A refrigeration unit with a secondary cooling component

Abstract

A refrigeration unit with a secondary cooling component The invention relates to a refrigeration unit having a PCM-based secondary cooling system with improved cooling speed over a conventional refrigeration unit. The invention provides a cost-effective, energy efficient, sustainable solution which overcomes some of the problems associated with the existing solutions. Various deployment options for secondary cooling system have been suggested for adoption within the existing structure of the refrigeration unit and compatible with the existing components of the refrigeration units used for various applications.

Description

[0001] A refrigeration unit with a secondary cooling component

[0002] FIELD OF THE INVENTION

[0003] The invention relates to a refrigeration unit having a secondary cooling system, particularly, the invention relates to a secondary cooling system comprising a phase change material (PCM).

[0004] BACKGROUND

[0005] A conventional refrigerator system includes a compressor, a condenser, an expansion device, an evaporator. Generally, when in use, refrigerators are required to have faster cooling speed to enable refrigerator’s temperature to decrease to the desired set temperature as fast as possible. In existing refrigerators, one way of attaining faster cooling speed is through a higher rating and higher horsepower compressor. However, when refrigerators are not in use, a high rating and higher horsepower compressor is considered oversized and is not energy efficient resulting in higher, unnecessary, component cost and higher electric power consumption.

[0006] Such a compressor also results in the release of more heat to the environment and requires a complicated configuration of compatible condensers, evaporators, and other components of the primary cooling system. The compressor runs only at full speed (ON) or stops (OFF). It switches OFF when it reaches a low setpoint temperature and switches back ON when the temperature rises above the high setpoint temperature. The repeated switching between ON and OFF modes consumes more energy and generates noise. As the refrigerator becomes old, the repeated switching between ON and OFF modes puts a strain on the refrigerator parts such as compressor and fan which leads to wear and tear of the refrigeration unit thereby affecting the operation of the refrigeration unit.

[0007] To overcome the high electric power consumption due to high rating compressor during low usage period, an inverter compressor is currently available as an option. Inverter compressors automatically adjust to increase or decrease the compressor motor speed based on the required setpoint temperatures, although the compressor does not stop completely. Reduced running speed of the compressor and reduction in ON / OFF mode switching helps save energy. Inverter compressors can provide energy savings of up to 25% to 30%. However, these energy savings come at the cost of higher equipment costs and maintenance cost. Another way to increase cooling speed is to deploy a secondary cooling system in the refrigerator to support the primary cooling system in its cooling role. A secondary cooling system which relies on a PCM to absorb latent heat would offer a more energy-efficient passive support to the primary cooling system to improve the overall cooling speed of the refrigerator. The secondary cooling system would also help to reduce stress on the primary cooling system, thereby potentially extending the operational life of the refrigerator so equipped. However, for a PCM-based secondary cooling system to perform effectively, it should be deployed in a manner which not only promotes heat transfer within the storage compartment but also complements the internal structure and design of the refrigerator.

[0008] It is an object of the invention to provide a refrigeration unit incorporating a PCM-based secondary cooling system with improved cooling speed over a conventional refrigeration unit. It is another object of the invention to provide a method for providing a secondary cooling component to a refrigeration unit with a PCM-based secondary cooling system to improve its cooling speed and to extend its operational life.

[0009] SUMMARY OF THE INVENTION

[0010] The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.

[0011] It is an object of the invention to provide a refrigeration unit having a high set point and a low set point temperature. The refrigeration unit comprises a storage compartment, a fan for circulation of air in the storage compartment, an air conduit cover having an outlet for exit of air wherein the outlet is located at an axial end of the air conduit cover and a thermally conducting receptacle containing a PCM having a phase change temperature. The thermally conducting receptacle is positioned in the storage compartment proximate to the air conduit cover wherein the volume of the PCM is 2 to 10% of the volume of the storage compartment. The phase change temperature is below the high set point temperature and above the low set point temperature.

[0012] The invention provides a cost-effective, energy efficient, sustainable solution which not only overcomes some of the problems associated with the existing solutions but at the same time helps promote the life of a new refrigeration unit or provide new lease of life to an old refrigeration unit. The invention provides a solution to the problem of attaining a faster cooling speed which comes at the cost of high electric power consumption, maintenance and equipment costs. The refrigeration unit according to the invention helps to achieve energy efficiency and increases the coefficient of performance (CoP) of refrigerator. The reduction of compressor on-off cycling reduces temperature fluctuation inside the storage cabinet and maintains a stable temperature resulting in better food quality.

