U.S. patent application number 10/891938 was filed with the patent office on 2006-01-19 for refrigerant system with tandem compressors and reheat function.
Invention is credited to Alexander Lifson, Michael F. Taras.
Application Number | 20060010907 10/891938 |
Document ID | / |
Family ID | 35597987 |
Filed Date | 2006-01-19 |
United States Patent
Application |
20060010907 |
Kind Code |
A1 |
Taras; Michael F. ; et
al. |
January 19, 2006 |
Refrigerant system with tandem compressors and reheat function
Abstract
A refrigerant system incorporates at least two compressors that
act in tandem to provide variable control over the refrigerant
system performance. The tandem compressors can be of conventional
or economized type and are configured for maximum performance
utilization. Further, a reheat circuit can be incorporated into the
refrigerant system at several different locations. The reheat cycle
provides additional control over sensible and latent capacity of
the refrigerant system, and is particularly advantageous when
utilized in combination with the tandem compressors. As a result,
multiple steps of unloading can be implemented in all operation
regimes, the external load demands are satisfied with much greater
precision, eliminating undesirable variations in temperature and
humidity, system efficiency and reliability are augmented and
equipment life-cycle cost is reduced.
Inventors: |
Taras; Michael F.;
(Fayetteville, NY) ; Lifson; Alexander; (Manlius,
NY) |
Correspondence
Address: |
CARLSON, GASKEY & OLDS, P.C.
400 WEST MAPLE ROAD
SUITE 350
BIRMINGHAM
MI
48009
US
|
Family ID: |
35597987 |
Appl. No.: |
10/891938 |
Filed: |
July 15, 2004 |
Current U.S.
Class: |
62/513 ;
62/510 |
Current CPC
Class: |
F25B 2400/075 20130101;
F25B 2400/13 20130101; F25B 41/20 20210101; F24F 3/153
20130101 |
Class at
Publication: |
062/513 ;
062/510 |
International
Class: |
F25B 29/00 20060101
F25B029/00; F25B 1/10 20060101 F25B001/10; F25B 41/00 20060101
F25B041/00 |
Claims
1. A refrigerant system comprising: an inlet manifold providing a
supply of refrigerant to at least two compressors, and a discharge
manifold receiving compressed refrigerant from said at least two
compressors, said discharge manifold supplying refrigerant to a
condenser; refrigerant flowing to said condenser from said at least
two compressors, and refrigerant flowing from said condenser to a
main expansion device, refrigerant from said main expansion device
flowing to an evaporator, and refrigerant from said evaporator
returning to said inlet manifold; an air moving device for moving
air to an environment to be conditioned over said evaporator; and a
reheat coil communicating to a refrigerant line in said system,
said reheat coil being positioned in a path of at least a portion
of air having passed over said evaporator.
2. The refrigerant system as set forth in claim 1, wherein said
reheat coil communicating to the refrigerant line at a position
between said discharge manifold and said condenser.
3. The refrigerant system as set forth in claim 2, wherein an inlet
to said reheat coil includes a selectively opened valve for
controlling flow of refrigerant to said reheat coil.
4. The refrigerant system as set forth in claim 2, wherein said
reheat coil returns the refrigerant to a location upstream of said
condenser.
5. The refrigerant system as set forth in claim 3, wherein an
outlet of said reheat coil is positioned downstream of said
condenser and downstream of said valve, but upstream of said main
expansion device.
6. The refrigerant system as set forth in claim 1, wherein said
refrigerant system further includes an economizer circuit, said
economizer circuit receiving a tapped flow of refrigerant from a
location downstream of said condenser, and passing said tapped flow
of refrigerant through an economizer expansion device, said tapped
flow of refrigerant and a main flow of refrigerant passing through
an economizer heat exchanger.
7. The refrigerant system as set forth in claim 1, wherein a bypass
line selectively bypasses said condenser, and a control bypassing
fluid around said condenser if humidification control is desired
with less temperature control.
8. The refrigerant system as set forth in claim 6, wherein said
economizer circuit is upstream of said position at which said
reheat coil communicates with said refrigerant line but downstream
of said condenser.
9. The refrigerant system as set forth in claim 6, wherein said
economizer circuit is downstream of said position at which said
reheat coil communicates with said refrigerant line.
10. The refrigerant system as set forth in claim 6, wherein said
economizer circuit is in parallel arrangement with said reheat
coil.
12. The refrigerant system as set forth in claim 6, wherein at
least one said compressor has an intermediate injection port.
