U.S. patent application number 12/307631 was filed with the patent office on 2009-11-26 for tandem compressors with pulse width modulation suction valve.
Invention is credited to Alexander Lifson, Mark A. Lifson, George M. Taras, Michael F. Taras.
Application Number | 20090288432 12/307631 |
Document ID | / |
Family ID | 39033292 |
Filed Date | 2009-11-26 |
United States Patent
Application |
20090288432 |
Kind Code |
A1 |
Lifson; Alexander ; et
al. |
November 26, 2009 |
TANDEM COMPRESSORS WITH PULSE WIDTH MODULATION SUCTION VALVE
Abstract
A refrigerant system is provided with tandem compressors. A
tandem compressor arrangement includes at least two compressors
operating in parallel and having at least one common manifold. A
control may operate the compressors either simultaneously, or in
some predetermined sequence to provide control over refrigerant
system capacity. At least one of the tandem compressors is provided
with a pulse width modulation control on a suction line. In this
manner, the amount of refrigerant, compressed by the compressor,
can be precisely controlled to exactly meet thermal load demands in
the conditioned space.
Inventors: |
Lifson; Alexander; (Manlius,
NY) ; Taras; Michael F.; (Fayetteville, NY) ;
Lifson; Mark A.; (Fairport, NY) ; Taras; George
M.; (Fayetteville, NY) |
Correspondence
Address: |
CARLSON, GASKEY & OLDS, P.C.
400 WEST MAPLE ROAD, SUITE 350
BIRMINGHAM
MI
48009
US
|
Family ID: |
39033292 |
Appl. No.: |
12/307631 |
Filed: |
August 8, 2006 |
PCT Filed: |
August 8, 2006 |
PCT NO: |
PCT/US06/30884 |
371 Date: |
January 6, 2009 |
Current U.S.
Class: |
62/115 ;
62/510 |
Current CPC
Class: |
F25B 2400/075 20130101;
F25B 5/02 20130101; F25B 6/02 20130101; F25B 2600/0251 20130101;
F25B 41/22 20210101; F25B 49/022 20130101; F25B 2400/13 20130101;
F25B 2600/2521 20130101 |
Class at
Publication: |
62/115 ;
62/510 |
International
Class: |
F25B 1/00 20060101
F25B001/00 |
Claims
1. A refrigerant system comprising: at least two compressors
operating in parallel to compress refrigerant and deliver
refrigerant downstream to at least one condenser, at least one
expansion device positioned downstream of said at least one
condenser, and at least one evaporator positioned downstream of
said at least one expansion device; and refrigerant returning from
said at least one evaporator through at least one suction line to
said at least two compressors, and a suction valve provided between
said evaporator and at least one of said at least two compressors,
said suction valve being provided with a pulse width modulation
control to control the amount of refrigerant being delivered to
said at least one of said at least two compressors.
2. The refrigerant system as set forth in claim 1, wherein at least
two of said at least two compressors have at least one common
manifold.
3. The refrigerant system as set forth in claim 2, wherein said at
least one common manifold is a suction manifold.
4. The refrigerant system as set forth in claim 2, wherein said at
least one common manifold is a discharge manifold.
5. The refrigerant system as set forth in claim 1, wherein at least
two of said at least two compressors deliver refrigerant to a
single condenser.
6. The refrigerant system as set forth in claim 1, wherein a single
expansion device receives refrigerant from at least two of said at
least two compressors.
7. The refrigerant system as set forth in claim 1, wherein a single
evaporator delivers refrigerant to a suction manifold returning
refrigerant to at least two of said at least two compressors.
8. The refrigerant system as set forth in claim 7, wherein said
suction valve is provided on said suction manifold, and thus
regulates the flow of refrigerant to at least two of said at least
two compressors.
9. The refrigerant system as set forth in claim 7, wherein said
suction valve is provided downstream of said suction manifold and
on a line delivering refrigerant to at least one of said at least
two compressors.
10. The refrigerant system as set forth in claim 1, wherein there
are at least two of said condensers separately receiving
refrigerant from said at least two compressors.
