U.S. patent application number 11/101347 was filed with the patent office on 2006-10-12 for refrigerant system with variable speed compressor in tandem compressor application.
This patent application is currently assigned to Carrier Corporation. Invention is credited to Alexander Lifson, Michael F. Taras.
Application Number | 20060225445 11/101347 |
Document ID | / |
Family ID | 37081837 |
Filed Date | 2006-10-12 |
United States Patent
Application |
20060225445 |
Kind Code |
A1 |
Lifson; Alexander ; et
al. |
October 12, 2006 |
Refrigerant system with variable speed compressor in tandem
compressor application
Abstract
A refrigerant system is provided with tandem compressors. As is
known, tandem compressors operate in parallel to provide a
refrigerant system designer with the ability to achieve a stepped
capacity control of the refrigerant system. At least one of the
tandem compressors is provided with a variable speed drive.
Further, at least one of the tandem compressors may be provided
with the economizer and/or unloader functions. System
configurations with multiple compression stages and multiple
injection ports are disclosed. In this manner, the stepless
capacity control can be achieved.
Inventors: |
Lifson; Alexander; (Manlius,
NY) ; Taras; Michael F.; (Fayetteville, NY) |
Correspondence
Address: |
CARLSON, GASKEY & OLDS, P.C.
400 WEST MAPLE ROAD
SUITE 350
BIRMINGHAM
MI
48009
US
|
Assignee: |
Carrier Corporation
|
Family ID: |
37081837 |
Appl. No.: |
11/101347 |
Filed: |
April 7, 2005 |
Current U.S.
Class: |
62/175 ;
62/228.4; 62/510; 62/513 |
Current CPC
Class: |
Y02B 30/70 20130101;
F25B 2400/13 20130101; F25B 2400/075 20130101; F25B 2600/021
20130101; F24F 3/153 20130101; Y02B 30/741 20130101; F25B 2600/0251
20130101; F25B 1/10 20130101; F25B 2600/0261 20130101; F25B 49/022
20130101 |
Class at
Publication: |
062/175 ;
062/228.4; 062/510; 062/513 |
International
Class: |
F25B 7/00 20060101
F25B007/00; F25D 17/02 20060101 F25D017/02; F25B 1/00 20060101
F25B001/00; F25B 49/00 20060101 F25B049/00; F25B 1/10 20060101
F25B001/10; F25B 41/00 20060101 F25B041/00 |
Claims
1. A refrigerant system comprising: at least two tandem compressors
operating in parallel, with at least one compressor having a
variable speed drive for varying a speed of said at least one
compressor; a condenser downstream of said compressor and an
evaporator downstream of said condenser; and a control for
selectively varying said speed of said at least one compressor.
2. The refrigerant system as set forth in claim 1, wherein an
economizer heat exchanger is positioned intermediate to said
condenser and said evaporator, said economizer heat exchanger
selectively receiving a tapped refrigerant to subcool a main
refrigerant flow passing through said economizer heat exchanger,
and said tapped refrigerant being returned to least one of said
compressors and said control being operable to vary the speed of at
least said one compressor to provide variation in capacity control
between a level with said economizer heat exchanger operational,
and a level without said economizer heat exchanger operational.
3. The refrigerant system as set forth in claim 2, wherein there
are a plurality of intermediate ports where said tapped refrigerant
is returned to said at least one of said compressors.
4. The refrigerant system as set forth in claim 1, wherein at least
one of said two tandem compressors is provided by a multi-stage
compressor.
5. The refrigerant system as set forth in claim 1, wherein said
control changing said speed of said at least one compressor in
incremental steps.
6. The refrigerant system as set forth in claim 1, wherein at least
one of said at least two compressors is provided with an unloader
function.
7. The refrigerant system as set forth in claim 1, wherein at least
one of said at least two compressors is not provided with a
variable speed drive.
8. The refrigerant system as set forth in claim 1, wherein there
are more than two of said at least two compressors, and at least
two of said compressors are provided with a variable speed
drive.
9. The refrigerant system as set forth in claim 1, wherein a fan or
pump associated with a component other than the compressor is also
provided with the variable speed drive.
10. The refrigerant system as set forth in claim 1, wherein said at
least two compressors have different capacities.
