U.S. patent application number 12/672904 was filed with the patent office on 2011-09-08 for tandem compressor of different types.
Invention is credited to Alexander Lifson, Michael F. Taras.
Application Number | 20110214439 12/672904 |
Document ID | / |
Family ID | 40549442 |
Filed Date | 2011-09-08 |
United States Patent
Application |
20110214439 |
Kind Code |
A1 |
Lifson; Alexander ; et
al. |
September 8, 2011 |
TANDEM COMPRESSOR OF DIFFERENT TYPES
Abstract
A refrigerant system having tandem compressors includes at least
two compressors of different types. By utilizing the two distinct
compressor types, a greater difference in the provided capacity of
the two compressors can be achieved at part-load conditions, as
well as a particular compressor type can be engaged at specific
environmental conditions to provide the most efficient operation of
the refrigerant system.
Inventors: |
Lifson; Alexander; (Manlius,
NY) ; Taras; Michael F.; (Fayetteville, NY) |
Family ID: |
40549442 |
Appl. No.: |
12/672904 |
Filed: |
October 10, 2007 |
PCT Filed: |
October 10, 2007 |
PCT NO: |
PCT/US07/80871 |
371 Date: |
February 10, 2010 |
Current U.S.
Class: |
62/115 ; 62/500;
62/510 |
Current CPC
Class: |
F25B 2400/0751 20130101;
F25B 49/022 20130101; F25B 1/04 20130101; F25B 2400/13
20130101 |
Class at
Publication: |
62/115 ; 62/510;
62/500 |
International
Class: |
F25B 1/10 20060101
F25B001/10; F25B 1/06 20060101 F25B001/06; F25B 1/00 20060101
F25B001/00 |
Claims
1. A refrigerant system comprising: a tandem compressor unit
including at least two compressors receiving refrigerant from the
refrigerant system, compressing the refrigerant and delivering the
refrigerant into the refrigerant system; a heat rejection heat
exchanger positioned downstream of said tandem compressor unit, an
expansion device positioned downstream of said heat rejection heat
exchanger, and an evaporator positioned downstream of said
expansion device, refrigerant passing from said tandem compressor
unit to said heat rejection heat exchanger, through said expansion
device to said evaporator, and back to said tandem compressor unit;
and said at least two compressors of said tandem compressor unit
being of distinct types.
2. The refrigerant system as set forth in claim 1, wherein said at
least two compressors of said tandem compressor unit have a common
suction manifold and a common discharge manifold.
3. The refrigerant system as set forth in claim 1, wherein said at
least two compressors of said tandem compressor unit have at least
one of a common suction manifold and a common discharge
manifold.
4. The refrigerant system as set forth in claim 1, wherein said at
least two compressors of said tandem compressor unit are of
different sizes.
5. The refrigerant system as set forth in claim 1, wherein an
economizer cycle is incorporated into the refrigerant system.
6. The refrigerant system as set forth in claim 5, wherein said
economizer cycle returns a tapped refrigerant to an intermediate
compression point in at least one of said at least two compressors
of said tandem compressor unit.
7. The refrigerant system as set forth in claim 6, wherein said
economizer circuit returns refrigerant to an intermediate
compression point only in some of said at least two compressors of
said tandem compressor unit.
8. The refrigerant system as set forth in claim 7, wherein said
some of said at least two compressors have a common intermediate
pressure manifold.
9. The refrigerant system as set forth in claim 5, wherein said at
least two compressors of said tandem compressor unit have a common
suction manifold and a common discharge manifold.
10. The refrigerant system as set forth in claim 5, wherein said at
least two compressors of said tandem compressor unit have at least
one of a common suction manifold and a common discharge
manifold.
11. The refrigerant system as set forth in claim 5, wherein said at
least two tandem compressors of said tandem compressor unit are of
different sizes.
12. The refrigerant system as set forth in claim 1, wherein a
bypass function is included into the refrigerant system.
13. The refrigerant system as set forth in claim 1, wherein at
least one of said two compressors of said tandem compressor unit is
a scroll compressor.
14. The refrigerant system as set forth in claim 1, wherein at
least one of said at least two compressors of said tandem
compressor unit is a screw compressor.
15. The refrigerant system as set forth in claim 1, wherein at
least one of said at least two compressors of said tandem
compressor unit is a rotary compressor.
