Water heating system

Abstract

To further improve efficiency in a feedwater heating system using both of a heat pump circuit and a heat exchanger for heat recovery.SOLUTION: A feedwater heating system 1 includes: a vapor compression-type heat pump circuit 10 in which a compressor 11, a condenser 12, an expansion valve 13 and an evaporator 14 are annularly connected by a refrigerant circulation line L9, and which takes out hot heat by the condenser 12 by driving the compressor 11; a heat recovery heat exchanger 40; a heat source fluid line L5 for circulating the heat source fluid successively to the heat recovery heat exchanger 40 and the evaporator 14; a water supply line L1 for circulating feedwater W1 successively to the heat recovery heat exchanger 40 and the condenser 12; refrigerant flow rate adjustment means controlled on the basis of a superheating degree of a gas refrigerant R flowing into the compressor 11, and adjusting a flow rate of the refrigerant; feedwater flow rate adjustment means controlled on the basis of a hot water tapping temperature of the feedwater W1 flowing out from the condenser 12 and adjusting a feedwater flow rate; and control means for controlling the refrigerant flow rate adjustment means and the feedwater flow rate adjustment means.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a water heating system. [Background technology]

[0002] In recent years, factories and other business establishments have been working to utilize unused heat discarded from various facilities in order to reduce emissions of carbon dioxide, a greenhouse gas.As such, as shown in Patent Documents 1 and 2, an unused heat utilization system (feedwater heating system) has been proposed that heats boiler feedwater using a heat pump circuit that uses waste hot water as a heat source, thereby reducing the amount of fuel used by the boiler. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2013-210118 A [Patent Document 2] JP 2014-169819 A Summary of the Invention [Problem to be solved by the invention]

[0004] The feedwater heating systems described in Patent Documents 1 and 2 can be applied not only to heating boiler feedwater but also to heating service water in various production processes. The system according to Patent Document 1 is configured to circulate a heat source fluid (waste hot water) through an evaporator and a heat recovery heat exchanger in that order, and to circulate feedwater (cold water) through a heat recovery heat exchanger, a subcooler, and a condenser in that order. With this configuration, the system according to Patent Document 1 has succeeded in significantly increasing the COP (coefficient of performance: energy consumption efficiency) compared to conventional heat pump systems without a heat recovery heat exchanger and a subcooler. On the other hand, this system has a problem in that the heat recovery heat exchanger becomes ineffective when the temperature of the heat source fluid becomes relatively low (for example, below 40°C). In contrast, the system disclosed in Patent Document 2 is configured to circulate the heat source fluid (waste hot water) through the heat recovery heat exchanger and then the evaporator. With this configuration, in the system disclosed in Patent Document 2, if the temperature of the heat source fluid is higher than the feed water, the effectiveness of the heat recovery heat exchanger can be maximized. Although the system disclosed in Patent Document 2 enables heat recovery with a high COP for heat source fluids over a wide temperature range, further efficiency improvements are desired for business establishments that have set high carbon dioxide emission reduction targets.

[0005] The present invention has been made in consideration of the above problems, and has an object to achieve even higher efficiency in a water heating system that uses a heat pump circuit and a heat recovery heat exchanger in combination. [Means for solving the problem]

[0006] The present invention provides a water supply heating system comprising: a vapor compression heat pump circuit in which a compressor, a condenser, an expansion valve, and an evaporator are connected in a ring shape by a refrigerant circulation line, and in which heat is extracted by the condenser by driving the compressor; a water supply line for circulating water to the condenser; a heat source fluid line for circulating a heat source fluid to the evaporator; a heat source temperature sensor for detecting the temperature of the heat source fluid before flowing into the evaporator; and a control means for feedback controlling a valve opening degree of the expansion valve so that the superheat degree of the refrigerant flowing into the compressor becomes a target superheat degree, wherein the control means starts up the system by setting the target superheat degree to an upper limit value, and after the system is started up, sets the target superheat degree within a range from the upper limit value to a lower limit value according to the temperature detected by the heat source temperature sensor, When the target degree of superheat is set to the range from the upper limit value to the lower limit value and the temperature detected by the heat source temperature sensor is judged to fluctuate greatly during operation, the target degree of superheat is set to the upper limit value, and when the target degree of superheat is set to the upper limit value and the temperature detected by the heat source temperature sensor is judged to be stable, the target degree of superheat is set to the range from the upper limit value to the lower limit value according to the temperature detected by the heat source temperature sensor; The target degree of superheat is set to be lower as the temperature detected by the heat source temperature sensor becomes lower, and the lower limit value is a value that can prevent liquid compression in the compressor.

[0007] Also, The present invention provides a water heating system comprising: a vapor compression heat pump circuit in which a compressor, a condenser, an expansion valve, and an evaporator are connected in a ring shape by a refrigerant circulation line, and in which heat is extracted by the condenser when the compressor is driven; a water supply line for circulating water to the condenser; a heat source fluid line for circulating a heat source fluid to the evaporator; a heat source temperature sensor for detecting the temperature of the heat source fluid before it flows into the evaporator; and a control means for feedback-controlling the valve opening of the expansion valve so that the degree of superheat of the refrigerant flowing into the compressor becomes a target degree of superheat, The control means The target degree of superheat is set to an upper limit value and the system is started. After the system is started, the target degree of superheat is set in a range from the upper limit value to the lower limit value according to the temperature detected by the heat source temperature sensor.When it is determined that the fluctuation of the temperature detected by the heat source temperature sensor is large during operation with the target degree of superheat set in the range from the upper limit value to the lower limit value, the target degree of superheat is set to the upper limit value, and when it is determined that the temperature detected by the heat source temperature sensor is stable during operation with the target degree of superheat set to the upper limit value, the target degree of superheat is set to the range from the upper limit value to the lower limit value according to the temperature detected by the heat source temperature sensor. Water heating system .

[0008] The control means is provided with a suction temperature sensor that detects the suction temperature of the gas refrigerant flowing into the compressor, and a vapor pressure sensor that detects the vapor pressure of the gas refrigerant flowing out from the evaporator, and the control means determines the evaporation temperature of the liquid refrigerant from the pressure detected by the vapor pressure sensor, and calculates the degree of superheat of the gas refrigerant by subtracting the evaporation temperature from the temperature detected by the suction temperature sensor. as the feedback value. , this The calculated superheat degree is set to the target superheat degree. The amount of operation of the expansion valve is calculated by a PID calculation algorithm. It is preferable to do so.

[0009] Also, The system further includes a heat recovery heat exchanger, the water supply line is configured to pass water through the heat recovery heat exchanger and the condenser in this order, the heat source fluid line is configured to pass heat source fluid through the heat recovery heat exchanger and the evaporator in this order, and the heat source temperature sensor is disposed in the heat source fluid line to detect the temperature of the heat source fluid flowing out of the heat recovery heat exchanger. It is preferable. Effect of the Invention

[0017] According to the present invention, it is possible to achieve even higher efficiency in a feedwater heating system that uses a heat pump circuit and a heat recovery heat exchanger in combination. [Brief description of the drawings]

[0018] [Figure 1] 1 is a diagram showing a schematic diagram of a water heating system according to one embodiment of the present invention; [Diagram 2] FIG. 2 is a block diagram showing a control unit of the embodiment. [Diagram 3] 4 is a graph showing fluctuations in temperature detected by a heat source temperature sensor. [Figure 4] FIG. 11 is a diagram showing a settable range of target outlet heated water temperature in the embodiment. [Diagram 5] FIG. 2 is a Mollier diagram for explaining a heat pump cycle. [Figure 6A] FIG. 11 is a state transition diagram of the water flow mode switching control in the embodiment. [Figure 6B] 5 is a flowchart showing a flow of a process for setting a target degree of superheat in the embodiment. [Figure 6C] 5 is a flowchart showing a flow of preheating mode switching control in the embodiment. [Figure 7] FIG. 10 is a diagram showing a schematic diagram of a supply water heating system according to a modified example of the above embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Hereinafter, a preferred embodiment of the supply water heating system 1 of the present invention will be described with reference to the drawings. Note that the term "line" in this specification is a general term for a line, such as a flow path, a pathway, or a pipe, through which a fluid can flow.

[0020] Fig. 1 is a diagram showing a schematic configuration of a water heating system 1 according to this embodiment. As shown in Fig. 1, the water heating system 1 is a system that supplies water W1 heated by a heat recovery heat exchanger 40 and a heat pump circuit 10 as hot water W2 to a hot water demand point.

[0021] More specifically, the water supply heating system 1 of this embodiment includes a make-up water tank 70 for storing make-up water W used as water supply W1, a heat recovery heat exchanger 40 and a heat pump circuit 10 for heating the water supply W1, a hot water tank 60 for storing the heated water supply W1 as hot water W2, and a heat source water tank 50 for storing heat source water W5 as a heat source fluid. In addition, the water supply heating system 1 of this embodiment is equipped with a water supply line L1 that circulates the water supply W1 through the heat recovery heat exchanger 40 and the condenser 12 of the heat pump circuit 10 in that order, a return line L2 that circulates the hot water W2 in the hot water tank 60 upstream of the heat recovery heat exchanger 40, a bypass line L3 that bypasses the water supply W1 from the heat recovery heat exchanger 40, a hot water supply line L4 for supplying the hot water W2 in the hot water tank 60 to a hot water demand point, and a heat source fluid line L5 that circulates the heat source water W5 as a heat source fluid through the heat recovery heat exchanger 40 and the evaporator 14 of the heat pump circuit 10.

