Method for Defrosting a Freezer

Abstract

A method for controlling a defrosting process in a freezer cabinet 1 is provided. The freezer cabinet 1 has an evaporator heat exchanger 11 for cooling the air inside the freezer cabinet 1 and an evaporator fan 5 for sucking in air across the evaporator heat exchanger 11. The evaporator heat exchanger 11 is part of a refrigeration circuit 4 for cooling the freezer cabinet 1. The method includes switching the refrigeration circuit 4 from a cooling mode to a defrosting mode to heat the air inside the freezer cabinet 1; and simultaneously in the defrosting mode: measuring the air temperature at a first location 18 inside the freezer cabinet 1 remote from the evaporator heat exchanger 11; if the measured air temperature exceeds a first switching temperature, turning on the evaporator fan 5 to suck in air above the evaporator heat exchanger 11; and if the measured air temperature drops below a second switching temperature lower than the first switching temperature, turning off the evaporator fan 5. A refrigeration display system configured to execute the method is also provided.

Description

Technical Field

[0001] The present invention relates to a method for controlling a defrosting process in a freezer cabinet and a corresponding freezer cabinet. Background Art

[0002] When the freezer cabinet door is opened, air and water vapor can enter the freezer cabinet. When the water vapor contacts the cold air inside the freezer cabinet, it condenses and causes ice to deposit inside the freezer cabinet. The water vapor can also reach the cooling element used to cool the air inside the freezer cabinet, which may cause an accumulation of ice formed on the cooling element.

[0003] The formation of ice inside the freezer cabinet causes several problems. It inhibits the effective transfer of heat from the cabinet, especially when allowing a large amount of ice to accumulate on the cooling element, and may also reduce the available space inside the cabinet for storing goods. Therefore, icing and accumulation inside the freezer cabinet may lead to reduced efficiency, increased energy consumption, and increased operating costs.

[0004] These problems can be exacerbated by regularly and repeatedly opening and closing the freezer cabinet door, for example, by shoppers taking goods from the freezer cabinet in a supermarket, which allows a large amount of water vapor to enter the freezer cabinet.

[0005] Therefore, to solve these problems, it is known to provide the freezer cabinet with a defrost operation mode during which the air inside the cabinet is heated to melt the ice formed inside the cabinet. These defrost modes generally aim to either operate at regular intervals or, if a large amount of ice is detected inside the cabinet, to melt the ice inside the freezer cabinet and improve the cooling efficiency of the cabinet. Summary of the Invention

[0006] In a first aspect, the present invention provides a method for controlling a defrosting process in a freezer cabinet having an evaporator heat exchanger for cooling the air inside the freezer cabinet and an evaporator fan for drawing air across the evaporator heat exchanger, wherein the evaporator heat exchanger is part of a refrigeration circuit for cooling the freezer cabinet; the method comprising: switching the refrigeration circuit from a cooling mode to a defrost mode to heat the air inside the freezer cabinet; and while in the defrost mode: measuring the air temperature at a first position inside the freezer cabinet remote from the evaporator heat exchanger; if the measured air temperature exceeds a first switching temperature, turning on the evaporator fan to draw air across the evaporator heat exchanger; and if the air temperature drops below a second switching temperature lower than the first switching temperature, turning off the evaporator fan.

[0007] In the defrost mode, when the measured air temperature exceeds a first switching temperature, the evaporator fan is turned on, i.e., activated, and when the measured air temperature drops below a second switching temperature, the evaporator fan is turned off, i.e., deactivated. That is, when the measured temperature during defrosting is between the first and second switching temperatures, the evaporator fan operates only in the defrost mode. During the defrost mode, as the temperature varies between the first and second switching temperatures, the evaporator fan can be cycled on and off multiple times. For example, the method can use two or more switching cycles. The defrost mode typically involves deactivation of the refrigeration circuit, and thus switching from the cooling mode to the defrost mode can include, for example, stopping the circulation of the refrigerant fluid by deactivating the compression means of the refrigeration circuit.

[0008] The main purpose that the evaporator fan may have is to create an air circulation through the storage compartment of the freezer cabinet and draw in the storage compartment air above the evaporator, thereby cooling the storage compartment during the cooling mode. Thus, the evaporator fan can be a fan that operates in the cooling mode to supply cooled air to the storage compartment. The evaporator fan may be the only fan provided within the freezer cabinet for drawing in air above the evaporator. Thus, the freezer cabinet may not include other fans for drawing in air above the evaporator, and in particular, there may be no fan for the defrost mode that is not used during the refrigeration mode.

[0009] Switching from the cooling mode to the defrost mode can include turning off the evaporator fan so that at the start of the defrost mode, the evaporator fan is off until the measured temperature exceeds the first switching temperature. This way, before the air at the first location is actively transferred to one or more areas of the freezer cabinet, the air at the first location is allowed to heat up more evenly to a higher temperature, in the area where the hot air can cause removal of ice, i.e., defrosting. That is, the air at the first location is allowed to rise to the first switching temperature before being transferred to the area of the freezer cabinet for defrosting. If the evaporator fan is operated before the air temperature rises to the first switching temperature, the air flowing to the area of the freezer cabinet for defrosting may not be hot enough to melt the ice. Additionally, since once the air temperature rises to the first switching temperature, the hot air is actively transferred to these areas only by the action of the fan, the goods stored in these areas are not exposed to the hot air until the air reaches the first switching temperature. This improves the efficiency of the defrost process and results in a shorter defrost time, as it allows the use of hotter air during defrosting and also reduces the total heat experienced by the goods within the freezer cabinet during defrosting, which can reduce the degradation of the goods.

[0010] When the fan is not operated to draw air across the evaporator heat exchanger, for example when the fan is turned off, hot air may flow naturally, e.g., in accordance with natural convection towards areas of the freezer cabinet where it may start to melt ice, which may cause the air to become humid and entrained with water vapor. If the humid air is allowed to cool, e.g., if the water vapor in the air comes into contact with relatively cold air, the water vapor in the air may freeze and cause ice deposition within the freezer cabinet. When the evaporator fan is operating, e.g., turned on, air is driven by the fan and the water vapor entrained in the air is more dispersed and less dense than in naturally flowing air. This means that any ice deposits precipitating from the fan-driven air will be smaller and easier to subsequently remove. Thus, the operation of the fan can both assist in defrosting existing ice and reduce the risk of icing due to humid hot air from the defrost process.