16. The refrigerant system as set forth in claim 1, wherein at
least one of said at least two compressors of said tandem
compressor unit is a reciprocating compressor.
17. The refrigerant system as set forth in claim 1, wherein said at
least two compressors of distinct types being utilized for
selective unloading of the refrigerant system.
18. The refrigerant system as set forth in claim 1, wherein said at
least two compressors of distinct types being utilized for the
refrigerant system efficiency boost by selectively engaging a
certain compressor at certain environmental conditions.
19. The refrigerant system as set forth in claim 1, wherein a tap
selectively taps refrigerant upstream of said expansion device,
expands that tapped refrigerant to an intermediate pressure, and
returns it to an intermediate compression point in at least one of
said at least two compressors of said tandem compressor unit.
20. A method of operating a refrigerant system comprising the steps
of: providing a tandem compressor unit that includes at least two
compressors receiving refrigerant from the refrigerant system,
compressing the refrigerant and delivering the refrigerant into the
refrigerant system; positioning a heat rejection heat exchanger
downstream of said tandem compressor unit, positioning an expansion
device downstream of said heat rejection heat exchanger, and
positioning an evaporator downstream of said expansion device,
refrigerant passing from said tandem compressor unit to said heat
rejection heat exchanger, through said expansion device to said
evaporator, and back to said tandem compressor unit; and said at
least two compressors of said tandem compressor unit being of
distinct types.
21. The method as set forth in claim 20, wherein said at least two
compressors of distinct types being utilized for selective
unloading of the refrigerant system.
22. The method as set forth in claim 20, wherein said at least two
compressors of distinct types being utilized for the refrigerant
system efficiency boost by selectively engaging a certain
compressor at certain environmental conditions.
Description
BACKGROUND OF THE INVENTION
[0001] This application relates to refrigerant systems having
tandem compressors, wherein the compressors are of distinct
types.
[0002] Heating, ventilation, air conditioning and refrigeration
(HVAC&R) systems are utilized to condition various
environments. The HVAC&R systems typically use a refrigerant
circulating throughout a closed-loop circuit and are applied as air
conditioners, heat pumps, refrigeration units, etc. Various
enhancement techniques and system configurations are known and
implemented to provide a required performance over a wide spectrum
of environmental conditions to satisfy diverse thermal load
demands.
[0003] In a very basic refrigerant system, a compressor compresses
a refrigerant and delivers it downstream to a heat rejection heat
exchanger (a condenser in subcritical applications and a gas cooler
in transcritical applications). Refrigerant passes from the
condenser to an expansion device, and from the expansion device to
an evaporator. From the evaporator, refrigerant returns to the
compressor. This basic system is typically supplemented and
enhanced by a number of different options and features to satisfy
application requirements.
[0004] One such enhancement is the use of tandem compressors.
Tandem compressor configurations include a plurality of compressors
each receiving refrigerant from the refrigerant system, each
separately compressing the refrigerant and delivering the
refrigerant back to the refrigerant system. Tandem compressors have
at least one common manifold such, as for instance, a suction
manifold or a discharge manifold. Tandem compressors equipped with
the vapor injection function may also have a common intermediate
pressure manifold. Each of these compressors may be independently
turned on or off to vary refrigerant system capacity. In this
manner, the capacity provided by the compressor subsystem to the
overall refrigerant system can be tailored to the thermal load
demands in the conditioned space and environmental conditions.
Quite often, tandem compressor configurations include oil and vapor
equalization lines for functionality and reliability
enhancement.
[0005] To date, tandem compressors have always relied on the
compressors of the same type. As an example, there may be two or
more scroll compressors operating in tandem, two or more
reciprocating compressors operating in tandem, two or more screw
compressors operating in tandem, etc.
[0006] Since the compressor types were of the same design, their
sizes have tended to span a limited range of capacities. Normally,
the capacity would not differ by more than a ratio of 1:5, for
example.
[0007] For optimum capacity and pull down control, it would often
be desirable to have one of the compressors to be of a fairly large
size, and the other to be significantly smaller. This has been
difficult to achieve with the prior art tandem compressors.
SUMMARY OF THE INVENTION
[0008] In a disclosed embodiment of this invention, a tandem
compressor system incorporates at least two compressors that are of
distinct types. The compressors operate in tandem to receive a
refrigerant from a refrigerant system and to deliver the compressed
refrigerant back to the refrigerant system. Various refrigerant
system and tandem compressor subsystem enhancements may be
incorporated into this basic design.
