U.S. patent application number 11/916311 was filed with the patent office on 2009-05-07 for methods and apparatus for operating air conditioning systems with an economizer cycle.
This patent application is currently assigned to CARRIER CORPORATION. Invention is credited to Alexander Lifson, Michael F. Taras.
Application Number | 20090113900 11/916311 |
Document ID | / |
Family ID | 35695684 |
Filed Date | 2009-05-07 |
United States Patent
Application |
20090113900 |
Kind Code |
A1 |
Lifson; Alexander ; et
al. |
May 7, 2009 |
METHODS AND APPARATUS FOR OPERATING AIR CONDITIONING SYSTEMS WITH
AN ECONOMIZER CYCLE
Abstract
Methods and apparatus are provided for enhancing the performance
of rooftop air conditioning systems by operating such systems with
an economizer cycle and utilizing a blend incorporating R32 and
R125 refrigerants as a working medium, wherein such benefits are
related to at least the performance (e.g. capacity and/or the
energy efficiency ratio) of the rooftop air conditioning system
operating at various environments (e.g. temperatures at and above
95.degree. F.).
Inventors: |
Lifson; Alexander; (Manlius,
NY) ; Taras; Michael F.; (Fayetteville, NY) |
Correspondence
Address: |
MARJAMA MULDOON BLASIAK & SULLIVAN LLP
250 SOUTH CLINTON STREET, SUITE 300
SYRACUSE
NY
13202
US
|
Assignee: |
CARRIER CORPORATION
FARMINGTON
CT
|
Family ID: |
35695684 |
Appl. No.: |
11/916311 |
Filed: |
June 8, 2005 |
PCT Filed: |
June 8, 2005 |
PCT NO: |
PCT/US2005/020217 |
371 Date: |
June 20, 2008 |
Current U.S.
Class: |
62/77 ; 62/259.1;
62/335; 62/498 |
Current CPC
Class: |
C09K 5/045 20130101;
Y02P 20/124 20151101; Y02P 20/10 20151101; C09K 2205/22 20130101;
F25B 40/02 20130101; F25B 9/006 20130101; C09K 2205/24 20130101;
F25B 2400/13 20130101; F25B 2600/0261 20130101 |
Class at
Publication: |
62/77 ; 62/259.1;
62/498; 62/335 |
International
Class: |
F25B 45/00 20060101
F25B045/00; F25D 23/00 20060101 F25D023/00; F25B 1/00 20060101
F25B001/00; F25B 7/00 20060101 F25B007/00 |
Claims
1. An air conditioning system, comprising: a rooftop air
conditioning unit operated with an economizer cycle, wherein the
rooftop air conditioning unit utilizes at least one predetermined
refrigerant as a working medium.
2. The air conditioning system of claim 1, wherein the at least one
predetermined refrigerant is a blend of R32 refrigerant and R125
refrigerant.
3. The air conditioning system of claim 2, wherein the at least one
predetermined refrigerant is a blend of about 47% to about 53% by
weight of R32 refrigerant and about 53% to about 47% by weight of
R125 refrigerant.
4. The air conditioning system of claim 1, wherein the at least one
predetermined refrigerant includes at least one additive.
5. The air conditioning system of claim 4, wherein each of the at
least one additive is an oil.
6. The air conditioning system of claim 5, wherein each of the at
least one oil has a viscosity grade between about 20 and about 70
centistokes.
7. The air conditioning system of claim 5, wherein each of the at
least one oil is selected from the group consisting of polyolester
oil, polyvinylether oil, Alkyl Benzene oil, mineral oil, and a
mixture of two or more thereof.
8. The air conditioning system of claim 4, wherein the at least one
additive is an additional refrigerant.
9. The air conditioning system of claim 8, wherein the additional
refrigerant is R134a.
10. The air conditioning system of claim 9, wherein the amount of
R134a added to the system is up to and including 5% by weight.
11. The air conditioning system of claim 4, wherein the at least
one additive is a lubrication enhancement additive.
12. A rooftop air conditioning system which is operated with an
economizer cycle and which uses a working medium comprised of a
mixed refrigerant of R32 and R125.