[0011] When the evaporator fan is turned on, hot air will flow through the freezer cabinet and its temperature will be reduced as it melts ice and mixes with the colder air. This results in a reduction in the air temperature measured at a first location. When the temperature measured at the first location is below a second switching temperature, by turning off the fan, warm air can be prevented from becoming too cold to effectively melt the ice within the freezer cabinet.

[0012] The refrigeration circuit can include a compressor for compressing the refrigerant and thus, unlike other forms of refrigeration such as absorption chillers, the refrigeration circuit can be a compression refrigeration circuit. When operating, the compressor can serve to pump the refrigerant through the refrigeration circuit. As described above, switching the refrigeration circuit from the cooling mode to the defrost mode can include turning off (i.e., deactivating) the compressor. Switching the refrigeration circuit from the defrost mode to the cooling mode can include turning on (i.e., activating) the compressor. When the compressor is turned off, the refrigerant will not be compressed by the compressor or pumped through the refrigeration circuit. Thus, turning off the compressor will stop the evaporator from absorbing heat.

[0013] The refrigeration circuit can include a heat rejection heat exchanger, e.g., a condenser heat exchanger for removing heat from the refrigerant and / or an expansion valve for expanding and reducing the pressure of the refrigerant. The refrigeration circuit can be arranged such that the refrigerant can flow in a closed loop through the compressor, the heat rejection heat exchanger, the expansion valve, and the evaporator heat exchanger. When the refrigerant flows through the refrigeration circuit in this direction, the evaporator heat exchanger acts as a heat-absorbing heat exchanger and can be used to cool the air within the freezer cabinet.

[0014] When the refrigeration circuit is in the defrost mode, the air within the freezer cabinet can be at least partially heated by the local environment surrounding the freezer cabinet. That is, a heat source for heating the air within the freezer cabinet can be provided by the environment surrounding the freezer cabinet. For example, in the absence of cooling through the evaporator heat exchanger, the air temperature within the freezer can naturally rise towards the ambient temperature of the local environment.

[0015] During the defrost mode, the refrigeration circuit can operate in a heating mode to heat the air inside the freezer during the defrost mode. In the heating mode, the evaporator heat exchanger can be made to heat the air inside the freezer.

[0016] The refrigeration circuit can include a reversing valve that is used to reverse the flow of refrigerant through the circuit when in the heating mode. That is, the reversing valve can cause the refrigerant to flow sequentially through the compressor, the evaporator heat exchanger, the expansion valve, and the condenser heat exchanger. In this way, the hot compressed refrigerant from the compressor can be transferred to the evaporator heat exchanger. This can allow the evaporator heat exchanger to be used to heat the air inside the freezer. When the flow of the refrigerant is reversed, it can be said that the refrigeration circuit is in the heating mode. The reversing valve can be configured to be actuated, i.e., in response to the supply of current to the reversing valve, cause the refrigeration system to operate in the heating mode. During the defrost mode, the air inside the freezer can be heated by operating the refrigerant circuit in the heating mode. That is, the air inside the freezer can be heated by reversing the flow of the refrigerant within the refrigeration circuit using the reversing valve.

[0017] Alternatively or additionally, the freezer can include one or more heaters for heating the air inside the freezer. The one or more heaters can be one or more electric heaters. The heaters can be positioned adjacent to the evaporator heat exchanger such that, in addition to the evaporator heat exchanger, the operation of the evaporator fan also draws air over the heaters. During the defrost mode, the one or more heaters can be used to heat the air inside the freezer.

[0018] The provision of the one or more heaters and / or the reversing valve allows the air inside the freezer to be actively heated during the defrost mode. For example, the air can be heated by the one or more heaters and / or by the operation of the refrigeration circuit in the heating mode. This allows the air to be heated more quickly. The one or more heaters and / or the evaporator heat exchanger can be used to uniformly heat the air to a temperature to effectively melt the ice inside the freezer.

[0019] As described above, when the evaporator fan is turned on in the defrost mode, hot air will flow through the freezer and will decrease in temperature as it melts the ice and mixes with the colder air. As a result, the air temperature measured at the first location will decrease. When the temperature measured at the first location drops below a second switching temperature, the fan is turned off to reduce the mixing of the warm air with the colder air. Then the air can be uniformly heated back to the first switching temperature using the heaters and / or the evaporator heat exchanger.

[0020] In addition, when operating the evaporator fan, its function is to draw air above one or more heaters and / or evaporator heat exchangers, thereby allowing any water vapor in the air to be heated as the air passes over one or more heaters and / or evaporator heat exchangers. This prevents the cooling of the water vapor and minimizes the risk of ice deposition within the freezer cabinet, such as ice or snow resulting from the cooling of water vapor within the storage chamber.

[0021] The first switching temperature can be a temperature within the range including between -5°C and 11°C. For example, the first switching temperature can be -1°C or 10°C. This ensures that the air is heated sufficiently to melt the ice within the freezer cabinet.

[0022] The second switching temperature can be a temperature within the range including between -10°C and 5°C. For example, the second switching temperature can be -6°C or -1°C. This ensures that the hot air within the freezer cabinet is not cooled to a degree where it cannot melt the ice.

[0023] The location of the first position where the air temperature is measured within the freezer cabinet can affect what temperatures should be set as the first and second switching temperatures. For example, if the first position is a sheltered location within the freezer cabinet, the change in the air temperature measured at the first position during the defrosting process may be slower compared to if the temperature is measured at a more exposed location, and vice versa. Similarly, the temperature measured at the sheltered location may change more slowly than the air temperature in other areas of the freezer cabinet. Therefore, if the first position is a sheltered location, the first and second switching temperatures can be lower compared to if the first position is an exposed location. For example, if the first position is a sheltered location, the first and second switching temperatures can be -1°C and -6°C respectively, while if the first position is an exposed location, the first and second switching temperatures can be 10°C and 0°C respectively. Additionally, or alternatively, if the first position is a sheltered location, the difference between the first and second switching temperatures can be less compared to if the first position is an exposed location. For example, if the first position is a sheltered location, the first and second temperatures can differ by 7°C, while if the first position is an exposed location, the first and second switching temperatures can differ by 10°C. This can prevent overheating of the freezer cabinet during the defrosting process, which could potentially damage the goods stored therein.

