EPA/600/A-98/Q26
EVALUATING RESIDENTIAL AIR DUCT CLEANING AND IAQ:
RESULTS OF A FIELD STUDY CONDUCTED IN NINE SINGLE '
FAMILY DWELLINGS
Russell Kulp1, Roy Fortmatin2, Gary Gentry2, Douglas VanOsdeli3, Karin Foarde3, Tim
Hebert4, Robert Krell4, and Charlie Cochrane4
1 U.S. Environmental Protection Agency, Research Triangle Park, North Carolina, USA
2 Acurex Environmental Corporation, Research Triangle Park, North Carolina, USA
3 Research Triangle Institute, Research Triangle Park, North Carolina, USA
4 National Air Duct Cleaners Association, Washington, District of Columbia, USA
ABSTRACT
A nine-home field study was conducted to investigate the impact of mechanical air duct
cleaning (ADC) methods on indoor air quality (IAQ) and system performance. ADC services
were provided by the National Air Duct Cleaners Association (NADCA). Only mechanical
ADC methods were evaluated. Surface treatments, such as biocides or encapsulants, were not
part of the study, Pre- and post-ADC measurements were used to evaluate impacts. These
included deposited duct dust measurements, airborne particle and fiber concentrations,
microbial bioaerosol and surface sampling, and system performance factors such as
temperature, relative humidity, air flow rates, and static pressure. Surface sampling in ducts
indicated that mechanical ADC is effective in removing adhered dust and dirt. The particle
measurement data could not offer a clear indication that indoor levels can be reduced using
mechanical ADC because there was an apparent strong influence from outdoor particle mass
concentrations. Mechanical ADC did not significantly reduce bioaerosol or microbial density in
the houses studied. Measurements of system performance factors suggest that ADC may have
a positive effect. Supply air rates increased between 4 and 32% in eight of the houses and
return air flow rates increased 14 and 38% in two of the houses.
INTRODUCTION
The U.S. Environmental Protection Agency (EPA), Office of Research and Development
(ORD) and NADCA are actively engaged in research that is designed to focus on issues related
to IAQ, source management., and their relationship to the ADC industry (1). This paper
presents the results of a field study performed by the EPA and NADCA. Nine residences were
studied with the intention of improving our understanding of residential ADC procedures. The
objectives were to evaluate mechanical ADC methods commonly used to clean non-porous
surfaces and to measure pre- and post-ADC environmental system parameters to investigate
any impacts on IAQ and system performance. Surface treatments such as biocides and
encapsulants were not a part of the field study.
METHODS
The study was conducted in nine residential dwellings. Eight of the residences were occupied.
The ninth was the EPA's IAQ Test House (TH) in Gary, NC. Each house was equipped with a
I
-------
central heating and air-conditioning (HAC) forced air distribution system. ADC had not been
performed on the AHU (air handling unit) or duct system for at least 10 years, and all
occupants were nonsmokers. Table 1 shows the house characteristics. These houses presented
NADCA with a variety of system configurations for ADC. A week-long study was carried out
at each house. The Acurex Environmental Corporation and the Research Triangle Institute
performed all environmental and system measurements.
Table1. Characteristics of field study test houses
No.
1
2
3
4
5
6
7
8
9
House Age
(yrs)
20
22
18
10
9
28
25
26
35
Duct Age
(yrs)
20
22
18
10
9
not avail.
25
26
35
AHU Age
(yrs)
20
22
0.5
10
9
not avail.
not avail.
26
not avail.
Duct
Material
a
b
c
d
d
b
c
b
b
House Size
(m2)
121.2
141.2
134.7
183.9
185.8
181.6
92.9
185.8
139.3
No. of
Floors
1
1
1
2
2
1.5
1.5
2
2
a. Galvanized sheet-metal trunk ducts with internal fiberglass ductliner insulation and insulated flexible plastic
branch ducts
b. Galvanized sheet-metal ducts with external fiberglass wrap insulation
c. Galvanized sheet-metal trunk ducts with external fiberglass wrap insulation and insulated flexible plastic
branch ducts
d. Insulated flexible ducts
Sampling procedures and instrumentation were identical for each of the test houses. Pre- and
post-ADC measurements included supply and return air duct dust surface mass, airborne
particle mass (PM) and fiber measurements, microbiological measurements, temperature,
relative humidity, and carbon dioxide (CO2), and system performance factors such as static
pressure, air flow rates, motor current, and refrigerant temperature.