[0013] BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The summary above, as well as the following detailed description of illustrative embodiments, is better understood when read in conjunction with the appended drawings. For purpose of illustrating the present disclosure, exemplary constructions of the disclosure are shown in the drawings. However, the disclosure is not limited to specific methods and instrumentalities disclosed herein. Moreover, those in the art will understand that the drawings are not to scale. Wherever possible, like elements have been indicated by identical numbers.

[0015] Fig. 1 is a sectional view of a first embodiment of the refrigeration unit according to the invention.

[0016] Fig. 2 is an isometric view of a portion of the first embodiment of the refrigeration unit according to the invention.

[0017] Fig. 3 illustrates the cooling speed of the first embodiment of the refrigeration unit according to the invention (solid line) in comparison to the conventional refrigeration unit (dashed line) in terms of temperature over time after having been opened and closed.

[0018] Fig. 4 depicts the efficiency of cooling of first embodiment of the refrigeration unit according to the invention (solid line) in comparison to the conventional refrigeration unit (dashed line) in terms of temperature over time when the door of the refrigeration unit is opened and closed multiple times.

[0019] Fig. 5 is an isometric view of a second embodiment of the refrigeration unit according to the invention.

[0020] Fig. 6 is an isometric view of a third embodiment of the refrigeration unit according to the invention. DETAILED DESCRIPTION OF THE INVENTION

[0021] In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. The illustrative embodiments described in the detailed description, drawings and claims are not meant to be limiting. Other embodiments can be utilized, and other changes can be made, without departing from the spirit or scope of the subject matter presented herein.

[0022] Figures 1 , 2, 5 and 6 illustrate embodiments of a refrigeration unit 10 that is provided with a phase change material (PCM) 21.

[0023] The following description discloses the features that are common to the embodiments. The refrigeration unit 10 comprises a storage compartment 11 , a fan 18, an air conduit cover 12, and secondary cooling component 20.

[0024] The refrigeration unit 10 is an appliance for creating a cold environment in a confined space by keeping the air enclosed within a defined chamber as close to a desired set temperature as possible. The storage compartment 11 serves to contain items that are required to be chilled and is the enclosed chamber that is accessible through a door. The fan 18 serves to circulate air through the storage compartment 11.

[0025] The refrigeration unit 10 is equipped with a primary cooling system 19. The primary cooling system 19 comprises a compressor 22, a condenser 23, an expansion valve 24 and an evaporator 25. The primary cooling system 19 serves to maintain at a desired set temperature range.

[0026] The compressor 22, condenser 23, expansion valve 24 and evaporator 25 are connected via network of capillaries through which the refrigerant fluid flows. The evaporator 25 is the cooling component of the refrigeration unit 10. The evaporator 25 is located inside the refrigeration unit. The evaporator 25 absorbs heat from the contents within the refrigeration unit 10 via the refrigerant fluid as medium of heat absorption, thus, turning the refrigerant liquid into gas or vapours through evaporation. As a result of this, the evaporator 25 cools the surrounding air which is circulated within the storage compartment 11 via the fan 18. The compressor 22 is the pump that enables the flow of the refrigerant and works by increasing the pressure and temperature of the vaporized refrigerant flowing from the evaporator 25. The condenser 23 is a set of coiled tubes. The condenser 23 cools the vaporized refrigerant turning it back to liquid. The expansion valve 24 controls the flow of the liquid refrigerant flowing from the condenser 23. The refrigerant flows back into the evaporator 25 to be vaporized again and the cycle repeats. The expansion valve 24 is thermostatic. The expansion valve 24 responds to the temperature set at the thermostats used for customizing the temperature in the refrigeration unit 10 within the high and low set point temperatures. The condenser 23 and expansion valve 24 are located at the back of the refrigeration unit 10. The expansion valve 24 is in the liquid line between the condenser 23 and the inlet of the evaporator 25.

