REFRIGERATOR WITH A PHASE CHANGE MATERIAL AS A THERMAL STORE

Abstract

A refrigerator having a thermal store comprising a phase change material is disclosed. The refrigerator has a cooling chamber for containing an object to be cooled, and a vapor compression refrigeration system including a first evaporator for cooling the cooling chamber and a second evaporator for cooling the phase change material. A valve is provided to control the flow of refrigerant to the first and second evaporators depending on the cooling load on the refrigerator. When the refrigerator is subject to a relatively low cooling load, refrigerant flows to the second evaporator to cool the phase change material and, when the refrigerator is subject to a relatively high cooling load, refrigerant flows to the first evaporator such that increased cooling is provided to the cooling chamber by the first evaporator and the phase change material.

Claims

1. A refrigerator comprising: a cooling chamber configured and arranged to contain an object to be cooled; a thermal store including a phase change material; a vapor compression refrigeration system including a first evaporator for cooling the cooling chamber and a second evaporator for cooling the phase change material; and a valve and a valve position controller circuit configured and arranged to control flow of refrigerant to the first and second evaporators depending on the cooling load on the refrigerator, by when the refrigerator is subject to a relatively low cooling load, controlling a position of the valve with the valve position controller circuit to flow refrigerant to the second evaporator to cool the phase change material and, when the refrigerator is subject to a relatively high cooling load, controlling the position of the valve with the valve position controller circuit to flow refrigerant to the first evaporator such that increased cooling is provided to the cooling chamber by the first evaporator and the phase change material, relative to cooling provided when the refrigerator is subject to the relatively low cooling load.

2. The refrigerator of claim 1, wherein the valve and valve position controller circuit are configured and arranged to flow refrigerant to both the first and second evaporators when the refrigerator is subject to the relatively low cooling load.

3. The refrigerator of claim 1, wherein the valve and valve position controller circuit are configured and arranged to flow refrigerant substantially only to the first evaporator when the refrigerator is subject to a relatively high cooling load.

4. The refrigerator of claim 1, wherein the phase change material exhibits at least two phases, and the valve position controller circuit is configured and arranged to control the position of the valve based on relative proportions of the phase change material in each of the at least two phases.

5. The refrigerator of claim 1, wherein the valve is a bistable valve.

6. The refrigerator of claim 1, further including a temperature sensor configured and arranged to determine the temperature of the cooling chamber, wherein the controller circuit is configured and arranged with the temperature sensor to control the position of the valve based on temperature indicated by the temperature sensor.

7. The refrigerator of claim 1, further including sensor configured and arranged to determine the relative proportions of the phases of the phase change material, and wherein the valve position controller circuit is configured and arranged to control the valve position based on the relative proportions of the phases of the phase change material indicated via the sensor.

8. The refrigerator of claim 1, wherein the vapor compression refrigeration system includes a compressor, and wherein the valve position controller circuit is configured and arranged to control the amount of cooling provided to the cooling chamber by controlling the compressor.

9. The refrigerator of claim 1, wherein the refrigerator further comprises a fan configured and arranged to circulate air from the cooling chamber to the thermal store and the first evaporator for cooling, and the valve position controller circuit is configured and arranged with the fan to control the amount of cooling provided to the cooling chamber by controlling the operation or speed of the fan.

10. The refrigerator of claim 1, wherein the thermal store includes two opposing cooling surfaces configured and arranged to flow air over either side of the thermal store to pass across both cooling surfaces.

11. The refrigerator of claim 10, wherein the first evaporator is positioned downstream of the thermal store.

12. The refrigerator of claim 1, wherein the second evaporator is embedded within the thermal store.

13. The refrigerator of claim 1, wherein the valve and valve position controller circuit are configured and arranged to flow the refrigerant substantially only to the first evaporator in response to a temperature within the refrigerator exceeding a desired temperature and, in response to the temperature dropping back to the desired temperature, freezing the phase change material by flowing refrigerant to the second evaporator.

