GB2415490A - Cold-storage appliance - Google Patents

Abstract

A cold-storage appliance includes at least one insulated container(32) and walls (34) defining a container compartment from which the container can be withdrawn to open the container and afford access to its interior and to which the container can be returned to close the container for cold storage of any items within the container. The appliance further includes condenser means (35) adjacent at least one of the walls (34) defining the compartment, the condenser means (35) being disposed outboard of that wall outside the compartment, and wherein an air gap (36) is maintained between that wall and the container when the container is closed within the compartment. A refrigeration circuit (fig A1, not shown) includes a suction/liquid heat exchange accumulator vessel. A three-port change-over valve is used to switch between a full-bore suction line (used for cooling) and a capillary tube (used for heating).

Description

1 2415490

IMPROVEMENTS IN OR RELATING TO REFRIGERATION

The inventions herein relate to the art of refrigeration. In preferred embodiments, the inventions relate to refrigerators, freezers, combined refrigerator/freezers, cold storage compartments configurable as both refrigerators and freezers, coolers and air conditioners, all for domestic or commercial applications including fixed and mobile appliances and installations. For brevity, all such appliances and installations will be referred to herein collectively as refrigerators unless the context demands otherwise.

Whilst the inventions primarily relate to appliances and installations for cold storage and cooling, they does not exclude such appliances or installations that have the additional ability to heat to above-ambient temperatures, for example in defrosting.

The basic elements of a typical refrigerator are a compressor, a condenser, a metering or expansion device and an evaporator, connected in that order in a circuit through which refrigerant cycles in use. The compressor compresses gaseous refrigerant that enters the compressor at low pressure via a suction or return line. The high-pressure hot gaseous refrigerant emanating from the compressor via a hot gas line flows through the condenser where it cools to a liquid also at high pressure, the condenser most commonly rejecting heat to atmosphere. The cool highpressure liquid refrigerant emanating from the condenser via a liquid line is forced through the metering or expansion device to reduce its pressure so that its boiling point drops to a level suitable for cooling. The effect of the metering or expansion device is to maintain the necessary pressure difference between the condenser and evaporator. The cool low-pressure liquid refrigerant emanating from the metering or expansion device flows through the evaporator where it evaporates in a low- pressure environment to draw heat from a storage compartment cooled by the evaporator.

Finally, the low-pressure gaseous refrigerant emanating from the evaporator is drawn back into the compressor via the suction line to start the cycle again.

This inventions herein develop concepts described in prior patent applications filed by the Applicant. These prior patent applications are exemplified as follows. For brevity, the content of these applications is incorporated herein by reference: Country Application No Publication No United Kingdom 9921564.2 2354061 Patent Cooperation Treaty PCT/GBOO/03521 WO 01/20237 United Kingdom 0106164.7 2367353 United Kingdom 0316697.2 2387897 United Kingdom 0316698.0 2387898 United Kingdom 0118281.5 2368898 Patent Cooperation Treaty PCT/GB02/01139 WO 02/073107 United Kingdom 0229167.2 2387530 Patent Cooperation Treaty PCT/GB02/01155 WO 02/073105 Patent Cooperation Treaty PCT/GB02/01158 WO 02/073104 United Kingdom 0320856.8 2405688 United Kingdom 0320858.4 2398355 Patent Cooperation Treaty PCT/GB2004/003659 WO 2005/024315 Patent Cooperation Treaty PCT/GB2004/003796 WO 2005/024314 United Kingdom 0422117.2 United Kingdom 0422118.0 United Kingdom 0422119.8 United Kingdom 0422120.6 United Kingdom 0422121.4 United Kingdom 0504965.5 United Kingdom 0504970. 5 United Kingdom 0504971.3 United Kingdom 0514914.1 The inventions arise from customer feedback, identifying the following desiderata: In relation to drawer-type cold-storage appliances, a modular design for a flexible offering based on operational requirements (e.g. varying drawer sizes in different combinations, and numbers of drawers - there could be 1, 2, 3, 4 or more drawers).

A modular design that provides a smaller footprint in the restricted space of food service chain operated kitchens.