[0022] The make-up water tank 70 is a tank that stores make-up water W that is used as the supply water W1 to be heated in the heat recovery heat exchanger 40 and the heat pump circuit 10, and is connected to a water supply line L1.

[0023] The heat recovery heat exchanger 40 is an indirect heat exchanger that performs indirect heat exchange between the feed water W1 flowing through the water supply line L1 and the heat source water W5 flowing through the heat source fluid line L5. More specifically, the heat recovery heat exchanger 40 performs heat exchange between the feed water W1 before passing through the condenser 12 of the heat pump circuit 10 and the heat source water W5 before passing through the evaporator 14 of the heat pump circuit 10. The feed water W1 in the feed water line L1 passes through the heat recovery heat exchanger 40 and the condenser 12 in this order, and the heat source water W5 in the heat source fluid line L5 passes through the heat recovery heat exchanger 40 and the evaporator 14 in this order.

[0024] The heat pump circuit 10 is a vapor compression type heat pump circuit in which a compressor 11, a condenser 12, an expansion valve 13, and an evaporator 14 are connected in a circular manner by a refrigerant circulation line L9, and heat is extracted by the condenser 12 when the compressor 11 is driven. A refrigerant R flows through this refrigerant circulation line L9. The compressor 11 has an electric motor 15 as a drive source, and compresses gaseous refrigerant R such as fluorocarbon gas to produce high-temperature, high-pressure refrigerant R. The condenser 12 condenses and liquefies the refrigerant R from the compressor 11 by dissipating heat to the feed water W1 sent through the water supply line L1. The expansion valve 13 passes the refrigerant R sent from the condenser 12, thereby reducing the pressure and temperature of the refrigerant R. The evaporator 14 absorbs heat from the heat source water W5 sent through the heat source fluid line L5, and evaporates the refrigerant R sent from the expansion valve 13. In this way, in the heat pump circuit 10, the refrigerant R absorbs heat from the outside and vaporizes in the evaporator 14, while the refrigerant R dissipates heat to the outside and condenses in the condenser 12. Using this principle, the heat pump circuit 10 pumps heat from the heat source water W5 in the evaporator 14, and heats the supply water W1 in the water supply line L1 in the condenser 12.

[0025] The refrigerant circulation line L9 of the heat pump circuit is provided with an inlet temperature sensor 17 that detects the inlet temperature of the gas refrigerant R flowing into the compressor 11, and a vapor pressure sensor 18 that detects the vapor pressure of the gas refrigerant R flowing out of the evaporator 14.

[0026] Here, the expansion valve 13 constitutes a refrigerant flow rate adjusting means for adjusting the flow rate of the refrigerant R flowing through the refrigerant circulation line L9 of the heat pump circuit 10. Specifically, the expansion valve 13 is configured as a proportional control needle valve, and the flow rate of the refrigerant R can be adjusted by changing the stroke of the needle valve through control of the rotation speed of a driving stepping motor and adjusting the valve opening.

[0027] The hot water tank 60 is a tank that stores the feed water W1 heated by the heat recovery heat exchanger 40 and the heat pump circuit 10 as hot water W2. The hot water W2 stored in the hot water tank 60 can be circulated and heated. Specifically, the hot water W2 in the hot water tank 60 can be merged with the water supply line L1 through the return line L2, and can be passed through the heat recovery heat exchanger 40 and the condenser 12 again through the water supply line L1 to be heated, and can be returned to the hot water tank 60. The hot water tank 60 is provided with a hot water temperature sensor 61 that detects the temperature of the hot water W2 in the hot water tank 60. The hot water tank 60 is also provided with a water level detector 62 that detects the water level in the hot water tank 60. In this embodiment, the water level detector 62 is configured with an electrode-type water level detector that includes a plurality of electrodes. Specifically, two electrodes 621 and 622 of different lengths are inserted and held with their lower ends at different height positions. In this embodiment, the electrodes 621 and 622 are inserted into the hot water tank 60 with the lower ends lowered in height position in order. Each of the electrodes 621 and 622 detects the presence or absence of the water level at its lower end depending on whether its lower end is immersed in water or not. In this embodiment, the control unit 100 performs switching control of the water flow mode, which will be described later, using the detection results of the hot water temperature sensor 61 and the water level detection unit 62. The contents of this control will be described in detail later.

[0028] The heat-source water tank 50 stores heat-source water W5 as a heat source fluid for the heat pump circuit 10. For example, waste hot water from a factory is used as the heat-source water W5. The heat-source water tank 50 is provided with an overflow line (not shown) that allows a predetermined amount of heat-source water to overflow. The heat-source water tank 50 is also provided with a water level detector (not shown) for monitoring whether the heat-source water has fallen below a predetermined low water level.

[0029] The upstream side of the water supply line L1 is connected to the make-up water tank 70, and the downstream side is connected to the hot water tank 60. In the water supply line L1, from the upstream side, a water supply pump 21, a first check valve 23, a first water supply temperature sensor 24, a three-way valve 25 arranged at a bypass line branching portion, a heat recovery heat exchanger 40, a second water supply temperature sensor 26, a condenser 12, and an outlet hot water temperature sensor 27 are arranged in this order.

[0030] The rotation speed of the water supply pump 21 can be controlled by an inverter. By changing the rotation speed of the water supply pump 21, the flow rate of water supply to the hot water tank 60 via the water supply line L1 can be adjusted in a one-time water passing mode described below. In other words, the water supply pump 21 constitutes a water supply flow rate adjustment means in the one-time water passing mode. The first check valve 23 is provided upstream of a junction with a return line L2, which will be described later, to prevent the hot water W2 from flowing into the make-up water tank 70 in a circulating water flow mode, which will be described later. The first feedwater temperature sensor 24 is a pre-heat exchanger feedwater temperature sensor that detects the temperature of the feedwater W1 before it flows into the heat recovery heat exchanger 40. The first feedwater temperature sensor 24 is provided upstream of the branching portion of the bypass line L3. The three-way valve 25 is disposed at a branching portion of the bypass line L3. The three-way valve 25 is a means for switching whether or not the feed water W1 is to be bypassed with respect to the heat recovery heat exchanger 40, and constitutes a preheating mode switching means. The bypass line L3 is a bypass line for bypassing the feed water W1 with respect to the heat recovery heat exchanger 40. The second feed water temperature sensor 26 is a feed water temperature sensor that detects the temperature of the feed water W1 before it flows into the condenser 12 of the heat pump circuit 10. The second feed water temperature sensor 26 is disposed upstream of the condenser 12, and in this embodiment, is disposed downstream of the heat recovery heat exchanger 40. The outlet hot water temperature sensor 27 detects the outlet hot water temperature of the heated supply water W1 flowing out from the condenser 12.

[0031] The return line L2 is connected at its upstream side to the hot water tank 60, and at its downstream side to the water supply line L1. In addition, in the return line L2, a return pump 31 (circulation pump 31) and a second check valve 33 are arranged in this order from the upstream side.

[0032] The rotation speed of the reflux pump 31 can be controlled by an inverter. By changing the rotation speed of the reflux pump 31, in the case of a circulating water flow mode described later, it is possible to adjust the flow rate of the supply water circulating to return to the hot water tank 60 via the reflux line L2 and the water supply line L1. In other words, the reflux pump 31 constitutes a supply water flow rate adjustment means in the circulating water flow mode. The second check valve 33 is provided in the return line L2 upstream of the junction of the water supply line L1 and the return line L2, thereby preventing the makeup water W from the makeup water tank 70 from flowing into the hot water tank 60 in a one-pass water mode described below.

[0033] By providing such a water supply line L1 and a reflux line L2, when the water supply pump 21 is operated with the reflux pump 31 stopped, the make-up water W from the make-up water tank 70 can be supplied as the supply water W1 to the hot water tank 60 while being heated by passing it through the heat recovery heat exchanger 40 and the condenser 12 in that order. This is called a one-time water passing mode. On the other hand, when the water supply pump 21 is stopped and the reflux pump 31 is operated, the hot water W2 in the hot water tank 60 can be returned as the supply water W1 to the hot water tank 60 while being reheated by passing it through the heat recovery heat exchanger 40 and the condenser 12 in that order, thereby circulating the water stored in the hot water tank 60. This is called a circulation water passing mode. When both the water supply pump 21 and the reflux pump 31 are stopped, the water passing through the heat recovery heat exchanger 40 and the condenser 12 can be stopped. This is called a water passing stop mode.

[0034] That is, in this embodiment, the water supply pump 21 and the return pump 31 constitute a water flow mode switching means that switches between a one-time water flow mode in which water is passed through the condenser 12 without circulating hot water W2 through the return line L2, a circulating water flow mode in which water is passed through the condenser 12 while circulating hot water W2 through the return line L2, and a water flow stop mode in which water flow to the condenser 12 is stopped.

[0035] The hot water W2 in the hot water tank 60 is then supplied to hot water demand points via a hot water supply line L4. The hot water supply line L4 is provided with a hot water supply pump 63. An example of a hot water demand location is the use of water supply for a steam boiler. However, the use of the hot water W2 is not limited to a steam boiler. For example, the hot water W2 produced by the water supply heating system 1 of this embodiment may be used for container washing for food, beverages, and medicines, pasteurizer sterilization (sterilization of bottles), etc. In this case, the supply of hot water W2 in a high temperature range of about 60°C to 80°C may be required. According to the water supply heating system 1 of this embodiment, in such an application that requires the supply of hot water always at a temperature within a predetermined temperature range, for example, in a system in which only heated water supply W1 is supplied into the hot water tank 60 (a system in which unheated make-up water is not directly supplied into the hot water tank 60), the hot water can be efficiently heated and supplied while maintaining its temperature.

