DEFROSTING WITH HEAT GENERATED BY COMPRESSOR DRIVER

Abstract

 The present invention discloses a heat pump system including a refrigerant circuit, a compressor driver, and a heat storage means. The refrigerant circuit includes a compressor for compressing the refrigerant, a first heat exchanger for transferring heat between the refrigerant and the interior atmosphere, a throttling device for lowering the pressure of the refrigerant, and a second heat exchanger for transferring heat between the refrigerant and the exterior atmosphere. The first heat exchanger operates as a condenser to cool the refrigerant in a heating mode and operates as an evaporator to vaporize the refrigerant in a cooling mode. The second heat exchanger operates as an evaporator in the heating mode and operates as a condenser in the cooling mode. The compressor driver is electrically connected with the compressor for powering the compressor, and it generates heat in operation. The heat storage means for storing heat generated by the compressor driver is in heat transferable contract with the refrigerant in a defrost mode to transfer stored heat energy to the refrigerant. In this way, the possibility of extraction of heat from interior atmosphere is reduced, thereby improving thermal comfort of building interiors during the defrost mode.

Description

FIELD OF THE INVENTION

[0001] The present invention relates to a heat pump system, and more particularly to a heat pump system capable of defrosting an outdoor heat exchanger coil by using heat generated by a compressor driver.

BACKGROUND OF THE INVENTION

[0002] Heat pumps are well known and used for heating and/or cooling building interiors and the like. A basic heat pump typically has a refrigerant circuit including a compressor, a condenser, an expansion valve, and an evaporator, and a heat exchanger fluid (usually called a refrigerant) circulates in the refrigerant circuit to transfer heat from a first location to a second location. For an air-to-air heat pump, during a heating mode operation, outdoor air is used as a heat source, an outdoor heat exchanger acts as an evaporator and an indoor heat exchanger acts as a condenser. Thus, the refrigerant absorbs heat from exterior atmosphere through the evaporator and release heat to interior atmosphere via the condenser. Heat pumps are also designed so that operations can be reversed to transfer heat from the interior atmosphere to the exterior atmosphere in a cooling mode.

[0003] Outdoor heat exchangers usually take form of coil type heat exchangers. During a normal heating mode, an outdoor heat exchanger that is acting as an evaporator becomes colder than exterior atmosphere. When the exterior temperature is near or below the freezing point of water, moisture in the air gets frozen and turns to ice/frost building up on the coil of the outdoor heat exchanger. The formation of ice restricts the airflow across the coil, which causes heat energy absorbed from outdoor air to be reduced, thereby reducing the performance and efficiency of the heat pump system. In order to restore performance, the system will enter a defrost mode. A common method of defrosting the outdoor coil is known as reversing the operation of the heat pump system from the heating mode to the cooling mode. The effect of such mode reversal is to direct the hot refrigerant discharged by the compressor directly to the outdoor coil to melt the ice until a temperature of the outdoor coil is raised to a predetermined value to ensure removal of all of ice. During the period, the indoor space heating has to be stopped, moreover, since the interior heat exchanger functions as an evaporator at this time, it extracts heat from interior atmosphere with the result that the interior temperature decreases, which will obviously reduce the interior thermal comfort.

SUMMARY OF THE INVENTION

[0004] It is an object of present invention to provide a heat pump system that can defrost outdoor heat exchanger coil with heat generated by a compressor driver, thereby reducing the possibility of extraction of heat from interior atmosphere in the defrost mode.

[0005] According to one aspect of the present invention there is provided a heat pump system including a refrigerant circuit, a compressor driver, and a heat storage means. The refrigerant circuit includes a compressor for compressing the refrigerant, a first heat exchanger for transferring heat between the refrigerant and the interior atmosphere, a throttling device for lowering the pressure of the refrigerant, and a second heat exchanger for transferring heat between the refrigerant and the exterior atmosphere. The first heat exchanger operates as a condenser to cool the refrigerant in a heating mode and operates as an evaporator to vaporize the refrigerant in a cooling mode. The second heat exchanger operates as an evaporator in the heating mode and operates as a condenser in the cooling mode. The compressor driver is electrically connected with the compressor for powering the compressor, and it generates heat in operation. The heat storage means for storing heat generated by the compressor driver is in heat transferable contract with the refrigerant in a defrost mode to transfer stored heat energy to the refrigerant. In this way, the possibility of extraction of heat from interior atmosphere is reduced, thereby improving thermal comfort of building interiors during the defrost mode.

