constructed of modules to simplify cleaning and
allow substitution of new test components. Standard, commercially-available HAC equipment
was used when possible. The PACS consisted of the following systems: 1) supply and return
ventilation ducts, 2) air handling unit (AHU) including air conditioning coil and heat exchanger,
3) dust mixing room, 4) instrument room, and 5) dust generation system. As shown
schematically in Figure 1, the PACS was operated in two modes:
• normal operation with flow into both rooms, and
• bypass of the instrument room during dust injection.
So that evaluation methods could be developed for the three major duct materials,
completely separate PACS duct systems were constructed of the three duct materials commonly
utilized in residential HAC. A new air handler was installed for each duct type. Each completely
new system was then utilized in the PACS in separate tests as described below.
The laboratory within which the PACS was constructed had a roughly 3.7 m (12 ft)
ceiling height. It was air-conditioned laboratory space maintained at approximately 24 °C (75 °F)
under temperature control and without humidity control. All components of the PACS, including
the air conditioner condenser, were located within the laboratory.
11
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Dust
Mixing Room
X
1
f
Low-
Bypass
velocity
not used
Return
Open
Instrument
Room
Air
Handling
Unit
Normal PACS Operating Mode
f ( f f
IfVlf V
Dust
Mixing Room
L
Low- H Bypass
velocity Y used
Return
Blocked
Instrument
Room
Air
Handling
Unit
PACS Bypass Mode used during Dust Injection
Figure 1. Schematic showing PACS operational modes.
4.1.1.2 Design Reviews. The PACS design was reviewed internally and externally.
Design review meetings with representatives of interested industrial associations were held at
RTI on December 8, 1994 and at EPA on February 13, 1995. A third review with NAIMA was
presented in Washington, DC, on March 3, 1995. A special review to consider fiberglass
materials was held with NAIMA at RTI on April 13, 1996. Ideas presented by the reviewers
were incorporated into the design and the final design parameters for the pilot system are given in
Table 1.
The primary operational goal for the PACS was to achieve an ACS dust deposit that was
a reasonable challenge for residential ACS cleaning systems and that provided a reasonable test
bed of test methods and protocols proposed for the field study. Because residential heating and
12
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Table 1. PACS Design Parameters
Temperature
Thermostat control to 16 to 27 °C (60 - 80 °F) in instrument room.
Relative Humidity
Humidifier output set to hold about 50% in room with AHU on in normal operation.
Room Pressure
Positive to laboratory. Measured in room.
Air Circulation Rate:
As provided by AHU blower [approximately 0.33 m3/s (700 cfm.)]
Infiltration Rate
Limited by tight construction.
AHU Design
Commercial equipment sized for total load of about 5.3 kW (1.5 tons).
Duct System Design
Sized for total flow. Material varied for experimental purposes.
Duct Construction
System 1 - galvanized steel.
System 2 - fibrous glass duct liner in galvanized steel.
System 3 - fiberglass duct board.
All systems were constructed in accordance with SMACNA and NAIMA standards.
Register locations
Included floor, ceiling, and sidewall.
Test Dust
Previously collected ACS dust, re-dispersed for experiment.
air conditioning (HAC) systems vary greatly between installations, accumulate "dirt" over years
of operation while in both heating and cooling modes, and the sources and kinds of duct "dirt"
vary greatly, the PACS may not duplicate actual field conditions but provides a reasonable
representation. Normal operating parameters (temperature, humidity, pressure) of the pilot unit
were not considered critical because they vary greatly in the field. They were maintained within
commonly encountered ranges. As discussed further below, humidity was raised for a
conditioning period to achieve the important goal of an adhering dust deposit.
All the design and experimental discussions and reviews were accumulated in a
Work/QA Plan for the Phase I Research (RTI, 1995), which was transmitted to all participating
and reviewing parties.
4.1.2 Duct Systems
4.1.2.1 Objectives and Design. The duct system was designed so that it could be
constructed by a local air conditioning contractor from commercially available components. The
overall design and duct routing allowed fair access to all the duct and ventilation system
13
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components. As in actual duct systems, some components were more accessible than others so
that the ACS cleaning and the ACS cleaning field evaluation methods could be tested in
physically awkward situations. Though not typical of residential construction, bolted flanges
with foam gaskets were used on the duct sections where possible to give improved access (if
required experimentally) and to reduce assembly/disassembly times.
4.1.2.2 Apparatus. During the test program, the main supply and return trunks of the
PACS duct systems were constructed of:
1) bare galvanized steel with exterior insulation,
2) fibrous glass lined galvanized steel, and
3) fiberglass duct board.
Figure 2 gives an elevation view of the PACS duct systems and sample ports, all of which had
the same inside dimensions and sample location designations. The galvanized steel used was
chosen by the contractor as appropriate for the duct size. It was beaded every 30.5 cm (12 in.) for
strength. The FDL was specified to be the most common material used (as recommended by
NAIMA), which is acrylic polymer faced, 1 in. thick, and has a density of 1.5 lb/ft3. Examples
are CertainTeed Ultralite 150, Owens-Corning Aeroflex Plus 150, or Schuller Permacote
Linacoustic Standard. The choice of material was made by the duct contractor. The FDB used
Supply Air
Temp, RH, & Flow Sensors
Supply Air Sample Locations SI- S4
Suppl> Air Duct
m
Dust Mixing Room
Steam 1 1
Distribution
Hose i i
Air
Handling
Unit
Dust
Feed
Instrument'
Room '
Humidifier 1 1
R3
Return Air Duct R2
R4
S4—
Return Air Sample Locations Rl- R4
Figure 2.
Elevation of PACS showing features of duct systems.
14
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was also the most common variety, known a standard unfaced, 1 in. thick EI-475 material.
Examples are CertainTeed Ultraduct, Knauf Air Duct Board EI-475, Owens-Corning 475 FRK
Fiberglass, or Schuller Microaire 475. Again, the duct contractor chose the particular brand used.
Each return duct had internal dimensions of 30.5 cm high by 20.3 cm wide (12 by 8 in.).
A return air grille was placed at the entry from the mixing room. So the dust in the mixing room
would move throughout the ACS, no return air filter was used. The duct was connected to the
return air plenum at the base of the air handler. All return air ducts had the same internal
dimensions.
At the top of the air handler, the supply trunk duct attached to a flexible connector on the
AHU. Each supply trunk had internal dimensions of 25.4 cm wide by 30.5 cm high (10 by 12
in.) for most of its length, then was reduced to 30.5 cm high by 20.3 cm wide (12 by 8 in.). As
with the return, each of the three duct systems had the same internal dimensions.
All connections to supply registers were made with 15.2 cm (6 in.) diameter flexible duct.
The flexible ducts were attached to the take-off collars and supply registers with a double
mechanical connection using duct ties. Take-offs were sealed to the galvanized ducts with duct
sealant. The FDB system was sealed with tape.
4.1.3 Air Handling Unit
4.1.3.1 Objectives and Design. The design guidelines were for an AHU that was a
commercial unitary system with a direct expansion (DX) coil and heat exchanger installed. New
AHUs were installed for each pilot duct system so any residual dust from a used AHU would not
confound the duct dust measurements. The air conditioner (A/C) evaporator in the AHU was
challenged by the sensible and latent loads provided by the baseboard heaters and humidifier in
the mixing room. No cooling loads were provided to exercise the auxiliary heater that was
installed in the AHU. It was in the air stream only to collect dust and require cleaning.
4.1.3.2 Apparatus. The AHU used was a Heil Model BA3018QK heat pump, which is a
52.8 kW (1.5 ton) refrigeration capacity unit operating at 0.32 m3/s (680 cfm). The fan was
placed in a draw-through position. Within the unit, the rectangular coil, with 6 fins/cm (15
fins/in.) was installed diagonally across the air handler. The AHU was supported about 1 m (3 ft)
-------
above the floor on a angle iron stand and operated in upflow.
4.1.4 Dust Mixing Room
4.1.4.1 Objectives and Design. As shown in Figures 1 and 2, the PACS includes two
rooms - the dust mixing room and the instrument room. The dust mixing room, which was the
only room used while injecting dust, had the following design objectives:
• to serve as the "house" whose ducts had to be cleaned,
• to provide a mixing and settling volume for the test aerosol while soiling the PACS,
• to provide a load for the HAC system, and
• to provide thermal and humidification capacitance to smooth operation.
The dust mixing room contained heaters and a humidifier to provide the sensible and
latent loads for the air conditioning system. They were controlled to cause the A/C to be cycled
by the thermostat 4 to 6 times an hour.
4.2.4.2 Apparatus.
Figure 3 shows interior details of the dust mixing room, which was approximately 2.44 m
high by 2.44 m deep by 3.05 m wide (8 x 8 x 10 ft), with a volume of 18.2 m3 (640 ft3). During
PACS operation, all air from the AHU was passed through the mixing room, so the ventilation
rate in the room was much higher than commonly encountered in individual rooms in
residences. As intended, this high ventilation rate coupled with the mixing fan appeared to
effectively disperse the test aerosol (during loading) and the injected steam from the humidifier.
The room was built with conventional residential construction materials following
construction practices that minimize infiltration. The wall panels were installed with foam tape
behind the seams and the electrical and instrumentation cut-outs were sealed with caulk. The
wall panels were removable to allow design modifications when required.
The heaters were conventional baseboard heaters, each 1.2 m long with a rated maximum
output of approximately 1 kW. They were controlled by individual thermostats on each heater
unit and all three were limited by an overall heater thermostat mounted on the wall of the room.
Additional mixing was provided within the dust mixing room by a ceiling mounted
moisture resistant fan. It was controlled by a speed controller mounted outside the dust mixing
room. The fan was normally on at a medium speed to disperse the steam from the humidifier.
-------
Dust Mixing Room
Blower r
Dust_
Feed
Mixing Fan
~ Dust Injection
Return
to Dust
Generator
<1=
Supply
Supply
Return
I Air Grill
©
Steam
Injection
Port
Baseboard
Heaters
ti^Tftrnmrri 1111
Bypass Duct
and
Registers
Low Velocity
Return to Dust
Mixing Room
(Blocked in
I Bypass Mode)
Instrument
Room
Figure 3. Interior elevation of PACS showing construction detail.
The electronic steam humidifier had a capacity of 12 gallons/day at 115 VAC. Steam was
directed into the mixing room through a remote steam pipe from the humidifier, which was
mounted on the outside of the dust mixing room. It was controlled by a humidistat mounted
inside the dust mixing room in series with a flow-sensing pressure switch in the supply duct to
disable the humidifier if the AHU was not circulating air.
The AHU was controlled by a standard heat pump thermostat mounted in the dust mixing
room. The heater thermostat, humidistat, and AHU thermostat were used in concert to provide
an acceptable on / off time for the HAC equipment.
The equipment control concept for normal operation was to keep the heaters and
humidifier on continuously to generate a load for the air conditioner, which was allowed to cycle
on and off under conventional thermostatic control. The heater thermostat was used as a high
limit control (should the air conditioner fail.)
4.1.5 Instrument Room
4.1.5.1 Objectives and Design. The purpose of the instrument room was to allow
simultaneous comparison of the IAQ evaluation aerosol instruments slated for use during the
field study and to provide an indication of the magnitude of effects that might be caused by ACS
17
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cleaning. As shown in Figure 1, the room was bypassed and kept closed during the duct
contamination and cleaning phases of the PACS operation to keep it clean. The bypass was
removed and the low velocity return opened to achieve an air flow rate and return velocity
reasonable for a residential room when the PACS was operated to compare the instruments.
4.1.5.2 Apparatus. The instrument room was the same size as the dust mixing room:
approximately 2.44 m high by 2.44 m deep by 3.05 m wide (8 x 8 x 10 ft), with a volume of 18.2
m3 (640 ft3). The room was empty except for lights, a small mixing fan, and electrical power
outlets. The room was operated in two modes: 1) normal room operation and 2) bypass during
dust injection. As shown in Figure 1, when operated as a normal room the bypass duct was
disconnected from the sidewall supply vent and sealed with a metal plate. A diffuser was placed
over the sidewall supply vent, which then discharged into the instrument room as would normally
be expected for a residential forced air ventilation system. The low velocity filtered air return
between the dust mixing and instrument rooms was opened to allow ventilation air to flow
between the instrument and dust mixing rooms at relatively low velocity, much as would occur in
a residence in which ventilation air leaving a room returns through an open door. The low
velocity return was filtered (ASHRAE 60% dust spot filters) to prevent contamination from
readily backflowing due to movement or opening the door in the dust mixing room.
In the bypass mode, the sidewall diffuser grill was removed, the bypass duct connected,
and the low velocity air return sealed so that the instrument room was no longer part of the
ventilation system air flow. In this way, the PACS could be contaminated with high levels of
dust without contaminating the instrument room with high levels of particles that might overload
the instruments or be easily resuspended by people working on the instruments.
4.1.6 Dust Generation System.
4.1.6.1 Design. The primary design considerations for the dust generation system were to
provide a soiled ACS that was representative of, or a realisitic surrogate for, field contaminated
ACS and to contaminate the ACS within 24 hours. Duct dust has not been characterized in this
sense, so no quantitative measures are available. Resuspended duct dust was chosen rather than a
synthetic dust. In this context, reasonable surrogate dust was taken to mean:
1) Deposits with the same appearance as those found in the field,
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2) Deposits having the same apparent interparticle adhesion as those in the field,
3) Deposits having about the same apparent duct wall adhesion as those in the field,
4) Penetration into fibrous materials apparently about the same, as is found in the field.