[0036] In the heat source fluid line L5, a heat source supply pump 53, a first heat source temperature sensor 54, a heat recovery heat exchanger 40, a second heat source temperature sensor 55, and an evaporator 14 are arranged in this order from the upstream side. By operating the heat source supply pump 53, the heat source water W5 from the heat source water tank 50 can be circulated through the heat recovery heat exchanger 40 and the evaporator 14 in this order. The first heat source temperature sensor 54 is a pre-heat exchanger heat source temperature sensor that detects the temperature of the heat source water W5 before it flows into the heat recovery heat exchanger. In this embodiment, the first heat source temperature sensor 54 is provided in the heat source fluid line L5, but this sensor may be provided in the heat source water tank 50. The second heat source temperature sensor 55 is a heat source temperature sensor that detects the temperature of a heat source fluid that exchanges heat with the refrigerant R in the evaporator 14. In this embodiment, the second heat source temperature sensor 55 detects the temperature of the heat source water W5 before it flows into the evaporator 14. The second heat source temperature sensor 55 is disposed upstream of the evaporator 14, and in this embodiment, is disposed downstream of the heat recovery heat exchanger 40.

[0037] As described above, the heat source fluid line L5 has a connection configuration in which the heat source water W5 flows through the heat recovery heat exchanger 40 and the evaporator 14 in this order. In this way, by first flowing the heat source water W5 through the heat recovery heat exchanger 40, the amount of preheating of the feed water W1 can be increased, and the heat output of the heat recovery heat exchanger 40 can be increased. Note that the higher the temperature of the heat source water W5, the greater the effect of increasing the heat output.

[0038] In addition, as shown in Figure 1, the heat source fluid line L5 is configured so that the heat source water W5 and the feed water W1 are heat exchanged in a counterflow manner in the heat recovery heat exchanger 40, and then the heat source water W5 and the liquid refrigerant R are heat exchanged in a counterflow manner in the evaporator 14. In this way, by flowing the heat source water W5 through the heat recovery heat exchanger 40 and then the evaporator 14, and flowing it in a counterflow to the flow direction of the supply water W1 in each of the heat recovery heat exchanger 40 and the evaporator 14, the amount of heat recovery can be maximized.

[0039] Next, the control unit 100 of the feedwater heating system 1 of this embodiment will be described. Fig. 2 is a block diagram of the control unit 100 as a control means of the feedwater heating system 1 of this embodiment. The control unit 100 includes a target degree of superheat setting unit 111, a degree of superheat calculation unit 112, a refrigerant flow rate control unit 113, a target hot water outlet temperature settable range determination unit 121, a target hot water outlet temperature setting unit 122, a feedwater flow rate control unit 123, a water flow mode switching control unit 130, a preheat mode switching control unit 140, a signal input unit 150, and a memory unit 160.

[0040] The target superheat degree setting unit 111 acquires the temperature of the heat source water W5 as a heat source fluid detected by the second heat source temperature sensor 55 as a heat source temperature sensor, and sets the target superheat degree according to the temperature detected by the second heat source temperature sensor 55. For example, when the temperature of the heat source water W5 as a heat source fluid is low, the target superheat degree is set low. This increases the circulation flow rate of the refrigerant R, and the amount of heat recovered can be increased even for low-temperature heat source water W5. In this way, by setting an appropriate target degree of superheat according to the temperature of the heat source water W5 as the heat source fluid, it is possible to increase the amount of heat recovered in the evaporator 14 while preventing damage to the compressor 11 due to liquid compression or poor lubrication.

[0041] Furthermore, when it is determined that the fluctuation in the temperature detected by the second heat source temperature sensor 55 is large, the target superheat degree setting unit 111 may perform control to increase the target superheat degree. FIG. 3 is a graph showing the fluctuation of the detected temperature of the second heat source temperature sensor 55, with the vertical axis representing the detected temperature T of the second heat source temperature sensor 55 and the horizontal axis representing time t. For example, as shown in FIG. 3, when the change amount ΔT of the detected temperature T of the second heat source temperature sensor 55 per unit time t0 exceeds a predetermined threshold value ΔT0, it is determined that the fluctuation of the detected temperature of the second heat source temperature sensor 55 is large, and control is performed to increase the target degree of superheat. For example, when ΔT0=5°C, t0=1 min, and there is a fluctuation larger than 5°C / min, control is performed to increase the target degree of superheat. At this time, for example, if the target degree of superheat was set to 5°C up until then, the target degree of superheat is set to, for example, 10°C. In the example of FIG. 3, the decrease amount ΔT of the detected temperature T per unit time t0 is larger than the predetermined threshold value ΔT0. Therefore, since it is considered that the temperature of the heat source water W5 changes suddenly, the target degree of superheat is changed to, for example, 10°C.

[0042] As a result, even if a situation in which the temperature of the heat source water W5 serving as the heat source fluid changes suddenly is confirmed, the heat pump circuit 10 can be driven stably. For example, even in the case where the temperature of the heat source water W5 drops suddenly due to a sudden change in the temperature, the refrigerant R can be reliably vaporized in the evaporator 14 by setting the target superheat degree to a high value, thereby preventing damage to the compressor 11 due to liquid compression.

[0043] Furthermore, when it is determined that the temperature detected by the second heat source temperature sensor 55 is stable, the target superheat degree setting unit 111 may perform control to reduce the target superheat degree. For example, when the detected temperature T of the second heat source temperature sensor 55 is within a predetermined temperature range for a predetermined time, it is determined that the detected temperature of the second heat source temperature sensor 55 is stable. Also, when the change amount ΔT of the detected temperature T per unit time t0 is below a predetermined threshold ΔT0 for a predetermined time, it may be determined that the detected temperature of the second heat source temperature sensor 55 is stable. At this time, control is performed to reduce the target degree of superheat. For example, if the target degree of superheat was set to 10°C, the target degree of superheat is changed to, for example, 5°C.

[0044] In addition, by setting the lower limit of the target degree of superheat to, for example, 5° C., it is possible to prevent damage to the compressor 11 due to liquid compression. In addition, by setting the upper limit of the target degree of superheat to, for example, 10° C., it is possible to maintain the circulation flow rate of the refrigerant R at a predetermined flow rate or more and prevent a decrease in the amount of heat recovery.

[0045] In this way, when the temperature of the heat source water W5 as the heat source fluid is stable, the target superheat degree can be set to a low value to increase the circulation flow rate of the refrigerant R and increase the amount of heat recovered in the evaporator 14.

[0046] In this embodiment, the detection temperature of the second heat source temperature sensor 55 is used as the heat source temperature sensor to set the target degree of superheat, but the first heat source temperature sensor 54 may be used as the heat source temperature sensor that detects the temperature of the heat source water W5 before it flows into the evaporator 14 (heat source temperature before it flows into the evaporator). Although not immediately before it flows into the evaporator 14, the first heat source temperature sensor 54 can also indirectly detect the temperature of the heat source fluid that exchanges heat with the refrigerant R in the evaporator 14, and can confirm a situation in which the temperature of the heat source water W5 changes suddenly. However, it is more preferable to use the second heat source temperature sensor 55 to measure the temperature of the heat source water W5 immediately before it flows into the evaporator 14.

[0047] The superheat degree calculation unit 112 calculates the superheat degree of the refrigerant R flowing into the compressor 11. Specifically, the superheat degree calculation unit 112 obtains the evaporation temperature of the liquid refrigerant R from the pressure detected by the vapor pressure sensor 18, and calculates the degree of superheat of the gas refrigerant R by subtracting the evaporation temperature from the temperature detected by the suction temperature sensor 17.

[0048] The refrigerant flow rate control unit 113 controls the refrigerant flow rate control means and adjusts the flow rate of the refrigerant R so that the calculated degree of superheat (the value calculated by the superheat degree calculation unit 112) becomes the target degree of superheat (the value set by the target superheat degree setting unit 111). As a specific example of control, it is preferable to employ feedback control in which the calculated degree of superheat calculated in real time by the superheat degree calculation unit 112 is used as a feedback value, and the valve opening degree of the expansion valve 13 is adjusted so that the calculated degree of superheat converges to a target degree of superheat. In addition to proportional control (P control), the feedback control may employ a calculation algorithm for the manipulated variable that combines proportional control with integral control (I control) and / or differential control (D control).

[0049] In this way, the superheat degree calculation unit 112 accurately calculates the degree of superheat of the gas refrigerant R, and the refrigerant flow rate control unit 113 controls the degree of superheat to keep it constant, thereby stabilizing the heat output of the condenser 12 to the feed water W1. This reduces fluctuations in the flow rate of the feed water W1 that is heated and supplied as hot water.

[0050] The target hot water outlet temperature settable range determination unit 121 acquires the temperature of the supply water W1 before it flows into the condenser 12 detected by the second supply water temperature sensor 26 as a supply water temperature sensor, and determines the settable range of the target hot water outlet temperature according to the detected temperature of this second supply water temperature sensor 26.

