United States Environmental Protection Agency National Risk Management Research Laboratory Research Triangle Park, NC 27711 Research and Development EPA/600/SR-97/066 August 1997 SEPA Project Summary Phase I Pilot Air Conveyance System Design, Cleaning, and Characterization Douglas W. VanOsdell, Karin K. Foarde, and Roy Fortmann Air conveyance system (ACS) clean- ing, is advertised to homeowners as a service having a number of benefits, including the improvement of indoor air quality (IAQ). Because ACS clean- ing includes many procedures applied to many different duct systems, evalu- ation has been difficult and the effec- tiveness of ACS cleaning has not been adequately measured. The objective of this project was to develop and refine surface and airborne contamination measurement tech- niques that could be used to evaluate ACS cleaning. The research was in sup- port of a field study to be conducted later. To this end, a pilot air convey- ance system (PACS) using full-size resi- dential heating and air-conditioning (MAC) equipment was constructed and operated to provide a controlled, artifi- cially soiled, ACS environment. The PACS consisted of ducts, an MAC unit, a dust mixing room, an instrument room, and a dust generation and injec- tion system. Three types of duct sys- tems were evaluated with the proposed measurement methods under unsoiled and soiled conditions. Each duct sys- tems was then cleaned by professional ACS cleaners and reevaluated. As a result of the pilot study, the surface contamination measurement methods were evaluated over a range of conditions and improvements. Sur- face contamination (microbial and total dust) measurement methods and visual inspection showed that the pilot unit was effectively cleaned by the meth- ods applied during this study. Submi- cron and larger particle counts were reduced following ACS cleaning, and respirable particle mass was reduced for two of the three duct systems tested. The significance of these results in an actual residence was not determined. This Project Summary was developed by EPA's National Risk Management Research Laboratory's Air Pollution Prevention and Control Division, Re- search Triangle Park, NC, to announce key findings of the research project that is fully documented in a separate report of the same title (see Project Report ordering information at back). Introduction The overall objectives of the Air Pollu- tion Prevention and Control Division's (APPCD's) Air Duct Cleaning Program are to determine when and how to clean ven- tilation systems, and evaluate both the effectiveness of such cleaning and its im- pact on IAQ. Little published research data are available to support the IAQ improve- ment claims sometimes made by ACS cleaning contractors, and the data that are available are difficult to interpret. A two-phase research program was under- taken to develop evaluation methods to achieve these objectives. This report de- scribes research conducted under Phase I of the program. The research was a cooperative effort, led by RTI, with partici- pation by personnel from APPCD, Acurex Environmental, Inc., and the National Air Duct Cleaners Association (NADCA). Its objective was to develop and operate a PACS as a test bed suitable for: • Development and testing proposed ACS cleaning evaluation methods, and • Comparison of IAQ instrumentation, intended for use in the field, under controlled conditions that were also as realistic as possible. ------- Phase II, a field study to be reported separately, was undertaken to evaluate ACS cleaning in actual residential use. Though commonly referred to as "duct cleaning," ACS cleaning properly includes the cleaning of all air-side components of a ventilation system: air handler, heat exchanger, humidifier, blower, and duct system. It is sometimes advertised to homeowners as a service capable of pre- venting and possibly mitigating IAQ prob- lems and may improve the energy effi- ciency of the relatively dirty systems. ACS cleaning 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. Many combinations of clean- ing procedures can be used on any given system, and there are many types of sys- tems. Procedures Pilot Air Conveyance System A PACS was constructed in a high-bay laboratory to allow artificial soiling of air duct components using a reasonable test aerosol. As shown in Figure 1, the pilot system included commercially available components expected to accumulate dust in varying degrees (e.g., bends, diffusers, registers, grills, blowers, heat exchang- ers, expansions, contractions, regions of surface irregularity, and dampers) and