REFRIGERATION CYCLE DEVICE AND HOT WATER-PRODUCING DEVICE PROVIDED THEREWITH

Abstract

 A refrigeration cycle apparatus includes: a refrigerant circuit 2 configured by annularly connecting, to one another through a refrigerant pipe, a compressor 21, a radiator 22, a supercooling heat exchanger 23, a main expansion valve 24 and an evaporator 25 in this order; a bypass passage 3 which is connected to the compressor 21 or to the refrigerant circuit 2; and a control device 4. Before a defrosting operation for removing frost formed on the evaporator 25 by heat of refrigerant is started, the control device 4 executes a heat accumulating operation for reducing a flow rate of refrigerant flowing through the bypass passage 3, thereby increasing a heat accumulation amount. Therefore, also when frost is formed on the evaporator 25, it is possible to effectively utilize the bypass passage 3, the defrosting operation is efficiently carried out, and it is possible to enhance energy saving performance and comfort.

Description

[TECHNICAL FIELD]

[0001] The present invention relates to a refrigeration cycle apparatus for supercooling refrigerant, and to a hot water generator having the refrigeration cycle apparatus.

[BACKGROUND TECHNIQUE]

[0002] According to conventional refrigeration cycle apparatus and hot water generator of this kind, a supercooling heat exchanger is provided in a refrigerant circuit on the downstream side from the radiator, a portion of main stream refrigerant is expanded and is made to flow into the supercooling heat exchanger, and the main stream refrigerant which flows out from the radiator is supercooled. According to this, an enthalpy difference at an evaporator is increased and a portion of the main stream refrigerant is made to bypass. According to this, it is possible to reduce a pressure loss in the evaporator and a suction side pipe of a compressor. Therefore, it is possible to enhance heating/cooling ability and coefficient of performance of a system (see patent document 1 for example).

[0003] Fig. 5 shows a conventional refrigeration cycle apparatus described in patent document 1.

[0004] As shown in Fig. 5, the refrigeration cycle apparatus 100 includes a refrigerant circuit 110 through which refrigerant circulates and a bypass passage 120. The refrigerant circuit 110 is configured by annularly connecting, to one another through a pipe, a compressor 111, a radiator 112, a supercooling heat exchanger 113, a main expansion valve 114 and an evaporator 115.

[0005] The bypass passage 120 branches off from the refrigerant circuit 110 between the supercooling heat exchanger 113 and the main expansion valve 114, and is connected to the refrigerant circuit 110 between the evaporator 115 and the compressor 111 through the supercooling heat exchanger 113. The bypass passage 120 is provided with a bypass expansion valve 121 on the upstream side from the supercooling heat exchanger 113.

[0006] The refrigeration cycle apparatus 100 includes a temperature sensor 141 for detecting temperature (compressor discharge pipe temperature) Td of refrigerant discharged from the compressor 111, a temperature sensor 142 for detecting temperature (evaporator inlet temperature) Te of refrigerant flowing into the evaporator 115, a temperature sensor 143 for detecting temperature (bypass-side inlet temperature) Tbi of refrigerant flowing into the supercooling heat exchanger 113 in the bypass passage 120, and a temperature sensor 144 for detecting temperature (bypass-side outlet temperature) Tbo of refrigerant flowing out from the supercooling heat exchanger 113 in the bypass passage 120.

[0007] When a normal heating/cooling operation is carried out, target temperature Td (target) of a discharge pipe of the compressor is set from an evaporator inlet temperature Te detected by the temperature sensor 142. The main expansion valve 114 is controlled such that the discharge pipe temperature Td detected by the temperature sensor 141 becomes equal to the target temperature Td (target), and the bypass expansion valve 121 is controlled such that a difference (Tbo-Tbi) between the bypass-side outlet temperature Tbo and the bypass-side inlet temperature Tbi at the supercooling heat exchanger 113 becomes equal to a predetermined target value.

[PRIOR ART DOCUMENT]

[PATENT DOCUMENT]

[0008] [Patent Document 1] Japanese Patent Application Laid-open No.H10-68553

[SUMMARY OF THE INVENTION]

[PROBLEM TO BE SOLVED BY THE INVENTION]

[0009] In the conventional refrigeration cycle apparatus, however, a bypass circuit is utilized only when the normal heating/cooling operation is carried out, and a utilizing method of the bypass circuit when the defrosting operation is carried out for melting frost attached to the evaporator is not disclosed.