13. The rooftop air conditioning system of claim 12, wherein the
working medium is comprised of 47% to about 53% by weight of R32
refrigerant and about 53% to about 47% by weight of R125
refrigerant.
14. The rooftop air conditioning system of claim 12, wherein the
working medium includes at least one additive.
15. The rooftop air conditioning system of claim 14, wherein each
of the at least one additive is an oil.
16. The rooftop air conditioning system of claim 15, wherein each
of the at least one oil has a viscosity grade between about 20 and
about 70 centistokes.
17. The air conditioning system of claim 15, wherein each of the at
least one oil is selected from the group consisting of polyolester
oil, polyvinylether oil, Alkyl Benzene oil, mineral oil, and a
mixture of two or more thereof.
18. The air conditioning system of claim 14, wherein the at least
one additive is an additional refrigerant.
19. The air conditioning system of claim 18, wherein the additional
refrigerant is R134a.
20. The air conditioning system of claim 19, wherein the amount of
R134a added to the system is up to and including 5% by weight.
21. The air conditioning system of claim 14, wherein the at least
one additive is a lubrication enhancement additive.
22. A method of improving the performance of a rooftop air
conditioning system, comprising the steps of: providing a rooftop
air conditioning system; and operating the rooftop air conditioning
system with an economizer cycle.
23. The method of claim 22, further comprising the step of:
utilizing a mixture of R32 and R125 refrigerants as a working
medium for the system.
24. The method of claim 23, wherein the working medium includes at
least one additive.
25. The method of claim 24, wherein each of the at least one
additive is an oil.
26. The method of claim 25, wherein each of the at least one oil
has a viscosity grade between about 20 and about 70
centistokes.
27. The method of claim 25, wherein each of the at least one oil is
selected from the group consisting of polyolester oil,
polyvinylether oil, Alkyl Benzene oil, mineral oil, and a mixture
of two or more thereof.
28. The air conditioning system of claim 24, wherein the at least
one additive is an additional refrigerant.
29. The air conditioning system of claim 28, wherein the additional
refrigerant is R134a.
30. The air conditioning system of claim 29, wherein the amount of
R134a added to the system is up to and including 5% by weight.
31. The air conditioning system of claim 24, wherein the at least
one additive is a lubrication enhancement additive.
32. The method of claim 22, wherein the step of operating the
rooftop air conditioning system is performed in an outdoor ambient
temperature above 95.degree. F.
33. The method of claim 22, wherein the step of operating the
rooftop air conditioning system is performed in an outdoor ambient
temperature between about 95.degree. F. and about 125.degree..
34. A rooftop air conditioning system, comprising: a compressor; a
condenser in communication with the compressor via at least a first
refrigerant line; a first expansion device in communication with
the condenser via at least a second refrigerant line; an evaporator
in communication with the first expansion device via at least a
third refrigerant line and in communication with the compressor via
at least a fourth refrigerant line, a second expansion device in
communication with the condenser via at least a fifth refrigerant
line; and a heat exchanger in communication with the second
expansion device via at least a sixth refrigerant line and in
communication with the compressor via at least a seventh
refrigerant line; wherein the rooftop air conditioning system is
operated with an economizer cycle and utilizes at least one
predetermined refrigerant as a working medium.
35. The rooftop air conditioning system of claim 34, wherein the
system comprises at least two compressors.
36. The rooftop air conditioning system of claim 35, wherein at
least two compressors are tandem compressors.
37. The rooftop air conditioning system of claim 34, wherein the
system is a multi-circuit system.
38. The air conditioning system of claim 34, wherein the at least
one predetermined refrigerant is a blend of R32 refrigerant and
R125 refrigerant.
39. The air conditioning system of claim 38, wherein the at least
one predetermined refrigerant is a blend of about 47% to about 53%
by weight of R32 refrigerant and about 53% to about 47% by weight
of R125 refrigerant.
40. The air conditioning system of claim 34, wherein the at least
one predetermined refrigerant includes at least one additive.
41. The air conditioning system of claim 40, wherein each of the at
least one additive is an oil.
42. The air conditioning system of claim 41, wherein each of the at
least one oil has a viscosity grade between about 20 and about 70
centistokes.