With respect to all characteristics, the dust was evaluated by the project team during
sampling and by the NADCA representatives as they cleaned the PACS.
4.1.6.2 Apparatus. Previously collected duct dust was injected as an aerosol. The dust
was dry and free flowing as received from duct cleaning companies, and was not dried further
before injection. The dust was obtained from the a duct cleaning company in the Dallas/Ft.
Worth, TX area, and though not identical all injected batches were similar in appearance. The
dust had a high volume fraction of fibers, and these had a tendency to mat and clog the aerosol
generator. The dust was not screened, but large pieces of debris (coins, toys, candy, small
adhesive bandages, sticks, feathers, etc.) were not injected.
As shown in Figure 3, the primary dust dispersion device was a high volume blower that
discharged directly into the dust mixing room. The dust was resuspended and fed into the blower
using either an aspirator (for part of the first test) or a blade-mill aerosol generator. Both
resuspension devices were workable but had shortcomings. The aspirator was simple and
inexpensive, having no moving parts. Prior to aspiration, the duct dust deposit had to be cut with
a utility knife to shorten fibers and prevent plugging. Even with the preparation, the aspirator
plugged several times while in use. It would be more suitable for a screened and sifted dust. The
blade-mill generator was able to feed the dust without cutting (that operation being done by the
blades), but was still possible to plug if the dust was fed too fast. Overall, however, the dust
injection process was not sensitive to the type of generator used because only finely dispersed
aerosol entered the duct, while coarse aerosol settled in the mixing room. When contaminating
the duct, the instrument room was bypassed and the dust mixing room fan was on. The AHU
blower was on to transport the dust into the ducts, but the baseboard heaters were off and the A/C
was not on so that excessive dust would not collect on the wet coil. The target dust mass deposit
was 10 to 50 mg/100 cm2 of duct surface, which is 10 to 50 times the NADCA 92-1 Standard for
an acceptably clean duct.
Following dust injection, the high speed blower was repeatedly directed at the floor to
resuspend as much dust as possible. This effort was stopped after 10 to 20 minutes, by which
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time the blower no longer reentrained large quantities of dust from the mixing room floor. The
dust was then allowed to settle for a few hours. At this point, the dust was widely distributed in
the duct but was adhering only loosely to the duct material. Conditioning, which consisted of
several days of exposure to a high relative humidity, made the dust adhere tightly to the duct wall
in a manner qualitatively more representative of duct dust in field applications. Dust
conditioning was not quantitatively investigated. The humidifier was set to maximum output
with the HAC system in thermostat control, which resulted in near continuous humidification.
During conditioning the mixing room and duct humidities remained between 70 and 90%
(generally near 90%) while the temperature ranged from 23 to 27°C (73 to 80°F). Overnight
conditioning caused a noticeable increase in dust adhesion as evaluated by touching the dust and
by sampling with the various vacuum surface samplers.
Because the duct dust was not sterilized prior to injection, it contained whatever
microbiological contamination was present when it was collected. Not all of the material would
remain culturable during the storage period, but spores are hardy and can remain viable for
extended periods. The deposited dust was a suitable source for collection of microbiological
contamination deposited on the duct, but would not serve as a surrogate for actively growing
microbiological contamination.
4.1.7 HVAC Instrumentation
4.1.7.1 Objectives and Design. The objectives of the HAC instrumentation were to
monitor performance of the PACS during the various operational phases (duct soiling,
conditioning, after cleaning, etc.) so that approximately the same conditions could be reproduced
for all three duct materials. Because the temperature, relative humidity, and air flow were not
directly controlled, but were parameters resulting from the on-off time of the A/C system and its
interaction with the heaters, humidifier, and laboratory environment, inexpensive HAC
instrumentation was used in the PACS.
4.1.7.2 Apparatus. Temperature, RH, and air flow sensors were positioned in the supply
and return duct at the locations shown in Figure 2. Temperature and RH sensors were also
placed in the dust mixing room and in the ambient air of the room containing the PACS. The
temperature sensors were 1000Q platinum RTDs, while the RH sensors were based the resistance
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change of a polymer sensor. Air flow sensors of the averaging pitot type were placed in the
galvanized supply and return duct at the same approximate location. As discussed in Section 7,
the duct sensors were used only with the galvanized duct.
Continuous watt meters were placed on the baseboard heaters (in total), the air handler,
and the compressor/condenser unit. The energy use rates were used as on-off indicators for the
equipment and compared with air flow, temperature, and RH measurements to better understand
the operation of the PACS. To monitor refrigerant temperature changes, thermocouples were
installed under the refrigerant line insulation between the evaporator and condenser. These
thermocouples were continuously recorded.
All PACS continuous instrumentation was connected to an AID board, digitized, and
displayed on a computer screen for easy access. (Commercial HAC instrumentation requires
external monitoring devices.) Following the checkout operational phase, system performance
was monitored but not recorded.
Room pressure was measured during normal operation and while injecting dust to
evaluate the degree of pressurization of the PACS. It was not regularly monitored.
4.2 PACS Checkout
The checkout phase of the project was intended to ensure that all the equipment was
working properly and determining the proper operating values. In addition, the checkout allowed
the determination of which operating parameters were important to control and which to simply
monitor. The dust injection system, in particular, had not been tested and considerable
modification was thought possible before acceptable duct dust was achieved. The dust
conditioning procedure described above was developed at this time.
All portions of the system were fully exercised with the galvanized duct system in place.
The duct integrity was evaluated, some leaks sealed, and the infiltration evaluated using a C02
decay measurement. The infiltration rate was found to be 0.0145 m3/s (30.7 ft3/min) with the
AHU blower on low speed, which is about 8 percent of the total supply air flow. At the medium
blower speed, the infiltration rate was 0.0187 m3/s (39.4 ft3/min) or 7 percent of the supply flow
rate. The apparent infiltration rate with the air handler off (diffusion or sorption) was 0.002 m3/s
21
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(4.2 ft3/min). Careful examination of the ACS showed that many of the largest apparent leak
sites were in the air handling unit access door, and could only be prevented by modifying the
unit.
Dust was initially injected in 50 g increments. The target was to deposit 10 to 50 times
the amount of dust that can remain for in a cleaned ACS that passes NADCA Standard 92-1, or 1
to 5 g/m2 (10 to 50 mg/100 cm2) on the duct surface. The bottom horizontal surface area of the
ACS, (including 1/3 of the round duct surface) was about 11 m2 (120 ft2), which would require
about 1 g injected to deposit 1 mg / 100 cm2 assuming everything deposited on the bottom
surface. Because the larger, high mass particles preferentially dropped out in the mixing room,
only about 25% of the total dust injected actually deposited in the ACS. The mass of dust
actually injected into each duct system was between 300 and 500 g.
The duct dust distribution was visually evaluated for uniformity (axially and radially). As
described below, differences were noted between ACS types. Dust was present throughout the
ACS, with the heaviest deposits on the bottom of the return duct Substantial amounts of dust
penetrated to the supply side of the system. The duct sidewall and top deposits were much
lighter than those on the duct bottom. Quantitative evaluation was conducted during the method
evaluation, and the results are reported in Section 6.
4.3 PACS Operation
Once checkout was completed and the desired set-points were known, operation of the
PACS consisted of turning everything on, ensuring that the thermostat setting was correct, and
occasional inspection. The test series, as described below, required that the system be operated
briefly in particular non-routine configurations (i.e., fan only for dust loading, off while
sampling.) Except for those excursions, the PACS operated at all times with the heaters and
humidifier on and the air conditioner cycling on about every five minutes.
22
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5.0 EXPERIMENTAL PROCEDURES
5.1 Overview
The initial step in a test utilizing each type of duct system was to evaluate the duct system
background. Duct dust was then injected into the PACS. Once the PACS was soiled, the
experimental protocol consisted of conducting duct and air evaluation tests at various times in
the cleaning process: before, during, immediately after, and 24 hours after cleaning. In the
discussion below, all measurement procedures are presented in section 5.2 and their use in the
sampling plan is presented in section 5.3. Section 5.4 presents a discussion of the duct cleaning
methods as applied to the PACS.
5.2 Sampling and Measurement Procedures
The measurement parameters and sampling and analysis methods are summarized in
Table 2 and described in detail in the balance of this section.
The primary sampling method being evaluated (and hence, the parameter of greatest
interest) was measurement of the mass of dust on surfaces of the ACS components prior to and
following ACS cleaning. The dust mass sampling had the following purposes:
• To evaluate the MVDS and NADCA dust sampling methods by collection of samples at
multiple locations and by collection of replicate samples. Two different MVDS
collection nozzles were evaluated during the testing.
• To collect information on dust sampling to develop the sampling protocol for the field
study.
• To measure the mass of duct dust (particulate matter and fibers) on the surfaces at various
locations in the ACS prior to cleaning to determine the amount and pattern of dust
deposition in the ACS. This was necessary to ensure that the amount of dust on the
surfaces was adequate to assess the effectiveness of the ACS cleaning.
• To measure the mass of duct dust on the surfaces after ACS cleaning to evaluate the
effectiveness of the cleaning methods.
23
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Table 2. Measurement Parameters and Methods
Parameter
Sampling Method
Instrumentation
Analysis Method
Notes
Dust loading
Manual
MVDS - brush
Gravimetric
Primary method
Dust loading
Manual
MVDS - nozzle
Gravimetric
For FDB
Dust loading
Manual
NADCA method
Gravimetric
Un-lined galvanized only
Dust loading
Manual
High volume sampler
Gravimetric
Cooling coils only
Microbial
loading
Manual
Pipet tip sampler
Plate counting
Applied to all ducts
Bioaerosol
concentration
Integrated
Mattson-Garvin slit to
agar impactor
Plate counting
1-hr integrated samples
PM2.5
Integrated
MS&T impactor/filter
and 201pm pump
Gravimetric
24-hr integrated samples
PM10
Integrated
MS&T impactor/filter
and 201pm pump
Gravimetric
24-hr integrated samples
Particles >
0.5 pm
(counts)
Continuous : 10-
min averages
Climet CI-4100
Optical
(scattered light)
Recorded with IAQDS
and Climet
Particles >
5.0 pm
(counts)
Continuous: 10-
min averages
Climet CI-4100
Optical
(scattered light)
Recorded by Climet
Particle count
-16 channel
Continuous: 60-
min averages
LAS-X
Laser aerosol
spectrometer
Direct download to
laptop computer
Fibers
Integrated
Filter/SKC pump
Phase contrast
microscopy
NIOSH 7400 method -
24-hr integrated samples
Fibers
Semi-continuous
MIEFAM-1
Optical fiber
monitor
PDL-10 data logger
For the same reasons, a second important parameter measured was the number of
culturable microbial organisms deposited on the duct and HVAC surfaces. As with the dust mass
sampling the goals of the PACS measurement were method development and performance
evaluation, with a secondary goal of evaluating the impact of ACS cleaning on microbial
deposits in ducts. Because of the short time between injecting the dust and sampling during most
of these tests, microbial growth on the duct was not an issue during this research. Regions with
high microbial counts were potential areas for growth and amplification, particularly in the case
of fungi. Only an extremely wet region would be expected to support bacterial growth.
Other parameters were measured during the three tests, also for the purpose of instrument
24
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"shake-down," method evaluation, and collection of information for refining and finalizing the
sampling and monitoring protocols for the field study. Continuous optical particle monitors were
set up in the instrumentation room of the PACS. Integrated air samples and bioaerosol samples
were also collected in the room. Although the data, particularly that collected with the
continuous optical particle counters, showed changes in particle concentrations during the test,
the reader is cautioned not to draw conclusions about the impact of ACS cleaning on airborne
particle concentrations based on the data presented in this report due to the limited scope of the
measurements and the artificial nature of the dust deposits and physical arrangement of the room
in which the measurements were made.
5.2.1 Duct Dust Surface Mass Sampling
The levels of dust in ducts (g/m2) were determined by collection of dust samples at
selected locations with the MVDS, the NADCA Standard 92-1 vacuum test method, and a high
volume vacuum cleaner. Duct dust was defined as all particulate and fiber matter collected with
the method. Samples were analyzed gravimetrically; the composition of the dust was not
determined in this study. The methods used in these tests are described below.
5.2.1.1 NADCA Vacuum Test Method (Standard Method 1992-01). The NADCA
Vacuum Test Method is described in Standard Method 1992-01, Mechanical Cleaning of Non-
Porous Air Conveyance System Components (NADCA, 1992). The hardware for the method
consists of a vacuum pump operated at 10 L/min, a filter cassette, and a template for sampling.
An open-face 37-mm diameter plastic filter cassette is used as the nozzle. The purpose of the
method is to document the effectiveness of cleaning of non-porous ducts. During the tests
described in this report, a Thomas Model 2107CA20A dual diaphragm pump was used. An in-
line valve was used to adjust the air flow rate to 10 L/min which was determined from a
calibrated in-line rotameter. The NADCA Vacuum Test Method template consisting of two 25
cm by 2 cm slots was used in the study. The template, which is 0.4 mm (15 mil) thick, was
supplied by NADCA, and used to define the area from which the sample was collected
Collection efficiency for the NADCA Vacuum Test Method was evaluated in previous
testing. The initial evaluation showed the collection efficiency was low (47%) at low dust mass
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levels (3 mg/100 cm2). At higher dust levels, the collection efficiency was better, but highly
variable (70 ± 19%). All tests were conducted with unconditioned dust deposits. Sampling was
performed according to the NADCA sampling protocol (Appendix A of Standard 1992-01).