[0010] The present invention has been accomplished in view of such circumstances, and it is an object of the invention to provide a refrigeration cycle apparatus capable efficiently carrying out the defrosting operation for a short time by effectively utilizing the bypass circuit also when an evaporator is frosted.

[MEANS FOR SOLVING THE PROBLEM]

[0011] To solve the conventional problems, the present invention provides a refrigeration cycle apparatus comprising: a refrigerant circuit configured by annularly connecting, to one another through a refrigerant pipe, a compressor, a radiator, a supercooling heat exchanger, a main expansion apparatus and an evaporator in this order; a bypass passage which branches off from the refrigerant circuit between the radiator and the main expansion apparatus and which is connected to a compression chamber of the compressor or to the refrigerant circuit between the evaporator and the compressor through the supercooling heat exchanger; and a control device, wherein the control device executes a heating operation for heating a utilization heat medium in the radiator, and a defrosting operation for removing frost formed on the evaporator by heat of refrigerant, and the control device executes a heat accumulating operation for reducing a flow rate of refrigerant flowing through the bypass passage such that the flow rate becomes smaller than that when the heating operation is carried out before the defrosting operation is started.

[0012] According to this, since a bypass flow rate is reduced, enthalpy of refrigerant at the bypass outlet is increased, and suction enthalpy of the compressor is increased. Therefore, it is possible to raise discharge temperature of the compressor while reducing a pressure loss of the low pressure-side refrigerant pipe by introducing a portion of the refrigerant into the bypass passage. Hence, it is possible to increase the heat accumulation amount of a compressor body and a high pressure-side refrigerant circuit.

[EFFECT OF THE INVENTION]

[0013] According to the present invention, it is possible to provide a refrigeration cycle apparatus capable efficiently carrying out the defrosting operation for a short time by effectively utilizing the bypass circuit also when an evaporator is frosted.

[BRIEF DESCRIPTION OF THE DRAWINGS]

[0014] 

Fig. 1 is a schematic block diagram of a refrigeration cycle apparatus in an embodiment of the present invention;

Fig. 2 is a Mollier chart at the time of a heat accumulating operation of the refrigeration cycle apparatus;

Fig. 3 is a Mollier chart at the time of a defrosting operation of the refrigeration cycle apparatus;

Fig. 4 is a flowchart of operation control of the refrigeration cycle apparatus; and

Fig. 5 is a schematic block diagram of a conventional refrigeration cycle apparatus.

[EXPLANATION OF SYMBOLS]

[0015] 

1A

refrigeration cycle apparatus

2

refrigerant circuit

3

bypass passage

21

compressor

22

radiator

23

supercooling heat exchanger

24

main expansion valve (main expansion apparatus)

25

evaporator

31

bypass expansion valve (bypass expansion apparatus)

51

pressure sensor (saturation temperature detector)

61

first temperature sensor

62

second temperature sensor

63

third temperature sensor

[MODE FOR CARRYING OUT THE INVENTION]

[0016] A first aspect of the present invention provides a refrigeration cycle apparatus comprising: a refrigerant circuit configured by annularly connecting, to one another through a refrigerant pipe, a compressor, a radiator, a supercooling heat exchanger, a main expansion apparatus and an evaporator in this order; a bypass passage which branches off from the refrigerant circuit between the radiator and the main expansion apparatus and which is connected to a compression chamber of the compressor or to the refrigerant circuit between the evaporator and the compressor through the supercooling heat exchanger; and a control device, wherein the control device executes a heating operation for heating a utilization heat medium in the radiator, and a defrosting operation for removing frost formed on the evaporator by heat of refrigerant, and the control device executes a heat accumulating operation for reducing a flow rate of refrigerant flowing through the bypass passage such that the flow rate becomes smaller than that when the heating operation is carried out before the defrosting operation is started.

[0017] According to this, an amount of refrigerant flowing through the bypass passage is reduced for predetermined time before the defrosting operation, and enthalpy of refrigerant at the bypass passage outlet is increased. This increases suction enthalpy of the compressor, and discharge temperature of the compressor is raised.

[0018] That is, by making a portion of the refrigerant bypass, it is possible to raise the discharge temperature of the compressor in a state where a pressure loss reducing effect in the evaporator and the suction-side pipe of the compressor is secured. Especially in the case of a high pressure shell type compressor, more heat is given to a shell body and oil while high temperature refrigerant discharged from the compression chamber passes through the compressor body. Therefore, heat accumulation amount of the compressor body is increased.