43. The air conditioning system of claim 41, wherein each of the at
least one oil is selected from the group consisting of polyolester
oil, polyvinylether oil, Alkyl Benzene oil, mineral oil, and a
mixture of two or more thereof.
44. The air conditioning system of claim 40, wherein the at least
one additive is an additional refrigerant.
45. The air conditioning system of claim 44, wherein the additional
refrigerant is R134a.
46. The air conditioning system of claim 45, wherein the amount of
R134a added to the system is up to and including 5% by weight.
47. The air conditioning system of claim 40, wherein the at least
one additive is a lubrication enhancement additive.
Description
FIELD OF THE INVENTION
[0001] This invention relates to air conditioning systems, and, in
particular, to methods and apparatus for operating packaged air
conditioning systems (e.g. rooftop air conditioning systems) with
an economizer cycle so as to achieve measurable performance-related
benefits.
BACKGROUND OF THE INVENTION
[0002] It is known in the refrigeration art that various benefits
(e.g., increased system capacity and/or efficiency) can be derived
from operating a refrigeration system with a so-called "economizer
cycle." It is also understood that these benefits are magnified
when there is a high pressure ratio between compressor suction and
discharge, such as would occur when a high temperature differential
exists during operation of a refrigeration system. For example,
appreciable system benefits are achieved when operating a
supermarket or transport refrigeration system with an economizer
cycle in environments wherein the temperature differential (between
compressor saturated suction and saturated discharge temperature)
for the refrigerant circulated through the system is typically
about 130.degree. F.
[0003] In contrast, pressure ratios are much lower for air
conditioning systems. This is because the temperature differential
encountered during operation of air conditioning systems is
markedly less than that which is typically encountered in a
refrigeration context. Consequently, those in the air conditioning
field have been discouraged from operating air conditioning systems
with an economizer cycle, particularly since it is their belief
that doing so would add non-nominal costs and complexities to the
systems that would not be recouped by performance-related benefits
and/or enhancements. Thus, those who manufacture, sell and/or
utilize air conditioning systems have been unable, thus far, to
reap the various benefits that perhaps could be realized through
operation of such air conditioning systems with an economizer
cycle.
[0004] While that alone is problematic, it is made more difficult
by the recent introduction of various legislation and industry
regulations, which have greatly affected the air conditioning
industry by defining minimum efficiency standards for air
conditioning systems and by instituting a gradual phase-out of
(followed, over time, by a total ban on) certain thermodynamically
suitable and efficient refrigerants that also happen to contain
hydrochlorofluorocarbons (HCFCs), e.g., R22 refrigerant.
[0005] The phase-out/ban on R22 is particularly significant to
those in the art, since there is a concern that the performance of
air conditioning systems may be negatively impacted due to the
resultant introduction of alternate, "environmentally friendly"
refrigerants that have thermo-physical properties considerably
different than those of R22. Among the most widely utilized of
these alternate refrigerants is the R410A refrigerant blend, which
most in the art believe exhibits performance deficiencies under
certain environmental conditions (e.g., at high ambient
temperatures) as compared to R22 refrigerant.
[0006] Thus, there is a need to develop air conditioning systems,
methods and equipment that can be utilized within the scope of
legislation and industry regulations yet that still can provide
measurable performance-related benefits when operated with an
economizer cycle.
SUMMARY OF THE INVENTION
[0007] These and other needs are met by the present invention,
which provides methods and apparatus for operating air conditioning
systems with an economizer cycle, (or so-called "vapor injection
cycle"). In particular, the present invention provides for
operating a rooftop air conditioning system or unit with an
economizer cycle under certain conditions (e.g., in certain
temperature ranges and/or using certain refrigerants) so as to
achieve performance-related benefits with regard to at least the
capacity and/or the energy efficiency ratio of the air conditioning
system as compared to an air conditioning system that is operated
utilizing a conventional (i.e., non-economized) cycle. These
benefits are especially important because they are achieved while
complying with all applicable legislative and industrial
regulations.