Measured dust levels were not corrected for collection efficiency. The NADCA Vacuum Test
Method was used only for post-cleaning measurements on galvanized ducts to document cleaning
effectiveness. The method was not developed for pre-cleaning sample collection or for
collection of dust from porous surfaces.
Gravimetric analyses of filters to determine tare weights and final weights were
performed in the EPA weighing facility at the EPA Annex in Research Triangle Park, NC.
Filters were conditioned in the controlled environment weighing facility for 24 hours prior to
weighing. Mass determinations were performed using the Cahn C-31 microbalance located in
the facility. Gravimetric mass was determined as the difference between the final weight and the
tare weight of the filter.
5.2.1.2 Medium Volume Dust Sampler (MYDS). A medium volume vacuum method
was developed for use in the field study and was initially evaluated under laboratory conditions.
It was further evaluated during the three ACS cleaning tests. The sampler consists of the
following components:
• Thomas Model 2107CA20A dual diaphragm vacuum pump with nominal free air flow of
50 L/min,
• Gelman Model 2220 stainless steel 47 mm diameter in-line low pressure filter holder,
• Whatman EPM 2000, 47 mm, high-volume air sampling filters rated at 99.997% retention
for 0.3 pm DOP,
• Brooks rotameter, 0-50 L/min range, in-line, calibrated with a wet test meter,
• Six inch long, 0.5 inch O.D. stainless steel tube for attachment of nozzles,
• Nozzle developed by Acurex Environmental - stainless steel, 30 mm X 3 mm inlet (0.9
cm2 face area of nozzle), and
• Brush nozzle - nylon bristle brush, oval shaped, with an opening of approximately 18
mm by 10 mm, with 10 mm long nylon bristles (Source: Enervac Battery-Powered
Vacuum Cleaner).
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The sampler was operated at 40 L/min. Initial evaluation of the sampler with the stainless
steel nozzle was performed in the laboratory. Dust collection efficiency with the nozzle was 98%
from galvanized duct, 86% from duct liner, and 76% from fiberboard when the estimated
background fiber contribution was subtracted. Tests were performed with nominal loading of 3
g/m2 (30 mg/100 cm2).
The first tests in the PACS indicated that the nozzle was suitable for collection of newly-
deposited dust, but that the brush was required for conditioned dust that adheres more strongly
and realistically on the duct materials. The brush was used as the primary method during the
study.
The sampler was used with templates having an area of 100 cm2. Three different
templates were tested during the study. They included the NADCA template (two slots 25 cm X
2 cm), a template with three 20 cm X 2 cm slots, and a 10 cm X 10 cm template. The NADCA
template was too large and the multiple slot template did not offer any substantial advantages
over the 10 cm X 10 cm template, which was used for most sampling.
Tare weights and final weights were determined by weighing on the balance in the EPA
controlled environment weighing facility at the EPA Annex in Research Triangle Park, NC.
5.2.1.3 High Volume Sampler. A high volume vacuum sampler consisting of a Dirt Devil
Can Vac with a reported flow rate of 20 cfm, a cyclone for particle collection, a collection jar,
flow controller, magnehelic gauge, associated tubing, and nozzle was proposed for use in this
study to sample dust from the cooling coils. The sampler could not be used to collect pre-
cleaning samples because it had to be applied over a large area, and effectively it cleaned the
cooling coils. Post-cleaning samples were collected from the cooling coils with the high volume
sampler for the galvanized and FDL tests. But the post-cleaning samples collected with this
method were of limited value without precleaning data. Therefore, use of the sampler was
discontinued and the results are not reported.
5.2.2 PM10 and PM25 Particle Mass Measurements
Integrated samples of PM10 and PM2 5 mass were collected during selected time periods
with size selective impactors developed at Harvard University, referred to as the MS&T sampler.
27
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The sampling method is the same as that used in the EPA Office of Research and Development
(ORD) Large Buildings Study and in the EPA Indoor Environment Division's Building
Assessment and Survey Evaluation (BASE) program. Samples were collected over nominal 24-
hr periods using Air Diagnostics and Engineering, Inc. (Naples, MA) pumps that operated at 20
L/min. Samples were collected on 37 mm, 2.0 |im pore size, Teflon filters (Gelman Sciences,
Inc.). Pump air flow rates were measured at the start of the sampling period with a calibrated
Sierra TopTrak mass flow meter.
Gravimetric analyses of filters to determine tare weights and final weights were
performed in the EPA weighing facility at the EPA Annex in Research Triangle Park, NC.
Filters were conditioned in the controlled environment weighing facility for 24 hours prior to
weighing. Mass determinations were performed using the Cahn C-31 microbalance located in
the facility. Gravimetric mass was determined as the difference between the final weight and the
tare weight of the filter.
5.2.3 Particle Concentration Measurements - Laser Particle Counter
Airborne particle concentrations were measured during the tests with a Climet CI-4100
Laser Particle Counter. The particle sensor is a forward light scattering design. The instrument
collects particle counts in two size fractions: > 0.5 |im and > 5.0 [im in diameter. The monitor
has internal data storage for both channels or data can be output (4 - 20 mA proportional to
concentration) for one channel. During this study the data for the > 0.5 |_im channel was output
to the Blue Earth data acquisition system of the EPA Indoor Air Quality Data Station. Data were
saved as 10-min. averages. Data for the > 5.0 |im channel could not be output simultaneously.
But the data were obtained by downloading the data directly from the Climet using a laptop
computer and ProCom software. The Climet can store only 33 hours of 10-min. averages
requiring daily data downloading. During some periods, the averaging time was changed to 20
minutes to extend the period between data downloading.
5.2.4 Particle Concentration Measurements - Laser Aerosol Spectrometer
28
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Particle concentrations were also measured during the first two duct system tests with a
LAS-X Laser Aerosol Spectrometer, which is a high resolution optical particle counter with an
especially small lower size limit. The instrument collects particle counts in 16 channels over the
range from 0.1 to 7.5 |_im diameter. The spectrometer was operated in a 60-min. acquisition
mode and data were output in real-time via an RS-232 connection to a dedicated computer.
5.2.5 Fiber Monitoring and Sampling Methods
Fiber concentrations were monitored continuously in the instrumentation room during
tests with the galvanized steel duct system and the FDL system using an MIE FAM-1 Fibrous
Aerosol Monitor. The FAM-1 uses an oscillating high-intensity electric field to both align and
cause oscillatory motion in airborne fibers. Light pulses scattered by the individual fibers as they
pass through the focused continuous wave laser are detected. The FAM-1 electronics accept only
pulses synchronous with the oscillatory electric field, thus discriminating against particles that
are not fibers. Pulse sharpness, which is proportional to length, is electronically determined. The
FAM-1 returns a fiber count that has been calibrated against a fiber count by phase contrast
microscopy. Data were recorded with an MIE PDL-10 data logger. An acquisition (integration)
time of 100 minutes was used to obtain a detection limit of 0.1 fiber/cm3.
Integrated samples of airborne fibers were collected according to the NIOSH Method
7400, Asbestos and Other Fibers by PCM. Samples were collected on 25 mm cellulose ester
membrane filters (0.8 |um pore diameter) housed in a conductive cowl. A nominal sample
volume of 2800 liters was collected over a 24-hour time period. Total fiber concentrations were
determined by phase contrast microscopy in accordance to the NIOSH Method 7400 B counting
rules.
Fiber samples were collected in duplicate in the instrumentation room. Samples were
also collected outside of the room to verify that there was not a significant source of fibers in the
facility in which the PACS was housed.
29
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5.2.6 Microbial Surface Sampling
The primary microbial measurement was of the culturable microbial surface loading,
expressed as colony forming units (cfu) per cm2. Samples of deposited materials within a
template defined area of 10 cm2 were obtained by two techniques:
1) Suctioned at 10 L/min through a sterile pipet tip nozzle directly into a filter cassette, from
which they were eluted, and plated onto Trypicase Soy Agar (TSA) and Sabourauds
Dextrose Agar (SDA) for culture, identification, and colony counting.
2) Collected with a sterile swab that had been wetted in a saline solution. The sample was
then eluted into a saline solution and plated onto TSA and SDA for culture, identification,
and colony counting.
For both methods, the samples plated onto TSA were evaluated for fungal growth and the SDA
plates for bacterial growth. The plates were evaluated by counting colonies and reporting the
results as colony forming units (cfu) per area for surface samples or air volume for the bioaerosol
sampling. The methods are described in Air Conveyance System Cleaning Pilot System
Development, Characterization, and Operation: Project Work and QA Plan (RTI, 1995) and
Field Microbiological Investigation of Ventilation System Cleaning: Project Work/QA Plan
(RTI, 1996).
These measurements were conducted near where the dust mass loading measurements
were made to permit evaluation of the correlation between dust mass and microbial populations.
Co-located vacuum and swab samples were collected in most cases to allow comparison of the
two methods. While the use of swabs to obtain surface samples is a traditional technique for non-
porous surfaces, its use on rough-surfaced or porous materials cannot be quantitative because
contact between the swab and the surface is imperfect. The vacuum technique was developed for
improved efficiency on porous materials. The pilot unit afforded an opportunity for a direct
comparision of the two microbial sampling methods with each other and the gravimetric tests
described above. Because duct dust deposits can vary greatly over small areas in the relatively
small residential ducts, differences between duplicate tests and co-located samples can reflect
dust non-uniformity as much or more than measurement variability.
30
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5.2.7 Bioaerosol Sampling
Bioaerosol samples were obtained with Mattson-Garvin slit-to-agar samplers operated
over 60-minute periods with a fungal media. The Mattson-Garvin sampler draws air directly
from the room at 28.3 L/min through a 0.15 mm slit allowing a broad range of airborne particles
to be impacted upon the surface of a 150 mm rotating agar plate. The agar plate is then incubated
and the number of colonies present counted and the organisms identified. Details of the
sampling method can be found in Field Microbiological Investigation of Ventilation System
Cleaning: Project WorkJQA Plan (RTI, 1996). The sampler was disinfected with 70% ethanol
before the initial sampling and between each individual sample. Two samplers were operated
simultaneously to obtain duplicate fungal samples.
5.3 Test Protocol
The overall pilot unit ACS cleaning test matrix, given in Table 3, included a test series
for each duct type. The duct systems all had nominally identical internal dimensions
(construction details caused some differences, particularly in fittings) and were installed
sequentially following the same paths. Flexible ducts were used for the supply drops in all cases.
The flexible duct and the air handler were new for each test series.
Table 3. Test Matrix
Test ID
Duct System Design
Target Dust Loading
Cleaning Method
Test 1
Trunks of conventional galvanized
duct, insulated outside. Supply
feeders of flex duct to registers.
10 to 50 g/m2
(100 to 500 mg/100 cm2)
As chosen on site by
NADCA representatives
Test 2
Trunks of acrylic polymer faced, 1 in.
thick, 1.5 lb/ft3 FDL with flex duct
feeders to registers.
10 to 50 g/m2
(100 to 500 mg / 100 cm2)
As chosen on site by
NADCA representatives
Test 3
Trunks of unfaced, 1 in. thick EI-475
FDB with flex duct feeders to
registers.
10 to 50 g/m2
(100 to 500 mg / 100 cm2)
As chosen on site by
NADCA representatives
31
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5.3.1 Dust Injection and Deposition.
To achieve the target dust loading, approximately 300 - 500 grams of collected duct dust
were injected over a period of about one hour. The amount of dust injected was not considered
critical, and varied depending on the frequency of dust injector plugging and the amount of dust
lost when restoring operation. As expected, a large fraction of the injected dust never entered the
duct system, settling instead in the dust mixing room. Distributed evenly over the approximately
11 m2 of duct bottom surface (where most of the dust deposited), 400 grams would amount to
36g/m2. The actual measured deposition was around 25% of the injected total.
When injecting dust, the pilot HAC was operated in "fan-only" mode. The air
conditioning coil was allowed to dry before injecting the dust to allow as much dust as possible
to penetrate past the coil into the supply ducts. (Krafthefer and Bonne, 1986, showed that coils
"retain particulates more efficiently than common lint or dust stop filters.") The instrument room
was bypassed, and the mixing fan in the dust mixing room was on at high speed. The humidifier
was turned off.
Following duct soiling, the humidifier and the air conditioner were turned back on to
condition the dust by exposure to several days of high humidity. The humidistat was set to
maximum to give continuous humidifer output, the dust mixing room thermostat to 23.5°C
(74°F), and the AHU fan to low speed. This resulted in mixing room and duct RH's of 90% or
higher for most of the time and temperatures ranging from 23 °C (73 °F) to 27° (80°F). The air
conditioner cycled on 4 or 5 times an hour for about 5 minutes, and during that time briefly
reduced the mixing room humidity to about 70%. Conditioning was continued as long as
allowed by the testing schedule. For the galvanized duct test, this allowed about 6 weeks of
conditioning while the other two duct systems were allowed only 2 to 3 days. The conditioning
process was not investigated. Subjectively, the individuals operating the surface sampling
equipment were of the impression that the character of the dust was similar for each run.
The dust deposited differently in the different types of ACS. The deposit was most non-
uniform in the bare galvanized sheet metal duct. This dust deposit was visibly thick in the
stiffening beads, and in some places, particularly near flow obstructions, was not uniform across
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the width of the duct. The non-uniformity was evident on a large scale in the supply duct near
the flexible duct takeoffs, where dust was deposited in swirled deposits on the order of 10 cm in
size immediately next to relatively clean areas.