[0027] The refrigeration unit 10 has a high set point temperature and a low set point temperature that are controlled by a thermostat. The desired set temperature or the desired set temperature range is between the low and high set point temperatures. The high set point temperature of the refrigeration unit 10 is a temperature beyond which the compressor 22 operates in an on mode. The turning on of the compressor 22 actuates the primary cooling system 19 to initiate refrigeration which continues to run the cycles of refrigeration until the low set point temperature of the storage compartment 11 is achieved. The low set point temperature of the refrigeration unit 10 is a temperature when the compressor 22 switches to off mode and no further cooling of air is required.

[0028] The primary cooling system 19 has a predetermined cooling capacity. Cooling capacity is the refrigeration unit’s 10 ability to remove heat from within the storage compartment 11. The fan 18 acts in conjunction with the primary cooling system 19 and the secondary cooling component 20 to circulate cooled air through the storage compartment 11. The fan 18 may be located close to the evaporator 25 and serves as a means to circulate the air cooled by evaporator 25 within the storage compartment 11 by directing the air through an air conduit 27. The fan may be positioned within the air conduit 27.

[0029] The air conduit 27 is a channel for guided flow of air before being circulated within the storage compartment 11. The air conduit 27 is defined by the air conduit cover 12. The air conduit cover 12 is a cuboid structure having a transverse face 29 extended along a longitudinal axis. In an embodiment, the air conduit cover 12 is open at two ends. The two opposite axial ends of the longitudinal axis serve as the entry and exit point of air through and out of the air conduit 27. The cooled air from the area surrounding the evaporator 25 is directed by the fan 18 towards air conduit 27 through the inlet (not shown) formed by one of the open ends of the air conduit cover 12. The cooled air exits through an outlet 16, the axial opening at the distal end of the air conduit cover 12. In an embodiment, the air conduit cover 12 is composed of a thermally conducting materials such as copper, aluminium and stainless steel. In an alternative embodiment, the air conduit cover 12 is composed of a thermally conducting mixture of materials. Such adaptations are meant for applications such as commercial freezers, supermarket freezers. In alternative embodiments, the air conduit cover 12 may be composed of plastic or coated with plastic for applications such as household refrigerators.

[0030] The secondary cooling component 20 aids the primary cooling system 19 to control the temperature in the storage compartment 11. The secondary cooling component 20 comprises the thermally conducting receptacle 13 having the PCM 21 disposed therein. The thermally conducting receptacle 13 is positioned proximate to the air conduit cover 12. In an embodiment, the thermally conducting receptacle 13 is positioned within the storage compartment 11 such that it does not obstruct the outlet 16. In an embodiment, the thermally conducting receptacle 13 is composed of a thermally conducting material such as copper, aluminium and stainless steel. In an alternative embodiment, the thermally conducting receptacle 13 may be composed of a mixture of thermally conducting materials.

[0031] Phase change materials are characterized by phase change temperature. Phase change materials store latent heat energy by virtue of their chemical composition. They typically contain salt hydrates, paraffins, or some other bio-material capable of storing heat. When the PCM changes from a solid to a liquid, it absorbs and stores heat energy from its surrounding. When PCM changes from a liquid to a solid, it releases that energy back into the surroundings. The chemical composition of PCM affects the PCM’s phase change temperature. The chemical composition of the selected PCM is such that the phase change temperature is between the low and high set point temperatures of the refrigeration unit 10.

[0032] PCM 21 has a phase change temperature below the high set point temperature. In an embodiment, the phase change temperature of the PCM 21 is about 2 to 4 degrees Celsius, preferably 1 to 3 degrees Celsius below the high set point temperature. Preferably, the phase change temperature is above the low set point temperature of the refrigeration unit 10. In an embodiment, the phase change temperature of the PCM 21 is 2 to 4 degrees Celsius, preferably 1 to 3 degrees Celsius above the low set point temperature. In another embodiment, the phase change temperature of the PCM 21 is same as desired set temperature of the refrigeration unit 10. For example, if the low and high set point temperatures are -24 and -20 degrees Celsius respectively, the PCM 21 selected may have a phase change temperature of -22 degrees Celsius. If the low and high set point temperatures are -22 and -18 degrees Celsius respectively, the PCM 21 having a phase change temperature of -20 degrees Celsius may be selected.

[0033] The required volume of PCM 21 to be held within the thermally conducting receptacle 13 depends on the intrinsic latent heat capacity of the PCM 21 and the volume of the storage compartment 11. The latent heat capacity of the PCM should be sufficient to bring down the temperature of refrigeration unit 10 to the desired high set point temperature over the duration taken to achieve the desired high set point temperature before the PCM changes from solid to liquid.