11. A method of controlling a refrigerant system comprising the
steps of: (1) providing at least two tandem compressors operating
in parallel, with at least one compressor having a variable speed
drive for varying a speed of said at least one compressor,
providing a condenser downstream of said compressor and an
evaporator downstream of said condenser, and a control for
selectively varying said speed of said at least one compressor to
achieve varying levels of capacity control; and (2) determining a
desired capacity, and operating one or the other, or both of said
at least two compressors, and varying a speed of said at least one
compressor to achieve said determined desired capacity.
12. The method as set forth in claim 11, wherein an economizer
function is provided with the refrigerant system, and selectively
actuating said economizer function to provide additional capacity
or increase operation efficiency if necessary to achieve the
desired capacity of step 2.
13. The method as set forth in claim 12, wherein refrigerant from
corresponding economizer heat exchangers is returned to a plurality
of ports associated with said at least two tandem compressors.
14. The method as set forth in claim 11, wherein at least one of
said at least two compressors is provided by a multi-stage
compressor.
15. The method as set forth in claim 11, wherein said control
changes said speed of said at least one compressor in incremental
steps.
16. The method as set forth in claim 11, wherein an unloader
function is provided to unload at least one of said at least two
compressors o achieve the desired capacity of step 2.
17. The method as set forth in claim 11, wherein at least one of
said at least two compressors is not provided with a variable speed
drive.
18. The method as set forth in claim 11, wherein there are more
than two of said at least two compressors, and at least two of said
compressors being provided with a variable speed drive, and said
control varying the speed of said at least two variable speed
driven compressors.
19. The method as set forth in claim 11, wherein said at least two
compressors are provided with different capacities.
20. The method as set forth in claim 11, wherein at least one fan
or pump associated with another component in said refrigerant
system is provided with a variable speed drive.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to a variable speed motor for driving
a compressor that is incorporated into a refrigerant system with
tandem compressors.
[0002] Refrigerant systems are utilized in many air conditioning
and heat pump applications for cooling and/or heating the air
entering an environment. The cooling or heating load on the
environment may vary with ambient conditions, and as the
temperature and/or humidity levels demanded by an occupant of the
building change.
[0003] In some refrigerant systems, a single compressor is utilized
to compress the refrigerant and move the refrigerant through the
cycle connecting indoor and outdoor heat exchangers in a closed
loop. However, under many circumstances, it would be desirable to
have the ability to vary the capacity, or amount of cooling or
heating provided by the refrigerant system. Thus, known refrigerant
systems may be provided with tandem compressors. Tandem compressors
are essentially at least two compressors operating in parallel,
where the compressors are interconnected with each other via common
suction and/or discharge manifolds. For instance, a control for the
two-compressor system may actuate both of the compressors or either
one of the two compressors. The two compressors may have different
sizes to provide distinct stages of capacity during part-load
operation. Rather than having a single level of capacity, a
refrigerant system provided with tandem compressors would have
several discrete levels of capacity.
[0004] In the prior art, controls can be programmed to optionally
actuate the tandem compressors. However, the capacity control
provided by the tandem compressors is increased or decreased in
large discrete steps. It would be desirable to provide the ability
to improve system control capability to continuously vary capacity
between these discrete steps to precisely match external load
demands at a wide spectrum of environmental conditions.
[0005] Variable speed drives are known for driving compressors at a
variable speed in a refrigerant system. By driving the compressor
at a higher or lower speed, the amount of refrigerant that is
compressed per unit of time changes, and thus the system capacity
can be adjusted.
[0006] Variable speed drives have not been utilized in refrigerant
systems incorporating tandem compressors, where a selected number
of the tandem compressors is driven by a variable speed drive, for
the purpose of varying the system capacity to control temperature
and humidity levels within the conditioned space.
SUMMARY OF THE INVENTION
[0007] In the disclosed embodiment of this invention, a variable
speed drive is provided into at least one compressor in a
refrigerant system having tandem compressors. By selectively
controlling this one compressor, capacity adjustment between the
discrete steps provided by tandem compressor operation can be
achieved.
[0008] A control identifies a desired cooling capacity, and then
achieves this desired capacity by first actuating the tandem
compressors to accurately approximate the necessary capacity in the
most efficient and reliable manner. Then, the speed of the at least
one compressor provided with variable speed is changed
incrementally. The capacity is then monitored. When a desired level
is finally achieved, the at least one compressor is operated at
that new speed. If the capacity still needs to be adjusted, then
the speed is again adjusted incrementally, and the resulting
condition is again monitored.