[0019] Therefore, it is possible to increase heat quantity utilized at the time of the defrosting operation while restraining the operation efficiency from deteriorating before the defrosting operation. Therefore, defrosting time is shortened and energy saving performance is enhanced.

[0020] According to a second aspect of the invention, especially in the first aspect, the refrigeration cycle apparatus further includes a bypass expansion apparatus connected to the bypass passage located on an upstream side from the supercooling heat exchanger, and a first temperature sensor which detects temperature of discharged refrigerant of the compressor, the control device controls operation of the bypass expansion apparatus such that a detection value of the first temperature sensor when the heat accumulating operation is carried out becomes greater than that when the heating operation is carried out.

[0021] According to this, since the bypass expansion apparatus is controlled such that a flow rate of refrigerant flowing through the bypass passage is reduced, it is possible to raise the discharge temperature of the compressor.

[0022] Therefore, since control is reliably performed such that the discharge temperature of the compressor is raised, heat accumulation amount is reliably increased.

[0023] According to a third aspect of the invention, especially in the first aspect, the refrigeration cycle apparatus further includes a saturation temperature detector which detects saturation temperature of refrigerant in the bypass passage, and a second temperature sensor which detects temperature of refrigerant at an outlet of the bypass passage, when the heat accumulating operation is carried out, the control device controls operation of the bypass expansion apparatus such that a superheat degree of refrigerant at the outlet of the bypass passage which is determined based on a detection value of the saturation temperature detector and a detection value of the second temperature sensor becomes equal to a predetermined superheat degree.

[0024] According to this, refrigerant at the bypass passage outlet is brought into a desired superheated state (enthalpy), and it is possible to raise the discharge temperature of the compressor to desired temperature.

[0025] Therefore, discharge temperature of the compressor is raised in just proportion, and a heat accumulation state can always be formed appropriately.

[0026] According to a fourth aspect of the invention, especially in the third aspect, the refrigeration cycle apparatus further includes a third temperature sensor which detects temperature of refrigerant between the radiator and the supercooling heat exchanger, the predetermined superheat degree is determined based on the detection value of the saturation temperature detector and a detection value of the third temperature sensor.

[0027] According to this, since it is possible to grasp a temperature difference between high temperature-side refrigerant and low temperature-side refrigerant in the supercooling heat exchanger, it is possible to grasp an appropriate value of superheat degree of refrigerant at the bypass passage outlet which differs depending upon operation conditions.

[0028] Therefore, it is possible to always form the optimal heat accumulation state under various operating conditions.

[0029] According to a fifth aspect of the invention, especially in any one of the second to fourth aspects, when the defrosting operation is carried out, the control device controls operation of the bypass expansion apparatus such that refrigerant sucked into the compressor is brought into a wet state.

[0030] According to this, sucked refrigerant is brought into a two-phase state, and heat quantity accumulated in the compressor body can be absorbed utilizing latent heat of the refrigerant.

[0031] Therefore, at the time of defrosting operation, heat quantity accumulated in the compressor body can efficiently be absorbed by refrigerant.

[0032] A sixth aspect of the invention provides a hot water generator including the refrigeration cycle apparatus according to any one of the first to fifth aspects, the utilization heat medium is water or antifreeze liquid, and the utilization heat medium heated by the radiator is used for hot water supply or space heating.

[0033] According to this, it is unnecessary that a kind of the radiator is limited to a refrigerant-water heat exchanger or a refrigerant-antifreeze liquid heat exchanger.

[0034] Therefore, heat medium heated by the radiator can widely be used for a heater (fan forced heater, radiator, floor heating panel) and a water heater, and the same effects as those of the first to fifth aspects can be obtained.

[0035] An embodiment of the present invention will be described below with reference to the drawings. The invention is not limited to the embodiment.

(First Embodiment)

[0036] Fig. 1 is a schematic block diagram of a refrigeration cycle apparatus and a hot water generator in an embodiment of the present invention. In Fig. 1, the refrigeration cycle apparatus 1A includes a refrigerant circuit 2 through which refrigerant circulates, a bypass passage 3 and a control device 4. As refrigerant, it is possible to use zeotropic refrigerant mixture such as R407C, pseudo azeotropic refrigerant mixture such as R410A and single refrigerant.