[0034] In general, the higher the latent heat capacity, the lesser is the volume of the PCM 21 needed. In an embodiment, the PCM 21 volume is about 2% to 10% of the volume of the storage compartment 11. Preferably, the PCM 21 volume is about 5% to 8% of the volume of the storage compartment 11. More preferably, the PCM 21 volume is about 3% to 8% of the volume of the storage compartment 11. An example of food-grade PCM is water based PCM. Given the density of water is roughly 1 g / ml. Therefore, one Litre of water based PCM may be equivalent to one kilogram of water based PCM. For example, if the storage compartment’s capacity is 400 litres, the needed volume of a water based PCM should be about 16 to 40 litres, or equivalent to 16 to 40 kg.

[0035] The PCM 21 with high latent heat capacity may be required in a lesser volume whereas if the selected PCM has lower latent heat capacity, a larger quantity of PCM may be needed to provide similar cooling efficiency comparable to that of a PCM 21 with higher latent heat capacity. In an embodiment, the latent heat capacity of the PCM 21 is about 260 kJ / kg (246 BTU / kg) to 300 kJ / kg (284 BTU / kg). The corresponding phase change temperature may range from -26 °C to -19 °C. Preferably, the latent heat capacity is 305 kJ / kg (289 BTU / kg) at -22 °C. In an alternative preferred embodiment, the latent heat capacity is 234 kJ / kg (222 BTU / kg) at -22 °C.

[0036] It is desired to keep the volume of the PCM 21 as low as possible but sufficient to meet the cooling needs of the refrigeration unit 10. The excessive volume of PCM 21 may reduce the otherwise accessible storage space within the storage compartment 11. Also, higher volume of PCM 21 may add to the cost of deployment of PCM 21 as secondary cooling means.

[0037] Alternatively, the total needed PCM 21 may be determined from the rated cooling capacity (kJ / h) of the refrigeration unit 10 and the latent heat capacity of the PCM 21 as follows. The time taken by the refrigeration unit 10 having a rated cooling capacity of A (kJ / h) to bring down the temperature of the refrigeration unit 10 to desired set temperature is B (h). The latent heat capacity of the selected PCM 21 is C (kJ / kg). The phase change temperature of the PCM 21 is equivalent to the desired set temperature of the refrigeration unit. Accordingly, the amount (in kg) of PCM to effectively increase the cooling speed of the refrigeration unit 10 can be calculated as follows: Weight of PCM 21 = (A x B / C)

[0038] Preferably, the efficiency of secondary cooling component (X) is taken into account. The X value is always smaller than 1. Ideally, the range of X is between 0.1 to 0.5. Therefore, the preferable amount (in kilogram) of PCM to effectively increase the cooling speed of the refrigeration unit 10 can be calculated as follows:

[0039] Weight of PCM 21 = 1 / X x (A x B / C)

[0040] The X value may be determined on the basis of the following criteria:

[0041] - Surface area of thermally conducting receptacle 13

[0042] - Thermal conductivity of the material of the thermally conducting receptacle 13. For example, a plastic receptacle tends to have lower X value. A material with good thermal conductivity such as copper and aluminum has a higher X value.

[0043] Distance of the thermally conducting receptacle 13 from the outlet 16 and / or opening 17.

[0044] In an embodiment, for a refrigeration unit 10 having rated cooling capacity of 250 kJ / h and requiring 4.5 hours to cool the refrigeration unit 10 to the desired set temperature and the PCM 21 has latent heat capacity of 300 kJ / kg at the desired set temperature. Assuming the X value to be 0.3;

[0045] The required PCM (kg) = 1 / 0.3 x (250 x 4.5 / 300) = 12.5 kg

[0046] With reference to Fig. 1 , 2, 5 and 6, when in operation, the primary cooling system 19 absorbs heat from the air circulated within the storage compartment 11 , the air, thus cooled, is circulated by the fan 18 which is located above the primary cooling system 19. The cooled air directed by the fan 18 towards the air conduit 27 is guided by the air conduit cover 12 and exits through the outlet 16. In the embodiments wherein the air conduit cover 12 is made up of a thermally conducting material, the cooled air is in thermal communication with the air conduit cover 12, while passing through the air conduit 27 and before exiting through the outlet 16 and dissipating within the storage compartment 11 .