[0009] These and other features of the present invention can be
best understood from the following specification and drawings, the
following of which is a brief description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 shows a first schematic.
[0011] FIG. 2 shows a second schematic.
[0012] FIG. 3 shows a third schematic.
[0013] FIG. 4 shows a fourth schematic.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0014] A refrigerant system 20 is illustrated in FIG. 1, and has a
relatively large compressor 22, and a smaller compressor 24
operating in tandem and receiving a refrigerant from a common
suction manifold 36 while delivering a compressed refrigerant to a
common discharge manifold 28. As shown in FIG. 1, an oil
equalization line 26 may be installed to connect oil sumps of
tandem compressors 22 and 24 to prevent oil pumpout from one of the
tandem compressors while having it accumulated within the other
tandem compressor. As known, refrigerant vapor equalization line
(not shown) may be also installed to equalize refrigerant pressure
between the tandem compressors.
[0015] The compressors 22 and 24 are of a distinct type. Any one of
the two compressors could be, for instance, a scroll compressor, a
rotary compressor, a screw compressor or a reciprocating
compressor. In particular, in disclosed embodiments, one of the
tandem compressors is a scroll compressor and the other is a rotary
compressor, or one is a scroll compressor and the other is a screw
compressor. By utilizing tandem compressors of different types,
greater differences in compressor sizes and capacity can be
achieved. Also, the overall unit cost can be substantially reduced,
as some compressor types are more cost effective to be manufactured
in certain capacity ranges (sizes) in comparison to the other
types. For example, rotary compressors are very cost effective for
manufacturing in smaller sizes, with the electrical power
consumption of the compressor motor being in the range of one to
three kilowatts. On the other hand, scroll compressors might be the
most cost effective for manufacturing in the compressor motor size
range from three to fifteen kilowatts. Therefore, it might be cost
effective to build refrigerant system where a rotary compressor is
operated at light operational loads and the scroll compressor is
operated at high operational load.
[0016] From the common discharge manifold, the refrigerant flows to
a heat rejection heat exchanger 30 and passes through an expansion
device 32 and an evaporator 34 in sequence. From the evaporator 34,
the refrigerant returns through a common suction manifold 36 to the
tandem compressors 22 and 24. As is known, dependent upon
environmental conditions and thermal load demand in a
climate-controlled space, either of the tandem compressors 22 and
24 can be shut down, or both of the compressors 22 and 24 can be
operated at the same time. In this manner, the performance of the
refrigerant system 20 can be controlled to tailor the provided
capacity to thermal load demands in the climate-controlled space.
By utilizing the distinct compressor types, a greater difference in
sizes and provided capacity between the two compressors is achieved
at part-load operating conditions. This allows the refrigerant
system 20 to be better respond to a wide range of potential thermal
loads in the climate-controlled space without cycling compressors
on and off, and consequently provide better temperature and
humidity control, enhance operational thermodynamic efficiency of
the refrigerant system 20 and improve reliability of the tandem
compressors 22 and 24. Of course, more than two compressors and
more than two compressor types can be utilized.
[0017] Also, different compressor types have a "sweet" spot at
different operating conditions. For instance, fixed volume ratio
compressors such as screw and scroll compressors provide the most
efficient full-load operation in the region of the pressure ratios
corresponding to the built-in volume ratio in accordance to the
polytropic compression process. On the other hand, reciprocating
compressors provide poor volumetric efficiency at large pressure
ratios, due to the clearance volume refrigerant re-expansion.
Therefore, even having the same size (capacity) tandem compressors
22 and 24 within the refrigerant system 20 benefits the system
operation, since different compressors could be operated at
different environmental conditions to optimize the refrigerant
system efficiency at these environmental conditions.
[0018] An economized refrigerant system 40 is illustrated in FIG.
2. Again, the tandem compressors 22 and 24 are of distinct types,
as mentioned above. The tandem compressors 22 and 24 have the
common discharge manifold 28. Downstream of the heat rejection heat
exchanger 30, a portion of refrigerant is tapped into a tap
refrigerant line 42, passed through an economizer expansion device
44, and through an economizer heat exchanger 46. In the economizer
heat exchanger 46, the refrigerant that has been tapped and
expanded to an intermediate pressure and temperature, cools
refrigerant in a liquid refrigerant line 38 passing through the
main expansion device 32, and then through the evaporator 34. While
the tapped refrigerant is shown passing through the economizer heat
exchanger 46 in the same direction as the main refrigerant flow, in
practice, it is typically desirable to arrange the two refrigerant
passes in counterflow relationship. However, for illustration
simplicity, they are shown flowing in the same direction.