was designed to allow application of all as- pects of the proposed evaluation methods with the exception of evaluation of IAQ in residences, including pre- and post-clean- ing inspections and evaluations. The MAC equipment was all scaled for a small resi- dence. The PACS was constructed of the following modules to simplify cleaning and allow substitution of new test components: 1) supply and return air ducts, 2) MAC unit including air-conditioning coil and heat exchanger, 3) dust mixing room, 4) instru- ment room, and 5) dust generation sys- tem. The PACS was operated in two modes: • normal operation with flow into both rooms, and • bypass of the instrument room during dust injection. Standard, commercially available MAC equipment was used when possible. So that evaluation methods could be devel- oped for the three major duct materials, completely separate PACS duct systems were constructed of the three duct materi- als commonly utilized in residential MAC: galvanized steel, fibrous glass duct liner (FDL), and fibrous glass duct board (FOB). A new air handler was installed for each duct type. Supply air sample locations S1-S4 53—7 Dust feed r^Oj S4- S2- \ Supply air Temp, RH, and flow sensors ,— S1 Dust mixing room Humidifier Supply air duct I I I I I I I Tim Instrument room R1 . Return air duct R2 R3 Air handling unit R4 Return air sample locations R1-R4 Return air temp RH, and flow sensors Figure 1. Elevation view of PACS. ------- >ACS Cleaning Measurement Methods The measurement parameters and sam- pling and analysis methods evaluated were: 1) total surface dust loading, 2) culturable microbial surface loading, 3) re- spirable aerosol concentrations (PM10 and PM25), 4) size dependent particle number concentration, 5) airborne fiber mass and counts, and 6) fungal bioaerosol concen- trations. The primary sampling method being evaluated (and hence, the parameter of greatest interest during the study) was measurement of the mass of dust on sur- faces of the ACS components prior to and following ACS cleaning. Several variations of vacuum sample collection were evalu- ated, the most promising being the Me- dium Volume Dust Sampler (MVDS), which drew 10 L/min of air through a small brush or a custom designed slit nozzle. A second important parameter mea- sured was the number of culturable mi- crobial organisms deposited on the duct and MAC surfaces within a 10 cm2 tem- plate area, as measured with a swab tech- nique and a 10 L/min vacuum method. Because of the short time between inject- ing the dust and sampling during most of these tests, microbial growth on the duct was not an issue during this research. Airborne particle mass was measured with integrated size dependent impactor samplers at 10 L/min. Continuous optical particle monitors were set up in the instru- mentation room of the PACS, measuring number concentration in three ranges: greater than 0.5 urn, greater than 5 urn, and over 16 differential channels between 0.1 and about 10 |jm Bioaerosol samples were also collected in the room using a 28.3 L/min slit to agar impactor. Although the data, particularly those 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 con- centrations based on the data presented in the report due to the limited scope of the measurements and the artificial na- ture of the dust deposits and physical arrangement of the room in which the measurements were made. Application of the Test Methods in the PACS A complete test series for a single duct system consisted of a number of operat- ing periods: 1) installation of the new duct system and checkout; 2) pre-soiling eval- uation of the duct and MAC unit, 3) duct soiling and deposited dust conditioning, 4) post-soiling, pre-cleaning evaluation of the duct and MAC unit, 5) post-soiling, pre- cleaning air sampling, 6) cleaning the ven- tilation system, 7) post-cleaning evalua- tion before restarting the MAC unit, 8) immediate post-cleaning air sampling, 9) post-cleaning air sampling for total par- ticles after cleaning, and 10) post-clean- ing (24-hr) sampling. ACS Cleaning Methods Several procedures used during the cleaning phase of PACS operation were common to all three duct systems: 1) the supply and return grills were removed, power washed, and replaced as one of the final steps; 2) the interior of the MAC unit and the blower were cleaned each time; 3) the evaporator coil in the MAC unit was inspected and cleaned each time using a commercial coil cleaner; 4) nega- tive system pressure was achieved each time by placing large portions of the duct system under vacuum so that the dust and debris loosened and entrained