13. The refrigerant system as set forth in claim 1, wherein an
unloader allows selective unloading of at least one of said at
least two compressors.
14. A method of operating a refrigerant system comprising the steps
of: (1) providing an inlet manifold to supply refrigerant to at
least two compressors and a discharge manifold receiving compressed
refrigerant from said at least two compressors, said discharge
manifold supplying refrigerant to a condenser, providing an
expansion device downstream of the condenser, an evaporator
downstream of the expansion device, and a reheat coil for
selectively receiving refrigerant, and an air moving device for
passing air into an environment to be conditioned, and over said
evaporator and said reheat coil; and (2) selectively operating one
or both of said at least two compressors to achieve a desired
cooling capacity, and selectively communicating refrigerant into
said reheat coil to provide a desired temperature to said air
passing into said environment to be conditioned.
15. The method as set forth in claim 14, wherein said reheat coil
is communicated into a refrigerant line at a position between said
discharge manifold and said condenser.
16. The method as set forth in claim 15, wherein said reheat coil
returns refrigerant to a location upstream of said condenser.
17. The method as set forth in claim 14, wherein an outlet of said
reheat coil is positioned downstream of said condenser, but
upstream of said main expansion device.
18. The method as set forth in claim 14, further providing an
economizer circuit, said economizer circuit receiving a tapped flow
of refrigerant from a location downstream of said condenser, and
including the steps of selectively passing said tapped flow of
refrigerant through an economizer expansion device, and passing a
main flow of refrigerant through an economizer heat exchanger along
with selectively passing said tapped flow of refrigerant through
said economizer heat exchanger.
19. The method as set forth in claim 18, wherein said tapped flow
of refrigerant is returned to at least one of said at least two
compressors at an intermediate compression point.
20. The method as set forth in claim 18, wherein said economizer
circuit is positioned to be upstream of a position at which said
reheat coil communicates with said refrigerant line, and downstream
of said condenser.
21. The method as set forth in claim 18, wherein said economizer
circuit is positioned to be downstream of said position at which
said reheat coil communicates with said refrigerant line.
22. The method as set forth in claim 18, wherein said economizer
circuit is positioned to be in a parallel arrangement with said
reheat coil.
23. The method as set forth in claim 14, wherein at least one of
said at least two compressors is provided with an unloader, and
said unloader is controlled to provide variable system performance.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to refrigerant cycles incorporating a
reheat coil, and wherein a tandem compressor arrangement is
utilized. The resulting cycles provide an enhanced control over
both humidity and temperature in the conditioned space as well as
improve efficiency, reliability and life-cycle cost of the
equipment.
[0002] Refrigerant cycles are utilized to change the temperature
and humidity, or otherwise control the environment, in the
conditioned space. In particular, a refrigerant cycle will
typically include a compressor delivering a compressed refrigerant
to a condenser, and from the condenser to an expansion device. The
refrigerant exchanges heat with an outdoor environment at the
condenser, and is expanded in the expansion device to a lower
pressure and temperature. From the expansion device, the
refrigerant continues to an evaporator at which it exchanges heat
with an indoor environment, or an environment to be conditioned.
From the evaporator, the refrigerant returns to the compressor.
[0003] The amount of cooling that can be supplied by a refrigerant
cycle is known as its "capacity." There are numerous ways to
provide control over the capacity for a refrigerant cycle. One way
is to substitute multiple compressors acting in tandem for a single
compressor. In such an arrangement, the compressors can be
selectively operated or shut down in response to an external heat
load demand. Also, tandem compressors of different sizes can be
utilized such that the various steps in the total capacity can be
achieved. Moreover, both economized and conventional compressors
can be employed in the tandem configuration, allowing for switching
between various compressor modes of operation and further
increasing a number of the unloading steps. Lastly, the tandem
compressor configuration can be selectively chosen for any of the
independent circuits of a multi-circuit system.
[0004] Another way of controlling an environment in the conditioned
space with a refrigerant cycle is the incorporation of a reheat
coil. Typically, a reheat coil is provided in the path of air that
has been blown over the evaporator. The air passes over the reheat
coil to regain heat from a refrigerant that is at a temperature
hotter than the temperature of air leaving the evaporator. The
reheat coil is thus able to raise the temperature of the air
leaving the evaporator. Hence, the air dehumidified and overcooled
in the evaporator is reheated back to a comfortable temperature
level in the reheat coil. In other words, in the system with the
reheat coil, the humidity in the conditioned space is mainly
controlled by the evaporator and its temperature--by the reheat
coil.
