GB2131143A - Preventing misting of refrigerated enclosure transparent doors - Google Patents

Abstract

A transparent door for a refrigerated cabinet comprises an outer pane 26, an inner pane 28 and an intermediate pane 30 disposed in parallel planes. The outer pane 26 is electrically heated continuously or intermittently at regular intervals to prevent condensation thereon. Electrical heating of the inner pane 28 is commenced when the door is opened and is continued for a period after the door has been closed again to remove condensation on the inner pane 28 occurring as a result of moist warm air from outside the cabinet striking the cold surface of the inner pane. To promote de-misting of the inner pane 28, a uniform air flow may be provided over the pane 28 by an internal circulating fan 40. <IMAGE>

Description

SPECIFICATION Improvements in or relating to refrigerated enclosures THIS INVENTION relates to refrigerated enclosures, and in particular to transparent doors or other panels of such enclosures and to a method of preventing or counteracting misting of such transparent panels.

It has become the practice, in the retailing of frozen foodstuffs, particularly in self-service establishments, to display such foodstuffs in refrigerated cabinets, popularly referred to as 'freezers' having transparent door panels through which the produce within the cabinets can be viewed. There are, however, certain problems presented by the use of such panels in that ambient atmospheric moisture tends to condense on the outerly presented surface of the transparent panel because the latter is cooled by the refrigeration of the interior of the enclosure. The last-noted difficulty may be alleviated somewhat by making such transparent panels of double-glazed construction.Furthermore, when a cabinet door is opened by a customer, for the removal of a desired item, the relatively moist ambient air comes into contact with the surface of the transparent panel which is normally presented to the interior of the enclosure and the moisture in said ambient air condenses on said surface thus producing misting of the panel.

It is among the objects of the present invention to provide an improved transparent door or other panel for a refrigerated enclosure and a refrigerated enclosure incorporating such a panel.

It is also an object of the invention to provide a method of controlling misting of a transparent panel of a refrigerated enclosure.

According to one aspect of the invention there is provided a transparent door or other panel for a refrigerated enclosure, comprising an array of two or more transparent panes spaced apart so that a first said pane forms one side of the array and a second said pane forms the opposite side of the array, and respective means for heating the two panes on said opposite sides of the array, whereby misting of the panes, due to condensation of moisture thereon, can be counteracted.

According to another aspect of the invention there is provided a refrigerated enclosure having a panel according to the above noted aspect of the invention and wherein the means for heating said second pane is operable to heat said second pane intermittently, while the means for heating said first pane may be adapted to heat said first pane continuously, or may be adapted to heat said first pane intermittently, for example at regular intervals.

According to a further aspect of the invention there is provided a method of controlling misting of a transparent panel of a refrigerated enclosure, said panel separating the interior of the enclosure from the surroundings, and wherein the panel comprises an array of two or more transparent panes spaced apart so that a first said pane forms the side of the array which is presented outwardly from the enclosure and a second said pane forms the opposite side of the array, which is presented towards the interior of the enclosure, the method comprising heating said second pane intermittently.

An embodiment of the invention is described below with reference to the accompanying drawings in which: Figure 1 is a view, partly in perspective and partly in section, of a refrigerated cabinet embodying the invention and, Figure 2 is a view to an enlarged scale, partly in perspective and partly in section showing part of a door of the cabinet of Fig.

1.

Referring to Fig. 1, a refrigerated cabinet comprises a rear wall 10, bottom and top walls 12 and 14 respectively and side walls (not shown) which, together with doors 20, define a freezer compartment within which are located a series of shelves 22 disposed one above the other, for supporting frozen food produce.

A refrigeration unit 24 of known kind is operable to maintain the interior of the cabinet at the desired low temperature, (usually - 1 8'C to - 23"C).

The doors 20 each comprise a rectangular frame 32 bounding a rectangular transparent panel through which produce on the shelves 22 may be viewed without opening the doors 20, until such time as it is necessary to gain access to an item of produce on a shelf 22.

The cabinet shown is particularly intended for use in a self-service shop and the doors 20 are fitted with appropriate readily operable latch arrangements, magnetic catches or the like (not shown) and may be provided with appropriate self closing facilities, (not shown, but known per se), in order to ensure that the doors 22 are not inadvertently left open by customers.

