U.S. patent application number 13/191639 was filed with the patent office on 2013-01-31 for loading and unloading of compressors in a cooling system.
The applicant listed for this patent is Dennis R. Dorman. Invention is credited to Dennis R. Dorman.
Application Number | 20130025304 13/191639 |
Document ID | / |
Family ID | 47596089 |
Filed Date | 2013-01-31 |
United States Patent
Application |
20130025304 |
Kind Code |
A1 |
Dorman; Dennis R. |
January 31, 2013 |
LOADING AND UNLOADING OF COMPRESSORS IN A COOLING SYSTEM
Abstract
A system and method of loading and unloading a compressor in a
cooling system. The method includes detecting a temperature,
determining a compressor should be turned on/off to supply/stop
supplying cooling based on the temperature, turning the compressor
on/off, and opening/closing a plurality of valves when the
compressor is turned on/off.
Inventors: |
Dorman; Dennis R.; (La
Crosse, WI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Dorman; Dennis R. |
La Crosse |
WI |
US |
|
|
Family ID: |
47596089 |
Appl. No.: |
13/191639 |
Filed: |
July 27, 2011 |
Current U.S.
Class: |
62/115 ;
62/126 |
Current CPC
Class: |
F25B 49/022 20130101;
F25B 2500/27 20130101; F25B 2400/075 20130101; F25B 2600/2519
20130101; F25B 5/02 20130101; F25B 2600/01 20130101; F25B 41/043
20130101; F25B 2600/0251 20130101; F25B 2700/2104 20130101; F25B
2500/26 20130101 |
Class at
Publication: |
62/115 ;
62/126 |
International
Class: |
F25B 49/02 20060101
F25B049/02; F25B 1/00 20060101 F25B001/00 |
Claims
1. A method of loading and unloading a compressor in a cooling
system, the method comprising: detecting a temperature; determining
a compressor should be turned on to supply cooling based on the
temperature; determining a point in time when the impact of turning
on a motor of the compressor is minimized using point-on-wave
analysis; and turning on the compressor at about the determined
point in time.
2. The method of claim 1, further comprising determining a
compressor should be turned off to stop supplying cooling based on
the detected temperature; determining a second point in time when
the impact of turning off the motor of the compressor is minimized
using point-on-wave analysis; and turning off the compressor at
about the determined second point in time.
3. The method of claim 2, further comprising closing a compressor
intake valve and a compressor output valve when the compressor is
turned off.
4. The method of claim 1, further comprising opening a compressor
intake valve and a compressor output valve when the compressor is
turned on.
5. The method of claim 1, wherein the cooling system is a
residential air conditioner.
6. The method of claim 1, wherein the power to the compressor is
applied by closing a DC contactor.
7. The method of claim 1, further comprising anticipating that
cooling will be required, wherein the compressor is turned on prior
to a set-point temperature being reached.
8. The method of claim 1, wherein the compressor is one of a
plurality of compressors for the cooling system, and the acts of
claim 1 are performed for loading each of the plurality of
compressors.
9. The method of claim 1, further comprising opening an evaporator
valve when the compressor is turned on and closing the evaporator
valve when the compressor is turned off.
10. A method of loading and unloading a compressor in a cooling
system, the method comprising: detecting a temperature; determining
a compressor should be turned on to supply cooling based on the
temperature; turning on the compressor; and opening a plurality of
valves when the compressor is turned on.
11. The method of claim 10, wherein the plurality of valves
includes a compressor intake valve and a compressor outlet
valve.
12. The method of claim 10, further comprising determining the
compressor should be turned off to stop supplying cooling based on
the temperature; turning off the compressor; closing the plurality
of valves when the compressor is turned off.
13. The method of claim 10, wherein the plurality of valves
includes a compressor intake valve and a compressor outlet
valve.
14. The method of claim 10, wherein a pressure across the
compressor is maintained when the compressor is off by the closing
of the plurality of valves.
15. A cooling system, the system comprising: a compressor; a
temperature sensor configured to provide an indication of a
temperature; a compressor intake valve coupled to an input of the
compressor; a compressor output valve coupled to an output of the
compressor; and a controller coupled to the compressor, the
temperature sensor, the compressor intake valve, and the compressor
output valve, the controller configured to receive the indication
of the temperature from the temperature sensor, determine that the
compressor should be turned off to stop providing cooling based on
the indication of temperature received from the temperature sensor,
turn off the compressor, close the compressor intake valve, and
close the compressor output valve, wherein closing the compressor
intake valve and the compressor output valve maintains a pressure
of refrigerant across the compressor while the compressor is
off.