[0047] With reference to Fig. 2, in the first embodiment of the refrigeration unit 10, two thermally conducting receptacles 13 are positioned adjacent to the air conduit cover 12. Preferably, the thermally conducting receptacles 13 are positioned on opposite sides of the air conduit cover 12 along the longitudinal axis. The two thermally conducting receptacles 13 are positioned to the air conduit cover 12 such that the outlet 16 is not blocked. The thermally conducting receptacles 13 are fastened to the air conduit cover 12. The overall cooling capacity of the PCM 21 is provided by the total volume of the PCM 21 in the thermally conducting receptacles 13. The total volume of the PCM 21 is provided by the total amount of the PCM 21 distributed in all the thermally conducting receptacles 13.

[0048] When in operation, in the embodiment of the refrigeration unit 10 according to Fig. 2, the air conduit cover 12 is in thermal communication with the cooled air flowing in the air conduit 27 as well as with the thermally conducting receptacle 13. As soon as the cooled air directed by fan 18 enters air conduit 27, the PCM 21 within the thermally conducting receptacle 13 acts as heat sink for the cooled air.

[0049] The positioning of the secondary cooling component 20 as described above ensures continuous and quick heat absorption from the cooled air as long as the cooled air temperature is above the phase change temperature. This results in the air flowing past the secondary cooling component 20 is cooler than the air flowing past the evaporator 25. The cooled air directed by the fan 18 towards the secondary cooling component 20, guided by air conduit cover 12, eventually results in faster cooling, thus, ensuring quicker restoration of the desired set temperature of the storage compartment 11. Further, such a placement of secondary cooling component 20 does not interfere with the flow of cooled air from the air conduit cover 12 via outlet 16, ensuring efficient circulation of the cooled air is maintained within the storage compartment 11.

[0050] Figure 3 demonstrates comparison of the cooling speed of the refrigeration unit 10 according to the first embodiment of the invention as referred in Fig. 1 and 2 to that of the conventional refrigeration unit. In the event after the door remains open for a prolonged period, e.g. 15 minutes and then closed, the refrigeration unit 10 equipped with the secondary cooling component 20 is able to attain the lower temperature at any given point faster than the conventional refrigeration unit without the secondary cooling component 20. It is evident from Fig. 3 that the refrigeration unit 10 according to the first embodiment of the invention has higher cooling speed and accordingly helps in attaining the desired set temperature of the storage compartment rather quickly compared to the conventional refrigeration unit without the secondary cooling component 20. In other words, the refrigeration unit equipped with the secondary cooling component 20 is better suited to maintain a stable cooling environment within the storage compartment 11 compared to its conventional counterpart without the secondary cooling component 20.

[0051] As shown in Fig.3, the refrigeration unit 10 having the secondary cooling system 20, results in a faster cooling speed and thus shortens the cooling duration to bring down the temperature to high set point temperature. The increased rate of the cooling speed can shorten the cooling duration between 25% to 50%. The increased rate of cooling speed is seen on a conventional refrigeration unit 10 after a long opening on of the door. Thereafter, upon reaching high set point temperature, compared to normal refrigeration unit, the refrigeration unit 10 with the secondary cooling system 20 will take a longer time to reach to low set point temperature as this period is used to remove the heat gain on PCM and to reinstate the PCM’s latent heat capacity.

[0052] Figure 4 shows the comparison of refrigeration unit 10 according to the first embodiment of the invention and as depicted in Fig. 1 and 2, with the conventional refrigeration unit in their efficiency of cooling the air within the storage compartment. As shown, every encounter of door opening of refrigerator is accompanied by an increase in temperature of the storage compartment above the desired set temperature. Also shown is the corresponding drop when the refrigerator door is closed and the primary cooling system is working to bring the temperature down to desired set temperature. As demonstrated, during the 12 events of door opening and door closing, the refrigerator unit 10 according to the first embodiment of the invention is able to bring the temperature spike down faster, thus reducing the state of temperature shock within the storage compartment 11 due to the temperature difference between the storage compartment 11 and the external warmer air. Also, the refrigeration unit 10 equipped with secondary cooling component 20 experiences lesser degree of temperature fluctuation compared to that of the conventional refrigeration unit. Moreover, the recorded drop in the temperature for the refrigeration unit 10 according to the first embodiment of the invention as shown in Fig. 1 and 2 is higher than that recorded for the conventional refrigeration unit. The higher the recorded drop in the temperature the quicker is the restoration of the storage compartment 11 to the desired set temperature. Thus, it is evident from this figure that the refrigeration unit 10 equipped with secondary cooling component 20 helps in maintaining a stable cooling environment within the storage compartment by minimising the temperature fluctuations resulting due to repeated opening and closing of the refrigerator door. Taken together, the figure demonstrates that the efficiency as well as speed of cooling of refrigeration unit 10 according to the first embodiment of the invention is superior compared to the conventional refrigeration unit, attributable to the strategic positioning of secondary cooling component 20 within the refrigeration unit 10 according to the method of the invention.

