GB2449408A

GB2449408A - Refrigeration systems

Info

Publication number: GB2449408A
Application number: GB0704738A
Authority: GB
Inventors: Benedict Gummer; Nicholas Cox; Oliver Close-Brooks; John Mousley
Original assignee: ICWL Ltd
Current assignee: ICWL Ltd
Priority date: 2007-03-12
Filing date: 2007-03-12
Publication date: 2008-11-26
Also published as: WO2008110800A2; WO2008110800A3; GB0704738D0

Abstract

A plug-in refrigerator cassette 4, 5 for cooling a refrigerator cabinet 1 or a refrigerator service cassette for servicing a refrigerator cabinet are disclosed. Each cassette is removably engageable with the refrigerator cabinet and includes a guide means 10 to guide the cassette into or out of engagement with the refrigerator cabinet. Preferably, during engagement of the refrigerator cassette and the refrigerator cabinet the guide means align service connection means, such as electrical connections 8 and fluid connections 9, for connecting the refrigerator cassette to the refrigerator cabinet. The engagement of the refrigerator cassette with the refrigerator cabinet may also actuate a switch 15 to control a supply of electricity to the cassette. Preferably, the guide means comprise a resilient spring mounted wheel 11 connected to the cassette for cooperation with a guide rail 12, where the wheel is engageable in a depression 13 in the guide rail for positively connecting the cassette to the cabinet. A locking mechanism 14 may also be provided for locking together the cassette and the cabinet. An apparatus and method for defrosting a refrigerator by means of reversing a flow of refrigerant are also disclosed, where the refrigerator comprises a first heat exchanger (17, fig.3A) and a second heat exchanger (18, fig.3A) connected in a refrigerant circuit with a valve (24, fig.3A) arranged to direct a flow of refrigerant through the heat exchangers in a first direction, whereby heat is extracted from the first heat exchanger and transmitted to the second heat exchanger, and a second direction, whereby heat is extracted from the second heat exchanger and transmitted to the first heat exchanger. The second heat exchanger is connected to heat conducting means 2 for transferring heat to or from the refrigerator. Preferably, the heat conducting means comprises a fluid flow loop such as a chilled water loop.

Description

I

Refrigeration Systems The present invention relates to refrigeration systems, in particular to refrigeration cassettes for cooling refrigerator cabinets. The invention also relates to methods of defrosting refrigerators.

The invention is primarily applicable to commercial refrigeration systems, such as those used in superstores for cooling or freezing food products, but the concepts disclosed herein may be applied in other settings where refrigeration is required, and in air conditioning systems and so on.

Various types of refrigerator cabinet are in common usage, such as upright chiller cabinets and display freezers, chest freezers with or without a lid and walk-in cold/freezer rooms, for example, and the invention is applicable to all such refrigerator cabinets. Some refrigeration systems utilise one or more separate refrigerator cassettes also known as refrigerator "plugs", containing e.g. a condenser, an evaporator and a fan. The cassette is removably attachable to the refrigerator cabinet for cooling the cabinet's interior. By virtue of using a refrigerator cassette separate to the refrigerator cabinet, downtime of the refrigerator can be significantly reduced because the refrigerator cassette can be simply replaced if a malfunction occurs, or if the cassette is being serviced.

Further, any service and repair of the cassette can be carried out off site, avoiding inconvenience and potential dirtying of the refrigerator site.

The present invention provides a refrigerator cassette for cooling a refrigerator cabinet, removably engageable with the refrigerator cabinet, including guide means to guide the cassette into or out of engagement with the refrigerator cabinet.

Advantageously, the guide means provides accurate guidance of the refrigerator cassette into engagement with the refrigerator unit, thereby helping to avoid damage to the cassette or the refrigerator unit, and facilitating assembly of the refrigeration system.

Further, locking means can be provided allowing the cassette to be positively connected to the refrigerator unit. The locking means may be part of the guide means.