16. The method of claim 15, the controller is further configured to
determine a point in time when an impact on the motor is minimized
using point-on-wave analysis, and to turn on the compressor at the
determined point in time.
17. The cooling system of claim 15, wherein the controller is
further configured to determine that the compressor should be
turned on to provide cooling based on the indication of temperature
received from the temperature sensor, turn on the compressor, open
the compressor intake valve, and open the compressor output
valve.
18. The cooling system of claim 15, wherein the compressor is a
scroll compressor.
19. The cooling system of claim 15, wherein the temperature sensor
is a thermostat.
20. The cooling system of claim 15, wherein the cooling system
includes a plurality of compressors, and the controller is
configured to perform the acts for each compressor of the plurality
of compressors.
Description
BACKGROUND
[0001] The invention relates to cycling of compressors,
specifically rapid cycling of scroll compressors.
[0002] Compressors are integral parts of cooling systems (e.g., air
conditioners, refrigerators, etc.). Compressors compress
refrigerant which later expands and draws heat out of the
environment. The amount the refrigerant is compressed is directly
related to the amount of heat the evaporating refrigerant can
remove from the environment. The compressors are turned on or off
(loaded/unloaded) to control the pressure of the refrigerant and
the cooling capacity of the system. The turning on and off of a
compressor causes wear and tear on the compressor that can lead to
higher maintenance costs and reduce the life of the compressor. The
wear and tear is increased when the compressor is cycled on and off
too rapidly. Thus, compressors are controlled to have
minimum-cycle-times (e.g., a minimum of three minutes on and a
minimum of three minutes off) to reduce the wear and tear on the
compressor. These-cycle-times reduce the ability to tightly control
the cooling effects of the system (e.g., resulting in excessively
wide temperature swings), and reduce the efficiency of the system
(e.g. resulting in increased energy usage).
SUMMARY
[0003] In one embodiment, the invention provides a method of
loading and unloading a compressor in a cooling system. The method
includes detecting a temperature, determining a compressor should
be turned on to supply cooling based on the temperature,
determining a point in time when the impact of turning on a motor
of the compressor is minimized using point-on-wave analysis, and
turning on the compressor at about the determined point in
time.
[0004] In another embodiment the invention provides a method of
loading and unloading a compressor in a cooling system. The method
includes detecting a temperature, determining a compressor should
be turned on to supply cooling based on the temperature, turning on
the compressor, and opening a plurality of valves when the
compressor is turned on.
[0005] In another embodiment the invention provides a cooling
system. The cooling system includes a compressor; a temperature
sensor, a compressor intake valve, a compressor output valve, and a
controller. The temperature sensor is configured to provide an
indication of a temperature. The compressor intake valve is coupled
to an input of the compressor. The compressor output valve is
coupled to an output of the compressor. The controller is coupled
to the compressor, the temperature sensor, the compressor intake
valve, and the compressor output valve. The controller is also
configured to receive the indication of the temperature from the
temperature sensor, determine that the compressor should be turned
off to stop providing cooling based on the indication of
temperature received from the temperature sensor, turn off the
compressor, close the compressor intake valve, and close the
compressor output valve, wherein closing the compressor intake
valve and the compressor output valve maintains a pressure of
refrigerant across the compressor while the compressor is off.
[0006] Other aspects of the invention will become apparent by
consideration of the detailed description and accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a block diagram of a single compressor cooling
system.
[0008] FIG. 2 is a block diagram of a multiple compressor cooling
system.
[0009] FIG. 3A is a graph showing the operation of a prior-art
cooling system.
[0010] FIG. 3B is a graph showing the operation of a cooling system
employing the invention.
DETAILED DESCRIPTION
[0011] Before any embodiments of the invention are explained in
detail, it is to be understood that the invention is not limited in
its application to the details of construction and the arrangement
of components set forth in the following description or illustrated
in the following drawings. The invention is capable of other
embodiments and of being practiced or of being carried out in
various ways.
[0012] The examples described below show various cooling systems.