At a given sampling location, the FDL and FDB duct systems appeared more uniformly
soiled than did the bare galvanized duct system. The galvanized duct system had by far the
longest operating period between dust injection and sampling (4 months compared to a few
days), so the difference may have been caused by redistribution during the extended period of
operation. For FDL, the pattern of non-uniformity across the bottom of the duct was similar at
all sample points, with dust trapped in the depressions associated with attachment pins and lesser
amounts of dust in rough spots in the lining. Poorly fit joints also caused dust deposits. No large
swirled deposits were noted.
The dust deposit was most uniform for the FDB system, with poor joints causing areas of
increased deposition, as did the surface depressions. The non-uniformity was at a smaller scale
than for bare galvanized metal, and there were no attachment pins.
5.3.2 Application of the Test Methods in the PACS
A complete test series for a single duct system consisted of a number of operating
periods:
1) installation of the new duct system and checkout;
2) pre-soiling measurements to evaluate measurement backgrounds in ACS,
3) ACS soiling and deposited dust conditioning,
4) post-soiling, pre-cleaning evaluation of duct and AHU,
5) measurements conducted after soiling the ACS, but prior to cleaning to evaluate
the dust deposit and particle loading,
6) cleaning the ACS,
7) surface mass and microbiological measurements made after cleaning the ACS and
before restarting the AHU,
8) air sampling during and shortly after AHU startup,
9) integrated air sampling for total particles after cleaning, and
10) air sampling 24 hours and more after cleaning.
Table 4 shows the operating periods during which the various parmeters were measured.
33
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Table 4. Measurement Schedule
Parameter
Pre-
soiling
Pre-
soiling
AHU
on
Soiling
Post-
Soiling
AHU
off
Post-
soiling,
AHU
on
Clean-
ing
Post-
clean,
before
starting
Post-
clean,
AHU
on
24
hour
Post-
clean
Dust loading,
MVDS
X
X
X
Dust loading,
NADCA
X
X
Microbial
loading
X
X
X
Bioaerosol
concentration
60 min
60 min
60 min
60 min
pm7,
24 hr
tmw
24 hr
PMln
24 hr
24 hr
24 hr
Particles > 0.5
|im (counts)
contin-
uous
contin-
uous
contin-
uous
Particles >5.0
|im (counts)
Contin-
uous
Contin-
uous
Contin-
uous
Particle count -
16 channel
Contin-
uous
Contin-
uous
Contin-
uous
Fibers, filter
21 In-
24 hr
: 24 hr
Fibers, counter
Contin-
uous
Contin-
uous
Contin-
uous
5.4 Air Conveyance System Cleaning Operations Applied in the PACS
5.4.1 Operations Applied to All Systems
The following procedures used during the cleaning phase of PACS operation were
common to all three duct systems:
• Safety Precautions. All duct cleaning operations were conducted while wearing safety
glasses and safety shoes. Lock-out / tag-out procedures were applied to the air handler
electrical mains. Respirators were used when working close to the duct.
• Grill Removal and Cleaning. The supply and return grills were removed as one of the
first steps, power washed and hand-scrubbed with a commercial detergent solution when
necessary, rinsed, and allowed to air dry. They were replaced as one of the final steps.
34
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• Air Handler and Blower. The interior of the air handling unit (AHU) was cleaned each
time by hand vacuuming with a soft brush attachment to a HEPA-filtered portable
vacuum. The design of the AHU was such that the interior insulation was readily
accessible. The AHU blower was removed each time the AHU was cleaned, the motor
disconnected, and the blower wheel and case cleaned with the power washer (again using
a commercial, biodegradeable detergent), and hand-scrubbed if needed.
• Coil Cleaning. The evaporator coil in the AHU was inspected and cleaned each time
using a commercial coil cleaner, mixed as directed, and sprayed from a common
pneumatic garden sprayer. While care was taken to minimize wetting the equipment
liner, some overspray was observed. The coil was cleaned from the downstream side as
much as possible.
• Negative System Pressure is achieved by placing large portions of the duct system under
vacuum so that the dust and debris loosened and entrained by the cleaning devices is
transported and removed from the system. For the PACS, negative system pressure was
provided by a commercial vacuum blower capable of drawing 2000 cfm through two
prefilters and discharging it back into the room through HEPA filters. The vacuum
blower suction hose was temporarily fixed in the the air handler, in the side (supply or
return) being cleaned, and loosely sealed in place using temporary connections. It
remained running as long as NADCA continued cleaning operations.
5.4.2 Galvanized Steel Duct
With the duct system isolated and under negative pressure, the galvanized steel duct was
cleaned using primarily a stiff, abrasive-coated, cylindrical rotary power brush to loosen the dust.
Cleaning access was through the supply and return registers as well as the access doors shown in
Figure 2. The test dust adhered well and multiple passes were required to clean corners and the
stiffening beads in the duct. Following brushing, air washing was used to entrain and transport
any remaining dislodged dust to the collector. Air washing is done by injecting compressed air
against the duct walls through flexible hoses or nozzles mounted at the end of an air line that has
been inserted some distance into the duct. The air jets blow the dust into the moving negative
35
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air, which transports the dust to the collector. The dust and debris are always kept moving
towards the negative air collector.
The flexible duct used to supply individual registers was cleaned using a soft-bristle
cylindrical rotary power brush and with air whips to loosen the dust and entrain it into the
negative air flow. As in all cleaning, the brush was run from clean to dirty, which for these ducts
meant from the supply registers toward the AHU.
5.4.3 Fibrous Glass Lined Duct
With the duct system isolated and under negative pressure, the FDL duct was cleaned
using primarily a cylindrical rotary power brush of cloth strips to loosen the dust. Multiple
passes were used as required to clean the duct. Following brushing, air washing (moving through
the system toward the main vacuum source) was used to entrain and transport any remaining
dislodged dust to the collector. The other aspects of cleaning the FDL duct were very similar to
the galvanized duct.
5.4.4 Fiberglass Duct Board System
With the duct system isolated and under negative pressure, the FDB duct was cleaned
using primarily a cylindrical rotary power brush of cloth strips to loosen the dust. Multiple
passes were used as required to clean the duct. Following brushing, air washing (moving through
the system toward the main vacuum source) was used to entrain and transport any remaining
dislodged dust to the collector. Frequent inspection was used to ensure that the duct surface was
not damaged. Some sections of the duct were hand-brushed to complete the cleaning process.
The other aspects of cleaning the FDB duct system were very similar to the galvanized duct.
36
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6. RESULTS AND DISCUSSION
6.1 Pilot Ventilation System Operation
PACS operation during soiling and dust conditioning was described in Section 5.3.
Normal operation for the PACS was intended to mimic normal residential use as much as
possible, and was used except during soiling, conditioning, and cleaning. In normal operating
mode, the bypass duct was disconnected, and supply air entered the instrument room through a
conventional wall diffuser, mixed within the room with the small mixing fan on, and flowed into
the dust mixing room through the open low air velocity return. The instruments being compared
were located on the floor or on portable stands near the center of the room. The door to the
instrument room was closed.
When in normal operating mode the thermostat, located in the dust mixing room, was set
to 21 °C (70°F) and the humidistat to 70%. At these settings, the air conditioner was required 4
to 5 times an hour, running for about 5 minutes each time. The temperature in the dust mixing
and instrument rooms was 22°C - 2/+3°C, with the temperature dropping after the air
conditioner came on and rising more slowly after it shut off. Similarly, the humidity in the
mixing room dropped when the air conditioner was on and then rose after it was off. Relative
humidity ranged from 30 to 70% but was normally about 50% to 60%. As estimated by C02
injection and decay, the PACS infiltration rate from the surrounding laboratory was about 0.02
m3/s (40 cfm), or 5% of the HAC circulation rate.
6.2 Surface Deposit Measurements
6.2.1 Gravimetric Duct Dust Measurement Results
Duct dust samples were collected prior to ACS cleaning and following ACS cleaning for
tests with each of the three duct systems (galvanized steel, FDL, and FDB). Duct dust was
defined as any material that could be collected with the MYDS or NADCA sampling methods.
As defined, duct dust could include inorganic particulate matter, organic particulate matter, and
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fibers. The MVDS was the primary sampling method used in this study. Most samples were
collected with the MVDS fitted with the brush. The nozzle, which was determined early in the
study to have a lower collection efficiency, was used to collect a limited number of samples, as
described below. The NADCA sampling method was used only for the galvanized steel duct
system for collection of samples after ACS cleaning. The objectives of the duct dust sampling
were to:
• Determine the dust mass that was deposited on the surfaces at various locations in
the duct and on other components of the ACS system,
• Evaluate the sampling methods proposed for use in the field study, and
• Collect information to develop and refine sampling protocols for the field study.
6.2.1.1 Galvanized Steel Duct System
Results for duct dust measurements performed during the testing with the galvanized steel
duct system are summarized in Tables 5 (pre-cleaning samples) and 6 (post-cleaning samples).
Results are shown for locations in the supply, return, and flexible ducts. The locations are
depicted in Figure 2 above. Samples were also collected from the cooling coil, side wall of the
plenum box, and the foil liner in the air handler.
All samples were collected with the brush attachment on the MVDS during this test.
Collection efficiency using the MVDS with the stainless steel nozzle was poor based on visual
observation; dust remained on the galvanized steel surface after collection with the nozzle. The
NADCA method was developed only for post-cleaning sample and was not used for pre-cleaning
sampling. Previous evaluation of the method indicated that collection efficiency was poor at the
dust mass levels present in ducts prior to cleaning.
Dust samples collected prior to cleaning demonstrated that deposition of dust in the ducts
was not uniform, as was apparent after visual inspection. The deposits in the return duct were
especially non-uniform in that a noticeable amount of dust had collected in the stiffening beads
(1 cm wide depressions in the sheet metal extending the full width of the duct). In the supply
duct, the effects of non-uniform flow were evident near the flexible duct takeoffs. To the extent
possible, the samples were taken to be representative of the region near the access doors.
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Table 5. Dust Levels in the Galvanized Duct System Prior to Cleaning
Duct
Location
Sampler Nozzle
Surface Sampled
g/m2
Supply
S-l
MVDS
Brush
Bottom
2.66
S-2
MVDS
MVDS
Brush
Brush
Bottom - Primary
Bottom - Duplicate
Avg. ± SDa
7.29
4.27
5.78 ±2.14
S-3
S-4
MVDS
MVDS
Brush
Brush
Bottom
Bottom
6.43
1.86
Return
R-l
R-2
MVDS
MVDS
Brush
Brush
Bottom
Bottom
5.04
7.51
R-3
MVDS
MVDS
Brush
Brush
Bottom - Primary
Bottom - Duplicate
Avg. ± SDa
14.73
13.02
13.87 ± 1.21
R-4
MVDS
Brush
Bottom
1.40
Flexible
F-l
MVDS
MVDS
Brush
Brush
Bottom - Primary
Bottom - Duplicate
Avg. ± SDa
1.17
1.38
1.27 ±0.12
F-2
F-3
F-4
MVDS
MVDS
MVDS
Brush
Brush
Brush
Bottom
Bottom
Bottom
1.14
1.47
1.83
AHb
Coils MVDS
Plenum MVDS
Foil Liner MVDS
Brush
Brush
Brush
Upstream
Bottom
Side-wall
1.22
0.72
0.64
a Average ± Standard Deviation for duplicate dust samples collected at adjacent locations
b Samples collected from the air handler
39
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Table 6. Dust Levels in the Galvanized Duct System After Cleaning
Duct
Location
Sampler
Nozzle
Surface Sampled
g/m2
Supply
S-l
MVDS
Brush
Bottom
0.26
MVDS
Nozzle
Bottom
0.15
NADCA
Bottom
< MDLa
S-2
MVDS
Brush
Bottom
0.37
MVDS
Brush
Sidewall
0.16
MVDS
Nozzle
Bottom
0.09
NADCA
Bottom
0.01b
Return
R-2
MVDS
Brush
Bottom
0.36
MVDS
Brush
Sidewall
0.14
MVDS
Nozzle
Bottom
0.30
NADCA
Bottom
0.02c
Average Residual Dust ± SD on Galvanized Surfaces Sampled with 0.26 ±0.11
the MYDS/Brush (N=5)
Flexible F-l
F-4
MVDS
MVDS
MVDS
MVDS
Brush
Nozzle
Brush
Nozzle
Bottom
Bottom
Bottom
Bottom
Average Residual Dust ± SD on Flexible Duct Surfaces Sampled
with the MVPS-Brush (N=2)
0.17
0.22
0.38
0.30
0.28 ±0.15
AHU Coils MVDS Brush Bottom
Plenum MVDS Brush Bottom
Foil MVDS Brush Bottom
Liner
b Equals 0.1 mg/100 cm2
c Equals 0.2 mg/100 cm2
d Samples collected in air handler
0.26
0.33
0.28
Less than the minimum detection limit of 0.01 g/m (0.1 mg/100 cm )
40
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As shown in Table 5, dust levels in the return duct ranged from 1.4 to 14.7 g/m2. In the
supply duct, the dust levels ranged from 1.9 to 7.3 g/m2. The lowest dust levels in the galvanized
steel ducts were at the sampling location in the supply duct farthest away from the air handler.
