United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park, NC 27711
Research and Development
EPA/600/SR-92/008 March 1992
EPA Project Summary
Radon Pressure Differential
Project, Phase I Florida Radon
Research Program
James B. Cummings, John J. Tooley,; Jr., and Neil Moyer
The report gives results of tests on
70 central Florida houses to assess
and characterize pressure differentials!
in new (age 5 years or less) Florida
houses. Blower door tests determined
house airtightness and air distribution
system leakage. The 70 houses had
an average airtightness of 7.23 air
changes per hour at 50 Pa* (ACH50).
Significant leaks were found in the
ductwork in most houses tested, both
on the supply and return sides of the
air handler. When the air distributiori
system was sealed off, house ACH50
decreased to 6.421, indicating that
11.2% of the house leak area is in the
duct system. \
Differential pressure measurements
were taken between the main body of
each house and sub-slab areas, out:
doors, and many locations within the
house. These measurements indicated
significant pressure differentials in the
house due to a number of factors. Re-
turn .leaks produced a maximum whole-
house pressurization of 5.5 Pa. Supply
leaks produced a maximum whole-
house depressurization of -4.8 Pa.
Closed interior doors produced a maxi-
mum closed-room pressurization of Sir
Pa and a maximum main-body depres-
surization of -14.8 Pa. Turning on all
exhaust fans and interior dryers typi-
cally depressurized the house to 0 to
-4 Pa, but one very tight house was
depressurized to -37 Pa.
One of the most important findings
of this study is that large-magnitude
(*) 1 Pa = 0.004 In. WG
localized depressurization occurs be-
cause of return plenum leaks. Subslab
depressurization of up to 6 Pa have
been found 5.5 m" from the return ple-
num. Depressurization of -6 Pa in a
garage and a -4 Pa in a utility room has
been observed.
This Project Summary was developed
by EPA's Air and Energy Engineering
Research Laboratory, Research Tri-
angle 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
Radon intrusion into buildings is a func-
tion of radon resource strength in the soil,
the permeability of the soil, the cumulative
size of penetrations in the house/soil in-
terface, and the pressure differences
across the house/soil interface. Pressure
differences are a function of the natural
forces of wind and thermal buoyancy, and
mechanical forces of air-moving equip-
ment. This equipment includes central
conditioning-air-moving systems, exhaust
fans in the bathrooms and kitchens, cook-
top grill exhausts, clothes dryers, whole-
house fans, attic exhaust fans, and cen-
tral vacuum cleaner systems.
The impact of these mechanical sys-
tems is a function of the volume of ex-
haust air flow, house airtightness, and the
fraction of the time that they operate. Cen-
tral air conditioning systems operate auto-
matically according to thermostat control.
(**)1 m = 3.28 ft
Printed on Recycled Paper
-------
Typical daily run times range from 20 to
60%, depending upon a number of vari-
ables: the size of the space conditioning
unit in relation to the conditioning load,
the thermostat setpoint, the mechanical
condition of the space conditioning unit
and the duct system, and the fraction of
time that interior doors are kept closed.
Operation time of other air moving equip-
ment is a function of family demographics
and lifestyle. The number of exhaust fans
in a house and whether the clothes dryer
is located within the house are obviously
important variables as well.
An additional source of differential pres-
sures in Florida houses is closure of inte-
rior doors. Since most houses have only
one or two returns, and since generally
both are located in the main body of the
house, return air comes back to the air
handler through open doors. If the doors
are closed, much of the return air flow is
blocked. The closed rooms go to high
pressure and the main body of the house
goes to negative pressure, as ft is starved
for air. The pressures significantly in-
crease the infiltration rate of the house
and increase the potential for radon to be
sucked in from the soil. The pressure
buildup in the closed rooms is a function
of the amount of supply air to the room,
the airtightness of the room, and the
amount of door undercut. None of the 70
houses tested in this study had transfer
registers to assist return air flow.
In this project, pressure differences have
been measured across the house floor,
from indoors to outdoors, from indoors to
the garage, and from one area to another
within the house with various combina-
tions of mechanical systems operating.
The main body of the house was consid-
ered the reference point for pressure dif-
ferential measurement — this means that
the main body was always considered to
be at 0 Pa pressure. Pressure differen-
tials reported assume the outdoors as the
reference pressure (outdoors = 0.0 Pa)
unless otherwise noted.
The airtightness of the house and the
air distribution system has been measured
by blower door testing. The location, type,
and estimated size (cubic feet per minute)
of duct leaks have been obtained from
visual inspections using tracer smoke. The
objectives of this study include character-
ization of pressure differences within
Florida houses and across their slabs as
a result of naturally and mechanically in-
duced effects, and identifying the causes
of these pressure differences.