However, the invention has application in other constructions such
as heat pumps as well.
[0013] FIG. 1 is a block diagram of a cooling system 100 (e.g., a
residential air-conditioner). The system 100 includes a compressor
105, a condenser 110, a controller 115, an expansion valve 120, an
evaporator 125, a temperature sensor 130, a first valve 135 (a
compressor intake valve), a second valve 140 (a compressor output
valve), and a third valve 145 (an evaporator valve).
[0014] The controller 115 receives an indication of a temperature
from the temperature sensor 130. Depending on the system, the
temperature can be an air temperature (e.g., a direct cooling
system) or a temperature of a coolant (e.g., chiller water or a
refrigerant).
[0015] The controller 115 determines if cooling is needed, turning
on the compressor 105 when cooling is needed, and turning off the
compressor 105 when cooling is not needed. In some embodiments, the
controller 115 anticipates the need for cooling, turning the
compressor 105 on prior to the temperature reaching a turn-on
set-point, and turning off the compressor 105 prior to reaching a
turn-off set-point. In some constructions, the controller uses a
proportional-integral-derivative (PID) control scheme to operate
the compressor 105. U.S. Pat. No. 5,415,346, filed Jan. 28, 1994,
and entitled "Apparatus and Method for Reducing Overshoot in
Response to the Setpoint Change of an Air Conditioning System," the
entire content of which is hereby incorporated by reference,
describes such a method of controlling the operation of an air
conditioning system. In some embodiments, as described below, the
controller 115 also controls the compressor 105 using a scheme
designed to reduce wear and tear on the compressor 105.
[0016] When the controller 115 turns the compressor 105 on, the
compressor 105 compresses a refrigerant in the cooling system 100
to provide cooling capacity for the system 100. The refrigerant
flows through piping to the condenser 110 which condenses the
refrigerant into a liquid. The refrigerant continues on to the
expansion valve 120. The expansion value 120 causes the refrigerant
to expand and transform into a gas. This process occurs as the
refrigerant passes through the evaporator 125. As this happens, the
refrigerant, in the evaporator 125, removes heat from the air
surrounding the evaporator 125, resulting in the air (or water)
being cooled. The refrigerant then continues on back to the
compressor 105.
[0017] In addition to turning the compressor 105 on and off, the
controller 115 also opens (when turning on the compressor 105) and
closes (when turning off the compressor 105) the first, second, and
third valves 135, 140, and 145. As the pressure of the refrigerant
varies significantly throughout the cooling system 100, closing the
valves 135, 140, and 145 traps the pressure of the refrigerant in
zones or sections of the system 100. This enables the refrigerant
exiting the compressor 105 to achieve its full pressure nearly
immediately upon the compressor 105 being turned on, improving the
performance of the system 100. Other schemes are contemplated as
well, including sequencing of the opening and closing of the valves
135, 140, and 145, and timing the opening and closing of the valves
135, 140, and 145 such that they open or close before or after the
compressor 105 is turned on/off.
[0018] In some constructions, the temperature sensor 130 is a
thermostat. The thermostat 130 provides a signal to the controller
115 (e.g., a motor controller) indicating whether the controller
115 should turn on the compressor 105 or turn off the compressor
105 based on a temperature set-point, and a dead-band. The
thermostat 130 may or may not have intelligence enabling the
thermostat 130 to anticipate the thermal inertia of the area to be
cooled.
[0019] FIG. 2 is a block diagram of an exemplary large-scale
cooling system 200 (e.g., for cooling a commercial building, for
cooling a plurality of refrigerated display cases, etc.). The
cooling system 200 includes at least one compressor 205, a
condenser 210, a receiver 215 (optional), a controller 220, a
suction header 230, a plurality of expansion valves 235, a
plurality of evaporators 240, a plurality of intake valves 245, and
a plurality of output valves 250. In some constructions, where all
of the compressors 205 are operated in unison (i.e., all the
compressors 205 are turned on and turned off at the same time), a
single intake valve 245 is used prior to the suction header 230
and/or a single output valve 250 is used after common piping for
the compressors 205. In addition, the system 200 includes an
evaporator valve 255 between the receiver 215 and the expansion
valves 235. In some constructions, multiple evaporator valves 255
are used, e.g., an evaporator valve 255 positioned before each
expansion valve 235.
