U.S. patent application number 12/090411 was filed with the patent office on 2008-11-20 for method and apparatus of optimizing the cooling load of an economized vapor compression system.
Invention is credited to Wayne P. Beagle.
Application Number | 20080282718 12/090411 |
Document ID | / |
Family ID | 38092539 |
Filed Date | 2008-11-20 |
United States Patent
Application |
20080282718 |
Kind Code |
A1 |
Beagle; Wayne P. |
November 20, 2008 |
Method and Apparatus of Optimizing the Cooling Load of an
Economized Vapor Compression System
Abstract
A vapor compression system includes a variable speed single
stage compressor, a heat rejecting heat exchanger, an expansion
device, and a heat accepting heat exchanger. The speed of the
compressor is varied to control the refrigerant flow rate and match
the cooling load requirements of the vapor compression system. A
temperature sensor measures an air temperature in the refrigerated
container. When the temperature sensor detects that the air
temperature is above a threshold temperature, the microcontroller
increases the speed of the compressor to increase the refrigerant
flow rate and the cooling capacity of the vapor compression system.
When the air temperature sensor detects that the air temperature is
within a predetermined range from the set point temperature, the
microcontroller sends a signal to slightly decrease the speed of
the compressor, allowing fine adjustment of the cooling capacity of
the vapor compression system to prevent overcooling of the
refrigerated container.
Inventors: |
Beagle; Wayne P.;
(Chittenango, NY) |
Correspondence
Address: |
CARLSON, GASKEY & OLDS, P.C.
400 WEST MAPLE ROAD, SUITE 350
BIRMINGHAM
MI
48009
US
|
Family ID: |
38092539 |
Appl. No.: |
12/090411 |
Filed: |
December 1, 2005 |
PCT Filed: |
December 1, 2005 |
PCT NO: |
PCT/US2005/043368 |
371 Date: |
April 16, 2008 |
Current U.S.
Class: |
62/228.4 ;
62/513 |
Current CPC
Class: |
Y02B 30/70 20130101;
F25B 2600/0253 20130101; F25B 2400/13 20130101; F25B 1/10 20130101;
Y02B 30/741 20130101; F25B 49/025 20130101; F25B 2700/21173
20130101; F25B 2700/2104 20130101; F25B 2700/21172 20130101 |
Class at
Publication: |
62/228.4 ;
62/513 |
International
Class: |
F25B 49/00 20060101
F25B049/00 |
Claims
1. A vapor compression system comprising: a variable speed single
stage compressor to compress a refrigerant to a high pressure; a
heat accepting heat exchanger for exchanging heat between the
refrigerant and an airflow to heat the refrigerant and cool the
airflow, wherein the airflow is provided to an area; a temperature
sensor to detect an air temperature of air in the area; and a
controller that adjusts a speed of the variable speed single stage
compressor based on the air temperature to match a cooling load
requirement of the vapor compression system to cool the area.
2. The system as recited in claim 1 further including a heat
rejecting heat exchanger for cooling the refrigerant and a main
expansion device to expand the refrigerant to a low pressure.
3. The system as recited in claim 2 further including an economizer
heat exchanger, wherein the refrigerant from the heat rejecting
heat exchanger is split into an economized path which is reduced to
an intermediate pressure in an economizer expansion device and a
main path, wherein the refrigerant in the main path and the
refrigerant in the economized path exchange heat therebetween in
the economizer heat exchanger, and wherein the refrigerant in the
economized path is injected into an economizer port of the variable
speed single stage compressor and the refrigerant in the main path
is expanded in the main expansion device.
4. The system as recited in claim 3 wherein the variable speed
single stage compressor includes a compression chamber and a piston
that moves in the compression chamber, wherein the piston moves in
a first direction to expand a volume of the compression chamber
during a suction stroke and prevent the refrigerant in the
economized path from entering the compression chamber and the
piston moves in an opposing second direction to reduce the volume
of the compression chamber during a discharge stroke to compress
the refrigerant and prevent the refrigerant in the economized path
from entering the compression chamber.
5. The system as recited in claim 4 wherein the compression chamber
is a single compression chamber.
6. The system as recited in claim 1 further including a motor to
control the speed of the variable speed single stage compressor and
adjust a mass flow rate of the refrigerant through the vapor
compression system.
7. The system as recited in claim 1 wherein the controller
increases the speed of the variable speed single stage compressor
when the air temperature detected by the temperature sensor is
greater than a threshold temperature programmed in the controller
to reduce the air temperature to a set point temperature.