[0006] Preferably, the heat storage means obtains heat from the compressor driver via a flowing work medium in the heating mode and/or the cooling mode.

[0007] In one embodiment, the heat storage means is switched to be connected with the first heat exchanger in the defrost mode, in order to release stored heat energy to the refrigerant as the working medium and the refrigerant pass through the first heat exchanger.

[0008] Preferably, the system further includes a space heating/cooling circuit connectable with the first heat exchanger for heating or cooling the interior atmosphere, and the space heating/cooling circuit is disposed in parallel with the heat storage means.

[0009] Preferably, when a temperature of the working medium decreases to a lower limit value while a temperature of the second heat exchanger does not reach a predetermined value in the defrost mode, the space heating/cooling circuit is activated to provide heat energy to the refrigerant passing through the first heat exchanger instead of the heat storage means. Although the extraction of heat from interior atmosphere could not be avoided, since the amount of heat energy extracted from interior atmosphere is much smaller than that needed in a traditional defrost mode, the temperature of interior atmosphere would not be decreased significantly, thus the interior thermal comfort can be assured.

[0010] In an alternative embodiment, the system further includes an additional heat exchanger connected in the refrigerant circuit, and the heat storage means is switched to be connected with the additional heat exchanger in the defrost mode for releasing stored heat energy to the refrigerant as the working medium and the refrigerant pass through the additional heat exchanger.

[0011] Preferably, the additional heat exchanger is placed next to the first heat exchanger to transfer stored heat energy from the working medium to the refrigerant before or after the refrigerant passing through the first heat exchanger.

[0012] Preferably, the system further includes a space heating/cooling circuit connected with the first heat exchanger for heating or cooling the interior atmosphere; wherein, when a temperature of the working medium decreases to a lower limit value while a temperature of the second heat exchanger does not reach a predetermined value in the defrost mode, the space heating/cooling circuit is activated to provide heat energy to the refrigerant passing through the first heat exchanger. By this means, only smaller amount of heat energy is extracted from the interior atmosphere, thus the interior thermal comfort can be assured.

[0013] Preferably, the heat storage means includes a tank with a phase change material.

[0014] Preferably, the connection of the heat storage means is switched via a first three-way valve.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

Fig. 1A is a schematic diagram showing a heat pump system performing in a normal heating or cooling mode in accordance with a first embodiment of present invention;

Fig.1B is a schematic diagram showing the heat pump system of Fig. 1A performing in a defrost mode, wherein the system offers defrost of an outdoor heat exchanger coil with only heat generated by a compressor driver;

Fig.1C is a schematic diagram showing the heat pump system of Fig. 1A performing in the defrost mode, wherein the system offers defrost of an outdoor heat exchanger coil with both heat generated by the compressor driver and heat extracted from an interior atmosphere;

Fig.2A is a schematic diagram showing a heat pump system performing in a normal heating or cooling mode in accordance with a second embodiment of present invention;

Fig.2B is a schematic diagram showing the heat pump system of Fig. 2A performing in a defrost mode, wherein the system offers defrost of an outdoor heat exchanger coil with only heat generated by a compressor driver;

Fig.2C is a schematic diagram showing the heat pump system of Fig. 2A performing in the defrost mode, wherein the system offers defrost of an outdoor heat exchanger coil with both heat generated by the compressor driver and heat extracted from an interior atmosphere.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Reference will now be made to the drawing figures to describe the preferred embodiments of the present invention in detail. However, the embodiments can not be used to restrict the present invention. Changes such as structure, method and function obviously made to those of ordinary skill in the art are also protected by the present invention.