A modular design that will reduce installed costs so that the benefits of the Applicant's inventions can be enjoyed in a wider variety of applications, and not just in those that can afford expensive equipment. Examples are retail display, healthcare, and consumer applications.

A modular design that retains the benefits offered by the Applicant's previous designs.

The inventions herein are particularly applicable to solid drawers exposed to ambient or above-ambient air on their external surfaces, although ideas relating to refrigeration processes as opposed to freezing may be of wider application.

From one aspect, the inventions include a cold-storage appliance having: at least one insulated container; and walls defining a container compartment from which the container can be withdrawn to open the container and afford access to its interior and to which the container can be returned to close the container for cold storage of any items within the container, wherein the appliance includes condenser means adjacent at least one of the walls defining the compartment, the condenser means being disposed outboard of that wall outside the compartment, and wherein an air gap is maintained between that wall and the container when the container is closed within the compartment.

By way of example, the condenser means may be adjacent at least a bottom wall defining the compartment, and/or adjacent at least a rear wall defining the compartment and/or adjacent at least a side wall defining the compartment. The walls of the compartment may be structural components of the appliance.

Preferably, the condenser means is mounted to said wall. The air gap within the compartment preferably constitutes an internal air passage and an external air passage is provided outboard of the condenser means. In that case, the external air passage is suitably defined within the appliance and the internal air passage preferably introduces heat to minimise condensation upon external surfaces of the container within the compartment. Also, the internal air passage may be maintained at aboveambient pressure. Air discharged from the internal air passage may then be directed through the external air passage.

Other options are a means for maintaining a partial vacuum in the internal air passage, and means for directing non-air purge gases through the internal air passage. A water evaporator associated with the condenser may discharge water vapour into the internal air passage, or a water evaporator associated with the condenser may discharge water vapour into the external air passage.

Means may be provided for rejecting heat by conduction from the condenser to structural parts of the appliance or to heat-exchanging attachments to the condenser.

In order that the inventions may be more readily understood, reference will now be made by way of example to the accompanying drawings.

Figures 1 and 2 show a prior art warm cabinet condenser unit, Figure 1 being a plan view l O and Figure 2 being a partial section on line X of Figure 1. Here, condenser pipe coils 29 are attached to the casing of a refrigerator cabinet 30 and PU foam 31 is injected to form an insulated structure defining a cold-storage volume. In effect, the coils 29 are sandwiched between the foam insulation 31 and the casing of the cabinet 30. Such an arrangement can commonly be provided on three vertical walls of the cabinet 30, namely two side walls and a back wall, and in theory could be employed on other walls too e.g. top and bottom. It rejects heat to ambient air and provides a means for controlling condensation when condenser surfaces are close to or touching other surfaces, for example where a refrigerator is placed between kitchen storage units. It will be noted that the casing 30, condenser coils 29 and insulation 31 are all fixed in relation to each other, requiring disassembly or destruction of the unit should it ever be desired to separate those components.

Figures 3 and 4 show a cold-storage appliance modified in accordance with the present invention. Figure 3 is a plan view and Figure 4 is a detail plan view of region Y marked in Figure 3. Here, an insulated container 32 such as a drawer can be moved in and out of a cabinet 33 defined by condenser casing walls 34. Thus, the insulation moves relative to condenser and the casing, in normal use of the appliance. A condenser pipe coil 35 visible in Figure 4 is located to the outboard side of a condenser casing wall 34 and so faces away from the container 32. This arrangement, if used with a flat sheet condenser casing, provides for separation of the pipe coil 35 from an air gap 36 between the container 32 and the condenser casing wall 34.

There are several significant benefits to this arrangement. For example, the internal flat condenser casing provides a smooth wipe-clean surface without dirt traps. Separate air passages can be created on respective sides of the condenser casing to the benefit of airflow, and each air passage can be designed for specific requirements. For example, the internal air passage can be designed to supply only the minimum amount of heat required for anti-condensation requirements, without adding unnecessary cooling load to the refrigeration system, and the external air passage can be designed to reject the remaining portion of the unwanted heat. The or each air passage may be ventilated, for heat exchange, by natural convection or by forced air flow (e.g. by fans).