[0005] The reheat coil has not been utilized in a combination with
tandem compressors, however. Thus, the refrigerant cycles with
tandem compressors have not had as complete control over
temperature and humidity levels as may be desired. It has to be
noted that this invention is not related to any particular reheat
concept or tandem compressor configuration, but rather provides
advantages, that could not be obtained before for a refrigerant
system, by integrating both design features in a single cycle.
Consequently, a system with any reheat schematic or tandem
compressor configuration can take advantages from the
invention.
SUMMARY OF THE INVENTION
[0006] In disclosed embodiments of this invention, a refrigerant
system incorporates tandem compressors. At least two compressors
each separately compress a refrigerant and deliver it into the
refrigerant cycle. A reheat coil is also incorporated into the
refrigerant system, and receives air having passed over the
evaporator to reheat the air to a desired temperature when
required. In one embodiment, the reheat coil is positioned in the
refrigerant cycle to receive a hot gas. Other embodiments may
position the reheat coil such that it utilizes a two-phase mixture
of refrigerant, or a liquid refrigerant. Also, some embodiments
allow the condenser to be bypassed by at least a portion of
refrigerant flow, when desired. Further, the reheat cycle may be
incorporated in a system utilizing either economized or
conventional tandem compressors, or a combination of both, in other
embodiments. Also, in one embodiment, at least one compressor may
be unloaded to provide even greater capacity control.
[0007] 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
[0008] FIG. 1 shows a first embodiment of the present
invention.
[0009] FIG. 2 shows a second embodiment of the present
invention.
[0010] FIG. 3 shows a third embodiment of the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0011] FIG. 1 shows a refrigerant system 20 incorporating a pair of
conventional tandem compressors 22 and 24 for compressing a
refrigerant and passing the refrigerant downstream to a discharge
manifold 30, and then to condenser 36. The compressors 22 and 24
may or may not have oil equalization line 12 and pressure
equalization line 13 connecting the two compressors for the purpose
of potentially improving the oil management in the connected
compressors. Furthermore, compressors 22 and 24 can be of different
sizes and may have shutoff or check valves 32 located on the
compressor discharge line to enhance system performance upon
shutdown of one of the compressors.
[0012] A three-way valve 34 selectively communicates at least a
portion of the refrigerant to a reheat coil 44. The valve 34 can be
of a fixed orifice design, a regulating device, or can be
substituted by a pair of solenoid valves. The refrigerant passes to
a line 39 downstream of the reheat coil 44 through the check valve
46, and rejoins the main refrigerant circuit at point 41. Point 41
is upstream of condenser 36. A main expansion device 38, and an
evaporator 40 are downstream of condenser 36. Thus, refrigerant
flows from the main expansion device 38 to the evaporator 40, and
then is returned to a suction manifold 26, communicating through
lines 28 to the suction port of each compressor 22 and 24.
[0013] As is known, an indoor airflow 45 is driven over the
evaporator 40. As the air is cooled, the moisture content in the
air stream is typically reduced, and, thus, the air supplied to the
conditioned space has been dehumidified. If the temperature of air
leaving the evaporator is lower than desired for the conditioned
space, reheat coil 44 is utilized to reheat the air stream 45 to a
required temperature level. As shown, air moving device 42 drives
air stream 45.
[0014] A control 19 for the refrigerant system 20 can operate the
system to achieve various goals. In particular, one or both of the
compressors 22 and 24 can be operated by controlling motors and
closing shut-off valves 32. Thus, the total amount of refrigerant
being compressed and circulated throughout the refrigerant system
can be controlled to achieve different capacity levels. Moreover,
the three-way valve 34 may be controlled to direct at least a
portion of refrigerant into the reheat coil 44. Under many
conditions it is not necessary to circulate refrigerant through the
reheat coil. However, when it is desirable to achieve
dehumidification to the extent that the air stream 45 would
otherwise be cooled below the desired temperature, then circulating
at least some refrigerant through the reheat coil 44 will allow the
temperature of the air stream 45 to be raised to a comfortable
level, while the moisture content had been reduced in the
evaporator 40. Thus, system sensible and latent capacity can be
controlled in both cooling and dehumidification modes of operation
to a much greater extent by selectively operating tandem
compressors 22 and 24.
[0015] As known, each of the tandem compressors 22 and 24 may be
provided with a means of unloading, where part of the compressed
refrigerant is by-passed back to the compressor suction (internal
or external of compressor) and allow for additional steps in
capacity control. This is particularly true when the capacities of
the two compressors are selected to be different. Control 19 can
close either shut-off valve 32 or leave both valves open (in
conjunction to controlling the respective compressor motor
shutdowns) to achieve several capacity steps. Further, at each
capacity step, there is greater humidification control by
selectively opening valve 34, utilizing the reheat coil 44.
