Patent Publication Number: US-9885504-B2

Title: Heat pump with water heating

Description:
FIELD OF TECHNOLOGY 
     The embodiments disclosed herein relate generally to a heat pump system. More specifically, the embodiments described herein relate to a heat pump system that can heat up a liquid, such as water. 
     BACKGROUND 
     Heat pumps are reversible refrigeration systems capable of conditioning a space by heating or cooling the air within the space. Heat pumps can also be used for heating a liquid (e.g., water) for domestic or other purposes. 
     SUMMARY 
     The embodiments described herein relate to heat pump systems and methods for providing chilled/hot liquid such as for air-conditioning and/or such as for hot water used for example in residential applications. 
     The heat pump systems described herein can include a first heat exchanger, a second heat exchanger and a third heat exchanger (e.g., a hot-water heat exchanger). At least one expansion valve can be disposed at a downstream position of the hot-water heat exchanger and between the hot-water heat exchanger and the first and second heat exchangers. The at least one expansion valve can be fluidly connected to the first heat exchanger and/or the second heat exchanger and shared by the first, second and third heat exchangers. The terms “downstream” and “upstream” described herein refer to relative positions of components of a heat pump system through which refrigerant can flow in a refrigeration circle where a compressor is taken as the start point. 
     In one embodiment, compressed refrigerant from a compressor can be directed to two directions, one to a four-way valve and the other to a hot-water heat exchanger. Two valves can be utilized to control refrigerant flow to the two directions. 
     In some embodiments, the heat pump system includes an enhanced vapor injection (EVI) component. The EVI component can be disposed at a position downstream of the hot-water heat exchanger and upstream of the at least one expansion valve. 
     The heat pump systems described herein can provide six operation modes, including a cooling mode, a heating mode, a water-heating mode, a heat-recovery mode, a simultaneous heating and water heating mode, and a defrost mode. 
     The embodiments provided herein can work in an operation range, for example, a working temperature down to, for example, about −15° C., and increase a hot water outlet temperature to, for example, about 65° C., and make the heat pump system more energy-efficient and environmentally-friendly. 
     In one embodiment, a refrigeration circuit includes a compressor, a first heat exchanger, a second heat exchanger, a third heat exchanger, and at least one expansion valve being disposed at a downstream position of the third heat exchanger. The first, second and third heat exchangers share the at least one expansion valve that is disposed between the third heat exchanger and the first and second heat exchangers. 
     In another embodiment, a method for providing air-conditioning and/or hot water, is provided. Compressed refrigerant is directed to a hot-water heat exchanger for heating water. The refrigerant from the hot-water heat exchanger is directed to an expansion valve. The expansion valve is shared with a first heat exchanger and/or a second heat exchanger. The expansion valve is disposed between the hot-water heat exchanger and the first and second heat exchangers. The second heat exchanger is configured to provide air-conditioning. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Referring now to the drawings in which like reference numbers represent corresponding parts throughout. 
         FIG. 1  illustrates a schematic diagram of a heat pump system, according to one embodiment. 
         FIG. 2  illustrates a schematic diagram of a heat pump system, according to one embodiment. 
         FIG. 2 a    illustrates a schematic diagram of the heat pump system of  FIG. 2  in a cooling mode, according to one embodiment. 
         FIG. 2 b    illustrates a schematic diagram of the heat pump system of  FIG. 2  in a heating mode, according to one embodiment. 
         FIG. 2 c    illustrates a schematic diagram of the heat pump system of  FIG. 2  in a water-heating mode, according to one embodiment. 
         FIG. 2 d    illustrates a schematic diagram of the heat ump system of  FIG. 2  in a heat-recovery mode, according to one embodiment. 
         FIG. 2 e    illustrates a schematic diagram of the heat pump system of  FIG. 2  in a heating and water-heating mode, according to one embodiment. 