Levels of dust in the ducts (grams per square meter) were determined by collection of
deposited dust samples at selected locations using two methods, the Medium Volume
Deposition Sampler (MVDS) (2) and the NADCA Standard Method 1992-01 (3); The MVDS
was developed for this study so that both pre- and post-cleaning deposition dust levels could
be evaluated. The current NADCA Standard Method 1992-01 can be used to evaluate only
post-cleaning levels.
PM ranges of 2.5 fj,m (PM2 5) and 10 /^m (PM10) were measured at three locations, outdoors
and at two indoor locations. Measurements were taken using the size selective impactors
developed for use in the EPA's Building Assessment Survey Evaluation (BASE) Program (4).
-------
Additional particle sampling (particles per cubic meter) was performed using a Climet model
CI-4100. The monitor was used in the >0.5 /zm particle size mode so that all particles greater
than that size were counted. These real-time measurements of particle number concentrations
were augmented by use of a LAS-X particle size/counter. The LAS-X was collocated with the
Climet and was used to measure room concentrations in the size fraction of approximately 0.1
to 3 /mi geometric diameters.
Fiber concentrations were monitored continuously using a MIE FAM-1 Fibrous Aerosol
Monitor. Also, integrated samples of airborne fibers were collected using the NIOSH Method
7400, Asbestos and Other Fibers by PCM (5). Total fiber concentrations were determined in
accordance with NIOSH Method 740GB counting rules. Additionally, a filter sample collected
prior to ADC and one collected after ADC were analyzed by scanning electron microscope
(SEM) to determine the relative abundance of different types of fibers, such as fiber glass,
cellulose fibers, and hair.
Bioaerosol samples were taken in the ducts and in the houses using either a Mattson-Garvin
slit-to-agar sampler or a 1-stage Andersen cascade sampler. Microbial surface density
measurements were conducted near where the duct dust deposition samples were taken using
filter cassette and sterile swab techniques.
Temperature, relative humidity, and CO2 concentrations were monitored continuously in the
primary living area of each house using the IAQ data logging system developed by the EPA.
The mechanical ADC methods and equipment employed by NADCA varied according to the
house air distribution system, configuration, and accessibility. ADC methods included portable
negative air systems to collect and remove loosened dust and debris. Silica-carbide rotating
brushes, air washing with compressed air and air whips, contact vacuuming, and hand-wiping
were used to loosen the dust and debris.
A substantial effort was expended in cleaning the AHU. It was substantially disassembled and
cleaned using hand-wiping and contact vacuuming. The fan, impeller, and scroll housing were
removed and wet-cleaned using a non-toxic cleaning fluid. The condensate drain pan, piping,
and pumps were inspected and cleaned as necessary. System filters were removed and cleaned
or replaced. System cooling coils were wet-cleaned in place using a non-toxic cleaner. Heating
coils were wiped and hand vacuumed.
NADCA routinely performed a high level of visual inspections during the cleaning to ensure
that the ADC process was proceeding satisfactorily. Access to the ductwork was generally
through end caps and flexible duct connections. Access doors were installed in the ductwork
when access to work areas was difficult. Registers and difiusers were removed and wet-
cleaned using a non-toxic cleaning fluid.
