United Statoa
Environmantal Protsction
Ag«ncy
QWiceof
Toxic Substances
Washington, D.C. 20460
EPA 560/5-88-004
June 1988
Toxic Substance*
In a
To
in Indoor Air
-------
Bg/7'iq.' i .... . .. •. .-..---. i
REPORT DOCUMtNTATION »• •««*«• "^ gg0/5_88-004 *" V
., nil* »nd suu«iti» , , . ,
Preliminary Experiments 1n a Research House to investigate
Contaminant Migration in Indoor Air
''Author.,t Dcto
June 1988
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68-02-4254
Type af Rocvort & f>*riod Cov«r«d
Final Report
14.
The EPA Project Officer was Elizabeth Bryan; the EPA Task Manager was Patrick
Kennedy. _^^ -
.«. Abstract (LImH: 200
Controlled experiments were performed in an unoccupied research house to provide
m a detailed characterization of the migration patterns of contaminants released
indoors from consumer products and (2) a basis for assessment of the exposure
Implications of contaminant migration and the accuracy of currently -used exposure
assessment models. To enable relatively detailed spatial and temporal monitoring
with readily available instrumentation, carbon monoxide (CO) was chosen as a
surroqate contaminant for the investigation. A point source was simulated In the
master bedroom by releasing CO from a pressurized tank through a pnematic line over
a 1. 25-hour period.
During the release period, measured CO concentrations typically were 3 to 4 times
hiaher In the release area than in other areas on the floor of release.- Within an
hour after the release was terminated, concentrations approached spatial uniformity
even though a central air circulation fan that would have promoted contaminant
migration was turned off as part of the experimental design. A single-chamber
Indoor air quality model provided closer approximation of passive than active
exposures. Use of a two-chamber model resulted in better estimates of each type of
exposure. * ,
17. Doeymant Analytl* », D«eriptefll
Exposure Assessment
Indoor Air Quality Monitoring
Indoor Air Quality Modeling
T«rm»
Contaminant Migration Indoors
Active Exposure
Passive Exposure
e. CO1ATI Flald/Qraup
IS. Availability Stateman;
Distribution Unlimited
19. S*eurft» Claw CTH*» *wort}
Unclassified
ZO. S«curtty Ctosa ff»a« •"*«»>
Unclassifie
21. No. o) P*8
85
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S«< AN31-Z39.1S)
Sea
(MTtonAt. romi 27:
(Fe*Tt«riy HTIS-35J
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EPA 560/5-88-004
JUNE 1988
PRELIMINARY EXPERIMENTS
IN A RESEARCH HOUSE
TO INVESTIGATE CONTAMINANT
MIGRATION IN INDOOR AIR
by
Michael D. Koontz, Harry E. Rector,
Roy C. Fortmann, Nlren L. Nagda
EPA Contract No. 68-02-4254
Project Officer
Elizabeth F. Bryan
Exposure Evaluation Division
Office of Toxic Substances
Washington, D.C, 20460
U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF PESTICIDES AND TOXIC SUBSTANCES
WASHINGTON, D.C. 20460
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DISCLAIMER
This document has been reviewed and approved for publication
by the Office of Toxic Substances, Office of Pesticides and Toxic
Substances, U.S. Environmental Protection Agency. The use of
trade names or commercial products does not constitute Agency
endorsement or recommendation for use.
ii
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ACKNOWLEDGMENTS
This report r=prsp=rea by GEOMET Technologies , _
Germantown, Wara"dl,!?L^e ^posure Assessment Branch (EAB),
1
in addition to the authors of this report a
11
i.
Program Management -
Task Management -
4.
Technical Support -
Editing -
i
Secretarial/Clerical
Gavaneh Contos, Versar
oaycui*
H. Lee Schultz, Versar
Nlren Nagda, GEOMET
Donald Cade, GEOMET
David Skidmore, GEOMET
Laura Mehegan, GEOMET
jo Ann Koffman, GEOMET
Jean Fvock, GEOMET
jeanette Behnke, GEOMET
Dana Cue, GEOMET
ill
-------
TABLE OF CONTENTS
Page
Executive Summary ^x
1. Introduction *
l.l. Background 1
1.2. Objectives and Scope 2
2. Experimental Design and Research Methods 5
2,1, Research Setting 5
2.2. Contaminant Release and Monitoring 5
2.3. Ancillary Measurements 14
2,4. Quality Assurance and Control Procedures 14
2.5. Data Processing and Analysis Procedures 20
3, Analysis of Experimental Results 23
3.1. Experimental Conditions 23
3.2. Data Quality 27
3.3, Concentration Profiles 33
3.4. Integration Across Experiments 42
4. Analytical Modeling 49
4.1. Single-Chamber Mass Balance Model 49
4.2. Multiple-Chamber Modeling 56
5. Discussion 63
5.1. General Perspective and Needs 63
5.2. Insights from the Current Investigation 67
6. Conclusions and Recommendations 73
6.1. Conclusions ?3
6.2. Recommendations 74
7, References . 77
Appendix A. Indoor Air Quality Modeling Concepts
and Formulations ?9
Preceding page blank
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LIST OF FIGURES Page
1 Floor plan of GEOMET research houses. 6
2 Three possible stages of contaminant history. 7
3 Spacing of protable continuous monitors to form a
vertical sampling string. 10
4 General locations of the release point, the vertical
sampling planes, and the stationary monitoring network, 12
5 Daily checklist form. 18
6 Operational checklist for experiments. 19
7 Functional relationships among vertical sampling strings
of the detailed monitoring network and stationary
monitoring sites. 22
8 Response of one CO detector to 0 and 9.06 ppm during
multipoint calibrations and daily zero and span checks. 32
9 vertical concentration gradients with CO detectors
arrayed in the master bedroom. 34
10 Horizontal concentration gradients with CO detectors
arrayed in the master bedroom. 36
11 Vertical concentration gradients with CO detectors
arrayed in adjacent bedrooms. 37
12 Horizontal concentration gradients with CO detectors
arrayed in adjacent bedrooms. 39
13 vertical concentration gradients with CO detectors
arrayed in the hallway. 40
14 Horizontal concentration gradients with CO detectors
arrayed in the hallway, 41
15 Concentration profiles across all experiments at the
anchor point. 44
16 Concentration profiles for each experiment at the
midlevel anchor point in the hallway and stationary
monitoring sites. 45
vil
Preceding page blanfc
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Page
17 Spatial profile of CO concentrations upstairs during the ^
release period.
18 Spatial profile of CO concentrations upstairs following
the release period.
19 Single-chamber mass balance model calculations for
generalized experimental conditions. 50
20 Comparison between single-zone model predictions and
measurements near the release area, bl
21 Comparison between single-zone model predictions and
measurements in the hallway and front bedrooms. 5J
22 comparison between single-zone model predictions and
measurements at stationary monitoring locations that
represent likely sites of passive exposures. b4
23 Comparison between single-chamber model predictions and
volume-weighted average indoor concentrations for three
morning experiments.
24 Airflows used as inputs to a two-chamber model. 58
25 Comparison between two-chamber model predictions and
*" - i _i_*__^ j — .*. A .mtt f-f ***r\ r* •£>*"*iv m/*"* V n "1 fl rf
S_.i*JlllL/Q L, J.O Wii iXii* V»£* wr " '>-' •»«**•«-...--—— _..- — ^
measured concentrations in each zone for morning
experiment type 2.
28 Proposed array of PFT sources for future contaminant
migration experiments.
59
26 Overview of consumer exposure model, 64
Illustrative monitorirv
migration experiments.
27 illustrative monitoring array for future contaminant
69
viii
-------
LIST OF TABLES Page
l Characteristics of Release Scenario 9
2 Sequence of Contaminant-Release Experiments 13
3 Specifications for Ancillary Measurement Parameters 15
4 Instrumentation for Ancillary Measurement Parameters 16
5 Summary of Prevailing Conditions During Each Experiment 24
6 Summary of External Audit Results for Five CO. Analyzers 28
7 Accuracy and Precision of Five CO Analyzers at Audit
Concentration of 10.34 ppm 28
8 Accuracy, and Precision of all CO Analyzers Used in the
Investigation at Final Calibration Input of 9.06 ppm 29
9 Changes in Slopes and Intercepts Between Beginning and
Ending Calibrations for CO Detectors Used in the
Investigation 31
i.0 Comparisons of Model Estimates and Measured value? for
Peak and Time-Weighted Average Concentration During and
After Contaminant Release 60
11 Important Inputs to Model Lookups and Calculations and
Associated Data Sources 65
12 Utility of PFT Data Base and Research House Experiments 66
ix
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EXECUTIVE SUMMARY
Over recent years, advances have been made in the development
and application of methods for the assessment of exposure to
chemical contaminants released from consumer products to the
indoor environment. In spite of these advances, there still exist
siqnificant gaps in our understanding of the behavior of
contaminants following their release and the implication of this
behavior for human exposure. In particular, the extent of passive
exposure (i.e., that arising from contaminant migration to indoor
air spaces from the space where a contaminant is released) is
poorly understood.
The OTS exposure-assessment process has recognized passive
exposure as an issue of concern; however, appropriate information
to provide quantitative treatment of this issue is not currently
available. As a result, significant uncertainties exist with
reqard to the accuracy of Indoor air exposure estimates. The
objectives of the investigation described in this report were {!)
to perform a detailed characterization of contaminant migration
patterns in an unoccupied research house through a series of
controlled experiments, (2) to assess the exposure implications of
contaminant migration, and (3) to assess the accuracy of c^rently
used exposure assessment models and explore model refinements that
could lead, to improved estimates of active and passive exposures.
To enable detailed spatial and temporal monitoring with
readily available instrumentation, carbon monoxide (CO) was chosen
as a surrogate contaminant for the investigation. CO was released
from a point source in the master bedroom of the research house at
a constant, known rate over a period of 1.25 hours. A network of
nine portable continuous CO detectors was arrayed to measure
horizontal and vertical concentration gradients in each of three
configurations—(1) in the release area, (2) down a connecting
hallway, and (3) in entrances to nearby bedrooms. An anchor
siring of three vertically arrayed detectors located just outside
the entrance to the master bedroom provided continuity across the
three different arrays of detectors. In addition, a stationary
network of sampling locations representing likely passive exposure
sites was sampled on a rotating basis with a nondlspersive
infrared analyzer. The simulated contaminant release was
performed one! in the morning and once in the afternoon for each
array of CO detectors. Ancillary parameters such as outdoor CO
concentrations, meteorological conditions, and air infiltration
rates were also monitored.
xl
Preceding page blank
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During the release period, measured CO concentrations
typically were 3 to 4 times higher in the release area than in
other upstairs areas of the house. However, within 45 to 60
minutes after the release was terminated, concentrations
throughout the upstairs of the house approached spatial
uniformity, eventhough a central air circulation fan that would
have promoted contaminant migration was turned off as part of the
experimental design. Some evidence of contaminant migration to
the downstairs living area of the house was observed during
forces is involved in the mixing and transport of contaminants.
interestingly, a single-chamber model— similar to that
currently used in OTS assessments of active exposures in
residential environments-provided a closer approximation of
oassive than active exposures. Use of a two-chamber model
?esSlted if better estimates of each type of exposure. Thus even
t hnnoh a comolex set of forces may underlie contaminant mixing and
transport patterns tSS concept of treating general interchamber
lirrlnw natterns as a steady-state condition into which
consimer?pro^SI emissions are injected and transported appears
valid and useful for improving exposure estimates.
To provide a basis for continued refinements and improvement
to currently used models for exposure assessment s aad itional
research hoSse experiments need to be performed for a Ji*«
k f f%
IxSeriSlntal results can be easily compared. Future contaminant-
mifratTof SpeltSnts should include measurement of time-varying
and integrated airflows as a routine component. In ^dition, the
transferability of results from research houses to different
hSSSin|types should be assessed by replicating selected experi-
ments in a limited number of local residences.
