United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park, NC 27711
Research and Development
EPA/600/SR-92/017 April 1992
& EPA Project Summary
The Performance of Chlorine-
Free Binary Zeotropic
Refrigerant Mixtures in a Heat
Pump
Jiirgen Pannock and David A. Didion
This study uses a simulation model
and an experimental heat pump appa-
ratus with counterflow heat exchang-
ers to show that two hydrof luorocarbon
(HFC) refrigerant mixtures, HFC-32/-
152a and HFC-32/-134a, may be
considered replacements for hy-
drochlorofluorocarbon (HCFC)-22 if the
appropriate mixture compositions are
chosen. Data indicate that multiple
tradeoffs exist in mixture performance
for different compressor speeds and
mixture compositions.
If the results for the HFC-32/-152a
mixture are compared at the same com-
pressor speed and capacity at which
the HCFC-22 results were obtained, the
improvements over HCFC-22 range
from 14% for the high-temperature cool-
ing mode to 2% for the low-tempera-
ture heating mode. The global warming
potential of the tested mixture is about
25% of the value of HCFC-22. However,
this zeotropic mixture is flammable in
the whole composition range.
The test results for the HFC-32/-134a
mixture, for mixtures containing more
than 35 mass percent of HFC-32, show
similar performance to the HFC-32M52a
mixture. Since HFC-134a is not flam-
mable, the HFC-32/-134a mixture exists
in a certain range as a nonflammable
mixture. The test results for both mix-
tures show no problems with respect
to extreme pressures or temperatures
in the tested composition range.
This Project Summary was devel-
oped by EPA's Air and Energy Engi-
neering Research Laboratory, 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 growing concern about the envi-
ronmental compatibility of currently used
refrigerants requires development and use
of new refrigerants and refrigerating meth-
ods. The incompatibility of chlorofluorocar-
bon (CFC) and hydrochlorofluorocarbon
(HCFC) refrigerants with the Earth's ozone
layer and their influence on the green-
house effeict make it desirable to investi-
gate ozone-safe refrigerants with low
greenhouse warming potentials (GWPs)
that operate efficiently in refrigeration sys-
tems. This study investigated such ozone-
safe refrigerants as zeotropic mixtures for
heat pump' applications.
The refrigerants considered in this study
are chemical derivatives of methane and
ethane. With the requirement that the ozone
depletion potential (OOP) of the consid-
ered substances has to be zero, it follows
that they cannot contain any chlorine or
bromine (chlorine and bromine are consid-
ered the main catalytic substances de-
stroying the ozone layer). With this in mind,
the following substances were selected to
find a suitable working fluid for heat pump
applications: hydrofluorocarbon (HFC)-23,
-32, -125, -134a, -143a, and -152a.
In order to evaluate their performance,
the refrigerants were compared to HGFC-
22 which is the commonly used refrigerant
in heat pumps in the United States.
In the theoretical part of the report, a
suitable refrigerant mixture for the possible
replacement of HCFC-22 was determined
by applying a simulation program for the
Printed on Recycled Paper
-------
different substances and their mixtures
under certain operating conditions. The
results of this computer study were com-
pared and analyzed with respect to the
performance data.
The experimental part of this research
project consisted of tests with the theoreti-
cally best performing refrigerant mixtures,
tha binary zeotropic mixtures HFC-32/-134a
and HFC-32/-152a. These tests were con-
ducted in a Mini-Breadboard Heat Pump
(MBHP).
Theoretical Study
The results of the computer study show
that there are two binary mixtures of MFCs
that indicate a better performance than the
currently used HCFC-22: HFC-32/-152a
arid HFC-32/-134a. Although the pure com-
ponents of these mixtures show either lower
coefficients of performance (COPs) and
higher volumetric capacities or higher COPs
and lower capacities, wide ranges of mix-
ture compositions perform better in COP
and show a higher volumetric capacity.
The HFC-32/-152a mixture is flammable
since both pure substances are flammable.
Both of these two refrigerants appear to
have tow toxicities. The mixture also has
the lowest GWP of all considered mix-
tures. Operating temperatures and pres-
sures are within acceptable limits.
