United States
Environmental Protection
Agency
National Risk Management
Research Laboratory
Research Triangle Park, NC 27711
Research and Development
EPA/600/SR-97/137 May 1998
Project Summary
Results of a Pilot Field Study to
Evaluate the Effectiveness of
Cleaning Residential Heating and
Air-Conditioning Systems and the
Impact on Indoor Air Quality and
System Performance
Roy Fortmann, Gary Gentry, Karin Foarde, and Douglas VanOsdell
The U.S. Environmental Protection
Agency (EPA), Air Pollution Prevention
and Control Division (APPCD) in con-
junction with the National Air Duct
Cleaners Association (NADCA) per-
formed a pilot field study to evaluate
the effectiveness of air duct cleaning
(ADC) as a source removal technique
in residential heating and air condition-
ing (MAC system) systems and its im-
pact on airborne particle, fiber, and
bioaerosol concentrations. Data were
also collected to assess the potential
impact of cleaning on performance of
the air handler and cooling system.
The field study was conducted at
EPA's Indoor Air Quality (IAQ) Test
House and eight occupied homes in
the Research Triangle Park area of
North Carolina. Week-long studies con-
ducted at each home involved back-
ground air monitoring and sampling,
cleaning of the MAC system by NADCA,
and post-cleaning monitoring and sam-
pling. Measurement parameters in-
cluded airborne particle, fiber, and fungi
concentrations; microbiological and
dust deposition sampling in the supply
and return air ducts; various system
related parameters including air flows,
static pressures, temperature, and rela-
tive humidity; and environmental pa-
rameters indoors and outdoors.
The report discusses the technical
approach for the study and the study
results. Results are presented on the
effectiveness of ADC, its impact on se-
lected IAQ parameters, and an assess-
ment of its impact on system perfor-
mance. Recommendations are provided
in the report on future research needs.
Results of this pilot study will be
useful to the EPA for preparing a strat-
egy for further research on heating,
ventilating, and air conditioning (HVAC)
system cleaning and development of
consumer information.
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
MAC system source removal is com-
monly referred to as air duct cleaning
(ADC). It generally involves the physical
removal of deposits of dirt, dust, particu-
late matter, and debris from air distribu-
tion systems including system components
such as fans, heating and cooling coils,
and control devices such as dampers and
turning vanes. In recent years there has
been a substantial increase in the number
of companies offering ADC services both
in commercial and residential buildings.
Despite some claims that ADC improves
IAQ and reduces heating and cooling en-
ergy costs, there is little published re-
search data on its effectiveness to meet
these claims. A research program has
been initiated by the EPA's National Risk
Management Research Laboratory
(NRMRL)to develop and provide informa-
-------
tion relevant to these issues. The research
is being conducted in conjunction with the
NADCA.
The objectives of this project included:
• Evaluate sampling and analysis meth-
ods that may be used to quantita-
tively assess the effectiveness of
cleaning (source removal) of non-po-
rous ductwork and components of
residential MAC systems.
• Collect information on the effective-
ness of currently available cleaning
methods for removal of dust and de-
bris from MAC systems in residences.
• Evaluate monitoring, sampling, and
analysis methods to determine if they
can be used to quantitatively assess
the impact of source removal from
MAC systems on airborne particulate
and fiber concentrations.
• Collect information on the impact of
MAC system cleaning on airborne par-
ticulate and fiber concentrations in
residences.
• Collect information on the impact of
cleaning on the performance of the
MAC system in residences.
• Collect information that can be used
to develop a research strategy for
further assessing the effectiveness
and impact of HVAC cleaning in resi-
dential and non-residential buildings.
Technical Approach
To evaluate ADC effectiveness, a pilot
field study was designed and implemented.
The study was conducted in the Research
Triangle Park area of North Carolina dur-
ing the summer of 1996. Participants were
recruited into the study who had central
(whole-house) cooling systems and forced
air distribution systems. The study was
performed at the unoccupied EPA Indoor
Air Quality Test House and eight occu-
pied houses that were purposefully se-
lected. Homes were selected for the study
that had a range of "dust" levels in the
supply and return ducts of the HAC sys-
tem, that varied in size and layout (e.g.,
two-story, single-story, and split-level
homes), and that differed with respect to
accessibility and complexity of the
ductwork. A week-long study was per-
formed at each home. Background air
monitoring and sampling were performed
for 2 to 4 days, then the system was
cleaned by NADCA. The air distribution
ducts and air handler components were
cleaned using methods commonly used in
the ADC industry and accepted for use by
NADCA in this study. No proprietary meth-
ods or truck-mounted systems were used
in this study. Sources were removed by
mechanical cleaning. Chemical biocides
were not used in this study. Monitoring
and sampling were performed for 2 to 4
days following cleaning.