8. The system as recited in claim 7 wherein the controller
decreases the speed of the variable speed single stage compressor
when the air temperature is less than a second threshold
temperature programmed in the controller, and the second threshold
temperature is greater than the set point temperature.
9. The system as recited in claim 1 wherein the air temperature is
a return air temperature of the air drawn from the refrigerated
container.
10. A vapor compression system comprising: a variable speed single
stage compressor to compress a refrigerant to a high pressure; a
motor to control a speed of the variable speed single stage
compressor and adjust a mass flow rate of the refrigerant through
the vapor compression system; a heat rejecting heat exchanger for
cooling the refrigerant; a main expansion device to expand the
refrigerant to a low pressure; an economizer heat exchanger,
wherein the refrigerant from the heat rejecting heat exchanger is
split into an economized path which is reduced to an intermediate
pressure in an economizer expansion device and a main path, wherein
the refrigerant in the main path and the refrigerant in the
economized path exchange heat therebetween in the economizer heat
exchanger, and wherein the refrigerant in the economized path is
injected into an economizer port of the variable speed single stage
compressor and the refrigerant in the main path is expanded in the
main expansion device; a heat accepting heat exchanger for
exchanging heat between the refrigerant and an airflow to heat the
refrigerant and cool the airflow, wherein the airflow is provided
to an area; a temperature sensor to detect an air temperature of
air in the area; and a controller that adjusts the speed of the
variable speed single stage compressor based on the air temperature
to match a cooling load requirement of the vapor compression system
to cool the area.
11. The system as recited in claim 10 wherein the controller
increases the speed of the variable speed single stage compressor
when the air temperature detected by the temperature sensor is
greater than a threshold temperature programmed in the controller
to reduce the air temperature to a set point temperature.
12. The system as recited in claim 11 wherein the controller
decreases the speed of the variable speed single stage compressor
when the air temperature is less than a second threshold
temperature programmed in the controller, and the second threshold
temperature is greater than the set point temperature.
13. The system as recited in claim 10 wherein the variable speed
single stage compressor includes a single compression chamber.
14. A method of optimizing a cooling capacity of a vapor
compression system comprising the steps of: compressing a
refrigerant to a high pressure in a variable speed single stage
compressor; heating the refrigerant in a heat accepting heat
exchanger by accepting heat from an airflow to cool the airflow;
providing the airflow to cool an area; detecting an air temperature
of air in the area; and controlling a speed of the variable speed
single stage compressor based on the air temperature to match a
cooling load requirement of the vapor compression system to cool
the area.
15. The method as recited in claim 14 further including the steps
of cooling the refrigerant in a heat rejecting heat exchanger and
expanding the refrigerant to a low pressure in a main expansion
device.
16. The method as recited in claim 15 further including the steps
of: splitting the refrigerant from the heat rejecting heat
exchanger into an economized path and a main path; expanding the
refrigerant in the economized path to an intermediate pressure in
an economizer expansion device, exchanging heat between the
refrigerant in the main path and the refrigerant in the economized
path, injecting the refrigerant in the economized path into an
economizer port of the variable speed single stage compressor, and
expanding the refrigerant in the main path in the main expansion
device.
17. The method as recited in claim 14 further including the step of
increasing the speed of the variable speed single stage compressor
when the air temperature is greater than a threshold temperature to
reduce the air temperature to a set point temperature.
18. The method as recited in claim 17 further including the step of
then decreasing the speed of the variable speed single stage
compressor when the air temperature is less than a second threshold
temperature, wherein the second threshold temperature is greater
than the set point temperature.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates generally to a method of
optimizing the cooling load of an economized vapor compression
system by varying a speed of a single stage compressor.
[0002] A vapor compression system includes a compressor, a heat
rejecting heat exchanger, an expansion device, and a heat accepting
heat exchanger. Refrigerant circulates though the closed circuit
system. The refrigerant exits the compressor through a discharge
port at a high pressure and a high enthalpy. The refrigerant then
flows through the heat rejecting heat exchanger at a high pressure
and rejects heat to an external fluid medium. The refrigerant then
flows through the expansion device, which expands the refrigerant
to a low pressure. After expansion, the refrigerant flows through
the heat accepting heat exchanger and absorbs heat from an air
stream to cool a refrigerated container. The refrigerant then
re-enters the compressor through a suction port, completing the
cycle.