[0024] The method can further include measuring the air temperature at a second location within the freezer cabinet. The second location can be adjacent to the evaporator heat exchanger and / or one or more heaters. The defrost process can continue until the measured temperature of the air at the second location exceeds a defrost termination temperature. That is, when the temperature measured at the second location exceeds the defrost termination temperature, the freezer cabinet can be switched from the defrost mode to the cooling mode. The defrost termination temperature can be a temperature within a range including between 2°C and 25°C, and it can vary depending on the type of freezer cabinet and the location of the sensor used to detect the defrost termination temperature. For example, the defrost termination temperature can be approximately 3°C, approximately 10°C, or approximately 15°C. When the temperature at the second location reaches the defrost termination temperature, by stopping the defrost process, it can be ensured that the conditions do not become too hot for the goods within the freezer cabinet. Thus, it can be ensured that the goods do not reach a temperature above which they may be damaged or degraded. This is particularly beneficial in frozen food storage, where the food may become unfit for consumption and may have to be discarded if it is subjected to unacceptable high temperatures.

[0025] The air temperature at the first location and / or the air temperature at the second location can be measured by using one or more temperature sensors. For example, a temperature sensor can be located at the first location to measure the air temperature at the first location, and / or a temperature sensor can be located at the second location to measure the air temperature at the second location. The temperature sensor can be a thermal switch for providing direct mechanical control of a circuit that powers a fan and / or a heating component. For example, the temperature sensor can be a bimetallic mechanical switch. Alternatively, the temperature sensor can be an electrical sensor. For example, the temperature sensor can be a thermistor sensor, a semiconductor sensor, and / or a thermocouple. In the case where the temperature sensor is an electrical sensor, the freezer cabinet can include a digital controller for receiving a signal from the electrical sensor and controlling the operation of the fan and / or the heating component.

[0026] The freezer cabinet can include a storage compartment for accommodating goods in a temperature-controlled environment. The storage compartment can define an internal volume in which goods can be stored. The storage compartment can have a first inlet for allowing air to flow into and out of the lower part of the storage compartment. The storage compartment can include a second inlet for allowing air to flow into and out of the upper part of the storage compartment. It will be appreciated that the direction of the air flow through one or more inlets can vary depending on the activation of the evaporator fan and / or other factors (such as the air flow caused by a temperature difference). One or more inlets allow the chamber air from the storage compartment to flow into and / or out of the evaporator heat exchanger.

[0027] The first location can be the location of the first inlet. That is, measuring the temperature of the warm air at the first location can include measuring the temperature of the warm air at the first inlet. The first location can be downstream of the heating component in a first direction.

[0028] The evaporator heat exchanger and / or heater can be located outside the storage chamber. Thus, the air heated by the evaporator heat exchanger and / or heater can enter the storage chamber through the first and / or second inlets.

[0029] The evaporator fan can be arranged to direct air from the evaporator heat exchanger and / or one or more heaters through the second inlet into the storage chamber. That is, in operation, i.e., when the evaporator fan is turned on, the fan can cause air from the evaporator heat exchanger and / or one or more heaters to flow into the upper part of the storage chamber via the second inlet. The fan can be arranged to push the air in a second direction opposite to the first direction. That is, the evaporator fan can be arranged such that in operation, the evaporator fan causes the air to be pushed in a direction away from the first position and / or the first inlet.

[0030] The freezer can be a plug-in type, semi-plug-in type, or remote type. The freezer can be part of a refrigeration display system. The refrigeration display system can include a freezer and a refrigeration circuit, which can include a compressor, a heat rejection heat exchanger, an expansion valve, an evaporator heat exchanger, and (when present) a reversing valve.

[0031] The refrigeration circuit can be completely contained within the freezer, which can thus have a plug-in type. That is, the compressor, the heat rejection heat exchanger, the expansion valve, the evaporator heat exchanger, and / or the reversing valve can all be housed within the freezer. Thus, it can be said that the present invention provides a method for controlling the defrosting process in a freezer having a refrigeration circuit that includes an evaporator heat exchanger for cooling the air within the freezer and an evaporator fan for drawing air across the evaporator heat exchanger, the method comprising: switching the refrigeration circuit from a cooling mode to a defrost mode to heat the air within the freezer; and simultaneously in the defrost mode: measuring the air temperature at a first position within the freezer remote from the evaporator heat exchanger; if the measured air temperature exceeds a first switching temperature, turning on the evaporator fan to draw air above the evaporator heat exchanger; and if the air temperature drops below a second switching temperature lower than the first switching temperature, turning off the evaporator fan.

[0032] Alternatively, the refrigeration circuit can be at least partially located outside the freezer. For example, the compressor, the heat rejection heat exchanger, the expansion valve, and / or the reversing valve can be located outside the freezer. The components of the refrigeration circuit located outside the freezer can be located remotely from the freezer, for example, in a separate room such as a mechanical room.

[0033] A refrigeration display system may include a plurality of freezers. For example, the refrigeration display system may include 2, 5 or 10 freezers. The plurality of freezers may each include an evaporator heat exchanger for cooling the air within the freezer and a fan for drawing air across the evaporator heat exchanger. The evaporator heat exchanger of each freezer may form part of a refrigeration circuit of the refrigeration display system, whereby each freezer is thus connected to a common refrigeration circuit. Thus, in another aspect, the present invention may provide a method for controlling a defrosting process in a refrigeration display system, the method comprising: a refrigeration circuit that includes one or more evaporator heat exchangers for cooling the air within the freezer, and one or more freezers each including one of the one or more evaporator heat exchangers and an evaporator fan for drawing air across the evaporator heat exchanger, the method comprising: switching the refrigeration circuit from a cooling mode to a defrosting mode to heat the air within the one or more freezers; and while in the defrosting mode: measuring the air temperature at a first location in each of the one or more freezers remote from the evaporator heat exchanger; if the measured air temperature exceeds a first switching temperature, turning on the evaporator fan to draw air above the evaporator heat exchanger; and if the air temperature drops below a second switching temperature that is lower than the first switching temperature, turning off the evaporator fan.