Various parameters related to IAQ and
system performance were measured prior
to and following cleaning. The IAQ mea-
surements included 24-hr integrated par-
ticle mass concentrations (PM25 and PM10),
continuous measurements of particle con-
centrations (particles/cubic meter) with a
two-channel optical monitor, continuous
measurements of particle concentrations
with a 16-channel spectrometer, integrated
and continuous measurements of fiber con-
centrations, and airborne fungi concentra-
tions. Parameters related to the perfor-
mance of the air handling unit (AHU) in-
cluded air flows for the supply and return
air, static and differential pressures, cool-
ant line temperatures, AHU blower motor
current, supply and return temperature and
relative humidity (RH), and system on-
time. Additionally, temperature and RH
were measured indoors and outdoors. To
assess ADC effectiveness, the levels of
dust (particulate and fibrous combined)
were measured in the supply and return
ducts prior to and following, cleaning us-
ing a medium volume vacuum sampler
with collection on an in-line filter. Micro-
bial loading on duct surfaces was evalu-
ated using a vacuum/filter method for col-
lection of samples from a defined area.
Results and Discussion
The mass of dust (particulate and fi-
brous) deposited on the bottom surfaces of
the supply air ducts prior to cleaning ranged
from an average of 1.5 to 26.0 g/m2 at the
nine houses (Table 1). Dust levels were
higher on the bottom surfaces of the return
air ducts, ranging from an average of 5.3 to
35.1 g/m2. The HAC system cleaning meth-
ods employed in the study effectively re-
moved dust and debris. Post-cleaning dust
levels ranged from 0.06 to 1.97 g/m2 and
the average was 0.43 g/m2 for 58 samples
collected from the surfaces of supply and
return ductwork during the study.
Measurements of residual dust on
ductwork surfaces after cleaning with the
NADCA Standard 1992-01 vacuum
method ranged from 0.01 to 0.36 mg/100
cm2, meeting the NADCA criterion that
residual dust must be less than 1.0 mg/
100 cm2 to demonstrate that the cleaning
was effective. Side-by-side measurements
with the NADCA vacuum method and the
medium volume dust sampler (MVDS),
which was developed for this study,
showed that the collection efficiency of
the MVDS was higher than the NADCA
method. The results suggest that the cri-
terion for demonstrating that ADC is ef-
fective should be higher, probably 5 mg/
100 cm2, if the post-cleaning samples are
collected with the MVDS.
The impact of mechanical cleaning with-
out the use of chemical biocides on the
levels of bacteria in samples collected from
the surfaces of the HAC system was highly
variable. Bacterial pre-cleaning surface lev-
els in the ducts ranged from 5 to 1100 cfu/
cm2 in the supply side and from 5 to 2300
cfu/cm2 in the return, with a mean of less
than 200 cfu/cm2 in most homes. Mean
concentrations of bacteria in samples col-
lected from surfaces of return ducts were
lower after cleaning in six of seven houses
with return duct samples. But the bacteria
levels were lower in surface samples from
the supply ducts in only four of the occu-
pied homes and the pre-cleaning versus
post-cleaning difference was generally
small.
Fungal levels in samples collected from
duct surfaces were generally higher than
bacterial levels. Cleaning had the most
impact on the ducts with the highest lev-
els of fungi and noticeably reduced the
level of fungi in samples collected from
ductwork in most houses (Table 2).
There was no correlation between lev-
els of dust collected from surfaces of fur-
nishings in the homes and levels of dust
measured in either the supply or return
ducts. There was also little correlation be-
tween surface microbial loads and the dust
levels measured in the houses.
Indoor respirable (PM25) and inhalable
(PM10) particle mass concentrations were
low at the houses, ranging from 4.2 to
32.7 |ig/m3 (Table 3), consistent with re-
sults from past studies in houses without
tobacco smoking or other major sources.