RESULTS
The mechanical ADC methods employed appeared to be effective in removing deposited dust
from duct surfaces. Figure 1 shows pre- and post-cleaning measurements in the supply ducts at
-------
all of the test houses using the MVDS. Pre-cleaning supply duct deposition ranged from 1.48
g/m2 at house no. 5 to 26.03 g/m2 at house no. 9. Figure 1 shows that post-cleaning supply
duct measurements ranged from 0.18 g/m2 at house no. 7 to 0,79 g/m2 at house no. 9. These
measurements do not meet the NADCA criterion that residual dust must be less than 0.1 g/m2
(3).
o
Q.
ju -
75 -
"?n .
i*i -
m „
0 -
I
m
1
|
|
TH
sa—
•
s
%
1^_
|L
1
23456
House number
ESSH**
m
I
7
J?!|_
8
M
n
t
'%.
1
1
•M
4,
P
1
S_
9
m
Pre-clean
Post-clean
Figure 1. Supply duet deposition measurements using MVDS
On the other hand, post-cleaning supply duct measurements using the NADCA Standard
Method, which are not shown,' ranged from 0.003 g/m2 at house no. 8 to 0.036 g/m2 at house
no. 2. These measurements meet the NADCA criterion for residual dust (3).
Baseline indoor respirable (PM2 5) and inhalable (PM10) particle mass concentrations were low
at the houses, ranging from 4.2 to 32.7 ^g/m3, consistent with studies in houses without
tobacco smoking (6). Interpretation of the PM measurement data is difficult because outdoor
concentrations will have an impact on indoor concentrations. The outdoor concentrations
varied over the course of each week-long study making it difficult to determine if the changes
in indoor concentrations after ADC were the result of cleaning or due to changes in either
outdoor concentrations or occupant activities.
For the same reasons, the Climet data were inconclusive with respect to determining ADC
impact. Again, these data suggest that the outdoor PM concentrations may have such a strong
influence on indoor levels that airborne particle differentials from pre- to post-ADC cannot be
detected.
A comparison of average pre- and post-ADC bioaerosol levels shows a reduction in airborne
fungi; however, these reductions are not considered substantial. None of the test houses were
considered to be biocontaminated; therefore, a small change would not be surprising. Pre-ADC
airborne fungi levels in the supply ducts ranged from 14 to 646 cfij/m3 while the post-ADC
-------
levels ranged from 2 to 300 efu/m3, >
Bacteria in samples collected from the surfaces of the HAC system were highly variable; Pre-
ADC bacteria levels ranged from 5 to 1100 cfli/cm2 in the supply ducts and from 5 to 2300
cfu/cm2 in the return ducts, with a mean for all samples of less than 200 cfu/em2. Mean
concentrations of return air bacteria levels were lower after ADC in six of seven houses;
however, in the supply ducts, this was true for only four of the occupied houses, Pre- versus
post-ADC differences were generally small.
Fungal levels were generally higher than bacteria levels, and ADC had the most impact on the
ducts with the highest levels of fungi and noticeably reduced the level of fungi in surface
samples collected from ducts in most houses.
Measurements of system performance factors suggest that ADC had a positive impact.
Because of the small sample size and the limited duration of the measurements, it is not
possible to quantitatively determine the significance of ADC on system performance and
energy use. Generally it resulted in increased air flow to the house. Supply air flows increased
between 4 and 32% at eight houses based on measurements at the floor registers and diffusers
in the house. Part of the increase in supply air flow rates may have been attributable to minor
duct repair. Return air flows measured at the return air grilles increased 14 to 38% at two
houses, but were not substantially different after ADC at the other seven houses.
AHU blower mot or'current increased after ADC at the four field study houses where the
measurements were performed. Static pressure increased in the return air duct at the six
houses with complete measurements. The increases in both blower motor current and static
pressure in the return air ducts suggest improved system performance. There was no clear
trend for changes in static pressure in the supply ducts or the differential pressures across the
cooling coil. Refrigerant line surface temperatures did not provide useful information.
DISCUSSION
Heating, ventilating, and air-conditioning (HVAC) systems contaminated with adhered dirt and
dust deposition are potential IAQ emission sources (7). Research shows that HVAC total
volatile organic compound emission rates and odors may be effectively reduced by removing
deposition (8)(9)(10). This field study demonstrated that mechanical ADC methods can be an
effective source management tool when applied to non-porous bare sheet-metal ducts. Porous
surfaces, such as fibrous glass duct lining (FGDL), were not evaluated because houses with
FGDL systems, but without visible surface mierobial contamination, could not be found. When
FGDL becomes microbiaOy contaminated, the EPA and N1OSH recommend removal and
replacement rather than any form of ADC (i 1). Further research is required to evaluate ADC
effectiveness on porous surfaces.