[0008] In accordance with an exemplary aspect of the present
invention, such benefits occur when a rooftop air conditioning unit
is operated with an economizer cycle using R410A or a similar blend
as a refrigerant (i.e., working medium), and/or wherein the rooftop
system is operated in an outdoor setting having an ambient
temperature at or above the standard ARI rating/point--for certain
equipment--of 95.degree. F.
[0009] In accordance with another exemplary aspect of the present
invention in which R410A or a similar composition blend is utilized
as the refrigerant for the rooftop air conditioning system, the
blend can be comprised of about 47% to about 53% of R32 refrigerant
and about 53% to about 47% of R125 refrigerant.
[0010] In accordance with yet another exemplary aspect of the
present invention, the refrigerant blend for the rooftop air
conditioning system can further include other additives such as
oils (e.g., polyolester oils, polyvinylether oils, mineral oils,
Alkyl Benzene oils, and combinations of one or more of these and/or
other oils) and/or lubrication enhancement additives, wherein small
amounts of the additive(s) are circulated within the air
conditioning system along with the refrigerant blend.
[0011] Still other aspects, embodiments and advantages of the
present invention are discussed in detail below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] For a fuller understanding of the nature and desired objects
of the present invention, reference is made to the following
detailed description taken in conjunction with the accompanying
figures, wherein like reference characters denote corresponding
parts throughout the views, and in which:
[0013] FIG. 1 is a schematic view of an economizer cycle for an air
conditioning system;
[0014] FIG. 2 is a schematic view of an alternative economizer
cycle for an air conditioning system;
[0015] FIG. 3 is a graph depicting the absolute pressure versus
specific enthalpy (i.e., a P-h diagram) for the economizer cycles
of FIGS. 1 and 2;
[0016] FIG. 4 is a graph depicting the comparatively beneficial
results relating to capacity that were obtained when operating a
rooftop air conditioning system with an economizer cycle using an
R410A refrigerant; and
[0017] FIG. 5 is a graph depicting the comparatively beneficial
results relating to energy efficiency ratio that were obtained when
operating a rooftop air conditioning system with an economizer
cycle using an R410A refrigerant.
DETAILED DESCRIPTION
[0018] The present invention provides methods and apparatus for
operating a rooftop air conditioning system with an economizer
cycle. As noted above, those in the air conditioning field had
largely written off the possibility of operating an air
conditioning system with an economizer cycle within the confines of
legislation and industrial regulations yet so as to receive
performance-related benefits that would not be more than offset by
the added costs and complexities of running the system. However, in
accordance with the present invention it was unexpectedly
discovered that operating packaged air conditioning systems (e.g.,
rooftop air conditioning systems) with an economizer cycle under
certain operation conditions (e.g., in certain temperature ranges
and/or using certain refrigerants) results in measurable
performance-related benefits while complying with applicable
legislative and/or industrial regulations.
[0019] An exemplary economizer vapor injection cycle 100 for an air
conditioning system is depicted in FIG. 1. In accordance with the
economizer vapor injection cycle ("economizer cycle") 100, a
compressor 10 delivers high pressure refrigerant to a discharge
line 20 and then to a condenser 30. The refrigerant exits the
condenser through a liquid line and is split between a main flow
line 40 and an auxiliary flow line 50. Although the percentages of
refrigerant that are routed to the main flow line 40 and to the
auxiliary flow line 50 can vary, it is currently preferred that
between about 8% and about 12% by weight of the total refrigerant
flow be fed to the auxiliary flow line 50, wherein the balance of
the refrigerant is routed to the main flow line 40.
[0020] From the main flow line 40, refrigerant is fed through an
economizer heat exchanger 95 to a main expansion device 60, then to
an evaporator 70, and finally back to the compressor 10. From the
auxiliary flow line 50, auxiliary refrigerant flow is fed to the
economizer expansion device 90 (which reduces the pressure and
temperature of the auxiliary refrigerant as compared to the
pressure and temperature of the refrigerant in the main flow line
40) and to the economizer heat exchanger 95 in a predetermined
manner, preferably in a counter-flow configuration with respect to
the main refrigerant flow. The auxiliary refrigerant flow is then
fed back to the compressor 10 at an intermediate (i.e., between
suction and discharge) pressure. A bypass valve 80 is present to
allow a portion of partially compressed refrigerant to flow back to
compressor suction (e.g., in a conventional/non-economized mode of
operation) should there be a desire to unload the compressor.