The present invention further provides a refrigerator comprising first and second heat exchangers disposed in a circuit in which a refrigerant can be located and a valve arranged to direct a flow of refrigerant through the first and second heat exchangers in a first direction whereby heat is extracted from the first heat exchanger and transmitted to the second heat exchanger and a second direction whereby heat is extracted from the second heat exchanger and transmitted to the first heat exchanger, the second heat exchanger being connected to heat conducting means for transferring heat to or from the refrigerator.

The first heat exchanger can be located in the refrigerator cabinet, and the second heat exchanger located outside the cabinet, e.g. in a refrigerator cassette. By virtue of changing the direction of flow of refrigerant, the refrigerator can effectively be reversed so that the inside of the cabinet is heated. This allows quick and convenient defrosting operations to be carried out. Further, energy savings result because heat is taken from the heat conducting means (e.g. a chilled water loop) and transferred to the cabinet. Consequently the work required to chill the water in the chilled water loop is reduced.

The invention also provides a method of defrosting a refrigerator which includes first and second heat exchangers disposed in a circuit, in which a refrigerant can be located, the second heat exchanger being connected to heat conducting means for transferring heat to or from the refrigerator comprising the step of reversing the direction of flow of the refrigerant through the first and second heat exchangers.

A problem of refrigeration systems in general is the service and repair of the cabinet condensing units. These cabinets are almost always in retail outlets which are full of customers. Any service or repair being carried out is inconvenient, often requiring shelves to be unloaded or cabinets moved. To address this issue, the invention further provides a refrigerator service cassette, for servicing a refrigerator cabinet, removably engageable with the refrigerator cabinet, including guide means to guide the service cassette into or out of engagement with the refrigerator cabinet.

Further advantageous features of the invention disclosed herein include: * Environmentally friendly hydrocarbon (low Global Warming Potential) refrigerants can be used throughout.

* The plugs can condense at an extremely low temperature. Therefore, their compressor power input is proportionally lower.

* Being suitable for both high and low temperature, the plug units can defrost on demand.

* It is possible to replace any separate refrigeration plug during system operation.

* The chiller that supplies the chilled water is of a high efficiency heat recovery configuration. Should there be a heat requirement within the premises for: potable hot water; underfloor heating; air curtain etc, the chiller should be able to supply the total requirement.

* In case of chiller failure, the cooling loop can be supplied by mains water.

* The system may also contain an energy free pre-cooler to reduce or eliminate the need for the chiller. For example, the pre-cooler may comprise an air to water heat exchanger utilised when the ambient air temperature is below the required temperature of the chilled water. It is also possible to use ground water extracted from a borehole. This water is generally relatively warm, but it can be used during periods of low refrigeration load e.g. over night, when the temperature of the water in the chilled water loop may be allowed to exceed 12 C.

Further advantages of the refrigerator cassette are as follows: The plug-in refrigerator cassette can be fully self-contained with all necessary controls for high-low temperature applications and can be built in a number of configurations to suit a variety of normal commercial applications e.g. display cases, cold rooms and cellars.

* A run of supermarket display cases of mixed temperature can be served by the same self contained plug-in system.

* Each cassette is totally interchangeable with another, whether it be a high or low temperature application. This is made possible by the services docking point. The services docking point can contain all the required interconnections to the chilled water loop, condensate drain, power supply and control/monitoring system.

* The above also means that trading can proceed uninterrupted as, should the need arise, replacement plug-in units may be kept on site and changed by unskilled labour within minutes.

The refrigeration cassette can comprise a trolley onto which the refrigeration equipment is mounted. The following components can be included in the refrigerator cassette.

Refrigerant -This can be a hydrocarbon or hydrocarbon blend. A blend of propene (R1270) and propane (R290) has been found to perform well under test conditions. Hydrocarbons were originally introduced as refrigerants to replace chlorofluorocarbons (CFCs) and hydrochiorofluorocarbons (HCFCs) which are both strongly ozone depleting and hydrofluorocarbons (HFCs) which have high global warming potential (GWP). Hydrocarbons are flammable so extra safety precautions need to be taken.