by the cleaning devices were transported to a large vacuum blower/filter unit capable of drawing 1 m3/s (2000 cfm). It remained running as long as debris was being gen- erated. The three duct systems were cleaned using similar techniques. With the duct system isolated and under negative pres- sure, the galvanized steel duct was cleaned using primarily a stiff, abrasive- coated, cylindrical rotary power brush to loosen the dust. The test dust adhered well, and multiple passes were required to clean corners and the stiffening beads in the duct. Following brushing, air washing (configured to move debris through the system toward the main vacuum source) was used to entrain and transport any remaining dislodged dust to the collector. Cleaning of the fiberglass lined and the duct board ducts was different primarily in that the rotary power brush was con- structed of cloth strips to loosen the dust while minimizing damage to the duct ma- terial. Frequent inspection was used to prevent over cleaning and consequent damage to the duct. Hand-brushing was used where required. Results and Discussion An overview of the sampling conducted during this research is provided in Table 1. The discussion below presents selected results. Total Duct Dust Sampling The MVDS brush method worked well on the galvanized steel duct surface. Be- cause there was no concern about dis- lodging surface materials, it could be used aggressively to obtain maximum collec- tion efficiency. The method also worked well on the FDL used in this study. Al- though 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 col- lected from galvanized steel duct surfaces, flexible duct surfaces, and foil liner after ACS cleaning. The precision of the MVDS/brush sam- pling method was generally very good for duplicate side-by-side samples in spite of the variability of particle deposition in the ducts. Duplicate samples were obtained in locations similar in apparent dust load- ing. Over all the sampling in the three duct types and the flexible feeder ducts, the standard deviation of duplicates was between 8 and 40% of the mean mass for the pre-cleaning samples. This level of precision is probably adequate for sam- pling duct dust from ACS components be- cause the dust loading at different loca- tions in an ACS can be expected to be highly variable. The NADCA sampling method was used only to collect post-cleaning samples from galvanized steel duct surfaces. This is cur- rently the only application for which the method is recommended. It is not an effi- cient sampling method. The average mass collected on the cleaned galvanized steel duct surfaces was 0.26 + 0.11 g/m2, while prior to cleaning the average of all samples was 7.0 + 4.4 g/m2. On the flexible duct surface, the bottom-of-duct average prior to cleaning was 4.3 + 4.0 g/m2 while after cleaning the overall average 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 galva- nized 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 appropri- ate criterion for cleaning effectiveness is probably residual dust of less than 0.5 g/ m2 based on the results of these tests. The sampling results for the duct board system are inconclusive because all sample contained a large fraction of fibers that confounded efforts to measure re- moval of deposited dust. ------- Table 1. Measurements Conducted Parameter Dust loading Dust loading Dust loading Dust loading Microbial loading Bioaerosol concentration Sampling Method Manual Manual Manual Manual Manual Integrated Instrumentation EADS - brush EADS - nozzle NADCA method High volume sampler Pipettip sampler Mattson-Garvin slit to agar impactor Analysis Method Gravimetric Gravimetric Gravimetric Gravimetric Plate counting Plate counting Notes Primary method For duct board Un-lined galvanized only Cooling coils only Applied to all ducts 1-hr integrated samples PIVL PM10 Integrated Integrated MS&T impactor/filter and 20 Ipm pump MS&T impactor/filter and 20 Ipm pump Gravimetric Gravimetric 24-hr integrated samples 24-hr integrated samples Particles > 0.5|im (counts) Particles > 5.0|im (counts) Particle count - 16 channel Fibers Fibers Continuous: 10-min averages Continuous: 10-min averages Continuous: 60-min averages Integrated Semi-continuous ClimetCI-4100 ClimetCI-4100 LAS-X Filter/SKC pump MIE FAM-1 Optical (scattered light) Optical (scattered light) Laser aerosol spectrometer Phase contrast microscopy Optical fiber monitor Recorded with IAQDS and Climet Recorded by Climet Direct download to laptop computer NIOSH 7400 method - 24-hr integrated samples PDL-10data logger Microbial Surface Samples The microbial