[0053] Depending on the design and structure of the other components disposed within the refrigeration unit 10, the spatial constraints as well as the volume of the storage compartment 11, the thermally conducting receptacles 13 may be configured and shaped complementarily to expose a suitable surface area for heat exchange with the cooled air directed towards them via the air conduit cover 12 as described in the embodiments below. Moreover, the number of thermally conducting receptacles 13 may be increased to provide more surface area for heat absorption by PCM 21 and also to meet the demand of the increased volume of the storage compartment 11 as well as the number of the items stored within the storage compartment 11 when in use of the refrigeration unit 10.

[0054] With reference to Fig. 5 and 6, there is provided a refrigeration unit 10 with a plurality of shelves 30 slotted within the storage compartment 11 . The plurality of shelves 30 are slotted at regular intervals throughout the length of the storage compartment 11 and are held in place by a pair of ridged projections 31 along the sides of the storage compartment 11 facing the interior of the storage compartment 32. The width and depth of the plurality of the shelves 30 span across transverse section of the storage compartment 11. The plurality of the shelves 30 serve as a means of increasing the storage space within the storage compartment 11. The rear end of the plurality of shelves 30 is in contact with the air conduit cover 12. In a variation of this embodiment, the air conduit cover 12 may be composed of non-conducting material and is not in the thermal communication with the secondary cooling component 20.

[0055] With reference to Fig. 5, there is provided a second embodiment of the invention depicting the refrigeration unit 10 wherein the plurality of the shelves 30 have perforations 15. The perforations 15 ensure efficient circulation of the cooled air within the storage compartment 11. The plurality of the shelves 30 are thermally conducting or are coated with thermally conducting material. A shelf 14 may be positioned as the top-most shelf. The shelf 14 does not block the outlet 16. The plurality of secondary cooling components 20 are positioned at regular intervals on the shelf 14. The secondary cooling components 20 are fastened to the shelf 14 such that the positions of the secondary cooling components 20 are not disturbed while placing the items to be stored in the storage compartment 11 on the shelf 14. The fastening of the secondary cooling components 20 to the shelf 14 also ensures that the outlet 16 is not obstructed while the items to be stored within the storage compartment 11 are placed or moved on the shelf 14.

[0056] When in operation, in the second embodiment of the refrigeration unit 10 according to Fig. 5, the plurality of secondary cooling components 20 positioned on shelf 14. The cooled air emerging out of the outlet 16 is directed to the plurality of the secondary cooling components 20 on the shelf 14 which are in thermal communication with the cooled air. The perforations 15 on the shelf 14 facilitate the direct, unobstructed thermal contact of the cooled air with the thermally conducting receptacle 13 and thereby with PCM 21 . It is critical that the outlet 16 is not obstructed either by the shelf 14 or by the secondary cooling components 20 to ensure the uninterrupted heat absorption by PCM 21. The secondary cooling components 20 are in thermal communication with the air being circulated within the storage compartment 11. The PCM 21 absorbs the heat from the cooled air as soon as it emerges from the outlet 16. As a result of the thermal communication between the cooled air emanating out of outlet 16 and the secondary cooling components 20 on the shelf 14 the cooled air undergoes another round of cooling by PCM 21 before being dissipated within the storage compartment 11.