The measurements of respirable and
inhalable particle mass concentrations in-
doors and outdoors suggest that, during
this study, the indoor concentrations were
strongly impacted by outdoor concentra-
tions. The indoor/outdoor ratios for the
integrated particle samples were less than
1.0 for all but two of 72 sets of samples
collected at the nine study homes. The
ratio of the post-cleaning to the pre-clean-
ing concentrations of respirable particles
measured indoors was greater than 1.0 at
seven of the nine houses (Table 3). How-
ever, at all but one of these seven houses,
the post-cleaning/pre-cleaning ratio was
also greater than 1.0 for the outdoor re-
spirable particle concentrations. The post-
cleaning/pre-cleaning ratios of PM10 con-
centrations indoors and outdoors followed
similar, but less clear, trends. Indoor par-
ticle mass concentrations may also have
been impacted by occupant activity and
other indoor sources. The results of the
particle mass measurements suggest that,
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Table 1. Mean and Maximum Dust Levels Measured on Surfaces of MAC System Ductwork in the Study Homes
Supply
Duct Dust Mass (g/m2)
Return
House
TH
1
2
3
4
5
6
7
8
Summary
Statistic
Mean
Max
Mean
Max
Mean
Max
Mean
Max
Mean
Max
Mean
Max
Mean
Max
Mean
Max
Mean
Max
Pre-Cleaning
2.33
4.66
8.62
26.30
3.37
5.79
1.91
3.00
1.48
1.69
2.28
2.62
2.30
2.45
3.34
5.93
26.03
36.07
Post -Cleaning
0.74
1.24
0.30
0.41
0.21
0.30
0.25
0.35
0.27
0.34
0.59
0.87
0.18
0.18
0.50
0.69
0.79
1.13
Pre-Cleaning
_a
_a
19.83
13.10
24.13
40.80
7.80
13.15
7.89
9.55
11.34
11.49
5.26
6.99
12.91
16.78
35.11
51.10
Post -Cleaning
_a
_a
0.58
0.63
0.44
0.60
0.28
0.42
0.12
0.17
1.11
1.97
0.15
0.19
0.32
0.34
0.39
0.59
1 Return air duct replaced; no samples collected.
Table 2. Results of Surface Samples of Fungi in the Supply and Return Ducts
Cfu/cm2
Summary
House Statistic
1 Mean
Max
2 Mean
Max
3 Mean
Max
4 Mean
Max
5 Mean
Max
6 Mean
Max
7 Mean
Max
8 Mean
Max
Supply
Pre-Cleaning
35700
250000
9217
19000
4604
8300
73400
1 60000
35
110
113
250
1089
3900
63
170
Post-Cleaning
1206
4700
138
640
740
1700
15890
36000
46
120
61
130
49
150
7
15
Return
Pre-Cleaning
2650
4800
280
320
22333
26000
850
1200
58
90
613
2600
2200
2400
196
320
Post-Cleaning
_a
_a
153
260
147
190
617
1000
71
140
7
15
23
40
10
15
1 No sample collected
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Table 3. Impact of ADC on Airborne PM25 and PM10 Concentrations
House
TH
1
2
3
4
5
6
7
8
Location3
Outdoor
Primary
Secondary
Outdoor
Primary
Secondary
Outdoor
Primary
Secondary
Outdoor
Primary
Secondary
Outdoor
Primary
Secondary
Outdoor
Primary
Secondary
Outdoor
Primary
Secondary
Outdoor
Primary
Secondary
Outdoor
Primary
Secondary
Pre-Cleaningb
23.3
7.5
7.8
8.6
6.5
6.3
11.6
11.8
10.5
35.0
16.5
16.7
24.6
11.8
10.8
14.4
5.7
5.2
14.8
6.5
8.3
21.3
11.7
11.3
13.7
11.3
7.7
PM25
|ig/m3
Post-Cleaning11
20.4
10.3
10.8
28.1
15.3
16.0
29.3
16.9
16.8
25.3
13.3
12.3
33.8
25.7
21.9
22.8
10.3
10.7
21.6
6.8
8.3
12.5
8.5
7.7
17.4
13.2
10.9
Ratio
Post/Pre
0.88
1.37
1.38
3.27
2.36
2.56
2.53
1.43
1.60
0.72
0.80
0.74
1.37
2.17
2.03
1.59
1.81
2.05
1.46
1.05
1.01
0.59
0.73
0.68
1.27
1.17
1.42
Pre-Cleaningb
28.1
11.1
9.5
14.4
10.7
8.6
18.7
15.2
12.1
42.1
17.7
18.9
28.8
15.6
12.6
19.0
10.0
8.7
23.4
10.3
9.7
26.2
14.3
13.2
26.2
10.9
15.7
PM10
|ig/m3
Post-Cleaning11
26.1
29.0
14.2
33.8
22.1
18.7
32.8
19.2
13.1
28.5
17.4
16.2
41.5
33.6
11.0
30.3
13.6
13.8
20.6
9.7
8.4
21.0
11.4
11.3
22.1
12.7
13.7
Ratio
Post/Pre
0.93
2.61
1.49
2.35
2.08
2.17
1.75
1.26
1.08
0.68
0.98
0.86
1.44
2.15
0.87
1.59
1.36
1.59
0.88
0.94
0.87
0.80
0.79
0.86
0.84
1.17
0.87
' Measurements were performed at an outdoor location and in two rooms in the home, generally a family room (primary) and a secondary, lesser used room.