Dust levels in the flexible ducts were lower than in the galvanized supply duct and the return
duct, ranging from l.lto 1.8 g/m2. Dust levels were also lower on the components of the air
handler. During this test, all dust samples were collected from the bottom of the ducts, where the
dust deposition was highest. During the initial testing with the galvanized duct system, samples
were collected from the top and side of the duct at location R-2. Dust levels were substantially
lower than on the bottom, being 1.0 g/m2 on the sidewall and 0.3 g/m2 on the top surface. Based
on visual observation, loading on the sidewalls and top of the duct appeared to be light and
relatively uniform. Therefore, additional samples were not collected during the test.
Duplicate samples collected in the return duct at location R-3 showed good precision with
a relative standard deviation (RSD) of 8.7%. Similar precision was observed for duplicate
samples collected at one location in a flexible duct. The precision was not as good (RSD of
37%) for the duplicates collected in the supply location S-2. This was expected becausevisual
inspection showed a highly variable dust deposition pattern at this location.
The post-cleaning measurement results (Table 6) showed that the cleaning methods
effectively removed the dust from the system. Visual inspection indicated that all but a light
"film" of dust had been removed from the galvanized steel duct surfaces. The dust mass was less
than 0.4 g/m2 (4 mg/100 cm2) for all samples. The average dust mass on the galvanized steel
duct surfaces after cleaning was 0.26 ± 0.09 g/m2 (2.6 mg/100 cm2) when measured with the
MVDS fitted with the brush. Using the nozzle on the MVDS, the average was 0.18 ± 0.11 g/m2.
In contrast, the mass of dust measured on the galvanized steel ducts with the NADCA Vacuum
Test method was 0.1, 0.2, and less than 0.01 mg/100 cm2, meeting the requirement of NADCA
Standard 1992-01 that dust weight after cleaning be less than 1 mg/100 cm2. The higher
efficiency MVDS measurement gave results that were greater than the NADCA criterion for
cleanliness of 1 mg/100 cm2, while the results with the NADCA method were below the
criterion.
These tests with the galvanized duct system showed that the nozzle developed for the
MVDS would probably be inadequate for pre-cleaning sampling in the field. Although the
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nozzle had a high collection efficiency for "newly-deposited" dust on galvanized steel surfaces
during laboratory tests, visual observation indicated that it could not effectively collect dust
adhering to the steel surface. It was necessary to use a brush to dislodge dust adhered to the
surface. As a result of the test in the PACS, the brush was used as the primary method of
sampling in the field study.
Results of the pre-cleaning sampling in the galvanized system confirmed that dust levels
were in the range desired for the cleaning test. The results also showed that dust deposition was
variable, as expected. The results suggested that sampling of duct dust in the field study would
require sampling at multiple locations and extensive visual inspection of the ducts in the system
to identify representative areas for sample collection.
6.2.1.2 Fibrous Glass Duct Liner System. Results for duct dust measurements performed
during the testing with the system constructed of FDL in the supply and return trunks and flexible
feeder ducts are summarized in Tables 7 (background dust samples), 8 (pre-cleaning samples)
and 9 (post-cleaning samples). Background samples were collected to determine the amount of
dust on the components of the system that may have resulted from manufacturing and
construction activities or that may have been dislodged from the surface of the materials during
sampling. This was of particular concern for the FDL because previous testing showed that the
sampling method could dislodge loose material from the surface of this product. The sampling
locations are those depicted previously in Figure 2. Location R-4 was not used in this test.
Background and pre-cleaning samples were collected with the brush attachment on the MVDS,
the most aggressive and most efficient sampling method.
Samples collected from the "clean" surfaces of the ACS components prior to loading the
test dust into the system contained measurable background material (Table 7). The average mass
collected from the FDL surfaces in the supply and return ducts was 0.38 ± 0.08 g/m2. The
material collected was weighed but not identified; its source is unknown. Although, the source
of the background material on the FDL was not determined in this study, it is interesting to note
that background material was also measured on the flexible duct and on surfaces in the air
handler. The amount of background dust collected on the flexible duct surface and foil liner of
the air handler was similar to that collected from the FDL surfaces, suggesting that the source of
the material is the manufacturing process or deposition during construction of the system. It
42
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Table 7.
Background Dust Levels from the Surfaces in the FDL System Prior to Soiling
Duct Location Sampler Nozzle Surface Sampled
g/m2
Supply S-2 MVDS Brush Bottom
S-3 MVDS Brush Bottom
0.42
0.44
Return R-l MVDS Brush Bottom
0.21
0.43
0.43
0.40
0.36
R-l MVDS Brush Top
R-l MVDS Brush Sidewall -Outside
R-l MVDS Brush Sidewall - Inside
R-3 MVDS Brush Bottom
Average Background Dust ± SD for FDL Surfaces N=7")a
0.38 ± 0.08
Flexible F-2
MVDS Brush
0.35
AHb
Coils MVDS Brush
Foil Liner MVDS Brush
0.27
0.24
Avg. Background Dust ± SD for all Surfaces fN=10)
0.36 ± 0.09
a Average ± Standard Deviation for seven samples collected on the FDL surfaces
b Samples collected from the air handler
should be noted that the background mass collected from the new, "clean, surfaces of the air
handler components and flexible duct was nearly identical to the mass collected from similar
surfaces after cleaning the galvanized steel duct system (Table 6).
Dust levels on the surfaces of the ACS components of the FDL system prior to cleaning
are presented in Table 8. The mass of dust on the bottom surface of the FDL return ranged from
4.78 to 11.32 g/m2. At location R-l, dust mass was lower on the top (1.20 g/m2) and two
sidewalls (1.47 and 1.12 g/m2) than on the bottom surface of the duct. In the supply, the dust
loading ranged from 0.65 to 1.4 g/m2 on the bottom. The dust mass on the top and sides of the
duct at location S-l was in the same range as the mass on the bottom of the duct at the three
sampling locations. The mass of dust deposited in the components of the FDL system was
generally less than that in the galvanized system (Table 5).
43
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Table 8.
Dust Levels in the Fibrous Glass Duct Liner System Prior to Cleaning
Duct
Location
Sampler
Nozzle
Surface Sampled
g/m2
Supply
S-l
MVDS
Brush
Bottom - Primary
0.73
MVDS
Brush
Bottom - Duplicate
0.65
Avg. ± SDa
0.69 ± 0.06
MVDS
Brush
Top
1.15
MVDS
Brush
Sidewall - Outside
0.50
MVDS
Brush
Sidewall - Inside
0.82
S-2
MVDS
Brush
Bottom
1.42
S-3
MVDS
Brush
Bottom
1.23
Return
R-l
MVDS
Brush
Bottom
5.99
MVDS
Brush
Top
1.20
MVDS
Brush
Sidewall - Outside
1.47
MVDS
Brush
Sidewall - Inside
1.12
R-2
MVDS
Brush
Bottom
4.78
R-3
MVDS
Brush
Bottom - Primary
11.32
MVDS
Brush
Bottom - Duplicate
7.95
Avg. ± SDa
9.64 ± 2.38
Flexible
F-l
MVDS
Brush
Bottom - Primary
1.31
MVDS
Brush
Bottom - Duplicate
0.73
Avg. ± SDa
1.02 ±0.41
F-2
MVDS
Brush
Bottom
0.83
F-3
MVDS
Brush
Bottom
0.50
F-4
MVDS
Brush
Bottom
0.66
AHb
Coils
MVDS
Brush
Bottom
0.80
Plenum
MVDS
Brush
Side
0.54
Foil liner
MVDS
Brush
0.53
a Average ± Standard Deviation for duplicate dust samples collected at adjacent locations
b Samples collected from the air handler
44
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Table 9. Dust Levels in the FDL System After Cleaning
Duct Location in Sampler Nozzle
System
Surface Sampled
g/m2
Supply
S-l
MVDS Brush
MVDS Nozzle
MVDS Brush
Bottom
Bottom
Sidewall - Inside
0.45
0.25
0.29
S-2
MVDS Brush
MVDS Brush
Bottom - Primary
Bottom - Duplicate
Avg. ± SDa
0.35
0.49
0.42 ±0.10
Return R-l MVDS Brush Sidewall - Outside
R-2 MVDS Brush Bottom
MVDS Nozzle Bottom
Average Residual Dust ± SD on FDL Surfaces Sampled with the
MVPS-Brush (N=6)
0.45
0.31
0.36
0.39 ±0.08
Flexible F-l MVDS Brush Bottom - Primary 0.24
MVDS Brush Bottom - Duplicate 0.34
Avg. ± SDa 0.29 ± 0.07
F-4 MVDS Brush Bottom 0.33
Average Residual Dust ± SD on Flexible Duct Surfaces Sampled with 0.30 ± 0.06
the MVDS-Brush (N=3)
AH
Coils MVDS Brush
Plenum MVDS Brush Bottom
Foil Liner MVDS Brush Bottom
0.26
0.25
0.24
a Average ± Standard Deviation for duplicate dust samples collected at adjacent locations
b Samples collected in air handler
45
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Duplicate samples collected in the return duct at location R-3 had a relative standard
deviation of 25%. Precision of the duplicates collected in the supply was better (%RSD = 8%).
Visual inspection indicated that the deposition was more uniform in the supply ducts. The
precision for the duplicate samples collected in the flexible duct was poor (%RSD = 40%). The
poorer precision may reflect non-uniform dust deposition in the duct. It may also reflect sample
loss caused by movement of the duct material to gain access or the fact that collection of samples
out of the end of the flexible duct was difficult due to the small size of the opening.
The post-cleaning measurement results (Table 9) showed that the cleaning methods
effectively removed the dust from the system. The dust mass was less than 0.5 g/m2 (5 mg/100
cm2) for all samples collected with the MVDS with the brush attachment. The average dust
mass collected with the MVDS-brush sampler from the FDL surfaces in the supply and return
ducts was 0.39 ± 0.07 g/m2. This compared to an average residual mass of 0.30 ± 0.06 g/m2 on
the flexible duct surface and 0.25 ±0.1 g/m2 on the air handler components sampled with the
MVDS, indicating that the residual dust on the FDL surfaces was not substantially different from
that on other types of surfaces. The amount of dust collected after cleaning of the flexible ducts
and the air handler components was similar in both the galvanized steel duct and FDL system
tests. Comparison of the measurement results for samples collected on "clean" surfaces prior to
loading of the dust into the test system (Table 7) with the results for samples from the same
surfaces after cleaning (Table 9) shows that the levels are similar. The average background on
"clean" FDL surfaces was 0.38 ± 0.18 g/m2 which was not significantly different from the post-
cleaning dust mass of 0.39 ± 0.07 g/m2.
6.2.1.3 Fiberglass Duct Board System. Results for duct dust measurements performed
during the testing with the system constructed of FDB for the supply trunk and return ducts and
flexible feeder ducts are summarized in Tables 10 (background samples and pre-cleaning
samples) and 11 (post-cleaning samples). The measurement locations are those depicted
previously in Figure 2. Background samples were collected from the FDB surface prior to
installation in the system because laboratory evaluation of the MVDS showed that the sampler
would collect a substantial amount of fibers from new FDB. Background sampling would
determine the mass of fibers dislodged during sampling as well as the amount of dust and fiber
mass on the surface of the FDB that may have resulted from manufacturing, storage of the
-------
Table 10.
Dust Levels in the FDB System Prior to Cleaning
Duct
Location
Sampler
Nozzle
Surface Sampled
g/m2
Background Samples
- New FDB
Pre-Loadinga
MVDS
Nozzle
0.99
MVDS
Nozzle
1.29
MVDS
Nozzle
1.43
Avg. ± SDb for the MVDS/Nozzle
1.24 ±0.18
MVDS
Brush
1.26
Pre-Cleanine Samples
i - Dust Loaded
Supply
S-l
MVDS
Nozzle
Bottom
1.92
S-2
MVDS
Nozzle
Bottom - Primary
0.50
MVDS
Nozzle
Bottom - Duplicate
0.51
Avg. ± SDb
0.50 ±0.10
S-3
MVDS
Nozzle
Bottom
0.51
Supply
S-l
MVDS
Brush
Bottom
1.74
S-2
MVDS
Brush
Bottom
0.44
Return
R-l
MVDS
Nozzle
Bottom
3.00
R-3
MVDS
Nozzle
Bottom
0.67
R-3
MVDS
Nozzle
Sidewall- Inside
2.65
Return
R-l
MVDS
Brush
Bottom
17.0
R-2
MVDS
Brush
Bottom
7.57
R-3
MVDS
Brush
Bottom
5.02
R-3
MVDS
Brush
Sidewall - Inside
2.73
Flexible
F-l
MVDS
Brush
Bottom - Primary
0.18
MVDS
Brush
Bottom - Duplicate
0.15
Avg. ± SDb
0.17 ±0.02
AHC
Foil liner
MVDS
Brush
0.38
a Samples were collected after duct fabrication but prior to assembly of the system.
b Average ± Standard Deviation for duplicate dust samples collected at adjacent locations
c Samples collected from the air handler
47
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Table 11.
Dust Levels in the FDB System After Cleaning
Duct Location Sampler Nozzle Surface Sampled g/m2
Supply S-l MVDS Nozzle Bottom 0.16
S-2 MVDS Nozzle Bottom - Primary 0.20
MVDS Nozzle Bottom - Duplicate 0.33
Avg. ± SDa 0.27 ± 0.09
Return R-l MVDS Nozzle Bottom 0.17
R-2 MVDS Nozzle Bottom 0.54
Average Residual Dust ± SD on FDB Surfaces Sampled with the MVDS- 0.28 ± 0.16
Nozzle (N=5)
Flexible F-l MVDS Brush Bottom 0.15
AHb Coils MVDS Brush 0.12
Foil Liner MVDS Nozzle 0.02
a Average ± Standard Deviation and % Relative Standard Deviation for duplicate dust samples
collected at adjacent locations
b Samples collected in air handler
material, or construction activities.