[0034] The present invention also extends to a corresponding refrigeration display system that includes a freezer, which may be a freezer for storing goods for consumer access, such as a refrigerated display case. Thus, in a second aspect, the present invention provides a refrigeration display system that includes a refrigerated cabinet for storing goods in a temperature-controlled environment, the system comprising: a refrigeration circuit that includes an evaporator heat exchanger in the refrigerated cabinet for cooling the air in the refrigerated cabinet; a fan for drawing air across the evaporator heat exchanger and circulating the air within the freezer; and a control system for controlling the operation of the fan and the refrigeration circuit; wherein the control system is configured to, during a defrosting process, switch the refrigeration circuit from a cooling mode to a defrosting mode to heat the air within the freezer, measure the air temperature at a first location within the freezer remote from the evaporator heat exchanger, and operate the fan to draw air above the evaporator heat exchanger only if the measured air temperature exceeds a first switching temperature. As described above, other parts of the refrigeration circuit may be within the freezer or outside the freezer.

[0035] The refrigeration display system of the second aspect may be configured to perform the above method and may include one or more or all of the above optional features. Thus, for example, the control system may be configured to operate in accordance with the above features.

[0036] The control system can be configured to measure the air temperature at a second location within the freezer cabinet. The second location can be adjacent to the evaporator heat exchanger and / or one or more heaters. If the air temperature measured at the second location is higher than the defrost termination temperature, the control system can be configured to end the defrost process. For example, the control system can be configured to switch the refrigeration circuit from the defrost mode to the cooling mode when the temperature measured at the second location exceeds the defrost termination temperature. The defrost termination temperature can be between 2°C and 25°C. For example, the defrost termination temperature can be approximately 3°C, approximately 10°C, or approximately 15°C.

[0037] The control system can include one or more temperature sensors for measuring the air temperature at the first location and / or the second location. For example, the control system can include a first temperature sensor located at the first location for measuring the air temperature at the first location; and a second temperature sensor located at the second location for measuring the air temperature at the second location. The one or more temperature sensors can be the same as the temperature sensors discussed above with respect to the first aspect.

[0038] The control system can include a circuit for powering the fan, the refrigeration circuit, and / or one or more heaters. In the case where the one or more temperature sensors include a thermoswitch, the thermoswitch can form part of the circuit. For example, the circuit can include a first thermal switch located at the first location. The first thermal switch can be configured to complete the circuit and allow current to flow to the fan when the temperature at the first location exceeds a first switching temperature. The first thermal switch can be configured to open the circuit to prevent current from flowing to the fan when the temperature at the first location drops below a second switching temperature. Thus, the first thermal switch can be configured to turn the evaporator fan on and off depending on the air temperature at the first location.

[0039] The circuit can include a second thermal switch located at the second location. The second thermal switch can be configured to prevent the evaporator heat exchanger and / or one or more heaters from heating the air when the temperature at the second location exceeds the defrost termination temperature. When the air temperature at the second location exceeds the defrost termination temperature, the second thermal switch can be configured to prevent current from flowing to the reversing valve, thereby causing the refrigeration circuit to exit the heating mode. Optionally, the second thermal switch can be configured to prevent current from flowing to one or more heaters when the air temperature at the second location exceeds the defrost termination temperature. Thus, the second thermal switch can be configured to end the defrost process when the air temperature at the second location exceeds the defrost termination temperature.

[0040] In the case where the temperature sensor includes an electrical temperature sensor, the control system may further include a digital controller arranged to receive data from the electrical temperature sensor. The digital controller may include a processor. The controller may be configured to turn on the fan if the data received from the first temperature sensor indicates that the air temperature at the first location is higher than a first switching temperature. The controller may be configured to turn off the fan if the data received from the first temperature sensor indicates that the air temperature at the first location is lower than a second switching temperature. Optionally, if the data received from the second temperature indicates that the air temperature at the second location is higher than a defrost termination temperature, the controller may be configured to prevent the evaporator heat exchanger and / or the heater from heating the air.

[0041] The location of the first temperature sensor can affect the temperatures set as the first and second switching temperatures. For example, during a defrost process, the air temperature in a sheltered location of the freezer may change more slowly compared to the air in a more exposed location, and vice versa. Thus, if the first temperature sensor is located in a sheltered location, the measured air temperature may change more slowly than the air temperature in other areas of the freezer. Therefore, if the first temperature sensor is located in a sheltered location, the first and second switching temperatures can be set lower compared to if it were located in an exposed location. For example, if the first temperature sensor is located in a sheltered location, the first and second switching temperatures can be -1 °C and -6 °C respectively, while if the first temperature sensor is located in an exposed location, the first and second switching temperatures can be 10 °C and 0 °C respectively. Selecting the correct switching temperatures for the location of the first temperature sensor can prevent overheating of the freezer during the defrost process. This protects the goods stored in the freezer, which may potentially be damaged if heated to too high a temperature.

[0042] Optionally, the freezer includes a spoiler located at the first inlet for regulating the air flow through the first inlet. The length of the spoiler can be between 20 mm and 60 mm. For example, the spoiler can have a length of 30 mm or 50 mm. The spoiler can be positioned to cover or obscure all or part of the first inlet. The spoiler allows manipulation of the air flow through the first inlet and can result in a more uniform flow of air through the inlet. This means that the air temperature at the first inlet is more uniform and is less likely to experience random fluctuations in temperature. Thus, providing a spoiler at the first inlet can result in a more consistent and indicative measurement of the air temperature at the first location. Description of the Drawings

[0043] Certain preferred embodiments of the present invention will now be described, by way of example only, with reference to the following drawings, in which:

[0044] Figure 1 A cross-section through the freezer is shown;

[0045] Figure 2 is Figure 1 an enlarged view of the refrigeration system of a freezer

[0046] Figure 3 is Figure 1 a perspective view of a freezer; and

[0047] Figure 4 is a graph showing the fluctuations of the air temperature inside the freezer during an exemplary defrosting process. Detailed Description

[0048] Figure 1 shows a cross-section through the freezer 1. The freezer 1 includes a housing 2 that defines a storage chamber 3 for accommodating goods such as perishable food in a temperature-controlled environment; and a refrigeration circuit 4 for controlling the temperature inside the storage chamber 3; and an evaporator fan 5 for controlling the air flow inside the freezer 1.

