Mcquay-perfex Inc.

Jerome D Powlas

Kenneth E Vogel

Condensing head pressure in a refrigeration system having its condenser exposed to low outside ambient temperatures is controlled to provide the minimum head pressure required for a given mode of operation. A hierarchy of operating modes, each with its associated pressure is established, including normal refrigeration, evaporator defrost and heat reclaim. The control system prevents system head pressure from going below the minimum required for the operating mode in effect at a given time, with modes requiring higher pressure overriding lower pressure modes when required. In heat reclaim operation, high pressure gas from the compressor is diverted through a heat reclaim coil, and a subcooling sensor or other sensing means controls system head pressure to the minimum pressure that will maintain full condensing in the heat reclaim coil, which is the most economical mode of operation. In a multiple system, head pressures of the various systems are brought up sequentially to the pressure for full condensing in their heat reclaim coils so that if additional heat is needed the next stage is brought in, rather than further increasing the pressure of the previous stages. This has been found to be more economically efficient than providing further increases in head pressure above the optimum point of just fully condensing all vapor entering the reclaim coil to liquid.

Head pressure control for heat reclaim refrigeration systems

A control system for a refrigeration system having an air-cooled condenser exposed to normal year round ambient temperatures. Head pressure is controlled in response to sensed subcooling of the refrigerant in the liquid line near the entrance to the expansion device, so as to prevent the occurrence of flash gas at the expansion device, while still allowing minimum head pressures so as to improve energy efficiency. In alternate embodiments, additional controls are provided for assuring at least a predetermined minimum pressure differential across the thermostatic expansion valve. In one preferred embodiment a two-bulb sensing technique is used for subcooling and pressure differential sensing. Both series and parallel condenser-receiver connection systems are disclosed, as are a number of different subcooling sensing and control embodiments.

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Minneapolis, MN, United States of America

Jerome D Powlas