[0057] With the arrangement of secondary cooling component 20 disposed within the storage compartment 11 as shown in Fig. 5, the refrigeration unit 10 is equipped to achieve the desired set temperature of the storage compartment 11 quickly following a temperature spike after a door opening event and reduces the burden on the primary cooling system 19. There may be a need to increase the volume of PCM 21 for the refrigeration units having an increased demand for cooling and quicker restoration of desired set temperature within the storage compartment 11 in the event of door opening. Therefore, to accommodate the required volume of PCM 21 to be disposed within the thermally conducting receptacle 13, the number of the secondary cooling components 20 can be varied according to this embodiment of the invention. The increase in number of the secondary cooling components 20 provides for greater surface area available for heat transfer across the thermally conducting receptacle 13. These adaptations are suitable for large capacity refrigerators and for all those applications that require refrigerator door to be opened for long periods of time but lower frequency of opening and closing of refrigerator door. For example, frozen vending machine and commercial or household refrigerators.

[0058] With reference to Fig. 6, there is provided a third embodiment of the invention depicting the refrigeration unit 10 wherein the air conduit cover 12 has at least one opening 17 being located on a transverse face 29 of the air conduit cover 12. The at least one opening 17 is centrally disposed on the transverse face 29. At least one shelf 30 is positioned adjacent to the at least one opening 17. In an embodiment, a plurality of openings 17 are disposed on the transverse face 29 of the air conduit cover 12. Preferably, the openings 17 are aligned along the transverse face 29 of the air conduit cover 12. The plurality of shelves 30 are positioned adjacent to the respective openings 17 such that the cooled air exiting out of the openings 17 is not blocked. The secondary cooling component 20 is positioned on each shelf 30. In the embodiment, the plurality of the shelves 30 and the air conduit cover 12 are made up of nonconducting materials. In this embodiment of the refrigeration unit 10, the thermally conducting receptacle 13 is L shaped in cross section. The L shape provides for greater surface area available for heat transfer across the thermally conducting receptacle 13. The L shape of the thermally conducting receptacle 13 compensates for the number of secondary cooling components 20 to accommodate the volume of PCM 21 amenable to be disposed within the thermally conducting receptacle 13 as opposed to the number of secondary cooling components 20 such as in the embodiment according to Fig. 5. The one thermally conducting receptacle 13 per shelf 30 ensures that the efficiency of cooling is maintained within the storage compartment 11 in the absence of perforations 15 in the plurality of the shelves 30 such as in the embodiment according to Fig. 5. The L shaped thermally conducting receptacle 13 has a horizontal plane 33 and a vertical plane 34 wherein the horizontal plane 33 is affixed to the plurality of the shelves 30 and the vertical plane 34 is aligned with the opening 17 such that the vertical plane 34 does not obstruct the path of the opening 17. In an embodiment, the vertical plane 34 lies on the left side of the opening 17. In alternate embodiment, the vertical plane 34 lies on right side of the opening 17. The depth of the thermally conducting receptacle 13 may vary depending on the volume of the PCM 21 required to be disposed within the thermally conducting receptacle 13.

[0059] When in operation, in the third embodiment of the refrigeration unit 10 according to Fig. 6, the cooled air emanating from the opening 17 is in thermal communication with the secondary cooling component 20. The cooled air is directed sidewise to be in thermal communication with the vertical plane 34 by virtue of its alignment with the opening 17. The horizontal plane 33 is not only in thermal communication with the vertical plane 34 but is also in thermal contact with the unobstructed cooled air from opening 17 because of its vicinity to the opening 17. The PCM 21 absorbs the heat from the cooled air as soon as it emerges from the opening 17. As a result of thermal communication within the vertical plane 34 and the horizontal plane 33, the cooled air undergoes another round of cooling by the secondary cooling component 20 before being dissipated within the storage compartment 11. The secondary cooling components 20 are in thermal communication with the air being circulated within the storage compartment 11.

[0060] With the arrangement of secondary cooling component 20 disposed within the storage compartment 11 as shown in Fig. 6, the volume of PCM 21 can be accommodated by varying the depth of the L-shaped secondary cooling component 20 according to the cooling needs of the refrigeration unit. These adaptations of placement and shape of secondary cooling component 20 provide faster cooling for refrigeration units having non-conducting air vent cover with openings 17. Such adaptations are suitable for the refrigeration units used meant for applications such as household refrigerators.

