This invention relates to controlling the operation of refrigeration systems which contain multiple compressors. More particularly, the present invention is concerned with refrigeration systems of the type having multiple compressors fed from a common suction manifold and which deliver refrigerant gas under pressure to a common head pressure manifold.
It is known from U.S. Pat. No. 3,599,006 to John L. Harris granted Aug. 10, 1971 and entitled "Condition Control Device and System" to provide multiple compressors in a refrigeration system. The system is arranged so that the compressors are started in sequence, allowing each compressor to come up to speed before the next compressor is started. The system also interposes a delay between the stopping and restarting of the respective compressors so that a compressor is not started under heavy load. The system is essentially an electromechanical system responsive to analog signals and completely analog in nature.
It is known from U.S. Pat. No. 4,128,854 to Robert T. Ruminsky issued Dec. 5, 1978 and entitled "Compressor Minimum Off-time System" to place a current transformer in a circuit which controls the switching of a compressor. The current transformer, in turn, provides a control signal to a minimum off-time circuit. The purpose of the delay effected by the off-time circuit is to prevent start-up under heavy load. Like the system disclosed in Harris, supra, the system is analog in nature and is responsive to analog signals.
It is known from U.S. Pat. No. 3,636,369 to Donald G. Harter, granted on Jan. 18, 1972 and entitled "Refrigerant Compressor Control-relay to Control Two Time Delays" to provide a refrigerant compressor with a relay arrangement which controls two time delays. One time delay keeps the compressor deenergized at least for a predetermined period after each stop action. The other time delay keeps the compressor energized for at least a predetermined period after each start action.
It is known from U.S. Pat. No. 4,033,738 to Carl R. Metrola et al., granted on July 5, 1977 and entitled "Heat Pump System with Multi-stage Centrifugal Compressors" to arrange multistage compressors in series. The start of the second compressor is delayed for a sufficiently long period to enable the first compressor to reach its design speed.
The use of a microprocessor and timed solid state logic circuitry to control automatically sequencing of compressors in a refrigeration system is disclosed in U.S. Pat. No. 4,152,902 granted May 8, 1979 to Lawrence E. Lush and entitled "Control for Refrigerator Compressors".