Compressor -A small horizontal scroll compressor can be used. This requires a minimal amount of space and also minimises the refrigerant charge size.

Evaporator -A tube-in-tube evaporator can be used. This is an evaporator coil which has an extra tube running within and parallel to the main refrigerant carrying tube. The refrigerant only occupies the circumference between the two tubes. This can allow further reductions in refrigerant charge and maximise the heat transfer to the refrigerant. The evaporator can alternatively be situated in the refrigerator cabinet.

Cabinet -The cabinet can be a conventional supermarket refrigerator or freezer cabinet, but without the refrigeration components, except for temperature sensors.

A space can be provided at the bottom of the cabinet into which the refrigeration or freezing cassette can be placed. In this space is the means to connect the chilled water supply, electricity supply and data network to the plug.

Expansion Device -A capillary expansion device can be used to eliminate the cost of a complex expansion valve. Thermostatic expansion valves can be used.

Fan Motor -non-sparking low voltage DC fan motors can be used. These eliminate the risk of leaked hydrocarbon igiition from the sparks inherent in a conventional AC motor.

Services Connections -A services docking point is incorporated, which can allow power, data, chilled water and drain connections to be made to the cassette or, in the absence of the cassette, service to be shut off. The object of this connector is to remove the possibility of bad or incorrect connections being made to the refrigeration plug due to human error or any other reason.

Data Network -A data network can be provided in the store in order to relay information between the cassettes and a central server, via an on site monitoring device. This device can also be responsible for the control of the plugs.

On Site Monitoring Device -The job of this device, as mentioned above, is to monitor and provide control of the refrigeration plugs and chillers within a store, via the data network. The control system can perform control operations both on the macro (system) scale and on the micro (plug) scale. This allows: * Continuous control and optimisation of the whole system, such as overall water flow rate, chiller operating point and optimisation of energy/heat use in terms of process integration.

* Continuous control and optimisation of each plug, such as refrigerant and water flow rates through the plug, compressor switching and maintenance alerts.

The monitoring device can also communicate with the central server via GPRS or an Internet link. This is so that a service agent can log performance Statistics for all cassettes in service and each overall system. It will also provide the basis of the billing system. In the case where a plug breaks down or requires service, this information can also be communicated by this means.

Defrost -Freezer plugs can incorporate a means of defrost. This could be in the form of reverse cycle hot-gas defrost or a spark proof defrost heater. The advantage of reverse cycle is that heat is actually absorbed from the cooling loop during defrost, reducing the duty on the chiller.

Lighting -The cabinets can incorporate cold lighting. This removes the extra load that conventional heat producing lights would put on the refrigeration cycle.

There follows a detailed description, by way of example only, of embodiments of the invention with reference to the accompanying drawings in which Fig. 1 is a schematic plan of a refrigeration cabinet array and a pair of refrigerator cassettes; Fig. 2A is a schematic side view of guide means shown with the refrigerator cassette disengaged from the cabinet; Fig. 2B corresponds to Fig. 2A with the refrigerator cassette engaged with the cabinet; Fig. 3A is a schematic diagram of a refrigerator capable of reverse cycle defrosting, with refrigerant flowing in a normal direction; Fig. 3B corresponds to Fig. 3A with the refrigerant flowing in the opposite direction; and Fig. 4 is a schematic plan of a room containing several refrigerators.

Fig. 1 shows schematically a plan view of a refrigeration system including a cabinet or an array of cabinets 1. In this embodiment, heat conducting means 2 comprising a fluid pipe extends through the cabinet array 1, and an electrical circuit represented by a dashed line 3 also extends through the cabinet array 1.

The conducting means 2, serves to take away heat which is rejected by the refrigerator cassette. The fluid pipe 2 branches off to connect with a number of fluid connection means 9, and correspondingly the electrical circuit 3 branches off to connect with a number of electrical connection means 8.