As shown in Fig. 2, each door 20 is a triple-glazed construction comprising three parallel planar glass panes spaced apart in a direction perpendicular to their planes to afford air spaces therebetween, these panes comprising a first, outermost pane 26, which affords the outwardly presented major surface of the door, a second, innermost pane 28, which provides the side of the door which is presented inwardly towards the interior of the cabinet and an intermediate pane 30 disposed between the panes 26 and 28. The panes 26 to 30 are appropriately fitted within the frame 32, in a peripheral rebate in the frame, and are for example, separated, from one another by spacers 34. The frame 32 is provided, in known manner, with a rubber seal 36 on its inner side.

Means, not shown, are provided for heating the pane 26 and the pane 28 electrically.

Such means preferably comprises a respective electrical heater for each of the two panes 26, 28. Each such heater may comprise, for example, a respective electrically resistive track or coating deposited on one surface of the respective pane 26, 28, (preferably, in order to protect the track or coating from damage, on the surface of the respective pane which faces towards the pane 30).

Electrical supply and control means (not shown) are provided for passing electrical current through the electrically resistive tracks or coatings to heat the panes 26 and 28. The electrical supply and control means is so arranged that the heater of the pane 28 is normally de-energised, but is energised when the door 20 is opened and remains energised for a period after the door has been closed again. To this end, said control means includes appropriate sensing means (not shown), for example a microswitch, magnetically operated switch, proximity switch or the like, for detecting when the door is open and closed. The heater of the pane 26 may be arranged to be supplied with current continuously and steadily, or may be arranged to be supplied with current intermittently, for example for short periods at regular intervals, to reduce power consumption.

An ultra-violet filter may be incorporated in the door glazing, for example carried by the intermediate pane 30.

The purpose of the heating of the pane 26 is to prevent the latter from becoming so cooled, by loss of heat to the interior of the cabinet, that moisture from the ambient air will condense thereon, thus obscuring the view, through the door, of the contents of the cabinet.

The purpose of the intermittent heating of the pane 28 is as follows. In an equilibrium state, when the doors 20 have remained closed for an extended period, the moisture content of the atmosphere within the cabinet is relatively low, so that, despite the low temperature of the interior of the cabinet, there is no condensation of moisture of the pane 28, although the latter is at a similarly low temperature. However, when the door 20 is opened, in the absence of heating of the panel 28, moisture from the more moist, warmer ambient air would condense upon the cool inner pane 28, causing misting, and would remain, obscuring the view through the door 20, for a considerable period after the door has been closed again.However, with the described heating arrangement for the pane 28, as soon as the door 20 is opened, heating of the pane 28 begins, thus rapidly evaporating again any moisture which does initially condense thereon and substantially shortening the period over which the pane 28 is at a sufficiently low temperature, whilst exposed to the ambient atmosphere, to cause moisture condensatiom It has been found 3d- visable to continue the heating of the pane 28 for a period after the subsequent closure of the door 20 in order to ensure that any condensation remaining on the inner pane 28 when the door is closed will be evaporated shortly after such closure.

The rate at which heat s suppl ed to the inner pane 28 during the period when it is heated is preferably substantially greater than the rate of continuous heating of the outer pane 26. Thus, whilst it has been found appropriate to supply some 8 watts of heating energy per square foot of pane area to the outer pane 26, heat may be applied to the inner pane 28, during the period when it is being heated, at a rate of some 65 watts per square foot of pane area.The intermittent nature of the heating of the inner pane 28 thus makes it possible to heat the inner pane 28 sufficiently intensely to ensure a rapid dispersal of any condensation, at times when such dispersal is actually required, without a high average heat loss by the inner pane 28, which would detract from the refrigeration of the interior of the cabinet and would also, of course, be wasteful of energy.

Preferably the timing of the initiation end termination of the heating of the pane 28 is variable in dependence upon such factors as the period over which the door has been opened, the period over which the door has previously remained closed, the frequency of door opening, etc. Preferably the length of the period elapsing after the closure of the door until termination of the heating of the panel 28 is greater, at least over a esrtein range.

the greater the length of time for which the door has previously been opened and conversely, but is less if the door, over a certain time previously, has been opened frequently or over a protracted period (whnch wo'ld mean that the pane 28 would has attained a relatively high temperature througEllout and would thus have an appreciable residual heat at the time the door was closed.

