U.S. patent application number 12/088022 was filed with the patent office on 2008-09-18 for refrigerant system with pulse width modulated components and variable speed compressor.
Invention is credited to Alexander Lifson, Sriram Srinivasan.
Application Number | 20080223057 12/088022 |
Document ID | / |
Family ID | 37968080 |
Filed Date | 2008-09-18 |
United States Patent
Application |
20080223057 |
Kind Code |
A1 |
Lifson; Alexander ; et
al. |
September 18, 2008 |
Refrigerant System with Pulse Width Modulated Components and
Variable Speed Compressor
Abstract
A variable speed drive is provided for operating a compressor
motor in a refrigerant system. When a low load situation has been
determined by the refrigerant system controls, the variable speed
drive operates the compressor motor at lower speed mode of
operation. Further, the operation of the variable speed drive is
combined with a pulse width modulation control of different system
components. In particular, at least one valve or compressor can be
can be rapidly cycled by the control to regulate amount of
refrigerant passing through the valve or compressor. Example valves
would include a shut-off valve for an economizer cycle, an unloader
valve, or a suction modulation valve.
Inventors: |
Lifson; Alexander; (Manlius,
NY) ; Srinivasan; Sriram; (Manlius, NY) |
Correspondence
Address: |
CARLSON, GASKEY & OLDS, P.C.
400 WEST MAPLE ROAD, SUITE 350
BIRMINGHAM
MI
48009
US
|
Family ID: |
37968080 |
Appl. No.: |
12/088022 |
Filed: |
October 26, 2005 |
PCT Filed: |
October 26, 2005 |
PCT NO: |
PCT/US05/38726 |
371 Date: |
March 25, 2008 |
Current U.S.
Class: |
62/228.4 |
Current CPC
Class: |
F04C 28/08 20130101;
F25B 2600/2521 20130101; Y02B 30/70 20130101; F25B 49/025 20130101;
F25B 2600/0261 20130101; F25B 41/22 20210101; F25B 2400/13
20130101; F04C 29/042 20130101; F04C 28/26 20130101; F25B 2600/0253
20130101; F25B 1/04 20130101 |
Class at
Publication: |
62/228.4 |
International
Class: |
F25B 41/04 20060101
F25B041/04; F25B 41/00 20060101 F25B041/00; F25B 49/00 20060101
F25B049/00 |
Claims
1. A refrigerant system comprising: a compressor and an electric
motor for driving said compressor, a variable speed drive for
varying a speed of operation of said electric motor; a condenser
downstream of said compressor, an expansion device downstream of
said condenser, and an evaporator downstream of said expansion
device; said variable speed drive moving said motor to low speed
operation, and said variable speed drive operating said motor at a
low level of speed; and a pulse width modulation control for
controlling at least one system component.
2. The refrigerant system as set forth in claim 1, wherein said
pulse width modulation control controls at least one valve.
3. The refrigerant system as set forth in claim 2, wherein an
economizer circuit is incorporated into the refrigerant system.
4. The refrigerant system as set forth in claim 3, wherein the said
at least one system component is a shut-off valve associated with
said economizer circuit.
5. The refrigerant system as set forth in claim 2, wherein said
compressor is provided with an unloader circuit.
6. The refrigerant system as set forth in claim 5, wherein said at
least one system component is a valve associated with said unloader
circuit.
7. The refrigerant system as set forth in claim 2, wherein the
refrigerant system is provided with both an economizer circuit and
an unloader circuit.
8. The refrigerant system as set forth in claim 7, wherein said at
least one system component includes a valve associated with said
economizer circuit and a valve associated with said unloader
circuit.
9. The refrigerant system as set forth in claim 2, wherein said at
least one system component is a valve for controlling the mass flow
of refrigerant delivered to said compressor from said
evaporator.
10. The refrigerant system as set forth in claim 1, wherein said at
least one system component is external to a shell for said
compressor.