         FIG. 2 f    illustrates a schematic diagram of the heat pump system of  FIG. 2  in a defrost mode, according to one embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The embodiments described herein relate to heat pump systems and methods for providing chilled/hot liquid such as for air-conditioning and/or such as for hot water used for example in residential applications. The heat pump systems described herein can include a first heat exchanger, a second heat exchanger and a third heat exchanger e.g., a hot-water heat exchanger). At least one expansion valve can be disposed at a downstream position of the hot-water heat exchanger and between the hot-water heat exchanger and the first and second heat exchangers. The at least one expansion valve can be fluidly connected to the first heat exchanger and the second heat exchanger and shared by the first, second and third heat exchangers. 
     In one embodiment, compressed refrigerant from a compressor can be directed to two directions, one to a four-way valve and the other to a hot-water heat exchanger. Two valves can be utilized to control refrigerant flow to the two directions. 
     In some embodiments, the heat pump system includes an enhanced vapor injection (EVI) component. The EVI component can be disposed at a position downstream of the hot-water heat exchanger and upstream of the at least one expansion valve. 
     The heat pump systems described herein can provide six operation modes, including a cooling mode, a heating mode, a water-heating mode, a heat-recovery mode, a simultaneous heating and water heating mode, and a defrost mode. 
     References are made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration of the embodiments in which the methods and systems described herein may be practiced. The term “heat pump circuit” generally refers to, for example, a reversible vapor-compressing refrigeration circuit including a compressor, at least two heat exchangers, and at least one expansion valve. 
       FIG. 1  illustrates a schematic diagram of a heat pump system  100  including a heat pump circuit that includes a hot-water heat exchanger for supplying hot water, according to one embodiment. The heat pump system  100  includes a component  110 . The component  110  can integrate a refrigeration circuit including a compressor such as, for example, a compressor  1  shown in  FIG. 2 , an expansion valve such as, for example, an expansion valve  8  shown in  FIG. 2 , a hot-water heat exchanger such as, for example, a hot-water heat exchanger  14  shown in  FIG. 2 , a first heat exchanger such as a first heat exchanger  3  shown in  FIG. 2 , a second heat exchanger such as a second heat exchanger  10  shown in  FIG. 2 , and valves such as, for example valves  16  and  17  shown in  FIG. 2 , for controlling refrigerant flow. The heat pump system  100  further includes an outdoor heat exchanger  105  and indoor units  120   a - b  that are fluidly connected to the component  110 . In one embodiment, the outdoor heat exchanger  105  can be, for example, a geothermal heat exchanger. The outdoor heat exchanger  105  can use water as a heat exchange medium to conduct a heat exchange with a geothermal source. A geothermal heat exchanger and a geothermal source are well known. The indoor unit  120   a  can be, for example, an indoor heat exchanger for cooling indoor air. The indoor unit  120   b  can be, for example, an indoor heat exchanger for heating an indoor floor. 
     The heat pump system  100  further includes a hot-water tank  130  that is in fluid communication with the hot-water heat exchanger of the component  110 . It is to be understood that the hot-water heat exchanger can be integrated with the hot-water tank  130 . 
     The component  110  can supply chilled water to the indoor unit  120   a  for cooling indoor air, supply warm water to the indoor unit  120   a  for heating the indoor air, supply warm water to the indoor unit  120   b  for floor heating, and/or heat the water of the hot-water tank  130 . 
     In some embodiments, when the hot-water heat exchanger is in the component  110 , water can be circulated between the hot-water tank  130  and the component  110 . The hot-water heat exchanger can heat up the water to be circulated. When the hot-water heat exchanger is integrated with the hot-water tank  130 , the component  110  can supply refrigerant to the hot-water heat exchanger to heat up the water in the hot water tank  130 . The warm water can be supplied to a water-to-water heat exchanger of the hot-water tank  130 . 
     In some embodiments, when in a cooling mode, the component  110  can supply chilled air-conditioning water to the indoor unit  120   a  where the chilled air-conditioning water can take an amount of thermal energy away from the indoor air to cool down the indoor air and heat the air-conditioning water. The component  110  can take the amount of thermal energy away from the heated air-conditioning water through the first heat exchanger to cool down the air-conditioning water. The component  110  can bring that amount of thermal energy plus a component power input into a source water through the second heat exchanger to heat the source water. The heated source water can bring the thermal energy into the ground through the outdoor heat exchanger  105 . 