[0051] Fig. 4 is a diagram showing the settable range of the target hot water outlet temperature, which is determined according to the temperature detected by second supply water temperature sensor 26. The horizontal axis of Fig. 4 is the temperature detected by second supply water temperature sensor 26 (supply water temperature before flowing into the condenser), and the vertical axis is the corresponding target hot water outlet temperature. In this embodiment, the settable range of the target hot water outlet temperature is the triangular area shown in settable range A. That is, in this embodiment, the target hot water outlet temperature can be set to a value between an upper limit value and a lower limit value, and the lower limit value is a value obtained by adding a predetermined value to the temperature detected by second feed water temperature sensor 26, and the higher the temperature detected by second feed water temperature sensor 26, the higher the value becomes. More specifically, the lower limit value is a value obtained by adding 15°C to the temperature detected by second feed water temperature sensor 26, and the upper limit value is a fixed temperature, 75°C in this embodiment.

[0052] The predetermined value (e.g., 15° C.) for setting the lower limit is stored in the storage unit 160 described below. In this case, it is preferable that this predetermined value can be set by external input or the like. Alternatively, the lower limit based on this predetermined value may be stored in the storage unit 160.

[0053] In this way, by setting the target hot water outlet temperature to the region shown in the settable range A, the system is controlled so that the temperature difference between the supply water W1 on the inlet and outlet sides of the condenser 12 is sufficiently large, thereby preventing insufficient supercooling of the refrigerant R flowing through the heat pump circuit 10 and suppressing excessive supply water flow rate of the supply water W1 in the control of the supply water flow rate adjustment means by the supply water flow rate control unit 123 described below.

[0054] Even if the settable range of the target outlet hot water temperature is a rectangular region with constant upper and lower limit values, i.e., even if the lower limit value is constant, if the settable range is a region such as that shown in settable range B in Fig. 4, it is possible to prevent insufficient supercooling of the refrigerant R and suppress an excessive water flow rate of the water supply W1. However, in this case, the allowable range of heat source water temperature and the settable range of the target outlet hot water temperature are narrowed.

[0055] Furthermore, if the target outlet temperature is set to a temperature lower than the lower limit value indicated in the settable range A, for example, if it is not significantly different from the temperature detected by the second supply water temperature sensor 26, there is a possibility that the refrigerant R will not be supercooled enough.

[0056] This will be explained using the Mollier diagram (ph diagram) shown in Figure 5. The vertical axis of this Mollier diagram is the pressure (p) of the refrigerant, and the horizontal axis is the specific enthalpy (h) of the refrigerant. The Mollier diagram also shows a saturated liquid line Y1 and a saturated vapor line Y2. Such a Mollier diagram can show the change in state of the refrigerant R during the heat pump cycle. The refrigerant R is in a supercooled liquid state (liquid refrigerant R state) to the left of the saturated liquid line Y1, a wet vapor state that is a gas-liquid mixture state between the saturated liquid line Y1 and the saturated vapor line Y2, and a superheated vapor state (gas refrigerant R state) to the right of the saturated vapor line Y2.

[0057] In FIG. 5, the solid lines indicated by R (a→b→c→d) indicate the transition of the state of the refrigerant R in a heat pump cycle in an appropriate state. The gas refrigerant R in a superheated vapor state drawn into the compressor 11 is adiabatically compressed in the compressor 11 to become a gas refrigerant R in a high-temperature and high-pressure superheated vapor state (a→b), then condensed and supercooled in the condenser 12 to become a liquid refrigerant R in a supercooled liquid state (b→c), and then adiabatically expanded in the expansion valve 13 to become the refrigerant R in a wet vapor state (c→d). The refrigerant R in the wet vapor state is then evaporated and heated in the evaporator 14 to become a gas refrigerant R in a superheated vapor state (d→a). The refrigerant R circulates in this cycle. The process (b→c) in FIG. 5 will be described in detail below. The condenser 12 releases latent heat and sensible heat of the gas refrigerant R to change the gas refrigerant R to a liquid refrigerant R and supercools the liquid refrigerant R.

[0058] Here, if the target hot water outlet temperature is set to a temperature lower than the lower limit value indicated in the settable range A, the temperature difference between the supply water W1 on the inlet side and the outlet side of the condenser 12 will be small, and the refrigerant R may not be sufficiently condensed or supercooled in the condenser 12 (b → c'). As a result, the position of "c'", which indicates the state of the refrigerant R after passing through the condenser 12, will shift to the right compared to the proper case. In other words, the refrigerant R in the "c'" state is insufficiently supercooled. It is also possible that the refrigerant R is not sufficiently in a liquid state. In this case, it cannot be said that the heat pump cycle is operating properly. However, in this embodiment, the lower limit is set to a value obtained by adding a predetermined value to the temperature detected by the second feedwater temperature sensor 26, so that the system is controlled so that the temperature difference between the feedwater W1 on the inlet side and the outlet side of the condenser 12 is at least greater than a predetermined value, and the above problem does not occur. In other words, the heat pump cycle can be operated in an appropriate state.

[0059] Target outlet hot water temperature setting unit 122 sets a target outlet hot water temperature within the above-mentioned settable range of the target outlet hot water temperature according to the temperature detected by second supply water temperature sensor 26. For example, any target outlet hot water temperature can be set within the above-mentioned settable range A based on the requirements of the hot water demand location, etc. That is, target outlet hot water temperature setting unit 122 acquires the temperature detected by second feed water temperature sensor 26, and can set the target outlet hot water temperature by adding a predetermined value to the acquired temperature detected by second feed water temperature sensor 26, with the lower limit being a higher value the higher the temperature detected by second feed water temperature sensor 26. This makes it possible to operate the heat pump cycle in an appropriate state, and also makes it possible to widen the setting range of the target outlet hot water temperature.

[0060] Alternatively, a value obtained by adding a predetermined value to the temperature detected by second supply water temperature sensor 26 may be automatically set as the target outlet hot water temperature.

[0061] The water supply flow rate control unit 123 controls the water supply flow rate adjustment means so that the temperature detected by the outlet water temperature sensor 27 becomes the target outlet water temperature (the value set by the target outlet water temperature setting unit 122), and adjusts the flow rate of the water supply W1. As a specific example of control, it is preferable to employ feedback control in which the outlet hot water temperature detected in real time by outlet hot water temperature sensor 27 is used as a feedback value, and the drive frequency of water supply pump 21 or reflux pump 31 is adjusted so that this outlet hot water temperature converges to a target outlet hot water temperature. In addition to proportional control (P control), the feedback control can employ a calculation algorithm for the manipulated variable that combines this with integral control (I control) and / or differential control (D control).

[0062] In the below-described one-pass water flow mode, the inverter-controllable feed water pump 21 constitutes the feed water flow rate adjustment means, and in the circulating water flow mode, the inverter-controllable reflux pump 31 constitutes the feed water flow rate adjustment means.

[0063] The water supply flow rate adjustment means may be configured in other ways. For example, when the water supply pump 21 and the return pump 31 are configured as pumps that can only be turned on and off, proportionally controllable flow rate adjustment valves may be provided downstream of each pump, and these may serve as the water supply flow rate adjustment means. Alternatively, a proportionally controllable flow rate adjustment valve may be provided downstream of the junction of the water supply line L1 and the return line L2, and this may serve as the water supply flow rate adjustment means. As an alternative to the supply water pump 21 and the return pump 31, an on-off valve may be provided in the supply water line L1 and the return water line L2, or a three-way valve may be provided at the junction of the supply water line L1 and the return water line L2, and an inverter-controlled pump may be provided downstream of the junction of the supply water line L1 and the return water line L2, and this may serve as a supply water flow rate adjustment means.

[0064] In this way, by setting an appropriate target outlet temperature according to the temperature of the feed water W1 before it flows into the condenser 12, it is possible to prevent insufficient supercooling in the condenser 12, excessive feed water flow rate, etc. Furthermore, by setting a lower limit of the range of target hot water outlet temperatures that can be set according to the temperature of the feed water W1 before it flows into the condenser 12, it is possible to reliably prevent insufficient supercooling in the condenser 12 and stabilize the amount of heat recovered in the evaporator 14. Also, by preventing the flow rate of the feed water W1 from becoming excessive, it is possible to suppress deterioration of the feed water pump 21 and the like due to overload.

[0065] In this embodiment, the temperature detected by second feed water temperature sensor 26 is used to set the target hot water outlet temperature, but first feed water temperature sensor 24 may be used as a feed water temperature sensor that indirectly detects the temperature of feed water W1 before it flows into condenser 12 (feed water temperature before flowing into condenser). However, in order to perform more stable control, it is preferable to use second feed water temperature sensor 26 to measure the temperature of feed water W1 immediately before it flows into condenser 12.

[0066] As described above, in the feed water heating system 1 of this embodiment, the heat source water W5 flows through the heat recovery heat exchanger 40 and the evaporator 14 in that order. The feed water heating system 1 of this embodiment includes a refrigerant flow rate adjustment means that is controlled based on the degree of superheat of the gas refrigerant R flowing into the compressor 11 and adjusts the refrigerant flow rate. The feed water heating system 1 of this embodiment also includes a feed water flow rate adjustment means that is controlled based on the outlet temperature of the feed water W1 flowing out of the condenser 12 and adjusts the feed water flow rate. The control unit 100 includes a refrigerant flow rate control unit 113 that controls the refrigerant flow rate adjustment means, and a feed water flow rate control unit 123 that controls the feed water flow rate adjustment means.