11. The refrigerant system as set forth in claim 1, wherein said at
least one system component is internal to a shell for said
compressor.
12. The refrigerant system as set forth in claim 1, wherein said
compressor is selected from the group consisting of a scroll
compressor, a rotary compressor, a reciprocating compressor, and a
screw compressor.
13. The refrigerant system as set forth in claim 1, wherein said at
least one component is a pulse width modulated control to hold the
orbiting and non-orbiting scroll member in a scroll compressor
together or allow them to move away from each other.
14. The refrigerant system as set forth in claim 1, wherein said
system is selected from the group consisting of a container
refrigeration system, a truck/trailer system, a supermarket
refrigeration system, a residential air conditioning system, a
residential heat pump system, a commercial air conditioning system,
a commercial heat pump system, and a water heating system.
15. A method of operating a refrigerant system comprising the steps
of: (1) providing a compressor with a variable speed drive, and
monitoring a load on a refrigerant system associated with said
compressor; (2) identifying a low load situation, and moving said
compressor to a low speed operation when a low load situation has
been identified; and (3) providing pulse width modulation control
for a system component to allow the variation of capacity from the
refrigerant system by both varying the speed of the compressor, and
varying the operation of said other component.
16. The method as set forth in claim 15, wherein said pulse width
modulation control controls at least one valve.
17. The method as set forth in claim 16, wherein an economizer
circuit is incorporated into the refrigerant system, and said at
least one system component a shut-off valve associated with said
economizer circuit.
18. The method as set forth in claim 16, wherein said compressor is
provided with an unloader circuit, and said at least one system
component at is a valve associated with said unloader circuit.
19. The method as set forth in claim 16, wherein the refrigerant
system is provided with both an economizer circuit and an unloader
circuit, and said at least one system component includes a valve
associated with said economizer circuit and a valve associated with
said unloader circuit.
20. The method as set forth in claim 15, wherein said at least one
component is external to a shell for said compressor.
21. The method as set forth in claim 15, wherein said at least one
component is internal to a shell for said compressor.
22. The method as set forth in claim 15, wherein said other
component is a valve for controlling the amount of refrigerant
delivered to said compressor from said evaporator.
23. The method as set forth in claim 15, wherein said at least one
component is a pulse width modulated control to hold the orbiting
and non-orbiting scroll member in a scroll compressor together or
allow them to move away from each other.
Description
BACKGROUND OF THE INVENTION
[0001] This application relates to a control for a refrigerant
system having a variable speed compressor, and wherein pulse width
modulation technologies are utilized to provide further control
over the system.
[0002] Refrigerant systems are utilized in many applications to
condition an environment. In particular, air conditioners and heat
pumps are employed to cool and/or heat air entering the
environment. The cooling or heating load of the environment may
vary with ambient conditions, occupancy level, other changes in
sensible and latent load demands, and as the temperature and/or
humidity set points are adjusted by an occupant of the
environment.
[0003] A feature that is known for improving the efficiency of
refrigerant systems is the use of a variable speed drive for the
compressor motor. Often, the compressor need not be operated at
full speed, such as when the cooling load on the refrigerant system
is relatively low. Under such circumstances, it might be desirable
to reduce the compressor speed, and thus reduce the overall energy
consumption of the refrigerant system. Implementation of a variable
speed drive is one of the most efficient techniques to enhance
system performance and reduce life-cycle cost of the equipment over
a wide spectrum of operating environments and potential
applications, especially at part-load conditions.
[0004] However, compelling reliability concerns set a lower limit
to the desirable compressor speed reduction. As an example,
inadequate lubrication of the compressor elements may present a
problem at low operating speeds. Further, certain types of
compressors require a minimum operating speed to provide radial
compliance. As an example, a scroll compressor could have a
dramatic loss in performance due to a loss of radial compliance
should it operate below a minimum speed.