To increase the applicability of exposure assessment models to
f,^
"Saged airflow rates among selected zones of a residence should
be analyzed as soon as these results are assembled in a
computer-accessible format,
xii
-------
in parallel with expanded data collection, assimilation, and
analysis efforts, activities'to refine and improve current
exposure assessment models should be initiated. This process
should begin with the development of a generalized multichamber
model and continue with refinements and expansions as critical
inputs are obtained through supplemental efforts such as those
recommended in this report.
xiii
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PRELIMINARY EXPERIMENTS IN A RESEARCH HOUSE
TO INVESTIGATE CONTAMINANT MIGRATION IN INDOOR AIR
1, INTRODUCTION
1.1. Background
Over recent years, advances have been made in the development
and application of methods for the assessment of exposure to
chemical contaminants released from consumer products to the
indoor environment. An overall analytical structure has evolved
to guide such evaluations, as have a variety of methods for
calculating the indoor air contaminant concentrations to which
receptors are exposed. Data bases quantifying consumer product
use patterns and the chemical makeup of many consumer products
have also been developed to support the application of the
assessment process.
In spite of these steps, significant gaps exist in our
understanding of contaminant behavior following release and the
implication of this behavior for human exposure. In particular,
the extent of passive exposure (i.e., that arising from
contaminant migration to indoor air spaces from the space where a
contaminant is released) is poorly understood.
The OTS exposure assessment process has recognized passive
exposure as an issue of concern; however, appropriate information
to provide quantitative treatment of this issue is currently
lacking. As a result, significant uncertainties exist regarding
the accuracy of indoor air exposure estimates. Thus, specific
needs exist (1) to investigate the issue of passive exposure to
determine whether it warrants further attention and (2) if so, to
develop strategies for obtaining appropriate levels of
quantitation.
In a recent report (GEOMST 1987a), average Interior airflows
and air infiltration rates measured with multiple perflourocarbon
tracers (PFTs) for a typical residence were used as inputs to a
multicharnber indoor air quality model. This model was used to
demonstrate the implications of passive exposure to chemical
substances released from a consumer product within any of three
zones in the house. For one of these cases, it was shown that
within 2 hours after the 10-minute release period, concentrations
were higher in another zone than in the zone where the substance
was released. This analytical exercise demonstrated that the
issue of passive exposures to chemical substances released from
consumer products warrants concern and further investigation.
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1,2. Objectives and Scope
The results of the analysis described above indicated that a
data base maintained by Brookhaven National Laboratory, which
contains results from PFT measurements in approximately 4,000
U.S. residences, may be a valuable input to future exposure
assessments concerning the use of consumer products in residential
environments. However, the PFT measurement technique is generally
limited to quantifying average airflows over time periods of
several days or longer. Consequently, the use of such data may
still introduce inaccuracies in exposure assessments because many
consumer products are used for shorter durations on the order of
hours or minutes.
In concept, general airflow patterns derived from PFT
measurements can be treated as a steady-state or slowly changing
condition into which emissions from consumer products are injected
and transported. Although this concept provides for facile
incorporation of readily available data, it represents an untested
extrapolation.
Consequently/ a limited series of experiments was designed to
quantify contaminant migration over detailed temporal and spatial
scales in an unoccupied research house maintained by GEOMET.
These experiments were exploratory in nature and were Intended to
improve our understanding of underlying physical processes rather
than to mimic any specific exposure scenario. The major
objectives of this effort were as follows:
« To examine the basic time scales and variations for
contaminant migration to adjacent airspaces;
• To examine the relative levels and durations of
passive exposure In adjacent airspaces due to
contaminant migration;
To examine the dilution effects of contaminant
migration to adjacent rooms and air exchange
with the outdoors; and
» To assess the ability of single- or multi-chamber
models to predict active and passive exposures.
The experimental design involves the controlled release of a
surrogate contaminant in one room of the research house and
monitoring of contaminant mixing and migration to other rooms
through a detailed network of sensors. The results of these
-------
experiments will enable a quantitative assessment of the utility
of existing and readily obtainable data relating to interroom
airflows,
The research setting, experimental design, and measurement
methods are described in Section 2 of this report. Experimental
results are presented in Section 3 and modeled in Section 4. The
implications of the results are discussed in Section 5 in terms of
model accuracies, applicability of existing data on interior
airflows, and future research needs. Conclusions and
recommendations stemming from this investigation are outlined in
Section 6.
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2.
EXPERIMENTAL DESIGN AND RESEARCH METHODS
This section describes the setting in which experiments were
conducted, together with contaminant release and monitoring
methods. Measurement techniques for ancillary parameters such as
outdoor meteorological conditions, indoor temperatures, and air
infiltration rates are also described. The section concludes with
a description of quality assurance/control, data processing, and
analysis procedures. Portions of this section are extracted from
a recent GEOMET report (1987b) describing sampling and analytical
protocols for the investigation.
2.1. Research Setting
GEOMET's research house facility consists of two bilevel,
wood-frame houses that were constructed in the fall of 1982, The
houses, located on adjacent lots in Gaithersburg, Maryland, are
identically oriented, facing 19° east of north (i.e., north-
northeast). Floor plans for the houses are shown in Figure 1.
The main living area is upstairs; the downstairs area is divided
into an unfinished living area and an Integral garage. The total
upstairs living area of each house is 130 rn2 (1400 ft^). The
upper and lower levels are connected by a stairway with one
landing at the house entryway.
The research houses were constructed using "closed-wall"
techniques. Siding, sheathing, insulation, vapor barrier, and
windows were assembled at the factory to form complete wall
panels. The completed wall panels were installed at the building
site to form the building shell. Insulation for the re-^arch
houses features a continuous polyethylene vapor barrier with glass
fiber batts between the wall joints (R-value of 11). The attic
contains 8 inches of loose fill insulation between the ceiling
joists {R-value of 30).
Abbreviations that are used later in this report for selected
rooms or areas of the house are also indicated in Figure 1.
2.2. Contaminant Release and Monitoring
The experimental strategy was designed to monitor contaminant
history from a constant point source through three possible stages
(Figure 2};
Source cloud—in the immediate vicinity of the
source, concentrations are controlled by the
Preceding page Wank
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-e&-
Haittr Btdroon
(HBR)
_">
^x!
T-T
K lichen
Ofnlns Room
/
Cornir
Bedroom
\
-O=t-
W7
Front
Bcdrooa
Entry
Llvlnj Room
UPST4IRS
Csrsac
^ Unftflijhtd
Living Ana
L
DOWNSTAIRS
0 5m
icale: 1 1
Figure 1. Floor plan of GEOMET research houses
-------
Source Cloud
Transition
Steady-State
Figure 2. Three possible stages of contaminant history.
-------
amount of material released and the dimensions of the
source cloud;
• Transition—once the source cloud approaches the
dimensions of the room, concentrations begin to
be affected by air exchange and migration to
adjacent airspaces; and
• Steady state—concentrations throughout the general
airspace change in response to air exchange, room-
to-room flows, and (as applicable) continuing
emissions and chemical decay.
The basic experimental sequence began with a controlled
release of a surrogate contaminant from the center of the master
bedroom in one of the research houses. The measurement
strategy involved a set of portable continuous analyzers that were
arranged to form a sampling plane that was "walked" through the
concentration patterns created by controlled repetition of a
single-release scenario. General characteristics of the release
scenario are summarized in Table 1.
Carbon monoxide (CO) was selected as the surrogate
contaminant. CO was released from a pressurized tank located
outdoors that contained approximately 1 percent CO in air.
Pneumatic lines were used to direct the contaminant from the tank
to the release point in the master bedroom; the gas feed was
controlled externally so that the technician would not need to
enter the house during the conduct of any experiment. To prevent
undue mixing from momentum of the release flow, a,ceramic frit was
installed on the outlet at the release point. Based on a
preliminary experiment, a release rate of 1.2 L/min and duration
of 1.25 hours 'were chosen; these conditions resulted in short-term
CO peaks on the order of 10 parts per million (ppm) in the master
bedroom and concentrations,below 5 ppm elsewhere in the house.
Evolution of the source-cloud and transition stages was
monitored by arranging nine portable continuous CO monitors
(General Electric Model 15ECS3C03) to form a vertical sampling
plane. The vertical sampling plane was made up of three vertical
sampling strings. As illustrated in Figure 3, the nominal
floor-to-celling dimension of the upstairs of the research house
is 2.3 meters. Sampling heights of 0.38, 1.16, and 1.93 meters
were specified for each vertical string to systematically divide
the vertical sampling plane into three layers that were each 0.77
meters deep.
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Table l. characteristics of Release Scenario
l. General conditions
All exterior openings (doors, windows) closed
All interior doorways on main floor open
Doorway to downstairs opened
Doorway to garage closed
Operation of central circulation fan suppressed
2. Release conditions
• Location—geometric center of master bedroom
Rate—1.2 L/min from tank containing 0.9844 percent CO
in air
Duration—1.25 hours
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Height
(meters)
Ceiling . . — 2'31
Top level + 1'93
1.54
Mid level + 1<16
i , , 0.77
Low level + 0<38
Floor , —
Figure 3. Spacing of portable continuous monitors to form a
vertical sampling string. Crosses (+) denote monitoring height
for top, raid, and low levels situated between floor and ceiling,
10
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To provide continuity from experiment to experiment, °ne
locatioS was designated as the anchor point for all ^angements
of the vertical sampling strings. This point (designated as point
A in Figure 4} was centrally located in the hallway equidistant
from the doorways of all three bedrooms . For the initial
experiment vertical strings 2 and 3 were set up to bracket tne
rSwsS^oint, giving a sailing plane defined by the anchor plus
positions S2 and S3 indicated in Figure 4.
For experiment type 2, vertical strings 2 and 3 were relocated
to the hallway (positions H2 and H3 in Figure 4). For experiment
type 3, the Sampling plane was folded to extend into the corner
bedroom and the front bedroom by placing sampling strings 2 and 3
at locations D2 and D3, respectively.
Data from the nine portable monitors were collected every
6 seconds and processed by a data logger for storage as l -minute
averages during each experiment.
A stationary sampling network was operated to continually
measure CO concentrations in each major room of the research
hoSse except for the room of release. This second network, also
indicated 11 Figure 4, consisted of a single continuous analyzer
(Beckman Model 886) that was automatically sequenced among five
sampling points on a 3-minute schedule, providing a measurement of
eS point every 15 minutes. For consistency wjjh previous
monitoring protocols, indoor CO measurements with the stationary
network were taken at a height of 1.07 meters.
Experiments were conducted during the period December 1-4,
1987. As summarized in Table 2, the controlled-release scenario
was conducted twice for each array of the vertical strings-once
during morning hours (10:00 to 11:15 a.m.) and once during evening
hours (4:00 to 5:15 p.m.). The afternoon experiment for type 2
was repeated, and the data from this seventh experiment were held
in reserve. To restore indoor CO concentrations to background
levels between morning and evening experiments, windows were
opened at 2:00 p.m. and closed at 3:00 p.m., allowing an hour for
cessation of anj air movement patterns due to the window openings.
A possible source of interference for these experiments was
local lutomobile traffic. However, historical data from the
research site indicated that brief outdoor transients coinciding
e
witeary morning and late afternoon traffic peaks would be
relatively rare and on the order of 5 ppm or lower should they
occSr. The extent of interference from any outdoor CO spikes was
quantified with the stationary monitoring network, through which
outdoor CO concentrations were measured every 15 minutes.
11
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ODD
D
\
DOWNSTAIRS
Figure 4. General locations of the release point (denoted by an
asterisk), the vertical sampling planes (denoted by crosses joined
by broken lines), and the stationary monitoring network (denoted
by filled circles).
12
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Table 2. Sequence of Contaminant-Release Experiments
Date
Release
period
Experiment type
(array of vertical
sampling strings)
December l
December 2
December 3
December 4
4:00 to 5:15 p.m.
10:00 to 11:15 a.m.
4:00 to 5:15 p.m.
10:00 to 11:15 a.m.
4:00 to 5:15 p.m.
10:00 to 11:15 a.m.
4:00 to 5:15 p.m.
Type 1
Type 2
Type 2
Type
Type
Type
Type 2,
13
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2.3. AQCillary_Measurements
The GEOMET research house facility contains a complete indoor
and outdoor network of continuous sensors for indoor environmental
conditions, operating status of major appliances, and
meteorological conditions outdoors. The parameters selected to
assist in data interpretation included indoor air temperature and
the meteorological parameters of windspeed and direction, solar
radiation, outdoor air temperature, and precipitation. Siting
criteria for these parameters are listed in Table 3.