Air pressure and airflow directions can be optimised between the internal and external air passages. For example, the internal air passage could receive filtered air that positively pressurises the cubicle to prevent unclean air ingress, keeping internal surfaces clean and hot condenser air out. The external air passage can be at a lower pressure (negative) relative to the internal air passage. Unfiltered ambient and/or air discharged from the internal air passage can be directed though the external air passage.

Other variations including the use of purge gases and the creation of a partial vacuum can be envisaged. Vacuum storage can also be useful for dehydration.

Where the condenser is to be used to evaporate water emanating from the use of defrost or condenser means, a choice can be made as to which air passage or surface should be used to reject that water. For example, it may be desirable to maintain a higher humidity around the external surfaces of the drawer, in which case the water can be discharged to the internal air passage. More likely, however, it will be preferable to discharge the water outside the inner air passage and hence into the external air passage.

Further variations employing slots, dampers, louvers and so on between the air passages can be envisaged. Heat rejection could be wholly to either the internal or external side of the condenser casing. Heat can also be rejected by conduction to structural or heat exchanging attachments to the condenser casing.

Again, such an arrangement can commonly be provided on three vertical walls of the cabinet 33, namely two side walls and a back wall, and in theory could be employed on other walls too e.g. top and bottom. In some applications, the bottom wall under the drawer could be enough on its own to achieve the necessary heat transfer.

The casing defined by the condenser casing walls 34 may or may not be structural: it can be self-supporting and structurally independent, or it may take support from adjacent units such as kitchen cabinets to which it is attached. The casing could be a self-contained module including other components such as drawer lids or drawer runners. The condenser casing warms the surrounding air and adjacent surfaces by radiation and convection, which prevents condensation by using a portion of the rejected heat from the condenser. Where the casing is fixed to an adjacent structure, heat rejection from the condenser may also be by conduction.

Additionally, defrost water and condensation from a cooling fan coil may be drained to the condenser plate and evaporated locally to the unit. This arrangement saves the complexity of running a pipe to a convenient drain point, which is particularly useful for unitary installations. A further variant envisages a fan or the like forcing air to circulate through the condenser heat exchange and around the external surfaces of the insulated cold-storage container and evaporator fan coil.

Moving on, Symbols and Notes A and Figure 5 are as disclosed in UK Patent Application No. 0320856.8 and International Patent Application No. PCT/GB2004/003796, with slight amendments to the Symbols and Notes page.

Figure 5 is included as a preferred embodiment of a capillary 'pipe branch' concept.

Figure 6 shows an improvement to Figure 5, where a further branch pipe and capillary are added to bleed liquid refrigerant straight into the suction/liquid heat exchange accumulator vessel. The bleed line ensures that liquid is always present in the vessel so that heat can be exchanged between the LP suction and HP liquid.

Under normal conditions liquid will flood back to the LP accumulator from the evaporators. However, on start-up and periods of high load, liquid may be starved from the LP accumulator. Under these conditions the strut- off solenoid valve is opened to provide liquid directly into the LP accumulator.

Figure 7 shows a variant of Figures 5 and 6 that is suitable for modular distribution. The most significant variances are: The common condenser is replaced by local condensers sized to match the requirements of each evaporator served by the distributed modular arrangement.

The common LP Suction accumulator heat exchanger is replaced by local units sized to match the requirements of the evaporator and condenser used in each l O distributed modular arrangement.

Local modular condensers and liquid lines can be used too; boil off defrost water, control condensation, and heat seals.

l S A common item is one or more compressor(s) which can be mounted separately from the drawers. The common compressor will save space over several unitary compressors and it is anticipated that energy will also be saved.

The above arrangement is similar to the material disclosed in International Patent Application No. PCT/GB2004/003796, but for multiple modules rather than just unitary appliances.

Moving on to Figures 1001 to 1002, these diagrams show plan(s) of an insulated drawer with lid mounted fan coils shown in dashed line above (fan coils could equally be of the rear mounted type with duct connections through the lid).

Figure l OOl a shows a normal drawer with single fan coil above, while Figure 1 OOlb shows a drawer with two separate fan coils.

