EP A/600/A-98/006
Large Indoor Air Test Chamber Characterization
Elizabeth M. Howard and Mark A. Mason
U.S. Environmental Protection Agency
Office of Research and Development, National Risk Management
Research Laboratory, Air Pollution Prevention and Control Division
MD-54, Research Triangle Park, North Carolina 27711
phone (919)541-7915; fax (919)541-2157; bhoward@engineer.aeerl.epa.gov
Roy Fortmann and Zhishi Guo
Acurex Environmental Corporation
4915 Prospectus Drive
Durham, North Carolina 27709
Abstract
The U.S. Environmental Protection Agency's Indoor Environment Management Branch (IEMB)
has designed and installed a state-of-the-art large indoor air quality test chamber in their Research
Triangle Park facility. The room-sized (30 m3) stainless steel test chamber and sophisticated analytical
instrumentation will permit characterization of emissions from products and processes that cannot
readily be studied using small chambers. Initial experiments have been conducted to evaluate the
performance of the chamber, and to evaluate comparability to two other chambers recently built in
Canada and Australia. Tests have been conducted that were designed to evaluate critical factors that may
influence experiments. These tests evaluated 1) chamber system air leakage rate; 2) the ability of the
chamber control system to maintain a wide variety of temperature and relative humidity set points; 3) air
speed within the chamber at different flow conditions; and 4) mixing of pollutants at different flow and
temperature conditions. Results of these tests show the capabilities of the large chamber system,
demonstrate its limitations, and point to opportunities for improving its operation.
Introduction
EPA has been conducting experiments to characterize and understand the behavior of sources of
indoor air pollution. Most experiments to date have been conducted in small (53 liter) chambers, in a test
house, or with a Field and Laboratory Emission Cell (FLEC). Using this equipment, IEMB has
developed a model to estimate the exposures of residential occupants to chemicals from sources and
mass-transfer based models describing vapor-phase-controlled (evaporative) emissions from several
sources. These models have been verified at the whole-house scale using the test house. Figure 1 shows
IEMB's research facilities.
These experimental facilities have provided a good beginning, but they cannot be used to
characterize all sources of interest. In order to expand its capability, IEMB has constructed a large (30
m3) test chamber 1 (see Figure 2). This chamber may operate with any combination of the three following
flow modes:
• Mode 1 — Fresh air flow. Fresh air is cleaned to remove particles and organic compounds, then
flows through the chamber and is exhausted outside;
• Mode 2 — Air from the chamber return is recirculated back into the chamber supply; and
• Mode 3 -- Air from the chamber return is mixed with the cleaned fresh air (if any), sent to the
conditioning system for adjustment of temperature and humidity, then recirculated back into the
chamber supply.
The chamber is controlled for temperature, relative humidity, flow rate (of all three modes), and pressure
using a PID (proportional integral derivative) control system. Flow and pressure are controlled using a
system of computer-actuated flow valves and variable-speed blowers. Temperature and relative humidity
are controlled by a steam heating coil, a cooling coil, and a steam humidifier contained in a conditioning
box in the fresh air and mode 3 (conditioned recirculation) loops, after the mode 3 and fresh air are
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mixed.
This chamber will allow investigations not possible with other equipment:
• Testing of large sources, such as office equipment, that won't fit in small chambers;
• Very tightly controlled source tests at loading and air exchange conditions similar to those found
in a residence;
• Scaleup testing under highly controlled conditions of models developed using small chamber test
data;
• Testing of sources where a reduction in wall adsorption of chemicals is important;
• Measurement of emissions during human activities, such as painting or cleaning; and
• Evaluation of source management and control strategies.
Similar-sized chambers have been constructed by others, including the Australian Commonwealth
Scientific and Industrial Research Organization (CSIRO) and the National Research Council (NRC)
Canada1. Large chambers are commonly used by composite wood manufacturers to measure emissions
from products used in manufactured housing, in order to meet a regulatory standard set by the U.S.
Department of Housing and Urban Development (HUD)2. Several commercial testing firms use large
chambers of various designs to do product emission testing.
It is critical to understand the characteristics of a large chamber system before conducting
experiments in it. This permits researchers to better control experimental conditions, and to differentiate
between the behavior of the source being measured and the chamber itself. Chamber characterization
also provides a baseline of performance that can be compared between different chambers and used to
develop standardized test methods that different laboratories can use to test sources and get reproducible,
comparable results. The characterization described in this paper includes tests for leak tightness;
temperature, humidity, pressure, and flow control; air speed; and mixing.