In addition to environmental parameters, air infiltration
rates were measured using the tracer-dilution method (ASTM 1981),
with sulfur hexafluoride (SFg) as the tracer. Before each
experiment, SPg was injected into the research house with an
automated system that provided rapid mixing through the central
forced-air heating and cooling system. Following the period of
SFg injection, the air circulation system was kept off throughout
each experiment. Indoor sampling locations for SPg were identical
to those used for the stationary CO monitoring network; a single
analyzer was used to sequentially sample each location, enabling
calculation of air infiltration rates over periods as short as
.15 minutes. The instruments used to monitor SFg concentrations
and environmental parameters are listed in Table 4.
2.4. Quality_Assurance and Control Procedures
Data quality objectives were stipulated in the protocol
document (GEOMET 1987b) in terms of accuracy, precision, and
completeness of data collected during the experiments. For most
parameters, the targeted accuracy and precision levels were
±10 percent; the targeted completeness of the data across all
measurement parameters and experiments was 95 percent. Specific
procedures used to ensure the"collection of high-quality data
included external audits, multipoint calibrations, zero and span
checks, and additional routine activities performed by technicians
responsible for conducting the experiments and maintaining the
research houses.
The most recent external audit at the research houses,
conducted during September 1987, involved (l) challenging GEOMET's
gas analyzers with known concentrations of National Bureau of
Standards (NBS)-traceable standard gases and (2) colocating
NBS-traceable instruments with GEOMET's meteorological and
indoor-environment sensors for parallel monitoring and comparison
of instrument responses. Audit parameters of relevance to this
investigation Included the Beckman analyzer used for the
stationary CO network, four of the nine portable GE CO detectors,
the SFg analyzer, all outdoor meteorological sensors, and a subset
of the indoor-temperature sensors.
14
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Table 3. Specifications for Ancillary Measurement Parameters
Parameter
Windspeed
Wind direction
Solar radiation
Number
of
indoor
sites
0
0
0
Number
of
outdoor
sites
1
1
1
Location
10 m above ground3
10 m above ground3
Roof of house3
(total)
Air temperature
Precipitation
Air exchange rate
Indoor: Centroid
of each major room";
Outdoor: 1.5m
above ground3
Gauge opening 0.3m
above ground3
Colocated with
stationary probes
for CO
a In general accordance with Section 3.0 of the EPA Quality
Assurance Handbook f or Air Pollution Measurement Systems :
Volume IV. Meteorologi^4-...,JJ^MM.f5lf-S-^, (EPA-6QQ/4-82-Q6Q) .
In accordance with criteria established through previous
experimentation reported in "Energy Use, Infiltration, and
Indoor Air Quality in Tight, Well-Insulated Residences" (EPRI
Report No. EA/EM-4117), prepared by GEQMET for the Electric
Power Research Institute,
15
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Table 4. instrumentation for Ancillary Measurement Parameters
parameter instrumentation Manufacturer Model
SF Gas chromato- S-Cubed 215BGC
graph/electron
capture detector
Temperature Thermistor Omega OL-700
Windspeed Anemometer climatronics WM-III
Wind direction Vane climatronics WM-III
Solar radiation Pyranometer Matrix MKI-G
Precipitation ' Tipping bucket Quallmetrics 6021A
16
-------
Multipoint calibrations were conducted for all gas analyzers
at the beginning and end of the 4-day period during which
contaminant-release experiments were conducted, in addition, zero
anl spaSChecks were performed before each morning £P«^ fs
conducted, the results of which were recorded on control charts.
Based on historical performance data, control limits of ±0.75 ppm
at zero and ±1.5 ppm at span (9 ppm) were established for all CO
monitors. Any CO monitor exhibiting a response outside the
control limits was recalibrated before a new experiment was
initiated.
On arrival at the research houses each day, the technician
first performed routine operational checks of various types of
eouipment. Findings and observations were recorded on a daily
checklist form (Figure 5) to establish the degree of general
readiness for planSd activities. The experiments were designed
to operate without intervention by the technician. Principal
areas of attention included physically rearranging the detailed
network of CO analyzers, verifying the readiness of the analyzers
(based on zero and span checks) and data acquisition systems and
initiating/terminating the source release. Measurements of air
infiltration and other auxiliary parameters proceeded through a
computer-controlled system with specified intervals for sampling
and recording instrument signals.
Critical daily actions were recorded on an operational
checklist (Figure 6). A typical dally schedule involved the
following sequence of events:
(1) After making the types of operational checks
described above, the data file containing results
from the previous day's experiments was closed and a
new file was opened for recording results from the
current day's experiments.
(2) After verifying that concentrations from the previous
afternoon's experiment had receded to acceptable
levels, the technician reconfigured the detailed
network of CO analyzers as necessary and performed
zero and span checks.
(3) source-feed connections to the release room were
checked and the morning release was Initiated. The
technician reviewed the progress of the experiment
by monitoring selected parameters on the CRT screen
for the central data acquisition system.
17
-------
H'/AC on-line: 14
15
Gas [ ] C ]
Electric ( J [ ]
Other [ ] [ ]
Date;
J.O.; ~^~
Time:
Technician:
Daily Checklist - Instrumentation
Performance Checks (Verify reasonableness of data and check)
parameters
Room temperature
Energy
HVAC and duct temperatures
RH and room velocity
Pressure and velocity
Furnace fan status change
Furnace gas counter (verify operation)
Pollutants & meteorology
Record screen display values for the following (during HVAC operation):
14 IS 14 15
14 IS Channels
[ ] [ ] AQ - C07
f
f
[
[ :
£ ]
[
f
*
c :
MM
CIO - CIS
DO — £03
KH — £09
£10 — PCS
£04 or 601
H03
10 — 115
AO ^,:SR Temp)
84 (IR Tanp}
Oil (Supply Temp)
014 (Return Temp)
Status/Logical Checks (Verify status or parameter change after system begins operation)
14 IS
Furnace fan
Furnace gas valve
Supply temperatures Increase
Furnace thermocouple
HVAC system initiated at appropriate room temperature
Instrumentation checks (verify operation, flows, reasonableness of data-
insert "1" if operational or "0" if off-line)
1
[ ] SFe zone sequence [ ]
Pollutant zone sequence
DAS clocks
SFg Analyzer
Pollutant Analyzers
N0X/NQ A ]
NOX/NO 8
C02-A
C02-8
C ] [ 1 C 1 C ] RADON
[ ] [ } [ ] [ ] RADON PROGENY
Pressure sensors [specify any off-line)
Halocarbons
CO-A
CQ-B
02
Other:
0. Comments:
Figure 5, Daily checklist form.
18
-------
c.
CHECKLIST—CONTAMINANT MIGRATION EXPERIMENTS
Experimental Configuration:
Instrumentation
GS CO Detectors
Channel Serial No. Status
1
Source Release Data
Daytime
Start
Time:
Stop
Time:
Plow:
Tank Concentration
% CO in Air
Data Files
Campbell Datalogger
File Name;
Start:
End:
Clock Status [ ]
Comments:
Placement in
Sampling Plane
7
8
9
4
5
6
I
2
3
Start
Time:
Overnight
Stop
Time:
Flow:
Tank Concentration
% CO in Air
Site DAS
File Name:
Start:
End: ~~
Clock status [ ]
Figure 6. Operational checklist for experiments.
19
-------
(4) After completion of the morning experiment, the
technician verified that concentrations had declined
to acceptable levels and initiated the afternoon
release of CO. The. afternoon experiment then pro-
ceeded to automatic shutdown of the CO release and
continuing measurements under program control.
2.5. Data Processingand Analysis Procedures
All instrument signals were scanned, averaged, and recorded at
prescribed intervals by computer-controlled data acquisition
systems. Instruments measuring meteorological parameters were
scanned at l-minute intervals and recorded as hourly averages.
Measurements with the stationary sampling network for CO and SFg
were recorded at 3-mlnute intervals corresponding to the times at
which various locations were sequentially sampled. A separate
data acquisition system was devoted to the network of nine CO
detectors to enable the recording of 1-minute averages at each
sampling site. All instrument outputs were recorded as voltages
on iBM-PC-compatible diskettes.
Calibration factors (slope and intercept) derived from
multipoint calibrations were applied to the raw data at GEOMET's
data center through programs implemented on IBM personal computers
and compatibles. The calibrated data were reviewed for
unreasonable values such as negative concentrations and sharp
excursions from smooth trends ^e.g,, a temporary decline of one
data point to near-zero values during a period of otherwise steady
growth). Questionable values were flagged to alert analysts to
sections of valid and Invalid data.
Data analysis efforts were keyed to the basic objective of
these experiments—exploring the implications of contaminant
migration patterns for current methods of estimating human
exposures. Fundamental avenues of analysis included (1)
comparisons across experiments through graphical and statistical
methods, (2) comparisons of measured values with those predicted
by currently used models, and (3) evaluations of model
refinements.
Initial stages of data analysis focused on basic concentration
profiles as well as similarities and differences across different
experiments. This comparative analysis was applied to CO
concentrations as well as to air infiltration rates, indoor
temperatures, and meteorological conditions. In particular, the
spatial and temporal profiles of CO concentrations near the
doorway to the master bedroom were assessed for consistency across
experiments; the vertical string of CO analyzers at this
20
-------
location was the anchor point for linking results across the three
types of experiments.
The functional relationships among the vertical strings
constituting the detailed CO sampling network and stationary CO
monitoring sites are illustrated in Figure 7, To summarize and
integrate results across experiments, statistics such as peak and
average CO concentrations were used in additiqa to graphical
summaries.
The general mass balance model currently used for indoor air
exposure assessments was applied to estimate Indoor concentrations
in the region of the source and at remote locations, based on
measured values of air infiltration rates, source release rates,
and outdoor CO concentrations. The general framework for mass
balance models is summarized in Appendix A.
Model residuals (algebraic differences between calculated and
measured concentrations) were analyzed to identify model
assumptions or outdoor conditions that led to significant
differences as well as good correspondence. Particular attention
was given to identifying conditions where the single-chamber model
provided poor estimates of passive or active exposures.
The final stages of data analysis explored various avenues of
model refinement including multichamber models for estimating
passive exposures. Results from previous PFT measurements at the
research house under similar outdoor conditions were included as
inputs to the multichamber model.
21
-------
(Corner Bedroom]
\ probe /
\
* Release
Point
\
\
S2
ANCHOR
(8|, Di. Hi)
D
{Front Bedroom!
Prob©
H,
, \ .
Basement
Prob»
H3
i
I
Mixing in Room of Release
.— Transport to Adjacent Rooms
rrr •—"• Transport to Remainder of House
-„-- Associations Between Vertical
Strings (indicated by S\, Of, H|)
and Stationary Sites (indicated
in parentheses)
, \
/Livina Area)
\ Prob« /
Figure 7. Functional relationships among vertical sampling
strings of the detailed monitoring network and stationary
monitoring sites.
22
-------
3. ANALYSIS OF EXPERIMENTAL RESULTS
Outdoor conditions prevailing during each of the experiments
are summarized in Section 3.1, and data quality levels associated
with critical measurement parameters are summarized in Section
3.2. Concentration profiles for each experiment are presented in
Section 3.3, and the results across all experiments are integrated
in Section 3,4.
3.1. Sxpe r imental Conditions
Sampling was conducted during the first 4 day.' of December
1987. Three different configurations of portable CO detectors
were used In the master bedroom, hallway, and other bedrooms. Two
experiments were performed for each configuration, one starting at
10 a.m. and another starting at 4 p.m.
Both ambient and indoor conditions can influence the
concentrations and rates of migration of contaminants in indoor
environments. Indoor temperatures, ambient carbon monoxide
concentration, air infiltration rate, and meteorological
conditions (winds, temperature, and solar radiation) were used as
a basis for summarizing the prevailing conditions during each
experiment. Average values, standard deviations, and ranges for
these parameters during the 4-hour period of CO release and decay
for each experiment are given in Table 5.
During each of the six experiments, both indoor and outdoor
temperatures remained within 10 percent of the mean value.