The calculations for HFC-32/-134a show
a smaller performance improvement than
for HCFC-32/-152a but still a significant
Increase compared to HCFC-22. Both of
these refrigerants are in the class of low
toxfcity, and only HFC-32 is flammable. If
flammabilily tests show that a nonflam-
mable refrigerant mixture exists within the
composition range of performance improve-
ment, this mixture would clearly be the
substance of choice with respect to safety
considerations. The GWP of HFC-32/-134a
is higher than that of HFC-32/-152a. How-
ever, it still is significantly lower than that of
HCFC-22. Again, the operating tempera-
tures and pressures do not appear to pose
any problems.
Given the results of the computer study,
tests were conducted with these two refrig-
erant mixtures within certain composition
ranges. The ranges of the tested mixtures
were determined largely by the desire to
find a mixture that achieves at least the
same volumetric capacity and the same
COP as HCFC-22. This should be the
case for all operating conditions. At the
same time, excessive amounts of HFC-32
should not be used in order to provide for
acceptable discharge pressures even un-
der extreme operating conditions. Tests
were run for both refrigerant mixtures in a
range between 15 and 40 mass-percent
HFC-32. For all these compositions, the
pressures are expected to be well within
acceptable ranges.
Experimental Study
Tests over a wide range of mixture
compositions using an experimental HFC
heat pump apparatus with counterf low heat
exchangers show that refrigerant mixtures
HFC-32/-152a and HFC-32/-134a may be
considered replacements for HCFC-22 if
the appropriate mixture compositions are
chosen. Data indicate that multiple trade-
offs exist in mixture performance for differ-
ent system compressor speeds and mixture
compositions.
If results for HFC-32 and -152a are
compared at the same compressor speed
and capacity at which the HCFC-22 results
were obtained, the predicted improvements
in COP are very close to the measured
COPs. These improvements over HCFC-
22 range from 14% for the high-tempera-
ture cooling mode to 2% for the low
temperature heating mode. Operating pres-
sures and temperatures of this mixture are
well within acceptable limits. The GWP of
the tested mixture is about 25% of the
value of HCFC-22. However, this zeotropic
mixture is flammable in the whole compo-
sition range.
The other mixture, .HFC-32/-134a, is
not predicted to perform as well as the
HFC-32/-152a mixture. However, the test
results indicate that, for mixtures contain-
ing more than 35 mass percent of HFC-32,
the performance is very similar to that of
the HFC-32/-152a mixture. In the 'heating
mode, slightly higher COPs were obtained,
and in the cooling mode slightly lower COPs
were measured (compared to the HFC-32/
-152a mixture at the same HFC-32 mass
fractions). The performance improvement
over that of HCFC-22 at the compressor
speed and capacity equivalent to the
HCFC-22 tests ranges from 5% in the
high-temperature mode to 2% in the low
temperature heating mode. Since HFC-
134a is not flammable, the HFC-32/-134a
mixture exists in a certain range as a non-
flammable mixture. Flammability tests will
be conducted to determine this range. The
test results for the HFC-32/-134a mixture
show no problems with respect to extreme
pressures or temperatures in the tested
composition range.
The achieved COP increases for both
mixtures offer enough potential that even
cross-flow heat exchange systems (as cur-
rently used in household heat pumps)
should benefit from the use of these mix-
tures.
The test results of the mixtures were
compared with those of HCFC-22 at the
same heating/codling capacity. The test
results for the different refrigerants were
achieved with the same test apparatus,
meaning that there is no optimization with
respect to system pressure drops, com-
pressor efficiency, and other operating fac-
tors.
•&U:S. GOVERNMENT PRINTING OFFICE: 1992 - «48-0«OA4022K
-------
-------
JQrgen PannockandDavidA. Didhn are with the National Institute of Standards and
Technology, Gaithersburg, MD 20899.
Robert V. Hendrlks is the EPA Project Officer (see below).
The complete report, entitled "The Performance of Chlorine-Free Binary Zeotropic
Refrigerant Mixtures in a Heat Pump," (Order No. PB92-149814/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-92/017
------- |