WO1990014035A1

WO1990014035A1 - Improvements relating to refrigerated display units

Info

Publication number: WO1990014035A1
Application number: PCT/GB1990/000786
Authority: WO
Inventors: Michael Paul Nicholls
Original assignee: Clares Equipment Ltd
Priority date: 1989-05-18
Filing date: 1990-05-18
Publication date: 1990-11-29
Also published as: CA2057876A1; AU5648490A; GB2231947A; GB9011235D0; GB8911459D0; GB2231947B; EP0472576A1

Abstract

A refrigerated display unit (10) having a display cabinet adapted to store and provide access to refrigerated food has a refrigeration system arranged to provide cold air to the cabinet, and temperature control means to enable cold air supplied to a relatively forward part of the cabinet to be at a lower temperature than cold air supplied to a relatively rearward part of the cabinet.

Description

IMPROVEMENTS RELATING TO REFRIGERATED DISPLAY UNITS This invention relates to refrigerated display units and in particular to improvements in the thermal performance of such units.

Refrigerated display units are widely used in the retail food industry for the display of chilled foods such as pre-cooked meals, fresh meat, dairy produce and any other products which benefit from being kept at low temperatures.

Typical display units of this kind generally have several shelves on which food is stored and displayed, and are open at the front so that customers can easily select the goods which they wish to purchase. Because of heat from the surroundings, products which are at the front of a conventional refrigerated display unit are warmer than the cold air passing over and around them from the refrigeration system. In order to try and shield products at the front of the shelves from the ambient temperature of the surroundings an air curtain may be provided by diverting cold air from the refrigeration system to pass across the front of the unit from top to bottom. The temperature of such an air curtain must be several degrees colder than that at which the food is to be stored to counter the effect of the higher temperature of the surroundings. However, air from the same low temperature supply will also pass into the display unit via the back panel. Products at the back of the shelves, which are not subject to the heat from the surroundings, will therefore experience a lower temperature than that at which they should ideally be stored. The chosen operating temperature of a display unit is therefore a compromise between two extremes to keep a reasonably low temperature at the shelf front without causing freezing of products at the back of the shelf.

The invention aims to provide means by which even product temperatures can be achieved across shelves in a refrigerated display unit.

According to a first aspect of the invention there is provided a refrigerated display unit comprising a display cabinet adapted to provide access to refrigerated food from the front thereof, a refrigeration system arranged to provide cold air to the cabinet, and temperature control means to enable a first cold air supply to a relatively forward part of the cabinet to be at a lower temperature than a second cold air supply to the rear of the cabinet.

According to a second aspect of the invention there is provided a refrigerated display unit comprising a display cabinet adapted to provide access to refrigerated food from the front thereof, and a refrigeration system arranged to provide cold air for circulation in the unit and to supply cold air to a relatively forward part of the cabinet to form an air curtain and to the rear of the cabinet, wherein said refrigeration system comprises a first evaporator arranged to cool all of the circulating refrigerated air and a second evaporator to further cool a part of the circulating refrigerated air for said supply to the air curtain, the circulating refrigerated air supplied to the rear of the cabinet having been cooled only by said first evaporator.

According to a further aspect of the invention there is provided a refrigerated display unit comprising a display cabinet adapted to provide access to refrigerated food from the front thereof, and a refrigeration system arranged to provide cold air for circulation in the unit, wherein all of the circulating refrigerated air supplied to a relatively forward part of the cabinet to form an air curtain is at a temperature lower than that of circulating refrigerated air supplied to the rear of the cabinet.

According to another aspect of the invention there is provided a refrigerated display unit comprising a display cabinet adapted to provide access to refrigerated food from the front thereof, and a refrigeration system arranged to provide cold air for circulation in the unit, wherein circulating refrigerated air is supplied to the rear of the cabinet and to a relatively forward part of the cabinet to form at least a part of an air curtain, all of said circulating refrigerated air being at a temperature at least as low as that of the air supplied to the rear of the cabinet, and at least a part of the air curtain being at a temperature lower than that air supplied to the rear of the cabinet. In order that the invention may be better understood embodiments thereof will be described, by way of example, with reference to the accompanying drawings wherein:

Figure 1 shows a vertical section through a first refrigerated display unit according to the invention; Figure 2 shows a vertical section through a second refrigerated display unit according to the invention.

As explained hereinbefore, conventional refrigerated display units with a cold air curtain give rise to problems in food storage because the back portions of the shelves in such units are colder than the required product storage temperature. In order to maintain an even temperature from the front to the back of the shelves the temperature of the air curtain at the front of the unit is preferably of the order of 4°C or 5°C colder than the temperature of the air supplied to the back of the display cabinet.