[0061] Referring to Fig. 1 , 2, 5 and 6, the refrigeration unit 10 with the secondary cooling component 20 accompanying the adaptations suited to the refrigeration design and applications as mentioned in the method providing the secondary cooling component 20 to the refrigeration unit 10 such as positioning, number, and shape of the secondary cooling component 20 are advantageous because:

[0062] • The frequency of compressor of primary cooling system to switch between on or off mode decreases, reducing the strain on the compressor of the primary cooling system.

[0063] • Upon reaching to low set point temperature the compressor 22, is in OFF mode, without the help of cooling fan 18, the secondary cooling component 20 will work at passive mode to slow down the heat gain within the refrigeration unit, this increases the duration for temperature rise to high set point temperature. The duration required to arrive at the high set point temperature can be prolonged with deliberate positioning of the secondary cooling component in a manner that maximises the contact of cooled air with the secondary cooling component.

[0064] • A stable environment with the cooled air is maintained for prolonged duration, thus reducing the temperature fluctuations.

[0065] • The overall coefficient of performance (CoP) of the refrigerator is increased by enabling same primary cooling system consuming same energy yet achieving faster cooling with the introduction of secondary cooling component as passive secondary means of cooling.

[0066] • Introduction of secondary cooling component into an old refrigeration unit offers a (nonmechanical) cost-effective, low maintenance, energy saving solution.

[0067] • Promotes circular economy by providing new lease of life to the old refrigeration units or promoting the life of a new refrigeration unit without modifying existing designs.

[0068] • Various deployment options for secondary cooling component 20 have been suggested for adoption within the existing structure of the refrigeration unit and compatible with the existing components of the refrigeration units used for various applications.

Claims

CLAIMS1 . A refrigeration unit (10) having a secondary cooling component (20) and having a high set point and a low set point temperature, the refrigeration unit (10) comprising: a storage compartment (11); a fan (18) for circulation of air in the storage compartment (11); an air conduit cover (12) having an outlet (16) for exit of air wherein the outlet (16) is located at an axial end of the air conduit cover (12); and the secondary cooling component (20) comprising a thermally conducting receptacle (13) containing a phase change material (21 ) having a phase change temperature, the thermally conducting receptacle (13) being positioned in the storage compartment (1 1 ) proximate to the air conduit cover (12) wherein the volume of the phase change material (21 ) is 2% to 10% of the volume of the storage compartment (1 1 ) and the phase change temperature is below the high set point temperature and above the low set point temperature.

2. The refrigeration unit (10) according to claim 1 wherein the weight of the phase change material (21 ) is determined as 1 / X x (A x B / C) wherein A is rated cooling capacity (kilojoules / hour) of the refrigeration unit 10 and wherein B (hour) is duration to bring down the temperature of the refrigeration unit 10 to a desired set temperature wherein C (kilojoules / kilogram) is the latent heat capacity of the phase change material (21 ), the phase change temperature of the PCM (21 ) being equivalent to the desired set temperature of the refrigeration unit 10 and wherein X is the efficiency of secondary cooling component (20).

3. The refrigeration unit (10) according to claim 1 or claim 2 wherein the thermally conducting receptacle (13) is L shaped in cross section.

4. The refrigeration unit (10) according to any one of claims 1 to 3 wherein the thermally conducting receptacle (1 1 ) is positioned on a shelf (14).

5. The refrigeration unit (10) according to claim 4 wherein the shelf (14) is thermally conducting.

6. The refrigeration unit (10) according to claim 4 or claim 5 wherein the shelf (14) has perforations (15).

7. The refrigeration unit (10) according to any one of claims 1 to 6 wherein the thermally conducting receptacle (13) is fastened to the shelf (14).

8. The refrigeration unit (10) according to any one of claims 4 to 7 wherein the shelf (14) is positioned above the outlet (16).

9. The refrigeration unit according to any one of claims 4 to 8 wherein the air conduit cover (12) has at least one opening (17) being located on a transverse face (29) of the air conduit cover (12) and the shelf (14) is positioned adjacent to the at least one opening (17).

10. The refrigeration unit (10) according to any one of claims 1 to 9 wherein the high set point temperature is 2 to 4 degrees Celsius above the phase change temperature and the low set point temperature is 2 to 4 degrees Celsius below the phase change temperature.1 1 . The refrigeration unit (10) according to any one of claims 1 to 10 wherein the high set point temperature is 1 to 3 degrees Celsius above the phase change temperature and the low set point temperature is 1 to 3 degrees Celsius below the phase change temperature.

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