[0003] An economized cycle is commonly used to enhance performance
and increase both capacity and efficiency of the vapor compression
system. In an economized cycle, the refrigerant is split into two
flow paths after exiting the heat rejecting heat exchanger. The
refrigerant in an economizer flow path is expanded to an
intermediate pressure and exchanges heat with the refrigerant in a
main flow path in an economizer heat exchanger. The refrigerant in
the economizer flow path is injected into an economizer port of the
compressor. The refrigerant in the main flow path is expanded in
the expansion device. By further cooling the refrigerant in the
main flow path, the inlet enthalpy to the heat accepting heat
exchanger decreases, increasing the cooling capacity of the vapor
compression system.
[0004] Prior vapor compression systems employ a fixed speed
multi-stage reciprocating compressor including at least two
compression stages. Refrigerant is compressed in a first stage. The
refrigerant in the economizer flow path is injected at an
intermediate pressure between the first stage and a second stage.
The refrigerant is then compressed in the second stage. A drawback
to employing a multi-stage compressor is that it is expensive.
Additionally, multi-stage compressors do not perform as well as
single stage compressors in certain operating conditions. Finally,
as the speed of the multi-stage compressor is fixed, the compressor
is unable to be controlled to match the load requirements of the
vapor compression system.
[0005] Hence, there is a need in the art for a method of optimizing
the cooling load of an economized vapor compression system that
overcomes the drawbacks and shortcomings of the prior art.
SUMMARY OF THE INVENTION
[0006] A vapor compression system includes a single stage
compressor, a heat rejecting heat exchanger, an expansion device,
and a heat accepting heat exchanger. Refrigerant circulates though
the closed circuit vapor compression system. The refrigerant is
compressed in the compressor and exits the compressor through a
suction port. The refrigerant then enters the heat rejecting heat
exchanger, such as a condenser or gas cooler, and rejects heat to
an external fluid medium. The refrigerant then splits into a main
flow path and an economizer flow path. Refrigerant in the
economizer flow path is expanded to an intermediate pressure in an
economizer expansion device and exchanges heat with the refrigerant
in the main flow path in an economizer heat exchanger. The
refrigerant in the economizer flow path is returned to the
compressor through an economizer port. The refrigerant in the main
flow path is expanded by the expansion device. After expansion, the
refrigerant flows through the heat accepting heat exchanger and
accepts heat from an air stream to cool a refrigerated container.
The refrigerant then re-enters the compressor through a suction
port, completing the cycle.
[0007] The speed of the compressor is varied to match the cooling
load requirements of the vapor compression system. The compressor
includes a motor that operates the compressor at a variable speed.
By adjusting the speed of the compressor, the mass flow rate of the
refrigerant through the vapor compression system can be controlled
to efficiently cool the refrigerated container. Increasing the
speed of the compressor increases the mass flow rate of the
refrigerant and the capacity of the heat accepting heat exchanger
to cool the refrigerated container. Decreasing the speed of the
compressor decreases the mass flow rate of the refrigerant and the
capacity of the heat accepting heat exchanger to cool the
refrigerated container.
[0008] The vapor compression system includes an air temperature
sensor that measures an air temperature in the refrigerated
container. A desired set point temperature is programmed into a
microcontroller. When the air temperature sensor detects that the
air temperature is above a threshold temperature, the
microcontroller increases the speed of the compressor to increase
the mass flow rate of the refrigerant and therefore the cooling
capacity of the vapor compression system.
[0009] When the air temperature sensor detects that the air
temperature is within a predetermined range from the set point
temperature, the microcontroller sends a signal to slightly
decrease the speed of the compressor. This allows for fine
adjustment of the cooling capacity of the vapor compression system
to prevent overcooling of the refrigerated container. Once the air
temperature sensor detects that the air temperature equals the set
point temperature, the microcontroller sends a signal to slow down
the motor of the compressor to maintain the set point temperature
and match the cooling load of the vapor compression system.