[0005] Various other features are known for providing variations in
system capacity in a manner other than lowering the speed of the
compressor. As an example, economizer cycles are known as are
unloader cycles. However, even with the provision of these cycles
in a system having a variable speed drive for its compressor, it
would be desirable to provide even more variability in the system
capacity.
[0006] Another approach which has been utilized in the prior art to
change the capacity of a refrigerant system is the use of pulse
width modulation to control valves such as a shut-off valve on an
economizer cycle, and/or a shut-off valve on an unloader line,
and/or a shut off valve on a suction. By rapidly cycling these
valves utilizing pulse width modulation techniques, additional
capacity control is provided. The pulse width modulation of the
internal scroll elements can also be applied in conjunction with
variable speed drive operation. In this case, as known in the art,
the scroll elements are separated from each other in a pulse width
manner to control the amount of refrigerant pumped by the
compressor. These pulse width modulation techniques for control of
a valve or internal scroll compression elements have not been
utilized, however, in refrigerant systems having a variable speed
drive compressor.
SUMMARY OF THE INVENTION
[0007] In the disclosed embodiment of this invention, a compressor
is provided with a variable speed drive. When a need for a low
capacity is detected, the compressor is moved to a low speed to
maintain adequate conditions in the environment without switching
to a start-stop mode of operation. The compressor is incorporated
into a refrigerant system, which has a pulse width modulation
control for cycling some component in the system, other than
cycling on and off the compressor motor. In disclosed embodiments,
the cycled component is a valve, and may be a suction valve, and/or
an economizer cycle shut-off valve and/or an unloader valve and/or
cycled component is one of the scroll compressor pumping elements.
By cycling these components on and off, the amount of refrigerant
delivered to various locations in the refrigerant cycle is lowered,
and thus the capacity can be lowered without lowering the
compressor motor speed beyond the safe regime.
[0008] Although, for illustrative purposes, the operation of the
valves in this invention is described in relation to refrigerant
systems incorporating scroll compressors, it could be applicable to
any variable speed compressor.
[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. 1A is a schematic view of a refrigerant system
incorporating the present invention.
[0011] FIG. 1B shows an alternative embodiment.
[0012] FIG. 2 shows another schematic of a refrigerant system.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0013] A refrigerant system 19 is illustrated in FIG. 1 having a
scroll compressor 21 incorporating a non-orbiting scroll member 22
and an orbiting scroll member 24. As is known, shaft 26 is driven
by an electric motor 28 to cause the orbiting scroll member 24 to
orbit. As shown, a variable speed drive 30 is schematically
connected to drive the electric motor 28. An oil sump 32 and an oil
passage 34 in the shaft 26 supply oil to the various moving
elements in the compressor 21, as known.
[0014] A condenser 36 is positioned downstream of the compressor
21, an expansion device 38 is located downstream of the condenser
36, and an evaporator 40 is positioned downstream of the expansion
device 38, as known. As is also known, the compressor 21 is driven
by the electric motor 28 to compress the refrigerant vapor and to
drive it through the refrigerant system 19. Oil from the oil sump
32 is delivered to the compressor elements to provide proper
lubrication of the compressor components such as the crankcase
bearing 100, orbiting scroll bearing 102, the non-orbiting scroll
22 and the orbiting scroll 24, while some amount of oil leaves the
compressor 21 with the refrigerant and is circulated through the
refrigerant system 19. One of the most typical oil delivery systems
of a scroll compressor is also shown in FIG. 1, where the oil from
the oil sump 32 is picked up by the oil pick up tube 110, and
delivered along the oil passage 34 to various compressor components
as described above. Some of the oil can also be delivered through
the suction port 120 by a refrigerant entering the compressor.