In one arrangement which may be adopted, the control circuitry for the heater for the pane 28 may incorporate a timer and an up/down counter controlling the timer. In this arrangement, the up-down counter is arranged to count up pulses produced at a first regular rate whilst the door is closed, and to count down pulses produced at a second, faster rate when the door is open, the counter being arranged, for example, to remain at its maximum count for pulses received, after the dooi is closed, in excess of the number required to take the counter to its maximum count, and to remain at its minimum count for pulses received, after the door is opened, in excess of the number required to take the counter to iis minimum count.The timer is arranged, in this embodiment, to take the count which is in the counter at the time that the door is closed as a basis for the determination of the length of the period elapsing after the closure of the door until termination of the heating of the panel 28, so that if the count at this time is high, that period will be relatively long, whilst if the count is low, that period will be relatively short. The length of said period is not necessarily directly proportional to the count in the counter at the time the door is closed, or linearly related thereto, for it may be advantageous to have a non-linear relationship between the length of said period and the count in the up/down counter when the door is closed.

It has also been found advantageous, in addition to the energisation of the heater for the pane 28 in response to door opening and closing, to energise the heater for the pane 28 for short periods occurring at regularly spaced substantially longer intervals, whilst the door is closed, as this helps to keep the inner pane 28 clear.

The control of the timing of the energisation and de-energisation of the heaters in response to the variables noted, and any other relevant variables, may conveniently be affected by a micro-computer or micro-processor incorporated in the freezer control system.

The de-misting of the inner pane 28 may be increased by providing a uniform air flow over the pane 28 when the door is closed.

Such airflow is preferably of the order of 0.3 to 0.5 metres per second and may be provided by an internal circulating fan within the cabinet, such as indicated at 40 in Fig. 1.

Whilst, in the preferred embodiment described, each door 20 comprises three panes of glass 26, 28 and 30, the same selective heating of the inner and outer panes may, of course, be utilised where only two panes are provided, (i.e. where the door is only double glazed), or where the door comprises four or more contiguous panes.

Claims (14)

1. A transparent door or other panel for a refrigerated enclosure, comprising an array of two or more transparent panes spaced apart so that a first said pane forms one side of the array and a second, said pane forms the opposite side of the array, and respective means for heating the two panes on said opposite sides of the array, whereby misting of the panes, due to condensation of moisture thereon, can be counteracted.

2. A refrigerated enclosure having a panel according to claim 1 wherein said second pane provides the side of the array facing into the interior of the enclosure and said first pane provides the side of the array facing outwardly from the enclosure and wherein the means for heating said second pane is operable to heat said second pane intermittently.

3. A refrigerated enclosure according to claim 2 including means for sensing when a door of said enclosure is opened and closed and arranged to initiate heating of said second pane when the door is opened and to terminate heating of said inwardly presented panel after the door has been closed.

4. A refrigerated enclosure according to claim 3 wherein the arrangement is such that heating of said second pane is terminated after the elapse of a period after the door is closed.

5. A refrigerated enclosure according to claim 3 or claim 4 wherein said panel is formed by, or incorporated in, the door of the enclosure.

6. A method of controlling misting of a transparent panel of a refrigerated enclosure, said panel separating the interior of the enclosure from the surroundings, and wherein the panel comprises an array of two or more transparent panes spaced apart so that a first said pane forms the side of the array which is presented outwardly from the enclosure and a second said pane forms the opposite side of the array, which is presented towards the interior of the enclosure, the method comprising heating said second pane intermittently.

7. A method according to claim 6 where in heating of said second pane is commenced when a door of the enclosure is opened, and is terminated after said door has been closed again.

8. A method according to claim 7 wherein heating of said second pane is continued for a period after the door has been closed and is terminated at the end of said period.

9. A method according to claim 8 wherein the duration of said period is, at least partly determined by reference to the time for which said door remains open.

10. A method according to claim 8 or claim 9 wherein the duration of said period is dependent on the period for which the door is open, and/or the frequency of door opening, and/or the period for which the door is closed.

11. A transparent door or other panel for a refrigerated enclosure, substantially as herein before described with reference to, and as shown in, the accompanying drawings.

12. A refrigerated enclosure substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.

13. A method of controlling misting of a transparent panel of a refrigerated enclosure, substantially as hereinbefore described with reference to the accompanying drawings.

14. Any novel feature or combination of features disclosed herein.