[0021] The temperature difference between the main refrigerant and
the auxiliary refrigerant can vary, and is dependent on system
design and operating conditions; however, according to a currently
preferred embodiment of the present invention, the auxiliary
refrigerant will have a temperature of about 25.degree. F. to about
40.degree. F. less than that of the main refrigerant, wherein about
15.degree. F. to about 35.degree. F. of the extra temperature
reduction is obtained due to heat transfer interaction between the
main and auxiliary refrigerant flows in the economizer heat
exchanger 95.
[0022] Thus, the economizer cycle 100 is beneficial because it
causes a certain percentage (e.g., about 88% to about 92%) of
refrigerant to be further subcooled (e.g., by about 15.degree. F.
to about 35.degree. F.) to a temperature lower than the temperature
that would be achieved if the air conditioning system of FIG. 1
were to be operated in a conventional (i.e., non-economized) cycle.
As a result, the refrigerant will have a greater cooling potential
while reaching evaporator 70.
[0023] FIG. 2 depicts an air conditioning system that operates with
an alternate economizer cycle 100A. The FIG. 2 economizer cycle
100A is identical to the FIG. 1 cycle 100, with the exception that
the auxiliary flow in the FIG. 2 cycle is originated downstream of
the economizer heat exchanger 95, rather than upstream as it is in
the FIG. 1 cycle.
[0024] FIG. 3 is a P-h diagram for the economizer cycle 100 of FIG.
1 and the economizer cycle 100A of FIG. 2, wherein the points 1, 2,
3, 4, 5, 6, 7, 7' and 7 in the FIG. 3 diagram correspond to those
same labeled points within the economizer cycles of FIGS. 1 and
2.
[0025] Still further alternate embodiments of the economizer cycles
100, 100A of FIGS. 1 and 2 are within the scope of the present
invention, including but not limited to those described in the U.S.
Pat. No. 6,658,867 to Taras et al., the entirety of which is
incorporated by reference herein. For example, either or both of
the economizer cycles 100, 100A of FIGS. 1 and 2 can be modified to
incorporate a tandem compressor arrangement, wherein at least two
compressors 10 are arranged and operated in parallel in which one
or more of the at least two compressors can be selectively started
and stopped to provide part-load operation for the refrigerant
systems depicted in FIGS. 1 and 2. Additionally, multi-circuit
systems (i.e., systems with multiple independent circuits, as are
known in the art) can benefit from the present invention. In such
systems, multiple circuits can be operated to provide similar
part-load capability, such as in the case of the tandem
compressors, which are known in the art.
[0026] It has been unexpectedly discovered in accordance with the
present invention that utilizing either of the economizer cycles
100, 100A of FIGS. 1 and 2 or any of those described in the '867
patent to Taras et al. in certain contexts can provide highly
beneficial results with regard to air conditioning system
performance, especially with regard to the capacity and the energy
efficiency ratio (EER) of a rooftop air conditioning system. For
purposes of the present invention a "rooftop air conditioning
system" refers to a packaged air conditioning system (in contrast
to what is referred to in the art as a "split air conditioning
system") that is sited above ground, e.g., on top of a building or
structure. Also, for purposes of the present invention, an
"economizer cycle" refers to the economizer cycle 100 of FIG. 1,
the economizer cycle 100A of FIG. 2, one of the economizer cycles
depicted and/or described in the '867 patent to Taras et al., or
any other known economizer cycles.