[0037] The refrigerant circuit 2 is configured by annularly connecting, to one another through a pipe, a compressor 21, a radiator 22, a supercooling heat exchanger 23, a main expansion valve (main expansion apparatus) 24 and an evaporator 25. In this embodiment, a sub-accumulator 26 and a main accumulator 27 which separate gas and liquid from each other are provided between the evaporator 25 and the compressor 21. The refrigerant circuit 2 is provided with a four-way valve 28 for switching between a normal operation and a defrosting operation.

[0038] In this embodiment, the refrigeration cycle apparatus 1A configures heating means of the hot water generator which utilizes hot water produced by the heating means for space heating or hot water supply, and the radiator 22 is a heat exchanger for exchanging heat between refrigerant and water to heat water.

[0039]  More specifically, a supply pipe 71 and a collecting pipe 72 are connected to the radiator 22, water is supplied to the radiator 22 through the supply pipe 71, and water (hot water) heated by the radiator 22 is collected through the collecting pipe 72. Hot water collected by the collecting pipe 72 is sent to a heater such as a radiator directly or through a hot water tank and according to this, space heating or hot water supply is carried out.

[0040] In this embodiment, the bypass passage 3 branches off from the refrigerant circuit 2 between the supercooling heat exchanger 23 and the main expansion valve 24. The bypass passage 3 is connected to the refrigerant circuit 2 between the sub-accumulator 26 and the main accumulator 27 between the evaporator 25 and the compressor 21 through the supercooling heat exchanger 23. A bypass expansion valve (bypass expansion apparatus) 31 is provided in the bypass passage 3 located on the upstream side from the supercooling heat exchanger 23.

[0041] In Fig. 1, a flowing direction of refrigerant when a normal heating operation is carried out is shown by solid line arrows. Variation in a state of refrigerant in a heating operation will be described below.

[0042] High pressure refrigerant discharged from the compressor 21 flows into the radiator 22 through the four-way valve 28, and dissipates heat to utilization heating medium such as water and antifreeze liquid which pass through the radiator 22. High pressure refrigerant which flows out from the radiator 22 flows into the supercooling heat exchanger 23. The high pressure refrigerant which flows into the supercooling heat exchanger 23 is supercooled by low pressure refrigerant which is decompressed by the bypass expansion valve 31. The high pressure refrigerant which flows out from the supercooling heat exchanger 23 is distributed to the refrigerant circuit 2 and the bypass passage 3.

[0043] High pressure refrigerant flowing through the refrigerant circuit 2 is decompressed and expanded by the main expansion valve 24 and then, the refrigerant flows into the evaporator 25. The low pressure refrigerant which flows into the evaporator 25 absorbs heat from air in the evaporator 25.

[0044] High pressure refrigerant which flows through the bypass passage 3 is decompressed and expanded by the bypass expansion valve 31 and then, the refrigerant flows into the supercooling heat exchanger 23. The low pressure refrigerant which flows into the supercooling heat exchanger 23 is heated by high pressure refrigerant which flows out from the radiator 22. Thereafter, the low pressure refrigerant which flows out from the supercooling heat exchanger 23 merges with the low pressure refrigerant which flows out from the evaporator 25, and the merged refrigerant is sucked into the compressor 21 again.

[0045] The refrigeration cycle apparatus 1A of this embodiment makes a portion of high pressure liquid refrigerant flow into the bypass passage 3 at the time of the heating operation, and the refrigeration cycle apparatus 1A makes the refrigerant bypass through the supercooling heat exchanger 23, thereby increasing an enthalpy difference at the evaporator 25. A pressure loss at a low pressure portion of the refrigerant circuit 2 is reduced by suppressing an amount of gas phase refrigerant which flows through a low pressure portion of the refrigerant circuit 2 and which has a small heat-absorbing effect, and heating ability or coefficient of performance is enhanced.

[0046] Here, if the heating operation is carried out, moisture in air freezes and frosts in the evaporator 25 which is brought into low temperature, heat transfer performance of the evaporator 25 is deteriorated and this deteriorates heating ability or coefficient of performance. In such a case, it is necessary to judge a frosting degree from outside temperature, driving time or temperature of the evaporator, and to carry out the defrosting operation for melting and defrosting the frost by heat of refrigerant.

