Method of defrosting a multiple heat absorption heat exchanger refrigeration system

A method of operating a refrigeration system. The method includes operating a multi-temperature refrigeration system that has a plurality of heat absorption heat exchangers in a single temperature mode. A number of the plurality of heat absorption heat exchangers are determined that require defrosting a single heat absorption heat exchanger is directed into a different operational state when the number of heat absorption heat exchangers that require defrosting is equal to one. E of the plurality of heat absorption heat exchangers is directed into a defrost mode when the number of heat absorption heat exchangers that requires defrosting is more than one.

BACKGROUND

Typically, refrigeration systems are used to transport and distribute cargo, or more specifically perishable goods and environmentally sensitive goods (herein referred to as perishable goods) that may be susceptible to temperature, humidity, and other environmental factors. Perishable goods may include but are not limited to fruits, vegetables, grains, beans, nuts, eggs, dairy, seed, flowers, meat, poultry, fish, ice, and pharmaceuticals. Advantageously, cold chain distribution systems allow perishable goods to be effectively transported and distributed without damage or other undesirable effects.

Refrigerated trucks and trailers are commonly used to transport perishable goods in a cold chain distribution system. A transport refrigeration system is mounted to the truck or to the trailer in operative association with a cargo space defined within the truck or trailer for maintaining a controlled temperature environment within the cargo space.

Conventionally, transport refrigeration systems used in connection with refrigerated trucks and refrigerated trailers include a transport refrigeration unit having a refrigerant compressor, a condenser with one or more associated condenser fans, an expansion device, and an evaporator with one or more associated evaporator fans, which are connected via appropriate refrigerant lines in a closed refrigerant flow circuit. Air or an air/gas mixture is drawn from the interior volume of the cargo space by means of the evaporator fan(s) associated with the evaporator, passed through the airside of the evaporator in heat exchange relationship with refrigerant whereby the refrigerant absorbs heat from the air, thereby cooling the air. The cooled air is then supplied back to the cargo space. During operation, the cargo space may be accessed frequently, which leads to temperature and moisture variations in the cargo space.

SUMMARY

In one exemplary embodiment, a method of operating a refrigeration system. The method includes operating a multi-temperature refrigeration system that has a plurality of heat absorption heat exchangers in a single temperature mode. A number of the plurality of heat absorption heat exchangers are determined that require defrosting a single heat absorption heat exchanger is directed into a different operational state when the number of heat absorption heat exchangers that require defrosting is equal to one. E of the plurality of heat absorption heat exchangers is directed into a defrost mode when the number of heat absorption heat exchangers that requires defrosting is more than one.

In a further embodiment of the above, the plurality of heat absorption heat exchangers includes at least three heat absorption heat exchangers.

In a further embodiment of any of the above, the single heat absorption heat exchanger requires defrosting.

In a further embodiment of any of the above, the refrigeration system continues to operate in the single temperature mode when the number of heat absorption heat exchangers that require defrosting is equal to one.

In a further embodiment of any of the above, the single heat absorption heat exchanger in the different operational state is fluidly separated from a remainder of the multi-temperature refrigeration system by closing an expansion device corresponding to the single heat absorption heat exchanger.

In a further embodiment of any of the above, a fan associated with the single heat absorption heat exchanger in the different operation state is disengaged when the single heat absorption heat exchanger is located in a frozen compartment.

In a further embodiment of any of the above, the different operational state operates a fan adjacent the single heat absorption heat exchanger when the single heat absorption heat exchanger is located in a perishable compartment.

In a further embodiment of any of the above, It's determined if a second heat absorption heat exchanger requires defrosting in addition to the single heat absorption heat exchanger and directing the refrigeration system into the defrost mode when the single heat absorption heat exchanger and the second heat absorption heat exchanger require defrosting.

In a further embodiment of any of the above, the multi-temperature refrigeration system includes at least three heat absorption heat exchangers.