[0067] As a result, by first flowing the heat source water W5 through the heat recovery heat exchanger 40, the heat output of the heat recovery heat exchanger 40 is increased, and the preheat amount of the supply water W1 is increased. Note that the higher the heat source water temperature, the greater the effect of increasing the heat output. When the heat recovery amount of the heat recovery heat exchanger 40 is increased, the heat recovery amount of the heat pump circuit 10 can be relatively reduced. In other words, to obtain the same system heat output as when the heat source water W5 is flowed through the evaporator 14 and then the heat recovery heat exchanger 40, the compressor output can be reduced to reduce the power consumption of the heat pump circuit 10. At this time, by flowing the heat source water W5 through the heat recovery heat exchanger 40 first, the temperature of the heat source water W5 flowing into the evaporator 14 decreases; however, by adding further control, i.e., by combining the adjustment of the refrigerant flow rate based on the degree of superheat and the adjustment of the water supply flow rate based on the hot water outlet temperature, the COP of the system can be significantly increased in a configuration in which the heat source water W5 flows through the heat recovery heat exchanger 40 first, due to the multiple effects of, for example, increasing the heat input to the evaporator 14 by adjusting the refrigerant flow rate in accordance with a low superheat setting, and further increasing the heat output of the heat recovery heat exchanger 40 and the heat output of the evaporator 14 by adjusting the water supply flow rate in accordance with a low hot water outlet temperature setting.

[0068] The water flow mode switching control unit 130 performs water flow mode switching control to switch between a one-time water flow mode, a circulating water flow mode, and a water flow stop mode. More specifically, the water flow mode switching control unit 130 controls the water supply pump 21 and the reflux pump 31 as water flow mode switching means to perform control to switch between a one-time water flow mode in which water is passed through the condenser 12 without passing hot water W2 through the reflux line L2, a circulating water flow mode in which water is passed through the condenser 12 while passing hot water W2 through the reflux line L2, and a water flow stop mode in which water flow to the condenser 12 is stopped.

[0069] In the transient water flow mode, the drive of the return pump 31 is stopped, while the water supply pump 21 is driven, and the heat source supply pump 53 and the compressor 11 of the heat pump circuit 10 are driven. In the circulating water flow mode, the drive of the water supply pump 21 is stopped, while the return pump 31 is driven, and the heat source supply pump 53 and the compressor 11 of the heat pump circuit 10 are driven. In the water flow stop mode, the drive of the water supply pump 21 and the return pump 31 is stopped, and the drive of the compressor 11 of the heat pump circuit 10 is also stopped. It is also preferable to stop the drive of the heat source supply pump 53.

[0070] In this embodiment, the water supply pump 21 and the return pump 31 constitute the water flow mode switching means, but the water flow mode switching means may be constituted in other ways. For example, the water flow mode switching means may be constituted by a three-way valve provided at the junction of the water supply line L1 and the return line L2, and a water supply pump provided downstream of the junction of the water supply line L1 and the return line L2. In this case, the water flow mode is switched by switching the three-way valve and turning the water supply pump on and off.

[0071] In this way, by enabling operation in the circulating water flow mode in addition to the passing water flow mode, the hot water tank 60 can be circulated and heated as necessary to maintain the stored hot water temperature. In addition, in the circulating water flow mode, the return line L2 is used to allow the stored water in the hot water tank 60 to flow in front of the heat recovery heat exchanger 40, so that when the temperature of the heat source water W5 is higher than the temperature of the hot water W2 stored in the hot water tank 60, the hot water W2 flowing as the supply water W1 is heated not only by the condenser 12 but also by the heat recovery heat exchanger 40 before that. Thus, it is efficiently heated.

[0072] Here, the water flow mode switching control unit 130 controls the water supply to the hot water tank 60, and can also control the switching of the water flow mode based on the temperature of the hot water W2 in the hot water tank 60. Specifically, the water flow mode switching control unit 130 controls the water flow mode switching means to execute a one-time water flow mode when new water supply is performed to the confluence of the return line L2, controls the water flow mode switching means to execute a circulating water flow mode when new water supply to the confluence is stopped and the temperature detected by the hot water temperature sensor 61 is below a predetermined set temperature, and controls the water flow mode switching means to execute a water flow stop mode when new water supply to the confluence is stopped and the temperature detected by the hot water temperature sensor 61 is above a predetermined set temperature.

[0073] This water flow mode switching control will be described in detail with reference to the state transition diagram shown in FIG. 6A. During execution of each water flow mode, water flow mode switching control unit 130 monitors the water level of hot water W2 in hot water tank 60 using water level detection unit 62, and monitors the temperature of hot water W2 in hot water tank 60 using hot water temperature sensor 61. During execution of the water flow stop mode, if the water level exceeds the detection position of electrode rod 622 of water level detection unit 62 and the detected temperature of hot water temperature sensor 61 exceeds a first set temperature (for example, a temperature 2 to 3°C lower than the target hot water outlet temperature), water flow mode switching control unit 130 continues the water flow stop mode.

[0074] <Event E1> During the water flow stop mode, if the water level in the hot water tank 60 drops below the detection position of the electrode rod 622 of the water level detector 62, the water flow mode switching controller 130 drives the water supply pump 21 while keeping the return pump 31 stopped. Driving the water supply pump 21 causes new makeup water W to be supplied to the junction of the return line L2, so the water flow mode switching controller 130 drives the heat source supply pump 53 and the compressor 11 to transition to the one-time water flow mode. In the one-time water flow mode, hot water W2 adjusted to a predetermined target hot water outlet temperature is supplied to the hot water tank 60.

[0075] <Event E2> During execution of the transitory water flow mode, if the water level in the hot water tank 60 rises and exceeds the detection position of the electrode rod 621 of the water level detection unit 62, the water flow mode switching control unit 130 stops the water supply pump 21 while keeping the return pump 31 stopped. Since stopping the water supply pump 21 stops the supply of new makeup water W to the joining point of the return line L2, the water flow mode switching control unit 130 stops the heat source supply pump 53 and the compressor 11 and transitions to the water flow stop mode. In the water flow stop mode, the supply of hot water W2 to the hot water tank 60 is stopped.

[0076] <Event E3> During the water flow stop mode, if the temperature detected by the hot water temperature sensor 61 falls below the set temperature, the return pump 31 is driven while the water supply pump 21 remains stopped. Driving the return pump 31 causes the stored water to be circulated with the supply of new makeup water W to the confluence of the return line L2 stopped, so the water flow mode switching control unit 130 drives the heat source supply pump 53 and the compressor 11 to transition to the circulating water flow mode. In the circulating water flow mode, hot water W2 reheated to a predetermined target hot water outlet temperature is supplied to the hot water tank 60.

[0077] <Event E4> During the execution of the circulating water flow mode, if the temperature detected by the hot water temperature sensor 61 exceeds the set temperature, the water flow mode switching control unit 130 stops the reflux pump 31 while keeping the water supply pump 21 stopped. Then, the heat source supply pump 53 and the compressor 11 are stopped, and the mode transitions to the water flow stop mode. In the water flow stop mode, the circulation of the hot water W2 to the hot water tank 60 is stopped.

[0078] <Event E5> During the execution of the circulation water supply mode, when the water level in the hot water tank 60 drops and falls below the detection position of the electrode rod 622 of the water level detection unit 62, the water supply mode switching control unit 130 of The heat source supply pump 53 and the compressor 11 are stopped, and the water supply pump 21 is driven. By driving the water supply pump 21, new makeup water W is supplied to the joining point of the return line L2, so the water flow mode switching control unit 130 transitions to the one-time water flow mode while driving the heat source supply pump 53 and the compressor 11. In the one-time water flow mode, hot water W2 adjusted to a predetermined target hot water outlet temperature is supplied to the hot water tank 60. In this embodiment, the mode does not switch from the one-time water flow mode to the circulating water flow mode. The mode is switched to the one-time water flow mode when the demand for hot water is high, and this is because the supply of makeup water W to the hot water tank 60 is given priority and the water level is quickly restored. In addition, since the outlet hot water temperature in the one-time water flow mode is higher than the hot water temperature stored in the hot water tank 60, the stored hot water temperature can be raised in a short time.

[0079] The set temperature for determining whether to continue the stopped water flow mode and the set temperature for determining whether to transition from the stopped water flow mode to the circulating water flow mode may be the same or different. If they are different temperatures, the latter set temperature is set to a lower temperature than the former set temperature.

[0080] In addition, when controlling the switching of the water flow mode described above, the determination of whether new water supply using make-up water W or the like is being performed at the confluence point of the return line L2 may be made based on the driving state of the water supply pump 21 (driving command signal or driving feedback signal). In addition, a flow rate sensor (not shown) may be disposed on the water supply line L1 upstream of the junction with the return line L2, and the determination may be made based on the detection result of this flow rate sensor.

[0081] According to the mode switching control in accordance with the state transition diagram of Fig. 6A, when there is sufficient demand for hot water and it is necessary to supply makeup water W, the system can be operated in a one-time water flow mode in which the system COP is maximized. When the demand for hot water is small and it is not necessary to supply makeup water W, the temperature of the stored water in the hot water tank 60 can be increased in a circulating water flow mode when the temperature of the stored water in the hot water tank 60 drops. When the demand for hot water is small and it is not necessary to supply makeup water W, if there is substantially no drop in the temperature of the stored water in the hot water tank 60, the system can wait in a water flow stop mode.

[0082] With the above-described configuration, hot water W2 at or above the set temperature can be constantly ensured in the hot water tank 60. In addition, the circulating water mode is executed only when the temperature of the stored water in the hot water tank 60 drops, so there is no wasteful power consumption due to excessive water circulation.