surface samples showed that duct cleaning significantly reduced the microbial loading (by factors of 10 to 20). However, the loadings were low and not amplification sites, so the results cannot be applied to microbial problem ducts. The nozzle technique gave results comparable to but generally lower than the swab on the galvanized and duct liner system, and higher on the duct board. Overall, the nozzle system was preferable for all sys- tems. Aerosol Measurements The aerosol measurements were all con- ducted as an instrumentation and proce- dure shakedown study, and were not in- tended to establish the effect of ACS clean- ing on indoor air quality. Integrated PM25 and PM10 samples were collected in the instrument room during pre- and post- cleaning nominal 24-hr periods for each duct system. All concentrations were low (1.8 to 11.8 |j,g/m3 while the National Am- bient Air Quality PM10 Annual Primary Standard is 50 u,g/m3). The effect of the ACS cleaning was not clear-cut, given the small number of samples and lack of con- trol over the particle content of infiltrating air. Following cleaning of the galvanized duct system, the inhalable particle mass was lower; it was higher for the fibrous glass liner; and about the same for the duct board system. The instrument shake- down that was the study's major purpose was successful, as pump and timer op- eration and flow stability were verified. The mean optical particle counter re- sults (an integrated sample) were simi- larly inconclusive with respect to the ef- fect of duct cleaning but productive as an equipment shakedown test. Post-cleaning particle counts for particles >0.5 and >5.0um were mostly lower following clean- ing, but the differences are probably not significant. Examination of the particle counter re- sults as a function of time during the tests gave additional information. During most of the 24 hour period, particle counts in the instrument room actually were lower following cleaning of each duct. However, a burst of particles was emitted on start- up that raised the after-cleaning mean. This decrease occurred with both particle size ranges, and was especially clear for the >0.5 um particles. The optical particle counter results show clearly that particle concentrations change from day to day even in a simple system such as the PACS and that aerosol samples must be taken over several days to make valid compari- sons. Airborne Fiber Measurements Fibers were generally found to be be- low detection limits using both the inte- grated mass sampler and an optical de- tector. Bioaerosols The bioaerosol concentration was low in the instrument room for all tests. Con- centrations high enough to allow pre- and post-cleaning comparisons were only reached with the galvanized duct. In this case, the overall culturable fungal con- centration rose following AHU start-up (from about 20 cfu/m3 during the back- ground, dirty duct, and during-cleaning ------- samples) to 104 cfu/m3 in the hour imme- diately following system startup. However, over 80% of that increase was sampled in the first 15 minutes of the 60-minute sample. After 45 minutes, the fungal con- centration was down to about 2 cfu/m3. Conclusions and Recommendations Overall, the PACS was successful as a test bed for sampling method develop- ment. That is, dust could be injected and conditioned, and the system cleaned such that the PACS was a reasonable labora- tory surrogate for a residential ACS. Op- erated for only short periods, as was true of this work, it was not suitable for biocontaminant studies because active growth was not present. Conclusions from this research are summarized below: 1. Previously collected duct dust can be dispersed into a duct system and con- ditioned 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 practi- tioners, had reasonable distribution in the duct system and adhesion to the duct. 2. A pilot ventilation system can be used to investigate some aspects of ACS cleaning under controlled conditions and provide results that may be appli- cable to field ACS cleaning. Additional research is needed to understand all the parameters involved in obtaining a suitable ACS dust deposit, including dust injection and conditioning. 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 galva- nized steel, FDL, and foil liner sur- faces of ACS components. Collection efficiency of the MVDS with the brush was higher than the MVDS with a slotted nozzle or the NADCA Vacuum Test Method. The MVDS with brush is recommended to sample dust mass deposited on surfaces during the Phase II field study. NADCA Standard 1992-01 should be only used as in- tended. 