[0047] As typical defrosting operations, there are a reverse cycle defrosting operation and a hot gas defrosting operation. In the reverse cycle defrosting operation, the four-way valve 28 is switched to reverse a circulation direction of refrigerant, high temperature and high pressure gas refrigerant discharged from the compressor 21 is introduced into the evaporator 25, and frost is melted by heat of condensation of the gas refrigerant. In the hot gas defrosting operation, the four-way valve 28 is not switched, and a bypass circuit which introduces high temperature and high pressure gas refrigerant discharged from the compressor 21 directly into the evaporator 25 is provided, thereby melting frost. In this embodiment, variation in a state of refrigerant will be described while taking the reverse cycle defrosting operation as an example.

[0048] Broken line arrows in Fig. 1 show a flowing direction of refrigerant when a general reverse cycle defrosting operation is carried out.

[0049] High pressure refrigerant discharged from the compressor 21 flows into the evaporator 25 through the four-way valve 28, dissipates heat to accumulated frost and melts the frost. Liquid refrigerant which flows out from the evaporator 25 passes through the main expansion valve 24, enters the radiator 22, absorbs heat in the radiator 22, and again returns to the compressor 21. In this cycle, heat used at the time of the defrosting operation compresses refrigerant in the compressor 21, the body of the compressor 21, a high pressure portion of the refrigerant circuit 2, a body of the radiator 22 and hot water dissipate heat to the heat used at the time of the defrosting operation, and the heat is absorbed by refrigerant.

[0050] To stably continue the heating operation, the defrosting operation is absolutely necessary. Heat of discharged refrigerant which is originally used for heating hot water is consumed for melting frost, heat is absorbed from hot water in the radiator 22, and the heat is utilized for defrosting. Hence, there are demerits that coefficient of performance is deteriorated, temperature of hot water is reduced and comfort of space heating is deteriorated.

[0051] To reduce these demerits and to enhance the energy saving performance and comfort, it is necessary to reduce a heat absorption amount from hot water and to shorten defrosting operation time.

[0052] Hence, in this embodiment, the heat accumulating operation is carried out for predetermined time. Although details of the heat accumulating operation is described later, in the heat accumulating operation, the control device 4 controls the bypass expansion valve 31 such that a superheat degree of refrigerant at the outlet of the bypass passage 3 becomes equal to a predetermined superheat degree before the refrigeration cycle apparatus 1A starts the defrosting operation, a flow rate of refrigerant of the bypass passage 3 is reduced, and temperature of discharged refrigerant of the compressor 21 is raised.

[0053] According to this, concerning the state of refrigerant at the outlet of the bypass passage 3, since enthalpy is increased from point a to point a' in Fig. 2, main stream refrigerant and suction refrigerant enthalpy of the compressor 21 after merging are also increased from point b to point b' in Fig. 2.

[0054] Hence, refrigerant whose enthalpy is increased is discharged from the compression chamber of the compressor 21 as shown by point c' in Fig. 2, heat is given to the body of the compressor 21, the high pressure portion of the refrigerant circuit 2 and the body of the radiator 22. Therefore, heat accumulation amounts thereof are increased. Especially when the compressor 21 is of a high pressure shell type, since refrigerant discharged from the compression chamber passes through the body of the compressor 21, heat is accumulated also in the shell body and oil.

[0055] For example, there are: a conventional method in which an opening degree of the main expansion valve 24 is reduced, evaporation temperature is lowered, a heat absorption amount in the evaporator 25 is increased, and a circulation amount of refrigerant of the refrigerant circuit 2 is reduced, thereby raising temperature of discharged refrigerant of the compressor 21; a conventional method in which the number of rotations of the compressor 21 is increased, thereby raising temperature of discharged refrigerant of the compressor 21; and a conventional heat accumulating method in which coefficient of performance in the heating operation is largely lowered. Unlike these methods, since a portion of refrigerant is made to bypass to reduce a pressure loss at the low pressure portion of the refrigerant circuit 2 also during the heat accumulating operation, the heat accumulating operation is carried out in a state where deterioration of coefficient of performance is suppressed, and a heat quantity utilized when the defrosting operation is carried out is increased.

[0056] In this embodiment, when the defrosting operation of the refrigeration cycle apparatus 1A is carried out, the control device 4 controls the bypass expansion valve 31 such that suction refrigerant of the compressor 21 is brought into a wet state.

