shogun7
27-04-2004, 03:33 AM
When refrigeration engineers design supermarkets, they tend to use reach-in glass door cabinets as their low-temperature display cases. Although this makes shopping a little less convenient for customers, they are less problematic than open display cases because open display cases at low temperatures are more sensitive to a store’s environment.
Engineers will use either mechanical or electronic temperature controls to regulate case temperature; electronic controllers are used more often today. The temperature controls are wired to control either a liquid line solenoid or suction stop valve, depending on the design.
The refrigeration system normally is tied into a parallel rack system located either on the roof or at the rear of the building. To ensure that the evaporator is fully active, a service technician can measure the superheat at the outlet of the evaporator coil. An acceptable superheat setting for the thermostatic expansion valve on these cases is 3 F to 5 F. This will ensure that the evaporator is being used to its fullest capacity and that there is no liquid returning to the compressors at the rack.
When checking or adjusting the superheat setting, it is important to make sure the evaporator is not iced over and that the case is within 10 F of its desired operating temperature. When making adjustments be sure not to make more than 1/4 to 1/2 turn at a time. Once an adjustment has been made let the system stabilize for a minimum of 15 minutes, recheck the setting and make any additional adjustments.
The defrost systems on reach-in glass door cases can be either electric heaters or hot gas, and the service technician must be able to identify which defrost system is being used. Exposing the electrical wiring at the kickplate and inspecting it can aid the technician in identifying the type of defrost system. Each system has its advantages. The electric defrost systems normally will obtain a better and less problematic defrost, but are more costly to operate. Hot gas systems essentially are cost-free since they employ the system’s hot gas to defrost the evaporator. However, these systems are more problematic and can cause an incomplete defrost of the evaporator coil if not properly set up.
The service technician may need to adjust the termination setting to allow the case to properly defrost. A common location for the defrost termination sensor is at the return elbow at the coil end opposite the thermostat expansion valve. On some electric defrost systems, it may be located upstream of the evaporator coil in the rear channel of the case. On some hot gas systems it may be located on the dump line of the evaporator.
A typical setting for termination is 55 F to 60 F for hot gas systems and 65 F to 75 F for electric defrost. The actual termination setting should be obtained from the manufacturer’s specifications.
Engineers will use either mechanical or electronic temperature controls to regulate case temperature; electronic controllers are used more often today. The temperature controls are wired to control either a liquid line solenoid or suction stop valve, depending on the design.
The refrigeration system normally is tied into a parallel rack system located either on the roof or at the rear of the building. To ensure that the evaporator is fully active, a service technician can measure the superheat at the outlet of the evaporator coil. An acceptable superheat setting for the thermostatic expansion valve on these cases is 3 F to 5 F. This will ensure that the evaporator is being used to its fullest capacity and that there is no liquid returning to the compressors at the rack.
When checking or adjusting the superheat setting, it is important to make sure the evaporator is not iced over and that the case is within 10 F of its desired operating temperature. When making adjustments be sure not to make more than 1/4 to 1/2 turn at a time. Once an adjustment has been made let the system stabilize for a minimum of 15 minutes, recheck the setting and make any additional adjustments.
The defrost systems on reach-in glass door cases can be either electric heaters or hot gas, and the service technician must be able to identify which defrost system is being used. Exposing the electrical wiring at the kickplate and inspecting it can aid the technician in identifying the type of defrost system. Each system has its advantages. The electric defrost systems normally will obtain a better and less problematic defrost, but are more costly to operate. Hot gas systems essentially are cost-free since they employ the system’s hot gas to defrost the evaporator. However, these systems are more problematic and can cause an incomplete defrost of the evaporator coil if not properly set up.
The service technician may need to adjust the termination setting to allow the case to properly defrost. A common location for the defrost termination sensor is at the return elbow at the coil end opposite the thermostat expansion valve. On some electric defrost systems, it may be located upstream of the evaporator coil in the rear channel of the case. On some hot gas systems it may be located on the dump line of the evaporator.
A typical setting for termination is 55 F to 60 F for hot gas systems and 65 F to 75 F for electric defrost. The actual termination setting should be obtained from the manufacturer’s specifications.