Transportation refrigeration system with unequal sized heat exchangers

A transportation refrigeration system includes a refrigeration circuit that includes a compressor, a condenser, a first expansion device upstream of a first heat exchanger and a second expansion device upstream of a second heat exchanger. The first heat exchanger includes a first cooling capacity that is different from a second cooling capacity of the second heat exchanger.

BACKGROUND

This application relates to refrigeration systems having at least two heat absorption heat exchangers in parallel for cooling an enclosed cargo space.

Refrigeration systems are known. Generally, a compressor compresses a refrigerant and delivers it into a condenser. The refrigerant is cooled and passes through an expansion valve. The refrigerant is expanded and passes through an evaporator. The evaporator cools air to be delivered into an environment to be conditioned.

One application for such refrigeration systems is in a transportation refrigeration system. As an example, a truck may have a refrigerated trailer. It is known to provide distinct temperatures at distinct compartments within a common trailer. Individual refrigeration circuits are often utilized to provide the distinct temperatures.

SUMMARY

In one exemplary embodiment, a transportation refrigeration system includes a refrigeration circuit that includes a compressor, a condenser, a first expansion device upstream of a first heat exchanger and a second expansion device upstream of a second heat exchanger. The first heat exchanger includes a first cooling capacity that is different from a second cooling capacity of the second heat exchanger.

In a further embodiment of the above, a first compartment passageway has a first compartment passageway inlet that is located upstream of the first heat exchanger. A first fan is located downstream of the first heat exchanger.

In a further embodiment of any of the above, a first nozzle is downstream of the first fan and has a first compartment outlet.

In a further embodiment of any of the above, a second compartment passageway has a second compartment passageway inlet that is located upstream of the second heat exchanger. A second fan is located downstream of the second heat exchanger.

In a further embodiment of any of the above, a second nozzle is downstream of the second fan and has a second compartment outlet.

In a further embodiment of any of the above, the first compartment outlet is spaced from the second compartment outlet.

In a further embodiment of any of the above, the first cooling capacity is greater than the second cooling capacity. The first fan includes a first maximum flow rate. The second fan includes a second maximum flow rate that is less than the first maximum flow rate.

In a further embodiment of any of the above, the first cooling capacity includes at least 55% of a total cooling capacity of the refrigeration system. The second cooling capacity includes no more than 45% of the total cooling capacity of the refrigeration system.

In a further embodiment of any of the above, the first cooling capacity includes at least two thirds of the total cooling capacity of the refrigeration system. The second cooling capacity includes no more than one third of the total cooling capacity of the refrigeration system.

In a further embodiment of any of the above, the first heat exchanger includes a first fin density and the second heat exchanger includes a second fin density. The first fin density is different from the second fin density.

In a further embodiment of any of the above, the first heat exchanger includes a first exchanger face surface area. The second heat exchanger includes a second exchanger face surface area. The first exchanger face surface area is greater than the second exchanger face surface area.

In a further embodiment of any of the above, the first expansion device is a first electronically controlled expansion valve. The second expansion device is a second electronically controlled expansion valve. A controller is configured to control refrigerant flow to the first heat exchanger by controlling the first electronically controlled expansion valve. The controller is configured to control refrigerant flow to the second heat exchanger by controlling the second electronically controlled expansion valve.

In another exemplary embodiment, a method of operating a refrigeration cycle includes the steps of conditioning a first compartment in a cargo space to a first temperature with a first heat exchanger that has a first cooling capacity. A second compartment in the cargo space is conditioned to a second temperature with a second heat exchanger that has a second cooling capacity. The first cooling capacity is greater than the second cooling capacity.

In a further embodiment of any of the above, the first cooling capacity includes at least 55% of a total cooling capacity of the refrigeration system. The second cooling capacity includes no more than 45% of the total cooling capacity of the refrigeration system.

In a further embodiment of any of the above, the first cooling capacity includes at least two thirds of the total cooling capacity of the refrigeration system. The second cooling capacity includes no more than one third of the total cooling capacity of the refrigeration system.

In a further embodiment of any of the above, the first heat exchanger includes a first fin density and the second heat exchanger includes a second fin density. The first fin density is different from the second fin density.

In a further embodiment of any of the above, the first heat exchanger includes a first exchanger face surface area. The second heat exchanger includes a second exchanger face surface area. The first exchanger face surface area is greater than the second exchanger face surface area.

In a further embodiment of any of the above, a first fan associated with the first heat exchanger is operated at a first maximum flow rate. A second fan associated with the second heat exchanger is operated at a second maximum flow rate that is less than the first maximum flow rate.

In a further embodiment of any of the above, the method of operating the first fan includes drawing air from the first compartment into a first compartment passageway inlet, over the first heat exchanger and through a first nozzle having a first compartment passageway outlet.

In a further embodiment of any of the above, the method of operating the second fan includes drawing air from the second compartment into a second compartment passageway inlet, over the second heat exchanger and through a second nozzle having a second compartment passageway outlet spaced from the first compartment passageway outlet.

DETAILED DESCRIPTION

FIG. 1illustrates a transport refrigeration system20associated with a cargo space22, such as a refrigerated cargo space. In the illustrated example, the cargo space22is divided into a first compartment22A and a second compartment22B by a dividing wall23.