[0009] In disclosed embodiments, one of the tandem compressors may
be provided with the variable speed drive while the other is not.
In other embodiments, plural compressors are provided with a
variable speed drives.
[0010] Embodiments are disclosed which incorporate economizer
cycles and unloader cycles into the schematic along with the
variable speed drive.
[0011] 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
[0012] FIG. 1 shows a first embodiment refrigerant system.
[0013] FIG. 1A shows other possible circuit schematics.
[0014] FIG. 1B shows other possible circuit schematics.
[0015] FIG. 1C shows other possible circuit schematics.
[0016] FIG. 2 shows a second embodiment refrigerant system.
[0017] FIG. 3 shows the capacity control provided by the prior
art.
[0018] FIG. 4 shows the capacity control provided by the present
invention.
[0019] FIG. 5 is a flowchart of a control algorithm according to
the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0020] A refrigerant system 20 is illustrated in FIG. 1. A
compressor 22 is provided with a variable speed drive 24. A second
compressor 26 is not provided with a variable speed drive, and
operates in tandem with the compressor 22. As shown, a shut-off
valve 28 may allow the compressor 26 to be isolated from the
discharge manifold, should a control for the system determine that
only the compressor 22 is necessary for achieving a given capacity.
As is known, the compressors 22 and 26 deliver refrigerant to a
common discharge line 30 leading to a condenser 32. While the
system 20 is illustrated as an air conditioning system, it should
be understood that the present invention would also apply to heat
pumps and chillers.
[0021] As is known, the two compressors 22 and 26 may preferably be
provided with distinct capacities such that varying total levels of
capacity can be achieved by operating one or the other, or both of
the compressors 22 and 26. In this case, it is at the system
designer's discretion to select whether a larger or smaller
compressor is provided with a variable speed drive. The decision
will depend on many factors including (but not limited to)
application requirements, cost, system operation efficiency, etc.
An expansion device 34 is positioned downstream of the condenser
32, and an evaporator 36 is located downstream of the expansion
device 34. A common suction line 38 leads to distinct suction lines
39 for returning refrigerant to the compressors 22 and 26.
[0022] As also shown, an economizer circuit can be incorporated
into the FIG. 1 schematic. An economizer heat exchanger 40 receives
a tapped refrigerant from a line 42 having passed through an
economizer expansion device 44. As is known, by passing the tapped
refrigerant through the expansion device 44, its pressure and
temperature are lowered. Thus, in the economizer heat exchanger 40,
this tapped refrigerant subcools a refrigerant in a main liquid
line 45, which also passes through the economizer heat exchanger
40. The economizer function is known in the prior art, and allows
increased capacity and/or efficiency of the refrigerant system
20.
[0023] As shown, the tapped refrigerant is returned through a line
46 to an intermediate compression point 48 in at least one of the
compressors, here illustrated as compressor 22. While refrigerant
in the tap line 42 is shown flowing through the economizer heat
exchanger 40 in the same direction as refrigerant in the main
liquid line 45, it should be understood that in a preferred
embodiment, the two flows would actually be in counter-flow
arrangement.
[0024] A bypass line 50 is also incorporated, and allows a portion
of refrigerant from the intermediate compression point 48 in the
compressor 22 to be returned to the suction line 39. When it is
desired to have unloaded operation, a valve 52 is opened while the
expansion device 44 is preferably (but not necessarily) closed. In
this way, refrigerant that has been partially compressed by the
compressor 22 will be returned to the suction line 39, thus
providing the unloading function.
[0025] It has to be understood that the economized compressor 22
may have more than one injection port 48 and more than one
associated economizer heat exchanger 40. Also, as known, the
economizer heat exchanger arrangement can be substituted by a flash
tank. Further, multi-stage compression system may be employed
instead of a single economized compressor. In such multi-stage
compressor system, one or several of the stages may be provided
with a variable speed drive.
[0026] As shown, electric motors 200 are associated with fans for
blowing the air over the condenser 32 and evaporator 36. One or
other of these electric motors 200 may be provided with a variable
speed drive 202. A worker of ordinary skill in the art would
recognize when the variable speed control of the fan, or other
components such as a secondary loop pump, motors associated with
the refrigerant system might be desirable.
[0027] FIG. 1A shows another circuit schematic 100 wherein one of
the two compressors, e.g. compressor 22, is replaced by two
compressor stages 104 and 106. While both of the compressor stages
104 and 106 are shown connected to the variable speed drive 102,
only one stage or the other could be connected instead. As shown,
the return line 108 from the economizer heat exchanger extends
simply between the two stages, rather than into compression
chambers in either of the stages.