Although temperature differences between the morning and afternoon
experiments were observed, the overall temperature difference
between indoors and outdoors was quite similar across the pair of
experiments for each configuration of CO detectors. Air
infiltration rates usually were slightly higher during the
afternoon than morning experiments.
The average windspeed was typically as high or higher during
morning than afternoon experiments. Solar radiation levels were
also higher during morning than afternoon experiments, mainly
because the afternoon decay period included hours after sunset.
The highest ambient CO concentration during any experiment was
1.4 ppm. This relatively low level, coupled with upstairs air
infiltration rates averaging about 0.3 air changes per hour,
implies that outdoor CO concentrations had negligible impacts on
indoor concentration levels.
23
-------
Table 5, Summary of Prevailing Conditions During Each Experiment
Date/period
of experiment
Parameter
Part A: Experiment Type I—Vertical Sampling
Horning
(12/04/87)
Afternoon
(12/01/87)
Air temperature (*F)
Ambient outdoor
Master bedroom
Corner bedroom
Front bedroom
Hallway
Living room
Downstairs
Upstairs infiltration rate (h"
Ansblont outdoor CO (ppm)
Windspetd (tn1/h)
Wind direction (degrees)
Solar radiation (Btu/ft2)
A1r temperature (*F)
Ambient outdoor
Master bedroom
Corner bedroom
Front bedroom
Hallway
Living room
Downstairs
Upstairs Infiltration rate (h
Ambient outdoor CO (ppn)
Wlndspeed (nl/h)
Wind direction (degrees)
Solar radiation (Btu/ft2)
Average
Strings In
38.2
63.3
63.0
63.5
64.5
64.2
63.0
•1) 0.30
0.8
5,0
291
21
44.3
64.6
64.4
64.7
65.6
65.3
64.1
-1) 0.29
0,7
2.8
231
1
Standard
deviation
Range
Master Bedroom
0.7
1.3
1.2
1.3
1.3
1.3
0.9
0.02
0.1
0.6
11.5
5.4
0.6
1.3
1.3
1.3
1,1
1.2
0.7
0.07
0.5
1.1
22.1
2
37.6 to 39.1
61.9 to 64.9
61.7 to 64.6
62.1 to 65.1
63.2 to 66.2
62.8 to 65.8
62.0 to 64.1
0.28 to 0.33
0.6 to 0.9
4.4 to 5.8
278 to 303
14 to 16
43.9 to 45.2
63.3 to 66.2
63.0 to 66.1
63.3 to 66.3
64.4 to 67.0
64.0 to 66.8
63.3 to 65.0
0.23 to 0.36
0.3 to 1,4
1.8 to 4.3
211 to 258
0 to 4
(Continued)
24
-------
Table 5. Summary of Prevailing Conditions During Each Experiment (Continued)
Date/period
of experiment Parameter Average
Part B: Experiment Type 2— Vertical Sampling Strings
Morning
(12/02/87)
Afternoon
(12/02/87)
A1r temperature (*F)
Ambient outdoor
Master bedroom
Corner bedroom
Front bedroom
Hallway
Living room
Downstairs
Upstairs Infiltration rate (h'1)
Ambient outdoor CO (ppm)
Wlndspeed (ml/h)
Wind direction (degrees)
Solar radiation (Btu/ft*)
A1r temperature (*F)
Ambient outdoor
Master bedroom
Corner bedroom
Front bedroom
Hallway
Living room
Downstairs
Upstairs Infiltration rate (h"1)
Ambient outdoor CO (ppm)
Wlndspeed (ml/h)
Wind direction (degrees)
Solar radiation (Btu/ft2)
41.
67.
66.
66.
68.
68.
0.
0.
10.
310
95
36.
63.
62.
63.
64.
63.
62.
0.
0.
6.
333
2.
Standard
deviation
Range
In Hallway
7
9
3
6
3
0
30
3
2
6
6
6
0
g
8
3
36
7
6
5
1
1
0
0
0
0
0
0
2
52
35
2
2
1
1
1
1
0
0
0
1
3
.2
.0
,4
.4
.4
.6
.02
.2
.1
.2
.8
.0
.2
.8
.8
.7
.8
.9
.05
.2
.4
.5
5
40.
66.
66.
66.
67.
67,
0.
0.
7.
263
42
34.
61.
60.
61.
63.
61.
61.
0.
0.
5.
329
0
0
9
1
4
8
2
26
0
7
6
2
6
1
0
8
3
29
5
1
to
to
to
to
to
to
to
to
to
to
to
to
to
to
to
to
to
to
to
to
to
to
to
42.
69.
67.
67,
68.
68.
0,
0.
12.
357
121
39.
66.
64.
65.
66.
66.
63.
0.
7
2
0
2
7
7
32
4
2
2
3
7
2
9
0
4
42
1.0
8.2
337
10
(Continued)
25
-------
Table 5. Summary of Prevailing Conditions During Each Experiment (Concluded)
Date/period
of experiment
Paraneter
Average
Part C: Experiment Type 3— Vertical Sampling Strings
Morning
(12/03/87)
A1r temperature
Ambient outdoor
Master bedroom
Corner bedroom
Trent badrooB
Hallway
Living room
Downstairs
OF)
Upstairs Infiltration rate (h"1}
Ambient outdoor CO (ppm)
Wlndspeed («1/h)
Wind direction (degrees)
Afternoon
(12/03/87)
Solar radiation
A1r temperature
Ambient outdoor
Master bedroom
Corner bedroom
Front bedroom
Hallway
Living room
Downstairs
(BtU/ft2)
OF)
Upstairs Infiltration rate (h"1)
Ambient outdoor
Wlndspeed (m1/h)
CO (ppm)
Wind direction (degrees)
Solar radiation
(BtU/ftz)
41.
66.
65.
65.
66.
66.
0.
0.
6.
194
95
40.
61.
62.
62.
63.
63.
62.
0,
0.
6
175
1.
Standard
deviation
Range
1n Doorways of Adjacent Bedrooms
0
2
1
5
6
9
26
2
4
3
9
0
2
0.
0.
0.
o;
0.
0.
0.
0.
0.
7,
31.
8
8
5
6
6
6
04
3
4
1
3
1.8
1.4
1.5
1.3
,4 1.2
,0
,5
,31
.3
.6
.5
1
1
0
0
1
54
1
.3
.0
.03
.2
.2
.1
.7
40.
65.
0
1
64.5
64.8
65.
66.
0,
0,
5,
189
51
37
60
60
60
62
61
61
0
0
5
97
0
,8
,0
.22
,0
.9
.9
.4
.4
.8
.0
.6
.5
.28
.1
.2
to
to
to
to
to
to
to
to
to
to
to
to
to
to
to
to
to
to
to
to
to
to
to
41.
66.
65.
66.
67.
67.
7
9
6
1
1
4
0.32
0.
,5
6.8
205
123
42
63
63
63
64
64
63
0
0
8
214
4
.0
,6
.8
,9
.9
.7
.7
.35
.5
.2
26
-------
3.2. Data Quality
Data quality levels associated with this investigation are
summarized in this subsection in terms of measurement accuracy and
precision. The focus is on the primary measurement parameter for
the investigation--concentrations of the surrogate contaminant
(CO) Results from a recent external performance audit, as well
as multipoint calibrations and zero and span checks co- -ring the
specific period of investigation, were used as inputs ^o the
assessment of data quality for this parameter. The performance of
measurement systems for air infiltration rates and meteorological
parameters is also characterized.
During September 1987, an external performance audit was
conducted at GEOMET's research house facility by the Center for
Environmental Quality Assurance of Research Triangle ^titute
(RTI 1987). Four of the CO detectors and the Beckman CO analyzer
used in this project were included in the audit. Each analyzer
was challenged with zero air and with CO concentrations of 5, 10,
20 30 and 45 ppm. The audit results are summarized in Table 6
in'terms of a regression equation expressing the relationship
between analyzer response and audit concentration. Perfect
agreement would be indicated by a slope of one, an intercept of
zero, and a correlation coefficient of one. As shown in the
table, slopes for all analyzers were within ±0.01 of unity, and
intercepts were relatively small in magnitude for all analyzers
except GE detector #108, which exhibited a negative bias of 1 ppm.
All correlation coefficients were either 1 or 0,9999.
The accuracy and precision of the analyzers at an audit
concentration of 10.34 ppm are summarized in Table 7. The
accuracy objective of 10 percent was met or exceeded by all
detectors. Aside from GE detector #108,, which had an accuracy
level of -10 percent due to the 1-ppm negative bias, the accuracy
of the detectors was within 3 percent. The precision across
detectors was ±5 percent, well within the objective of ±10
percent. Thus, these results indicate that the performance of the
CO analyzers was quite satisfactory at the time of the audit.
Accuracy and precision of all nine CO detectors and the
Beckman analyzer used during the Investigation are shown in
Table 8, based on responses to a final calibration concentration
of 9.06 ppm. The accuracy of the analyzers ranged from -2.4 to
+2.5 percent, and the precision across all analyzers was ±1.4
percent. Thus, accuracy and precision levels at the final
calibration were well within data quality objectives of ±10
percent.
27
-------
Table 6. Summary of External Audit* Results for Five CO Analyzers
Regression of analyzer
response on audit concentration
Correlation
Analyzer Slope Intercept coefficient
GE detector #142
GE detector #119
GE detector 4108
GE detector #104
Beckman model 866
0.99
0.99
1.01
0.99
1.00
-0.12
-0.07
-1.01
0.16
0,26
1.0000
0.9999
0.9999
1.0000
1.0000
Audit conducted on September 21, 1987.
Table 7. Accuracy and Precision of Five CO Analyzers
at Audit Concentration of 10.34 ppm
Analyzer Response, ppm
GE detector #142
GE detector #119
GE detector #108
GE detector #104
Beckman model 866
Average, all analyzers
Standard deviation
precision, percent
10.10
10,24
9.31
10.37
10.79
10.16
0.54
±5.3
Accuracy, percent
-2.3
-1.0
-10.0
+0.3
+ 3.1
28
-------
Table 8, Accuracy and Precision of all CO Analyzers Used in
the Investigation at Final Calibration3 Input of 9.06 ppra
Analyzer
GE detector #037
GE detector #104
GE detector #108
GE detector #119
GE detector #123
GE detector #130
GE detector #142
GE detector #147
GE detector #153
Beckman model 866
Response, pprn
9,12
9.07
8,84
9.11
8.87
9.00
9,07
9.29
9.11
9.11
Accuracy, percent
+ 0.7
+0.1
-2.4
+0.6
-2.1
-0.7
+0.1
+2.5
+0.6
+0.6
Average, all analyzers 9.06
Standard deviation 0.13
Precision, percent ±1.4
a Final calibration conducted on December 7, 1987.
29
-------
Changes in slopes and intercepts for the CO detectors between
beginning and ending calibrations are summarized in Table 9,
Changes in slopes were minimal--? percent at most and 2 percent or
less for six of the nine detectors. Drift in the intercepts was
somewhat more pronounced; eight of the nine detectors exhibited a
downward drift in the intercept, averaging 0.5 ppm. This downward
drift was most likely due to the sensitivity of the CO detector to
temperature; as indicated in Section 3.1, indoor temperatures
during the experiments were between 60 and 70 "F because the
central heating system was turned off during the conduct of each
experiment.
Intermediate zero and span checks were performed on 36
occasions (nine detectors on 4 days each); in seven of these
cases, detectors drifted to an out-of-control state. However,
four of these cases were associated with a single detector (#108).
In contrast to the beginning and ending calibrations that were
performed in the laboratory adjacent to the house, zero and span
checks were performed Inside the research house so that the
detectors would not be removed from the testing environment.
Bags filled with zero and span gases were used for the zero and
span checks, as opposed to multipoint calibrations that fed the
gases directly to the detectors from cylinders. This practice
resulted in a slight negative bias in detector response to the
zero and span checks, as illustrated for one detector in Figure 8.
Thus, because virtually all detectors exhibited a downward drift
between the beginning and ending calibration and because the use
of bags for zero and span checks resulted in a negative bias in
detector response, the control limits used as criteria for reca-
libration were stricter than intended. Thus, detectors may have
been recalibrated in selected cases when calibration was not
necessary. However, the only Impact of extra calibrations, if any,
would be a minor improvement in accuracy.
