Abstract:
A cooling system that has an electrical controller that controls an electric expansion valve and the defrost cycle using a reversing valve. The need for heater circuit to achieve defrost is eliminated. The system permits the defrosting the evaporator system in less time required for conventional defrost methods. The cooling system also eliminates the need for a head pressure control valve and check valves. Due to the less wiring and lower operating costs, the invention provides significant cost savings.

Description:
This invention relates generally to space cooling systems, in particular to apparatus for controlling a space cooling system with respect to the defrost cycle. This application claims benefit of priority under 35 U.S.C. §119(e) to U.S. Provisional Application Ser. No. 60/485,836 filed on Jul. 10, 2003. 

   BACKGROUND OF THE INVENTION 
   Field of the Invention 
   A typical space cooling system includes at least one evaporator system contained within the space that is to be cooled, a condenser system that is located outside of the cooled space, and a compressor positioned between the condenser system outlet and the evaporator system inlet and, finally, an expansion valve which completes the loop joining together the condenser system outlet and the evaporator system inlet. A refrigerant is circulated within the loop which cools the space as follows. The refrigerant is compressed by the compressor which raises the temperature and pressure of the refrigerant. The hot pressurized refrigerant gas then flows through the condenser system which serves as heat exchanger to allow the refrigerant to dissipate the heat of pressurization. The refrigerant condenses into a liquid and then flows through the expansion valve, where the liquid refrigerant moves from a high pressure zone into a low pressure zone, thus expanding and evaporating. In evaporating, the refrigerant becomes cold where it then passes into coils of the evaporator, thus absorbing heat from inside the space that is to be cooled and the cycle then repeats until the space reaches the desired temperature. 
   In addition to these major components, additional components are also included. A fan assist the heat transfer from the cooled space to the coils of the evaporator system and another fan is used to assist the heat transfer from the coils of the condenser to outside environment. A negative pressure differential is present on the evaporator outlet when the device is operating in a refrigeration mode thereby suctioning the gas refrigerant to the compressor. Further, thermistor sensors are placed at the inlet and outlet of the evaporator system for measuring the level of superheat across the evaporator. A sensor located on the outlet side of the compressor measures the discharge temperature of compressor. The ambient temperature of the spaced to be cooled is measured by still another sensor. Finally, the need to defrost the evaporator from any ice build-up due to the cooling process is determined by another sensor that is associated with evaporator so that defrosting procedures can be monitored. 
   There are two basic options for providing a defrost cycle. U.S. Pat. No. 5,551,248, issued to Derosier on Sep. 3, 1996, discloses the use of a controller to control the operation of a space cooling system. While this device permits the use of an electrically controlled expansion valve, either utilizing an electrically operated solenoid or an electrically operated step motor, Derosier also teaches the use of heater which is activated on a programmed time schedule, either a time between successive defrost cycles or a compressor run time. The use of heater for providing defrost function requires the additional expense of the heater as well as associated valving, piping and supply wiring connections. Additionally, there must a pumpdown condition present before defrost procedures can begin and the fans must remain on during pumpdown. 
   Another option is disclosed by Russell of Brea, Calif. in its HIGH SIERRA model refrigeration device. This device teaches the use of reversing valve which permits the elimination of the heater. However, the HIGH SIERRA model requires the use of check valve at the outlet of the compressor and another check valve in the drain pan circuit as well as additional piping and connection fittings. Most importantly, the HIGH SIERRA model does not disclose or suggest the use of an electrical controller which permits, among other things, the use of electrically controlled expansion valve such as taught by Derosier. 
   An refrigeration apparatus that has both an electrical controller that responds to evaporator superheat and return air temperature to the expansion valve as well as controls a reversing valve which provides for a defrosting cycle, eliminates the need for electric heaters, check valves, head pressure control valve as well as the associated piping and connections is not found in the prior art. 
   SUMMARY OF THE INVENTION 
   It is an aspect of the invention to provide a refrigeration system that provides an electrical controller that controls the electric expansion valve and the defrost cycle using a reversing valve. 
   It is another aspect of the invention to provide a refrigeration system that eliminates the need for a heater circuit to achieve a defrost of the evaporator system. 
   It is still another aspect of the invention to provide a refrigeration system that permits defrosting the evaporator system in less than the time required for a conventional electronic defrost system. 
   Further, another aspect of the invention is to provide a refrigeration system that leaves the evaporator coil virtually clean after each defrost cycle. 
   It is another aspect of the invention to provide a refrigeration system that eliminates the need for a head pressure control valve. 
   Another aspect of the invention is to provide a refrigeration system that eliminates the need for check valves and an expansion valve at the condenser. 
   Still another aspect of the invention is to provide a refrigeration system that has less wiring and is less expensive to produce and operate than present devices. 
   It is another aspect of the invention to provide a refrigeration system that requires no pumpdown before the defrost cycle has been initiated. 
   It is another aspect of the invention to provide a refrigeration system that enables the compressor to run during defrost. 
   It is still another aspect of the invention to provide a refrigeration system wherein the need to defrost is determined by the controller and defrost will only occur when it is necessary thus saving energy costs associated with unnecessary defrost. 