14. A method for use with a refrigerator having a cooling chamber configured and arranged to contain an object to be cooled, a thermal store including a phase change material, a vapor compression refrigeration system including a first evaporator for cooling the cooling chamber and a second evaporator for cooling the phase change material, the method comprising: when the refrigerator is subject to a relatively low cooling load, cooling the phase change material by flowing refrigerant to the second evaporator, and when the refrigerator is subject to a relatively high cooling load, providing increased cooling to the cooling chamber from the first evaporator and the phase change material by flowing refrigerant to the first evaporator.

15. The method of claim 14, wherein flowing refrigerant to the second evaporator and flowing refrigerant to the first evaporator include using a valve and a valve position controller circuit to control flow of refrigerant to the first and second evaporators based on the cooling load.

16. The method of claim 14, further including flowing refrigerant to the first evaporator when the refrigerator is subject to the relatively low cooling load.

17. The method of claim 14, wherein providing increased cooling to the cooling chamber from the first evaporator includes flowing refrigerant substantially only to the first evaporator.

18. The method of claim 14, wherein flowing refrigerant to the second evaporator includes flowing the refrigerant based on relative proportions of the phase change material in respective phases.

19. The method of claim 14, wherein providing the increased cooling to the cooling chamber includes flowing air over the thermal store and the first evaporator.

20. The method of claim 14, wherein providing the increased cooling includes flowing the refrigerant substantially only to the first evaporator in response to a temperature within the refrigerator exceeding a desired temperature, further including, in response to the temperature dropping back to the desired temperature, freezing the phase change material by flowing refrigerant to the second evaporator.

Description

[0030] The invention will now be described by example with reference to the following figures in which:

[0031] FIG. 1 is a part schematic side sectional view of a refrigeration display cabinet in accordance with the invention;

[0032] FIG. 2 is a schematic drawing of a refrigeration circuit in accordance with the invention; and

[0033] FIG. 3 is a part schematic side view illustrating the thermal store.

[0034] With reference to FIG. 1, a refrigeration display cabinet comprises a thermally insulating casing 1 with a glass door 2. The casing is preferably made from vacuum-formed insulating panel combined with high-density polyurethane for structural rigidity. The glass door may be double-glazed or preferably triple-glazed. Krypton gas may be provided between the glass plates to increase insulation. The cabinet rests on a base which holds components of a vapour compression refrigeration including a compressor 3, a condenser 4, and a fan 5 associated with the condenser 4.

[0035] The cabinet 1 has a compartment 6 in which products to be held are cooled. Lighting may be provided for the compartment 6, which is preferably energy-efficient LED lighting. The lighting power supply is preferably located outside the compartment 6. In order to decrease the appliance heat load still further, the LED light source may also be located outside the compartment 6 and the light guided in to the compartment 6 by appropriate means, such as light guides, fibre optics, aerogels, etc.

[0036] Air is drawn from compartment 6 into ducting 7 by a fan 7A in order to be cooled. The ducting 7 is defined in part at least by a gap between internal walls 6A which form the compartment 6 and the inner wall of the insulating casing 1. The base of the compartment 6 may be defined by a first evaporator 10 (referred to below) or casing thereof.

[0037] FIGS. 1 and 2 show the refrigerant circuit. Condensed refrigerant from the condenser 4 can flow optionally along one of two path ways back to the compressor 3. A first pathway 8 carries refrigerant through a first expansion device 9A and first evaporator 10, typically a fin and tube evaporator. The second pathway 11 carries refrigerant through a second expansion device 9B and a second evaporator 12 which is embedded within a thermal heat storage unit 13 holding a phase change material (PCM) 14, in this case water.

[0038] Flow of refrigerant is controlled by a valve 15 downstream of the condenser 4. The position of the valve 15 is controlled by a controller 16, which is also used to control compressor 3, condenser fan 5 and ducting fan 7A.

[0039] As shown in FIGS. 1 and 2, the system is arranged such that refrigerant that has flowed from the second evaporator 12 then flows back to the compressor 3 via the first evaporator 10. Other arrangements are possible, including two separate pathways which merge up-stream of the compressor 3.

[0040] Returning to FIG. 1, both the first evaporator 10 and the thermal storage unit 13 are mounted so that the air circulating through the ducting 7 passes across cooling surfaces of the thermal storage unit 13 and the first evaporator 10 to cool the air.