[0083] The preheating mode switching control unit 140 performs preheating mode switching control to switch between a water supply preheating mode and a preheating stop mode. More specifically, the preheating mode switching control unit 140 controls the three-way valve 25 as a preheating mode switching means to perform control to switch between a water supply preheating mode in which the water supply W1 and the heat source water W5 are simultaneously circulated through the heat recovery heat exchanger 40, and a preheating stop mode in which the water supply W1 is circulated through the bypass line L3.

[0084] In this embodiment, the three-way valve 25 constitutes the preheating mode switching means, but the preheating mode switching means may be constituted in other ways. For example, two-way valves may be provided on the upstream side of the junction with the bypass line L3 in the water supply line L1 and on the bypass line L3, respectively, and these two-way valves may constitute the preheating mode switching means.

[0085] The bypass line is not limited to one that bypasses the supply water W1 from the heat recovery heat exchanger 40, but may be one that bypasses the heat source water W5 from the heat recovery heat exchanger 40. In this case, in the pre-heating stop mode, the heat source water W5 is caused to flow through the bypass line. In other words, the system may be configured to have one or two bypass lines that bypass the supply water W1 from the heat recovery heat exchanger 40 and / or bypass the heat source water W5 from the heat recovery heat exchanger 40, and the preheating mode switching means switches between a supply water preheating mode in which the supply water W1 and the heat source water W5 are circulated simultaneously through the heat recovery heat exchanger 40, and a preheating stop mode in which at least one of the supply water W1 and the heat source water W5 is circulated through the bypass line. This allows the heat recovery heat exchanger 40 to be selectively used depending on the situation.

[0086] Here, the preheating mode switching control unit 140 acquires a first detected temperature (supply water temperature before entering the heat exchanger) by the first supply water temperature sensor 24 (supply water temperature sensor 24 before entering the heat exchanger) which detects the temperature of the supply water W1 before it flows into the heat recovery heat exchanger 40, and a second detected temperature (heat source temperature before entering the heat exchanger) by the first heat source temperature sensor 54 (heat source temperature sensor 54 before entering the heat exchanger) which detects the temperature of the heat source water W5 before it flows into the heat recovery heat exchanger 40, and is able to control the switching of the preheating mode based on these first detected temperature and second detected temperature. Specifically, the preheating mode switching control unit 140 compares the first detected temperature by the first water supply temperature sensor 24 with the second detected temperature by the first heat source temperature sensor 54, and if the first detected temperature is lower than the second detected temperature, controls the preheating mode switching means to execute the water supply preheating mode, and if the first detected temperature is higher than the second detected temperature, controls the preheating mode switching means to execute the preheating stop mode. By automatically switching the preheating mode in accordance with the supply water temperature and the heat source water temperature in this way, it is possible to maximize the system COP.

[0087] The preheating mode switching control unit 140 can switch the preheating mode switching means between each preheating mode at least when the water flow mode is the circulating water flow mode. In this case, the preheating mode switching control unit 140 may set the preheating mode switching means to the preheating mode when the water flow mode is the passing water flow mode, and may set the preheating mode switching means to the preheating stop mode when the water flow mode is the water flow stop mode. As a result, for example, in a one-time water flow mode in which makeup water W, which often has a relatively low temperature, is used as the supply water W1, the heat recovery heat exchanger is actively utilized, while in a circulating water flow mode in which stored water in the hot water tank 60, which often has a relatively high temperature, is used as the supply water W1, the heat recovery heat exchanger can be selectively utilized depending on the temperature relationship between the supply water W1 and the heat source water W5. However, in order to enable efficient heating under various conditions of make-up water temperature and heat source water temperature, the preheating mode switching control unit 140 may be configured to switch the preheating mode switching means between each preheating mode when the water flow mode is the circulating water flow mode or the one-time water flow mode.

[0088] The signal input unit 150 includes a first signal input unit 151 that receives a water flow mode designation signal that designates one of a passing water flow mode, a circulating water flow mode, and a water flow stop mode. The water flow mode switching control unit 130 controls the water flow mode switching means to execute the one-time water flow mode, the circulating water flow mode, or the water flow stop mode in accordance with the water flow mode designation signal input to the first signal input unit 151. When the water flow mode or the water flow stop mode is executed, the water flow mode switching control unit 130 stops new water supply to the junction of the return line L2 by controlling the water supply pump 21, for example. This allows, for example, operation in a transient water flow mode where the system COP is maximized by using an external signal with make-up water, or operation in a circulating water flow mode where the stored water is kept warm by using an external signal without make-up water.

[0089] The signal input unit 150 also includes a second signal input unit 152 that receives a pre-heating mode designation signal that designates either the water supply pre-heating mode or the pre-heating stop mode. The preheating mode switching control unit 140 controls the preheating mode switching means in accordance with the preheating mode designation signal input to the second signal input unit 152 so as to execute the water supply preheating mode or the preheating stop mode. This makes it possible to maximize the system COP by switching between preheating modes in response to an external signal.

[0090] The storage unit 160 stores various information necessary for control, such as various threshold values.

[0091] Next, an example of the flow of control by the control unit 100 of this embodiment will be described.

[0092] FIG. 6B is a flowchart showing an example of the flow of a process for setting a target superheat degree by the target superheat degree setting unit 111 of the control unit 100.

[0093] First, when the system is started, the target superheat degree setting unit 111 sets the target superheat degree to a relatively high temperature, for example, 10° C., in step S1.

[0094] Next, in step S2, it is determined whether the temperature detected by the second heat source temperature sensor 55 is stable and is equal to or lower than a predetermined heat source temperature threshold (e.g., 60°C). If it is determined that the temperature detected by the second heat source temperature sensor 55 is stable (ΔT≦ΔT0, see FIG. 3) and is equal to or lower than the predetermined heat source temperature threshold (step S2: YES), the target degree of superheat is set to a small value, for example, 5°C, in step S3. On the other hand, if it is determined that the temperature detected by the second heat source temperature sensor 55 is not stable or exceeds the predetermined heat source temperature threshold (step S2: NO), the process returns to step S1, and the target degree of superheat is maintained at 10°C.

[0095] After setting the target degree of superheat to 5°C in step S3, it is determined in step S4 whether the fluctuation in the temperature detected by the second heat source temperature sensor 55 is large or exceeds a predetermined heat source temperature threshold. If it is determined that the fluctuation in the temperature detected by the second heat source temperature sensor 55 is large (ΔT>ΔT0, see FIG. 3) or that the predetermined heat source temperature threshold is exceeded (step S4: YES), the target degree of superheat is increased in step S5, for example, to 10°C. On the other hand, if it is determined that the fluctuation in the temperature detected by the second heat source temperature sensor 55 is not large and is equal to or lower than the predetermined heat source temperature threshold (step S4: NO), the process returns to step S3, and the target degree of superheat is continued to be maintained at 5°C. As a result, even if a situation in which the temperature of the heat source water W5 serving as the heat source fluid changes suddenly is confirmed, the heat pump circuit 10 can be driven stably.

[0096] Next, the preheating mode switching control will be described. The water flow mode switching control is as described above (see FIG. 6A). 6C is a flowchart showing an example of the flow of preheating mode switching control for switching between the water supply preheating mode and the preheating stop mode by the preheating mode switching control unit 140 of the control unit 100. In this example, the preheating mode switching control unit 140 controls the switching of the preheating mode based on the detection results of the first detected temperature (water supply temperature before flowing into the heat exchanger) by the first water supply temperature sensor 24 (water supply temperature sensor before flowing into the heat exchanger) and the second detected temperature (heat source temperature before flowing into the heat exchanger) by the first heat source temperature sensor 54 (heat source temperature sensor before flowing into the heat exchanger).

[0097] In step S11, the preheating mode switching control unit 140 determines whether or not the circulating water flow mode is being executed. If the circulating water flow mode is being executed (step S21: YES), in step S12, the first detection temperature by the first feedwater temperature sensor 24 is compared with the detection result of the second detection temperature by the first heat source temperature sensor 54. Then, if the first detection temperature is lower than the second detection temperature (step S12: YES), in step S13, the feedwater preheating mode is executed. On the other hand, if the first detection temperature is not lower than the second detection temperature (step S12: NO), in step S14, the preheating stop mode is executed.

[0098] In addition, in step S11, it may be determined whether the one-time water flow mode or the circulating water flow mode is being executed, and if the one-time water flow mode or the circulating water flow mode is being executed, control may be adopted to proceed to step S12.

[0099] FIG. 7 is a diagram illustrating a modified example of the supply water heating system 1 of the first embodiment. The condenser 12 of the heat pump circuit 10 in this embodiment has the functions of condensing and supercooling the refrigerant R. However, as shown in this modified example, the condenser of the heat pump circuit 10 may be divided into a condenser 12A that mainly has the function of condensing the refrigerant R and a supercooler 12B that mainly has the function of supercooling the refrigerant R. In this case, the refrigerant R of the heat pump circuit 10 preferably releases latent heat in the condenser 12A and releases sensible heat in the supercooler 12B. That is, in the condenser 12A, the gas refrigerant R is condensed to become a liquid refrigerant R, and the liquid refrigerant R is supplied to the supercooler 12B, where the liquid refrigerant R is further cooled (supercooled). The subcooler 12B is an indirect heat exchanger that exchanges heat between the feed water W1 sent to the condenser 12A and the refrigerant R flowing from the condenser 12A to the expansion valve 13. The subcooler 12B can subcool the refrigerant R flowing from the condenser 12A to the expansion valve 13 using the feed water W1 to the condenser 12A, and can warm the feed water W1 to the condenser 12A using the refrigerant R flowing from the condenser 12A to the expansion valve 13. In this way, by using separate heat exchangers for condensing and subcooling the refrigerant R, the design of the heat exchanger becomes easier and costs can be reduced. In addition, it becomes possible to use a general-purpose heat exchanger. In addition, in this modified example, the second feed water temperature sensor 26, which serves as a feed water temperature sensor that detects the temperature of the feed water W1 before it flows into the condenser 12 of the heat pump circuit 10, is preferably arranged upstream of the supercooler 12B.