[0016] Also, more than two compressors can be configured into a
tandem arrangement offering multiple steps of unloading and control
over various system operation parameters.
[0017] FIG. 2 shows another embodiment 50. There are tandem
economized compressors 22 and 24 delivering refrigerant to a
discharge manifold 30. Downstream of this manifold is a condenser
36, a main expansion device 38, and an evaporator 40. An air moving
device 42 blows air over evaporator 40. Refrigerant is returned to
a suction manifold 26, and through lines 28 back to the individual
suction ports of compressors 22 and 24. Compressors 22 and 24 also
have intermediate pressure, or economizer, ports communicating
through lines 61 and economizer manifold 57 to the refrigerant
system. Economizer lines 61 may incorporate shutoff valves 59 in
order to switch between economizer and conventional modes of
operation for each individual compressor. Bypass valves 51 allow
the compressors to be unloaded, such that either or both of the
compressors can be operated at a reduced capacity.
[0018] An economizer loop is incorporated in the refrigerant system
50 downstream of the condenser 36. In the economizer cycle, an
economizer heat exchanger 52 receives a tapped refrigerant flow 54,
and a main refrigerant flow 55. As can be seen, the tapped
refrigerant flow in this embodiment is tapped from the main
refrigerant flow 55 downstream of condenser 36. The tapped
refrigerant passes through an economizer expansion device 56. After
having passed through the economizer expansion device 56, the
tapped refrigerant is at a lower pressure and temperature, and is
able to cool the main refrigerant flow 55 in the economizer heat
exchanger 52. In a preferred embodiment, the flow of the tapped
refrigerant through the economizer heat exchanger 52 is preferably
in the reverse direction to that illustrated (that is in the
opposed direction to the flow 55). However, the flows are
illustrated in the same direction to simplify the drawing.
[0019] The tapped refrigerant is typically returned as a vapor to
be injected into the compressors 22 and 24 through the economizer
manifold 57 communicating with separate economizer return lines 61,
each having a shut off valve 59.
[0020] In this embodiment, the control 19 has the ability to open
the valves 59 and adjust expansion device 56 to control the
economizer loop. This control strategy is employed in combination
with the abovementioned control methodology for operating the
valves 32 to utilize either or both of the compressors. In
addition, the bypass or unloader valves 51 provide further ability
to reduce the refrigerant flow into the cycle. A worker of ordinary
skill in the art would recognize the times when a controller would
like to utilize each of these options. Valves 32, 51 and 59 may be
either shutoff valves or regulating flow control devices, allowing
for more flexibility in the refrigerant flow control.
[0021] The economizer loop may or may not be engaged. To turn off
the economizer loop, the economizer expansion device 56 may be
closed down such that no refrigerant is tapped. Furthermore, to
disengage an economizer cycle for each individual compressor, a
respective valve 59 needs to be closed. Similarly, to turn off the
reheat coil 60, which is now positioned downstream of the condenser
36 and utilizes a two-phase mixture or liquid refrigerant for the
reheat purpose, the three-way valve 58 may be moved to such a
position that no refrigerant is tapped through the reheat coil 38.
It has to be noted, that the illustrated position of the reheat
coil 60 and the economizer heat exchanger 52 is not critical to
take advantage of the invention benefits, and various possible
arrangements become obvious to a person ordinarily skilled in the
art.
[0022] Further, as is shown, a bypass line 64 with a valve 65
selectively bypasses refrigerant around the condenser 36. The valve
65 preferably allows a metering of flow around the condenser 36.
Now, when the system is utilized under conditions such that
humidity control is desirable, but no significant temperature
change is necessary, a significant portion of the refrigerant may
be bypassed through line 64, through valve 65, and around the
condenser 36. This refrigerant is not cooled in the condenser 36,
and when mixed with the refrigerant passing through the condenser
has more heating capacity to be realized in the reheat coil 60,
reheating refrigerant overcooled in the evaporator 40. On the other
hand, if greater temperature reduction is desired, then more or
most of the refrigerant passes through the condenser 36, and the
system operates as in a standard cooling and dehumidification
cycle, utilizing liquid refrigerant in the reheat coil 60. Thus,
any of these reheat loop controls may be employed independent of
each other, in combination with the economizer loop controls and
tandem compressor control strategy, or none of them need be used.