However most of the oil delivery is accomplished by delivering the
oil from the oil sump as described above. In the prior art, when a
variable speed drive has been implemented in a refrigerant system,
the designer has been limited by a minimum operational speed of the
shaft 26 for the compressor 21. If the speed dropped below a
certain level for extended period of time, an insufficient amount
of oil would be delivered through the oil passage into the
compressor components that need to be lubricated. Thus, for a low
cooling load situation, where only a small amount of the compressed
refrigerant mass flow is needed to be circulated through the
system, a minimum speed requirement (for example 45 Hz) is often a
limiting factor in ensuring that adequate amount of oil is provided
to the compressor components. Further, the operation above a
minimum speed would also ensure that the radial compliance
necessary for efficient operation of the scroll compressor is not
lost due to unduly low motor speed. As known, it is important to
match the delivered capacity to the system load. Since the
compressor operating speed often cannot be reduced below a certain
threshold for capacity shedding, additional efficient means are
required to reduce the capacity delivered by the unit without
cycling the unit on and off for tight temperature control within
the cooled environment. The description below provides additional
means of efficiently shedding the capacity by coupling the
compressor variable speed operation with pulse width modulation of
different system components.
[0015] FIG. 1 shows additional features that may be incorporated
into the refrigerant system 19. As an example, an economizer cycle
is included and has an economizer heat exchanger 18. A main liquid
line 13 has a tap line 11 tapped off of the main liquid line and
passed through an economizer expansion device 115. The tap line 11
and the main liquid line 13 both pass through the economizer heat
exchanger 18. In fact, and in practice, the refrigerant flow in the
tap line is typically in the counterflow direction through the
economizer heat exchanger in relation to the flow in the main
liquid line 13. However, to simplify the illustration in this
figure, they are shown in the same direction. As is known, the
economizer circuit subcools the refrigerant in the main liquid
line, and thus enhances performance (capacity and/or efficiency) of
the refrigerant system 19. An economizer injection line 20 is shown
extending back to the compressor 21, and injects an intermediate
pressure refrigerant into compression chambers through passages
such as passage 23. The function and structure of the economizer
circuit is known, however, its inclusion with the inventive motor
control 30 provides a refrigerant system that has even greater
flexibility to enhance operation of the refrigerant system 19.
[0016] An optional unloader line 17 includes an unloader valve 200.
The unloader valve 200 is selectively opened to return partially
compressed refrigerant from the compression chambers through the
passages 23 back to a suction port 120 of the compressor 21. The
unloader function presents a refrigerant system designer with an
extra degree of freedom for performance adjustment and
optimization. The unloader valve can be located inside or outside
of the compressor, as known.
[0017] Essentially, when a greater system capacity is desired, the
economizer function may be utilized with the unloader valve shut.
Alternatively, if a lower capacity is necessary, the economizer
expansion device 115 (or a separate shut-off device) is shut, with
the unloader valve 200 opened. In this manner, the amount of
compressed refrigerant delivered to the condenser 36 is reduced.
Also, if desired to provide another intermediate stage of capacity
for the refrigerant system 19, the economizer function can be
combined with the unloader function by opening both the economizer
expansion device 115 and the unloader valve 200. Shutting the flow
in the economizer injection line and closing the unloader valve 200
also achieve another alternate intermediate stage of capacity
unloading.
[0018] These system configurations in combination with the variable
speed motor control disclosed below provides even greater freedom
and flexibility to a refrigerant system designer for controlling
the delivered system capacity
[0019] In this case, the control 30 may incorporate more than a
variable speed drive, but may also be a microprocessor or other
type control that is capable of providing pulse width modulation
control to the economizer valve 115 (which in this case would be a
shut-off valve), and/or the unloader valve 200, and/or a suction
modulation valve 210.
[0020] Also as known in the art, the pulse width modulation can
also be used to pulse width modulate the scroll compression
elements itself, in this case the scroll elements would be
separated from each other in a pulse width manner to control the
amount of the refrigerant pumped by the compressor.
[0021] FIG. 1B shows an embodiment 301, schematically. It is known
that the orbiting scroll member 302 and the non-orbiting scroll
member 304 may be biased together by a gas in a chamber 306.