Background and pre-cleaning samples were collected with both the stainless steel nozzle
and the brush attachment on the MVDS. For the FDB surfaces, the nozzle was considered the
primary sampler because the brush would dislodge fibers from the surface during sampling. As
shown in Table 10, the average background mass was 1.24 g/m2 for three samples collected with
the nozzle. One sample collected with the brush gave similar results (1.26 g/m2), but only
because it was not used aggressively; it was pulled across the surface very gently. Although the
composition of the background material was not determined analytically, visual observation
suggested that the mass collected was primarily fibers.
Results for measurements of duct debris (particles and fibers) collected after loading of
the dust into the system are also shown in Table 10. The results are difficult to interpret. Using
the MVDS nozzle sampler, the mass loadings ranged from 0.67 to 3.0 g/m2 on the FDB surfaces
in the return and 0.5 to 1.92 g/m2 on the FDB in the supply. These loadings were substantially
48
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lower than measured in the tests with the galvanized steel ducts and the FDL. In the previous
tests, the galvanized return ducts had mass loading that ranged from 5.0 to 14.7 g/m2 at the
corresponding locations. In the FDL system, the dust mass on the bottom of the duct (collected
with the brush) ranged from 4.8 to 11.3 g/m2. The loading of dust on the FDB was comparable to
previous tests, however, if the measurements with the MVDS brush sampler were used. As
shown in Table 10, the mass of dust (and fibers) in samples collected from the bottom of the
return duct ranged from 5.0 to 17 g/m2 using the MVDS brush sampler. Visual inspection of the
samples, however, showed that there was a substantial amount of fiber material on the filters.
Confidence in the accuracy of the measurements of dust on FDB surfaces is considered to be
low. Visual inspection of surfaces sampled with the nozzle indicated that particulate matter was
still present on the surface, which will result in an under-estimate of the particle mass on the
surface. Inspection of the samples collected with the brush indicated that substantial amounts of
fibers were collected, which will result in an over-estimate of the particle loading on these
surfaces. Therefore, neither sampling method appears to give accurate measurements of the dust
deposited on the surfaces.
In the supply, the pre-cleaning measurements with the MVDS-nozzle were 1.92 g/m2 at
S-l and 0.5 g/m2 at S-2. The collocated samples with the brush were nearly the same, being 1.74
g/m2 at S-l and 0.44 g/m2 at S-2. These mass loadings are nearly the same as the background
measurements. Based on visual observation, the loading in the supply duct was very low; dust
was barely visible on the surface. Visual inspection of the filters indicated a large amount of
fibrous material on filters used for both the nozzle and filter samplers. Therefore, the results in
the supply may be more indicative of background contribution from the fibers than the amount of
dust deposited on the surface.
The amount of dust collected prior to cleaning from the surface of the flexible duct used
in the FDB system was 0.17 g/m2, which was lower than on comparable surfaces in the previous
tests. The mass of dust collected from the foil liner in the air handler in the test with the FDB
system was also lower than in previous tests. This may have resulted from higher deposition
rates on the fibrous surface of the return duct in this test.
Measurements of dust in the FDB system following cleaning are presented in Table 11.
The average mass collected with the MVDS-nozzle from five locations on the cleaned FDB in
-------
the supply and return was 0.28 ±0.16 g/m2. This was substantially lower than either the pre-
cleaning or background samples collected from FDB surfaces. The mass of dust on the one
flexible duct location sampled was 0.15 g/m2, nearly the same as the pre-cleaning sample.
6.2.1.4 Evaluation of the Duct Dust Sampling Methods - Summary. The MVDS-brush
method worked well on the galvanized steel surface. Because there was no concern about
dislodging surface materials it could be used aggressively to obtain the maximum collection
efficiency. The method also worked well on the FDL used in this study. Although background
mass was collected from surfaces of the new FDL prior to loading of the dust into the system, the
amount of background mass from "clean" FDL was not substantially higher than that collected
from the surface of flexible duct and foil liner in the same system. The amount of mass collected
from "clean" FDL surfaces was also similar to that collected from galvanized steel duct surfaces,
flexible duct surfaces, and foil liner after ACS cleaning. Visual inspection of surfaces sampled
with the MVDS fitted with the nozzle for sample collection indicated that the nozzle could not
effectively collect dust adhered to the surfaces of ACS components. The nozzle was not
considered to be adequate for dust sampling based on this study and was not used in the field
study.
The precision of the MVDS/brush sampling method was generally very good for
duplicate side-by-side samples in spite of the variability of particle deposition in the ducts. The
%RSD for duplicates was 9% and 37% for galvanized steel surfaces in pre-cleaning samples. On
the FDL surface, the % RSD was 8 and 25 % for pre-cleaning samples. The precision of the
method for samples from flexible duct surfaces was 11%, 24%, and 40%. This level of precision
is probably adequate for sampling duct dust from ACS components because the dust loading at
different locations in an ACS can be expected to be highly variable. During this study, the
precision of the NADCA method was not evaluated. It was evaluated in the laboratory and in the
field study by collecting duplicate samples.
The NADCA sampling method was used only to collect post-cleaning samples from
galvanized steel duct surfaces. This is currently the only application for which the method is
recommended. Previous laboratory testing indicated that it was not applicable for collection of
dust samples prior to cleaning because of the low collection efficiency and because particulate
-------
matter was lost from the filter if the amount of particulate mass was high. Testing in the PACS,
as shown in Table 6 indicated that results with the NADCA method were substantially lower
than with the MVDS-brush method. The samples collected with the NADCA method
demonstrated that the ACS cleaning was effective based on the NADCA criterion that residual
dust can not exceed 0.1 g/m2 (1 mg/100 cm2). But the criterion was not met if the MVDS-brush
method was used to sample from galvanized steel duct surfaces. For collocated samples with the
NADCA and MVDS-brush method, the MVDS method mass measurements results were 18, 26,
and 37 times higher than the NADCA method results. Measurements with the MVDS-nozzle
method were 9, 15, and 30 times higher providing additional evidence that the NADCA sampler
has low collection efficiency.
Results from the three tests suggest that the NADCA criterion of 1 mg/100 cm2 (0.1 g/m2)
for verification of cleaning effectiveness is too low when samples are collected with an efficient
sampler. The average mass collected on the cleaned galvanized steel duct surfaces was 0.26 ±
0.11 g/m2 (2.6 mg/100 cm2). On flexible duct surface, the average mass was 0.27 ± 0.09 g/m2.
The mass on the cleaned foil liner of the air handler was 0.28 g/m2 in the galvanized duct system.
Similar results were observed in the FDL system where the average mass on surfaces after
cleaning was 0.39 ± 0.08 g/m2 on FDL, 0.30 ± 0.06 g/m2 on flexible duct, and 0.24 g/m2 for the
one foil liner sample. When efficient sampling methods such as the MVDS brush method are
used, a more appropriate criterion for cleaning effectiveness is probably residual dust of less than
0.5 g/m2 (5 mg/100 cm2) based on the results of these tests.
6.2.2 Microbiological Surface Samples
6.2.2.1 Galvanized Steel Duct System. The results of the microbiological surface
sampling of the galvanized duct system using the two methods - swab and vacuum - are
summarized in Table 12. The test locations are the same as used in the dust mass sampling, and
are shown on Figure 2. The culturable fungi for all samples were below the minimum detection
level. On the other hand, culturable bacteria were found above the detection limit at all locations
prior to cleaning. Comparison of the precleaning bacterial loadings with the dust loadings
(Tables 6 and 12) shows that the bacterial loading is somewhat correlated with the dust loading
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Table 12. Microbial Results for Galvanized Steel in cfu/cm2
Duct
Location
Sample Type
Fungi
Bacteria
preclean
postclean
preclean
postclean
Supply
SI
Vacuum
<5
<5
5
< 5
Swab
<5
<5
20
<5
S3
Vacuum3
<5
<5
10
<5
Swab
<5
<5
25
<5
Swab3
<5
<5
130
<5
Return
R1
Vacuum
< 5
<5
5
<5
Swab
< 5
<5
40
<5
R2
Vacuum
5
<5
85
5
R3
Vacuum
5
<5
190
<5
Swab
5
<5
120
<5
a Swab sample collected from same area after vacuum sample completed.
but that large variation is present. The ratio of bacterial counts to dust mass varied from 2.2xl04
to 11.3 x 104 cfu/g. All the loadings are low and would not represent serious contamination.
Comparison of the swab and vacuum technique results shows that the ratio of swab to
vacuum counts ranged from 0.63 to 8 with a mean of 5.6. The wide ranges are not surprising
because the measurements include dust spatial variability, variability in the particles with which
the microbiological material is associated, and measurement variability. On the whole, the swab
samples of galvanized duct appear to sample a larger culturable bacterial sample than does the
vacuum technique.
6.2.2.2 Fibrous Glass Duct Liner System. The results of the microbiological surface
sampling of the FDL system using the two methods - swab and vacuum - are summarized in
Table 13. The test locations are the same as were used in the dust mass sampling, and are located
on Figure 2. Prior to cleaning, the culturable fungi for many samples were below the minimum
detection level while for others, the fungal levels were measurable. Following cleaning, all
fungal levels were below the detection limit of 5 cfu/cm2. As with the galvanized system,
culturable bacteria were found above the detection limit at all locations prior to cleaning.
52
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Table 13. Microbial Results for FDL in cfu/cm2
Duct
Location
Sample Type
Fungi
Bacteria
preclean
postclean
preclean
postclean
Supply
SI
Vacuum
<5
<5
25
5
Swab
5
<5
5
<5
S3
Vacuum
< 5
<5
<5
30
Swab
<5
< 5
50
<5
Return
R1
Vacuum
10
< 5
200
< 5
Swab
<5
<5
15
<5
R2
Vacuum
5
<5
30
<5
Swab
5
<5
160
<5
R3
Vacuum
10
<5
100
5
Swab
5
<5
70
<5
Following cleaning they were found to be at or below the detection limit.
Comparison of the pre-cleaning microbial loadings with the dust loadings (Tables 8 and
13) shows that the range of culturable bacterial counts to dust loading was 9 x 104 to 44 x 104
cfu/g. As with the galvanized steel duct, on average swab sampling collected more bacterial
counts than did the vacuum technique, though the levels are again low. However, individual site
ratios ranged from 0.2 to 10 with a mean of 3.3 and a very large standard deviation of 4.4.
6.2.2.3 Fiberglass Duct Board System. The results of the microbiological surface
sampling of the FDB system using the two methods - swab and vacuum - are summarized in
Table 14. The test locations are the same as were used in the dust mass sampling, and are located
on Figure 2. Prior to cleaning, the culturable fungi ranged from the minimum detection level to
450/cm2. The duct dust was apparently more highly loaded microbially than were the other two
injected dust samples. Following cleaning, the fungal levels ranged from below the detection
limit to 50 cfu/cm2, a significant reduction in numbers, but leaving ample spores for growth to
occur should conditions become favorable. As shown in the last two columns, culturable
53
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Table 14.
Microbial Results for FDB in cfu/cm2
Duct Location Sample Type Fungi Bacteria
preclean
postclean
preclean
postclean
Supply
SI
Vacuum
55
10
25
<5
Swab
20
5
15
15
S2
Vacuum
not obtained
10
not obtained
5
S3
Vacuum
50
not obtained
25
not obtained
Swab
<5
<5
10
<5
Return
R1
Vacuum
450
20
200
15
Swab
190
25
130
5
R2
Vacuum
220
50
260
10
Swab
220
<5
130
25
R3
Vacuum
180
45
65
15
Swab
50
<5
35
5
bacteria were found be present at about the same levels as the fungi before cleaning and to be
removed with approximately the same efficiency. Comparison of the microbial loadings with the
dust loadings (Tables 10 and 14) again shows that the culturable bacterial loading per gram of
dust ranged from 11 x 104 to 75 x 104 cfu/g. On this more open-pored material, the ratio of swab
to vacuum results was uniformly less than one, with a mean of 0.43 for fungi and 0.57 for
bacteria. Relative to the other two duct systems, these fungal and bacterial values are high
enough to have greater significance for comparison of the two methods. This result is consistent
with the observation that the FDB visibly retained more dust below the surface than did the other
duct material, where it was available to the vacuum sampling technique but not to the swab.
