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Trim heating power control for refrigerated display cabinets

IP.com Disclosure Number: IPCOM000007441D
Publication Date: 2002-Mar-26
Document File: 2 page(s) / 26K

Publishing Venue

The IP.com Prior Art Database

Related Documents

US 5778689: PATENT

Abstract

The disclosure relates to the control of trim heaters for preventing the formation of condensation on areas of a refrigerated display cabinet. The power supplied to the trim heaters is varied as a fraction of the maximum power, depending on the ambient temperature and relative humidity. The same fraction of maximum power is applied to multiple trim heaters located in different positions with respect to the refrigerated load and ambient surroundings; these positions have already been taken into account when the maximum power of the trim heaters is set during the design process.

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Title

Trim heating power control for refrigerated display cabinets

Abstract

The disclosure relates to the control of trim heaters for preventing the formation of condensation on areas of a refrigerated display cabinet. The power supplied to the trim heaters is varied as a fraction of the maximum power, depending on the ambient temperature and relative humidity. The same fraction of maximum power is applied to multiple trim heaters located in different positions with respect to the refrigerated load and ambient surroundings; these positions have already been taken into account when the maximum power of the trim heaters is set during the design process.

Related Documents

US 5778689

Classification

G05D 23/19

F25D 21/04

Description

It is undesirable for condensation to form on the areas of a display cabinet that are on the interface of the cooled envelope and ambient air.  These areas include glass surrounds at the top of well cases, the door surround of a “doored” cabinet etc.  To avoid condensation and, possibly frost or ice forming, localised heating is provided.  This is referred to as “trim heating”.

The amount of heating installed on cabinets is normally excessive.  More and more heating is installed on the prototype cabinet until condensation does not form in the worst design condition.  This then becomes the standard for that type of cabinet.

It follows that, in most cases, excessive heat is being used.  This is inefficient in itself; additionally some of the extra heat costs doubly as it has to be provided and then removed again by the refrigeration system.  The aim of this invention is to control the trim heating to reduce this waste.

The amount of heat required depends on:-

                    The relative humidity around the case

                    The temperature around the case

                    The load temperature of the case

                    The absolute position of the trim

For a given design of cabinet, the load temperature can be taken as a defined constant (e.g. –20 degrees for frozen.)  The absolute position of the trim leads to a “natural trim temperature”.  This varies with ambient temperature.  It is the temperature at which the trim exists in the absence of trim heating.  This “natural trim temperature” can be taken to be a certain percentag...