Refrigeration – Automatic control – Refrigeration producer
Patent
1997-02-14
1998-05-12
Bennett, Henry A.
Refrigeration
Automatic control
Refrigeration producer
62225, 62213, F25B 4100
Patent
active
057492387
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a control arrangement for a cooling apparatus, having a cooling circuit in which a compressor, a condenser and at least one branch with an expansion valve and a downstream evaporator are connected in series, having a controller, a measuring device for the superheat temperature of the vapour of a liquid coolant evaporated in the evaporator and a sensor for the ambient temperature of the evaporator, the controller controlling the expansion valve in dependence on the difference in the desired value and actual value of the superheat temperature for the purpose of reducing the difference, and the flow of liquid coolant to the evaporator being controllable in dependence on the measured value of the ambient temperature sensor for the purpose of maintaining the ambient temperature at a constant value.
In a known cooling apparatus of that kind, it is usual for the ambient temperature, for example, the air temperature in the cooling area, to be controlled in dependence on the ambient temperature of the evaporator by means of an on-off action thermostat valve lying in the liquid coolant line upstream of the expansion valve, which expansion valve controls the superheat temperature of the liquid coolant evaporated in the evaporator. The repeated opening and closing of the thermostat valve causes the ambient temperature of the evaporator to be subject to considerable fluctuation. Since the switching-on and switching-off temperature values of the thermostat valve have to be different in order to avoid too frequent a switching, but on the other hand the temperature of the goods to be cooled may not exceed an upper limit value for too long, the mean value of the ambient temperature, or the temperature of the goods to be cooled, resulting from switching on and off the thermostat valve lies comparatively far below the admissible upper limit value of the temperature of the goods to be cooled. The mean value of the refrigeration output, which is higher, the lower is the temperature to be maintained, is consequently always higher than necessary. Moreover, the output of the compressor is also subject to considerable fluctuation, either its speed or its pressure being continuously or discontinuously changed, the latter as a consequence of its output being switched on and off or being changed in steps, as in the case of a multi-stage compressor, which leads to additional energy loss on account of the inertial mass of its moving parts.
Then, however, the use of two valves before the evaporator is expensive.
SUMMARY OF THE INVENTION
The invention is based on the problem of providing a control arrangement of the kind mentioned in the introduction, which provides greater efficiency of the cooling apparatus combined with a simpler construction.
According to the invention that problem is solved in that the controller has a continuous action and is connected to the ambient temperature sensor, and that on reaching a refrigeration temperature in a first operating mode in which the superheat temperature is controlled whilst complying with the maximum admissible state of fill of liquid coolant in the evaporator, the controller is switchable to a second operating mode in which the state of fill of liquid coolant in the evaporator is controlled by the expansion valve for the purpose of maintaining the refrigeration temperature.
With this solution, at the beginning, if desired, after a starting-up and de-frosting operation, in a first operating phase in which the first operating mode is applied, the goods to be cooled are cooled very rapidly to the desired low temperature by the superheat temperature control with the liquid coolant at maximum state of fill in the evaporator; then, in a second operating phase, in which the second operating mode is applied, that is to say, by continuous control of the ambient temperature, the temperature of the goods to be cooled is maintained at the desired low value by controlling the effective cooling surface of the evaporator solely in accordance with r
REFERENCES:
patent: 4112703 (1978-09-01), Kountz
patent: 4478051 (1984-10-01), Ibrahim
patent: 4674292 (1987-06-01), Ohya et al.
patent: 4735060 (1988-04-01), Alsenz
patent: 5109676 (1992-05-01), Waters et al.
Bennett Henry A.
Tinker Susanne C.
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