Differentials in indoor PM levels from pre- to post-ADC could not be detected. This is
consistent with previous research (12) and is probably due to the strong influence of outdoor
PM sources (6).
Mechanical ADC methods alone did not substantially reduce bioaerosol and culturable surface
-------
microbial levels. Surface treatments such as biocides or encapsulates may be required if it is
determined that substantial reductions are necessary. To folly evaluate this, future research
should include comparisons using mechanical ADC in combination with surface treatments.
The MVDS sampling method appeared to be an effective way to quantitatively assess both pre-
and post-cleaning duct deposition levels. The MVDS was specially designed for this study and
has a higher collection efficiency than the NADCA Standard Method due to the higher air flow
rate and use of a brush on the nozzle (3). The data from this study demonstrate that the
NADCA Standard 1992-01 criterion of 0.1 g/m2 to document the effectiveness of cleaning
should be applied only to samples collected with the Standard 1992-01 method. The criterion
of 0.1 g/m2 is not appropriate for samples collected with the MVDS sampling method. Results
from other EPA research (13) suggest that a criterion of approximately 0,5 g/m2 may be more
appropriate for samples collected with the MVDS.
Results of measurements of HAC system-related parameters suggest that there is a positive
impact on HAC system performance from mechanical ADC. These measured impacts cannot
be considered significant due to the small study population and the short monitoring period. To
substantiate these findings, further research is required.
REFERENCES
1. Kulp, R.N. EPA begins air duct cleaning research, Inside IAQ, EP A's Indoor Air
Quality Research Update. EPA/60Q/N-95/004, Spring/Summer 1995, pp. 10-11.
Environmental Protection Agency, Research Triangle Park, NC 27711; 1995.
2. Kulp, R.N. Update on EPA 's Air Duct Cleaning Research Activities. Proceedings of
Indoor Environment '97. IAQ Publications, Chevy Chase, MD 20815; 1997; pp. 24-34.
3. NADCA. Mechanical cleaning of non-porous air conveyance system components:
standard 1992-01. National Air Duct Cleaners Association. Washington, DC 20005;
1992.
4, Womble, S.E., J.R. Girman, and R. Highsmith. EPA BASE Program: collecting
baseline information on indoor air quality. Proceedings of IAQ'94: Engineering
Indoor Environments. American Society of Heating, Refrigerating and Air-
Conditioning Engineers, Inc. Atlanta, GA 30329; 1994.
5. NIOSH. Method 7400 - asbestos and other fibers by PCM. NIQSH Manual of
Analytical Methods. Fourth Edition. National Institute for Occupational Safety and
Health, Cincinnati, OH 45268; 1994.
6. Wallace, L. Indoor particles: a review. Journal of the Air & Waste Management
Association, Pittsburgh, PA 15222; 1996. 46:98-126.
7. Batterman, S. and H. Surge. HVAC systems as emission sources affecting indoor air
quality: a critical review. Report No. EPA-600/R-95-014 (NTIS PB95-178596).
Environmental Protection Agency. Research Triangle Park, NC 27711; February 1995.
-------
8, Ishikawa, K., T. Iwata, H. Ito, K. Kumagai, K. Kumura, and S. Yoshizawa. Field
investigation on the effectiveness of duct cleaning on indoor air quality with measured
results of WOC and perceived, air quality. Proceedings of Indoor Air '96, the 7*
International Conference on Indoor Air Quality and Climate, 1996. Vol. 2, pp. 809-
814.
9. Fanger, P.O. et al. Air pollution source in office and assembly halls, quantified by the
olfunit. Energy and Buildings. 1988. Pp. 1-6.