[0057] According to this, when the defrosting operation is carried out, heat is released in the evaporator 25, a portion of liquefied refrigerant returns to the compressor 21 through the bypass passage 3, and a flow rate of refrigerant which flows into the radiator 22 is reduced. Therefore, during the defrosting operation, the state of refrigerant is varied from the refrigerant state where bypassing action shown by a dotted line in Fig. 3 is not carried out to the refrigerant state shown by a solid line in Fig. 3. That is, a heat absorption amount from hot water in the radiator 22 is reduced, and a heat absorption amount from a body suction portion of the compressor 21 is increased by latent heat of gas/liquid two-phase refrigerant which is sucked into the compressor 21. Further, enthalpy of refrigerant discharged from the compression chamber of the compressor 21 is lowered, and heat absorption amounts of the body of the compressor 21 in which heat is previously accumulated and high pressure portion of the refrigerant circuit 2 are increased.

[0058] Action of operation control will be described below. The refrigerant circuit 2 includes a first temperature sensor 61 which detects temperature (discharge temperature) Td of refrigerant discharged from the compressor 21, a third temperature sensor 63 which detects temperature (high temperature-side refrigerant temperature) Th of refrigerant flowing out from the radiator 22 and flowing into the supercooling heat exchanger 23, and a fourth temperature sensor 64 which detects temperature (evaporation temperature) Te of refrigerant flowing into the evaporator 25. The fourth temperature sensor 64 is provided between the main expansion valve 24 and the evaporator 25.

[0059] The bypass passage 3 includes a pressure sensor 51 provided between the bypass expansion valve 31 and the supercooling heat exchanger 23 for detecting pressure (bypass refrigerant pressure) Pb of refrigerant flowing through the bypass passage 3, and a second temperature sensor 62 which detects temperature (bypass outlet refrigerant temperature) Tb of refrigerant flowing out from the supercooling heat exchanger 23.

[0060] The control device 4 changes the number of rotations of the compressor 21, switches the four-way valve 28, and adjusts opening degrees of the main expansion valve 24 and the bypass expansion valve 31 based on detection values detected by the various sensors 51, 61, 62, 63 and 64.

[0061] In this embodiment, the control device 4 operates the bypass expansion valve 31 such that the bypass outlet refrigerant temperature Tb detected by the second temperature sensor 62 when a normal heating operation is carried out becomes equal to bypass refrigerant saturation temperature Ts which is calculated based on bypass refrigerant pressure Pb detected by the pressure sensor 51.

[0062] The control device 4 detects frost on the evaporator 25 based on operation time and evaporation temperature Te detected by the fourth temperature sensor 64. When the control device 4 determines that the defrosting operation is necessary, the control device 4 executes the heat accumulating operation. In the heat accumulating operation, a bypass outlet refrigerant superheat degree SHb obtained by a difference between bypass outlet refrigerant temperature Tb and bypass refrigerant saturation temperature Ts is determined based on a temperature difference between high temperature-side refrigerant temperature Th and bypass refrigerant saturation temperature Ts, and the opening degree of the bypass expansion valve 31 is adjusted such that a bypass outlet refrigerant superheat degree target value SHt which is larger than that when a normal heating operation is carried out is obtained. After the heat accumulating operation is executed for predetermined time, the defrosting operation is started.

[0063] In the defrosting operation, after the control device 4 switches the four-way valve 28, the control device 4 opens the main expansion valve 24 up to the maximum valve opening degree. The control device 4 adjusts the opening degree of the bypass expansion valve 31 such that the bypass outlet refrigerant superheat degree SHb becomes zero K.

[0064] Next, control of the control device 4 at the time of the heat accumulating operation and the defrosting operation will be described in detail with reference to a flowchart shown in Fig. 4.

[0065] First, the control device 4 is monitoring whether defrosting conditions are established based on evaporation temperature Te detected by the fourth temperature sensor 64 at the time of the normal heating operation and based on heating operation time after the last time defrosting operation is completed. If the defrosting conditions are established (step S1), the procedure is shifted to the heat accumulating operation. In the heat accumulating operation, the control device 4 detects bypass refrigerant pressure Pb by the pressure sensor 51, and detects high temperature-side refrigerant temperature Th by the third temperature sensor 63 (step S2).