Figures 1002a and 1002b show the drawer with an insulated divider in place. The drawer is split to form two separate compartments. In 1 002a the temperature control will be common to both compartments while in 1002b, each may be controlled independently of the other.

It is assumed that a magnetic type lid seal (probably with trace heating) will be fitted to mate with the internal divider.

This arrangement will provide two drawers in one, saving space and cost over the normal side-by-side arrangement with an air gap in between the drawers. Clearly there can be more than one drawer division.

Figure 1010 shows a slight variation of the magnetic seal disclosed in GB 0320858.4 and PCT/GB2004/003659 where the seal is located outside of the bin rim. This provides maximum exposure to ambient air to prevent condensation and icing. On the inside edge of the bin rim a curved flexible membrane, or flap, forms an insulating air pocket to keep the coldest air off the internal face of the seal.

Figure 100 shows a bleed line capillary tube used on start-up/high load to dump cold liquid into the accumulator to enable heat exchange from the warm liquid line. An alternative is possible where the evaporators are fitted with fans or other means to promote heat exchange (i.e. a fan coil) . The simple method of getting cold liquid into the accumulator is to turn off the evaporator fans (preventing heat exchange in the evaporator) and returning cold liquid to the accumulator.

Figure 1020 (see also Symbols and Notes 1) show a variation on the refrigeration circuits for modular systems and distributed condensers with moving drawers. In this process circuit, a majority of the condensing/sub-cooling takes place in the compressor module.

However, sufficient heat is contained in the liquid line to each module to a) evaporate defrost water; b) provide anti-condensation heating; and c) provide seal heating (if required). The anti-condensation heater is applied to the module cabinet bottom/sides, and the insulated drawers move in and out of the cabinet just as in the distributed condenser version.

At each module there is a branch off the liquid line that is used during defrost of the evaporator (normally the defrost line solenoid valve is closed). The solenoid valve on the liquid line controls the flow of cooling refrigerant into the evaporator.

Liquid/suction line heat exchange (LSHX) takes place before the capillary tube. Any suction liquid that finds its way past the local LSHX is captured by the common Suction Line Accumulator (SLA) in the compressor module.

Each drawer module can be defrosted individually. On defrost, all drawer liquid line solenoid valves are closed. The normally-closed common condenser by-pass valve and hot gas valve on the module to be defrosted are opened. Hot gas from the compressors will then circulate though the evaporator and melt the accumulated ice. A useful by-product of this regular defrost process is that the hot gas travels at high velocity though the pipes and evaporators, entraining any oil carried over from the compressors, thus acting as an oil return system.

A further aspect of the invention is directed to cooling and heating of drawers. This aspect came about due to a large chain having an occasional, but regular, requirement for defrosting significant amounts of frozen chicken burgers. In between defrosts, the main requirement is for cooling. Currently, they have to use two different pieces of equipment, one of which is largely redundant, and this is wasteful of expensive retail floor space.

This invention allows the drawers to be employed in either cooling or heating mode, independently, and in any combination. The process uses a modified refrigeration cycle with parallel branches for maximum flexibility and simplicity of control. So, at the touch of a button a cooling drawer may be turned into a heated drawer and vice-versa.

When the cooling or heating process circuit is used in combination with a high volume secondary air circulation system, the drawers may be used for rapid chilling or defrosting (rethermalisation) of food product.

So, one unit can now do the job of five units: Chilling above 0 C.

Freezing below 0 C.

30. Blast chilling.

Heating above ambient.

Rethermalisation.

Each drawer can perform all five jobs and can be changed from one to any other at the touch of a button (in the case of rapid chilling and rethermalisation, a basket with integral fan also needs to be inserted into the drawer).

Whilst the following descriptions are directed to the Applicant's refrigerated drawer systems in food-service use, the invention has wider application: for example, it tht can be used with door cabinets and other forms of storage compartments and even HVAC.

In reviewing the following Figures, reference should be made to Symbols and Notes 2 which has been amended to reflect the standards used in this set of diagrams.

