Internal air circulation control in a refrigerated transport container

Abstract

Disclosed is a system for and a method of controlling internal air circulation within a refrigerated transport container (1), the refrigerated transport container (1) comprising a cooling unit (40), and a control unit, where the cooling unit (40) comprises at least a compressor (6) and an evaporator (16) comprising one or more evaporator fans (10) wherein the method comprises the step of: controlling the operation of the one or more evaporator fans (10) based on one or more predetermined heat load related indicators during periods where the compressor (6) is inactive wherein the one or more evaporator fans (10) are controlled to increase internal air circulation when the one or more predetermined heat load related indicators indicate a heat load increase and wherein the one or more evaporator fans (10) are controlled to decrease internal air circulation when the one or more predetermined heat load related indicators indicate a heat load reduction.

Description

[0001]Disclosed is a method for and system of controlling internal air circulation within a refrigerated transport container.BACKGROUND OF THE INVENTION[0002]Temperature in a refrigerated storage space is controlled within a temperature range adjacent to a setpoint temperature. The refrigerated storage space may for example comprise a transport volume of a refrigerated transport container. The setpoint temperature is chosen to keep the perishable produce such as meat, vegetables and fruit, at correct temperatures to avoid quality degradation. It is known in the art to apply temperature control protocols that selectively control operational states of heating units, cooling devices and evaporator fans, coupled to the refrigerated transport container, in order to maintain a setpoint or target air temperature inside the refrigerated transport container.[0003]One typical cooling unit or refrigeration unit used in refrigerated storage transport containers is based on the so-called vapour ...

AI Technical Summary

Benefits of technology

[0014]Adjusting the internal air circulation according to one or more predetermined heat load related indicators provides energy efficient operation while not or hardly increasing the temperature distribution throughout the container's transport volume.

[0093]In this way, emphasis on minimizing temperature distribution in the transport volume is provided and gives up the effort to save energy in specific temperature setpoint ranges. This is an attractive way of minimizing the risk of temperature-abuse in specific temperature segments in which extremely temperature-critical and valuable cargoes are frequently carried.

Problems solved by technology

In connection with evaporator fan systems having only two states (ON, OFF) and switching between these two states, energy usage is not efficient as the power consumption of a fan system is proportional to the third power of the air flow velocity generated by the fan system.

Would this fan speed reduction be done regardless of heat load then it would carry the risk of increasing temperature distribution throughout the container's transport volume.

Too many evaporator fan speed changes would carry the risk of hardware damages, for example by contactor wear.

If local hot spots have developed inside the transport volume the changed air flow distribution may cause sudden changes in measured return or supply air temperature, otherwise it won't.

Internal heat production is more vicious as temperatures in e.g. palletized fruit may rise multiple degrees Celsius before it has a noticeable effect on measured return air temperature.

Energizing the heating unit only increases heating capacity but does not further increase the internal air circulation.

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