The work described in this paper was done primarily to help IEMB understand and improve the
functioning of its large chamber system, but it also forms the scoping work for a proposed
interlaboratory comparison study1. This interlaboratory comparison will be similar to interlaboratory
comparisons conducted earlier in small test chambers3,4.
EXPERIMENTAL METHODS
Leak Test
Chamber system leakage must be checked after construction and after any subsequent
maintenance activity that involves disassembling any part of the system (e.g., the conditioning box) to
ensure the integrity of the system. A leaky system could cause error in experiments by leaking pollutants
emitted from the source to the laboratory space surrounding the chamber or by allowing the infiltration
of contaminants from the laboratory space into the chamber, depending on the pressure at the leak point
(positive or negative with respect to the laboratory), and the partial pressures of individual compounds.
Leakage was measured by injecting sulfur hexafluoride (SF6) into the chamber while operating
the chamber in a static mode (that is, no fresh air flow, just recirculation), and plotting the logarithm of
the SF6 concentration vs. time. The air exchange rate is calculated as the absolute value of the slope of
this line. This air exchange rate was compared to the air exchange rate attributable to the total sampling
air flow rate to determine whether there was significant leakage.
Set Point Tests
Set point tests were conducted during commissioning of the chamber in order to understand the
behavior of the chamber PID control systems. The variables examined were chamber temperature (T),
chamber relative humidity (RH), differential pressure between the chamber and the laboratory space (P),
and air flow rates in the supply, return, conditioned recirculation loop (mode 3), unconditioned
recirculation loop (mode 2), and exhaust (mode 1). Set point tests were run to determine whether the
chamber met design specifications set for these variables (Table 1), and whether it could run in a stable
manner at those conditions for a 48 hour period. The PID process control system parameters were
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adjusted until the chamber conditions came within the specifications. One set of PID parameters was
sought that could adequately control the chamber systems across their entire range of set points.
The procedure used for the set point tests was:
1) Start the chamber with set points at the designated temperature, RH, and flow. Conditions were
selected to reflect the most common modes of operation as well as the extremes;
2) Allow the system to come to steady operating conditions (usually overnight);
3) Measure all variables for the next 48 hours;
4) Compute maximum and minimum for each variable; and
5) Compare these to the specifications and adjust PID parameters, if needed.
Chamber Air Speed Tests
Air speed is an important variable to control and/or monitor in source characterization
experiments, because it can influence the emission rate of some sources. Preliminary measurements of
air speed were made approximately 1 cm above the surface of a 4 X 4 ft (1.2 X 1.2 m) wood floor
(placed in the chamber for a wood stain test), to determine whether air speeds were comparable to those
previously measured in our test house. A 4 X 4 line grid was marked on the floor, and measurements
were made over each intersection. Two types of measurements were made:
1) The air speed was measured over one point on the grid overnight to gain an understanding of the
stability of the air speed over time, and
2) Measurements were made over each grid intersection to determine the variation and range of air
speeds over the floor's surface.
A Bruel & Kjaar hot-wire anemometer with an omnidirectional probe was used for these measurements.
Mixing Tests
Tests were conducted to determine how quickly and how well a nonreactive gas introduced into
the chamber's inlet (supply) flow becomes mixed with the chamber air. A three-step approach was used:
1) Stabilize chamber conditions for air exchange rate, temperature, and relative humidity;
2) Dose the inlet stream with a known amount of tracer gas (SF6); and
3) Monitor the concentration of the tracer gas at the outlet of the chamber until the tracer gas
concentration falls below the analytical detection limit.
From these data, maximum concentration, time to reach maximum concentration, and decay rate of the
tracer gas were determined. The amount of time that elapsed between the end of the SF6 injection and the
maximum chamber concentration represents the approximate mixing time of the chamber.
If the chamber behaves as a well-mixed continuous-stirred tank reactor, the rise and fall of tracer
gas concentration can be predicted from the following equations:
K, (l-e'*2')
Dosing period: Ct = —— (1)
where: Ct= SF6 concentration at time (|Jg/m3)
= injection rate of the tracer gas (jjg/h)
K2 = air exchange rate (h"1)
t = time (h)
V = chamber volume (m3); and
Purging period: Ct = C0e K:' (2)
where: C0= SF6 concentration before purging starts (|Jg/m3)
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The results were also evaluated by examining the difference between the air exchange rate as
measured by the orifice meter in the chamber's exhaust duct and that calculated from the SF6 decay. The
air exchange rate was calculated as the slope of the logarithm of the SF6 concentration vs. time.
RESULTS
Leak Test
Results of several leak tests are shown in Table 2. The leak rate varied from 0.0014 to 0.0025 air
changes per hour (ACH), which was very close to the total sampling flow rate in these experiments
(0.0018 ACH).