The analyzer used to guantitate SFg concentrations for
calculation of air infiltration rates was also Included in the
external performance audit. Based on audit concentrations ranging
from zero to 800 parts per billion (ppb), the regression of analyzer
response on audit concentration resulted in a slope of 0.94, an
intercept of 7;2, and a correlation coefficient of 0.999. The
average difference between audit concentrations and analyzer
responses was 5.5 percent. Based on initial and final calibrations
surrounding the period of investigation, instrument drift was
negligible; Initial and final slopes were 1.02 and 0.99, and
initial and final intercepts were 4.1 and 6.5. At a calibration
concentration of 400 ppb, the midpoint of the analytical range of
the instrument, accuracy was +1 percent for the initial calibration
and +2 percent for the final calibration; precision at the 4QO~ppb
concentration was ±1 percent. Thus, the performance of the SFg
analyzer also was well within data quality objectives.
30
-------
Table 9. Changes in Slopes and Intercepts Between Beginning and Ending
Calibrations for CO Detectors Used in the Investigation
Beginning calibration
(11-30-87)
Detector
t037
1104
#108
1119
1123
*130
1142
#147
1153
Slope
0.99
0.97
0.98
0.99
.1.01
0.98
1.01
0.99
0.99
Intercept
0.26
0.48
0.13
0.11
0.10
0.45
-0.11
0.41
0.04
Ending
(12
Slope
0.99
0.97
1.05
0.92
0.99
0.99
1.05
1.01
0.99
calibration
-7-87)
Intercept
0.13
-0.23
-1.21
0.36
-0.59
-0.21
-0.41
0.26
-0.14
Change in
slope, percent
0.0
0.0
+7.1
- 7.1
-2.0
+1.0
+4.0
+2.0
0.0
Change in
intercept, ppm
-0.13
-0.71
-1.34
+0.25
-0.69
-0.66
-0.30
-0.15
-0,18
-------
E
a.
a
o
o
c
o
Q
o
o
I U
9_
8 —
7 -
5 ™"
4 -
3 -
2 -
1 -
0 -
-1
^ . ...
In!
Caltbi
tlal
•atlon
». —
"--— ^
Interrr
Che<
^_ — f
ilttent
;ks
^-"
Fin
Calibr
al
ation
[ _ -a
'it ii i 1
123456
Sequential Check Number
Zero Check o span Check
Figure 8. Response of one CO Detector to 0 and 9.06 ppm during
multipoint calibrations and daily zero and span checks.
32
-------
A representative subset of thermistors used to measure room
air temperatures was also included in the performance audit. Of
the 12 room thermistors audited, 8 differed from the audit reading
by less than 0.5'F, two differed by less than 2°F, and 2 failed to
meet data quality objectives. The two thermistors that failed
were immediately replaced, prior to this investigation. Subse-
quent checks have verified proper performance of all thermistors
in use at the research houses.
All meteorological instrumentation exhibited satisfactory
performance during the audit except the windspeed/direction
sensor. Windspeeds measured by the onsite sensor were low due to
bearing wear. The unit was returned to the manufacturer for
maintenance and calibration prior to this investigation, and
additional quality control procedures were implemented to verify
proper performance.
3,3. ConcentrationProfiles
This section summarizes basic patterns from the detailed
monitoring network that reflect mixing and transport of the CO
tracer. For each experiment, the monitoring points in the
sampling plane were first treated as three vertical strips to
examine trends in the vertical, and were then recompared by
viewing the data as three layers to examine horizontal trends.
3.3.1. Room of Release
In the room of release, tracer concentrations at all six
points began to rise rapidly very soon after tracer release was
initiated and continued to climb as the tracer release was
terminated (the end of the release period, 1.25 hours after the
start, is indicated by a vertical line in Figure 9 and in
subsequent figures). Peak concentrations were reached shortly
after the source was turned off and then declined smoothly.
As shown in Figure 9, transport through the open doorway
to the anchor string in the hallway was fairly rapid; concen-
trations at the anchor string rose and fell on essentially the
same timing as in the room. Concentration gradients persisted
during the release. At vertical string 82 (between the release
point and the doorway), concentrations were highest near the
floor. At vertical string 83, concentrations were highest near
33
-------
o
Morning Experiment
Anchor String
E
a
a
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1
Figure 9. Vertical concentration gradients with CO detectors
arrayed in the master bedroom.
14
12
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,*"""S»$:J
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34
-------
the ceiling. At the anchor string, the highest concentrations
occurred at midlevel. This pattern may be due to convective
transport in the master bedroom. The temperature network,
however, is insufficiently detailed to fully quantify such
effects on thermodynamic grounds.
When the data were recomposed to form horizontal layers
(Figure 10), the situation became clearer. Concentrations in the
middle layer (1.2 meter height) at the two strings in the room and
at the anchor string in the hallway were remarkably similar, rising
and falling 'in unison and showing essentially the same pattern for
the morning and evening experiments.
Convective circulation in the room of release could lead to
uneven transport in the room of release, creating and sustaining
concentrated packets that are slowly mixed into the general
volume. In the top and bottom layers, where highest concentrations
occurred in the room during tracer release, concentrations were as
much as 40 percent higher than in the middle layer. Once the
source was turned off, concentrations were rapidly equalized in
the room. Vertical gradients, however, were sustained at the anchor
string in the hallway for at least an hour after the source was
turned off, and substantial differences persisted in the top and
bottom layers between the room of release and the anchor point.
Although concentration profiles in the room of release appear
to be driven by convection, the pathways of transport within the
room cannot be fully appreciated because the sampling pl»ne only
provides a two-dimensional section through a three-dimensional
transport field. Many different plume configurations can be
envisioned that would lead to the same concentration profiles.
Nonetheless, the following insights can be drawn from the
perspective of mass balance modeling; (1) mixing proceeded rapidly
in the horizontal and slowly in the vertical under conditions of
natural air motions; and (2) in the room of release, convective
motions created and sustained concentration gradients that led to
poorly mixed conditions while the source was active. Concentration
gradients in the room of release dissipated rapidly once the source
was turned off.
3.3.2. Transport to Adjacent Rooms
Concentration profiles for the vertical sampling strings
erected inside the doorways of rooms that adjoin the room of
release are shown in Figure 11. Vertical gradients were largely
dissipated by the time contaminants reached the D£ string in the
corner bedroom and the 03 string in the front bedroom. Peak
concentrations were substantially lower than in the room of
release, and concentration profiles were delayed by approximately
35
-------
Morning Experiment
Top L©vel
Evening Experiment
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Figure 10. Horizontal concentration gradients with CO detectors
arrayed in the master bedroom.
36
-------
Morning Experiment
Anchor String
Evening Experiment
Anchor String
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Figure 11. vertical concentration gradients with CO detectors
arrayed in adj acent bedrooms,
37
-------
30 minutes and flattened. For the evening experiment, concentra-
tions in the bottom level at the anchor string were higher than at
the mid and top levels; this was the only experiment that deviated
from the basic pattern of higher concentrations at the midlevel
anchor.
Significant horizontal gradients persisted in the middle layer
between these two rooms and the anchor point. As shown in
Figure 12, midlevel concentrations were higher at the anchor for
as long as an hour after the source was turned off. During the
morning experiment, concentrations in the lower layers of the two
bedrooms rose and fell in unison, suggesting strong coupling in
the lower layer and rapid mixing within the two rooms.
During the evening experiment, horizontal gradients between
the bedrooms and the anchor point were sustained at all levels for
nearly an hour after the source was turned off. Nonetheless, the
concentration profiles in both bedrooms were very similar to each
other and to profiles from the morning experiment.
The following insights can be drawn from these two experiments:
(1) contaminant transport into the adjacent bedrooms was primarily
through the lower layers; and {2) mixing within these rooms was
fairly complete and rapid.
3.3.3. Transport Through the Hallway
Concentration profiles for the vertical sampling strings
erected along the hallway are shown in Figure 13. Vertical
concentration gradients were evident for essentially the entire
4-hour period at the % string (midway down the hall) and at the H3
string (just past the foyer). By the time the contaminant
transport reached the H2 string, the highest concentrations were
found near the floor. Concentrations at the H2 string were
consistently lower than at the anchor string. At the H3 string,
concentrations were even lower and more nearly homogeneous in the
vertical.
Regular pulsations were strongly evident in these concentration
profiles that did not prevail in the two bedrooms, supporting
convective coupling of the hallway and living area, possibly
including the basement zone through the stairwell. Recomposing
the data to layer form (Figure 14), it is .apparent that for the
evening experiment the oscillations in the middle layer after the
38
-------
Morning Experiment
Top Level
Evening Experiment
Top Level
14-
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Figure 12. Horizontal concentration gradients with CO
detectors arrayed in adjacent bedrooms.
39
-------
Morning Experiment
Anchor Siring
Evening Exporlmont
Anchor String
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Figure 14. Horizontal concentration gradients with CO detectors
arrayed in the hallway.
41
-------
source had been turned off were parallel and extended from the
living area (H3^ to at least midway down the hall (H2), but were
not reflected in the middle layer at the anchor string. |hese
oscillations were faintly reflected in tne top layer at the anchor
and at Ho, suggesting general downturn. Strong convectiye action
reflected in the middli and top layers at the anchor string was not
coupled to profiles at the H2 or H3 sites.
During the morning experiment, concentration profiles were
much smoother. Although some oscillations were evident, vertical
gradients were dissipated fairly slowly but smoothly at allthree
lites, while horizontal gradients in the bottom and top layers
dissioated within 30 to 45 minutes. In the middle layer,
horizontal gradients between the hallway sites largely disappeared
5?tiiS an hour, but did not equilibrate with the anchor position
until nearly 2 hours after the source had been turned off.
The following general insights can be drawn from these
experiments:
Concentrations in the hallway were lower than at
the anchor site;
Although vertical gradients were weaker in the hall,
some stratification existed with highest
concentrations prevailing near the floor; and
Convective motions In the hallway provided fine
structure to the concentration profiles.
3.4. integration Across Experiments
To view experimental results in terms of active and passive
exposures, unification of the three basic experimental types is
needed for synthesis of a general case linking the room of
release, adjacent rooms, and the remainder of the indoor volume.
The main elements that enable this integration of results are the
repetitive features of the experimental design.
in addition to strict repetition of time-related elements such
as release rate and duration, the experimental design featured a
stationary monitoring network to measure CO ^entrations at
three heights at the anchor site, at midlevel heights at ^ur
other indoor locations, and outdoors. As previously illustrated
42
-------
a
in Section 2.5 (Figure 7), each vertical sampling plane provided
a series of intermediate sampling sites connecting the anchor
point to each of the fixed monitoring points on the main floor ot
the research house and to the room of release.
The research house itself represents perhaps the most
powerful point of integration across the experiments in that it
is a realistic full-scale model responding to changing
environmental conditions; thus, the primary differences among
validated data from experiment to experiment are traceable to
naturally occurring changes in transport and mixing patterns.
Although this features does not necessarily lead to a simple
equivalence for uniting all experiments, it nonetheless presents
additional information on the range of variability that prevails
under real-world conditions.
Data integration across experiments was carried out from
three perspectives:
For each height level at the anchor location;
At the midlevel height for the anchor location plus
the stationary network; and
At the midlevel height for the anchor, stationary
network, and mobile sampling locations.
Concentration profiles at the anchor point *are compared across
all experiments in Figure 15. At the midlevel of the anchor,
which was strongly associated with events in the room of release
as well as in the adjacent rooms, peak concentrations varied by
nearly a factor of 2 across all experiments but rose and
fell in very similar fashion. This pattern indicates that
similar forces wers at work, but at different intensities. The
highest peak concentrations in the middle layer were associated
with morning experiments when convective coupling would be
assisted by solar gains. During the concentration decay period
following the end of CO tracer release, concentrations at all
levels converged to a fairly narrow interval.
When attention is shifted to the mid-height of the anchor
string in relation to the rest of the stationary monitoring
network (Figure 16), it can be seen that additional factors came
into play. Well-mixed conditions were usually approached within
an hour after the release was turned off, but concentration
43
-------
Top L@v@l Anchor String©
E
Q.