A first refrigerator cassette 4 is shown in the unplugged condition, comprising electrical connection means 6 corresponding to the electrical connection means 8 of the cabinet array 1. In the embodiment shown, the electrical connection means 6 of the refrigerator cassette 4 are of the male variety while the electrical connection means 8 of the cabinet array I are of the female variety, although any suitable connection arrangement may be utilised. The cassette 4 also comprises fluid connection means 7 for connection with the fluid connection means 9 of the cabinet array 1. Again, any suitable fluid connection arrangement may be utilised.

It is preferred that the fluid connection means 7, 9 include a self-actuating valve (not shown) to prevent any spillage of liquid during inter-connection and disengagement thereof. The fluid used in the heat conducting means 2 is water and, preferably the heat conducting means comprises a chilled water loop.

A second refrigerator cassette 5 is shown in the plugged-in condition wherein the fluid connection means 7, 9 and the electrical connection means 6, 8 are fully inter-engaged.

The electrical connection means 6, 8 allow the transmission of power to the refrigerator cassette 4, as well as control signals, so that the temperature in the cabinet can be maintained at a chosen level. The fluid connection means 7, 9, in addition to connecting the refrigerator cassette 4, 5 to the heat conducting means 2, also allows refrigerant to be transmitted between the refrigerator cassette 4, 5 and the cabinet 1 for cooling the cabinet.

Fig. 2A shows schematically guide means 10 for guiding the refrigerator cassettes 4, 5 into engagement with the cabinet array 1. The cassettes 4, 5 are mounted on wheels or a trolley for ease of movement thereof. In the embodiment shown, the guide means 10 comprises a guide rail 12 connected to the cabinet array I, including a sloped ramp portion 12 and a depression 13 for receiving a spring-mounted wheel 11 on the cassette 4, 5. As the cassette 4, 5 is brought into engagement with the cabinet array 1, the spring-mounted wheel 11 is pushed against the spring force as it rides up the ramp 12 and when the cassette 4, 5 is fully engaged, the wheel 11 snaps into the depression 13 positively connecting the cassette 4, 5 to the cabinet array 1. An automatic switch 15 shown in the open position in Fig. 2A is provided in the depression 13 and it is actuated when the spring wheel 11 is located in the depression 13. The switch 15 controls the supply of electricity to the cassette 4, 5, although a manually operated independent electrical control is also provided for each cassette. A locking mechanism 14 is provided adjacent the depression 13, and is shown in the open position in Fig. 2A.

The locking mechanism 14 is linked to the manual electrical control, whereby when the cassette is powered up, the locking mechanism 14 is engaged, locking the cassette 4, 5 to the cabinet 1. Therefore, the cassette 4, 5 cannot be removed during operation thereof.

In Fig. 2B, the spring wheel 11 is shown fully engaged with and locked in the depression 13. The electrical and fluid connections between the cassette 4, 5 and the cabinet I are fully made. The locking mechanism 14, in the embodiment shown, comprises an elongate rod 14 which is retractably mounted in the guide means 10 or in the cabinet 1 itself.

Fig. 3A shows schematically some of the features of the cassette, connected to the heat conducting means 2. A first heat exchanger 17 serves a cooling function and is located within a cabinet (not shown in Fig. 3A), while a second heat exchanger 18 rejects heat to the heat conducting means 2. A reversing valve arrangement 24 is provided, preferably in the cassette, for reversing the direction of flow of refrigerant. When the flow of refrigerant is reversed the first and second heat exchangers swap their roles as evaporator and condenser, whereby heat is taken out of the water circulating through the chilled water ioop 2 and is transmitted into the cabinet 1 for defrosting it. This allows quick and convenient defrosting of the cabinet and leads to increased efficiency by virtue of reducing the duty on a chiller that cools the water flowing in the chilled water loop. l0

Situated between the two heat exchangers is a parallel arrangement of first and second check valves 19, 22 and first and second expansion devices 20, 21. During normal operation of the cassette, i.e. during cooling of the cabinet, refrigerant flows through the first check valve 19 and the first expansion device 20, as shown by the arrowheads on one of the conduits 27. Refrigerant is prevented from flowing through the second expansion device 21 by the second check valve 22.