[0027] For example, as shown in the data reflected in FIGS. 4 and
5, it was discovered through experimentation and modeling that
utilizing R410A as a refrigerant with an economizer cycle for a
rooftop air conditioning system provides certain
performance-related benefits as compared to usage of R410A in a
rooftop system employing a conventional (i.e., non-economized)
cycle. FIG. 4 depicts a graph of the relative capacity (with
respect to the R22 conventional cycle) versus ambient temperature
results of modeling and experimental validation for a rooftop air
conditioning system that was operated (a) with an economizer cycle
using R410A as a refrigerant in accordance with the present
invention (described on the graph as "R410A Economized"), and (b)
with a conventional cycle using R410A as a refrigerant (described
on the graph as "R410A Conventional"). Similarly, FIG. 5 depicts a
graph of energy efficiency ratio (EER) versus ambient temperature
results of modeling and experimental validation for a rooftop air
conditioning system that was operated (a) with an economizer cycle
using R410A as a refrigerant in accordance with the present
invention (described on the graph as "R410A Economized"), and (b)
with a conventional (i.e., non-economized) cycle using R410A as a
refrigerant (described on the graph as "R410A Conventional").
[0028] It should be noted that for the experiments reflected in
both FIGS. 4 and 5, the equipment utilized to perform the "R410A
Economized" and "R410 Conventional" testing typically was not
identical, since the conventional system would include larger heat
exchangers than the economizer system, in order to obtain
performance parity at the ARI conditions of 80.degree.
F./67.degree. F. indoor dry bulb/wet bulb temperatures and
95.degree. F. ambient temperature. Upsizing heat exchangers is a
typical measure taken by those in the art in an attempt to improve
the performance (i.e., capacity and/or energy efficiency ratio) of
an air conditioning system.
[0029] As shown in FIGS. 4 and 5, the capacity and the energy
efficiency ratio of both the conventional system and the economizer
system are substantially equal at the standard ARI rating/design
point. These results indicate the benefits of the economizer system
of the present invention, since it was able to achieve capacity and
an energy efficiency ratio values comparable to those observed with
respect to the conventional system at the standard ARI
rating/design point of 80.degree. F./67.degree. F. indoor and
95.degree. F. ambient temperatures despite typically not being
equipped with larger heat exchangers. As used herein, the phrase
"ambient temperature" refers to the outdoor temperature where a
rooftop air conditioning system is sited, wherein such temperature
can be (and typically is) effectively higher than the temperature
reading that would be registered on a thermometer, e.g., due to a
direct sunlight. Also, saturated discharge temperatures
corresponding to specific ambient temperatures could be higher than
expected due to the natural aging of the air conditioning
equipment.
[0030] The results in FIGS. 4 and 5 also indicate that the benefits
of the economizer system of the present invention become even more
pronounced (versus the conventional system) as the systems are
operated at ambient temperatures above the ARI rating/design point
of 95.degree. F. For example, the data reflected in FIG. 4
indicates that the capacity of a rooftop air conditioning system
operated with a conventional cycle using R410A as a refrigerant
begins to show a noticeable degradation (i.e., decrease) at
temperatures above 95.degree. F. despite being equipped with larger
heat exchangers. Specifically, as shown in FIG. 4, the capacity
degradation of the conventional system is already 9% (in comparison
to an R22 system not equipped with enlarged heat exchangers) at
125.degree. F. ambient temperature. In contrast, and as also shown
in FIG. 4, when the rooftop air conditioning system was operated in
accordance with the present invention with an economizer cycle
using the same R410A blend as the refrigerant, the system exhibited
a much less precipitous capacity degradation, e.g., only 5% at
125.degree. F. ambient temperature.
[0031] Similarly beneficial results with respect to the energy
efficiency ratio (EER) are demonstrated with reference to FIG.
5--that is, there was a measurable benefit achieved though use of
refrigerant blends such as R410A with an economizer cycle for a
rooftop air conditioning system above 95.degree. F. in accordance
with the present invention. Specifically, a rooftop air
conditioning system operated with a conventional cycle using R410A
as a refrigerant exhibits an energy efficiency ratio degradation
(i.e., decrease) of 12% (once again, in comparison to an R22 system
not equipped with enlarged heat exchangers) at 125.degree. F.
ambient outdoor temperature, despite of being equipped with larger
heat exchangers, whereas a rooftop air conditioning system exhibits
only a 5% energy efficiency ratio degradation at 125.degree. F.
outdoor ambient temperature when operated with an economizer cycle
and utilizing R410A as the refrigerant in accordance with the
present invention.