Q.
14
12
10
8
6
•
4-
2-
n J
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+ AM2
o AM3
& PM1
x PM2
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»l'l*lIl*St It *****«*»«-.
1 2 3
Elapsed Time, Hours
Mid Level Anchor Strings
14
12
to
a
*.x;.
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Low Leva! Anchor String*
14
12^
10
8
6
4
2
0
2 •
Figure 15. Concentration profiles across all experiments at the
anchor point.
44
-------
Morning Experiment
Master Bedroom
Evening Experiment
Master Bedroom
1 2 3
E!apsod Tlmo, Hours
Hallway
Out
Down
CBR
FBR
Anchor
123
Elapsed Tim®, Hours
Hallway
12
Other Bedroom
Other Bedroom
Figure 16, Concentration profiles for each experiment at the
midlevel anchor point in the hallway and stationary monitoring
sites.
45
-------
profiles were sometimes affected by transport to the basement and,
during some of the evening experiments, by infiltration of out-
door CO concentrations from mild outdoor peaks due to local traf-
fic. There generally was greater separation between upstairs and
downstairs concentrations during morning than evening experi-
ments. Concentrations during the release period generally rose
much more quickly at the anchor site than at any other location.
The single exception to this trend was an evening experiment
during which concentrations in the corner and front bedrooms rose
near"!* in unison with those at the anchor.
To develop characteristic concentration profiles connecting
all measurements taken in the middle ." -er of the main floor, the
data sets were combined in three stage=». Firs^, site-specific
averages across all experiments were constructed for each location
that was common to all experiments (i.e., rnidlevel anchor and
the stationary network). Second, data from the midlevel of the
vertical sampling strings that were relocated from experiment to
experiment were normalized as a fraction of the corresponding
midlevel anchor concentration at the end of the release period
for each experiment. Third, the normalized values were
multiplied by the grand-average midlevel anchor value at the end
of the release period to rescale the normalized data in terms of
average conditions.
Concentration profiles obtained through this exercise were
examined as iS-minute snapshots. Throughout the release period
(Figure n), concentrations in the room of release and at the
anchor point in the nearby section of the hallway were virtually
identical. Concentrations tapered off substantially beyond the
anchor point, such that noticeable increases in the other
bedrooms and living room were not evidenced until 45 to 60
minutes after the release was started. Mixing within the
adjoining bedrooms appeared to be rapidly achieved, as indicated
by very similar concentrations near the doorway and center of
each room.
Following the release period (Figure 18), spatial uniformity
throughout the house was nearly achieved as concentrations in the
release area receded and concentrations in other areas continued
to rise. In particular, within 60 minutes after the release
period ended, concentrations began to recede in all upstairs
locations that were monitored, and concentrations in likely
receptor locations (each bedroom and the living room) were within
0.6 ppm of one another. Further unification of experimental
results and contaminant migration patterns can be obtained
through modeling efforts presented in the next section.
46
-------
15 ninetis »ft«r
30 mlnutai ifter reli4s« surted
UPSTAIRS
.-cm
Mtitir EtdrooB
3.5
u
Kttchffi
3,8 , 0,5 0.1
/\
v
\a.s
Corntr
Bodrooa
1.2
Frant
lldrgoa
1.2
Entry
Olntr.j a oar.
1.2
ROM
U?STAIBS
r*liiM ttirttd
Blnutti iftir must lUrtttt
UPSTAIRS
75 minutiJ »ftir rtltist ittrttd
(«nd of rtlillt p«rlod)
[,.,. 1,1, —
Hiitir Btdroc
6,9
sx \/ y
1.4
Corntr
Bidrooa
_ ^<4
'•M«^J '
x
\k
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bx
' V
X
M
/\
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5"
6
1
i
-I" ' ' '
y KUcnin
I dining Utan
Z.3 Z.I
Entry
Living ROM
i — t — i — i
UPSTAIRS
Figure 17, Spatial profile of CO concentrations (in ppm)
upstairs during the release period.
UPSTAIRS
47
-------
15 minutes after relent ended
30 nlrvytej after release ended
i ' — *" — ' ^4r-*~~^" 'S
7.0 H U
/\ A ^^v
J J 6.5 ,. 3.1
v \s y y^
lA £
x \/ v
\3.2
Corner Front
Sedroom Bedroom
3.7 2,9
t lnl t J — [ — !
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njfjj
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Entry
_JLi
Dining Room
2,9
Living Room
[_"f | ;
UPSTAIRS
3.8
' 1 , , ,, 1 3-7
v v' / ,
3-\ 1
V
Corner
Sedroon 8
3.5
[=3^ /
"In
tsJ^
/ 2-S
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3
Front
edroon
3,3
\ f? Kitchen
DfM
Jj
1.8
s\
Entry
1 Dining Roon
2.9
Living Root*
UPSTAIRS
Figure 18. Spatial profile of CO concentrations (in ppm)
upstairs following the release period.
48
-------
4. ANALYTICAL MODELING
The practical objectives of the work reported here involved
(1) examining advantages and limitations associated with
simplified mass balance modeling of complex scenarios^ and
(2) identifying avenues of useful improvements througn
multichamber modeling. Modeling activities began with the
generalized single-chamber mass balance model, using inputs of air
exchange, source rates, and indoor volume. Multichamber modeling,
using interzonal airflows from previous PFT measurements analyzed
by Brookhaven National Laboratory (BNL), was then carried out to
identify improvements resulting from this next level of model
complexity.
4.1.
Single-Chamber Mass Balance Model
The single-chamber mass balance model (see Appendix A) was run
on a 15-minute time step to calculate indoor concentrations at
time intervals consistent with averaging periods for the
stationary monitoring network. Separate calculations were
performed at air exchange rates of 0.2, 0.3, and 0.4 air changes
per hour (ACH) to cover the range of air infiltration rates that
occurred during the experimental period. All model calculations
assumed perfect mixing and negligible outdoor levels.
A3 shown in Figure 19, peak concentrations under nominal
conditions coincide with the end of CO tracer release and occupy a
fairly narrow concentration interval, ranging from 3.2 ppm for the
0 4-ACH case to 3.6 ppm for the 0.2-ACH case. By the end of the
experimental period, the dilution effects of the different levels
of air exchange decrease concentrations by half while broadening
the differences between cases.
The single-chamber model, when applied to the general air
volume of the main floor of the research house, significantly
underpredicts peak concentrations observed in the room of release
and at the anchor point. Figure 20 illustrates this lack of
correspondence for a morning experiment. In this figure,
concentration profiles from the middle levels at the anchor and
S->/S3 (master bedroom) strings are plotted together with model
estimates calculated at 0.3 ACH. The calculated peak
concentration of 3.4 ppm falls short of measured values by a
factor of 2, and the model does not approach measured values
until near the end of the decay period.
49
-------
£
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1 2
Elapsed Time, Hours
Figure 19. Single-chamber mass balance model calculations for
generalized experimental conditions.
50
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£
Q.
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tf
O
c
CD
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O
O
O
O
Anchor
+ S2
O S3
Predicted
Elapsed Time, Hours
Figure 20. Comparison between single-zone model predictions and
measurements near the release area (experiment type l, morning
run).
51
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Comparisons at monitoring points that are distant from the
release area, however, begin to show remarkable agreement. The
concentration profiles for distant strings of the hallway plane
(Figure 21, upper part) and the strings inside the doorways of
rooms adjacent to the room of release (Figure 21, lower part) are
largely reproduced by this simple model.
The primary shortfall of the model for areas distant from the
release point lies in the relative timing of peak concentrations.
Modeled peak concentrations occur at the end of the tracer-release
period. At the midlevel of the hallway, the measured peak at the
H2 string, midway down the hall, occurred 5 minutes after the
release ended. At the far end of the hall (the H3 string), the
peak occurred 30 minutes after the release had ended. At the D2
and D3 strings, located Just Inside the doorways of the second and
third bedrooms, measured peaks occurred 10 minutes after the
release ended. On the day of this experiment, ambient levels of
CO were at approximately 1 ppm as the experiment began; although
the outdoor concentration declined as the experiment progressed,
the outdoor influence resulted in a slight offset that was not
reflected in tne model.
Figure 22 illustrates the correspondence between the nominal
model case and 15-minute measurements from the stationary network.
Although the model estimates at these points indicate an earlier
occurrence of the peak concentration than do the measurements, the
general correspondence is excellent.
The single-chamber mass balance model does not account for
spatial gradients; it tracks the overall retention of the
contaminant, providing estimates that correspond to volume-
weighted averages. To examine this concept, volume-weighted
average concentrations were calculated on a 15-minute basis using
data from the stationary network and the midlevel probe of the
anchor string. As shown in Figure 23, these volume-weighted
averages are in good agreement with the nominal model case. Even
though concentrations near the release are up to 4 times higher,
they occupy only 20 percent of the total volume. The single-
chamber mass balance, then, provides a fairly close approximation
of general concentration profiles that relate to passive exposure,
but tends to underestimate concentration profiles that relate to
active exposure.
52
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Q
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15
14
13
12
1 1
10
9
8
7
6
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4
3
2
1
0
15
14
13
12
11
10
9
8
7
6
5
4
Hallway
Anchor
H2
H3
Predicted
Elapsed Time, Hours
Other Bedrooms
• Anchor
+ D2
O D3
— Predicted
Figure 21. Comparison between single-zone model predictions and
measurements in the hallway and front bedrooms (experiment types
2 and 3, morning runs).
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E
a
a.
c"
o
c
3
o
c
o
o
o
o
15
14
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12
11 -
10 -
9
8
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6 -
5 -
4
3 ~
2 -
1 II
0
« LR
+ CBR
O FBR
— Predicted
Elapsed Time, Hours
Figure 22. Comparison between single-char.iber model predictions
and measurements at stationary monitoring locations that represent
likely sites of passive exposures (experiment type 2, morning run).
54
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E
a
a.
c
o
c
o
o
c
o
o
o
o
14 -
12 -
10 -
0
Average Indoor Concentration
Predicted Concentration
1 2
Elapsed Time, Hours
Figure 23. Comparison between, single-chamber model predictions
and volume-weighted average indoor concentrations for three
morning experiments.
5S
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The single-chamber model cannot simultaneously estimate active
and passive exposures with equal accuracy because the emissions
-re dispersed (in the model) to the general indoor air volume and
-re therefore equal throughout the house. Prom these experiments,
>L is obvious that there was both confinement in the room of
release ^lus time-consuming transport to other rooms, resulting in
the strong spatial and temporal differences that were observea.
in concept, the single-chamber model could be exercised twice,
first using the volume of the release room to estimate active
exposure and then using the general volume to estimate passive
exposure. However, shrinking the reference volume to that of the
release area (master bedroom) would result in overestimates of
active exposure. For example, for these experiments substituting
the 40-m3 volume of the master bedroom lor the 215-mJ volume of
the main floor would increase peak modeled concentrations by the
ratio of the volumes (5.4), producing peak concentrations near
20 ppm where approximately 10-pprn levels were observed; this dis-
crepancy is due to the dilution effects of transport to other
rooms.
There are two alternatives for increasing prediction
accuracy—(1) developing empirical values to increase the
effective removal ite of contaminants when using a single-zone.
model to estimate active exposure and (2) using a multichamber
model to simultaneously estimate active and passive exposures.
The second alternative—using a mulcichamber model—would seem to
be a more natural and straightforward approach.
4.2. Multiple-Chamber Modeling
A two-chamber mass balance model was formulated using
interzonal flows derived from previous PFT measurements at the
research house. For this model analysis, the master bedroom was
defined as zone 1 (volume of 40 m3), and the living/dining area,
hallway, and the two smaller bedrooms were treated as the second
zone (volume of 175 n»3). Specific equations used in tMs analysis
are presented in Appendix A. For this synthetic case, flow
coupling between the upstairs and the basement was ignored. .As
shown previously {Section 3), CO tracer would be occasionally
transported to the basement zone, but this occurrence did not
significantly alter the general form of the concentration profiles
upstairs.
56
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The system of interzonal and infiltration/exfiltration flows
used in the two-chamber model is illustrated in Figure 24. These
airflows were directly adapted from PFT measurements that were
taken over an 18-hour period in January 1985 at the research house.