Figure 14 corresponds to Figure 14 of UK Patent Application No. 0320856.8 as a starting point of reference. This refrigeration process system includes hot gas defrost of the evaporator coils.

For the sake of clarity, this text will use 'defrost' to describe the process of removing ice build-up from the evaporator coil. 'Rethermalisation' is used to describe the process of raising a mass of frozen product to above its ice point temperature (including phase change) .

The process of Figure 14 is used to provide individual variable temperature cooling to each fan coil compartment and independent defrost to each evaporator coil. Defrost is performed by passing high pressure, high temperature gas from the compressor discharge through the evaporator to be defrosted. While defrosting a particular fan coil, the cooling is shut off to the other compartments. This is because the high pressure hot gas raises the pressure of the common suction line above that which can be used for cooling. However, because the defrost operation is normally quite short in duration (1 to 3 minutes), normal cooling is restored before the stored product is adversely affected in any storage compartment.

Therefore, the process of Figure 14 is not suitable where there is a requirement for significant or continuous heating of a compartment while maintaining cooling in other compartments.

Figure Al shows a modification of Figure 14 that incorporates additional features downstream of the evaporator on the suction line. The three-port change-over valve is used to switch between a full-bore suction line (used for cooling) and a capillary tube (used for heating).

In normal cooling mode the branches will operate in exactly the same way as Figure 14, with the down stream from the evaporator being directed through the three-port valve to the full bore suction line. Likewise, the hot gas defrost may operate in exactly the same way as Figure 14.

When the drawer is in heating mode, the evaporator upstream liquid line solenoid valve is shut and the hot gas valve is opened. The downstream three-port valve is switched so that the flow is diverted through the capillary tube. Under these conditions the evaporator actually becomes a condenser and the condensed liquid is expanded to a low pressure/temperature liquid through the capillary tube and discharged into the suction header. The low pressure/temperature liquid from the capillary will mix with discharge from the other evaporators. Hence the suction header can be maintained at a pressure that is low enough to sustain cooling in the adjacent storage compartments. Therefore the parallel processes will support the simultaneous cooling of some compartments while heating other compartments.

Once all four drawers are on cooling, the suction liquid/vapour mix from the fan coils is returned to the accumulator, where heat is added from the liquid line heat exchange and vapour is drawn off back to the compressor.

The number of drawers requiring heating or cooling and the loads associated with each drawer will vary infinitely. To maintain the heat and mass balance where the COOLING load exceeds the heating load, the excess heat will be rejected through the condenser (the compressor condenser). To maintain the heat and mass balance where the HEATING load exceeds the cooling load, the additional heat will be injected on the suction return line to the accumulator (the suction heat exchanger). The process will be controlled by monitoring the amount of superheat in the suction to the compressor. Temperature sensor TS 100 measures the liquid temperature in the accumulator and TS101 measures the vapour temperature returning to the compressor. Heat is added or subtracted to the system to maintain a superheat of about 3 C (the superheat protects the compressor).

External heat rejection and injection can be from a low-temperature source such as ambient air.

By way of example, the suction heat exchanger has a variable-speed fan to adjust the heat input into the system. A three-port valve provides a bypass around the suction heat exchanger for use during periods of cooling only, or for defrosting the heat exchange unit.

During periods of light heating load in the drawers, the variable speed fan (or other control means) on the compressor condenser may also be used to input heat into the accumulator through the suction / liquid heat exchanger. This process uses a three-pipe distribution system to each fan coil (liquid line, suction line, & hot gas line).

Figure A2 shows a slight variation on Figure Al, the main differences being the economy of solenoid valves. The liquid line solenoid has been moved to the evaporator downstream suction line, mainly overcoming the requirement for the three-port changeover solenoid valves.

On a cooling cycle, the evaporator down stream solenoid valve is open to enable the flow of refrigerant to the branch and the hot gas valve is closed. For a heating cycle the valve positions are reversed, where the hot gas valve is open and the suction valve is closed forcing the discharge from the evaporator through the down stream capillary tube.