Conversely, during reverse operation of the cassette, refrigerant flows through the second check valve 22 and second expansion device 21, as shown by the arrowheads in Fig. 3B.

The reversing valve arrangement 24 comprises a main valve body 25 including a slider 28, and a pilot valve 26 including a solenoid coil. When it is desired to reverse the flow of refrigerant, the solenoid coil is activated and the pilot valve 26 redirects the flow of refrigerant through the main valve body 25. This in turn causes the refrigerant to flow in the opposite direction through the first and second heat exchangers 17, 18. A compressor 23 is provided for driving the flow of refrigerant and for providing the refrigerant pressure needed to achieve a cooling effect. The flow of refrigerant through the compressor is always in the same direction regardless of whether the cassette is in reverse operation.

During normal operation of the cassette, water in the chilled water loop 2 coming into contact with the second heat exchanger 18 can have an incoming temperature of 6 C to 7 C for example and an outgoing temperature of 12 C for example, having been heated by the second heat exchanger 18. In reverse operation of the cassette, the incoming and outgoing temperature of the water in the chilled water loop may be for example 6 C to 7 C and 2 C respectively.

Fig. 4 shows schematically a complete refrigeration system 30 located in a room 34, including an array of six cabinets 1, some of which are freezers and some of which are fridges. A chilled water circuit 2 is provided with a main trunk section, comprising a cold outward conduit 2a and a relatively warmer return conduit 2b, extending along the middle of the array. The conduits 2a, 2b can be located underneath the floor, or at any convenient location. A series of branch conduits 36 connect the cold outward conduit 2a to the cabinets I and a corresponding series of return branch conduits 37 coriiiect the cabinets 1 to the return conduit 2b.

In this embodiment, the condenser and evaporator and the other working refrigerator components 35 are integral with the cabinets, but the system could equally be set up using the non-integral refrigerator cassettes 4, 5 described earlier.

Where non-integral refrigerator cassettes are utilised these generally contain the condenser, evaporator, fans and controls, but it is also possible to situate some of these components within the cabinet, e.g. the evaporator and/or fans.

It is also possible to have air conditioning units 31 connected to the chilled water loop 2, the air conditioning units having air vents 32.

An external chiller 33, preferably a VEF ("Very environmentally friendly") chiller, is provided outside the room 34, for cooling the water in the chilled water loop. Preferably, at least two such chillers are utilised. These chillers are designed for maximum efficiency and minimal effects on the environment and they reject their heat to the atmosphere or to a heating system. The chilled water loop 2 also includes a twin head pump and pressurisat ion unit (not shown).

In a further embodiment of the invention not shown in the drawings, there is provided a trouble free method of servicing and testing the cabinet in the event that a refrigeration plug needs to be replaced. This removes the need for qualified service personnel on site. All service and repair of the actual refrigeration cassettes can be carried out off site.

Accordingly, there is provided a service plug comprising a trolley which can be moved in and out of the base of the refrigeration cabinet, and onto which is mounted all the necessary service equipment. This trolley is identical to the trolley which can be used to carry the refrigerator cassette. In use the service plug is attached to the electricity supply, the chilled water loop, the data network, the cabinet evaporator (where the evaporator is situated in the cabinet) and the cabinet sensors.

The service equipment can include a compressor, a refrigerant storage vessel, a vacuum pump, relevant pipework and valves, connections to the evaporator and cabinet sensors and all appropriate controls and systems. The service plug can be transported in a specially adapted vehicle which will also transport spare refrigeration plugs.

When a refrigeration cassette breaks down or starts to malfunction, an alert will be transmitted via the data network as described above. This will alert a service team who will despatch a service vehicle. The faulty refrigeration plug is then to be removed and placed into the service vehicle. The services plug is then removed from the vehicle and slotted into the cabinet from which the refrigeration plug has been removed, and is locked into position. This action will activate the service plug which will make a visible indication as to the integrity of the electronic connections. This will be an indication to the service personnel whether to proceed.