4. Neither the MVDS with the slotted nozzle nor that with the brush was suitable for collection of dust from FOB. The brush dislodged a substantial amount of fibrous material from new FOB, while the nozzle did not effec- tively remove deposited dust on the fibrous surface. Accurate measure- ments of dust on FOB surfaces can not be made with the vacuum meth- ods used in this study. If FOB clean- ing is to be evaluated, a suitable sur- face sampling method must be devel- oped. 5. The dust loading on bare galvanized steel duct surfaces that were cleaned was less than 0.02 g/m2 when mea- sured with the NADCA Vacuum Test Method, meeting the NADCA Stan- dard 1992-01 criterion for effective cleaning. Collocated measurements with the MVDS-brush were 0.26, 0.37, and 0.36 g/m2 at the three locations, demonstrating the low collection effi- ciency of the NADCA Vacuum Test method. 6 For microbial sampling of dust depos- ited on the surface of various fibrous glass and galvanized metal surfaces, the vacuum method provided more consistently reliable results than the surface swab technique and should be used in future studies. It was par- ticularly superior on fibrous materials. 7. 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. The amount of dust measured on ACS components after cleaning was com- parable to those made prior to soiling in the PACS. 8. The impact of ACS cleaning of par- ticle concentration indoors remains unclear because infiltration and filtra- tion effects confounded the results. 9. The importance of collecting multiple integrated samples and the need to measure particle concentrations for ex- tended pre- and post-cleaning periods were evident in the indoor particle data. 10. No evidence was obtained for fiber emission from the cleaned duct sys- tems, but the scope of this research was too limited to allow a definitive conclusion on fiber emissions from FOB. 11. A brief pulse of particles was released when the galvanized ACS was re- turned to service following cleaning. This phenomenon was detected by both the bioaerosol and optical par- ticle samplers. 12. While not a focus of the study, as the research progressed it became ap- parent that ACS construction quality was an important variable in both PACS operation and the "cleanability" of an ACS. While poor construction practices did not interfere with this study, which focused on methods de- velopment 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 un- lined galvanized duct installed in the PACS had no apparent construction flaws. The butt joints between sec- tions 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 cleaning. The cut edges in the FOB system did not appear to be sealed and were not coated. These construction details, while not in ac- cordance with applicable construction standards, were flaws that the duct cleaning professionals considered to be very common. In addition to duct quality shortcom- ings, the air handler, though it was in "as received" condition, was not per- fectly sealed, and coil bypass and leaks occurred at several points. 13. 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 estab- lished in the ACS. Accomplishing this would present some risk of exposure for those working in the vicinity unless the PACS was redesigned for con- tainment to prevent exposure, and may be impractical. Such studies are needed, and use of smaller biocontamination study apparatus is thus recommended. 14. Biocides, encapsulants, and sealants are all used in residential ACS clean- ing 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. ------- Douglas I/I/ VanOsdell and Karin K. Foarde are with Research Triangle Institute, Research Triangle Park, NC 27709; Roy Fortmann is with Acurex Environmental Corporation, Research Triangle Park, NC 27709. Russell N. Kulp is the EPA Project Officer (see below). The complete report, entitled "Phase I Pilot Air Conveyance System Design, Cleaning, and Characterization, "(Order No. PB97-189682; Cost: $25.00, subject to change) will be available only from: National Technical Information Service 5285 Port Royal Road Springfield, VA 22161 Telephone: 703-487-4650 The EPA Project Officer can be contacted at: Air Pollution Prevention and Control Division National Risk Management Research Laboratory U.S. Environmental Protection Agency Research Triangle Park, NC 27711 United States Environmental Protection Agency Center for Environmental Research Information Cincinnati, OH 45268 Official Business Penalty for Private Use $300 BULK RATE POSTAGE & FEES PAID EPA PERMIT NO. G-35 EPA/600/SR-97/066 ------- |