When there is neither demand for cooling or heating through a branch, both the suction and hot gas valves will be closed. It will be appreciated that under these conditions there is still a refrigerant flow path through the upstream capillary, evaporator, and down stream capillary. However, the flow rate should be so small that there will be very little impact on the fan coil heat exchange. This is because the capillaries will act in series to create a high resistance path; additionally the evaporator will boil off the very low flow of refrigerant, creating even further resistance to flow in the down stream capillary (a similar mass of gas has a significantly higher flow resistance than that of liquid).

Because of the above permanent by-passes, a common liquid line solenoid has been added to facilitate a system pump down should this be required for operation or maintenance reasons (note; pump down transfers the refrigerant from the low side evaporators into the high side condensers).

Figure A2 details an alternative method of controlling the suction heat exchanger to alleviate icing problems when adding heat to the sub-zero liquid/vapour stream from ambient air (stream temperature can typically be -30 C). The stream is split so that some passes through the heat exchanger and some by-passes it, to be mixed again downstream of the exchanger. This has the advantage of being able to raise the whole surface area of the heat exchanger coil above 0 C (superheating the stream) and prevent the formation of ice.

The heat injection process can be controlled by cycling the solenoid valve and heat exchanger fan(s) in various combinations to meet the varying load. Otherwise the process is the same as Al.

Figure 1020 New Format shows exactly the same process as Figure 1020 described above but is drawn in a format similar to Al and A2 for easier comprehension. In this process the suction / liquid line heat exchange takes place locally at each drawer module, rather than in the accumulator. The warm liquid from the compressor condenser is used to evaporate defrost water and provide anti-condensation heating at each drawer module.

A bypass line and solenoid valve (two- or three-port) are used to divert the discharge from the compressors around the condenser so that hot gas can be transported through the liquid line to defrost a module fan coil. During defrost operation only the defrost solenoid valve of the fan coil to be defrosted is open, all other hot gas and liquid solenoids are closed (if required more than one fan coil can be defrosted simultaneously).

This process uses a two-pipe distribution system to each fan coil (liquid line and suction line).

Figure A3 shows a modification of Figure 1020 in line with the developments of Figure A2. It is the same as the modified parts of A2 over Figure 14. This process uses a three pipe distribution system to each fan coil (liquid line, suction line and hot gas line).

Figure A4 shows a development of Figure AS where the system condensing is distributed to each drawer module. Condensing may be completely or partially accomplished at the modular fan coils. Partial condensing at the fan coils will require a common condenser that is not shown on the diagram but will be similar to that of Figures Al to A3. Local modular condensers can have variable-speed fans to control the head pressure and accumulator suction return superheat. This process uses a two-pipe distribution system to each fan coil (liquid line & suction line).

The above figures and associated fan coils are satisfactory for normalcold storage and heated drawer holding requirements, where the heat exchange from the stored product does not have to particularly great (e.g. no rapid changes of product temperature). In these processes, the fan coil air velocities over the stored product are relatively low.

However, where rapid chilling and rethermalisation are required, a much higher product heat exchange is needed.

Figure AS shows the AIR side of a fan coil (shown in the dashed box) as the Primary heat exchange through the drawer lid. Inside the drawer is a very much larger air flow rate Secondary recirculating loop that exchanges heat with the stored product. Because the airflow rate in the secondary circuit is very high, the temperature rise/drop is small, say At=2 C. The air flow in the Primary circuit is much lower, so the temperature rise/drop is higher, say At=10 C (but the heat flow is the same). The low At in the Secondary circuit maintains the air temperature closer to the actual product temperature preventing heat and cold burns to stored product. The higher At in the Primary side keeps the component sizes down.

The secondary circuit forces large volumes of air at a relatively high velocity over the stored product to promote heat exchange for rapid cooling or heating. The Secondary side recirculation fan and air passages can be constructed in the form of a drop-in basket that can be placed in any drawer. The basket may be removed for cleaning or be put inside another drawer.

GENERAL NOTES

Figures A l to A4 do not involve a 'reverse cycle' as normally used in refrigeration cooling / heating applications. Each branch can be used for cooling or heating but the process flow is always in the same direction. This system requires very simple control and management making it attractive across a wide range of applications. It is anticipated that the energy consumption for a cooling drawer will be similar to that of a heating drawer.