[0010] These and other features of the present invention will be
best understood from the following specification and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The various features and advantages of the invention will
become apparent to those skilled in the art from the following
detailed description of the currently preferred embodiment. The
drawings that accompany the detailed description can be briefly
described as follows:
[0012] FIG. 1 schematically illustrates an economized vapor
compression system of the present invention employing a variable
speed single stage compressor;
[0013] FIG. 2A schematically illustrates the compressor when
refrigerant enters a compression chamber through a suction
port;
[0014] FIG. 2B schematically illustrates the compressor when
refrigerant enters the compression chamber through an economizer
port; and
[0015] FIG. 2C schematically illustrates the compressor when
compressed refrigerant exits the compression chamber through a
discharge port.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0016] FIG. 1 illustrates an example vapor compression system 20
including a single stage compressor 22, a heat rejecting heat
exchanger 24, an expansion device 26, and a heat accepting heat
exchanger 28. Refrigerant circulates though the closed circuit
vapor compression system 20. The refrigerant exits the compressor
22 through a discharge port 30 at a high pressure and a high
enthalpy.
[0017] The refrigerant then flows through the heat rejecting heat
exchanger 24, such as a condenser or gas cooler. An external fluid
medium 32, such as water or air, flows through the heat rejecting
heat exchanger 24 and exchanges heat with the refrigerant flowing
through the heat rejecting heat exchanger 24. The refrigerant
rejects heat to the external fluid medium 32 and exits the heat
rejecting heat exchanger 24 at a relatively low enthalpy and a high
pressure.
[0018] The refrigerant then splits into a main flow path 34 and an
economizer flow path 36. Refrigerant in the economizer flow path 36
is expanded to an intermediate pressure in an economizer expansion
device 38 and exchanges heat with the refrigerant in the main flow
path 34 in an economizer heat exchanger 40, cooling the refrigerant
in the main flow path 34. The refrigerant in the economizer flow
path 36 flows along an economizer return path 42 and is injected
into an economizer port 44 of the compressor 22 at an intermediate
pressure between a suction pressure and a discharge pressure.
[0019] The refrigerant in the main flow path 34 is expanded by the
expansion device 26, reducing the pressure of the refrigerant. The
expansion device 26 can be a mechanical expansion device (TXV), an
electronic expansion valve (EXV) or other type of known expansion
device.
[0020] After expansion, the refrigerant flows through the heat
accepting heat exchanger 28 and absorbs heat from an external air
stream 46 to cool a space inside a refrigerated container 48. In
one example, the refrigerated container 48 is used for shipping or
transporting items which need to be cooled. For example, the
refrigerated container 48 can be a cargo space or trailer of a
vehicle, such as a truck. The refrigerant exits the heat accepting
heat exchanger 28 at a relatively high enthalpy and a low pressure.
The refrigerant then enters a suction port 50 of the compressor 22,
completing the cycle.
[0021] As shown in FIG. 2A, the compressor 22 is a single stage
compressor that includes at least one compression chamber 52. The
compressor 22 can include a single compression chamber or multiple
compression chambers. During a suction stroke of the compressor 22,
the refrigerant from the heat accepting heat exchanger 28 enters
the compressor chamber 52 through the suction port 50 at the
suction pressure. A suction valve 54 allows the refrigerant to
enter the compression chamber 52. A piston 56 blocks the economizer
port 44 and prevents the refrigerant in the economizer return path
42 from entering the compression chamber 52 through the economizer
port 44. A seal 64 between the piston 56 and the walls of the
compression chamber 52 prevents refrigerant from flowing around the
piston 56. As the refrigerant enters the compression chamber 52
through the suction port 50, the piston 56 moves in direction A
away from the suction port 50, enlarging the compression chamber 52
to the position shown in FIG. 2B.
[0022] Towards the end of the suction stroke, the piston 56 no
longer blocks the economizer port 44, allowing the refrigerant in
the economizer return path 42 to enter the compressor chamber 52
through the economizer port 44. The intermediate pressure of the
refrigerant entering the compression chamber 52 through the
economizer port 44 causes the suction valve 54 to cover the suction
port 50, preventing the refrigerant from the heat accepting heat
exchanger 28 from entering the compression chamber 52 through the
suction port 50.
[0023] As shown in FIG. 2C, during a discharge stroke, the piston
56 moves in direction B opposite to the direction A, compressing
the refrigerant to the higher discharge pressure. The piston 56
blocks the economizer port 44 and prevents the refrigerant in the
economizer return path 42 from entering the compression chamber 52
through the economizer port 44. The increase in pressure of the
refrigerant opens a discharge valve 66, allowing the refrigerant to
exit the compression chamber 52 through the discharge port 30 and
flow to the heat rejecting heat exchanger 24.
