Mcquay-perfex Inc.

Kenneth E Vogel

Jerome D Powlas

Dean R Peterson

An improved system for control of defrost in a refrigeration system of the type wherein one or more evaporators are defrosted by hot gas from the compressor while one or more evaporators remain in refrigeration operation. Prior to operating diverting valves to establish defrosting gas flow in an evaporator, a liquid line valve is closed and the system is pumped down to a predetermined amount of refrigerant charge in the defrost loop. In a preferred embodiment, this is accomplished by first opening the liquid line valve to flood the system, then closing it for a predetermined time interval to pump down to the predetermined amount of charge prior to operating the diverting valves. The predetermined amount of refrigerant charge in the defrost loop, together with a flow through defrost receiver incorporated in the defrost loop assures optimum efficiency by avoiding situations of two little or too much charge in the defrost loop, either of which would impair efficiency of the defrosting and the ongoing refrigeration in the other evaporator or evaporators.

Refrigeration defrost control

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.

Refrigeration system subcooling control

Apparatus for defrosting a heat exchanger, comprises a plurality of spaced parallel heat exchanger fins having sets of circular, collared, axially aligned apertures. The collars of each set coacting to define an essentially continuous tube. Refrigerant tubes pass through the essentially continuous tubes defined by a majority of the sets of apertures and are sized for engagement by the collars of the apertures in intimate heat conductive relation. Axially replaceable electrical heating elements traverse the essentially continuous tubes defined by a minority of sets of apertures instead of refrigerant tubes and the heating elements are sized to fit loosely in the apertures so the heat is transmitted from the element to the collars both by radiation and by conduction and so that axial relative movement between the elements and the collars is enabled.

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Mound, MN, United States of America

Kenneth E Vogel