     In some embodiments, when in a heating mode, the component  110  can take an amount of thermal energy away from the source water through the second heat exchanger to cool the source water. The cool source water can take an amount of thermal energy away from the ground through the outdoor heat exchanger  105  to heat the source water. The component  110  can bring that amount of thermal energy plus a component power input into the air-conditioning water through the first heat exchanger to heat the air-conditioning water, then supply the heated air-conditioning water to the indoor unit  120   a  or  120   b  to heat the indoor air. 
     The heat pump system  100  can achieve cooling/heating of a space and heating of water at the same time via the hot-water heat exchanger. In one embodiment, the hot-water heat exchanger can be a unit through which tap water is pumped and heated by refrigerant passing therethrough. The heated tap water can be circulated out of and back to a domestic hot water heater. 
       FIG. 2  illustrates a heat pump system  200  that includes a heat pump circuit  210 . The heat pump circuit  210  includes a compressor  1  having an outlet  1   a , a first inlet  1   b , and a second inlet  1   c . Refrigerant from the outlet  1   a  can be directed to two directions, one to a four-way valve  2  and the other to a hot-water heat exchanger  14 , via valves  16 ,  17 , respectively. The valves  16  and  17  can be solenoid valves or other suitable valves for controlling refrigerant flow. The hot-water heat exchanger  14  includes an inlet  14   a  for receiving refrigerant from the compressor  1  and an outlet  14   b  for directing the refrigerant to a conjunction  2   j  of the heat pump circuit  210  via a valve  15 . 
     A four-way valve described herein such as the four-way valve  2 , includes four ports d, c, s and e for controlling refrigerant flows. The four-way valve can be set in a first state (e.g., powered-off) or a second state (e.g., powered-on). When the four-way valve is in the first state (e.g., powered-off), refrigerant flowing into the port d can flow out from the port c and refrigerant flowing into the port e can flow out from the port s. When the four-way valve is in the second state (e.g., powered-on), refrigerant flowing into the port d can flow out from the port e and refrigerant flowing into the port c can flow out from the port s. 
     The heat pump circuit  210  further includes a first heat exchanger  3 , and a second heat exchanger  10 , in addition to the hot-water heat exchanger  14  (third heat exchanger). The first heat exchanger  3  includes a first in/out port  3   a  fluidly connected to the port c of the four-way valve  2  and a second in/out port  3   b  fluidly connected to a conjunction  2   m  of the heat pump circuit  210 . The second heat exchanger  10  includes a first in/out port  10   a  fluidly connected to the port e of the four-way valve  2  and a second in/out port  10   b  fluidly connected to a conjunction  2   n  of the heat pump circuit  210 . Refrigerant from the conjunctions  2   m  and/or  2   n  can be directed to the conjunction  2   j  via the control of valves  4  and/or  12 . 
     The first in/out port  3   a  of the first heat exchanger  3  can be fluidly connected to the outlet  1   a  or the first inlet  1   b  of the compressor  1 , via the control of the four-way valve  2  and the valve  16 . The first in/out port  10   a  of the second heat exchanger  10  can be fluidly connected to the outlet  1   a  or the first inlet  1   b  of the compressor  1 , via the control of the four-way valve  2  and the valve  16 . Compressed refrigerant from the outlet  1   a  of the compressor  1  can flow into the first input port  3   a  or  10   a . The first inlet  1   b  of the compressor  1  can receive refrigerant from the first in/out port  3   a  or  10   a.    
     In one embodiment, the first heat exchanger  3  can be an outdoor heat exchanger through which outdoor air can be drawn in to form a heat exchange relationship with refrigerant passing through the first heat exchanger  3 . In another embodiment, the first heat exchanger  3  can be an intermediate heat exchanger through which refrigerant passing therethrough has a heat exchange with a liquid (e.g., water). The liquid circulates inside a geothermal heat exchanger such as the outdoor heat exchanger  105  shown in  FIG. 1  to exchange heat with the geothermal source. 