[0024] The speed of the compressor 22 is varied to match the
cooling load requirements of the vapor compression system 20. The
compressor 22 includes a motor 60 that operates the compressor 22
at variable speeds. Preferably, the compressor 22 operates at at
least two speeds. By adjusting the speed of the compressor 22, the
mass flow rate of the refrigerant flowing through the vapor
compression system 20 can be changed. Controlling the mass flow
rate of the refrigerant through the vapor compression system 20
allows the load requirements of the vapor compression system 20 to
be efficiently matched to optimally cool the refrigerated container
48. That is, by controlling the speed of the compressor 22, the
load requirements of the vapor compression system 20 can be matched
to optimally cool the refrigerated container 48.
[0025] Increasing the speed of the compressor 22 increases the mass
flow rate of the refrigerant and the capacity of the heat accepting
heat exchanger 28 to cool the refrigerated container 48. Decreasing
the speed of the compressor 22 decreases the mass flow rate of the
refrigerant and the capacity of the heat accepting heat exchanger
28 to cool the refrigerated container 48.
[0026] The vapor compression system 20 includes an air temperature
sensor 58 that measures an air temperature representative of an air
temperature in the refrigerated container 48. In one example, the
temperature sensor 58 measures the air temperature of the air drawn
from the refrigerated container 48. The air temperature sensor 58
communicates with a microcontroller 62. A desired set point
temperature of the air in the refrigerated container 48 is
programmed into the microcontroller 62.
[0027] When the air temperature sensor 58 detects that the air
temperature is above a threshold temperature, the microcontroller
62 increases the speed of the compressor 22 to increase the mass
flow rate of the refrigerant and therefore the cooling capacity of
the vapor compression system 20. The microcontroller 62 runs an
algorithm to determine the speed of the compressor 22 that matches
the cooling load requirements of the vapor compression system
20.
[0028] Once the air temperature sensor 58 detects that the air
temperature is within a predetermined range of the set point
temperature, the microcontroller 62 slightly decreases the speed of
the compressor 22. This reduces the mass flow rate of the
refrigerant and the cooling capacity of the vapor compression
system 20, allowing for fine adjustment of the cooling capacity of
the vapor compression system 20 to prevent overcooling of the
refrigerated container 48.
[0029] Once the air temperature sensor 58 detects that the air
temperature equals the set point temperature, the microcontroller
62 sends a signal to slow down the motor 60 of the compressor 22 to
reduce the mass flow rate of the refrigerant through the vapor
compression system 20.
[0030] Fine adjustment of the cooling capacity of the vapor
compression system 20 prevents overcooling of the refrigerated
container 48 that would make the vapor compression system 20
inefficient. Once the motor 60 of the compressor 22 is slowed down,
the heat accepting heat exchanger 28 continues to cool the
refrigerated container 48 for a short period of time. If the
compressor 22 continued to operate at the current speed with the
current cooling capacity until the set point temperature was
detected by the air temperature sensor 58, the heat accepting heat
exchanger 28 would continue to cool the refrigerated container 48,
and the temperature of the air in the refrigerated container 48
would drop below the set point temperature. This overcooling would
make the vapor compression system 20 inefficient. By readjusting
the speed on the compressor 22 when the air temperature is within
the predetermined range, greater control of the cooling capacity of
the vapor compression system 20 is possible. The compressor 22 can
be unloaded in other ways, and one skilled in the art would know
how to unload the compressor 22.
[0031] In one example, the set point temperature is 0.degree. F.
and the predetermined range is 10.degree. F. If the air temperature
sensor 58 detects that the air temperature increases above the
threshold temperature, the microcontroller 62 increases the speed
of the compressor 22 to increase the mass flow rate of the
refrigerant and the cooling capacity of the vapor compression
system 20. When the air temperature sensor 58 detects that the air
temperature is 10.degree. F. (within 10 degrees of the set point
temperature of 0.degree. F.), the microcontroller 62 decreases the
speed of the compressor 22 and therefore the amount of cooling
provided by the heat accepting heat exchanger 28. Once the air
temperature sensor 58 detects that the air temperature is 0.degree.
F., the microcontroller 62 sends a signal to slow down the motor 60
of the compressor 22.
[0032] The foregoing description is only exemplary of the
principles of the invention. Many modifications and variations of
the present invention are possible in light of the above teachings.
The preferred embodiments of this invention have been disclosed,
however, so that one of ordinary skill in the art would recognize
that certain modifications would come within the scope of this
invention. It is, therefore, to be understood that within the scope
of the appended claims, the invention may be practiced otherwise
than as specifically described. For that reason the following
claims should be studied to determine the true scope and content of
this invention.
* * * * *