Patent Application
20130025304
The invention relates to cycling of compressors, specifically rapid cycling of scroll compressors.
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).
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.
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.
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.
Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings.
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.
The examples described below show various cooling systems. However, the invention has application in other constructions such as heat pumps as well.
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).
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.
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.
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.
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.
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.
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.
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.
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.
These delays, caused by the cycle times, result in the compressor running longer (ΔD2) than necessary, wasting energy. In addition, the delays (ΔD1 and ΔD2) cause the temperature range (ΔT1) to be greater than necessary, potentially causing discomfort to occupants of the area cooled by the cooling system.
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Various features and advantages of the invention are set forth in the following claims.