     In one embodiment, the second heat exchanger  10  can be an indoor heat exchanger through which indoor air can be blown in a heat exchange relationship with refrigerant passing through the second heat exchanger. In another embodiment, the second heat exchanger  10  can be an indoor heat exchanger through which liquid (e.g., water) can be circulated in a heat exchange relationship with refrigerant passing through the second heat exchanger. The cooled/heated liquid can be utilized to cool/heat indoor air. 
     It is to be understood that the first and second heat exchangers  3  and  10  can be any suitable heat exchanger as long as the refrigerant passing therethrough can conduct a heat exchange with another heat exchanging medium. 
     In one embodiment, the hot-water heat exchanger  14  can be a condenser that is a unit through which a liquid (e.g., water) is pumped in a heat exchange relationship with refrigerant passing through the hot-water heat exchanger  14 . The liquid pumped through the hot-water heat exchanger  14  can be water circulated out of and back to a domestic/residential hot water heater. That is, the hot-water heat exchanger  14  is configured to conduct a direct or indirect heat exchange between the refrigerant and the water. 
     In the embodiment shown in  FIG. 2 , the heat pump circuit  210  farther includes an EVI component  25 . The EVI component  25  is disposed at a downstream position of the third heat exchanger  14  and connected to the outlet  14   h  of the third heat exchanger  14  via a valve  15 . The valve  15  allows refrigerant to flow from the third heat exchanger  14  to the EVI component  25  and blocks refrigerant flow is the opposite direction. The EVI component  25  includes an economizer  7  and an expansion valve  18 . The EVI component  25  is configured to receive refrigerant from a condenser such as, for example, from the first heat exchanger  3 , the second heat exchanger  10 , and/or the hot-water heat exchanger  14 , and to cool the refrigerant flow therethrough. It is to be understood that in other embodiments, the EVI component  25  can be optional. 
     In one embodiment, a portion of refrigerant through the economizer  7  can be extracted from the economizer  7  and expanded through the expansion valve  18 . The expanded refrigerant is vaporized to cool down the refrigerant that flows through the economizer  7 . The refrigerant vapor is injected back into the second inlet  1   c  of the compressor  1 , in one embodiment, the expansion valve  18  can be capillary, thermal expansion valve, or an electronic expansion valve. 
     In the embodiment shown in  FIG. 2 , the heat pump circuit  210  further includes an expansion valve  8  that is fluidly connected to the EVI component  25 . In one embodiment, the expansion valve  8  can be an electronic expansion valve. The expansion valve  8  is disposed at a downstream location of the EVI component  25 . The expansion valve  8  has an inlet  8   a  for receiving refrigerant from the EVI component  25  and an outlet  8   b  for directing the refrigerant to a conjunction  2   k  of the heat pump circuit  210 . The refrigerant from the conjunction  2   k  can be directed to the conjunction  2   m  and/or the conjunction  2   n  via the control of valves  9  and/or  13 . 
     Via the valves  4  or  12 , refrigerant from the first heat exchanger  3  or the second heat exchanger  10  can be received by the inlet  8   a  of the expansion valve  8 . Via the valves  13  or  9 , refrigerant from outlet  8   b  of the expansion valve  8  can be directed to the first heat exchanger  3  or the second heat exchanger  10 . In the embodiment of  FIG. 2 , the valves  4 ,  12 ,  13  and  9  each are a one-way valve that allows refrigerant to flow in one direction and blocks refrigerant flow in an opposite direction. 
     The expansion valve  8  is fluidly connected to the first heat exchanger  3 , the second heat exchanger  10 , and/or the hot-water heat exchanger  14 , depending on the specific mode the heat pump circuit  210  works on, which will be described further below. 
     A dry filter  5  and a receiver  6  are connected in series for filtering refrigerant before the refrigerant enters the EVI component  25 . An accumulator  11  is connected to the port s of the four-way valve  2  and to the first inlet  1   b  of the compressor  1 . The function of an accumulator is known in the art. It is to be understood that the dry filter  5 , the receiver  6  and the accumulator  11  can be optional. It is to be understood that the extracted refrigerant from the EVI component  25  can be directed to the accumulator  11 . 