Oil return to the compressor can be by high velocity hot gas as used in the defrost cycle in Figures 14 and 1020 (and can also be achieved by the arrangements of Figures Al to A4) or by an oil separator on the compressor discharge.

The hot gas from the compressor discharge may not be at a high enough temperature to suit some warming and holding applications which ideally should be above 70 C. It is anticipated that electric heaters can be added to the fan coils to boost' the supply air temperature to the required levels. This is common prior art and has not been shown in the diagrams.

The condenser, suction heat exchanger, and fan coils can use many well known methods of heat capacity control variable speed fans, multiple fans, regulating valves, on/off control etc. When heat injection is required the suction line heat exchanger could be substituted by using the condenser. This would require by-pass lines and valving arrangements to divert the compressor discharge around the condenser and the suction line through the condenser.

These arrangements are engineering developments that have not been detailed in the diagrams.

An interesting point is why it is advantageous to heat a drawer using refrigeration, rather than cooling with refrigeration and heating with, say, electricity. The first reason is physical size. The fan coil already has a refrigerant heat exchanger. An additional electric heat exchanger (on the air side) would approximately double the space requirement at each drawer, with no benefit to the customer.

Other reasons are safety and control. Electric heaters would almost certainly have to be 230V as low-voltage heaters would require huge transformers and power distribution systems. 230V heaters in a normally refrigerated fan coil that can be subject to condensation and icing will require expensive safety and protection engineering.

Another reason is power consumption and efficiency. The highest load for heating is during rethermalisation, and that requires relatively low temperatures that are conveniently available from condensing the compressor discharge stream. Additionally, heat injection at the suction heat exchanger should be 'for free' using ambient air.

A 'booster' heater may be used to raise the temperature of a warming drawer above 70C at times when the compressor discharge is not warm enough. The 'boost' heater will be a very small-duty device and would probably be electric. However, such a heater would warm the hot gas to a drawer and never be exposed to low temperatures or condensation.

Finally, further inventions relate to drawers and other access methods, and especially to manufacturing methods for placing magnetic seals in insulated drawers.

The problem An insulated drawer for use with a commercial refrigeration system is required to include a rectangular magnetic frame located at or beneath the upper (sealing) face. This magnetic frame attracts magnets of opposite polarity (or a ferritic strip) located within a flexible seal mounted in the refrigerator housing above the insulated drawer.

Since the insulated drawer is intended for food use, it must be simple to clean and be free from dirt traps. This requirement precludes two-piece assemblies of the insulated drawer since the joint presents a potential dirt trap.

The preferred method of manufacture of a one piece insulated drawer is by rotational moulding. Typically the materials used in the rotational moulding process would include: Polyethylene Polypropylene PVC Nylon Ethylene-Vinyl Acetate Ethylene-Butyl Acetate The preferred materials for food use would be polyethylene or polypropylene and since the former has better impact strength at lower temperatures, polyethylene is the chosen material for this application.

Polyethylene and polypropylene are both inert materials and do not bond well with other plastics. Consequently when flexible magnets are introduced into the mould tool of a rotational moulding, the result is a poorly bonded magnet with many dirt traps where the two dissimilar materials have failed to cross-link and fuse.

Solution I This solution improves the bonding of the flexible magnet to the rotational moulding by changing the composition of the binder used in the manufacture of the magnetic material to a type more compatible with the rotational moulding material being a plastics material such as polyethylene or polypropylene. In the magnetic strip a proportion of the flexible polymer binder is replaced with polyethylene or polypropylene so that during the moulding process the normal plastic fuses with the magnetic strip.

Flexible magnets are normally manufactured using approximately 90% magnetic dust and 10% flexible polymer binder. The magnetic dust is typically Strontium Ferrite or Barium Ferrite, and the flexible polymer binder is typically DuPont Hypalon (Chlorosutonated Polyethylene, an ozone resistant rubber) with Exxon Vistanex (Polyisobutylene, a soft inert polymer).

The moulding process (solution 1) The steps below describe the moulding process to seamlessly incorporate the magnetic strip into the rotational moulding process.