[0017] Refer to Fig. 1A, a heat pump system according to a first embodiment of present invention can be used for heating building interiors. The heat pump system includes a refrigerant circuit R and a heat storage circuit. The refrigerant circuit R typically includes a compressor 10, a first heat exchanger 20 operating as a condenser, a throttling device 30, and a second heat exchanger 40 operating as an evaporator. The compressor 10 generally uses electrical power to compress a refrigerant from a low pressure gas state to a high pressure gas state thereby increasing the temperature, enthalpy and pressure of the refrigerant. The first heat exchanger 20 is placed in indoor space and it can be a plate-type heat exchanger. The refrigerant leaving from the compressor 10 flows through the first heat exchanger 20 for being condensed at a substantially constant pressure to a saturated liquid state. In this process, a heat transfer medium, such as water is driven by a second pump 13 to pass through the first heat exchanger 20 to obtain heat from the refrigerant flow, and then flows through a space heating/cooling circuit 60 via lines 91, 92 to dissipate heat energy into building interiors. The space heating/cooling circuit 60 can be placed within a building (now shown) and allows hot or cold water acting as the heat transfer medium to pass therethrough for heating or cooling the building interiors.

[0018] The throttling device 30 can take form of an electronic expansion valve for being used to control the amount of the refrigerant entering into the second heat exchanger 40. The liquid refrigerant from the first heat exchanger 20 flows through the electronic expansion valve 30, result in the pressure of the liquid is decreased. In the process, the refrigerant evaporates partially causing the refrigerant to change to a mixed liquid-gas state, reducing its temperature down to a value that makes possible heat exchanges in the second heat exchanger 40. The second heat exchanger 40 is placed at an outdoor location, and it can be a coil type heat exchanger where the heat energy available in a heat transfer medium, like air flow is transferred to the refrigerant flow that evaporates inside from liquid to gas. The gas refrigerant discharged from the second heat exchanger 40 is sucked into the compressor 10 and repeats the refrigerant cycle for heating purpose.

[0019] It is well known that the refrigerant circuit R can further include a reversing valve (not shown), like a four-way valve for inversion of the refrigerant cycle for cooling purpose. In a normal cooling mode, the first heat exchanger 20 operates as the evaporator, and the second heat exchanger 40 operates as the condenser. In the first heat exchanger 20 (evaporator), the heat transfer medium, like water dissipates heat to the refrigerant for vaporizing the refrigerant, and the water becoming cold passes through the space heating/cooling circuit 60 for cooling the building interiors.

[0020] As shown in Fig. 1A, the heat storage circuit includes a compressor driver 11, a heat storage means 50, a first three-way valve 71, and a first pump 12. These components are serially connected via conduits or piping lines. The compressor driver 11 is electrically connected with the compressor 10 to convert the power with the normal shape of the mains supply into a waveform that is suitable for powering a motor of the compressor to achieve a required speed set-point. The compressor driver 11 generally includes a casing, and a lot of electronic components and specific circuits contained in the casing, such as MCU, IGBT(Insulated Gate Bipolar Transistor) modules, EMC filters, and PFC (Power Factor Correction) circuits. These electronic parts generate heat during the driver operation, and in order to avoid thermal overload, the driver can be equipped with a heat sink, like fins attached to the casing to dissipate heat with forced air flow.

[0021] The storage means 50 is used to store heat energy dissipated by the compressor driver 11, and it can be a normal water tank, or a tank with a phase change material. It is well known that a phase change material can be any material used for latent heat thermal storage, and it can be contained in a module to avoid mixing with water in the tank. The phase change material can store a lot of energy as latent heat so as to keep hot water within the tank for a longer time, also, it is able to transfer the stored heat energy to water when needed. It would be apparent to those skilled in the art that the heat storage means 50 can be connected with the compressor driver 11 via fluid pipes that can be made from appropriate metallic material, like aluminum, copper, or alloy containing aluminum or copper. Part of the fluid pipes encircles the casing of the compressor driver 11 or attached the heat sink so that the heat generated by the compressor driver 11 can be absorbed by a working medium flowing in the fluid pipes. The working medium is water in this embodiment. In an alternative embodiment, the working medium can also be in gaseous state. The working medium is driven to circulate in the heat storage circuit by operation of the first pump 12.