In a further embodiment of any of the above, each of the plurality of heat absorption heat exchangers is directed into a defrost mode. Each of the plurality of heat absorption heat exchangers is heated with a resistance heater.

In another exemplary embodiment, a controller for a refrigeration system includes a processor and a memory including computer-executable instructions that, when executed by the processor, cause the processor to perform operations. The operations include operating a multi-temperature refrigeration system that has a plurality of heat absorption heat exchangers in a single temperature mode. A number of the plurality of heat absorption heat exchangers that require defrosting is determined. A single heat absorption heat exchanger is directed into a different operational state when the number of heat absorption heat exchangers that require defrosting is equal to one. Each of the plurality of heat absorption heat exchangers is directed into a defrost mode when the number of heat absorption heat exchangers that requires defrosting is.

In a further embodiment of any of the above, the plurality of heat absorption heat exchangers includes at least three heat absorption heat exchangers.

In a further embodiment of any of the above, the single heat absorption heat exchanger requires defrosting.

In a further embodiment of any of the above, the operations further includes continuing to operate the refrigeration system in the single temperature mode when the number of heat absorption heat exchangers that require defrosting is equal to one.

In a further embodiment of any of the above, the operations further includes fluidly separating the single heat absorption heat exchanger in the different operational state from a remainder of the multi-temperature refrigeration system by closing an expansion device that corresponds to the single heat absorption heat exchanger.

In a further embodiment of any of the above, the operations further include a fan associated with the single heat absorption heat exchanger in the different operation state is disengaged when the single heat absorption heat exchanger is located in a frozen compartment.

In a further embodiment of any of the above, the different operational state operates a fan adjacent the single heat absorption heat exchanger when the single heat absorption heat exchanger is located in a perishable compartment.

In a further embodiment of any of the above, the operations further include determining if a second heat absorption heat exchanger requires defrosting in addition to the single heat absorption heat exchanger. The refrigeration system is directed into the defrost mode when the single heat absorption heat exchanger and the second heat absorption heat exchanger require defrosting.

In a further embodiment of any of the above, the multi-temperature refrigeration system includes at least three heat absorption heat exchangers.

In a further embodiment of any of the above, each of the plurality of heat absorption heat exchangers is directed into a defrost mode. Each of the plurality of heat absorption heat exchangers is heated with a resistance heater.

DETAILED DESCRIPTION

FIG.1illustrates a transport refrigeration system20associated with a cargo space22, such as a refrigerated cargo space. A controller24manages operation of the refrigeration system20to establish and regulate a desired product storage temperature within a refrigerated cargo space22. The cargo space22may be the cargo box of a trailer, a truck, a seaboard shipping container or an intermodal container wherein perishable cargo, such as, for example, produce, meat, poultry, fish, dairy products, cut flowers, and other fresh or frozen perishable products, is stowed for transport.

The refrigeration system20includes a refrigerant compression device26, a refrigerant heat rejection heat exchanger28, and a first expansion device30A, a second expansion device30B, and a third expansion device30C in fluid communication with a respective one of a first refrigerant heat absorption heat exchanger32A, a second refrigerant heat absorption heat exchanger32B, and a third refrigerant heat absorption heat exchanger32C in a closed loop refrigerant circuit and arranged in a conventional refrigeration cycle. Although only three heat absorption heat exchangers32A,32B, and32C are shown in the illustrated example, additional heat absorption heat exchangers could be used in connection with additional expansion devices30.

In the illustrated example, the expansion devices30A,30B,30C are electronic expansion valves and a first check valve31A, a second check valve31B, and a third check valve31C is located downstream of a respective first, second, and third heat absorption heat exchanger32A,32B,32C, respectively, to isolate a corresponding heat absorption heat exchanger32A,32B,32C when the controller24closes one or more of the first, second, or third expansion devices30A,30B,30C.