The present invention is mainly directed to providing the ability
to use all techniques in combination with each other, while
providing better control over the humidity and temperature, while
enhancing system efficiency by matching latent and sensible load
demands more closely and improving component reliability by
reducing a number of start-stop cycles. Also, it has to be
understood that the three-way valve 58 can be substituted by a pair
of conventional valves. If the expansion device 56 is of such a
type that it cannot be closed down completely, an additional
shutoff valve may be placed on the tap line 54.
[0023] When relatively low humidity and temperature levels are
desired in the air stream 45, or the capability to provide a
significant amount of sensible and latent capacity is required,
both economizer expansion device 56 and the three-way valve 58 are
moved to an open position to operate both the economizer heat
exchanger 56 and the reheat coil 60 and both tandem compressors 22
and 24 are controlled to provide maximum refrigerant flow with
valves 32 and 59 in open positions and valves 51 closed.
Refrigerant passing through the main line 55 will be subcooled by
the refrigerant from the tap 54. Thus, that refrigerant will have a
higher cooling capacity (both sensible and latent) when reaching
the evaporator 40. Consequently an air stream 45 leaving evaporator
40 can be cooled to a lower temperature. At this lower temperature,
more moisture can be removed from the air. Then, refrigerant in the
refrigerant cycle 50 passes through the reheat coil 60, where its
temperature is reduced further during the heat transfer interaction
with the indoor air stream 46 leaving the evaporator 40. As a
result, the refrigerant cooling capacity is boosted even further,
allowing for even more dehumidification in the evaporator 40. This
drier air then passes over the reheat coil 60, which will have a
higher temperature refrigerant, as it is positioned upstream of the
main expansion device 38. An air moving device 42, shown
schematically, drives air over the evaporator 40 and reheat coil
60. This hotter refrigerant in the reheat coil will reheat the air
stream 45 such that the desired temperature is reached. Moisture
has already been removed from this air stream in the evaporator 40.
Thus, by utilizing the combination of the economizer cycle, tandem
compressor configuration and the reheat coil, a refrigerant system
designer is able to achieve both desired temperature and humidity
levels, especially in hot and humid environments. Moreover, the
higher efficiency levels are achieved due to implementation of the
economizer cycle concept. Obviously, other external load demand
scenarios can be considered along with corresponding control
strategies for the refrigerant cycle 50. These scenarios are well
known to a person ordinarily skilled in the art.
[0024] Furthermore, this invention offers additional steps of
unloading. Turning a tapped refrigerant flow in the economizer heat
exchanger 26 on and off, the system capacity can be correspondingly
increased or decreased, depending on the external load
requirements. Also, one or both compressors 22 and 24 can be
operated in the conventional, economized or unloaded modes. Again,
this provides several distinct capacity control steps. This will
allow matching the desired temperature and humidity levels with a
greater precision as well as improve system reliability through the
reduction of the start-stop cycles. Also it has to be understood
that various configurations of this embodiment are possible
including (but not limited to) more than two compressors, and more
than one economizer heat exchanger.
[0025] FIG. 3 shows yet another embodiment 70. In embodiment 70,
the reheat coil 74 communicates with the main cycle refrigerant by
means of a three-way valve 72 downstream of the economizer heat
exchanger 52. Thus, there would be a warm liquid refrigerant
circulated through the reheat coil. Further, the compressors 22 and
24 are provided with a bypass line through valve 51 on only one of
the two compressors (here compressor 24). Further, the economizer
fluid is returned through line 28 to only one of the two
compressors (here compressor 24 as well). While this embodiment
does not provide the extreme number of steps of control provided by
FIG. 2 embodiment, it does provide additional control when compared
to a system that does not have tandem compressors, an economizer
cycle or a reheat coil. The two tandem compressors 24 and 22 can
still be operated independently, or in combination. The economizer
cycle would only be utilized in combination with operation of
compressor 24. Any number of economized and conventional
compressors can be employed in this embodiment and will function
and communicated to the refrigerant system 70 in the manner
described above.
[0026] It should be understood that a refrigerant cycle designer
would be able to identify many different options that would flow
from the several embodiments in this invention. Additionally, an
equivalent approach can be applied to each independent circuit of a
multi-circuit system to obtain similar benefits.
[0027] Thus, the invention presents a significantly enhanced
control over temperature and humidity precisely satisfying latent
and sensible capacity demands, while reaching superior efficiency
and reliability levels and reducing life-cycle cost of
equipment.
[0028] Although a preferred embodiment of this invention has 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.
* * * * *