11. The refrigerant system as set forth in claim 10, wherein each
of said at least two condensers is provided with a separate
expansion device.
12. The refrigerant system as set forth in claim 1, wherein there
are at least two evaporators, and said at least two evaporators
separately returning refrigerant to said at least two
compressors.
13. The refrigerant system as set forth in claim 12, wherein at
least two expansion devices are provided and separately pass
refrigerant to said at least two evaporators.
14. The refrigerant system as set forth in claim 1, wherein at
least one of said at least two compressors is provided with a
bypass function.
15. The refrigerant system as set forth in claim 14, wherein at
least one of said at least two compressors is provided with a
bypass function and said at least one compressor is associated with
said suction valve.
16. The refrigerant system as set forth in claim 1, wherein at
least one of said at least two compressors is provided with an
economizer cycle.
17. The refrigerant system as set forth in claim 16, wherein at
least one of said at least two compressors is provided with an
economizer cycle and said at least one compressor is associated
with said suction valve.
18. The refrigerant system as set forth in claim 16, wherein more
than one of said at least two compressors is provided with an
economizer cycle and these economized compressors are sharing at
least one of the economizer branch components.
19. The refrigerant system as set forth in claim 1, wherein at
least one of said at least two compressors is a compressor bank and
said suction valve is associated with at least one compressor in
the bank.
20. The refrigerant system as set forth in claim 1, wherein at
least one of said at least two compressors is selected from a set
of a scroll compressor, a rotary compressor, a screw compressor,
and a reciprocating compressor.
21.-39. (canceled)
Description
BACKGROUND OF THE INVENTION
[0001] This application relates to a refrigerant system
incorporating tandem compressors and pulse width modulation control
on a suction line leading to at least one of the tandem
compressors.
[0002] Refrigerant HVAC&R systems typically include a
compressor delivering a compressed refrigerant from a compressor
discharge port to a condenser, and then passing the refrigerant
from the condenser to an expansion device, an evaporator, and
finally back to the compressor suction port throughout a
closed-loop circuit. The thermal load demand on the refrigerant
system may vary and generally depends on indoor and outdoor
operational environments, thermal load generation in a conditioned
space and fresh air circulation requirements. At times, there may
be a need for a higher system cooling capacity, and hence higher
flow of refrigerant circulating throughout the refrigerant system
is required. At other times, a lower cooling capacity, and
consequently lower refrigerant flow, may be adequate to maintain
the conditioned space within the comfort zone. To provide
sufficient means of refrigerant flow control, some refrigerant
systems utilize tandem compressors to provide unloading capability
by switching off one of the tandem compressors to match the system
capacity to the thermal load in the conditioned space. In such
systems, two or more compressors may simultaneously deliver a
compressed refrigerant to a downstream heat exchanger, such as a
condenser. Typically, individual discharge lines communicate with
the discharge ports of the tandem compressors. These discharge
lines are then merged into a single discharge manifold connected to
a condenser. Similarly, individual suction lines communicate with
the suction ports of the tandem compressors. These suction lines
emerge from a single suction manifold connected to a line extending
from the evaporator exit. On the other hand, tandem compressor
systems are known, wherein separate condensers are associated with
each of the compressors, while the compressors are still connected
to the same evaporator. Analogously, tandem compressor systems may
be connected to separate evaporators, while still communicating to
the same condenser. The last two configurations are typically
utilized when either condensers or evaporators are associated with
separate indoor or outdoor environments that may have different
operational characteristics.
[0003] A control for a typical tandem compressor system will
operate one, or several compressors, depending on system thermal
load. Thus, the compressors can be controlled to provide discrete
steps in system capacity. Also, as known, tandem compressor
arrangements may include pressure and oil equalization lines to
prevent oil pumpout from compressors and improve reliability.
[0004] One method of providing finer control over the capacity of a
refrigerant system is the use of pulse width modulation controls
for a refrigerant system compressor. With such a control, a suction
pulse width modulation valve is cycled at a predetermined rate
between on and off positions to prevent and then allow the flow of
refrigerant to the compressor. Since the valve is cycled between
open and closed positions, the throttling or any other losses are
practically eliminated. In this manner, the amount of refrigerant
compressed by the compressor can be finely tailored to a desired
capacity, while maintaining efficient system operation. While pulse
width modulation controls are known in refrigerant systems, they
have not been incorporated into tandem compressor systems.