[0022] With reference to Fig. 1B, the heat storage circuit is connected to the first heat exchanger 20 via lines 94, 95. A second three-way valve 72 is disposed in the line 91, and the first and the second three-way valves 71, 72 are connected with the lines 94, 95 respectively. Refer back to Fig. 1A, when the system operates in the normal heating or cooling mode, the first and the second three-way valves 71, 72 are actuated to block lines 94, 95 respectively so that the working medium can only circulate in the heat storage circuit. The working medium absorbs heat when passing through the compressor driver 11 and stores heat energy in the heat storage means 50, then the working medium flows sequentially through the first three-way valve 71, a line 93, the first pump 12 and back to the compressor driver 11. Refer to Fig. 1B, when the system enters a defrost mode, the first and the second three-way valves 71, 72 are actuated to block the line 93 and allow the lines 94, 95 to be unobstructed. In this way, the heat energy stored in the heat storage means 50 is able to be extracted and released to the refrigerant as the working medium and the refrigerant pass through the first heat exchanger 20. Since the first heat exchanger 20 that is acting as an evaporator now can obtain needed heat only from the heat storage means 50 rather than interior atmosphere, thus, the extraction of heat from interior atmosphere can be avoided, which can improve thermal comfort of building interiors during the defrost mode.

[0023] In some circumstance, when the stored heat energy is not enough to melt all of ice formed on the coil of the outdoor heat exchanger (the second heat exchanger 40), the defrost cycle has to be completed with heat energy extracted from indoor space after all of stored heat energy is used up. With reference to Fig. 1C, at the beginning of the defrost mode, the first and the second three-way valves 71, 72 are actuated to allow heat energy stored in the heat storage means 50 to be transferred to the refrigerant at the first heat exchanger 20 for purpose of evaporation, just as shown in Fig. 1B. When a temperature of the working medium decreases to a lower limit value, which means the stored heat energy is used up, however, meanwhile a temperature of the outdoor heat exchanger coil does not reach a predetermined value that indicates all of ice is defrosted, at this moment, the first and the second three-way valves 71, 72 are actuated to block the lines 94, 95, and the second pump 13 is activated to circulate water in the space heating/cooling circuit to extract heat from interior atmosphere to the refrigerant as the refrigerant passes through the first heat exchanger 20. In this circumstance, although the extraction of heat from interior atmosphere could not be avoided, since the amount of heat energy extracted from interior atmosphere is much smaller than that needed in a traditional defrost mode, the temperature of interior atmosphere would not be decreased significantly, thus the interior thermal comfort can be assured.

[0024] Fig. 2A shows a second embodiment of the heat pump system. Compared with the first embodiment, the main difference is that an additional heat exchanger 80 is connected in the refrigerant circuit R. This additional heat exchanger 80 is placed next to the first heat exchanger 20. The heat storage circuit is connected to the additional heat exchanger 80 via lines 96, 97, and only the first three-way valve 71 is needed to switch the connection of the heat storage means 50 between the normal heating/cooling mode and the defrost mode. As shown in Fig. 2A, in the normal heating/cooling mode, the first switch 71 is actuated to block the lines 96, 97, and the working medium is circulated in the heat storage circuit to transfer heat dissipated by the compressor driver 11 to the heat storage means 50.