       FIGS. 2 a - f    illustrate the heat pump system  200  that works in six different modes, respectively.  FIGS. 2 a - f    differ in the position of selected valves and illustrate different refrigerant flow paths within the heat pump circuit  210  for different operation modes. In one embodiment, the heat pump system  200  can utilize a geothermal source as a heat sink/source. 
       FIG. 2 a    illustrates a schematic diagram of the heat pump system  200  in a cooling mode, according to one embodiment. In the cooling mode of operation, the heat pump circuit  210  achieves cooling of a space. The compressor  1  discharges compressed refrigerant via the outlet  1   a . The valve  16  is opened and the valve  17  is closed. The four-way valve  2  is in the first state (e.g., powered-off). The discharged refrigerant flows through the valve  16  and the ports d and c of the four-way valve  2 , and is directed to the first heat exchanger  3 . In one embodiment, the first heat exchanger  3  can be an outdoor exchanger where another heat exchanging medium can conduct a heat exchange with the refrigerant and absorb heat from the refrigerant for condensing the refrigerant. Condensed refrigerant flows out of the first heat exchanger  3 , through the valve  4 , the filter  5  and the receiver  6 , and is directed through the EVI component  25  to cool down. The refrigerant is then directed to the expansion valve  8 . The refrigerant from the expansion valve  8  then flows through the valve  9  and is directed into the second heat exchanger  10  that can act as an evaporator. In one embodiment, the second heat exchanger  10  can be an indoor heat exchanger where the refrigerant is vaporized by, for example, receiving heat from indoor air being blown through the second heat exchanger  10 . Thus the indoor air can be cooled to achieve cooling of the space. Refrigerant vapor out of the second heat exchanger  10  is directed through the ports e, s of the four-way valve  2 , through the accumulator  11 , and back to the compressor  1  via the first inlet  1   b . In the cooling mode the third heat exchanger  14  is idle. In some embodiments, the idle third heat exchanger  14  can be used to store liquid refrigerant. 
       FIG. 2 b    illustrates a schematic diagram of the heat pump system  200  in a heating mode, according to one embodiment. In the heating mode of operation, the heat pump circuit  210  achieves heating of a space. The compressor  1  discharges gaseous refrigerant via the outlet  1   a . The valve  16  is opened and the valve  17  is closed. The four-way valve  2  is in the second state (e.g., powered-on). The discharged refrigerant flows through the valve  16  and the ports d and e of the four-way valve  2  to the second heat exchanger  10  where indoor air can absorb heat from the refrigerant for heating the space. In one embodiment, the second heat exchanger  10  can be an indoor exchanger where indoor air is blown through the second heat exchanger  10  to condense the refrigerant passing therethrough. As a result the indoor air passing across the second heat exchanger  10  is heated. In another embodiment, the second heat exchanger  10  can be an indoor exchanger where liquid (e.g., cool water) is circulated therethrough to condense the refrigerant passing therethrough. The heated liquid is utilized to heat indoor air. It is to be understood that in other embodiments, the heated liquid can be used for other purposes. The condensed refrigerant flows out of the second heat exchanger  10 , flows through the valve  12 , the filter  5  and the receiver  6 , and is directed through the EVI component  25  to cool down. The refrigerant is then directed to the expansion valve  8 . The refrigerant then flows through the valve  13  and is directed into the first heat exchanger  3 . In one embodiment, the first heat exchanger  3  can be an outdoor exchanger where a geothermal source can act to absorb heat from the refrigerant gas flows through the first heat exchanger  3 . In one embodiment, the first heat exchanger  3  can be an outdoor heat exchanger where the refrigerant can be vaporized by receiving heat from the outdoor air being blown through the first heat exchanger  3 . Refrigerant vapor out of the first heat exchanger  3  is directed through the ports c, s of the four-way valve  2 , through the accumulator  11 , and back to the compressor  1  via the first inlet  1   b . In the heating mode the third heat exchanger  14  is idle. In some embodiments, the idle third heat exchanger  14  can be used to store liquid refrigerant. 