A controller24manages operation of the refrigeration system20to establish and regulate a desired product storage temperature within the first compartment22A and the second compartment22B of the 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, a first expansion device30A, a second expansion device30B, a first refrigerant heat absorption heat exchanger32A, and a second refrigerant heat absorption heat exchanger32B connected in a closed loop refrigerant circuit and arranged in a conventional refrigeration cycle. The first and second expansion devices30A,30B can be electrically controlled expansion valves controlled by the controller24to regulator refrigerant flow through each of the first and second heat absorption heat exchangers32A,32B, respectively. The refrigeration system20also includes one or more fans34associated with the heat rejection heat exchanger28and a first and second fan36A,36B associated with each of the first and second heat absorption heat exchangers32A,32B. In one example, the first and second heat absorption heat exchangers32A,32B are evaporators.

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 refrigerant heat rejection heat exchanger28to cool refrigerant vapor passing through the tubes.

The first and second heat absorption heat exchangers32A,32B may, 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 and second fans36A,36B are operative to pass air drawn from the temperature controlled cargo space22across the tubes of the heat absorption heat exchangers32A,32B to heat the refrigerant passing through the tubes and cool the air. The air cooled in traversing the heat absorption heat exchangers32A,32B is supplied back to a respective first and second compartments22A,22B in the cargo space22.

Prior to entering the refrigerant compression device26, the refrigerant passes through an outlet valve38. The outlet valve38controls a pressure and state of the refrigerant entering the refrigerant compression device26. 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 the various components of the refrigerant system20to provide and maintain a desired operating temperature within the 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, the first and second expansion devices30A,30B, the fans34,36A,36B, and the outlet valve38.

FIG. 2schematically illustrates air flow from the first and second compartments22A,22B through a respective first and second heat absorption heat exchanger32A,32B. The air flow from the first compartment22A flows through a first compartment passageway40A and back into the first compartment22A. The first compartment passageway40A includes a first compartment passageway inlet42A that accepts air from the first compartment22A into the first compartment passageway40A. From the first compartment passageway inlet42A, the air is drawn by the first fan36A over the first heat absorption heat exchanger32A and into a first nozzle44A. From the first nozzle44A, the air exits the first compartment passageway40A through a first compartment passageway outlet46A and travels back into the first compartment22A.

Similarly, the air flow from the second compartment22B flows through a second compartment passageway40B and back into the second compartment22B. The second compartment passageway40B includes a second compartment passageway inlet42B that accepts air from the second compartment22B into the second compartment passageway40B. From the second compartment passageway inlet42B, the air is drawn by the second fan36B over the second heat absorption heat exchanger32B and into a second nozzle44B. From the second nozzle44B, the air exits the second compartment passageway40B through a second compartment passageway outlet46B and travels back into the second compartment22B.

In the illustrated example, one of the first and second compartments22A,22B could be used to store perishable goods and the other of the first and second compartments22A,22B could be used to store frozen goods. Because the first and second compartments22A,22B are used to maintain products at different temperatures, the first and second heat absorption heat exchangers32A,32B do not need to be the same size or have the same cooling capacity.

The cooling capacities of the first and second absorption heat exchangers32A,32B are determined at a common set point temperature to eliminate capacity variation resulting from different air input temperatures. The first and second heat absorption heat exchangers32A,32B also each include a first exchanger face surface area and a second exchanger face surface area, respectively. The first and second exchanger face surface area are determined from a length and width of a respective inlet surface on the first and second heat absorption heat exchanger accepting the air from the cargo space22.

For example, if the first heat absorption heat exchangers32A is used to maintain the first compartment22A at a temperature for frozen goods and the second heat absorption heat exchanger32B is used to maintain the second compartment22B at a temperature for perishable goods, the first heat absorption heat exchanger32A is larger than the second heat absorption heat exchanger32B. The variation in size between the first and second heat absorption heat exchangers32A,32B can include varying a cooling surface area, fin density, number of coils, and/or number of coil banks between the first and second heat absorption heat exchangers32A,32B.

In one example, at least 55% of the total cooling capacity of the refrigeration system20is performed by the first heat absorption heat exchanger32A and no more than 45% of the total cooling capacity is performed by the second heat absorption heat exchanger32B. In another example, at least 60% of the total cooling capacity of the refrigeration system20is performed by the first heat absorption heat exchanger32A and no more than 40% of the total cooling capacity is performed by the second heat absorption heat exchanger32B. In yet another example, at least two thirds of the total cooling capacity of the refrigeration system20is performed by the first heat absorption heat exchanger32A and no more than one third of the total cooling capacity is performed by the second heat absorption heat exchanger32B.

Furthermore, because the first and second heat absorption heat exchangers32A,32B have different cooling capacities to meet the needs for the first and second compartments22A,22B, the first and second fans36A,36B are able to operate independently of each other as controlled by the controller24. Because the first and second fans36A,36B operate independently, the refrigeration system20is able to operate more efficiently by operating the first and second fans36A,36B at an optimal speed that does not exceed demand. In addition to variable speeds between the first and second fans36A,36B, the first and second fans36A,36B can have different maximum flow rates to meet the needs of the first and second compartments22A,22B.

Additionally, because the first and second heat absorption heat exchangers32A,32B are independently sized to the cooling needs of the first and second compartments22A,22B, the heat absorption heat exchanger that is more susceptible to icing can be enlarged to have a greater liquid capacity to reduce the frequency defrosting without adversely impacting the other heat absorption heat exchanger.