[0100] In addition, in cases where a certain degree of temperature drop in the hot water W2 in the hot water tank 60 is acceptable, such as when the hot water demand location is a steam boiler, a make-up water line (not shown) may be provided to enable direct supply of water from the make-up water tank 70 to the hot water tank 60 without passing through the heat recovery heat exchanger 40 and the heat pump circuit 10. In this case, when the water level of the hot water W2 in the hot water tank 60 falls below the detection position of an electrode rod longer than the electrode rod 622, for example, the make-up water W can be directly supplied from the make-up water tank 70 to the hot water tank 60 by driving a make-up water pump provided in the make-up water line.

[0101] In this embodiment, the heat source water W5 is used as the heat source fluid of the heat pump circuit 10, but the heat source fluid is not limited to the heat source water W5, and various fluids such as air and exhaust gas can be used. The heat source fluid is preferably a fluid that provides heat (sensible heat) to the feed water W1 in the heat recovery heat exchanger 40 while decreasing in temperature, and that provides heat (sensible heat) to the refrigerant R of the heat pump circuit 10 in the evaporator 14 while decreasing in temperature.

[0102] The drive source of the compressor 11 of the heat pump circuit 10 is not limited to an electric motor. For example, the compressor 11 may be driven by a steam motor that generates power using steam, or may be driven by a gas engine. In this case, the output of the compressor 11 may be adjusted by adjusting the amount of steam supplied to the steam motor or the amount of gas supplied to the gas engine, thereby adjusting the refrigerant flow rate.

[0103] The supply water heating system 1 of the first embodiment described above provides the following advantages (1A) to (11A).

[0104] (1A) The water supply heating system 1 of this embodiment comprises a vapor compression type heat pump circuit 10 in which a compressor 11, a condenser 12, an expansion valve 13 and an evaporator 14 are connected in a ring shape by a refrigerant circulation line L9, and in which warm heat is extracted by the condenser 12 by driving the compressor 11, a heat exchanger 40 for heat recovery, a heat source fluid line L5 for circulating a heat source fluid through the heat recovery heat exchanger 40 and the evaporator 14 in that order, a water supply line L1 for circulating water W1 through the heat recovery heat exchanger 40 and the condenser 12 in that order, a refrigerant flow rate adjustment means that is controlled based on the degree of superheat of the gas refrigerant R flowing into the compressor 11 and adjusts the refrigerant flow rate, a water supply flow rate adjustment means that is controlled based on the outlet temperature of the water supply W1 flowing out from the condenser 12 and adjusts the water supply flow rate, and a control means for controlling the refrigerant flow rate adjustment means and the water supply flow rate adjustment means. In this way, by first flowing the heat source water W5 as the heat source fluid through the heat recovery heat exchanger 40, the heat output of the heat recovery heat exchanger 40 is increased, and the preheat amount of the feed water W1 is increased. The higher the heat source water temperature, the greater the effect of increasing the heat output. Since the amount of heat recovered by the heat recovery heat exchanger 40 is increased, the amount of heat recovered by the heat pump circuit 10 can be relatively reduced. To obtain the same system heat output as when the heat source water W5 is flowed through the evaporator 14 and then the heat recovery heat exchanger 40, the output of the compressor 11 can be reduced to reduce the power consumption of the heat pump circuit 10. At this time, by flowing the heat source water W5 through the heat recovery heat exchanger 40 first, the temperature of the heat source water W5 flowing into the evaporator 14 decreases; however, by adding further control, i.e., by combining the adjustment of the refrigerant flow rate based on the degree of superheat and the adjustment of the water supply flow rate based on the hot water outlet temperature, the COP of the system can be significantly increased in a configuration in which the heat source water W5 flows through the heat recovery heat exchanger 40 first, due to the multiple effects of, for example, increasing the heat input to the evaporator 14 by adjusting the refrigerant flow rate in accordance with a low superheat setting, and further increasing the heat output of the heat recovery heat exchanger 40 and the heat output of the evaporator 14 by adjusting the water supply flow rate in accordance with a low hot water outlet temperature setting.

[0105] (2A) The heat source fluid line L5 of the water supply heating system 1 of this embodiment has a connection configuration in which the heat source fluid and the water supply W1 are heat exchanged in a counterflow manner in the heat recovery heat exchanger 40, and then the heat source fluid and the liquid refrigerant R are heat exchanged in a counterflow manner in the evaporator 14. In this way, by flowing the heat source water W5 through the heat recovery heat exchanger 40 and then the evaporator 14, and flowing it in a counterflow to the flow direction of the supply water W1 in each of the heat recovery heat exchanger 40 and the evaporator 14, the amount of heat recovery can be maximized.

[0106] (3A) The water supply heating system 1 of this embodiment is equipped with an inlet temperature sensor 17 that detects the inlet temperature of the gas refrigerant R flowing into the compressor 11, a steam pressure sensor 18 that detects the vapor pressure of the gas refrigerant R flowing out of the evaporator 14, and an outlet temperature sensor 27 that detects the outlet temperature of the water supply W1 flowing out of the condenser 12, and the control means determines the evaporation temperature of the liquid refrigerant R from the pressure detected by the steam pressure sensor 18, calculates the degree of superheat of the gas refrigerant R by subtracting the evaporation temperature from the temperature detected by the suction temperature sensor 17, controls the refrigerant flow rate adjustment means so that the calculated degree of superheat becomes a target degree of superheat, and controls the water supply flow rate adjustment means so that the temperature detected by the outlet temperature sensor 27 becomes the target outlet temperature. In this way, by accurately calculating the degree of superheat of the gas refrigerant R and keeping this value constant, the heat output of the condenser 12 to the preheated feed water W1 is stabilized. This reduces fluctuations in the hot water flow rate. Also, by appropriately increasing the feed water flow rate using the set value of the target hot water outlet temperature, for example, and keeping the flow rate within a constant range, a high heat output can be maintained.

[0107] (4A) The water heating system 1 of this embodiment is equipped with a heat source temperature sensor that detects the temperature of the heat source fluid before it flows into the evaporator 14, and the control means sets the target degree of superheat according to the temperature detected by the heat source temperature sensor. In this way, by setting an appropriate target degree of superheat depending on the temperature of the heat source fluid, it is possible to increase the amount of heat recovered in the evaporator 14 while preventing damage to the compressor 11 due to liquid compression. For example, when the heat source water temperature is low, the refrigerant circulation flow rate is increased by setting the target degree of superheat low. This makes it possible to increase the amount of heat recovered even with low-temperature heat source water W5. By setting the lower limit of the target degree of superheat to, for example, 5°C, it is possible to prevent damage to the compressor 11 due to liquid compression. Furthermore, by setting the upper limit of the target degree of superheat to, for example, 10°C, it is possible to maintain the refrigerant circulation flow rate at or above a predetermined flow rate and prevent a decrease in the amount of heat recovered.

[0108] (5A) The control means of the feedwater heating system 1 of this embodiment increases the target degree of superheat when it is determined that the fluctuation in the temperature detected by the heat source temperature sensor is large. This makes it possible to stably drive the heat pump circuit 10 even when a situation in which the temperature of the heat source fluid changes suddenly is confirmed. For example, even if the temperature of the heat source fluid drops suddenly, the refrigerant can be reliably vaporized in the evaporator 14 by setting the target superheat degree to a high value, thereby preventing damage to the compressor 11 due to liquid compression.

[0109] (6A) The control means of the supply water heating system 1 of this embodiment reduces the target degree of superheat when it is determined that the temperature detected by the heat source temperature sensor is stable. As a result, when the temperature of the heat source fluid is stable, the target degree of superheat can be set to a low value to increase the refrigerant circulation flow rate, thereby increasing the amount of heat recovered in the evaporator 14.

[0110] (7A) The feed water heating system 1 of this embodiment includes a feed water temperature sensor that detects the temperature of the feed water before it flows into the condenser 12, and the control means sets the target hot water outlet temperature according to the temperature detected by the feed water temperature sensor. In this way, by setting an appropriate target hot water outlet temperature according to the temperature of the feed water, it is possible to prevent insufficient supercooling in the condenser 12, an excessive feed water flow rate, and the like.

[0111] (8A) The water supply heating system 1 of this embodiment is equipped with a water supply temperature sensor that detects the temperature of the water supply before it flows into the condenser 12, and the target hot water outlet temperature can be set to a value between an upper limit and a lower limit. The lower limit is a value obtained by adding a predetermined value to the temperature detected by the water supply temperature sensor, and the higher the detected temperature of the water supply temperature sensor, the higher the value. In this way, by setting the lower limit of the range of target hot water outlet temperatures that can be set according to the feed water temperature, it is possible to reliably prevent insufficient supercooling in condenser 12 and stabilize the amount of heat recovered in evaporator 14. In addition, it is possible to prevent the feed water flow rate from becoming excessive and suppress deterioration of feed water pump 21 due to overload.

