Refrigeration – Automatic control – Time or program actuator
Patent
1998-07-31
1999-12-28
Wayner, William
Refrigeration
Automatic control
Time or program actuator
62200, 236 75, 25112905, F16K 3102, F25B 500
Patent
active
060065273
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a refrigeration system having a plurality of cooling surfaces, each of which is connected by way of a series-connected controlled valve to a common refrigerant supply device, and having a control arrangement connected to the valves.
The refrigerant supply device can here be formed by a heat-exchanger in which heat is extracted from brine. The heat is given up to a coolant which is cooled in a customary cooling circuit having one or more compressors, a condenser and a collector, the heat exchanger being provided with an expansion valve. The brine then flows through the cooling surfaces and absorbs heat there in order to cool the environment around the cooling surfaces. In another practical form, the cooling surfaces can also have refrigerant flowing directly through them, the refrigerant being channelled through a circuit containing one or more compressors, a condenser and a collector.
A refrigeration system of the kind mentioned in the introduction is known from EP 0 410 330 A2. The refrigeration system in that case has at least two compressors arranged in parallel in the refrigerant circuit, which compressors can be operated jointly or alternately individually to satisfy the cooling requirement at the various cooling points simultaneously. In this connection it is desirable for the frequency of switching-on of the individual compressors to be reduced in order to prolong their service life. A control arrangement which is connected to thermostatic valves is provided for controlling the compressors. The thermostatic valves relay only the necessary temperature information to the control unit, however, so that this controls the compressors accordingly. The control unit can also switch off individual cooling surfaces when their actual value falls below a predetermined reference value.
SUMMARY OF THE INVENTION
The invention is based on the problem of rendering loading on the refrigerant supply device more uniform.
In a refrigeration system of the kind mentioned in the introduction, this problem is solved in that the control arrangement generates for each valve a pulse-width modulated signal for operation of the valve, all signals having the same period, and in that the valves of the individual cooling surfaces open at staggered intervals with respect to one another.
There is a more uniform call upon the output of the refrigeration supply device with this construction. Since the individual valves open at staggered intervals, refrigerant is channelled through the cooling surfaces also at correspondingly staggered intervals. The control arrangement controls only the start of "refrigerant consumption", however. The end is determined for each cooling surface in dependence on its demand for refrigeration. The control arrangement controls the valve accordingly, that is, it closes it when sufficient refrigerant has flowed into the cooling surface. Viewed statistically, with a sufficiently large number of cooling surfaces a state will then be reached in which always a few cooling surfaces are being supplied with refrigerant, whilst other cooling surfaces are switched off. The larger is the number of cooling surfaces, the more uniform can one keep the loading on the refrigerant supply device. Useful results have also already been obtained in practice when only three or four cooling surfaces are operated in parallel with one another. Since all signals have the same period, that is, all valves open similarly but at staggered intervals, the refrigerating capacity can be distributed very uniformly via the distribution of the refrigerant, so that the loading on the refrigerant supply device is correspondingly uniform.
In a preferred construction, the period is constant. Not only are the periods for the individual valves the same, but also successive periods are the same. Control is therefore simplified. It is easier to define the parallelism of the individual valves during operation in that they are able to open at staggered intervals.
The valves are advantageously ON-OF
REFERENCES:
patent: 4510767 (1985-04-01), Komatsu et al.
patent: 5435145 (1995-07-01), Jaster
Bendtsen Christian
Hansen Kim
Danfoss A/S
Wayner William
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