Conclusions
Testing has been done on 70 central
Florida houses to assess and character-
ize pressure differentials in new (age 5
years or less) Florida houses. House
airtightness is substantially greater than in
older Florida housing. House airtightness
for these houses was 7.23 vs. 12.58
ACH50 in a sample of 90 mixed-age cen-
tral Florida houses. It was found that
11.6% of the house leak area is in the
duct system, similar to the 12.2% found in
the 90 older houses. However, since the
houses are tighter, the duct systems are
tighter as well. Ducts are looser in older
houses in this study. Those 1 or 2 years
old have duct ELA50 (equivalent leak area
at 50 Pa) or about 0.013 sq m,* while
those 4 or 5 years old have about 0.023
sq m ELA50. This can be interpreted
either that duct air distribution systems
are being constructed more airtight, or
that tape closure systems deteriorate over
a few years in a significant number of
houses. In others, tape has not shown
signs of failure. Mastic with fabric closure
systems showed no signs of failure.
Pressure differentials, which have the
potential to reduce or increase radon en-
try rates, are produced by natural forces
of wind and temperature, and mechanical
systems. Wind-produced depressurization
in a house is typically in the range of -0.5
to -1.5 Pa. The greater the wind speed,
the greater the depressurization.
Mechanical systems produced much
greater pressure differentials than wind in
many cases. Turning on the air handler
produced pressure differentials from about
-4 to +4 Pa. Supply leaks depressurize
the house, while return leaks pressurize
the house.
Return leaks depressurize local zones
within houses. Garages and utility rooms,
especially, experience depressurization
because of return leaks. Seventeen of 41
garage units depressurized the garage to
-1 Pa or more, and to more than -6 Pa in
one garage. Leakage of the depressur-
ization field from the return plenum into
adjacent wall cavities, and through cracks
and chases into the soil, also has the
potential to draw radon into the air distri-
bution system and thus into the house.
Closing of interior doors increased pres-
sure differentials. Position pressure in
nine closed rooms increased to as much
as 38 Pa relative to outdoors in some
houses, and the main body of the house
depressurized to as much as -14.8 Pa
relative to outdoors. Nearly a third of the
house depressurized to -4 Pa or greater
(in the main body of the house) when the
interior doors were closed.
Exhaust equipment and appliances de-
pressurize houses. The tighter the house
and the larger the exhaust air flow, the
larger the potential depressurization. One
tight (2.4 ACH50) house depressurized to
-376 Pa when four exhaust fans and a
dryer were operating. More typically, op-
eration of all exhaust equipment depres-
surizes houses to -1 to -5 Pa. Bathroom
exhaust fans depressurize bathrooms by
more than 1 Pa in more than half the
houses. Dryers alone depressurize the
entire house by -0.2 to -2 Pa in most
houses, and in one house to -9 Pa.
Pressure differentials across the slab
are similar in magnitude to those from
indoors to outdoors. However, in some
houses there is less of a pressure drop
across the slab, indicating some commu-
nication through the soil to the outdoors.
The cause and effect relationship be-
tween depressurization and radon entry
has not been investigated or demonstrated
in this study. Consequently, it cannot be
stated with certainty that duct leakage,
closing of interior doors, and exhaust
equipment operation increase radon entry
rates. If, as most believe, radon entry is
strongly related to pressure differential,
then these mechanical systems may be
significant contributors to radon in Florida
houses.
Several recommendations follow from
this. First, air distribution systems should
be constructed to be airtight and durable
for the life of the house. Materials and
construction methods which produce air-
tight and durable ducts should be adopted.
Second, return air pathways should be
provided for each closeable room so that
depressurization of the main body of the
house can be minimized. Third, operation
of exhaust equipment should be minimized.
Alternatively, exhaust flow can be balanced
by equal supply air to eliminate depres-
surization.
(*) 1 sq m = 1550 sq in.
•&U.S. GOVERNMENT PRINTING OFFICE: 1992 - 648-080/40214
-------
-------
J.B. Cummings Is with The Florida Solar Energy Center, Cape Canaveral, FL 32902;
and J.J. Tooley, Jr., and N. Moyer are with National Florida Retrofit, Inc.,
Montverdi, FL 34756-0301.
David C. Sanchez is the EPA Project Officer (see below).
The complete report, entitled "Radon Pressure Differential Project, Phase I Florida
Radon Research Program,"(OrderNo. PB92-148519/AS; Cost: $19.00; subject
to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Air and Energy Engineering 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
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
Official Business
Penalty for Private Use $300
EPA/600/SR-92/008
------- |