This particular set of PFT measurements was acquired to assess
baseline conditions for experiments being conducted at that time.
As with the experiments reported here, operation of the central
circulation fan was suppressed. Interzonal airflows derived from
the PPT data, although not necessarily equal to those that
occurred during the experiments reported here, nonetheless provide
characteristic values that are appropriate for model applications.
The two-chamber mass balance model provides substantial
improvement in estimating active exposure, while retaining the good
correspondence with passive exposures that was obtained with the
single-chamber model. As shown in Figure 25, calculated peak
concentrations reached 9.2 ppm in the master bedroom (zone 1) and
3.0 ppm in zone 2. Model calculations reproduce measured
concentration profiles in the midlevel at both the anchor site and
the far end of the hallway for the morning experiment when the
vertical sampling plane was placed along the hallway.
Even though environmental conditions varied across
experiments, the two-chamber model calculations, which are
predicated on nominal conditions, provide good estimates of peak
and average concentrations for all of the experiments. Table 10
summarizes the range of measured peak and average concentrations at
key indoor locations, along with estimates from the single- and
two-chamber models. The single-chamber model is in best agreement
with measurements in the living area, and increasingly
underestimates peak and average concentrations at locations that
are closer to the release area.
For the two-chamber model, calculated peak and average
concentrations for zone 1 are in the center of the observed range
for the six analyzers situated in the master bedroom for one of the
morning experiments. At the anchor site and other locations where
measurements are available for all experiments, the two-chamber
model passes through a transition phase where zone 1 estimates are
overtaken by zone 2 estimates in terms of agreement with measured
values. The anchor site represents perhaps the most important
transition between the two defined chambers.
57
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5.7 mi / h
38,5 m3 / h
3.1 m3/h
f
74.5 nf / h
77.1 nf /h
41.1 nf /h
Zone 1
Master Bedroom
Volume = 40 m3
Zone 2
Remainder of House
Volume - 175m3
Figure 24. Airflows used as inputs to a two-chamber model,
58
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£
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a
E
a.
a.
15
14
13 H
12
11 -
10 -
9 -
8 -
7 -
6 -
5 -
4 -
3 ~
2 -
1 -
0
Zone One Concentrations
Midlevel at anchor
1 2
Elapsed Time, Hours
Zone Two Concentrations
MldlQvel at H2
Elapsed Tims, Hours
Figxire 25. Comparison between two-chamber model predictions
(indicated by a line) and measured concentrations in each zone
(indicated by squares) for morning experiment type 2,
59
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Table 10, Comparisons o" .iodel Estimates and Measured Values
for Peak and Time-weighted Average Concentration
During and After Contaminant Release
Peak 4-h Average
concentration concentration
(ppm)
MODEL ESTIMATES
Single chamber 3.4 2.2
Two chamber—zone 1 9.2 4.5
Two chamber—zone 2 3.0 2.1
RANGE OF MEASURED VALUES
Master bedroom (7.1-11.0}a (3.7-5.0)a
Anchor site—midlevel 6.3-8.2 3.8-4.7
Corner bedroom 3.9-4.5 2,3-2.9
Front bedroom 3.7-3.8 2.3-2.7
Living room 2.9-3.6 2.1-2,7
a Range of values from six sensors in one experiment; all others
are range of values across all experiments.
60
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In the two-chamber model, the anchor site would be assigned to
the general air volume (zone 2) because it receives material from
the release zone and is physically outside the master bedroom.
However, as shown in Section 3, concentration profiles at the
anchor site differed from the convective patterns in the master
bedroom and from the well-mixed conditions that were approached in
other rooms. Developing a separate volume centered on the anchor,
supported by correcting flows to direct the transport to other
rooms, would be an interesting avenue of possible refinement to
the two-chamber model. Although such an approach would offer
refinements in reproducing time-related events such as the delay
to reach peak concentrations away from the release point, the
physical justification for defining additional volumes requires
additional information.
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5. DISCUSSION
An overall perspective relating to goals and needs for
assessment of consumer exposures is provided in Section 5.1.
Major insights gained from this investigation and future actions
that can be taken to fill specific types of information gaps are
discussed in Section 5.2.
5.1. General Perspective and Needs
An important objective pertaining to OTS exposure assessments
is to provide accurate estimates of active and passive exposures
resulting from different patterns of consumer product use in
residential environments. One means of meeting this objective is
by developing a computer model that can provide accurate
predictions of exposures for a wide variety of scenarios.
As indicated in Figure 26, a number of user inputs, table
lookups, and computer calculations are needed to support a
fully-specified computer model for active and passive exposures to
emissions from consumer products used in residential environments.
Many of the lookups and calculations go beyond the capabilities of
the Computerized Consumer Exposure Models (CCEM) in current use
but could be obtained through future data acquisition efforts.
in Table 11, vital inputs to model lookups and calculations
are shown in relation to various types of data sources that
currently exist or that could exist as a result of future data
acquisition efforts. Four possible sources of data—results from
chamber studies, consumer surveys, measurements with
perfluorocarbon tracers (PFTs), and experiments in research
houses--are Indicated in the table; in addition, surveys in which
contaminants released from consumer products are monitored in
residential settings will also be needed to. validate consumer
exposure models. Alternative approaches for filling information
gaps through chamber studies, consumer surveys, and monitoring
surveys were discussed in a recent report (GEOMET, 1987c) that was
prepared for EPA.
One of the most significant voids in current exposure
assessments is the lack of appropriate values for air infiltration
rates and interzonal airflows. As shown in Table 12, combining
data from past PFT measurements and future research house
experiments can substantially fill this gap. These two types of
data sources are very complementary; PFT measurements cover a
63
Preceding page blank
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Inputs from Model Users:
Type of product and application
Location and duration of use
Type of structure
Geographic area
Time of year
Type of heating/cooling system
Status of windows/exhaust fans
f
Model Lookups;
Structure/room volumes
Time-varying emission
and decay rates
Outdoor meteorology
Model Calculations:
Air infiltration rates
Extent of operation of
heating/cooling system
Interchamber airflows
Time-varying
concentrations of
contaminant(s)
f
Model Outputs:
Hourly and average
concentrations per
zone/room
Data files, tables, or
graphs
Time-varying
Receptor Locations
Exposure
Profiles
Figure 26. Overview of consumer exposure model
64
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Table 11. Important Inputs to Model Lookups and Calculations
and Associated Data Sources
Data sources
Research
Chamber Consumer PFT house
Type of input studies surveys data base experiments
Emission rate
Duration/rate of use X
for various products
Emission rate specific X
to product and usage
pattern
Decay rate X
Volume/mixing/transport
Configuration and/or
involvement of
floors/rooms
Extent of heating/
cooling system
operation
Air exchange
- Infiltration rate X (X) (x
\._x ^^
- Ventilation rate X fx
Interchamber airflows fxj (xj
X = Some data already exist.
'""x
X)= Data could be obtained through future acquisition/assimilation
efforts.
65
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Table 12. Utility of PPT Data Base
and Research House Experiments
Characteristic
PPT
data base
Research house
experiments
Structure types and
geographic areas
Spatial coverage
per structure
Weather conditions
per structure
Internal conditions
per structure
Resultant airflows
Various
1 to 4 zones
Limited
Largely unknown
Average
Limited
Individual rooms
Various
Various (can be
controlled)
Time-varying
or average
66
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broad array of geographic areas and structure types, but are
limited in spatial, temporal, and operational details for each
structure; by comparison, research house experiments provide much
greater detail on temporal and spatial variations for various
conditions of product use, but may have less generalizability.
However, the transferability of results from research house
experiments can be greatly aided by replicating selected
experiments in other common types of occupied structures, such as
apartments, townhouses, and selected configurations of
single-family detached homes.
As noted in a recent scoping report (GEOMET 1987a) on the topic
of room-to-room contaminant migration, a relatively rich
repository of data concerning time-averaged air infiltration rates
and interzonal airflows for a variety of structures and geographic
areas is currently maintained at Brookhaven National Laboratory,
The analytical potential of these data cannot yet be exploited
because the results are not fully unified in a computer-accessible
format, but efforts toward this end have begun. Such efforts,
coupled with future research house experiments, will significantly
reduce the current information void that must be filled to
quantitate contaminant migration rates and model the exposure
implications of such migration,
5 • 2. Insights from the Current Investigation
The specific scenario used for this preliminary investigation
involved a controlled point release of a surrogate contaminant
over a period of 1,25 hours. Although this scenario does not
necessarily represent any specific product or contaminant, the
experimental results have a number of implications for passive
exposures and modeling thereof. Contaminant concentrations were
generally 3 to 4 times higher in the room of release than in areas
where passive exposures could occur, but concentrations in the
other areas were dlstinguishably above background levels within
1 hour after the release was initiated. Further, spatial
uniformity in concentrations throughout the main floor of the
research house was approached within 45 to 60 minutes after the
end of release period, during which time concentrations near the
release area receded and concentrations in other areas continued
to rise. Interestingly, a single-chamber model—similar to that
currently used In OTS assessments of active exposures In
residential environments—more closely approximated passive than
active exposures; use of a multichamber model resulted in better
estimation of each type of exposure.
67
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Through detailed spatial and temporal monitoring the
research house experiments described and analyzed in this report
have provided substantial insights into short-term contaminant
migration patterns, but were restricted to one release scenario,
Further experiments are needed to address the following types and
conditions of simulated product use:
• Type of release—point versus area {e.g., wall or
floor);
* Location of release;
Duration of release;
* Status of interior doors (open or closed);
» Status of windows and exhaust fans; and
* Season and operation of heating/cooling systems.
Covering all possible combinations of these conditions would
require a prohibitively large number of experiments; however, all
combinations are not needed to obtain vital insights. The number
of experiments could be substantially reduced, for example, by
limiting the next round of investigation to (I) a standard type,
duration, and location of release, but under different conditions
relating to interior doors, windows, exhaust fans, and
heating/cooling system operation, and (2) varying types,
durations, or locations of release for a single set of conditions.
Results from a recent EPA-sponsored consumer survey (Westat 1987)
can be used to help determine the most common conditions
surrounding product use.
To facilitate the conduct of experiments for a broader set of
simulated product usage scenarios, a detailed stationary
monitoring network needs to be established in the research houses;
this can be accomplished by expanding the number of monitoring
sites at the sacrifice of vertical detail at each site. An
illustrative array of the CO detectors used In this investigation
for such a network is given in Figure 27; monitoring sites in the
bedrooms, living room, and downstairs living area represent
probable receptor locations, whereas sites in the stairway and
hallway areas represent likely pathways of contaminant migration.
68
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UPSTAIRS
Garage
\
Q
\
Unfinished
Living Area
DOWNSTAIRS
PL. 27, Illustrative monitoring array for future contaminant
mir-- i experiments (filled circles represent probable receptor
lc- »s; empty circles represent likely migration routes).
69
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Providing a linkage between these experimental results and the
PFT data base is vital to the ultimate goal of improving the
accuracy and generalizability of consumer exposure models.
Consequently, future experiments should include PFT measurements
and real-time multiple tracer measurements as a standard
component. An illustrative array of the four available types of
PFT sources is given in Figure 28; this particular array will 1)
enable quantitation of average airflows among the bedroom, living
>-oom and downstairs areas and (2) provide a means of assessing
whether flows between bodroom arid living room areas can be
inferred from upstairs-downstairs flows (important because, in
many cases for multistory structures, PFT sources are configured
to provide estimates of flows between but not within stories).
The transferability of results from research houses to a
variety of housing types can be significantly aided by replicating
selected research house experiments in the following types of
structures:
Single-story, slab-on-grade structure;
Single-story structure with basement;
Multistory above-grade structure (attached and
detached); and
» Apartment unit.
Structures inhabited by colleagues or acquaintances could be used
for pretests of this approach in a limited number of settings.
^s little as one structure of each type can provide substantial
insights regarding not only the transferability of research house
results but also the need for broader surveys of this type.
including a detailed temporal and spatial monitoring network in
each house and making simultaneous PFT measurements will
strengthen the linkage between the detailed research house results
and the time-averaged PFT results that are available for a greater
variety of structure types.