       FIG. 2 c    illustrates a schematic diagram of the heat pump system  200  in a water heating mode, according to one embodiment. In the water heating mode of operation, the heat pump circuit  210  achieves heating of a liquid. The compressor  1  discharges compressed refrigerant via the outlet  1   a . The valve  16  is closed and the valve  17  is open. The four-way valve  2  is in a second state (e.g., powered-on). The discharged refrigerant flows through the valve  17  to the third heat exchanger  14 . In one embodiment, the third heat exchanger  14  can be a hot-water heat exchanger where a liquid (e.g., water) is circulated through the third heat exchanger  14 . The circulated liquid condenses the refrigerant vapor passing therethrough and the liquid itself is heated to achieve heating of the liquid. The condensed refrigerant flows out of the third heat exchanger  14 , flows through the valve  15 , the filter  5  and the receiver  6 , and is directed through the EVI component  25  to cool down. The refrigerant is then directed to the expansion valve  8 . The refrigerant from the expansion valve  8  then flows through the valve  13  and is directed into the first heat exchanger  3  to be vaporized by the receipt of heat. In one embodiment, the first heat exchanger  3  can be an outdoor exchanger where a heat exchange medium can act to absorb heat from the refrigerant gas. Refrigerant vapor out of the first heat exchanger  3  is directed through the ports c, s of the four-way valve  2 , through the accumulator  11 , and back to the compressor  1  via the first inlet  1   b . In the water heating mode the second heat exchanger  10  is idle. In one embodiment, the second heat exchanger  10  can be an indoor heat exchanger located in an indoor space. During the water heating mode of operation, air in the indoor space can be unaffected as the second heat exchanger  10  can be idle. In some embodiments, the idle second heat exchanger  10  can be used to store liquid refrigerant. 
       FIG. 2 d    illustrates a schematic diagram of the heat pump system  200  in a heat-recovery mode, according to one embodiment. In the heat-recovery mode of operation, the heat pump circuit  210  achieves heating of a liquid and cooling of a space utilizing the liquid as a heat sink simultaneously. The compressor  1  discharges compressed refrigerant via the outlet  1   a . The valve  16  is closed and the valve  17  is opened. The four-way valve  2  is in the first state (e.g., powered-off). The discharged refrigerant flows through the valve  17  to the third heat exchanger  14 . In one embodiment, the third heat exchanger  14  is a hot-water heat exchanger where a liquid (e.g., water) is circulated through the third heat exchanger  14 . The circulated liquid condenses the refrigerant vapor passing therethrough and the liquid itself is heated to achieve heating of the liquid. The condensed refrigerant flows out of the third heat exchanger  14 , flows through the valve  15 , the filter  5  and the receiver  6 , and is directed through the EVI component  25  to cool down. The refrigerant is then directed to the expansion valve  8 . The refrigerant from the expansion valve  8  then flows through the valve  9  and is directed into the second heat exchanger  10 . In one embodiment, the second heat exchanger  10  can be an indoor heat exchanger where the refrigerant is vaporized by receiving heat from the indoor air being blown through the second heat exchanger  10 . The indoor air is cooled to achieve cooling of the space. Refrigerant vapor out of the second heat exchanger  10  is directed through the ports e, s of the four-way valve  2 , through the accumulator  11 , and back to the compressor  1  via the first inlet  1   b . In the heat-recovery mode the first heat exchanger  3  is idle. In some embodiments, the idle first heat exchanger  3  can be used to store liquid refrigerant. 
       FIG. 2 e    illustrates a schematic diagram of the heat pump system  200  in the heating and water heating mode, according to one embodiment. In the heating and water heating mode of operation, the heat pump circuit  210  achieves heating of a space and heating of a liquid simultaneously, utilizing, for example, outdoor air as a heat source. The compressor  1  discharges compressed refrigerant via the outlet  1   a . The valves  16  and  17  are opened. The four-way valve  2  is in the second state (e.g., powered-on). The discharged refrigerant is divided into a first flow and a second flow passing through the valves  16  and  17 , respectively. 