If the indication is to proceed, a button on the service plug is to be pressed, which will carry out tests as follows: I. Vacuum Test -The service plug's vacuum pump will remove refrigerant from the cabinet's evaporator, thus bringing about a state of partial vacuum. Once a predetermined pressure has been reached, valves will be closed and the pressure within the evaporator circuit monitored over a predetermined period of time. Any rise in pressure will indicate a leak into the evaporator, either due to a hole in the evaporator or pipework or a faulty connector. This will lead to a test failure.

2. Recharge -Assuming a test pass, the evaporator will be recharged with refrigerant from the refrigerant storage vessel to a pressure slightly higher than atmospheric. This is to account for any refrigerant lost during service plug removal and refrigeration plug replacement.

The service plug will then be returned to the service vehicle and a new refrigeration plug taken from the vehicle, placed into the cabinet and brought into operation.

If at any point during the test cycle, a fail is recorded, this will indicate the need for further investigation into the cause of the problem and this will require the presence of a qualified service person. It is intended that this will occur very infrequently. All information from the tests carried out will be transmitted to a central location via the data network.

There can be provided within the service vehicle the means to automatically refresh the refrigerant supply within the service plug. This will mean the service vehicle will be able to complete an entire day's work without returning to depot in order to replenish any supplies.

Claims

Claims I. A refrigerator cassette for cooling a refrigerator cabinet

removably engageable with the refrigerator cabinet, including guide means to guide the cassette into or out of engagement with the refrigerator cabinet.
2. A refrigerator cassette according to claim 1, wherein during engagement of the refrigerator cassette and the refrigerator cabinet the guide means aligns service connection means for connecting the refrigerator cassette to the refrigerator cabinet.
3. A refrigerator cassette according to claim 1 or 2, wherein engagement of the refrigerator cassette with the refrigerator cabinet actuates a switch.
4. A refrigerator cassette according to claim 3, wherein the switch controls a supply of electricity to the cassette.
5. A refrigerator cassette according to claim 2, wherein the service connection means comprises electrical connection means.
6. A refrigerator cassette according to claim 2 or 5, wherein the service connection means comprises fluid connection means.
7. A refrigerator cassette according to claim 6, wherein the fluid transmission means is connected to heat conducting means.
8. A refrigerator cassette according to any one of the preceding claims, wherein the refrigerator cassette is mounted on wheels.
9. A refrigerator cassette according to any one of the preceding claims, wherein the guide means comprises at least one guide rail.
10. A refrigerator cassette according to claim 9, wherein the guide means comprise a resiliently mounted wheel connected to the cassette, for cooperation with the guide rail.
11. A refrigerator cassette according to claim 10, wherein the resiliently mounted wheel is engageable in a depression in the guide rail for positively connecting the cassette to the cabinet.
12. A refrigerator cassette according to any one of the preceding claims, f'urther including locking means for locking together the cassette and the cabinet.
13. A refrigerator comprising first and second heat exchangers disposed in a circuit in which a refrigerant can be located and a valve arranged to direct a flow of refrigerant through the first and second heat exchangers in a first direction whereby heat is extracted from the first heat exchanger and transmitted to the second heat exchanger and a second direction whereby heat is extracted from the second heat exchanger and transmitted to the first heat exchanger, the second heat exchanger being connected to heat conducting means for transferring heat to or from the refrigerator.
14. A refrigerator according to claim 13, wherein the heat conducting means comprises a flow of fluid.
15. A refrigerator according to claim 14, wherein the fluid flows in a loop.
16. A refrigerator according to claim 14 or 15, wherein the fluid is water.
17. A refrigerator according to any one of claims 14 to 16, wherein the fluid is chilled.
18. A method of defrosting a refrigerator which includes first and second heat exchangers disposed in a circuit, in which a refrigerant can be located, the second heat exchanger being connected to heat conducting means for transferring heat to or from the refrigerator comprising the step of reversing the direction of flow of the refrigerant through the first and second heat exchangers.
19. A refrigerator service cassette, for servicing a refrigerator cabinet, removably engageable with the refrigerator cabinet, including guide means to guide the service cassette into or out of engagement with the refrigerator cabinet.
20. A refrigerator cassette substantially as herein described with reference to the accompanying drawings.
21. A refrigerator substantially as herein described with reference to the accompanying drawings.
22. A method of defrosting a refrigerator substantially as herein described with reference to the accompanying drawings.
23. A refrigerator service cassette substantially as herein described with reference to the accompanying drawings.