SUMMARY OF THE INVENTION
[0005] In a disclosed embodiment of this invention, two or more
tandem compressors are operated in a refrigerant system. A suction
line leading to at least one of two compressors is provided with a
suction valve having a pulse width modulation control. Thus, the
provided capacity of that compressor can be finely tailored to
thermal load demands in an environment to be conditioned. In one
embodiment, only one of the compressors is provided with such a
suction valve controlled by pulse width modulation. In another
embodiment, the suction pulse width modulation valve is provided on
a manifold leading to each of the compressors.
[0006] In various embodiments, the compressors may deliver
refrigerant to separate condensers, while still connected to a
single evaporator, or may receive refrigerant from separate
evaporators, while still communicating compressed refrigerant to a
single condenser. In other embodiments, the tandem compressor
refrigerant system may be provided with an economizer cycle and/or
a bypass feature to achieve even more flexible control over
supplied capacity.
[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 schematic refrigerant system.
[0009] FIG. 2 shows a second schematic.
[0010] FIG. 3 shows a third schematic.
[0011] FIG. 4 shows a fourth schematic.
[0012] FIG. 5 shows a capacity chart for the FIG. 1 schematic.
[0013] FIG. 6 shows a fifth schematic.
[0014] FIG. 7 shows a sixth schematic.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0015] FIG. 1 shows a refrigerant system 20 having two compressors
22 and 24 operating in tandem to compress refrigerant and deliver
the refrigerant to a common discharge manifold 28. A single
condenser 30 receives refrigerant from the common discharge
manifold 28 and delivers that refrigerant to an expansion device
32. An evaporator 34 is positioned downstream of the expansion
device 32. Refrigerant from the evaporator 34 passes into a common
suction manifold 26 and back to the compressors 22 and 24. As is
well known in the art, a control 38 for the system operates to
drive one or both of the compressors 22 and 24 to provide a desired
capacity for the refrigerant system 20. The compressors 22 and 24
can be of the same size, or can be of different sizes. The control
and operation of a tandem compressor refrigerant system are, as
known in the art, and thus no further description is deemed
necessary. What is inventive is the provision of a suction valve 36
having pulse width modulation control by the control 38, or by a
dedicated controller. Thus, as known, the control 38 cycles the
valve 36 at a predetermined rate between an open (normally fully
open position) and closed position (normally either fully closed or
nearly closed position) to control the flow of refrigerant to the
compressors 22 and 24. In this manner, the amount of refrigerant
delivered to the compressors 22 and 24 can be finely tailored to
achieve precise capacity values, no matter how many compressors are
operated at a particular moment of time. Since the pulse width
modulation valve 36 is cycled from an open to closed position,
there are minimal throttling or other losses that are associated
with the valve 36. The cycling rate and time interval for the valve
36 to stay in an open position are determined by the capacity to be
delivered to a conditioned environment, reliability requirements,
allowable comfort zone parameter variations and refrigerant system
thermal inertia. While two tandem compressors are shown,
refrigerant systems are known with three, four or even higher
number of tandem compressors. The present invention thus provides a
very powerful and efficient means of achieving a precisely tailored
refrigerant system capacity from a tandem compressor configuration,
while minimizing temperature and humidity variation in the
conditioned space, improving occupant's comfort and reducing power
consumption.
[0016] FIG. 2 shows another embodiment 220, wherein the tandem
compressors 122 and 124 again deliver refrigerant to a common
discharge manifold 28 and a downstream condenser 30. This system
configuration is distinct in that the refrigerant branches to two
separate expansion devices 132, and two separate evaporators 134A
and 134B. Such an arrangement is typically provided when the
evaporators are serving different conditioned/refrigerated zones
and having different operational characteristics. Thus, there is no
common suction manifold delivering refrigerant to each of the
compressors 122 and 124. In this embodiment, only one of the
compressors, the compressor 122, has a suction pulse width
modulated valve 136, mounted on its suction line leading to that
compressor, which is controlled by a pulse width modulation control
138. As above, the control 138 can be a separate control or
integrated into a system control for the refrigerant system 220.
