Refrigeration – Automatic control – Refrigeration producer
Reexamination Certificate
2002-05-03
2003-03-11
Esquivel, Denise L. (Department: 3744)
Refrigeration
Automatic control
Refrigeration producer
C062S230000
Reexamination Certificate
active
06530238
ABSTRACT:
The present disclosure relates to the subject matter disclosed in international application No. PCT/EP00/10994 of Nov. 8, 2000, which is incorporated herein by reference in its entirety and for all purposes.
BACKGROUND OF THE INVENTION
The invention relates to a transportable cooling unit for maintaining a transport volume at the defined temperature, comprising a closed cooling circuit serially including a multi-stage compressor, a condenser, an expansion device and an evaporator arranged in said transport volume as well as a speed-controlled electric motor driving said compressor.
Such transportable cooling units are, for example, disclosed in the article of R. D. Heap “Refrigerated containers in . . . ”.
The object of the present invention is to provide a transportable unit cooling which provides minimized energy consumption in combination with optimized temperature stability within the transport volume irrespective of the environment.
SUMMARY OF THE INVENTION
This object is achieved by a transportable cooling unit for maintaining a transport volume at a defined temperature, comprising a closed cooling circuit serially including a multi-stage compressor, a condenser, an expansion device and an evaporator arranged in said transport volume, a speed-controlled electric motor driving said compressor and a controller sensing a temperature present within said transport volume and controlling said electric motor so as to provide the cooling power demanded at said evaporator for maintaining said defined temperature and minimize energy consumption, said controller operating said closed cooling circuit between a minimum possible cooling power and a maximum possible cooling power in a sequence of different operational stages comprising a lowest operational stage (stage
1
) and a sequence of at least two upper operational stages (stage
2
to
4
), said controller operating said closed cooling circuit in each one of said upper operational stages (stage
2
to
4
) at a compressor speed related cooling capacity different from said compressor speed related cooling capacity in said other upper operational stages and within said respective upper operational stages in an uninterrupted mode and adjusting said cooling power provided by said closed cooling circuit by an essentially stepless speed control of said electric motor.
The advantage of the present invention is to be seen in the fact that due to the sequence of different operational stages the compressor can be run within a reasonable speed range which is advantageous for an optimized compressor design and optimized compressor energy consumption but within the speed range different levels of cooling power can be achieved by using different operational stages of the closed cooling circuit, which makes it possible to minimize energy consumption of the entire system.
According to the present invention control of the speed of the electric motor could be achieved by various means. It turned out to be advantageous for the speed controllable electric motor to be a frequency controlled AC-motor, because in such a frequency controlled AC-motor the energy consumption can be reduced in accordance with the speed of the controllable electric motor.
In accordance with the aforementioned definitions of the present invention it is not defined how the controller operates the compressor in said low operational stage. It is particularly advantageous if in said lowest operational stage said controller operates said compressor in an interrupted mode at low speed and adjusts said necessary cooling capacity by adjusting at least one of the parameters comprising interruption interval and speed.
The advantage of this embodiment of the present invention is that in the low operational stage it is allowed to switch the compressor on and off so as to be able to control low cooling power of the closed cooling circuit and to maintain the energy consumption dependent on the demanded cooling capacity but to maintain a certain level of speed if the compressor is operable for maintaining a reasonable level of compressor efficiency.
It is particularly advantageous if the controller in said low operational stage maintains said speed of said compressor essentially constant and varies the interruption interval, e.g. the intervals within which the compressor is switched on or off so that the cooling power is only controlled by controlling the interruption intervals.
In such an embodiment it is of particular advantage if in said lowest operational mode said speed of said compressor is in the dimension of the minimum possible speed for the compressor. This means that the compressor is run at the lowest allowable speed for proper operation and that if only cooling power is needed which is lower than the cooling power provided at that minimum speed a further reduction is performed by interrupting the compressor.
In connection with the aforementioned explanations of various embodiments of the present invention it has not been defined how the controller determines the cooling power demanded.
One manner of determining the cooling power demanded would be to only detect the temperature present within said transport volume and to reduce the speed of the compressor to the lowest possible level.
A more advantageous manner of determining the cooling power demanded is to compare the temperature present within that transport volume and the temperature of ambient air.
With respect to the temperature detection within the transport volume the location of detection has not been defined in connection with the explanation of the aforementioned embodiments.
Generally, the temperature within the transport volume can be detected anywhere therein.
For obtaining a fast response of the temperature detection it is advantageous if the controller senses the temperature in a stream of air circulating within said transport volume because in such a case the controller obtains the proper temperature values with a short response time.
In addition, it is advantageous to sense the temperature within said transport volume close to said evaporator because in this case the cooling power demanded can be determined more precise.
In general, the controller could start in the uppermost operational stage or in the lowermost operational stage and follow the sequence of operational stages until the desired temperature is obtained.
To be able to respond precisely to temperature changes it is of advantage if the controller selects the currently necessary operational stage in accordance with the cooling power demanded.
In accordance with the present invention, as discussed above, it would be possible to have a varying compressor speed related cooling capacity of said closed cooling circuit within at least one of said upper operational stages, however, for designing an easily controllable system it is of advantage if said compressor speed related cooling capacity of said closed cooling circuit is constant within each of said upper operational stages.
With respect to the lowest operational stage the compressor speed related cooling capacity could vary too. However, it is also of advantage if said compressor speed related cooling capacity of said closed cooling circuit is constant within said lowest operational stage.
With respect to a cost effective design of the inventive cooling unit it turned out to be advantageous for said compressor speed related cooling capacity of said closed cooling circuit to be the same as the compressor speed related cooling capacity in said one of said upper operational stages covering the lowest range of cooling power of said sequence of upper operational stages.
If the controller has the possibility to switch from one upper operational stage to another operational stage such a switching is advantageously defined by a respective cooling power. To avoid at this respective cooling power a fast witching back and forth between one upper operational stage and the other operational stage it is advantageous if the controller switches from one upper operational stage to another upper operational stage w
Esquivel Denise L.
Lipsitz Barry R.
Maersk Container Industri A/S
Norman Marc
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