In a non-magnetic aluminium mould, steel strips are positioned internally where the magnets are to be located.

Flexible magnets are placed on the steel locating strips.

The granular moulding material is introduced into the tool and the component is rotationally moulded.

During the rotational moulding process heat is added at approximately 250 C and the granular material melts and flows onto the mould surfaces.

The application of heat and the melting of the granular material acts on the similar material incorporated into the magnetic strip fusing the surfaces together.

15. The resultant moulding has a flexible magnet at the surface of the rim. The surface mounting of the magnet ensures maximum attraction to the corresponding magnet or ferritic strip in the mating seal.

The magnet is clearly visible since it is on the outside surface of the moulding.

Solution 2 This solution uses a normal flexible magnet (with no material modifications) and encapsulates it below the surface of the moulding. This is achieved by introducing a thin plastic strip of the moulding material between the magnet and the mould tool. During moulding the plastic strip fuses with the mould material.

The moulding process (solution 2! The steps below describe the moulding process to seamlessly incorporate the magnetic strip into the rotational moulding process.

As previously, a non-magnetic aluminium mould has steel locating strips internally at positions where the magnets are to be located (it is noted here that it is not imperative to use a non-magnetic mould as positioning of the magnet may be achieved by recess detail in the tool or through use of a positioning frame) A thin plastic sheet is applied against the inside surface of the mould tool where the magnet it to be positioned and the magnets are then placed against the sheet.

The moulding material is introduced into the tool and the component is rotationally moulded.

During the rotational moulding process heat is added at approximately 250 C and the granular material melts and flows onto the mould surfaces.

The application of heat and the melting of the granular material acts on the similar plastic material placed between the mould tool and the magnetic strip fusing the surfaces together.

The resultant moulding has a flexible magnet placed just below the surface of the rim. The small gap introduced between the magnet and the rim surface slightly reduces the magnetic attraction of the corresponding mating seal.

The magnet is still visible through the thin polyethylene sheet though this may be made less visible if thicker or more opaque sheet is used.

Claims (16)

1. A cold-storage appliance including: at least one insulated container, and walls defining a container compartment from which the container can be withdrawn to open the container and afford access to its interior and to which the container can be returned to close the container for cold storage of any items within the container; wherein the appliance includes condenser means adjacent at least one of the walls defining the compartment, the condenser means being disposed outboard of that wall outside the compartment, and wherein an air gap is maintained between that wall and the container when the container is closed within the compartment.

2. The appliance of Claim 1, wherein the condenser means is mounted to said wall.

3. The appliance of Claim 1 or Claim 2, wherein the air gap within the compartment constitutes an internal air passage and an external air passage is provided outboard of the condenser means.

4. The appliance of Claim 3, wherein the external air passage is defined within the appliance.

5. The appliance of Claim 3 or Claim 4, wherein the internal air passage introduces heat to minimise condensation upon external surfaces of the container within the compartment.

6. The appliance of any of Claims 3 to 5, wherein the internal air passage is maintained at above-ambient pressure.

7. The appliance of Claim 6, wherein air discharged from the internal air passage is directed through the external air passage.

8. The appliance of any of Claims 3 to 5, including means for maintaining a partial vacuum in the internal air passage.

9. The appliance of any of Claims 3 to 8, including means for directing non-air purge gases through the internal air passage.

10. The appliance of any of Claims 3 to 9, wherein a water evaporator associated with the condenser discharges water vapour into the internal air passage.

11. The appliance of any of Claims 3 to 9, wherein a water evaporator associated with the condenser discharges water vapour into the external air passage.

12. The appliance of any preceding Claim, comprising means for rejecting heat by conduction from the condenser to structural parts of the appliance or to heat-exchanging attachments to the condenser.

13. The appliance of any preceding Claim, wherein the condenser means is adjacent at least a bottom wall defining the compartment.

14. The appliance of any preceding Claim, wherein the condenser means is adjacent at least a rear wall defining the compartment.

15. The appliance of any preceding Claim, wherein the condenser means is adjacent at least a side wall defining the compartment.

16. The appliance of any preceding Claim, wherein the walls of the compartment are structural components of the appliance.