[0049] The storage chamber 3 defines an enclosed volume thermally isolated from the environmental conditions outside the freezer 1 to ensure control and maintenance of the temperature conditions inside the storage chamber 3. For example, the housing 2 can be made of insulating material to isolate the storage chamber 3 from the environmental conditions surrounding the freezer 1. In Figure 1 the embodiment shown, the storage chamber 3 includes shelves 6 on which goods can be placed.

[0050] The housing 2 surrounds the storage chamber 3 and includes at least one door 7 to provide access to the storage chamber 3. In this embodiment, the door 7 is arranged on the front side of the freezer 1, however it will be appreciated that it could be located elsewhere. For example, the door 7 could be positioned on the top side of the freezer 1 to provide access to the storage chamber 3 from above.

[0051] The refrigeration circuit includes a compressor 8, a condenser 9, an expansion valve 10, and an evaporator 11. The refrigeration circuit 4 is arranged such that refrigerant can flow in a closed loop through the compressor 8, the condenser 9, the expansion valve 10, and the evaporator 11. In this embodiment, the refrigeration circuit 4 further includes a reversing valve 12 to allow the flow of refrigerant through the circuit to be reversed. This allows the refrigeration circuit 4 to switch between a refrigeration mode, in which the refrigeration circuit 4 uses the evaporator fan 5 to cool the air inside the freezer 1 by drawing in chamber air over the evaporator 11, and a heating mode, in which the refrigeration circuit 4 heats the air inside the freezer, and vice versa.

[0052] For example, in the cooling mode, the refrigerant can flow through the refrigeration circuit 4 in a first direction, i.e., the refrigerant can pass through the compressor 8 and be compressed and superheated before passing through the condenser 9, and the refrigerant is cooled and condensed in the condenser 9. Then, the refrigerant can be transferred to the expansion valve 10 to reduce the pressure of the refrigerant and cause flashing of the refrigerant before the refrigerant is transferred to the evaporator 11, where the refrigerant is in a heat exchange relationship with the air in the freezer cabinet 1, resulting in cooling of the air and heating of the refrigerant. Then, the refrigerant can be returned to the compressor 8 to complete the cycle. It should be noted that this arrangement with a refrigerant circuit in the freezer cabinet is only an example of the type of refrigeration display system in which the proposed defrost mode can be used. The defrost mode described herein can also be advantageous for refrigeration display systems with different arrangements for providing cooling. For example, the defrost mode can be used in conjunction with: a plug-in system, where both the compressor and the condenser are inside the freezer cabinet; a remote system, where the compressor and the condenser are located in a special machinery room outside the freezer cabinet; and a semi-plug-in system, which can include a brine system connected to a condenser inside the freezer cabinet.

[0053] In the heating mode, the refrigerant is made to flow through the refrigeration circuit 4 in the opposite direction, i.e., such that the compressed refrigerant from the compressor 8 first passes through the evaporator 11, then through the expansion valve 10, the condenser 9, and then back to the compressor 8. In this way, the superheated refrigerant flowing through the evaporator 11 causes heating of the air inside the freezer cabinet 1. This reversal of the refrigerant flow is achieved by the reversing valve 12. The heating mode can be used, if necessary, for defrosting the freezer cabinet 1.

[0054] The reversing valve 12 is configured to place the refrigeration circuit 4 in the heating mode in response to an electric current flowing to the reversing valve 12. That is, when an electric current is supplied to the reversing valve 12, the reversing valve 12 operates to switch the refrigeration circuit 4 from the refrigeration mode to the heating mode by reversing the flow of the refrigerant. When the electric current is removed from the reversing valve 12, the refrigerant returns to its original flow direction and the refrigeration cycle switches back to the cooling mode.

[0055] Although in this embodiment, the refrigeration circuit 4 can be operated in the heating mode to heat the air inside the freezer cabinet 1, the freezer cabinet 1 can alternatively or additionally include an electric heater 13 for heating the air inside the freezer cabinet 1. The electric heater 13 can be used as an alternative or supplement to the evaporator 11 of the refrigeration circuit 4 (in the heating mode) to heat the air for defrosting the freezer cabinet 1. In an embodiment having the electric heater 13, the electric heater 13 can be located near the evaporator 11. There can be multiple electric heaters 13, for example Figure 1 the four heaters shown in

[0056] Other embodiments are also contemplated that do not include components for actively heating the air within the freezer 1. In all embodiments, the air within the freezer 1 will be heated by the ambient conditions surrounding the freezer 1. Thermal energy from the relatively warm environment surrounding the cabinet will conduct through the cabinet walls and cause the air temperature within the cabinet to rise. Thus, when the evaporator 11 is no longer used to cool the air, the air temperature will naturally rise during the defrost cycle. If the defrost process continues for an appropriate length of time, the air temperature within the cabinet will rise until it reaches thermal equilibrium with the ambient conditions outside the cabinet. In some cases, this natural warming can sufficiently heat the air to melt the ice within the cabinet during the defrost process. In such cases, no active air heating is required. However, it will be recognized that providing components for actively heating the air, such as a refrigeration circuit 4 and / or a heater 13 capable of heating the air, can allow the air to be heated more quickly and to a higher temperature compared to using only natural heating.

[0057] As Figure 1 shown, the refrigeration circuit 4 and the fan 5 are located outside and below the enclosed volume of the storage compartment 3. Air channels are provided within the freezer 1 to allow air to circulate between the refrigeration circuit 4 and the storage compartment 3. In this way, cooled and / or heated air can be transferred from the evaporator 11 to the storage compartment 3 through the air channels to change the temperature within the storage compartment 3.

[0058] The air channels include a rear air channel 14 located between the storage compartment 3 and the rear wall of the housing 2. The rear air channel 14 also extends above the storage compartment 3 between the storage compartment 3 and the top wall of the housing 2. Upper vents 15 are provided in the storage compartment 3 to allow air to flow between the rear air channel 14 and the storage compartment 3. As can be seen in Figure 1 it, the upper vents 15 allow air to pass from the evaporator 11 through to the upper part of the storage compartment 3.

[0059] The air channels also include a return air vent 16 located at the floor of the storage compartment 3 adjacent to the door 7. The return air vent 16 allows air to pass between the evaporator 11 and the lower part of the storage compartment 3.