[0025] Refer to Fig. 2B, when the system enters the defrost mode, the first switch 71 is actuated to block the line 93 and allow the lines 96, 97 to be unobstructed, so that the heat energy stored in the heat storage means 50 can be extracted and transferred to the refrigerant passing through the additional heat exchanger. It is apparent that the additional heat exchanger 80 operates as an evaporator in the defrost mode, and the first heat exchanger 20 is disabled during this period. In this way, the extraction of heat from interior atmosphere can be avoided, which can improve thermal comfort of building interiors during the defrost mode. Refer to Fig. 2C, when the stored heat energy is not enough to melt all of ice formed on the coil of the outdoor heat exchanger, the first heat exchanger 20 can be enabled as a supplement. In this case, at the beginning of defrost mode, the additional heat exchanger 80 is energized as an evaporator and the first heat exchanger 20 is disabled. When the temperature of the working medium decreases to a lower limit value while the temperature of the second heat exchanger 40 does not reach the predetermined value, the additional heat exchanger 80 is disabled by switching the first three-way valve 71, and the first heat exchanger 20 is enabled by activation of the second pump 13. By this means, only smaller amount of heat energy is extracted from the interior atmosphere, thus the interior thermal comfort can be assured.

[0026] It is to be understood, however, that even though numerous, characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosed is illustrative only, and changes may be made in detail, especially in matters of number, shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broadest general meaning of the terms in which the appended claims are expressed.

Claims

1. A heat pump system comprising:

a refrigerant circuit (R) operable in a plurality of modes to transfer heat between an exterior atmosphere and an interior atmosphere via a refrigerant, comprising a compressor (10) for compressing the refrigerant, a first heat exchanger (20) for transferring heat between the refrigerant and the interior atmosphere, a throttling device (30) for lowering the pressure of the refrigerant, and a second heat exchanger (40) for transferring heat between the refrigerant and the exterior atmosphere; said first heat exchanger operating as a condenser to cool the refrigerant in a heating mode and operating as an evaporator to vaporize the refrigerant in a cooling mode; said second heat exchanger operating as an evaporator in the heating mode and operating as a condenser in the cooling mode;

a compressor driver (11) electrically connected with the compressor for powering the compressor, said compressor driver generating heat in operation; characterized in that

a heat storage means (50) for storing heat generated by the compressor driver is in heat transferable contract with the refrigerant in a defrost mode to transfer stored heat energy to the refrigerant.

2. A heat pump system according to claim 1, characterized in that said heat storage means obtains heat from the compressor driver via a flowing work medium in the heating mode and/or the cooling mode.

3. A heat pump system according to claim 2, characterized in that said heat storage means (50) is switched to be connected with the first heat exchanger (20) in the defrost mode, in order to release stored heat energy to the refrigerant as the working medium and the refrigerant pass through said first heat exchanger.

4. A heat pump system according to claim 3, characterized in that said system further comprises a space heating/cooling circuit (60) connectable with the first heat exchanger (20) for heating or cooling the interior atmosphere, and said space heating/cooling circuit is disposed in parallel with the heat storage means.

5. A heat pump system according to claim 4, characterized in that, when a temperature of the working medium decreases to a lower limit value while a temperature of the second heat exchanger does not reach a predetermined value in the defrost mode, the space heating/cooling circuit (60) is activated to provide heat energy to the refrigerant passing through the first heat exchanger (20) instead of the heat storage means (50).

6. A heat pump system according to claim 2, characterized in that said system further comprises an additional heat exchanger (80) connected in the refrigerant circuit (R), and said heat storage means (50) is switched to be connected with the additional heat exchanger in the defrost mode for releasing stored heat energy to the refrigerant as the working medium and the refrigerant pass through said additional heat exchanger (80).

7. A heat pump system according to claim 6, characterized in that said additional heat exchanger (80) is placed next to the first heat exchanger (20) to transfer stored heat energy from the working medium to the refrigerant before or after the refrigerant passing through the first heat exchanger (20).

8. A heat pump system according to claim 6, characterized in that said system further comprises a space heating/cooling circuit (60) connected with the first heat exchanger (20) for heating or cooling the interior atmosphere; wherein, when a temperature of the working medium decreases to a lower limit value while a temperature of the second heat exchanger does not reach a predetermined value in the defrost mode, the space heating/cooling circuit (60) is activated to provide heat energy to the refrigerant passing through the first heat exchanger (20).

9. A heat pump system according to claim 1, characterized in that said heat storage means includes a tank with a phase change material.

10. A heat pump system according to claim 3 or 6, characterized in that the connection of said heat storage means is switched via a first three-way valve (71).

Drawing