B Mean for two days prior to and two days following ADC.
although the MAC system cleaning very
effectively removed one source of particu-
late matter in the study homes, the air-
borne concentrations before and after
cleaning were not substantially different in
the study homes due to the impact of
outdoor particle sources and other indoor
sources, such as occupant activity, cook-
ing, and pets.
Measurements of particle concentrations
(particles/cubic meter) indoors with a two-
channel optical particle counter and a 16-
channel laser aerosol spectrometer also
did not show substantial differences in
airborne particle concentrations before and
after cleaning. The mean concentrations
of particles in a >0.5 u,m size fraction
measured indoors following cleaning were
lower only at the Test House and at two
of the eight field study houses. The post-
cleaning/pre-cleaning ratio was near 1.0
at two houses, but higher than 1.0 at the
other four occupied field study homes.
Measurement results at two houses that
were cleaned on the same week and lo-
cated across the street from each other
suggest that the outdoor particle levels
had a strong impact on indoor particle
concentrations (Figure 1). At both houses,
indoor particle concentrations increased
on Sunday and Monday following clean-
ing, even though the houses were cleaned
on different days, the MAC system opera-
tion patterns differed, and occupant activi-
ties differed dramatically at the two houses.
The occupants of House 4 were not in the
home most of the Saturday through Mon-
day period.
Mechanical cleaning without the use of
chemical biocides did not appear to im-
pact fungal bioaerosol concentrations at
the nine study homes. With the exception
of one house, there was no substantial
difference between the pre-cleaning and
post-cleaning bioaerosol concentrations.
Measurements of parameters related to
system performance suggest that clean-
ing had a positive impact on system per-
formance. Because of the small sample
size (nine study homes) and the limited
duration of measurements, it was not pos-
sible to quantitatively determine the sig-
nificance of ADC on system performance
and energy use. ADC generally 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. Some of this increase in supply air
flow rates may have been attributable to
minor repairs of leaks in the ducts and
loose floor boots of supply registers. .
Return air flows measured at the return
air grilles increased 14 and 38% at two
houses, but were not substantially differ-
ent after cleaning at the other seven
houses.
AHU blower motor current increased af-
ter ADC at the four field study houses
where measurements were performed.
Static pressure increased in the return air
ductwork at the six houses with complete
measurements. The increase in blower
motor current and increase in static pres-
sure in the return 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 coil. Coolant line surface tem-
peratures did not provide useful informa-
tion.
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45000000
40000000
35000000
30000000 • -
CO
I 25000000 - -
J! t
o
^ 20000000 • •
Q_
15000000 - -
10000000••
5000000 - -
House 3
Climet: >0.5(im
Post-Cleaning
0 I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I"
0 12 0 12 0 12 0 12 0 12 0 12 0 12 0 12 0 12 0 12 0
Sun Mon Tue Wed Thu
Fri
Sat Sun Mon
Tue
45000000
40000000
35000000 +
30000000
CO
I 25000000 -I
"g
'•£ 20000000 •
Q_
15000000 - -
10000000••
5000000••
House 4
Climet: >0.5,um
Cleaning Day
Pre-Cleaning
0
0
12 0 12
Sun Mon
0 12
Tue
0 12
Wed
0 12
Thu
0 12
Fri
0 12 0 12 0 12
Sat Sun Mon
0 12
Tue
Figure 1. Concentrations of particles in the >0.5|im size fraction measured at two houses during the same week of the study.