Figure 1 shows a refrigerated display unit 10 with a series of display shelves 20 attached to a back panel 30. The front of the unit 10 is open to the surrounding ambient temperature. A refrigeration system produces cold air which is drawn into the base of the unit 10 by the action of a fan 40 at the back of the display unit. The refrigeration system may be incorporated in the display unit itself, or may be in a remote location. The cold air is directed up to the top of the display unit through a duct 45. At this point part of the cold air stream is diverted down behind the back panel 30 of the display unit 10 to pass forward through the panel into the display cabinet and the remainder continues across the top of the unit in a duct 46 to the front where it is directed downwardly to form an air curtain as shown.

Before being passed into the cabinet via the back panel 30 this part of the air supply is first passed over a small heater 50 which reheats it by a predetermined amount so that it is approximately 5^βC warmer than the air curtain supply. The embodiment illustrated in Figure 1 has temperatures of -7°C for the air supply to the air curtain and -2°C for the air supply to the cabinet via the back panel. The heater 50 can be a small electric heater, or may be in the form of a pipe carrying heat from the refrigeration system. It will be appreciated that any other small heating device may be used as the heater 50.

An alternative embodiment of the invention is shown in Figure 2. This refrigerated display unit is arranged so that the fan circulates cold air from the refrigeration system at the temperature required for supply to the cabinet via the back panel. Whilst part of the cold air supply is directed to pass upwardly behind the back panel and into the cabinet the remainder is directed through a heat exchanger to further reduce its temperature to that required for- supply to the air curtain as it is passed up to the top of the unit.

As seen in Figure 2, the circulating air is drawn into the base of the unit 10 at the front of the cabinet by a fan 40 and through an evaporator 60 which acts to cool the air to the temperature required for supply to the rear of the cabinet via the back panel 30. In the embodiment illustrated in Figure 2 this temperature is of the order of -1°C.

A second evaporator 65 is positioned in the duct 45 at the rear of the unit 10 towards the top of that duct. The Back pressure is created by evaporator 65 in the duct 45. This encourages some of the air to pass downwardly through holes in the back panel 30 over the shelves 20 as indicated. The air which passes through the second evaporator 65 is further cooled, in this embodiment to about -6°C. This colder air is ducted across the top of the unit 10, via duct 46, towards the front of the cabinet where it is directed downwardly across the open front of the cabinet to form the air curtain. The forward flowing air passing from the rear of the cabinet helps to prevent the air curtain from penetrating the shelf area of the cabinet. The air from the air curtain is drawn back into the base of the unit 10 together with some ambient air to be circulated and cooled again. Figure 2 also shows, in phantom, an alternative position for the first evaporator 60' and the fan 40'. This arrangement works in the same way as that just described, except that some of the air supplied to the rear of the cabinet through the back panel 30 passes downwardly after being cooled by the first evaporator 60' to provide air to the bottom part of the cabinet.

In both the embodiments described, all of the circulating refrigerated air which is supplied to the front of the cabinet to form the air curtain is supplied at a temperature lower than that of the air supplied to the rear of the cabinet via the back panel 30. It is envisaged that additional layers of air may be provided to the air curtain to form a multilayer air curtain as is known from the prior art. Thus, a multilayer air curtain may be provided of which at least a part is at a temperature lower than that of the air supplied to the rear of the cabinet through the back panel 30. In this case, all of the circulating refrigerated air is at a temperature at least as low as that air which is supplied to the rear of the cabinet. These additional layers of the air curtain may be supplied from the refrigerated air circulating in the unit or may be drawn into the cabinet by a fan, for instance through the top of the unit, from the ambient air surrounding the unit. The arrangement described in relation to Figure 2 provides an additional advantage in that it allows the defrost cycle of the refrigerated display unit to be improved.

Refrigerated display units of the general type of the invention usually require defrosting several times a day and the defrost process is carried out without unloading the shelves of the cabinet. It is known to defrost evaporators by switching off the refrigeration system and applying electrical heating or circulating warmed gases through the evaporator.

In the embodiment shown in Figure 2 the upper evaporator 65 requires the most heat to defrost as it is cooling air to the lowest temperature. The unit can be efficiently defrosted by heating only the upper evaporator 65 when the refrigeration system has been switched off. This will result in the temperature of the air supplied to the air curtain rising by a few degrees. The lower evaporator 60 or 60', is switched off and warmed by the incoming air only. Because it has thermal inertia the rise in temperature of the air which is supplied to the rear of the cabinet via the back panel 30 is extremely slow. The defrost cycle will finish before this temperature rise is enough to cause a significant increase in the temperature of the chilled foods stored on the shelves of the cabinet. In prior art devices the air temperature over the shelves at the end of the defrost cycle can rise to as much as 10°C, and the product temperature increase due to the defrost cycle can be as much as 2°C. With the improved defrost arrangement of the embodiment described above the maximum air temperature is only of the order of 3° or 4°C and the expected product temperature rise due to the defrost cycle is only about 0.5°C.