Again, when fine tailoring of the capacity delivered by the
refrigerant system 220, and the evaporator 134A in particular, is
desired, the compressor 122 would be operated, as it is able to
provide precise refrigerant flow control by its associated pulse
width modulation suction valve 136. Once again, although only two
tandem compressors are show in FIG. 2, with only one of them having
an associated pulse width modulation valve, a higher number of
tandem compressors, with several of them having associated pulse
width modulation valves, would be within the scope of the
invention.
[0017] FIG. 3 shows yet another embodiment 221, wherein each of the
compressors 22 and 24 deliver refrigerant to separate condensers
230 and 232, while still receiving refrigerant from the same
evaporator 34. Such an arrangement would be typically used when the
condensers reject heat into different environments (such as, for
instance, indoors and outdoors) and have different operational
characteristics. The condensers 230 and 232 deliver refrigerant to
individual expansion devices 233, and the refrigerant flows are
then combined before returning to the evaporator 34, and the common
suction manifold 26. Again, a pulse width modulation valve 36 is
mounted on the suction line leading to the tandem compressors 22
and 24 and controls refrigerant flow through the refrigerant system
221, no matter how many compressors are in operation. Similar to
the FIG. 2 embodiment, the pulse width modulation valve 36 can be
associated with only one of the compressors 22 or 24 and control
the refrigerant flow through that particular compressor and an
associated condenser, if desired (see further explanation below).
Once again, this embodiment can be extended to any number of tandem
compressors.
[0018] FIG. 4 shows a refrigerant system 222. This system is
somewhat similar to the FIG. 1 system; however, the pulse width
modulation valve 136 is positioned downstream of the common suction
manifold 26, and on a suction line delivering refrigerant only to
the compressor 122. With this arrangement, it may be desirable to
only operate one of the compressors 122 and 124 at any instant of
time, since compressor oil sumps of the two compressors 122 and 124
would be at a considerable pressure differential, when the pulse
width modulation control is activated for the valve 136. Otherwise,
cross-leakage between the compressors, oil pumpout and reliability
problems may take place. Again, the compressor 122 is capable of
providing precise control to the capacity provided by the
refrigerant system 222. Any number of tandem compressors may have
the associated pulse width modulated valves in this arrangement as
well.
[0019] A tailored refrigerant system capacity achieved by a pulse
width modulation valve of FIG. 1 is illustrated in FIG. 5. As shown
in this Figure, if full capacity is required then two tandem
compressors operate together with pulse width modulation valve
fully open. When the capacity requirements are reduced, the pulse
width modulation valve will cycle between open and closed
positions. As more capacity reduction is required, the valve would
stay in a closed position for longer periods of time than in an
open position. When the capacity requirements are sufficiently low,
then one of the tandem compressors is shut off, and the pulse width
modulation valve cycle is altered once again to be most of the time
in an open position. As the capacity requirements are reduced even
further, the system continues to operate with one compressor turned
off, and the cycle of the pulse width modulation valve adjusted,
such that the pulse width modulation valve stays in a closed
position for longer periods of time. The most appropriate time when
the controller turns off one of the tandem compressors is
determined and predominately based on the system capacity
requirements, while it can be adjusted further to take system
efficiency and reliability into consideration. While FIG. 5
illustrates adjustments in the pulse width modulation valve
position for schematic shown in FIG. 1, it can be applied in a
similar fashion to other embodiments of this invention as shown in
other Figures.