-------
Example engineering calculations
made to estimate the change in heat
transfer for the cooling coil following
cleaning suggests that the systems
performance improved. Using data for
House 5, which had a 38% increase
in return air flow, and House 6, which
had a 14% increase in return air flow,
the estimated increase in heat trans-
fer for the cooling coils was 14% at
House 5 and 23% at House 6.
Changes of this magnitude would
likely result in improved overall sys-
tem efficiency. However, the data
from this study are inadequate to cal-
culate overall system efficiency.
The evaluation of the methods and pro-
tocols in this study will provide valuable
information that can be used to develop
and refine EPA's research strategy in the
area of ADC. Results of this study demon-
strated that the medium volume dust sam-
pler method developed for this study could
be used to quantitatively assess the effec-
tiveness of source removal cleaning by
collection of dust samples from surfaces.
The methods and protocol for measure-
ments of airborne particles, fibers, and
bioaersols, however, were shown not to
be useful for quantitatively determining the
impact of ADC on these IAQ parameters.
Although cleaning effectively removed one
potential source of particulate and fibrous
matter in the study homes, neither inte-
grated sampling nor continuous monitor-
ing methods could detect a change in
airborne concentrations of the IAQ param-
eters. The study results suggest that physi-
cal measurements of IAQ parameters may
not be useful for assessing ADC impact
IAQ parameters in occupied homes be-
cause of the multiple sources of air con-
taminants, including outdoor sources and
occupant activities, and because temporal
variability of air contaminant concentra-
tions makes it difficult to discern an effect
on IAQ parameters.
Conclusions and
Recommendations
The results of the nine home field study
have demonstrated that mechanical clean-
ing methods and equipment commonly
used by ADC cleaning contractors for
source removal cleaning of HAC systems
effectively removed particulate and fibrous
contamination, thus removing a potential
source of particulate and fiber contamina-
tion. The impact of ADC on levels of bac-
teria and fungi on surfaces of the ductwork
could not be fully evaluated because
chemical biocides were not used in this
study. The medium volume dust sampler
developed for this study was shown to be
appropriate for quantitatively assessing the
effectiveness of ADC. Results of mea-
surements of system-related parameters
indicate a positive impact on HAC system
performance, although the impact could
not be quantified in this study due to the
small study population (nine homes) and
the short monitoring duration. The short-
term air monitoring and sampling meth-
ods and protocols, however, were not ad-
equate for assessing the impact of ADC
on airborne particle and fiber concentra-
tions. Due to the multiple sources of air
contaminants in the homes and tempo-
ral variability in airborne concentrations,
differences in these IAQ parameters
could not be determined between the
pre-cleaning and post-cleaning periods.
Results of this pilot study indicate the
need for further research on ADC in a
number of areas. Additional research, us-
ing alternative methods, will be required
to quantitatively determine the impact of
ADC on IAQ parameters. Research would
also help quantify the impact of ADC on
energy use for residential systems. That
research may be most effectively per-
formed in EPA's pilot scale test facility
where environmental conditions can be
controlled and long-term tests can be per-
formed. Additional areas of potential re-
search include: evaluation of methods for
cleaning porous duct materials, the use
of biocides during cleaning, effectiveness
and durability of encapsulants applied to
porous duct materials, and methods for
reducing contamination in HVAC systems.
Research could also include large HVAC
systems in office and public access build-
ings where the impact on IAQ and en-
ergy use may be greater.
-------
Roy Fortmann and Cary Gentry are with Acurex Environmental Corporation, Re-
search Triangle Park, NC 27709; and Karin Foarde and Douglas VanOsdell are
with Research Triangle Institute, Research Triangle Park, NC 27709.
Russell M. Kulp is the EPA Project Officer (see below).
The complete report, entitled "Results of a Pilot Field Study to Evaluate the
Effectiveness of Cleaning Residential Heating and Air Conditioning Systems and
the Impact on Indoor Air Quality and System Performance," (Order No. PB98-142
011; Cost: $51.00, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA22161
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
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