Amendments to the claims have been filed as follows 1. A refrigerator cassette for cooling a refrigerator cabinet removably engageable with the refrigerator cabinet, including guide means to guide the cassette into or out of engagement with the refrigerator cabinet.

2. A refrigerator cassette according to claim 1, wherein during engagement of the refrigerator cassette and the refrigerator cabinet the guide means aligns service connection means for connecting the refrigerator cassette to the refrigerator cabinet.

3. A refrigerator cassette according to claim 1 or 2, wherein engagement of the refrigerator cassette with the refrigerator cabinet actuates a switch. * ** S. S

4. A refrigerator cassette according to claim 3, wherein the switch controls a *.* supply of electricity to the cassette.

S..... * .

5. A refrigerator cassette according to claim 2, wherein the service connection : *.. means comprises electrical connection means. *..

S

*S.SSS * 6. A refrigerator cassette according to claim 2 or 5, wherein the service connection means comprises fluid connection means.

7. A refrigerator cassette according to claim 6, wherein the fluid connection means is connected to heat conducting means.

8. A refrigerator cassette according to any one of the preceding claims, wherein the refrigerator cassette is mounted on wheels.

9. A refrigerator cassette according to any one of the preceding claims, wherein the guide means comprises at least one guide rail.

10. A refrigerator cassette according to claim 9, wherein the guide means comprise a resiliently mounted wheel connected to the cassette, for cooperation with the guide rail.

11. A refrigerator cassette according to claim 10, wherein the resiliently mounted wheel is engageable in a depression in the guide rail for positively Connecting the cassette to the cabinet.

12. A refrigerator cassette according to any one of the preceding claims, further including locking means for locking together the cassette and the cabinet.

13. A refrigerator comprising first and second heat exchangers disposed in a circuit in which a refrigerant can be located and a valve arranged to direct a flow of refrigerant through the first and second heat exchangers in a first direction whereby heat is extracted from the first heat exchanger and transmitted to the second heat exchanger and a second direction whereby heat is extracted from the second heat exchanger and transmitted to the first heat exchanger, the second heat exchanger being connected to heat conducting means for transferring heat to or : from the refrigerator. S...

14. A refrigerator according to claim 13, wherein the heat conducting means comprises a flow of fluid.

15. A refrigerator aording to claim 14, wherein the fluid flOWS jfl a loop.

16. A refrigerator according to claim 14 or 15, wherein the fluid is water.

17. A refrigerator according to any one of claims 14 to 16, wherein the fluid is chilled.

18. A refrigerator according to any one of claims 13 to 17, wherein the first and/or second heat exchangers are located in a refrigerator cassette. tt

19. A method of defrosting a refrigerator which includes first and second heat exchangers disposed in a circuit, in which a refrigerant can be located, the second heat exchanger being connected to heat conducting means for transferring heat to or from the refrigerator comprising the step of reversing the direction of flow of the refrigerant through the first and second heat exchangers.

20. A refrigerator service cassette, for servicing a refrigerator cabinet, removably engageable with the refrigerator cabinet, including guide means to guide the service cassette into or out of engagement with the refrigerator cabinet.

21. A refrigerator cassette substantially as herein described with reference to the accompanying drawings. * **

22. A refrigerator substantially as herein described with reference to the **** accompanying drawings. *

*I**** * 23. A method of defrosting a refrigerator substantially as herein described with reference to the accompanying drawings. * ** * * * S...
24. A refrigerator service cassette substantially as herein described with reference to the accompanying drawings.