Alternatively, an electronic solenoid valve upstream of a thermal expansion valve could be used for the expansion devices30A,30B, and30C. The controller24would control refrigerant flow through controlling the electronic solenoid valves, while the thermal expansion valve would be mechanically based and operate independently of the controller24.

The refrigeration system20also includes one or more fans34associated with the heat rejection heat exchanger28. Additionally, each of the first, second, and third heat absorption heat exchangers32A,32B, and32C are associated with a respective first, second, and third fan36A,36B, and36C. The refrigeration system20may also include a first, second, and third electric resistance heater38A,38B,38C associated with a respective one of the first, second, and third heat absorption heat exchangers32A,32B, and32C. It is to be understood that other components (not shown) may be incorporated into the refrigerant circuit as desired, including for example, but not limited to, a suction modulation valve, a receiver, a filter/dryer, an economizer circuit.

The heat rejection heat exchanger28may, for example, comprise one or more refrigerant conveying coiled tubes or one or more tube banks formed of a plurality of refrigerant conveying tubes extending between respective inlet and outlet manifolds. The fan(s)34are operative to pass air, typically ambient air, across the tubes of the heat rejection heat exchanger28to cool refrigerant vapor passing through the tubes.

The first, second, and third heat absorption heat exchangers32A,32B, and32C may each, for example, also comprise one or more refrigerant conveying coiled tubes or one or more tube banks formed of a plurality of refrigerant conveying tubes extending between respective inlet and outlet manifolds. The first, second, and third fans36A,36B, and36C are operative to pass air drawn from the temperature controlled cargo space22across the tubes of the heat absorption heat exchanger32to heat refrigerant passing through the tubes and cool the air. The air cooled in traversing the heat absorption heat exchangers32A,32B, and32C is supplied back to the temperature controlled cargo space22.

The refrigerant compression device26may comprise a single-stage or multiple-stage compressor such as, for example, a reciprocating compressor or a scroll compressor.

In the refrigeration system20, the controller24is configured for controlling operation of the refrigeration system20including, but not limited to, operation of various components of the refrigerant system20to provide and maintain a desired thermal environment within the refrigerated cargo space22. The controller24may be an electronic controller including a microprocessor and an associated memory bank. The controller24controls operation of various components of the refrigeration system20, such as the refrigerant compression device26, expansion devices30A,30B,30C, the fans34,36A,36B, and36C, and the electric resistance heaters38A,38B, and38C.

During operation of the refrigeration system20, the first, second, and third heat absorption heat exchangers32A,32B, and32C, are capable of maintaining a respective separate first, second, and third compartment40A,40B,40C at separate temperatures. Alternatively, the first, second, and third heat absorption heat exchangers32A,32B, and32C, are capable of maintaining the respective separate first, second, and third compartments40A,40B,40C at a single temperature. Additionally, diving walls42used to separate the first, second, and third compartments40A,40B,40C in the cargo space22are removable such that the individual first, second, and third compartments40A,40B,40C become a single shared compartment that can be maintained at a single temperature when the controller24directs the refrigeration system20into a single temperature mode.

Depending on the application, the first, second, and third compartments40A,40B, and40C, can be of varying sizes and the respective first, second, and third heat absorption heat exchangers32A,32B, and32C can also be of varying sizes to accommodate the individual compartments. The first, second, and third heat absorption heat exchangers32A,32B, and32C can also have varying water capacities, such that the heat absorption heat exchangers can hold varying amounts of water before the heat absorbing function degrades and a defrost is needed.

Because the first, second, and third heat absorption heat exchangers32A,32B, and32C can be of varying sizes and water capacities, each of the first, second, and third heat absorption heat exchangers32A,32B, and32C may need to be defrosted at varying times. Furthermore, even if the first, second, and third heat absorption heat exchangers32A,32B, and32C were the same size and water capacity, their location within the cargo space22can lead to each of the heat absorption heat exchangers32A,32B, and32C requiring a defrosting at different times.