     The first flow is directed through the ports d and e of the four-way valve  2  to the second heat exchanger  10  where indoor air can absorb heat from the refrigerant for heating the space. In one embodiment, the second heat exchanger  10  can be circulated with water for exchanging heat with refrigerant passing through the second heat exchanger  10 . The hot water is for air-conditioning an indoor space. In another embodiment, the second heat exchanger  10  can be an indoor exchanger where indoor air is blown through the second heat exchanger  10  to condense the refrigerant passing therethrough. As a result the indoor air passing across the heat exchanger is heated to achieve heating of the space. The condensed first flow of refrigerant flows out of the second heat exchanger  10 , and flows through the valve  12  and to the conjunction  2   j.    
     The second flow of refrigerant flows through the valve  17  to the third heat exchanger  14 . As shown in  FIG. 2 e   , the third heat exchanger  14  is a hot-water heat exchanger where a liquid (e.g., water) is circulated through the third heat exchanger  14 . The circulated liquid condenses the refrigerant vapor passing therethrough and the liquid itself is heated to achieve heating of the liquid. The condensed second flow of refrigerant flows out of the third heat exchanger  14 , and flows through the valve  15  and to the conjunction  2   j.    
     The first and second flows of refrigerant converge at the conjunction  2   j . The converged refrigerant flows through the filter  5  and the receiver  6 , and is directed through the EVI component  25  to cool down. The refrigerant is then directed to the expansion valve  8 . The refrigerant from the expansion valve  8  then flows through the valve  13  and is directed into the first heat exchanger  3  to be vaporized by the receipt of heat. In one embodiment, the first heat exchanger  3  is an outdoor heat exchanger where the refrigerant is vaporized by, for example, receiving heat from the outdoor air being blown through the first heat exchanger  3 . Refrigerant vapor out of the first heat exchanger  3  is directed through the ports c, s of the four-way valve  2 , through the accumulator  11 , and back to the compressor  1  via the first inlet  1   b.    
       FIG. 2 f    illustrates a schematic diagram of the heat pump system  200  in the defrost mode, according to one embodiment. In the defrost mode of operation, the heat pump circuit  210  achieves melting frost on the first heat exchanger  3 . The compressor  1  discharges compressed refrigerant via the outlet  1   a . The valve  16  is opened and the valve  17  is closed. The four-way valve  2  is in the first state (e.g., powered-off). The discharged refrigerant flows through the valve  16  and the ports d and c of the four-way valve  2 , and is directed to the first heat exchanger  3 . In one embodiment, the first heat exchanger  3  can be an outdoor exchanger that may have frost thereon. The refrigerant flowing through the outdoor exchanger can heat the outdoor exchanger and melt the frost thereon to achieve defrosting the first heat exchanger  3 . In some embodiments, the first heat exchanger can use another heat exchanging medium (e.g., outdoor air) to conduct a heat exchange with the refrigerant and absorb heat from the refrigerant for condensing the refrigerant. In some embodiments, the first heat exchanger  3  can stop drawing outdoor air so as to accelerate melting of the frost on the first heat exchanger  3  and the refrigerant can be condensed during defrosting the first heat exchanger  3 . Condensed refrigerant flows out of the first heat exchanger  3 , through the valve  4 , the filter  5  and the receiver  6 , and is directed through the EVI component  25  to cool down. The refrigerant is then directed to the expansion valve  8 . The refrigerant from the expansion valve  8  then flows through the valve  9  and is directed into the second heat exchanger  10  that can act as an evaporator. In one embodiment, the second heat exchanger  10  can be an indoor heat exchanger where the refrigerant is vaporized by, for example, receiving heat from indoor air being blown through the second heat exchanger  10 . Thus the indoor air can be cooled to achieve cooling of the space. Refrigerant vapor out of the second heat exchanger  10  is directed through the ports e, s of the four-way valve  2 , through the accumulator  11 , and back to the compressor  1  via the first inlet  1   b . In the defrost mode the third heat exchanger  14  is idle. In some embodiments, the idle third heat exchanger  14  can be used to store liquid refrigerant. 
     With regard to the foregoing description, it is to be understood that changes may be made in detail, especially in matters of the construction materials employed and the shape, size and arrangement of the parts without departing from the scope of the present invention. It is intended that the specification and depicted embodiment to be considered exemplary only, with a true scope and spirit of the invention being indicated by the broad meaning of the claims.