10. AIVC. Duct cleaning - a literature survey. Air Infiltration Review, vol. 14, No. 4, Air
Infiltration and Ventilation Centre, Coventry, UK; 1993.
11. EPA, Building air quality: a guide for building owners and facility managers. EPA-
400/1-91-033 (GPO 055-000-00390-4). U.S. Environmental Protection Agency.
Washington, DC 20460. National Institute for Occupational Safety and Health.
Washington, DC 20468. 1991.
12. Fugler, D. and M: Auger. A first look at the effectiveness of residential duct cleaning.
Proceedings of the 87* Annual Meeting & Exhibition. Air & Waste Management
Association. Pittsburgh, PA 15222; 1994.
13. Van Osdell, D.W., Foarde, K.K., Fortmann, R.C., and Kulp, R.N. Pilot Air
Conveyance System Design, Characterization, and Cleaning. Proceedings of
Engineering Solutions to Indoor Air Quality Problems. Air & Waste Management
Association. Pittsburgh, PA 15222; 1997.
-------
NRMRL-RTP-P-249
TECHNICAL REPORT DATA
(Please read faftruetions on the reverse before con
2.
, TITLE AND SUBTITLE
Evaluating Residential Air Duct Cleaning and LAQ:
Results of a Field Study Conducted in Nine Single
Family Dwellings
5. REPORT DATE
6, PERFORMING ORGANIZATION CODE
AUTHORS E.Kulp (EPA); R. Fortmann and C. Gentry
(Acurex); D. VanOsdell and K.Foarde (RTI); and
T.Hebert. R.Krell. and C. Cochrane (NADCA)
8, PERFORMING ORGANIZATION REPORT NO.
. PERFORMING ORGANIZATION NAME AND ADDRESS
10. PROGRAM ELEMENT NO.
A curex Environmental Corp., RTF, NC
Research Triangle Institute, RTF, NC
National Air Duct Cleaners Assn, Washington, DC
11. CONTRACT/GRANT NO.
68-D4-0005 (Acurex), CR82
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 COVf
Published paper; FY95-9(
RED
14. SPONSORING AGENCY CODE
EPA/6QO/13
is. SUPPLEMENTARY NOTES
541-7980. Presented at
CD project officer is Russell M. Kulp.
IAQ '97, Washington, DC, 9/27-10 /2T/97.
Mail Drop 54, 919 /
IB. ABSTRACT
paper gj_ves results of a nine-home field study of the impact of mechan-
ical air duct cleaning (ADC) methods on indoor air quality (IAQ) and system perfor-
mance. ADC services were provided by the National Air Duct Cleaners Association
(NADCA). Only mechanical ADC methods were evaluated. Surface treatments, such
as biocides or encapsulants, were not part of the study. Pre- and post-ADC measure
ments were used to evaluate the impacts. These included deposited duct dust mea-
surements, airborne particle and fiber concentrations, microbial bioaerosol and
surface sampling, and system performance factors such as temperature, relative
humidity, air flow rates, and static pressure. Surface sampling in ducts indicated
that mechanical ADC is effective in removing adhered dust and dirt. The particle
measurement data could not offer a clear indication that indoor levels can be reduced
using mechanical ADC because there was an apparent strong influence from outdoor
particle mass concentrations. Mechanical ADC did not significantly reduce bioaero-
sol or microbial density in the houses studied. Measurements of system performance
factors suggest that ADC may have a positive effect. Supply air rates increased be-
tween 4 and 32% in eight of the houses, and return air flow rates increased between
14 and 38% in two of the houses.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFlERS/OPEN ENDED TERMS
c. COSATI Field/Group
Pollution Particles
Residential Buildings
Ducts Fibers
Ventilation Aerosols
Cleaning
Dust
Pollution Control
Stationary Sources
Indoor Air Quality (IAQ)
P articulate
Bioaerosols
13B
13 M
13K
ISA
13H
11G
14G
HE
07D
18. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGES
20. SECURITY CLASS (This page)
Unclassified
22. PRICE
EPA Form 2220-1 19-73)
------- |