Refrigeration – Automatic control – Time or program actuator
Patent
1984-03-07
1986-07-29
Wayner, William E.
Refrigeration
Automatic control
Time or program actuator
622283, 361 22, G05D 2332
Patent
active
046024840
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention pertains to refrigeration system energy controllers and especially to refrigeration system controllers that sense pressure and/or temperature in the refrigerant line and control the on-off cycle of the refrigeration compressor motor thus, providing a minimal use of electrical energy while maintaining desired refrigeration under varied ambient temperature and humidity conditions in the vicinity of the refrigeration unit.
BACKGROUND ART
It is well known in the art of refrigeration control systems to use a pressure control switch which responds to pressure conditions in the suction line between the evaporator and compressor. The purpose of this device is to act as a safety control to prevent the suction pressure from falling to a point where the compression ratio will be too great for the compressor design. It also prevents the suction pressure from falling to a point where other damage can occur from low temperature. This type of controller normally has an adjustable range or differential and serves to turn off the compressor at the lower end of the range (cut-out) when pressure (and therefore temperature) conditions have been satisfied. At the upper end of the range (cut-in), the compressor is turned on again. The average pressure (and temperature) of the suction line is therefore maintained at the average of cut-in and cut-out levels of the pressure control switch.
It should be noted that a temperature control switch such as a thermostat placed in the refrigeration compartment containing the evaporator will perform a similar function to that of the pressure control switch. The temperature control switch will normally have a temperature sensing means, and have cut-in and cut-out settings similar to that of the pressure control switch.
Since many refrigeration systems are required to maintain operation over a wide range of temperature conditions, the pressure control switch is subject to certain seasonal problems. During winter periods, compartment cooling may be required even though the outdoor temperature is quite low. Under such conditions, the condenser may condense refrigerant so effectively that the compressor is unable to maintain a satisfactory hot gas pressure for delivering sufficient refrigerant across the restriction between the high and low sides of the system. As a result, the evaporator may be semi-starved of refrigerant, especially at start-up. At start-up, the compressor may draw more refrigerant from the evaporator than can be replaced by the condenser, thus causing the suction line pressure to suddenly drop, thereby actuating the low pressure cut-out. The result is a short on-off-on cycling of the compressor which can place excessive strain and loading on the compressor motor.
In the warm summer months where energy conservation is extremely important, high ambient temperatures generally cause the compressor to run for very long periods followed by very brief off periods.
In most cases, it is desirable not to have to adjust the pressure (or temperature) limits and range of the pressure control switch seasonally. For example, ambient temperature conditions can at times change very rapidly, necessitating a high degree of alertness and maintenance care, if the refrigeration control system is not adaptible to these changing conditions.
To surmount these problems posed by changing temperature conditions in the vicinity of the refrigeration system, various modifications and improvements have been introduced to the art.
To avoid the short-cycling problem, the pressure control switch differential between cut-in and cut-out has often been increased. This, however, causes much longer on-off cycles than desired, especially under high ambient conditions where energy conservation is of prime importance.
In order to arrive at a satisfactory compromise to the problem of short-cycling and excessive compressor run-time, various refrigeration control devices have included a fixed compressor off-time delay implemented by either electro-mechanical or solid-state devices. This
REFERENCES:
patent: 3636369 (1972-01-01), Harter
patent: 3864611 (1975-02-01), Chang
patent: 4094166 (1978-06-01), Jerles
patent: 4142375 (1979-03-01), Abe et al.
patent: 4292813 (1981-10-01), Paddock
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