Set Point Tests
The large chamber control system met all set point specifications for relative humidity and air
flow (see Table 3); however, the temperature did not quite stay within ±0.5 °C for the highest and lowest
temperature settings. At the 15°C set point, the temperature exceeded the specified ±0.5 °C range by
+0.1 and -0.3°C. At the 35°C, 45% RH set point, the temperature went out of specification by -0.4°C.
At the 35 °C, 70% RH set point, condensation occurred in the ducts, making humidity control difficult.
Figure 3 provides an example of graphs showing the chamber's behavior at 15°C, 30% RH, 0.48 ACH
fresh air, and 4.8 ACH conditioned recirculation, a test that did not quite meet the chamber temperature
specification.
Chamber Air Speed Measurements
The results of overnight air speed measurements are shown in Figure 4. They demonstrate
stability over time. The measurements taken at the grid intersections across the surface of the floor show
some variation (Figure 5), but are all reasonably close to measurements previously made in our test
house. Mean air speeds in the large chamber ranged from 5 to 21 cm/s, with a median speed of 19 cm/s,
and a mean value of 15.8 cm/s. For comparison, in the test house living room, the mean air speed
measured 1.5 cm over a board placed on the floor was 10.1 cm/s (Table 4). Mean air speeds measured
near a wall ranged from 1.4 to 56 cm/s with a median of 7 cm/s, and a mean value of 14.3 cm/s. These
"near wall" air speeds were taken in conjunction with latex paint testing, so they represent air speeds
near the source surface. Figure 6 shows a histogram of air speed measurements made 1 cm from the
walls of the test house, and Figure 7 shows a histogram of the air speeds 1 cm from the oak floor placed
in the large test chamber.
Measurements of air speed near the chamber walls have not yet been completed. The chamber
design and construction are such that high velocities would be expected along the chamber walls. The
diffusers currently installed in the chamber are flat, solid steel plates which force the air to flow along
the wall surface, which is made of polished stainless steel. If the chamber is used for measurement of
source or sink behavior of a wall surface, the chamber supply diffusers will be reconfigured, and the
velocity measured and adjusted as necessary to achieve realistic flow conditions.
Mixing Tests
Air exchange rates calculated from the SF6 tracer gas data are consistent with those calculated
from the chamber's orifice plate readings, within experimental error (see Table 5). The uncertainty in the
air exchange measurements includes the error in the orifice meter readings, the error in the measurement
of the internal chamber volume, and the analytical uncertainty in SF6 measurement. Table 6 shows the
results for a series of individual tracer gas releases during one test.
The theoretical mixing curves shown in Figure 8 demonstrate that the theoretical curve, based on
a perfectly mixed chamber, fits the experimental data very nicely.
CONCLUSIONS
The large indoor air quality test chamber is capable of simulating a wide range of indoor
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conditions. Temperature and relative humidity can be controlled within about ±0.5°C, and 5% RH at
normal operating conditions of 23 °C and 50% RH . Slight deviations from these ranges occur at the
extremes of temperature (15 and 35 °C), and condensation on duct walls may be a problem during high
humidity operation, particularly at high temperatures. Experience has shown that tight control of the
temperature of the laboratory space around the chamber is vital to maintenance of constant chamber
temperature when the chamber is operated near room temperature. Measurements of the speed of air
movement 1 cm above the surface of a wood floor placed in the chamber are in approximately the same
range as measurements taken in the test house. Tracer gas tests have shown that the chamber is well
mixed when operated at normal conditions and leak-free.
REFERENCES
1. Howard, E.M., Mason, M.A., Zhang, J., and Brown, S., "A Comparison of Design Specifications for
Three Large Environmental Chambers," in "Engineering Solutions to Indoor Air Quality Problems,"
VEP-51; Air & Waste Management Association: Pittsburgh, 1995; pp. 61-70.
2.Department of Housing and Urban Development (HUD), Federal Register 1984 24 CFR 3280.308.
3. Colombo, A., DeBortoli, M., and Tichenor, B.A., "International Comparison Experiment on the
Determination of VOCs Emitted from Indoor Materials Using Small Test Chambers," Indoor Air '93,
Proceedings, Vol.2, pp 573-578. Helsinki, Finland, 1993.
4. Matthews, T.G., Wilson, D.L., Thompson, A.J., et al., JAPCA 1987 37, 1320-1326.
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Table 1 Design ranges and flow conditions.
Parameter
Specification
Temperature
15-35°C±0.5°C
Relative Humidity
20-70% ± 5%
Total Air Flow
0.26 - 26 ACHa
Leakage Rate
<1.7 m3/hr
Positive Pressure
0- 100 Pa
'Air changes per hour
Table 2 Results of leak tests.