[0060] A fan 5 is provided to enable air to circulate within the freezer 1. The fan 5 is arranged to draw air in through the evaporator 11 during use to circulate the air from the evaporator 11 and into the storage compartment 3. In particular, the fan 5 is arranged to draw air in above the evaporator 11 and cause it to pass through the rear air channel 14 and enter the storage compartment 3 via the upper vents 15.

[0061] As Figure 1As shown, the fan 5 is arranged behind the evaporator 11. That is to say, the fan 5 is located in the air flow path between the evaporator 11 and the rear air passage 14. When the fan 5 is turned on, it is used to suck air above the evaporator 11 and push the air through the rear air passage 14. However, when the fan 5 is turned off, it presents an obstruction in the air flow path between the evaporator 11 and the rear air passage 14, thus restricting the flow of air from the evaporator 11 to the rear air passage 14.

[0062] In this way, any hot air dissipated from the evaporator 11 (such as during the defrost cycle) is restricted by the fan 5 from flowing into the rear air passage 14, and instead flows from the evaporator 11 and towards the return air opening 16 through natural convection. Some of this warm air can enter the storage chamber 3 through the return air opening 16. This natural warm air flow can be reversed by turning on the fan 5 to push the air through the rear air passage 14.

[0063] In order to monitor and control the temperature inside the storage chamber 3, the freezer 1 further includes a control system 17, and the control system 17 includes a return air temperature sensor 18 and a defrost temperature sensor 19.

[0064] The return air temperature sensor 18 is located outside the storage chamber 3, adjacent to the return air opening 16, so as to be able to control the fan 5 in response to different air temperatures at the return air opening 16. The return air temperature sensor 18 is positioned such that it is located within the air flow path of the air leaving and entering the storage chamber 3 through the return air opening, and can be positioned at any location along the length of the return air opening 16. As Figure 3 shown, in this embodiment, the return air temperature sensor 18 is located behind the mullion 20 of the door 7.

[0065] The defrost temperature sensor 19 is positioned to sense the air temperature around the evaporator 11. The defrost temperature sensor 19 can be used, for example, to measure the increase in the air temperature around the evaporator 11 during the defrost cycle. Therefore, the defrost temperature sensor 19 can be positioned adjacent to the evaporator 11 within the air flow path of the air inside the freezer 1.

[0066] The return air temperature sensor 18 and the defrost temperature sensor 19 can be used to control the operation of the fan 5 and / or the refrigeration circuit 4. For example, during the defrost cycle, the fan 5 can operate differently compared to the cooling cycle of the freezer 1, such as operating at a different speed. Therefore, the temperature sensors 18, 19 can be used to determine when to switch between the cooling operation mode and the defrost operation mode for the fan 5 and / or the refrigeration circuit 4. For example, when the air temperature measured by the defrost sensor reaches a certain value, the fan 5 can be switched from the defrost operation mode to the cooling operation mode.

[0067] In the present embodiment, the return air temperature sensor 18 and the defrost sensor are bimetallic thermal switches. The control system 17 includes a circuit for supplying power to the components of the fan 5 and the refrigeration circuit 4. The thermal switches are arranged to provide direct mechanical control of the circuit.

[0068] The thermal switches are configured to open and close when they reach a certain temperature, enabling control of the power supply to the components of the fan 5 and the refrigeration circuit 4.

[0069] The return air temperature sensor 18 is configured to allow current to flow through the circuit to the fan 5 when it senses that the air temperature at the return air opening 16 is higher than the first switching temperature. The return air temperature sensor 18 is also configured to prevent current from flowing to the fan 5 when it senses that the air temperature at the return air opening 16 is lower than the second switching temperature. Thus, the return air temperature sensor 18 is configured to turn the fan 5 on and off according to the air temperature at the return air opening 16.

[0070] The defrost temperature sensor 19 is configured to allow current to flow to the reversing valve 12 when the air temperature at the evaporator 11 is lower than the defrost termination temperature. Thus, during the defrost process, when the air temperature at the evaporator 11 is lower than the defrost termination temperature, the refrigeration circuit 4 will operate in a heating mode, i.e., where the air is heated by the evaporator 11.

[0071] In addition, the defrost temperature sensor 19 is configured to prevent current from flowing to the reversing valve 12 when the air temperature at the evaporator 11 is higher than the defrost termination temperature. Thus, when the air temperature at the evaporator 11 is higher than the defrost termination temperature, the refrigeration circuit 4 will operate in a cooling mode, i.e., where the air is cooled by the evaporator 11.

[0072] Although in the described embodiment, the return air temperature sensor 18 and the defrost temperature sensor 19 are thermal switches, it should be recognized that any suitable temperature sensor can be used. For example, the return air temperature sensor 18 and the defrost temperature sensor 19 can include a thermistor sensor, a semiconductor sensor, and / or a thermocouple for measuring the air temperature. In certain embodiments, the return air temperature sensor 18 and the defrost temperature sensor 19 can send an electrical signal indicating the sensed air temperature to a controller that controls the power supply to the fan 5.

[0073] The spoiler 21 is located in the flow path of the air flowing through the return air opening. The spoiler 21 is arranged to change the air flow through the return air opening and provide a more uniform air flow. The spoiler 21 makes the temperature of the air flowing through the return air opening 16 and thus flowing above the return air temperature sensor 18 more uniform. Therefore, the air temperature flowing through the return air temperature sensor 18 and sensed by the return air temperature sensor 18 fluctuates less and is less likely to suffer from deviations caused, for example, by a cold air mass from the storage room 3 flowing through the return air opening 16.

[0074] Now, a defrosting method of the freezer 1 will be described with reference to Figure 1 the description below.

[0075] The defrosting process can be started automatically, for example, if a certain time has elapsed since the previous defrosting cycle, or it can be started manually. During the normal operation of the freezer 1, i.e., in the cooling mode, the refrigeration circuit 4 operates in the cooling mode to cool the air inside the freezer 1. The fan 5 is turned on to draw air in across the evaporator 11, and the cooled air passes through the rear air passage 14 and enters the storage compartment 3 through the upper vent 15.