Opening and closing the valve 310 can control pressure in chamber
306. As shown, the valve 312 communicates via line 308 with another
pressure source that is at different pressure than pressure in the
chamber 306 when the valve 310 is closed. When the pressure in the
chamber 306 is reduced below a certain level the scroll members
will separate from each and the amount of refrigerant pumped by the
compressor is then reduced. When the pressure in the chamber 306 is
increased above certain level the scrolls will come into contact
with each other and then the normal compression process will
resume. The valve can be controlled by a pulse width modulation
control 312. Thus, by modulating the pressure in the chamber 306,
the two scroll members 302 and 304 can be allowed to periodically
move away from, and come into contact with, each other. It should
be noted that the schematic shown in FIG. 1B is presented for an
illustration purpose only. For example, instead of allowing the
scroll 304 to move axially in and out of contact with the scroll
302, the scroll 302 can be allowed to move axially while the scroll
304 remains essentially stationary in the axial direction. The
valve 312 can be located internal or external to the
compressor.
[0022] While the schematic shows the control providing pulse width
modulation control to each of these valves and/or compressor
elements, in other embodiments any combination of the three vales
and/or compressor, or even other valves can be utilized. By rapidly
cycling these valves to open and closed position (closing can be
partial or complete), the amount of refrigerant passing through any
one of the valves and compressor can be varied to vary capacity. As
an example, once the compressor speed has been lowered, and
additional capacity reduction is desired, a valve or compressor can
be cycled to further reduce the system capacity. It should be noted
that normally the compressor speed reduction would be applied first
to shed the capacity, since this is the most efficient means to do
so than other methods of unloading.
[0023] The present invention provides efficient means to
efficiently and precisely control capacity of the refrigerant
system 19 by employing varying methods of pulse width modulation of
various system components coupled with the use of a variable speed
drive motor. The motor drive can be varied in speed when there is a
need for capacity adjustment. The economizer circuit can also be
turned on or off to vary capacity. The unloader function can also
be utilized. In addition, and in combination with each of the above
options for this control, the present invention also allows the
control to modulate the flow of refrigerant through any one of
valves 115, 200 and 210 and/or through modulation of the compressor
pumping elements itself. In this manner, the capacity can be
further reduced without unduly lowering the speed of the compressor
motor 28 beyond its safe threshold of operation.
[0024] FIG. 2 shows another embodiment 300 wherein the valves 200
and 210 are internal of the compressor shell as are the flow
passages. It should be noted that while in FIG. 2 the valves are
all shown as located inside the compressor, a compressor designer
may choose to locate some of them internally and some of them
externally. In addition, the shut-off valve 220 for the economizer
line is shown to be separate from the expansion valve. If the valve
220 is located externally, its function can be combined with the
use of an expansion valve. Also while valves are shown as separate
components, its function can be combined into a single three-way
valve as known in the art. Each or some of the valves 220, 200 and
210 can be controlled by pulse width modulation techniques.
[0025] It should be understood that the motor control 30 includes a
program that takes in inputs from various locations within the
refrigerant system, and determines when a lower speed for the
compressor motor would be desirable and when the pulse width
modulation of the pulse width modulated components needs to be
initiated. The controller can also decide when the system needs to
be operated in economized, non-economized, and by-pass unloading
modes or any of its combinations as described above. Controls
capable of performing this invention with such valves and
compressors are known.
[0026] A worker of ordinary skill in the art would recognize when a
lower speed might be desirable and preferred in comparison or in
addition to other available options.
[0027] It should be understood that although this invention is
described in relation to refrigerant systems incorporating scroll
compressors, it could be applicable to any variable speed
compressor, including scroll compressors, screw compressors,
reciprocating compressors, rotary compressors, etc. The application
of this technique can for example, be applied to refrigeration
systems used in transportation container units, truck/trailer
application, supermarket refrigeration application, as well as
cooling or heating industrial buildings and residential houses as
well as used for water heating applications. 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.
* * * * *