[0041] A temperature sensor 17 senses the temperature of the air coming out of the compartment 6 and provides a corresponding signal to controller 16.

[0042] The first evaporator 10 is positioned downstream of the thermal store 13, so that the warmest air passes over the thermal store 13 increasing thermal transfer from the PCM 14 during periods of high cooling loading.

[0043] As seen in FIG. 3, the second evaporator 12 is embedded within the thermal store 13 so that freezing of the PCM 14 occurs first in a central region 14A, which is primarily ice, outside of which are outer regions 14C formed primarily of water. The extent to which the PCM 14 has frozen/melted is detected through registering the position of the ice/water interface 14B. This is achieved by a sensor(s) 18 which measures the electrical conductivity of the PCM 14 at points between the outer wall of the thermal store 13 and the evaporator 12. The signals from the sensor(s) 18 are received by the controller 16. Such arrangements are known in the art of thermal stores incorporating PCMs.

[0044] To maximise the cooling surface presented by the thermal store 13 to the air within duct 7, the thermal store 13 is spaced from both wall 6A and casing 1 so that air can pass across either side of it.

[0045] Returning to FIGS. 1 and 2, the operation of the refrigerator will now be described. When the refrigerator is operating in a steady state mode, i.e. the temperature of the air flowing out of the compartment is at or near the desired temperature, the controller 16 operates valve 15 so that refrigerant is pumped along the second pathway 11 through the second evaporator 12 so as to cool and freeze the PCM 14 within the thermal store 13. Once the PCM 14 has frozen as determined by sensor 18, the controller 16 can cause the compressor 3 and condenser fan 5 to turn off/slow down to save energy. Typically, such compressors are either on or off, but a reduction in speed may be possible in some cases.

[0046] By applying such control, the state of freezing of the PCM 14 during steady state operation can be controlled for example between completely frozen and 20% melted to ensure sufficient PCM 14 is frozen to provide additional cooling during the next period of high cooling load. If during steady state operation it is determined that the PCM 14 is sufficiently frozen, the controller 16 can cause the compressor 3 to turn off or reduce in speed to reduce energy consumption.

[0047] In addition, the controller may control the operation or speed of fan 7A during this steady state, as a further way of adjusting and controlling the compartment air temperature.

[0048] In a specific embodiment of steady-state operation, refrigerant flows through both evaporators and the product temperature is controlled by regulating the air temperature leaving the compartment. The air temperature is controlled by adjusting the speed of the fan 7A and switching the compressor 3 and condenser fan 5 on and off. On top of this, if the quantity of frozen PCM as measured by sensor 18 drops below a threshold value, the compressor 3 and condenser fan 5 are activated. If the air temperature becomes too low, the speed of fan 7A is reduced. Once the PCM reaches or nears 100% frozen, the compressor/fan are deactivated and the thermal store/PCM cools the air. As air temperature increases, the fan speed is increased until another threshold temperature is reached and the compressor/fan are then activated.

[0049] During periods of relatively high thermal loading, as determined by sensor 17 detecting that the temperate of air from the compartment 6 is above the desired temperature (perhaps by more than an accepted range from the desired temperature), the controller 16 adjusts valve 15 so that refrigerant is preferentially directed to the first evaporator 10. This provides the first evaporator 10 with greater cooling power to cool the circulating air. The cooling load on the first evaporator 10 is also lessened by the cooling effect of the thermal storage unit 13 on the air which first passes across it.

[0050] Once it is sensed that the temperature has fallen to or around the desired temperature, the controller 16 will operate valve 15 to cause the or a portion of the flow of refrigerant to be directed through the second evaporator 12 to refreeze the PCM 14, and ultimately steady-state conditions will be reached.

[0051] It will appreciate that there are numerous possible variations to the embodiments described above without departing from the scope of the invention, which is defined by the claims. For example, the refrigerator may comprise more than two evaporators. The temperature sensor may instead be mounted in the compartment 6.

[0052] As mentioned above, the thermal store may enable the refrigerator to continue cooling in the event of a temporary power failure. However, a battery may also be provided to run the vapour compression system in the event of power failure.