Flow Regime
Mean leak
Standard
Number of tests
rate (ACH)
deviation
(ACH)
5 ACH unconditioned recirculation
0.0021
0.00075
3
5 ACH conditioned recirculation
0.0023
0.00049
4
Samnlinp flow onlv
0.0020
NA
1
Table 3 Set point test conditions.
Test
T
(°C)
RH
(%)
Fresh air
(ACH)
Conditioned
recirculation
(ACH)
Comments
1
22.8
45
0.5
0
Met all set point conditions.
2
22.8
30
0.5
0
Met all set point conditions.
3
22.8
70
0.5
0
Met all set point conditions.
4
23.2
70
5.0
0
Met all set point conditions.
5
23
30
5.0
0
Met all set point conditions.
6
23
45
5.0
0
Met all set point conditions.
7
15.2
31
5.0
0
Met set point conditions for 12 h, then
system shut down.
8
15.2
30
0.5
4.5
Temperature fluctuation beyond
specifications (14.2 to 15.6 °C).
9
35.6
45
5.0
0
Temperature slightly out of tolerance
(34.1 to 35.2 °C).
10
35.2
70
0.5
4.5
Reached 35 °C but could not maintain
it for 48 h.
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Table 4 Air speeds measured over a board on the floor of the test house.
Room
Air handler blower
Ceiling fan Air speed (cm/s)
Living Room
on
no fan
9.9
Living Room
on
no fan
10.5
Living Room
off
no fan
11.8
Living Room
off
no fan
11.3
Living Room
off
no fan
6.9
Den
on
high
62.5
Den
on
low
11.2
Den
on
high
47.8
Den
on
low
8.4
Den
on
off
6.8
Table 5 Mixing test conditions.
Paiameter
Test 1
Test 2
Temperature (°C)
15.2
23
Relative Humidity (%)
30
50
Fresh Air Flow (ACH)
0.5
0.5
Unconditioned Recirculation (ACH)
0
0
Conditioned Recirculation (ACH)
4.5
0
Mixing Fan?
no
yes
Difference3 (%)
4.6
5.3
"The Difference is computed as the difference between the SF6 value and the orifice plate value, divided by the orifice plate value.
Table 6 Air exchange rate from a series of tracer gas releases.
Release
Air exchange
orifice plate
(ACH)
Air exchange
sf6
(ACH)
Difference"
(%)
1
0.475
0.499
5.1
2
0.475
0.506
6.5
3
0.475
0.493
3.8
4
0.475
0.493
3.8
5
0.475
0.494
4.0
Mean
0.475
0.497
4.6
* The Difference is computed as the difference between the SF6 value and the orifice plate value, divided by the orifice plate value.
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Large
Chamber
Test
House
Figure 1 Indoor air quality testing facilities and approach.
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exhaust (Mode 1)
conditioned
recirculation
(Mode 3)
fresh air
Figure 2 Large chamber flow diagram.
unconditioned
recirculation
(Mode 2)
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Conditioned Recirculation
X
o
5 3
O
LL 2
Fresh Air
1 2
24
Time (h)
36
48
Figure 3 Large chamber control at 15°C and 30% RH.
10
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25
20
• • •
g 15
O
mean velocity
10
0
» • >
V
standard deviation
4 6 8 10 12 14
Time (h)
Figure 4 Air speed stability over one point on a wood floor.
-O 0.15
0
g_0.10
0/5 0.05
< 0.00
X (cm)
Figure 5 Air speed 1 cm above wood floor placed in center of large chamber floor.
11
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20
0
g 15
0
i_
i_
ZD
O
o
O 10
0
n
E
3
0
0
!
1
1
¦
¦
1
1
1
1
1
10 15 20 25 30 35
Air speed (cm/s)
40 45 50 55
Figure 6 Histogram of air speeds measured 1 cm from test house walls.
w c
Q)
o
c
® il
h 4
13
O
o
° 3
I
EE
8 10 12 14 16 18 20 22
Air speed (cm/s)
Figure 7 Histogram of air speeds measured 1 cm over wood floor in large chamber.
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80
0 3 6 9 12
Elapsed hours
Perfect Mixing o SF6 Data
Figure 8 Results of mixing test.
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NRMRL-RTP-P-240
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before comple
1. REPOR
EPA/600/A-98/006
3.
4. TITLE AND SUBTITLE
Large Indoor Air Test Chamber Characterization
5. REPORT DATE
6. PERFORMING ORGANIZATION CODE
7.AUTHOR(s)E
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