[0076] When switching from the cooling mode to the defrosting mode, the fan 5 is turned off. Optionally, the refrigeration circuit 4 is placed in the heating mode, or alternatively, the refrigeration circuit 4 is turned off, for example, by deactivating the compressor. Optionally, the electric heater 13 can be used during the defrosting mode. In the heating mode, the refrigeration circuit 4 heats the air inside the freezer 1. As described above, in the heating mode, the flow of the refrigerant through the refrigeration circuit 4 is reversed by the reversing valve 12, so that the refrigerant flowing through the evaporator 11 is hot, thereby heating the air inside the freezer 1. In this way, the air inside the freezer 1 around the evaporator 11 is heated. As a result, any ice accumulated on or around the evaporator 11 will start to melt.

[0077] During the defrosting mode, as described above, due to the positioning of the evaporator 11, the warmer air from the evaporator 11 naturally flows towards the air return opening 16 and enters the storage compartment 3. The air can be heated by the heater 13 and / or by the heating mode of the refrigeration circuit. This hot air is used to melt any ice and frost at the air return opening 16.

[0078] When the evaporator fan 5 is turned off, due to natural convection, the air only moves slowly over the evaporator 11. This means that the air can be heated to a higher temperature and heated faster compared to when the fan 5 is running.

[0079] The hot air passing through the air return opening 16 melts any ice near the air return opening 16. However, the melted ice causes water vapor to be entrained in the warm air. Therefore, the hot air entering the storage compartment 3 becomes humid. When the warm and humid air interacts with the cooler air inside the storage compartment 3, it starts to cool. This may cause the water vapor in the air to condense and freeze. If this cooling continues, ice may accumulate around the air return opening 16 on the front of the cabinet near the door 7.

[0080] To prevent such icing during the defrost mode, when the temperature sensed by the return air temperature sensor 18 reaches a predetermined first switching temperature, the evaporator fan 5 is turned on and then undergoes an on-and-off cycle as explained below. Operating the evaporator fan 5 stops the flow of moist hot air through the return air inlet 16 into the storage chamber 3 and causes hot air to be pushed from the evaporator 11 and through the rear air passage 14.

[0081] The air pushed by the evaporator fan 5 through the rear air passage 14 enters the storage chamber 3 through the upper air vent 15. In this way, hot air enters the storage chamber 3 to melt the ice accumulated in the storage chamber 3.

[0082] This flow of warm air entering the storage chamber 3 from the rear air passage 14 also causes the relatively cold air within the storage chamber 3 to move to the front and lower regions of the storage chamber 3 and through the return air inlet 16. This cold air is then heated as it passes through the evaporator 11. The heated air is then pushed by the evaporator fan 5 into the storage chamber 3 via the rear air passage 14 and the upper air outlet 15 to defrost.

[0083] The flow of cold air through the return air inlet 16 also causes the air temperature at the return air inlet 16 to decrease. This is sensed by the return air temperature sensor 18. To prevent ice from reforming at the return air inlet 16, when the temperature sensed by the return air temperature sensor 18 drops below a predetermined second switching temperature that is lower than the first switching temperature, the evaporator fan 5 is turned off. In this way, the force that causes hot air to be pushed from the evaporator 11 into the rear air passage 14 and through the rear air passage 14 is eliminated, and the hot air resumes its natural flow. That is, the hot air again begins to flow from the evaporator 11 and through the return air inlet 16 into the storage chamber 3. Thus, the return air inlet 16 is again heated by the hot air flow.

[0084] The first and second switching temperatures are set to ensure that the air at the return air inlet 16 is warm enough to melt the ice at the return air inlet 16. In addition, the switching temperatures ensure that once there is no longer a need to increase the heat of the air at the return air inlet 16, since the air temperature is sufficient to melt the ice, the heated air is used to melt the ice in other areas of the freezer 1. Since the evaporator fan 5 cycles on and off, this part of the defrosting of the freezer 1 is then completed by turning on the evaporator fan 5 to drive the hot air to other areas of the freezer 1.

[0085] The first and second sensing temperatures are set according to the position of the return air temperature sensor 18. In the present embodiment, as Figure 3 shown, the return air temperature sensor 18 is located behind the mullion 20 of the door 7. By positioning the return air temperature sensor 18 behind the door mullion 20, it is not easily damaged, for example, during the cleaning of the freezer 1.

[0086] Due to the proximity of the door mullion 20, air may not flow freely past the return air temperature sensor 18, and thus the air temperature at the return air temperature sensor 18 may not deviate as much, for example, due to the heating of the evaporator 11, to other areas of the freezer cabinet 1. That is, the temperature experienced by other portions of the return air opening 16 not covered by the door mullion 20 may be higher than those temperatures measured by the return air temperature sensor 18. Accordingly, in the present embodiment, the first switching temperature is set to -1 °C and the second switching temperature is set to -6 °C.

[0087] In an alternative embodiment, also shown in Figure 3 the return air temperature sensor 18' is positioned between successive door mullions 20. Although this positioning provides less protection for the return air temperature sensor 18', it means that air can flow more freely past the sensor. Accordingly, the temperature at the sensor more indicative of the air temperature at other portions of the return air opening 16. In this embodiment, the first switching temperature is set to 10 °C and the second switching temperature is set to 0 °C.

[0088] Depending on the air temperature sensed by the return air temperature sensor 18, a cycle of turning the evaporator fan 5 on and off continues until the air temperature sensed by the defrost temperature sensor reaches a maximum defrost temperature. Once the maximum defrost temperature is reached, the defrost cycle terminates. The maximum defrost temperature, also referred to as the defrost termination temperature, is set to ensure that the temperature within the storage compartment 3 does not exceed a maximum allowable temperature. For example, the maximum defrost temperature may be 15 °C. This ensures that the goods within the storage compartment 3 do not exceed the allowable temperature above which they may be damaged or degraded.

[0089] Figure 4 is a graph showing how the evaporator fan 5 operates during an exemplary defrost process. Line X indicates when the fan 5 is turned on or off. Lines Y and Z respectively show how the temperatures sensed by the return air temperature sensor 18 and the defrost temperature sensor change during the defrost process.

[0090] At time t0, the defrost process begins and the evaporator fan 5 is turned off. During the defrost process, the air within the freezer cabinet 1 is no longer cooled and thus the air temperature rises. This can be seen from lines Y and Z, which show the rise in temperature sensed by both the return air temperature sensor 18 and the defrost temperature sensor after time t0.