54
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6.3 Aerosol Measurements
6.3.1 PM10 and PM2 5 Particle Mass Measurements
Integrated samples of particulate matter were collected in the instrument room on one day
prior to ACS cleaning and on the day following cleaning during each of the three tests. Samples
of inhalable particles (PM10) and respirable (PM2 5) particles were collected using MS&T
samplers over nominal periods of 24 hours. The objective of the sampling was to shake-down
the instrumentation prior to use in the field study. In particular, the tests were performed to
determine if the air flow rates would be stable for a 24 hour sampling period and to verify that
the pump timers and elapsed time meters worked properly. The Climet optical particle counter
was operated concurrently in order to evaluate the relationship between particle counts and mass
determinations. Both methods were planned for use in the field study. The sampling was limited
in scope and not intended to determine the effect of ACS cleaning on IAQ, although the data may
be useful in designing future tests in pilot scale ACS facilities. Table 15 presents the results
Table 15. Comparison of PM10 and PM25 Integrated Air Samples and Concurrent Optical
Particle Measurements in the Instrument Room
Parameter - Sampling Period
Units
Galvanized
Steel Duct
Fibrous Glass
Liner
Fiberglas
Duct Board
PM1(I - Pre-Cleaning
|ig/m3
11.8
3.8
8.0
PM10 - Post-Cleaning
Hg/m3
1.7
10.3
6.5
PM2 5 - Pre-Cleaning
|ig/m3
10.5
3.2
8.5
PM2 5 - Post-Cleaning
Hg/m3
1.8
10.1
6.5
Particles >0.5 |am (Climet) -
Pre-Cleaninga
particles x 106/m3
1.61
2.67
5.81
Particles > 0.5 |im (Climet) -
Post-Cleaning11
particles x 106/m3
1.47
4.73
2.96
Particles >5.0 |_im (Climet) -
Pre-Cleaninga
particles x 106/m3
0.0011
0.0013
0.0004
Particles >5.0 |im (Climet) -
Post-Cleaning1'
particles x 106/m3
0.0012
0.0007
0.0003
a Average particle concentration during the period of integrated sampling
55
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integrated and optical sampling during concurrent periods. (All the optical data is not included.)
Qualitatively, the data collected in these tests show a relationship between airborne
particle concentrations and particle counts in the > 0.5 |am size fraction. In all three tests the
differences between pre- and post-cleaning PM10 and PM2 5 mass reflect temporal changes in the
particle concentrations measured with the Climet optical particle counter. However, there was no
clear correlation between the particle mass and particle concentrations. As an example, the
particle mass for PM2 5 in the pre-cleaning sample for the galvanized system was 10.5 |ag/m3 and
the corresponding average particle count was 1.61 million particles/m3, but for the PM2 5 sample
collected following cleaning of the FDL system, the particle the mass was similar, 10.1 |ig/m3,
but the average particle concentration was 4.73 million particles/m3 during the integrated
sampling period. Because of the limited number of samples, the correlation between the two
parameters could not be assessed. There also did not appear to be a relationship between particle
counts for the > 5.0 pm fraction and PM10 mass.
The reader is warned not to interpret the data in Table 15 to mean that particle mass and
particle counts increased in the instrumentation room following ACS cleaning. As will be shown
in the following sub-section, the results are an artifact of the time period during which the
integrated samples were collected.
The primary objective of the test, shakedown of the samplers, showed that they were
suitable for use in the field study to collect 24-hour samples; air flow rates were stable at the end
of the 24 hour period and the pumps and timers worked properly. However, as discussed below,
the data also showed that use of integrated samples may be inappropriate for evaluating the
impact of air duct cleaning on airborne particle concentrations if the particle concentrations are
highly variable.
6.3.2 Particle Concentrations - Optical Particle Counter
The Climet CI-4100 was used during each test to monitor particle concentrations in the
instrumentation room. Measurements were made in both channels; concentrations of particles in
the greater than 0.5 (am size fraction and in the greater than 5.0 |_im size fraction were measured.
The primary purpose of the measurements was to evaluate the instrument and the monitoring
-------
protocols proposed for use in the field study. Concentrations measured in the instrument room
were not intended to assess the impact of ACS cleaning on IAQ, but may be useful in designing
future testing in pilot scale ACS systems.
The time variation of particle concentrations in the two size fractions during the three
tests are depicted in Figures 4 through 9. Overall average particle concentrations during pre-
cleaning and post-cleaning time periods are presented in Table 16 (which includes data not in the
Table 15 concurrent period averages.)
The particle concentrations measured in the > 0.5 (am size fraction with the Climet were
generally below 4 million particles/m3 during the test with the galvanized duct system. As shown
in Figure 4, particle concentrations in the instrumentation room dropped on the day prior to
cleaning (pre-2) when the air bypass was disconnected and the air flow was restored to the
instrumentation room. This air was filtered as it moved from the instrument room to the mixing
room, causing the number of particles circulating in the system to drop. The average particle
concentrations for the period prior to ACS cleaning were 1.62 and 0.0011 million particles/m3 for
the > 0.5 (im and > 5.0 |im size fractions, respectively (Table 16).
Following the pulse of particles observed on system start-up, the particle concentrations
after ACS cleaning were similar to the period immediately before cleaning for both size fractions
(Figures 4 and 5). Particle concentrations did not vary substantially during either period, as
shown by the relatively flat concentration profiles. It should be noted that smoother curves
following cleaning of the galvanized and FDL systems are an artifact of the sampling protocol.
In the post-cleaning periods, data were saved as 20-min averages rather than as the 10-min
average used in the pre-cleaning period. This was necessary in order to save all data over the
weekend; the Climet has limited data storage capacity. This, however, had no impact on the
interpretation of the data except that information on very short-term variability was lost, as
indicated by the smoother concentration profile in the post-cleaning period.
Particle concentration profiles during the test with the FDL are depicted in Figures 6 (>
0.5 |_im fraction) and 7 (> 5.0 |im size fraction). During this test, the concentrations of particles
in the > 0.5 |nm fraction were higher and more variable than in either of the other two tests. For
an unexplained reason, particle concentrations increased dramatically on the day prior to
cleaning. But after cleaning the concentrations were lower and generally continued to decrease.
57
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20000000.0 -r
Galvanized Steel Duct
Climet: >0.5um
18000000.0
16000000.0
14000000.0 -
Cleaning
Post-Cleaning
Pre-Cleaning
12000000.0 --
n
E
¦2 10000000.0 -
'€
re
Q.
room bypass
disconnected
system re-started
8000000.0 -
6000000.0
4000000.0
2000000.0
0.0
-I 1
o
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CM
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CO
CD
CO
o
CD
ID
CO
O
CD
CO
O
CM
CD
CO
o
CD
Pre 1 Pre 2 Day 0 Post 1 Post 2 Post 3
Figure 4. Airborne particle concentrations in the > 0.5 }im size fraction during the test with the galvanized steel duct system
-------
100000.0
90000.0
80000.0
70000.0
60000.0
•g 50000.0
t
ra
a
40000.0
30000.0
20000.0
10000.0
Pre-Cleaning
o.o
i
room bypass
disconnected
Galvanized Steel Duct
Climet: >5.0um
-I H
Cleaning
Post-Cleaning
system re-started
OCOCNCOOCOCNJCOOIOCNCOO
5.0 |am size fraction during the test with the galvanized duct system
-------
20000000
Fibrous Glass Duct Liner
18000000
Pre-Cleaning
Cleaning
Post-Cleaning
16000000
14000000
12000000
n
E
-g 10000000
'£
ra
a
system re-started
room bypass
disconnected
8000000
6000000
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CO
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00
o
Pre 1 Pre 2 Day 0 Post 1 Post 2 Post 3
Figure 6. Airborne particle concentrations in the > 0.5 fim size fraction during the test with the fibrous duct liner system
-------
30000
Fibrous Glass Duct Liner
Climet: >5.0um
CD
25000
20000
u
'€
ra
Q.
15000
10000
5000
Pre-Cleaning
room bypass
disconnected
Cleaning
Post-Cleaning
system re-started
COCNCOOCOCNCOOCOCNCOOCOCNCOOCOCMCOOCOCNCOOCD
Pre 1
Pre 2
Day 0
Post 1
Post 2 Post 3
Figure 7. Airborne particle concentrations in the > 5.0 |am size fraction during the test with the fibrous duct liner system
-------
20000000
Duct Board
Climet: >0.5um
18000000
16000000 -
14000000
Pre-Cleaning
Cleaning
Post-Cleaning
12000000
r>
E
•2 10000000
€
(0
Q.
room bypass
disconnected
8000000
6000000
system re-started
4000000
2000000
OO
o
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Pre 1 Pre 2 Day 0 Post 1 Post
Figure 8. Airborne particle concentrations in the > 0.5 [im size fraction during the test with the FDB system
-------
3000
CT3
GO
2500
2000
re
Q.
1000
500
Pre-Cleaning
room bypass
disconnected
Duct Board
Climet: >5.0um
Post-Cleaning
Cleaning
system re-started
Pre 1
Pre 2
Day 0
Post 1
Post 2
Figure 9.
Airborne particle concentrations in the > 5.0 |am size fraction during the test with the FDB system
-------
Table 16. Average Particle Concentrations (particles X 106/m3) Measured with Climet During
Pre- and Post-Cleaning Periods in the Three Tests
Parameter/Test
Period
Galvanized
Steel Duct
Fibrous Glass
Liner
FDB
Particles >0.5 |am Pre-
particlesX106/m3
1.62
7.97
5.22
Cleaning
Particles > 0.5 |jm
particlesX106/m3
1.47
2.86
2.35
Post-Cleaning
Particles >5.0 |am Pre-
particlesX106/m3
0.0011
0.0017
0.0003
Cleaning
Particles >5.0 |am
particlesX106/m3
0.0011
0.0006
0.0003
Post-Cleaning
The pulse of particles observed on system re-start with the galvanized duct system was not
clearly evident with the FDL system. Particle concentrations in the >5.0 um fraction showed a
similar, although less dramatic, trend. As shown in Table 16, the average particle concentrations
in both fractions were substantially lower after cleaning.
Figures 8 and 9 show particle concentrations during the FDB test. The changes in
concentrations for both size fractions show a trend similar to that observed in the FDL test.
Concentrations were substantially higher in the pre-cleaning period. The average concentration
after cleaning was about half that of the pre-cleaning period (Table 16) for the > 0.5 |im fraction.
Average concentrations of the >5.0 (am fraction were similar in the pre- and post-cleaning
periods.
Measurements with the Climet optical particle counter in the instrument room during the
three cleaning tests showed lower average airborne particles concentrations during the post-
cleaning periods in all three tests. It is likely that the lower concentrations resulted from cleaning
of the ACS components. But it is difficult to draw definitive conclusions from this limited data
set. The instrumentation room door was kept closed except for entry to download data and to
change filter media. Therefore, intrusion of particles into the room from the outside was likely to
be low. However, we do not know whether higher particle concentrations in the pre-cleaning
periods may have been a function of the dust in the ACS components or if it was related to a
64
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higher level of activities in the building housing the PACS which might result in higher
concentrations in the instrument room.
As discussed in the previous sub-section, integrated samples were collected concurrently
with the optical particle measurements during a single period in the pre-cleaning period and again
in the post-cleaning period. The data collected with the Climets clearly show the limitations of
these integrated samples for evaluating the impact of ACS cleaning on airborne particle
concentrations. As reported in Table 15, both the PM2 5 and the PMI0 mass levels were higher in
post-cleaning than in pre-cleaning samples during the test with the FDL. However, the
continuous particle concentration data suggests that this was an artifact of the sampling protocol.
Pre-cleaning samples were collected on pre-cleaning day 1 which had lower particle
concentrations than pre-cleaning day 2. Had the integrated sample been collected on pre-
cleaning day 2, the data would probably have shown a substantially higher particle mass
concentration and changed the interpretation of the data as it related to ACS cleaning
effectiveness. The effect (i.e., artifact of sampling) observed in this test would likely be
important in occupied residences where particle concentrations may vary dramatically due to
occupant activity. This observation confirmed the need to collect multiple integrated samples
during the field study.
The testing of the Climets in the instrument room showed that they were suitable for use
in the field study. The primary limitation of the Climet CI-4100 was that only a single channel of
data could be output to the IAQDS data logger. During these tests, the >0.5 pm channel was
recorded with the IAQDS. Data for the > 5.0 pm fraction was saved internally in the Climet data
storage system, but could not be output simultaneously. Therefore, it was necessary to also
download the Climet with a laptop computer to obtain both the > 0.5 pm and the > 5.0 pm data.
With a 10-min averaging time, it was necessary to download the data once every 33 hours. This
was done during the tests in the PACS.
6.3.3 Particle Concentrations - Multi-Channel Spectrometer
The LAS-X spectrometer was used in the tests with the galvanized steel duct system and
the FDL system. There were problems with the computer used for data logging during both tests.
65
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Only two of the four data sets were retrieved. Due to concurrent ACS cleaning tests at the EPA
test house, the LAS-X was not available for use in the tests with the FDB system.
The average particle concentrations in the 16 size fractions are presented in Table 17 to
show the distribution of particles by size fraction. Although data were not collected that were
useful in evaluating the impact of ACS cleaning in the PACS, the objectives of the testing of the
LAS-X were met in that problems with the hardware and method were identified and resolved
prior to use of the instrument in the field.
Table 17. Average Particle Concentrations Measured With the LAS-X in the Instrumentation
Room (Particles X 106/m3)
Particle Size Fraction (|_im)
Galvanized - Post-Cleaning
FDL - Pre-Cleaning
0.10-0.12
10.383
51.272
0.12-0.15
10.912
52.414
0.15-0.20
11.103
70.405
0.20 - 0.25
4.484
47.587
0.25 - 0.35
3.854
52.126
0.35 - 0.45
1.268
20.020
0.45 - 0.60
0.379
4.965
0.60 - 0.75
0.038
0.562
0.75-1.0
0.037
0.376
1.0-1.5
0.029
0.160
1.5-2.0
0.009
0.033
2.0 - 3.0
0.006
0.014
3.0-4.5
0.003
0.005
4.5 - 6.0
0.001
0.002
6.0-7.5
0.0006
0.0007
>7.5
0.003
0.004
6.3.4 Fiber Concentrations
Concentrations of airborne fibers were measured with the integrated sampling method
prior to, and following, ACS cleaning in the three tests. The fiber samples were collected in
duplicate in the instrument room. A sample was also collected outside of the PACS in the large
66
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bay where the test facility was housed. The sampler was placed within 5 meters of the
instrumentation room and samples were collected concurrently. The minimum detection limit of
the sampling method was 0.001 fibers/cm3. Fibers were detected in only one of the 15 samples
collected during the study. In the pre-cleaning sample collected during the test with the
galvanized system, the concentration was 0.001 fibers/cm3 in one sample, but below the detection
limit in the duplicate sample. Fibers were not detected in any samples collected during tests with
the FDL system or the FDB system.