[0066] Next, bypass refrigerant saturation temperature Ts under pressure of refrigerant flowing through the bypass passage 3 is calculated from the bypass refrigerant pressure Pb detected by the pressure sensor 51 (step S3). The bypass refrigerant saturation temperature Ts is calculated using a physical property equation of refrigerant.

[0067] Next, the control device 4 calculates a temperature difference ΔTr between high temperature-side refrigerant temperature Th and bypass refrigerant saturation temperature Ts (step S4), and a predetermined bypass outlet refrigerant superheat degree target value SHt is calculated and determined based on SHt=f(ΔTr) (step S5). The function f(ΔTr) is an equation obtained by experimentally obtaining a bypass outlet refrigerant superheat degree target value SHt at which a sufficient heat accumulation amount can be secured without abnormally raising discharge pipe temperature Td under a large number of operating conditions using a temperature difference ΔTr as a parameter.

[0068] Thereafter, the control device 4 detects the bypass outlet refrigerant temperature Tb by the second temperature sensor 62 (step S6), and calculates the bypass outlet refrigerant superheat degree SHb based on SHb=Tb-Ts (step S7). Then, the opening degree of the bypass expansion valve 31 is adjusted such that the bypass outlet refrigerant superheat degree SHb becomes equal to the bypass outlet refrigerant superheat degree target value SHt (step S8).

[0069] Then, the control device 4 monitors and determines whether the heat accumulating operation is executed for preset predetermined time (step S9). If the execution time of the heat accumulating operation is less than the predetermined time (NO in step S9), it is determined that the heat accumulation amount is insufficient, and the procedure returns to step S2 as it is. If the heat accumulating operation is executed for predetermined time or longer (YES in step S9), it is determined that heat is sufficiently accumulated, the heat accumulating operation is completed and the defrosting operation is started.

[0070] In the defrosting operation, the control device 4 switches the four-way valve 28 and opens the main expansion valve 24 up to the maximum valve opening degree (step S10). The opening degree of the bypass expansion valve 31 is adjusted such that the bypass outlet refrigerant superheat degree SHb becomes 0K (step S11).

[0071] During the defrosting operation, the control device 4 monitors and determines whether or not the defrosting operation-completion conditions are established based on evaporation temperature Te detected by the fourth temperature sensor 64 and defrosting operation time (step S12). If the defrosting operation-completion conditions are not established (NO in step S12), it is determined that frost is remaining and the procedure returns to step S2.

[0072] On the other hand, if the defrosting operation-completion conditions are established (YES in step S12), it is determined that frost is completely melted, and the defrosting operation is completed. The four-way valve 28 is again switched and the heating operation is started.

[0073] As described above, in this embodiment, the refrigerant circuit 2 includes the first temperature sensor 61 which detects temperature of refrigerant discharged from the compressor 21, the third temperature sensor 63 which detects temperature of refrigerant flowing into the supercooling heat exchanger 23, the fourth temperature sensor 64 which detects temperature of refrigerant flowing into the evaporator 25, the pressure sensor 51 which detects pressure of refrigerant flowing through the bypass passage 3, the second temperature sensor 62 which detects temperature of refrigerant flowing out from the supercooling heat exchanger 23, and the control device 4. The control device 4 controls the bypass expansion valve 31 such that a superheat degree of refrigerant at the outlet of the bypass passage 3 becomes equal to a predetermined superheat degree before the refrigeration cycle apparatus 1A starts the defrosting operation, and executes the heat accumulating operation for predetermined time for reducing a flow rate of refrigerant flowing through the bypass passage 3, and raising temperature of discharged refrigerant of the compressor 21.

[0074] According to this, it is possible to raise the discharge temperature in the compressor 21 in a state where a pressure loss reducing effect in the evaporator 25 and the suction-side pipe of the compressor 21 is secured by making a portion of refrigerant bypass, more heat is given to the shell body and oil while high temperature refrigerant discharged from the compression chamber passes through the body of the compressor 21 and therefore, the heat accumulation amount of the body of the compressor 21 is increased.

[0075] Therefore, since it is possible to increase the heat quantity utilized when the defrosting operation is carried out while restraining the operation efficiency from deteriorating before the defrosting operation, the defrosting operation time is shortened and energy saving performance is enhanced.