[0032] The comparative capacity and energy efficiency benefits
shown in FIGS. 4 and 5 for the present invention are particularly
significant because they occurred for ambient temperatures at and
especially above 95.degree., which are routinely encountered at the
top of a structure or building (e.g., a roof) during the daytime in
certain hot, dry, populated climates (e.g., Nevada, Arizona, The
Middle East), and which is where such benefits are most needed
because an air conditioning systems are relied upon at such high
temperatures to deliver as much cooling as possible.
[0033] Moreover, the fact that these beneficial results occurred
with respect to a rooftop air conditioning system is also very
important. In standard (i.e., "split" or residential) air
conditioning systems, certain portions of the system (e.g., the
condensing unit) are typically installed on the side of a
structure, not atop the structure as they are for a rooftop system.
Thus, rooftop air conditioning systems are exposed to significant
additional heat loads not present in other (e.g., "split" or
residential) air conditioning applications because the hot ambient
air that blows over the evaporator and condenser coils is
additionally preheated by hot rooftop surfaces exposed to direct
sunlight, which also acts to provide extra radiant heat load by
directly or indirectly (e.g., through conduction and convection)
heating various components of the refrigerant system. Further, due
to the location and conditions under which they are operated,
rooftop air conditioning systems are vulnerable to edging and/or
infrequent maintenance, both of which can cause the effective
operation temperature of the system to be higher than usual.
[0034] Thus, it is very significant that air conditioning systems
of the present invention can be operated with an economizer cycle
under the demanding conditions of rooftop air conditioning systems
and with environmentally friendly refrigerant blends such as R410A
yet still exhibit comparatively less capacity and energy efficiency
degradation than air conditioning systems that are operated with a
conventional cycle and that are equipped with a larger heat
exchanger.
[0035] In summary, significant capacity benefits (e.g., a lower
capacity degradation) and energy efficiency benefits (e.g., a lower
energy efficiency ratio degradation) are achieved when a rooftop
air conditioning system is operated with an economizer cycle using
R410A refrigerant as compared to the same system being operated
with a conventional cycle and/or for standard (i.e., "split" or
residential) air conditioning applications. Moreover, these
benefits are especially pronounced when the system is operated
under conditions wherein the ambient outdoor temperature is above
95.degree. F., in the range of about 95.degree. F. to 125.degree.
F., or above 125.degree. F., and when extrapolated over the usable
lifetime of the rooftop air conditioning system.
[0036] It should be noted that although R410A is generally a blend
of 50% by weight of R32 refrigerant and 50% by weight of R125
refrigerant, any references to "R410A" herein should be interpreted
to refer to a blend of between about 47% and about 53% (both
inclusive) by weight of R32 and between about 53% and about 47%
(both inclusive) by weight percentage of R125. Moreover, these
ranges can be adjusted in accordance with the present invention,
and/or some amounts of other refrigerants (e.g., R134a) can be
added to the blend. In an embodiment wherein RI 34a is added, it is
currently preferred to add no more than 5% by weight thereof.
[0037] Further, one or more additives can be included in the
R410A-like refrigerant blend in accordance with the present
invention. Exemplary such additives include, but are not limited to
oils (e.g., polyolester (POE) oils polyvinylether (PVE) oils, Alkyl
Benzene oils, mineral oils, or a mixture or combination of one or
more of these oils, wherein the viscosity grades of such oils can
vary but are generally in the range of about 20 to about 70
centistokes and when the oil viscosity is measured without the
refrigerant at temperature of 100 F.) and/or one or more
lubrication enhancement additives known in the art. The additives
can be added to the refrigerant blend as is generally known in the
art, e.g., by being circulated within the air conditioning system
along with the refrigerant.
[0038] Although the present invention has been described herein
with reference to details of currently preferred embodiments, it is
not intended that such details be regarded as limiting the scope of
the invention, except as and to the extent that they are included
in the following claims--that is, the foregoing description of the
present invention is merely illustrative, and it should be
understood that variations and modifications can be effected
without departing from the scope or spirit of the invention as set
forth in the following claims. Moreover, any document(s) mentioned
herein are incorporated by reference in their entirety, as are any
other documents that are referenced within the document(s)
mentioned herein.
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