[0028] FIG. 1B shows another embodiment 110 wherein there are three
compressor stages 112, 114 and 116. The variable speed drive 118
controls both stages 114 and 116. Each of the stages is shown
associated with an unloader valve 120. Two separate economizer heat
exchangers 122 selectively deliver refrigerant through lines 124
back to points between the compressor stages. It is well known to a
person ordinarily skilled in the art that a number of compression
stages (as well as a number and particular position of compression
stages operating at variable speeds), a number of unloader valves
and a number of economizer heat exchangers are at a designer
freedom and depend on a particular application.
[0029] FIG. 1C shows another embodiment 130 wherein a first stage
of the compressor is provided by a pair of tandem compressors 134
and 136 feeding a second compressor stage 138. As shown, an
intermediate pressure refrigerant return line 140 extends between
the stages. A variable speed drive 132 is associated with the
compressor 134 only. Of course, many other schematics would come
within the scope of this invention, including (but not limited to)
a varying number of tandem and variable speed compressors.
[0030] FIG. 2 shows a distinct embodiment 60, wherein the two
tandem compressors are replaced by a bank of four compressors. As
shown, compressors 64 are each provided with a variable speed drive
62. Shut-off valves 66 are placed on the discharge lines for three
compressors 64, 68 and 70 to isolate those compressors when they
are stopped by the system control. A common discharge manifold 72
leads to a condenser 74, an expansion device 76, and an evaporator
78. A control for this refrigerant system 60 is configured to
operate the two compressors 64 at variable speeds, and the two
compressors 68 and 70 at fixed speed to achieve desired
capacity.
[0031] A control for either refrigerant system 20 and 60 is able to
identify a desired cooling capacity, and operate the tandem
compressors and/or the economizer and unloader functions as
necessary. Thus, as shown in FIG. 3, a prior art system that
incorporated the FIG. 1 schematic without the variable speed drive
could provide at least three stages A, B, and A+B of capacity
control. In fact, the schematic shown in FIG. 1 would have even
more stages, in that the operation of the unloader valve and
economizer function would provide additional capacity steps.
However, for purposes of understanding the remainder of this
invention, the simplified schematic of FIG. 3 will suffice. As can
be seen, there are several values between values A, B, and A+B that
cannot be provided by this prior art system. This is, of course, an
oversimplification of the system, yet this does provide a good
basis for understanding the present invention. The FIG. 2
embodiment would have many other levels of capacity control
available as well.
[0032] FIGS. 3 and 4 are an oversimplification of the FIG. 1
embodiment and the capacity levels it can provide. As mentioned, by
operating the unloader valve and economizer function, additional
capacity steps can be achieved. However, a control for this system
would operate one of the compressors (e.g., compressor 26) that may
be smaller than the compressor 22 to provide the level A. The other
compressor 22 can be operated to provide the level B, with the
compressor 26 stopped. By operating both compressors 22 and 26, the
level A+B can be achieved. Within each of these levels, by
increasing the speed of the motor for the compressor 22, a ramp R
above the step A, B, or A+B can be achieved. On the other hand, by
slowing the speed, the opposite can occur to move a ramp downwardly
from these values. A decision of switching between the compressor
speed adjustment and moving to a different mode of operation is
usually based on the amount of required cooling, efficiency and
reliability considerations. For instance, it may be unsafe to
operate the compressor below certain speed due to inadequate
lubrication provided to compressor elements. On the other hand,
running compressor at a relatively high speed may be inefficient in
comparison to switching to an economizer mode of operation.
[0033] FIG. 5 shows how the ramps would typically be achieved with
a standard variable speed motor control as is known in the prior
art. Ramps R as shown in FIG. 4 are an oversimplification. In fact,
the control typically moves in incremental steps, and then monitors
the operation of the refrigerant cycle after that incremental
change. Thus, there would be a plurality of step changes along each
ramp R, rather than the infinite number of changes as is
illustrated in FIG. 4. However, FIG. 4 does provide a good
illustration of the power of the present invention to provide
varying capacity.
[0034] It has to be noted that variable speed tandem compressors
can be utilized in conjunction with other system components such as
fans or pumps also operated at variable speeds.
[0035] Although preferred embodiments 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.
* * * * *