For example, when one of the first, second, and third heat absorption heat exchangers32A,32B, and32C is located near an access opening44in the cargo space22, that one heat exchanger will likely have to manage a greater amount of moisture in the air due to moisture entering the cargo space22through the access opening44during loading and unloading. Therefore, instead of placing all of the heat absorption heat exchangers32A,32B, and32C into a defrost mode when any one of the heat absorption heat exchangers32A,32B, and32C require defrosting, the control logic discussed below and illustrated inFIG.2will manage defrosting of the refrigeration system20.

FIG.2illustrates a flow diagram200of a method of operating the refrigeration system20. The method begins at block202with the refrigeration system20operating in a single temperature mode. In the illustrated example, the refrigeration system20is capable of operating each of the first, second, and third heat absorption heat exchangers32A,32B, and32C at varying degrees of refrigeration with the controller24controlling a respective one of the first, second and third, expansion devices30A,30B,30C.

During operation of the refrigeration system20, the controller24could determine that at least one of the first, second, and third heat absorption heat exchangers32A,32B,32C requires defrosting due to decreased cooling capacity from ice formation. If the controller24determined that more than 1 of the heat absorption heat exchangers32A,32B,32C requires defrosting (block204), the controller24will direct all of the heat absorption heat exchangers32A,32B,32C into a defrost mode (block206).

By requiring more than one of the heat absorption heat exchangers32to require defrosting before entering the defrosting mode for the refrigeration system20, the refrigeration system20as a whole will not be limited by the water capacity of the smallest heat absorption heat exchanger32A,32B,32C in the refrigeration system20. This allows the refrigeration system20to run for longer periods of time without being interrupted for defrosting. Once the refrigeration system20has passed through the defrosting mode, the system will continue to operate in the single temperature mode (block202).

If the controller24determines that refrigeration system does not have more than one heat absorption heat exchangers32requiring a defrost (block204), the controller will determine if a single heat absorption heat exchanger32requires a defrost (block208). Generally, first heat absorption heat exchanger32A will function as the master heat exchanger and have the greatest amount of cooling capacity and water capacity. The second and third heat absorption heat exchangers32B and32C have a reduced amount of cooling capacity and liquid retention when compared to the first heat absorption heat exchanger32A.

Because the second and third heat exchangers32B and32C have reduced water capacity compared to the first heat absorption heat exchanger32A, the second and third heat absorption heat exchangers32B and32C will likely require defrosting more frequently. Additionally, it is likely that the second and third heat absorption heat exchangers32B and32C are located in a portion of the cargo space22closer to the access opening44such that they will be impacted more by moisture entering the cargo space22during loading and unloading than the first heat absorption heat exchanger32A.

If the controller determines that only a single heat absorption heat exchanger32requires defrosting, the controller24will direct the single heat absorption heat exchanger32into a different operational state while continuing to operate the refrigeration system20in the single temperature mode (block210). The different operational state can include fluidly isolating the single heat absorption heat exchanger32from the refrigeration system20by closing the corresponding expansion device30. Additionally, the controller24can cause the corresponding fan36to continue to run even though heat exchanger has been fluidly isolated when the single heat absorption heat exchanger32is in a perishable compartment or disengaging the corresponding fan36when the single heat absorption heat exchanger32is in a frozen compartment.

Alternatively, the controller24can continue to allow refrigerant to run through the single heat absorption heat exchanger32in the different operational state in a regular manner. The controller24will continue to determine if more than one heat absorption heat exchanger32requires a defrost (block212). If the controller24determines that more than one heat absorption heat exchanger32requires a defrost, the controller24will direct all of the heat absorption heat exchangers32A,32B,32C into a defrost mode (block206). If only the single heat absorption heat exchanger32continues to require a defrost, the controller24will maintain the single heat absorption heat exchanger32in the different operational state (block214) while continuing to monitor for an addition heat absorption heat exchanger32requiring a defrost (block212).