The MEE FAM-1 Fibrous Aerosol Monitor was also used during selected periods during
the tests with the galvanized duct and the FDL. Fiber concentrations were below the limits of
detection of the instrument throughout the tests.
The method selected for fiber sampling was a standard method used for collection of
asbestos and non-asbestos man-made fibers. The detection limit was considered to be adequate
for the purposes of this testing. Although fibers could not be detected in air samples collected
during these tests, the method was still considered adequate for the field study.
6.3.5 Bioaerosols
The test dust was not sterilized prior to injection, and thus contained whatever
microbiological contaminants were present when it was collected. These particles had the
potential to become airborne during PACS operation. The concentrations of culturable fungi
were measured in the instrument room at four times through a duct system cleaning cycle.
(Bacteria are not a common indoor bioaerosol.) A background measurement was made prior to
soiling the duct, with the bypass in place. A dirty duct sample was collected following soiling
and conditioning, removal of the bypass, and with the system running. For the galvanized duct, a
duct cleaning sample was taken just as the system was restarted following cleaning. The post
clean sample was taken 24 hours following cleaning. The results for the galvanized duct are
given in Table 18.
The fungal concentrations reported in Table 18 are relatively low, and below what are
frequently encountered outdoors. However, they are well above the detection limit for the
Mattson-Garvin and the replication is good. Except for the post cleaning sample, all the samples,
67
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Table 18. Airborne Fungal Concentrations for Galvanized Steel Duct in cfu/m3
Galvanized Steel Duct
Time
replicate
mean
background
23
18
12
dirty duct
23
26
28
duct clean
31
19
7
post clean
119
104
88
including the background taken prior to dust injection, are about the same. The results of the
galvanized duct post clean sample taken beginning just as the PACS was started up following
cleaning was interesting in that detailed examination of the Mattson-Garvin plates showed that
most microorganisms were collected in the first 15 min (83%), with 11% collected in the second
15 min, 4% in the third, and 2% in the balance of the sample period.
The airborne concentrations for the FDL and FDB systems are given in Table 19. While
higher levels were detected for the galvanized duct, that may be related to the extended
conditioning period rather than any characteristic of the duct. The results for the FDL and FDB
Table 19. Airborne Fungal Data for FDL and FDB Systems, cfu/m3
Time
FDL
replicate
mean
FDB
replicate
mean
background
nd
nd
nd
nd
nd
nd
dirty duct
8
9
nd
nd
10
nd
duct clean
nd
nd
nd
nd
nd
nd
post clean
5
7
10
10
8
na
68
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duct systems indicate that few fungal spores became airborne from the freshly deposited and
conditioned dust, and the levels are so low that the samples do not provide any information about
performance of the systems. The post clean samples for the FDL and FDB systems were taken
after 24 hours rather than at startup because the presence of an initial particle pulse had been
previously reported and confirmed with the galvanized duct results. The effects 24 hours later
were thought to be more important.
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7.0 QUALITY ASSURANCE/QUALITY CONTROL
Quality control and quality assurance for this project were described in Air Conveyance
System Cleaning Pilot System Development, Characterization, and Operation: Project Work
and QA Plan (RTI, 1995). The project included method development and environmental
parameter measurement, as well as application of duct cleaning methods. The QA plan included
environmental measurement instrument calibration and adjustment during the equipment
checkout period and field blanks and duplicates for the sampling activities. The sampling
methods were largely developmental and followed written procedures that were modified as
required. The data quality indicators for the project are given in Table 20.
7.1 Quality Control
7.1.1 Environmental Instrumentation
The PACS thermocouples (as read through the data acquisition system) were compared to
a reference thermocouple at the time of installation. The PACS thermocouples were read with a
precision of 0.06°C (0.1 °F) and had a claimed bias of ± 0.06°C (0.1 °F). Using the reference
thermocouple, they were found to be calibrated to within ± 2°C for the in-room sensors and to
be identical for the in-duct sensors. Relative humidity was measured using a sensor with 0.1%
RH precision and a claimed ±3% bias. The sensors were compared to a sling psychrometer in
fan-only operation of the PACS. Relative to a sling psychrometer, the in-room sensors (low
flow) had a -7 to -9% RH bias. The in-duct RH sensors had a -10 to -11% RH bias. The values
reported in this report are uncorrected.
While the QA plan contemplated flow rate measurement using a velocity traverse, the
velocity pressure was marginally low for a standard pitot tube. An averaging pitot device with a
hydraulically amplified pressure differential was used instead. The measurement precision was 1
ft/min at 500 cfm and the bias was stated to be ± 1% at 500 ft/min. The supply and return
velocity probes were found to give the same velocity results, and the velocity was in agreement
with the air handler performance. No change in instrument reading was noted on dust injection,
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Table 20. Data Quality Indicator Goals.
Measurement Parameter
Precision
Bias
Completeness
PACS Temperature
1°C
1°C
90%
PACS Relative Humidity
2% RH
5%RH
90%
PACS Air Flow Rate
1%
5%
90%
MVDS Sampler
20%
>75%a
90%
NADCA Method 1992-01
20%
>75 %a
90%
High Volume Surface Sampler
20%
>75%a
90%
Microbial Surface Measurement
20%
>75%a
90%
Percent recovery from surface being sampled.
though the instruments became noticeably soiled.
As the experiment developed, the environmental parameter measurements were found not
to be critical measurements and the in-duct sensors were used only with the galvanized duct.
Primarily, these measurements were intended to characterize the air handling units and assist in
understanding dust transport. Initial dust loading experiments showed that no special effort was
required to disperse the dust, and that the mixing room temperature and RH measurements were
adequate to characterize the system. Thus the duct environmental measurements became of
secondary interest. In addition, physical access constraints made the instruments very difficult to
remove, clean, and reinstall. Time constraints on the dust loading, conditioning, and cleaning
phases of the research were also severe and prevented redesign of the instrumentation.
7.1.2 Dust Mass Sample QC
Duplicate samples were identified in the data tables presented in Section 6.2.1. The
precision of the MVDS/brush sampling method was generally very good for duplicate side-by-
side samples in spite of the variability of particle deposition in the ducts, except for the FDB.
The %RSD for duplicates was 9% and 37% for galvanized steel surfaces in pre-cleaning samples.
On the FDL surface, the % RSD was 8 and 25 % for pre-cleaning samples. The precision of the
71
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method for samples from flexible duct surfaces was 11%, 24%, and 40%. This level of precision
is probably adequate for sampling duct dust from galvanized and FDL ACS components because
the dust loading at different locations in an ACS can be expected to be highly variable.
Also discussed in Section 6.2.1 was the unsuitability of the tested methods when used
with FDB systems. The loading of dust on the FDB was comparable to previous tests, however,
if the measurements with the MVDS brush sampler were used, ranging from 5.0 to 17 g/m2 using
the MVDS brush sampler. Visual inspection of the samples, however, showed that there was a
substantial amount of fiber material on the filters. Confidence in the accuracy of the
measurements of dust on FDB surfaces is considered to be low. Visual inspection of surfaces
sampled with the nozzle indicated that particulate matter was still present on the surface, which
will result in an under-estimate of the particle mass on the surface. Inspection of the samples
collected with the brush indicated that substantial amounts of fibers were collected, which will
result in an over-estimate of the particle loading on these surfaces. Therefore, neither sampling
method appears to give accurate measurements of the dust deposited on the FDB surfaces.
During this study, the precision of the NADCA method was not evaluated. It was
evaluated in the laboratory and in the field study by collecting duplicate samples.
7.1.3 Microbiological Duct Sample QC
The microbiological duplicates were comparisons of swab and vacuum samples as
described in Section 6.2.2. The loadings were generally low and therefore of limited
comparative value. Treating the supply samples and the return samples as replicates for each
duct material, and considering the precleaning bacterial loadings, the vacuum method gave
%RSDs of 0 to 99% over the three materials. In the same way, the swab sample method results
gave %RSDs between 28 and 116%. Over all samples, the ratio of bacterial counts to dust mass
ranged from 2.2 to 75 cfu/g. Based on these measurements, the vacuum and swab sample
methods are estimated to be capable of measurement precision in the range of 20 to 50%, which
is greater than expected. Bias cannot be estimated.
7.1.4 Microbial Aerosol QC
Microbial aerosol measurements were made only for fungi because these organisms are
-------
the likely indoor microbial hazard. Only the galvanized steel duct gave moderate airborne fungal
levels, perhaps because some active growth occurred during the extended conditioning period.
Duplicates were run each time, and the mean %RSD for the galvanized steel test geries was 42%.
7.1.5 Aerosol Measurement QC
Pump air flow rates were measured at the start of the sampling period and required to be
within ± 5% of the target flow rate of 20 L/min. Gravimetric mass determinations were
performed in the EPA controlled environment weighing facility in the Annex at EPA-RTP in
accordance with the SOP cited on page 20, Section 5.2.2. The SOP specifies that prior to
analysis of filters, the balance span is set with a calibrated S class weight. The balance is also
zeroed prior to weighing. A daily check filter is then weighed. At the completion of each 10
filter weighings, the zero and span settings are rechecked.
The Climets, LAS-X, and aerosol fiber monitor were not calibrated prior to the tests in
the PACS. The objective was to shake-down the sampling and monitoring methods prior to use
in the field study, not to collect quantitative data on air contaminants in the PACS. The
instruments were calibrated prior to Phase n, the field study.
7.2 Method Performance
As discussed at length in Section 6.2.1.4, the MVDS-brush method was found to work
well for surface dust collection on the galvanized steel surface and on the FDL surface. The
MVDS-nozzle method was not satisfactory and its use is not recommended. No method worked
well for FDB. Similarly, no sampling method worked for air conditioner coils.
The NADCA method was found to greatly understate the dust mass remaining on the
surface when compared to the MVDS brush method.
For microbiological surface measurements, the vacuum method was found to be more
reliable on a variety of surfaces than the swab method, though either could be used for qualitative
measurements. The methods used were satisfactory.
The various particle and aerosol measurements were well developed and functioned as
expected. Comparison of particle mass samplers and various optical particle counters is
problematical in most applications and was so in this research. However, the instruments
-------
appeared to function properly.
7.3 Data Completeness
The data completeness goal for all sample types was 90%. This goal was met for all
sampling measurements, except the dirty duct bioaerosol sampling in the FDB system, which
were not collected.
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8. REFERENCES
Ahmad, I., B. Tansel, and J. D. Mitrani. 1994. Effectiveness of HVAC Sanitation Processes in
Improving Indoor Air Quality. Technical Publication No. 113, Department of
Construction Management, Florida International University, Miami, FL.
Carl, M. and J. Smilie. 1991. A Guide for Air Conditioning Tuneups for Small Business
Managers. Louisiana Department of Natural Resources, Sonya D. Davis, Program
Manager, Baton Rouge, LA.
EPA. 1991. Building Air Quality, a Guide for Building Owners and Facility Managers, EPA-
400/1-91-033, U.S. Environmental Protection Agency, Office of Air and Radiation,
Washington, DC. ISBN 0-16-035919-8.
Fellman, G. 1994. Results of Two Recent Studies on Residential Air Duct Cleaning Are
Questionable. DucTales, Vol. 6, No. 4, pp. 19-24. Published by National Air Duct
Cleaners Association, Washington, DC.
Fortmann, R., C. Gentry, K.K. Foarde, and D. W. VanOsdell. 1997. Results of the Pilot Field
Study to Evaluate the Effectiveness of Cleaning of Air Conveyance Systems and the
Impact on Indoor Air Quality in Residences. Report to U.S. Environmental Protection
Agency, Air Pollution Prevention and Control Division, Office of Research and
Development, Research Triangle Park, NC. June, 1997.
Fugler, D. and M. Auger. 1994. A First Look at the Effectiveness of Residential Duct Cleaning.
Paper 94-TP48.03, 87th Annual AWMA Meeting, Cincinnati, OH, June 19 -24, 1994.
Krafthefer, B.C. and U. Bonne. 1986. Energy Use Implications of Methods to Maintain Heat
Exchanger Coil Cleanliness. ASHRAE Transactions. Vol. 92, Pt. 1, pp. 420-430.
NADCA, 1992. Mechanical Cleaning of Non-porous Air Conveyance System Components,
NADCA Standard 1992-01. National Air Duct Cleaners Association. Washington, DC.
RTI, 1995. Air Conveyance System Cleaning Pilot System Development, Characterization, and
Operation: Project Work and QA Plan. Submitted to the National Risk Management and
Reduction Laboratory, U. S. Environmental Protection Laboratory, Research Triangle
Park, NC under Cooperative Agreement CR-822870.
RTI, 1996 Field Microbiological Investigation of Ventilation System Cleaning: Project
Work/QA Plan. Submitted to the National Risk Management and Reduction Laboratory,
U. S. Environmental Protection Laboratory, Research Triangle Park, NC under
Cooperative Agreement CR-822870.
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