United States
Environmental Protection
Agency
National Risk Management
Research Laboratory
Research Triangle Park, NC 27711
Research and Development
EPA/600/SR-96/116 November 1996
4>EPA Project Summary
Large Building HVAC
Simulation
L. Gu, M. V. Swami, and V. Vasanth
The report discusses the monitoring
and collection of data relating to in-
door pressures and radon concentra-
tions under several test conditions in a
large school building in Bartow, FL.
The Florida Solar Energy Center (FSEC)
used an integrated computational soft-
ware, FSEC 3.0, to simulate heating,
ventilation, and air-conditioning (HVAC)
system and multizone airflows, indoor
pressures, radon transport in the soil,
and slab and indoor radon levels in the
large building. The simulation was vali-
dated by measured data. A limited para-
metric study shows the influence of
outdoor airflow, ambient radon level,
and soil radium content on indoor ra-
don levels.
This Project Summary was developed
by EPA's National Risk Management
Research Laboratory's Air Pollution Pre-
vention and Control Division, Research
Triangle Park, NC, to announce key find-
ings of the research project that is fully
documented in a separate report of the
same title (see Project Report ordering
information at back).
Introduction
The report represents work performed
by the Florida Solar Energy Center (FSEC)
for the Environmental Protection Agency
(EPA) and the Florida Department of Com-
munity Affairs. Although individual tasks
were funded separately by the two agen-
cies, the report, for the sake of complete-
ness, represents the combined efforts of
all simulation-related tasks.
Project Goals
The primary goal of the project was to
establish the potential for using models to
analyze radon levels in large buildings.
This was done by applying modeling tools
developed in earlier work and integrated
in the computational platform, FSEC 3.0,
and to analyze pressures, airflows, and
indoor radon levels in a school building
monitored by the EPA and Southern Re-
search Institute (SRI). Simulation results
are compared with measured data. Pre-
liminary parametric analysis will be dis-
cussed.
Discussion
The effort of the EPA contract is to
simulate pressures of indoor and air distri-
bution system airflows of interzone and
supply and return, and indoor radon lev-
els in the Polk Life and Learning Center at
Bartow, FL, monitored by the EPA and
SRI.
First, only the air distribution system of
the school building was simulated to ob-
tain and refine the distribution system pa-
rameters. This was done by trial and error
while adjusting values of the distribution
system parameters and comparing the re-
sults with a test and balancing report pro-
vided by the Associated Air Balance
Council. After adjustments, the differences
between measured and predicted airflows
were less than 5%. Next, a steady-state
simulation of the soil/slab composite was
carried out, and the results were com-
pared with experimental data. Because of
the nature of the boundary conditions over
the slab, a three-dimensional discretization
was required to correctly model the soil/
slab composite. Soil/slab parameters were
adjusted by trial and error to obtain a
reasonable match between predicted and
measured values of pressures and air-
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flows. Results of the steady state simula-
tion comparison with measured indoor ra-
don levels agreed to within 6%. Due to a
paucity of detailed data, it is important to
note that the adjusted material properties
may not necessarily represent the true
values, and the calibration may not nec-
essarily translate to other cases.
Keeping the adjusted parameters ob-
tained from earlier runs constant, the next
step is to compare measured and calcu-
lated indoor radon levels for a transient 7-
hour period and a typical school day with
the system "on" for the first 12 hours and
"off for the remaining 12 hours. Figure 1
compares histories of predicted and mea-
sured indoor radon levels in one station
(Room 109) for a typical school day. It is
evident that while the agreement at the
beginning and end of the "on" cycle is
good, the model predicts higher radon di-
lution rates during the "on" cycle than
shown by the experiment. However, the
model and experiment compare very well
during the "off period. The disparity noted
during "on" times appears consistently in
all zones. This is a significant cause for
concern and is possibly due to two fac-
tors: (1) the model assumes well mixed
zones, which may not be true in actuality
(the ventilation efficiency may not be
100%, leading to different radon levels
within a zone, and a single-point mea-
surement may be insufficient); and (2) the
ambient radon level may be higher than
assumed. Due to the unavailability of data
on ambient radon levels during this pe-
riod, we assumed a constant of 3.5 pCi/L
for the simulation. Results of other work
for the Florida Radon Research Program
show that ambient radon levels may not
only be higher than established action lev-
els, but may also vary cyclically during a
24-hour day. Clearly, the model would pre-
dict lower rates of dilution and would ap-
proach measured values if higher ambient
radon levels were used in the simulation.
Undoubtedly, these two factors (ventila-
tion efficiency and ambient radon levels)
must be investigated further before an-
swering the question definitively.
Next, parametric analysis of the effect
of varying outdoor airflow, ambient radon
level, and soil radium content was carried
out for this specific building. Indoor radon
level decreases with increasing outdoor
airflow through the air distribution system,
due to dilution. When ambient radon level
and soil radium content are varied, there
appears to be a linear relationship be-
tween indoor radon level and ambient or
soil radium content. This determination is
specific to the building studied and is based
on assumptions stated in the report and
may not necessarily translate to other simi-
lar buildings.
Caveats
It is crucial to note that the nature of the
work performed here is exploratory, pri-
marily to establish the potential of using
models to analyze large buildings and to
identify the essential areas for experiment
and simulation to complement each other
in providing an accurate, yet cost efficient,
strategy to study radon in large buildings.
This objective was substantially achieved
through a preliminary simulation of air-
flows and pressures in a school building
monitored. Since only a limited set of ex-
perimental data were available, several
assumptions were made to successfully
complete the simulations. The results pre-
sented in this report should, therefore, be
viewed in light of the assumptions stated
and applied only to the specific problem
analyzed. The result should in no way be
construed to represent generalizations for
large buildings. The report concludes with
a list of areas that need further attention.
20
18
16
O 14
CL
g
io 12
Polk Life and Learning Center
Rm. 109 (Station 2) 4/21-4/22
10 -•
o
"S 8
6 --
4 -•
12 14 16 18 20
Time (hours)
22 24 26 28
30
Figure 1. Predicted/measured indoor radon levels.
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L. Gu, M. V. Swami, and V. Vasanth are with the Florida Solar Energy Center,
Cape Canaveral, FL 32920.
Marc Y. Menetrez is the EPA Project Officer (see below).
The complete report, entitled "Large Building HVAC Simulation," (Order No.
PB97-104715; Cost: $21.50, subject to change) will be available only from
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at
Air Pollution Prevention and Control Division
National Risk Management Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
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EPA/600/SR-96/116
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