Patent Publication Number: US-9903627-B2

Title: Method of operating an air conditioning system including reducing the energy consumed by the compressor crank case heaters

Description:
BACKGROUND OF THE INVENTION 
     The subject matter disclosed herein relates to climate control systems. More specifically, the subject disclosure relates to crank case heater operation for packaged air conditioning units. 
     Compressors are utilized in heating, cooling and refrigeration applications. These compressors require oil or other lubricant to lubricate moving parts of the compressor. The oil is housed in a crank case from where it is drawn into moving parts of the compressor. During normal operation of the refrigeration circuit, operating pressures and temperatures tend to keep the oil free from liquid refrigerant. When the compressor is not operating, however, refrigerant in the system tends to migrate to and condense in the coldest parts of the system, one of which is often the compressor crank case. Under such conditions, there is a danger that the crank case oil will be diluted with refrigerant reducing its viscosity to the point where if the compressor is then restarted, damage may occur. Crank case heaters are utilized to boil off the refrigerant from the crank case and to prevent migration of the refrigerant thereto. 
     Many packaged air conditioning units, such as those servicing large buildings or spaces, include multiple interlinked air conditioning circuits. Each circuit may include at least one compressor, at least one condenser, at least one evaporator, and at least one expansion valve. Each compressor in the air conditioning unit has a crank case heater connected to it to boil off liquid refrigerant when the compressor is in “off” mode. 
     In some environments, the compressors operate mostly on a seasonal basis, during which the compressors may sit idle for extended time periods, for example 3 to 6 months at a time. In current systems, the crank case heater for each compressor is then in operation for the entire time the compressors are idle to boil off the liquid refrigerant. This results in substantial energy usage by the crank case heaters. 
     BRIEF DESCRIPTION OF THE INVENTION 
     According to one aspect of the invention, a method of operating an air conditioning system includes cooling a selected space with the air conditioning system. The air conditioning system includes two or more compressors and two or more crank case heaters. Each crank case heater of the two or more crank case heaters is associated with a compressor of the two or more compressors. Operation of the two or more compressors is stopped, thus initiating operation of the two or more crank case heaters. The air conditioning system is switched to a conservation mode, including de-powering at least one compressor of the two or more compressors and an associated at least one crank case heater or the two or more crank case heaters thereby reducing energy consumption of the two or more crank case heaters. 
     According to another aspect of the invention, an air conditioning system includes two or more compressors and two or more crank case heaters. Each crank case heater is associated with a compressor of the two or more compressors to prevent condensation of refrigerant in a compressor lubricant crank case. At least one crank case heater of the two or more crank case heaters and at least one compressor of the two or more compressors are de-powered upon the air conditioning system entering a conservation mode to reduce energy consumption by the two or more crank case heaters. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1  is a schematic illustration of an embodiment of an air conditioning system; and 
         FIG. 2  is a schematic illustration of a method of operating an air conditioning system. 
     
    
    
     The detailed description explains the invention, together with advantages and features, by way of examples with reference to the drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Shown in  FIG. 1  and  FIG. 2  are schematic illustrations of an embodiment of a packaged air conditioning system  10  servicing a designated portion  24  of a building  12 , or other space. The air conditioning system  10  includes one or more air conditioning circuits  14 , each air conditioning circuit  14  including multiple compressors  16 , for example, four compressors  16  arranged in parallel, at least one condenser  18 , at least one expansion valve  20  and at least one evaporator  22 . While the embodiment of  FIG. 1  includes four compressors  16  in the air conditioning circuit  14 , it is to be appreciated that air conditioning systems  10  may include other quantities of compressors  16 , for example, 2, 8 or more compressors  16 . Each air conditioning circuit  14  may be assigned to cool the designated portion  24  of the building  10 , with operation of the air conditioning circuit  14  triggered by a thermostat  26  disposed in the designated portion  24  and operably connected to a control unit  28  of the air conditioning circuit  14 . 
     During normal operation of the air conditioning system  10 , when a temperature at the thermostat  26  in the designated portion  24  exceeds a threshold temperature or set point, the thermostat  26  signals the control unit  28 , which begins operation of the air conditioning circuit  14  by starting operation of the compressors  16 . Refrigerant flows through the circuit  14 , through the compressors  16 , condenser  18 , expansion valve  20  and evaporator  22 . A fan  40  blows air across the evaporator  22 , cooling the air, which is flowed into the designated portion  24 . When air temperature at the thermostat  26  is lowered to or under the set point, within a designated tolerance, the thermostat  26  signals the control unit  28  again, which stops operation of the compressors  16 . During typical operation of the air conditioning system  10 , once the compressors  16  are stopped by the control unit  28 , the control unit  28  subsequently starts operation of crank case heaters  30  disposed at a crank case  32  of each compressor  16 . The crank case  32  houses lubricant for the compressor  16 , and when the compressor  16  is turned off, refrigerant tends to migrate to and condense in the crank case  32 . The crank case heater  30  for each compressor  16  is used to boil off any liquid refrigerant in the crank case  32  and prevent additional refrigerant from condensing therein. 
     When installed in some environments, the compressors  16  may not operate for extended periods of time. For example, during a local winter season, the compressors  16  may not operate for 3 to 6 months. To conserve energy during these extended times of inactivity, the air conditioning system  10  is switched into a conservation mode, or winter mode. In winter mode, one or more of the compressors  16   a  and associated crank case heaters  30   a  are taken off line by the controller  28 . For example, in circuits  14  including four compressors  16 , two or three compressors  16   a  and crank case heaters  30   a  are taken off line and are not operational when the controller  28  has selected winter mode for operation. When there are needs for compressor  16  operation and cooling during such winter mode periods, it will typically be a low-load need, so the remaining operational compressor  16   b  or compressors  16   b  may be started in order to provide this periodic cooling. When the system  10  is switched from winter mode to normal mode, the offline compressors  16   a  and associated crank case heaters  30   a  are powered, and before starting operation of the compressors  16   a , the crank case heaters  30   a  are operated for a selected time, for example, 24 hours, prior to starting operation of the compressors  16   a.    
     Switching of the system  10  to and from winter mode at the controller  28  may be accomplished by any of several means. In some embodiments, the switch to and from winter mode is determined by a calendar date range programmed into the controller  28 . In other embodiments, the switch may be determined by an algorithm using trends in exterior air temperature and/or other factors. Finally, in other embodiments, the system  10  may be switched to or from winter mode manually by an operator at the controller  28 . 
     In winter mode, only the crank case heaters  30   b  corresponding to the operational compressors  16   b  are powered. Thus a significant energy savings may be realized. 
     While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.