[0076] When the defrosting operation is carried out, the control device 4 controls the bypass expansion valve 31 such that the suction refrigerant of the compressor 21 is brought into the wet state. Therefore, the heat absorption amount from hot water is reduced, evaporation latent heat of two-phase refrigerant is utilized, it is possible to make refrigerant efficiently absorb heat accumulated in the body of the compressor before the defrosting operation, and the energy saving performance is further enhanced.

[0077] Although the pressure sensor 51 is provided in the bypass passage 3 on the upstream side from the supercooling heat exchanger 23 in Fig. 1, the pressure sensor 51 may be provided anywhere in the bypass passage 3 and the refrigerant circuit 2 only if the pressure sensor 51 is located between the bypass expansion valve 31 and the compressor 21.

[0078] Although the bypass refrigerant saturation temperature is calculated by the pressure sensor 51 in the embodiment, temperature in the bypass passage 3 at a location where low pressure two-phase refrigerant flows may be used as the bypass refrigerant saturation temperature.

[0079]  It is not absolutely necessary that the bypass passage 3 branches off from the refrigerant circuit 2 between the supercooling heat exchanger 23 and the main expansion valve 24, and the bypass passage 3 may branch off from the refrigerant circuit 2 between the radiator 22 and the supercooling heat exchanger 23.

[0080] It is not absolutely necessary that the connecting portion of the bypass passage 3 is the suction pipe of the compressor 21. In the case of a compressor having an injection mechanism, the connection portion of the bypass passage 3 may be connected to an injection port for example.

[0081] It is not absolutely necessary that the main expansion apparatus and the bypass expansion apparatus of the present invention are expansion valves, and they may be expansion machines which collect power from expanding refrigerant. In this case, the number of rotations of the expansion machine by varying a load by a power generator connected to the expansion machine for example.

[INDUSTRIAL APPLICABILITY]

[0082] The present invention is especially effective for a hot water generator which produces hot water by a refrigeration cycle apparatus and utilizes the hot water for space heating or hot water supply.

Claims

1. A refrigeration cycle apparatus comprising:

a refrigerant circuit configured by annularly connecting, to one another through a refrigerant pipe, a compressor, a radiator, a supercooling heat exchanger, a main expansion apparatus and an evaporator in this order;

a bypass passage which branches off from the refrigerant circuit between the radiator and the main expansion apparatus and which is connected to a compression chamber of the compressor or to the refrigerant circuit between the evaporator and the compressor through the supercooling heat exchanger; and

a control device, wherein

the control device executes a heating operation for heating a utilization heat medium in the radiator, and a defrosting operation for removing frost formed on the evaporator by heat of refrigerant, and

the control device executes a heat accumulating operation for reducing a flow rate of refrigerant flowing through the bypass passage such that the flow rate becomes smaller than that when the heating operation is carried out before the defrosting operation is started.

2. The refrigeration cycle apparatus according to claim 1, further comprising a bypass expansion apparatus connected to the bypass passage located on an upstream side from the supercooling heat exchanger, and a first temperature sensor which detects temperature of discharged refrigerant of the compressor, wherein
the control device controls operation of the bypass expansion apparatus such that a detection value of the first temperature sensor when the heat accumulating operation is carried out becomes greater than that when the heating operation is carried out.

3. The refrigeration cycle apparatus according to claim 1, further comprising a saturation temperature detector which detects saturation temperature of refrigerant in the bypass passage, and a second temperature sensor which detects temperature of refrigerant at an outlet of the bypass passage, wherein
when the heat accumulating operation is carried out, the control device controls operation of the bypass expansion apparatus such that a superheat degree of refrigerant at the outlet of the bypass passage which is determined based on a detection value of the saturation temperature detector and a detection value of the second temperature sensor becomes equal to a predetermined superheat degree.

4. The refrigeration cycle apparatus according to claim 3, further comprising a third temperature sensor which detects temperature of refrigerant between the radiator and the supercooling heat exchanger, wherein
the predetermined superheat degree is determined based on the detection value of the saturation temperature detector and a detection value of the third temperature sensor.

5. The refrigeration cycle apparatus according to any one of claims 2 to 4, wherein when the defrosting operation is carried out, the control device controls operation of the bypass expansion apparatus such that refrigerant sucked into the compressor is brought into a wet state.

6. A hot water generator including the refrigeration cycle apparatus according to any one of claims 1 to 5, wherein
the utilization heat medium is water or antifreeze liquid, and
the utilization heat medium heated by the radiator is used for hot water supply or space heating.

Drawing