[0020] One or more temperature sensors may be used to detect the
temperature of an area or a coolant cooled by the evaporators 240.
The controller 220 receives an indication of the temperature from
the sensor, and controls the compressors 205 based on the
temperature as described above with respect to cooling system
100.
[0021] The compressor 205 compresses a refrigerant in the cooling
system 200 to provide cooling capacity for the system. In a cooling
system 200 with more than one compressor 205, the compressors 205
can turn on and off at the same or different times to meet the
demand required by the system. In some constructions, all of the
compressors 205 are of one or more fixed capacities, and the
controller 220 stages or loads the compressors 205 into the system
as necessary, for example as described in U.S. Pat. No. 5,123,256,
filed May 7, 1991, and entitled "Method of Compressor Staging for a
Multi-Compressor Refrigeration System," the entire content of which
is hereby incorporated by reference. When a compressor 205 is
turned off, the intake valve 245 and the output valve 250
associated with the compressor 205 are closed, maintaining
high-side and low-side pressures within the evaporator 110 and
condenser 125. When the compressor 205 is turned on, the intake
valve 245 and the output valve 250 associated with the compressor
205 are opened, and the compressor 205 gets to operating pressure
nearly immediately. If all of the compressors 205 in the system 200
are turned off, the evaporator valve 255 is also closed.
[0022] In some embodiments, the controller 220 controls the
compressors 105/205 using a scheme designed to reduce wear and tear
on the compressors 205. U.S. Pat. No. 7,812,563, the entire content
of which is hereby incorporated by reference, discloses a
technology referred to a point-on-wave (POW) switching. POW
switching determines when to power (i.e., switch on) a winding
(i.e., a phase) of a motor based on the relationship between the
wave of the phase of AC power to be supplied with the wave(s) of
the phase(s) of AC power presently supplied to the other winding(s)
of the motor. The invention monitors each phase of AC voltage
supplied to the windings of the motor(s) of the compressor(s)
through precision DC contactors (although AC contactors could be
used instead), switching a contactor and powering a phase only when
the relationship between the phases will result in the least amount
of stress on the compressor motor.
[0023] The use of POW switching, and the maintaining of pressure
zones using valves, enables the invention to reduce or eliminate
cycling delays for compressors of cooling systems, increasing
efficiency and comfort. Some prior art cooling systems have used
multiple smaller compressors to improve the performance of the
cooling system (e.g., to narrow the temperature control range). The
invention enables the use of a single larger compressor while
achieving the same or better levels of performance and efficiency,
than achieved using multiple smaller compressors.
[0024] FIG. 3A shows a graph of temperature TEMP versus a set
point, and a related on/off indication 400 of a compressor of a
prior art system. When the temperature TEMP is above the set point,
the controller turns the compressor on if a minimum off-cycle-time
has been met. Conversely, when the temperature TEMP is below the
set point, the controller turns the compressor off if a minimum
on-cycle-time has been met. In the graph shown in FIG. 3A, the
temperature is changing faster than the-cycle-times. Thus, there is
a delay of .DELTA.D.sub.1 between when the temperature TEMP rises
above the set point, and when the controller turns the compressor
on. A similar time delay .DELTA.D.sub.2 occurs when the temperature
TEMP drops below the deadband before the controller turns the
compressor off.
[0025] These delays, caused by the cycle times, result in the
compressor running longer (.DELTA.D.sub.2) than necessary, wasting
energy. In addition, the delays (.DELTA.D.sub.1 and .DELTA.D.sub.2)
cause the temperature range (.DELTA.T.sub.1) to be greater than
necessary, potentially causing discomfort to occupants of the area
cooled by the cooling system.
[0026] As shown in FIG. 3B, by being able to turn compressors on
and off at any time (i.e., without cycle delays), and maintaining
pressure in the compressors when they are off, the delays
(.DELTA.D.sub.1 and .DELTA.D.sub.2) are eliminated. In fact, the
compressors can be turned on and off in anticipation of the
temperature being above/below the set-point/deadband
(.DELTA.D.sub.3 and .DELTA.D.sub.4). This reduces energy usage, and
results in a much narrower temperature range (.DELTA.T.sub.2 versus
.DELTA.T.sub.1) increasing the comfort of occupants.
[0027] Various features and advantages of the invention are set
forth in the following claims.
* * * * *