In both embodiments described above, the difference in temperature between the air curtain and the air for supply to the cabinet via the back panel means that low even temperatures can be achieved across the shelves, products at the front of the display unit 10 being compensated for the heat of the surroundings by the cold air curtain, and those at the back also being at a suitable temperature for storage.

Claims

CLAIMS ;

1. A refrigerated display unit comprising a display cabinet adapted to provide access to refrigerated food from the front thereof, a refrigeration system arranged to provide cold air to the cabinet, and temperature control means to enable a first cold air supply to a relatively forward part of the cabinet to be at a lower temperature than a second cold air supply to the rear of the cabinet.

2. A refrigerated display unit according to claim 1 wherein said first and second cold air supplies are obtained from a common cold air supply generated by the refrigeration system.

3. A refrigerated display unit according to claim 2 wherein said temperature control means comprises means for heating a divided portion of said common cold air supply to provide the first cold air supply before it passes into said cabinet.

4. A refrigerated display unit according to claim 3 wherein said heating means is an electrical heater.

5. A refrigerated display unit according to claim 3 wherein said heating means comprises one or more pipes carrying heat from the refrigeration system.

6. A refrigerated display unit according to claim 2 wherein said temperature control means comprises means for cooling a_ divided portion of said common cold air supply to provide the second cold air supply before it passes to the forward part of the cabinet.

7. A refrigerated display unit according to claim 6 -wherein said cooling means is a heat exchanger.

8. A refrigerated display unit according to claim 6 or claim 7 wherein there is provided a first evaporator arranged to cool the air forming said common cold air supply, which constitutes all of the cold air provided to the cabinet, and said cooling means comprises a second evaporator, the air supplied to the rear of the cabinet having been cooled only by said first evaporator.

9. A refrigerated display unit according to claim 1 wherein all of the cold air circulating in the cabinet and supplied to the relatively forward part of the cabinet is at a temperature lower than that of the air supplied to the rear of the cabinet.

10. A refrigerated display unit according to claim 1 wherein all of the cold air circulating in the cabinet is at a temperature at least as low as that of the circulating cold air supplied to the rear of the cabinet, at least a part of the cold air supplied to the relatively forward part of the cabinet being at a temperature lower than that air supplied to the rear of the cabinet.

11. A refrigerated display unit according to any preceding claim wherein the' temperature difference between said first and second cold air supplies is at least 4°C.

12. A refrigerated display unit according to claim 3 or any claim dependent thereon wherein said refrigeration system is arranged to supply cold air to a position rearward of said cabinet, and said common cold air supply is ducted upwardly to an upper portion of said unit from where said first cold air supply is directed rearwardly of a back panel of said cabinet and said second cold air supply is carried in a duct to said forward part of the cabinet where it is directed downwardly to form an air curtain.

13. A refrigerated display unit according to claim 6 or any claim dependent thereon wherein said refrigeration system is arranged to supply cold air to a position rearward of said cabinet, from where said first cold air supply is directed upwardly and rearwardly of a back panel of said cabinet and said second cold air supply is carried in a duct via said cooling means to an upper portion of said unit from where it is carried in a duct to a forward part of the cabinet and is directed downwardly to form an air curtai .

14. A refrigerated display unit according to claim 12 or 13 wherein said back panel is provided with apertures whereby said first cold air supply can pass into said cabinet in between a plurality of shelves.

15. A refrigerated display unit comprising a display cabinet adapted to provide access to refrigerated food from the front thereof, and a refrigeration system arranged to provide cold air for circulation in the unit and to supply cold air to a relatively forward part of the cabinet to form an air curtain and to the rear of the cabinet, wherein said refrigeration system comprises a first evaporator arranged to cool all of the circulating refrigerated air and a second evaporator to further cool a part of the circulating refrigerated air for said supply to the air curtain, the circulating refrigerated air supplied to the rear of the cabinet having been cooled only by said first evaporator.

16. A refrigerated display unit comprising a display cabinet adapted to provide access to refrigerated food from the ront thereof, and a refrigeration system arranged to provide cold air for circulation in the unit, wherein all of the circulating refrigerated air supplied to a relatively forward part of the cabinet to form an air curtain is at a temperature lower than that of circulating refrigerated air supplied to the rear of the cabinet.

17. A refrigerated display unit comprising a display cabinet adapted to provide access to refrigerated food from the front thereof, and a refrigeration system arranged to provide cold air for circulation in the unit, wherein circulating refrigerated air is supplied to the rear of the cabinet and to a relatively forward part of the cabinet to form at least a part of an air curtain, all of said circulating refrigerated air being at a temperature at least as low as that of the air supplied to the rear of the cabinet, and at least a part of the air curtain being at a temperature lower than that air supplied to the rear of the cabinet.