70
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Bedroom Area
© ©
Living Room Area
(2} (T)
Garage
Downstairs
Living Area
Note: Source types (3)and (4) represent a commonly used array of
PPT sources for estimating flows between upstairs and
downstairs areas; addition of source types (T) and (2}
enables estimation of flows among three areaS--bedrooms,
living room, and downstairs—and can be used to assess
whether flows between bedrooms and living room could be
properly inferred if only source types (T) and (T) had
been used. ^^^
Figure 28. Proposed array of PFT sources for future
contaminant migration experiments.
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6. CONCLUSIONS AND RECOMMENDATIONS
Major findings and conclusions stemming from the study
results and modeling efforts given in Sections 3 and 4 are
summarized in Section 6.1. Recommendations drawn from the
discussion given in Section 5 are outlined in Section 6.2.
6.1. conclusions
The major findings and conclusions from this preliminary
investigation are as follows:
* During the 1.25-hour period when contaminant
release from a consumer product in the master
bedroom was simulated, resultant concentrations
were 3 to 4 times higher in the area of the
release than in other upstairs areas of the
house.
Within 45 to 60 minutes following the end of
the contaminant-release period, concentrations
throughout the upstairs of the house approached
spatial uniformity, even though the central
air circulation fan that would have promoted
contaminant migration was kept off as part of
the experimental design.
* Vertical gradients in contaminant concentrations
were most pronounced and variable in the release
area and along the migration path in the hallway,
suggesting that a fairly complex and somewhat
variable system of forces is involved in the
mixing and transport of contaminants.
• Concentrations at potential passive exposure sites
such as the living room and bedrooms adjacent to
the release area were generally similar in
magnitude, even during the release period; greater
variations were observed during afternoon than
morning experiments, possibly due to changing
forces at play around sunset.
Some evidence of contaminant migration downstairs
was observed during selected experiments; however,
even in these cases, downstairs concentrations were
substantially lower than those upstairs.
Preceding page blank 73
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Application of a one-zone model similar to that
used for current OTS exposure assessments resulted
in good estimates of passive exposure but
substantial underestimation of active exposure.
Application of a two-zone model resulted in good
estimates of both active and passive exposures
upstairs; thus, even though a complex set of forces
may be involved in contaminant mixing and
transport, the concept of treating general airflow
patterns as a steady-state condition into which
consumer-product emissions are injected and
transported appears valid and useful for improving
exposure estimates.
The success of the two-zone modeling effort in
estimating exposures for the release scenario
examined under this investigation suggests that PFT
measurement results coupled with continuing
experiments in research houses will provide a means
of substantially improving exposure estimates for a
variety of scenarios relating to use of consumer
products in residential environments.
6.2. Recommendations
A broaderarray of experiments should be conducted to
investigate contaminant migration fordifferent types of
releases and surrounding conditions^ Scenarios studied at the
research house should be expanded in terms of (1) the type,
location, and duration of release and (2) the status of interior
doors, windows, exhaust fans, and heating/cooling system, A
detailed stationary monitoring network should be established for
these experiments and measurements of time-.arying and
time-averaged interzonal airflows should be included as a routine
component of the monitoring design. Such experiments will
improve our understanding of contaminant migration patterns and
exposure implications for the greater variety of release types
and surrounding conditions that prevail in residential settings.
The method of point release used for the current
investigation should be repeated with the new monitoring design.
A point-source release of 1.25-hour duration should be repeated
in the master bedroom, first with the central air circulation fan
off at all times and then with the fan on at all times. These
two conditions should then be repeated with the release point
moved to the living room and then downstairs. Next, a different
74
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type of release (e.g., from an area source such as a wall or
floor) should be performed under similar conditions to evaluate
commonalities in migration patterns across different release
types. Following this sequence of experiments, the release type
and location should remain fixed but other conditions (e.g.,
interior doors, windows, and exhaust fans) should be varied,
first one at a time and then in selected combinations. Finally,
selected types of experiments should be conducted with a consumer
product in use—one for which detailed monitoring of the
associated contaminant(s) can be performed at a reasonable cost.
Selected types of research house experiments should be
replicated in a limited number of other structures to aid in
transferring the research results to variousresidential
settings^The number of scenarios should be restricted to four
at most, such as two release locations for each of two surrounding
conditions. Other types of structures should include
single-story detached residences with and without a basement, a
multistory above-grade residence, and an apartment unit. The
detailed monitoring network used at the research house should be
temporarily relocated to these other residences for this phase of
research.
As soon the the BNL data base of PFT measurement results has
been unified in a computer-accessible format, analytical efforts
should be initiated. The range and distribution of air
infiltration rates in different types of structures in different
geographic areas and at different times of the year should be
determined from the data base. Based on this analysis,
characteristic airflows should be estimated for specific
structure-area-season combinations as inputs to future modeling
efforts. The analysis should also assess whether any systematic
relationship exists between the magnitudes of air infiltration
rates and internal airflows.
In parallel with the research efforts described above,
activities to refine and improve currently used exposure
assessment models should be initiated. This process should begin
with the development of a generalised multichamber model and
continue with refinements and expansions, as critical Inputs are
obtained from the research efforts recommended above.
75
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7. REFERENCES
ASTM 1981. Standard Practice for Measuring Air Leakage by the
T'-acer Dilution Method, No. 6741-80. Philadelphia,
Pennsylvania: American Society for Testing and Materials.
GEOMET 1987a. Scoping and Feasibility Study; Room-to-Room
Contaminant Migration and OTS Indoor Air Exposure Assessments.
Report No. IE-1820. Germantown, Maryland: GEOMET Technologies,
GEOMET I987b. Preliminary Experiments to investigate
Contaminant Migration: Sampling and Analytical Protocol, Report
No. IE-1807A. Germantown, Maryland: GEOMET Technologies, Inc.
GEOMFT 1987C. Assessments of Human Exposure to Toxic
Substances in Residential Settings: Alternatives for Data
Collection Designs. Report No. IE-1826. Germantown, Maryland:
GEOMET Technolgies, Inc.
RTI 1987 Performance Audit for GEOMET's Indoor Environmental
Program Report No, RTI/3965/00-01F. Research Triangle Park,
North Carolina: Center for Environmental Quality Assurance,
Research Triangle Institute.
Westat inc. 1987. Household Solvent Products: A National
Usage Survey. Report No. EPA-OTS 560/5-87-005. Washington,
D.cT: U.S. Environmental Protection Agency, Office of Pesticides
and Toxic Substances.
Preceding page blank 77
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Appendix A
INDOOR AIR QUALITY MODELING CONCEPTS
AND FORMULATIONS*
The contents of this appendix have been excerpted from "Scoping
and Feasibility Study: Room-to-Room Contaminant Migration and
OTS Indoor Air Exposure Assessments," GEOMET Report No. IE-1820,
submitted to the Office of Toxic Substances, September 1987.
Preceding page blank
79
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The most widely used models for calculating contaminant
concentrations indoors represent the airspace of interest as a
single well-stirred chamber or as a series of interconnected
chambers. Rather than map the three-dimensional velocity and
dispersion field, these models track the amount of the contaminant
in the chamber(s) in terms of the mass balance defined by
generation; by inflow and outflow; and, for reactive contaminants,
by removal to sinks.
Because the mass balance approach incorporates important
physical factors and processes directly, it has become the main
theoretical framework for indoor air quality simulations. The
general mathematical expression of the mass balance is in the
form of a differential equation that, in solved form, constitutes
a user-implemented model. Such implementations include
code-intensive computer programs featuring numerical techniques
{Nazzaroff and Cass 1986) as well as simplified approaches
involving analytical solutions applied through programs on desk-
top computers (Nagda et al. 1985).
Single-chamber models define a given air space (e.g., a room,
a group of rooms or zone, or an entire building) as a single
well-mixed volume. To extend the single-chamber approach to
multiple cnambers for quantifying zone-to-2one migration, the
indoor volume must be represented as a network of interconnected
chambers. Contaminant mass balance is carried out for each of
these chambers; communicating flows with other chambers
(Figure A-l) are also considered.
Because conditions in a given chamber are determined by
interactions with all other connecting chambers, the rnultlchamber
model is stated as a system of simultaneous equations. The
mathematical framework for the multichamber description has been
reviewed by Sinden (1978) and by Sandberg (1984). General
equational forms for the single- and multichamber models are
presented in Table A-l.
From an operational standpoint, the most difficult decisions
concern appropriate model scenarios in terms of chambers and
airflows. The general patterns are of three basic types: (1) air
exchange between chambers and outdoors (Qio, Qoi), (2) chamber-
to-chamber airflows (Qij), and (3) air circulation within chambers,
These patterns are Illustrated in Figure A-2. The definition of a
chamber can entail (1) the entire building, (2) a zone or group of
rooms, (3) a single room, or (4) a part of a room.
81
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TRANSPORTED
OUTPUT TO
OUTDOORS
Qlo
TRANSPOR
OUTPUT TO
OUTDOORS
ED-*-
Qjo
INDOOR
SOURCES
SI
INDOOR
SOURCES
SJ
TRANSPOSED
INPUT FROM
OUTDOORS
TRANSPORTED
INPUT FROM
OUTDOORS
Figure A-l. Basic mass balance relationships
for multichamber approach.
82
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Table A-l. Single-Chamber and Multichamber Model Summary
dCin
V
Single-chamber
r~* 4- n * r** 4* o * c* *
— o T vQi^out violin
Multichamber
dCj_ n n
V-i Gi + S 0-i i C4 S
a i_ „,—"»•« — t _* *
QijCi
at
dt
00
CO
INPUTS
G = Source release rate (g/h)
V = Volume (m3)
Qoi = Flow from outdoors (m-Vh)
Qj_0 = Flow to outdoors (mVh)
= Outdoor concentration (g/
AIR MASS BALANCE
Qio = Qoi
INPUTS
Gi = Source release rate in ith chamber (g/h;
Vj_ = Volume of ith chamber (m3)
Q-H = Flow from jth to ith chamber (m3/h)
Q|^ = plow from ith to jth chamber (m3/h)
Cj - Concentration in jth chamber (g/ni3)
AIR MASS BALANCE
n n
Sr\ • • — p n * j
U^i - * Vij
OUTPUT
cin ~ Indoor concentration (g/ra3)
OUTPUT
i - Concentration in ith chamber (g/m3)
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Sutdoors
Chamber i
Chamber j
1, Air Exchange
« Natural Infiltration
• Natural ventilation
• Mechanical Ventilation
• Local Exhaust
2. Chamber-to-chamber Airflow
« Convective Circulation
• Advective Circulation
• Mechanical Circulation
3. Local Circulation
* Convective Mixing
* Mechanical Mixing
Figure A-2.
Basic patterns of air motion to be considered
in modeling.
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Local circulation relates to the completeness of mixing. In
the single-chamber description, effective volume and mixing factors
are sometimes employed to refine concentration estimates (Nagda
et al. 1987). Within the multichamber description, incomplete
mixing signals a need for designation of additional chambers. For
residential structures, this primarily involves defining zones
versus individual rooms. Relatively little quantitative work has
been reported that would lead to general rules for subdividing
individual rooms to accommodate vertical stratification.
Expanding the model perspective to the multichamber
description allows the exposure analyst to consider active
exposure and passive exposure simultaneously at the relatively
minor cost of additional complexity in calculations. The primary
needs for implementation center on defining attributes of the
exposure scenarios that relate to volumes and flows.
REFERENCES
Nagda NL, Koontz MD, and Rector HE, 1985. Energy Use,
Infiltration, and Indoor Air Quality in Tight, Well-Insulated
Residences, EPRI Report No. EA/EM-4117. Palo Alto, California:
Electric Power Research Institute.
Nagda NL, Rector HE, and Koontz MD. 1987. Guidelinesfor
Monitoring Indoor Air Quality. New York: Hemisphere Publishing
Corporation.
Nazzaroff WW, and Cass GR. 1986. Mathematical modeling of
chemically reactive pollutants in indoor air. Environ. Science
Technol. 20:924-34.
Sandberg M. 1984, The multi-chamber theory reconsidered from the
viewpoint of air quality studies. Build.Environ. 19(4):221-233.
Sinden FW. 1978. Multi-chamber theory of infiltration. Build.
Environ. (13):21-28.
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