   Finally, it is another aspect of the invention to provide a refrigeration system that prevents steaming and heat from being introduced into the cooled space during the defrost cycle. 
   These and other aspects of the invention will become apparent in light of the detailed description of the invention which follows. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic of the most basic embodiment of the invention operating during a refrigeration cycle. 
       FIG. 2  is a schematic of the embodiment shown in  FIG. 1  operating during a defrost cycle. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   While certain representative embodiments of the invention have been described herein for the purposes of illustration, it will be apparent to those skilled in the art that modification therein may be made without departure from the spirit and scope of the invention. Like parts are referenced in the specification and accompanying figures with the same reference call out numbers. Note that the drawings are not necessarily to scale and that some elements may be larger or smaller or otherwise oriented to more clearly depict the important features of the invention. 
   As shown in  FIG. 1 , which depicts the basic elements of the invention  10 , the refrigeration cycle is similar to that discussed above for the typical space cooling device discussed in the background. However, note that unlike prior art devices, invention  10  includes both a controller  12  and a reversing valve  24  which are discussed below. Refrigerant (not shown) is compressed by the compressor  26 . The temperature and pressure of the refrigerant is raised. The hot pressurized refrigerant gas then flows through the reversing valve  24  to the condenser system  22 . As above, condenser system  22  functions as a heat exchanger to allow the refrigerant to dissipate the heat of pressurization. The refrigerant condenses into a liquid and then flows through the expansion valve  20 , where the liquid refrigerant moves from a high pressure zone into a low pressure zone, thus expanding and evaporating. Electric expansion valve  20  is preferably a step motor such as manufactured by companies such as Sporlan, Alco, Parker or Danfoss. The refrigerant flow of the electric expansion valve  20  is controlled by controller  12  and is modulated to control the superheat of the evaporator  28 . The superheat of evaporator  28  is determined by measuring sensor  16  and  18  using techniques well known in the art. In evaporating, the refrigerant then passes into coils of the evaporator  28 , thus absorbing heat from inside the space  30  that is to be cooled and the cycle then repeats until the space reaches the desired temperature as provided by sensor  14 . 
   The controller  12  can be set to defrost mode that is either electric (using standard heater technology) or reverse cycle (utilizing the instant invention). When the reverse cycle defrost option is selected, the following sequence will be used as shown in  FIG. 2 . 
   When there is a demand for defrost whether by set time schedule or manual defrost or demand defrost as determined by the controller  12 , the controller  12  sends a signal to reverse valve assembly  24 . Reverse valve assembly  24  is readily available from companies such as Ranco, Alco, Danfoss and Sanhua. This type of valve is typically used on heat pumps. As shown in  FIG. 2 , the refrigerant flows change from refrigerating cycle to defrost cycle. 
   Simultaneously, the electrical expansion valve  20  is forced open ranging from 40% to 60% of maximum. Controller  12  then checks sensors  16  and  18 . If the temperature at sensor  18  indicates that it is greater than or equal to the defrost termination temperature (DTT), the defrost ends and then goes to a drip mode. The default setting on controller  12  is preferably ranges from 40° F. to approximately 50° F. If 40° F.&gt;Sensor  16 −DTT&gt;20° F., expansion valve  20  is changed ranging from 20% to 30% of the fully open position. The temperature monitored at sensor  16  will keep rising. If 99° F.&gt;sensor  16 &gt;=40° F.+DTT, the controller  12  will again close the expansion valve  20  ranging from 5% to 15% of the fully open position. Sensor  18  will continue to be monitored to determine whether the DTT temperature has been reached. As noted, once it has, the defrost ends. This process will repeat until sensor  18  indicates that the DTT temperature has been reached and then defrost ends. 
   The sensor  18  is monitored continuously by controller  12  to determine the coil temperature rise of evaporator  28  relative to the DTT temperature. When the temperature reading on sensor  18  is greater than or equal to the pre-set DTT, defrost is considered to be complete and controller  12  will enter the drip mode and close the expansion valve  20  completely. Compressor  26  may pumpdown the refrigerant and may be cut off by the low-pressure control of compressor  26 . While the compressor  26  is engaged in the pumpdown mode, the evaporator fans (not shown) remain off. Compressor  26  may also be shut off by controller  12  if so wired. 
   Reversing valve assembly  24  is not de-energized until the end of the drip mode. The refrigerant flows change from defrost cycle to refrigerating cycle when controller  12  enters the fan delay mode (cool mode if the fan delay mode is skipped) after drip mode. If the pumpdown after a defrost cycle takes longer than drip medel mode, the controller  12  will enter fan delay mode even though the pumpdown may not be completed. For example, if a pumpdown takes 4 minutes to complete and the drip time is pre-set to 3 minutes, when the 3 minute drip time expires, controller  12  will enter fan delay mode and expansion valve  20  will be modulating. Note the compressor  26  may be running through pumpdown mode, drip mode and fan delay mode. A reverse cycle defrost is considered complete when the controller  12  enters the fan delay mode. As noted above, when there is no defrost, all operations are the same as current version of the applicant&#39;s electric expansion valve refrigeration control system which is well known in the art. 
   Although the present invention has been described in considerable detail with reference to certain preferred versions thereof, other versions would be readily apparent to those of ordinary skill in the art. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred versions contained herein.