Downstream of the economizer heat exchanger 46, the tapped
refrigerant passes through an economized flow return refrigerant
line 48, and then into an economized flow injection refrigerant
line 50 leading to an intermediate pressure port in the compressor
22. An optional bypass refrigerant line 52 has a shutoff valve 54
that selectively allows for a return of at least a portion of the
refrigerant from the economized flow return refrigerant line 48
back to a common suction manifold 136. Alternatively, in a
non-economized mode of operation, the shutoff valve 54 may allow
for a return of at least a portion of a partially compressed
refrigerant from an intermediate pressure port to the suction port
of the compressor 22, unloading the compressor 22. Further, the two
refrigerant flows mentioned above may be combined and delivered to
the suction port of the compressor 22.
[0019] As known, there are different configurations of economized
refrigerant systems, including (but not limited to) refrigerant
systems where the economized refrigerant flow is tapped downstream
of the economizer heat exchanger or refrigerant systems with a
flash tank (in place of the economizer heat exchanger). Further, if
there are more than two economized compressors, they may have a
common intermediate pressure manifold. As explained above, vapor
equalization lines may be provided as well. These systems are
within the scope and can equally benefit from the invention. All
the advantages of the refrigerant system 20 of the FIG. 1
embodiment outlined above are also applicable to the refrigerant
system 40 of the FIG. 2 embodiment.
[0020] FIG. 3 shows another embodiment 60, wherein a liquid line 62
passes through an expansion device 64, an evaporator 66, and back
to the compressor 24. Another liquid line 67 passes through an
expansion device 68, an evaporator 70, and back to the compressor
22. In this embodiment, the two compressors 22 and 24 of different
types are associated with their own evaporators 70 and 66 and
expansion devices 68 and 64 respectively. Therefore, the tandem
compressors of different types 22 and 24 have distinct suction
manifolds 236A and 236B but still have the common discharge
manifold 28. Once again, all the benefits of the FIG. 1 embodiment
are equally applicable to the refrigerant system 60.
[0021] FIG. 4 shows yet another embodiment 72, wherein the
refrigerant flowing to the tandem compressors 22 and 24 passes in
series through a heat rejection heat exchanger 30, a main expansion
device 74 and an evaporator 76, returning to a common suction
manifold 136.
[0022] A refrigerant tap line 79 passes through an auxiliary
expansion device 78 connecting to a refrigerant injection line 110
that leads to an intermediate pressure point in the compressor 24.
This refrigerant injection through the intermediate pressure port
in the compressor 24 can be utilized for various functions, such
as, for instance, lowering the refrigerant discharge temperature.
Further, a bypass valve 82 positioned in a refrigerant bypass line
80 can be utilized to return at least a portion of that refrigerant
to the suction ports of the compressors 22 and 24. Again, a worker
ordinarily skilled in the refrigerant art would be aware of why and
when such an operational regime would be valuable. Alternatively, a
portion of partially compressed refrigerant in the compressor 24
can be passed from the intermediate pressure port of the compressor
24 into the suction ports of the compressors 22 and 24, through the
bypass valve 82 and the bypass line 80, to unload the compressor 24
and to reduce capacity of the refrigerant system 72. Further, in
another mode of operation, the two refrigerant flows from the
refrigerant tap line 79 and from the intermediate pressure port of
the compressor 24 can be combined to be diverted to the suction
side of the compressors 22 and 24. As described above, all the
advantages of the FIG. 1 embodiment are equally applicable to the
refrigerant system 72.
[0023] It should be pointed out that many different compressor
types could be used in this invention. For example, scroll, screw,
rotary, or reciprocating compressors can be employed.
[0024] The refrigerant systems that utilize this invention can be
used in many different applications, including, but not limited to,
air conditioning systems, heat pump systems, marine container
units, refrigeration truck-trailer units, and supermarket
refrigeration systems.
[0025] Although embodiments of this invention have been disclosed,
a worker of ordinary skill in this art would recognize that certain
modifications would come within the scope of this invention. For
that reason, the following claims should be studied to determine
the true scope and content of this invention.
* * * * *