[0020] FIG. 6 shows enhancement features that can be incorporated
into any of the above schematics, in a system 300. The tandem
compressors 302 and 304 are similar to the above embodiments, and
the compressor 302 has an associated pulse width modulation valve
303 with a pulse width modulation control 305. However, even more
flexibility in capacity control is provided in this arrangement. A
condenser 306 receives refrigerant from the tandem compressors 302
and 304, and delivers it to a liquid line. A portion of refrigerant
is tapped from the liquid line downstream of the condenser 306, and
the tapped refrigerant passes through an economizer expansion
device 310, where it is expanded to a lower pressure and
temperature, and into an economizer heat exchanger 312 for the heat
transfer interaction with the refrigerant circulating through the
main circuit. As is known, the refrigerant passing through a tap
line 308 subcools the refrigerant in a liquid line 314 flowing into
the main expansion device (not shown). This provides a greater
thermal potential for the refrigerant entering an evaporator (also,
not shown) and consequently enhances refrigerant system cooling
capacity and/or efficiency. The use of an economizer cycle is known
in the art. Although the flow from the tap line 308 and the liquid
line 314 are shown passing through the economizer heat exchanger
312 in the same direction, this is for illustration simplicity
only. In practice, they are preferably flowing in a counterflow
arrangement. The refrigerant from the tap line 308 is then flown
through a return line 316, having a shutoff valve 318, and a vapor
injection line 320. As is known in the art, the vapor injection
line 320 would inject the returned refrigerant from the line 316 to
an intermediate compression point in the economized compressor 302.
It should be noted that the shutoff valve 318 may not be need, if
the economizer expansion device 310 is equipped with a shutoff
capability.
[0021] In addition, and as shown schematically in FIG. 5, a return
line 330, shown in phantom, can also return refrigerant to the
second compressor 304, if the compressor 304 is of an economized
type as well. It should be noted that the compressors 302 and 304
may not necessarily share the same economizer branch components
such as economizer heat exchanger 312 and economizer expansion
device 310.
[0022] A bypass valve 322 may be opened to selectively bypass at
least a portion of partially compressed refrigerant back from the
compressor 302, through the vapor injection line 320, and a bypass
line 324 to a suction line. Typically (but not always), a bypass
function is utilized in a non-economized mode of operation.
Further, the compressor 304 may be also equipped with a bypass
function. Again, the use of the bypass for compressor unloading is
as known in the art. However, the addition of the bypass and/or
economizer function into a tandem compressor system having at least
one compressor provided with a pulse width modulation control
allows for even more flexible control over the provided capacity.
Since an economizer and bypass functions offer two additional
discrete steps of capacity control, the pulse width modulation
technique offers precision control for refrigerant system operation
within the economizer stage (when an economizer circuit is engaged)
and bypass stage (when the bypass function is activated). As a
result, superior accuracy control is provided in the conditioned
space and efficiency boost in the refrigerant system operation is
achieved. Once again, more than a single tandem compressor can be
equipped with economizer and bypass features (whether or not
sharing the economizer branch components such an economizer heat
exchanger and economizer expansion device) and associated with the
pulse width modulation control. Also, the economizer and bypass
function do not need to be combined with each other. For example,
only an economizer feature or only a bypass feature can be
associated with a particular compressor. Further, as known in the
art, it might be desirable to provide a small leak through a pulse
width modulation valve (or a small bypass around the valve), when
the valve is in a closed position to prevent the compressor
operating in a vacuum.
[0023] It should be pointed out that while the present invention
provides illustration for only two tandem compressors, as known in
the art, more than two tandem compressors can be connected together
in a tandem configuration. Also each compressor shown in the above
Figures can represent a bank of compressors connected together in
tandem and providing a nested arrangement. Within this nested
arrangement, any compressor can be equipped with a pulse width
modulated valve. For instance, a two-level nested tandem compressor
system, incorporating two compressor banks 422 and 424 and suction
modulation valves 436, is shown in FIG. 7. It also should be
pointed out that, in general, the pulse width modulation valve can
be associated with any compressor in the system or with any
compressor type, such as a scroll compressor, a rotary compressor,
a reciprocating compressor, a screw compressor, etc. Furthermore,
the described refrigerant systems can be of a single circuit
configuration or can be a part of a multi-circuit arrangement. In
multi-circuit configurations, only a single circuit may be equipped
with tandem compressors having a suction pulse width modulation
valve or multiple circuits may have tandem compressors and an
associated suction pulse width modulation valve.
[0024] 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.
* * * * *