[0091] The air temperature at the return air opening 16 continues to rise until time t1, at which point the temperature sensed by the return air temperature sensor 18 reaches the first switching temperature. In this embodiment, the first switching temperature is 10 °C. According to the invention, once the temperature sensed by the return air temperature sensor 18 exceeds the first switching temperature, the evaporator fan 5 is turned on. As can be seen from line X, the evaporator fan 5 is turned on at time t1.

[0092] As described above, the operation of the evaporator fan 5 causes the cooler air from the storage chamber 3 to pass through the return air opening 16. This causes the air temperature sensed by the return air sensor to decrease, as shown by line Y. At time t2, the temperature sensed by the return air temperature sensor 18 drops below the second switching temperature (0°C in this embodiment). As a result, the evaporator fan 5 is turned off.

[0093] The process continues until the temperature sensed by the defrost temperature sensor exceeds the defrost termination temperature. Since the air is not cooled by the refrigeration circuit 4 during the defrost process, the air temperature sensed by the defrost temperature sensor increases from time t1. The temperature sensed by the defrost temperature sensor increases until it reaches the defrost termination temperature at time t3. In this embodiment, the defrost termination temperature is 15°C. At time t3, the defrost process ends. Therefore, the refrigeration circuit 4 is switched back to the cooling mode to cool the air in the freezer 1. This is represented by lines Y and Z, which show that the air temperatures sensed by the return air sensor and the defrost temperature sensor start to decrease after time t3.

[0094] After the defrost process ends, there may be a delay before the temperature sensed by the return air temperature sensor 18 drops significantly due to the travel time required for the cold air to move from the evaporator 11 (i.e., the cooling source) to the return air opening 16.

Claims

1. A method for controlling a defrosting process in a freezer cabinet, the freezer cabinet having an evaporator heat exchanger for cooling air within the freezer cabinet and an evaporator fan for drawing air across the evaporator heat exchanger, wherein the evaporator heat exchanger is part of a refrigeration circuit for cooling the freezer cabinet; the method comprising: Switching the refrigeration circuit from a refrigeration mode to a defrost mode to heat the air within the freezer cabinet; and Simultaneously in the defrost mode: Measuring the air temperature at a first position within the freezer cabinet remote from the evaporator heat exchanger; If the measured air temperature exceeds a first switching temperature, turning on the evaporator fan to draw air above the evaporator heat exchanger; and If the measured air temperature drops below a second switching temperature below the first switching temperature, turning off the evaporator fan.

2. The method according to claim 1, comprising: Measuring the air temperature at a second position within the freezer cabinet; and When the air temperature measured at the second position exceeds a defrost termination temperature, switching the refrigeration circuit from the defrost mode to the cooling mode.

3. The method according to claim 2, wherein, The defrost termination temperature is between 2°C and 25°C.

4. The method according to any one of claims 1 to 3, wherein The second position is adjacent to the evaporator heat exchanger.

5. The method according to any one of claims 1 to 3, wherein, The refrigeration circuit includes a compressor for compressing refrigerant, and wherein switching the refrigeration circuit from the cooling mode to the defrost mode includes turning off the compressor.

6. The method according to any one of claims 1 to 3, wherein During the defrost mode, the air is at least partially heated by the environment surrounding the freezer cabinet.

7. The method according to any one of claims 1 to 3, comprising: During the defrost mode, operating the refrigeration circuit in a heating mode to heat the air within the freezer cabinet.

8. The method according to claim 7, wherein The evaporator heat exchanger is for heating the air within the freezer cabinet during the heating mode of the refrigeration circuit; and wherein the evaporator fan is for generating an air circulation through the storage chamber and above the evaporator heat exchanger.

9. The method according to claim 7, wherein, The refrigeration circuit includes a reversing valve for reversing the flow of refrigerant in the refrigeration circuit, and operating the refrigeration circuit in a heating mode includes using the reversing valve to reverse the flow of refrigerant in the refrigeration circuit.

10. The method according to any one of claims 1 to 3, wherein, The freezer cabinet may include a heater, and wherein, during the defrost mode, the heater is for heating the air within the freezer cabinet.

11. The method according to any one of claims 1 to 3, wherein, The first switching temperature is between -5°C and 11°C, and the second switching temperature is between -10°C and 5°C.

12. The method according to any one of claims 1 to 3, wherein The freezer cabinet includes a storage chamber for accommodating goods in a temperature-controlled environment, and wherein the first position is a first inlet for allowing air to flow into and out of the lower part of the storage chamber.

13. The method according to any one of claims 1 to 3, wherein, In operation, the evaporator fan pushes air in a direction away from the first position.

14. A refrigeration display system, which includes a freezer cabinet for storing goods in a temperature-controlled environment, the refrigeration display system comprising: A refrigeration circuit, which includes an evaporator heat exchanger in the freezer cabinet for cooling the air within the freezer cabinet; An evaporator fan, which is for drawing air across the evaporator heat exchanger and circulating air within the freezer cabinet; and A control system for controlling the operation of the fan and the refrigeration system; Wherein, the control system is configured to switch the refrigeration system from a cooling mode to a defrost mode during a defrost process to heat the air inside the freezer cabinet, measure the air temperature at a first position inside the freezer cabinet remote from the evaporator heat exchanger, and if the measured air temperature exceeds a first switching temperature, turn on the evaporator fan to suck air above the evaporator heat exchanger, and if the air temperature drops below a second switching temperature lower than the first switching temperature, turn off the evaporator fan.

15. The refrigerated display system according to claim 14, wherein, The evaporator fan is arranged such that in operation the evaporator fan pushes air away from the first position.

16. The refrigeration display system according to claim 14 or 15, wherein the freezer cabinet includes a storage chamber defining an enclosed volume for receiving goods, and wherein the refrigeration system is outside the enclosed volume.

17. The refrigerated display system according to claim 16, wherein, The storage chamber has a first inlet for allowing air to flow into and out of a lower portion of the storage chamber and / or a second inlet for allowing air to flow into and out of an upper portion of the storage chamber; and wherein, the evaporator fan is for generating an air circulation through the storage chamber and above the evaporator heat exchanger.

18. The refrigeration display system according to claim 17, wherein the freezer cabinet includes a spoiler positioned at the first inlet to control the air flow through the first inlet.

19. The refrigerated display system according to claim 17, wherein, The first position is the position of the first inlet.

20. The refrigeration display system according to claim 14 or 15, configured to perform the method according to any one of claims 1 to 13.

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