[0112] (9A) The water supply heating system 1 of this embodiment includes one or two bypass lines for bypassing the water supply W1 from the heat exchanger 40 for heat recovery and / or bypassing the heat source fluid from the heat exchanger 40 for heat recovery, and a preheating mode switching means for switching between a water supply preheating mode in which the water supply W1 and the heat source fluid are circulated simultaneously through the heat exchanger 40 for heat recovery, and a preheating stop mode in which at least one of the water supply W1 and the heat source fluid is circulated through the bypass line. As a result, by bypassing the heat recovery heat exchanger 40 under conditions in which the heat recovery heat exchanger 40 cannot perform its function, the pressure loss of the feed water W1 and / or the heat source water W5 can be reduced, and the system COP including the feed water pump 21 and the heat source supply pump 53 can be improved.

[0113] (10A) The water supply heating system 1 of this embodiment is equipped with a water supply temperature sensor 24 before entering the heat exchanger for detecting the temperature of the water supply W1 before flowing into the heat exchanger 40 for heat recovery, and a heat source temperature sensor 54 before entering the heat exchanger for detecting the temperature of the heat source fluid before flowing into the heat exchanger 40 for heat recovery. The control means compares a first detected temperature by the water supply temperature sensor 24 before entering the heat exchanger with a second detected temperature by the heat source temperature sensor 54 before entering the heat exchanger, and controls the preheating mode switching means to execute a water supply preheating mode when the first detected temperature is lower than the second detected temperature, and controls the preheating mode switching means to execute a preheating stop mode when the first detected temperature is higher than the second detected temperature. This automatic preheating mode switching based on the feed water temperature and heat source water temperature makes it possible to maximize the system COP.

[0114] (11A) The control means of the water supply heating system 1 of this embodiment has a signal input unit 150 that receives a preheating mode designation signal that designates the type of water supply preheating mode or preheating stop mode, and a preheating mode switching control unit 140 that controls the preheating mode switching means to execute the water supply preheating mode or the preheating stop mode in accordance with the preheating mode designation signal input to the signal input unit 150. By switching the preheating mode in response to an external signal, the system COP can be maximized.

[0115] Furthermore, the supply water heating system 1 of the first embodiment described above also provides the following advantages (1B) to (8B).

[0116] (1B) The water heating system 1 of this embodiment includes a vapor compression heat pump circuit 10 in which a compressor 11, a condenser 12, an expansion valve 13, and an evaporator 14 are connected in a ring shape by a refrigerant circulation line L9, and in which heat is extracted by the condenser 12 when the compressor 11 is driven, a heat recovery heat exchanger 40, a heat source fluid line L5 for circulating a heat source fluid through the heat recovery heat exchanger 40 and the evaporator 14, a water supply line L1 for circulating water W1 through the heat recovery heat exchanger 40 and the condenser 12 in this order, and a refrigerant generated by the condenser 12. the hot water tank 60 for storing the generated hot water W2; a return line L2 for returning the hot water W2 in the hot water tank 60 to the upstream side of the heat recovery heat exchanger 40; a water flow mode switching means for switching between a one-time water flow mode in which the hot water W2 is passed through the condenser 12 without passing through the return line L2, a circulating water flow mode in which the hot water W2 is passed through the condenser 12 while passing through the return line L2, and a water flow stop mode in which the water flow to the condenser 12 is stopped; and a control means for controlling the water flow mode switching means. In this way, by enabling operation in the circulating water flow mode in addition to the passing water flow mode, the stored hot water temperature can be maintained by circulating and heating the hot water tank 60 as necessary. In the circulating water flow mode, the stored water is flowed in front of the heat recovery heat exchanger 40, so when the stored water temperature is less than the heat source water temperature, efficient heating is possible.

[0117] (2B) The water supply heating system 1 of this embodiment is equipped with one or two bypass lines for bypassing the water supply W1 from the heat exchanger 40 for heat recovery and / or bypassing the heat source fluid from the heat exchanger 40 for heat recovery, and a preheating mode switching means for switching between a water supply preheating mode in which the water supply W1 and the heat source fluid are circulated simultaneously through the heat exchanger 40 for heat recovery, and a preheating stop mode in which at least one of the water supply W1 and the heat source fluid is circulated through the bypass line. This allows the heat recovery heat exchanger 40 to be selectively used depending on the situation.

[0118] (3B) The control means of the supply water heating system 1 of this embodiment can switch the preheating mode switching means between the supply water preheating mode and the preheating stop mode at least in the circulating water flow mode. This makes it possible, for example, to proactively utilize the heat recovery heat exchanger 40 in the pass-through water mode, and selectively utilize the heat recovery heat exchanger 40 in the circulating water mode.

[0119] (4B) The heat source fluid line L5 of the feedwater heating system 1 of this embodiment has a connection configuration in which the heat source fluid flows through the heat recovery heat exchanger 40 and the evaporator 14 in this order. As a result, the heat source water W5 as a heat source fluid is first flowed through the heat recovery heat exchanger 40, thereby increasing the amount of preheating of the feed water W1 and increasing the heat output of the heat recovery heat exchanger 40. The higher the heat source water temperature, the greater the effect of increasing the heat output.

[0120] (5B) The water supply heating system 1 of this embodiment is equipped with a hot water temperature sensor 61 that detects the temperature of the hot water W2 in the hot water tank 60, and the control means controls the water flow mode switching means to execute a one-time water flow mode when new water supply is being performed to the confluence of the return line L2, controls the water flow mode switching means to execute a circulating water flow mode when new water supply to the confluence is stopped and the temperature detected by the hot water temperature sensor 61 is below the set temperature, and controls the water flow mode switching means to execute a water flow stop mode when new water supply to the confluence is stopped and the temperature detected by the hot water temperature sensor 61 is above the set temperature. As a result, when there is sufficient demand for hot water and it is necessary to supply makeup water W, the system can be operated in a one-time water flow mode in which the system COP is maximized. Also, when there is little demand for hot water and it is not necessary to supply makeup water W, the temperature of the stored water in the hot water tank 60 can be raised in a circulating water flow mode when the temperature of the stored water drops.

[0121] (6B) The water supply heating system 1 of this embodiment is equipped with a water supply temperature sensor 24 before entering the heat exchanger for detecting the temperature of the water supply W1 before it flows into the heat exchanger 40 for heat recovery, and a heat source temperature sensor 54 before entering the heat exchanger for detecting the temperature of the heat source fluid before it flows into the heat exchanger 40 for heat recovery. The control means compares a first detected temperature by the water supply temperature sensor 24 before entering the heat exchanger with a second detected temperature by the heat source temperature sensor 54 before entering the heat exchanger, and if the first detected temperature is lower than the second detected temperature, controls the preheating mode switching means to execute the water supply preheating mode, and if the first detected temperature is higher than the second detected temperature, controls the preheating mode switching means to execute the preheating stop mode. This automatic preheating mode switching based on the feed water temperature and heat source water temperature makes it possible to maximize the system COP.

[0122] (7B) The control means of the water supply heating system 1 of this embodiment includes a first signal input unit 151 that receives a water flow mode designation signal that designates one of the one-time water flow mode, the circulating water flow mode, or the water flow stop mode, and a water flow mode switching control unit 130 that controls the water flow mode switching means to execute the one-time water flow mode, the circulating water flow mode, or the water flow stop mode in accordance with the water flow mode designation signal input to the first signal input unit 151, and the water flow mode switching control unit 130 stops new water supply to the confluence of the return line L2 when the circulating water flow mode or the water flow stop mode is executed. This allows the system to operate in a one-time flow mode where the system COP is maximized by using an external signal indicating that makeup water is being supplied, or to keep the stored water warm in a circulation mode by using an external signal indicating that makeup water is not being supplied.

[0123] (8B) The control means of the water supply heating system 1 of this embodiment has a second signal input unit 152 that receives a preheating mode designation signal that designates either the water supply preheating mode or the preheating stop mode, and a preheating mode switching control unit 140 that controls the preheating mode switching means to execute the water supply preheating mode or the preheating stop mode in accordance with the preheating mode designation signal input to the second signal input unit 152. This makes it possible to manually switch preheating modes in response to an external signal, for example, and maximize the system COP.

[0124] Furthermore, the supply water heating system 1 of the first embodiment described above also provides the following advantages (1C) to (7C).

[0125] (1C) The water heating system 1 of this embodiment includes a vapor compression type heat pump circuit 10 in which a compressor 11, a condenser 12, an expansion valve 13 and an evaporator 14 are connected in a ring shape by a refrigerant circulation line L9, and which extracts heat in the condenser 12 by driving the compressor 11, a refrigerant flow rate adjustment means for adjusting the flow rate of the refrigerant R flowing through the heat pump circuit 10, a heat source temperature sensor for detecting the temperature of the heat source fluid that exchanges heat with the refrigerant R in the evaporator 14, and a control means for controlling the refrigerant flow rate adjustment means, and the control means sets a target degree of superheat in accordance with the temperature detected by the heat source temperature sensor, and controls the refrigerant flow rate adjustment means so that the degree of superheat of the refrigerant R flowing into the compressor 11 becomes the target degree of superheat. In this way, by setting an appropriate target degree of superheat depending on the temperature of the heat source fluid, it is possible to increase the amount of heat recovered in the evaporator 14 while preventing damage to the compressor 11 due to liquid compression. For example, when the heat source water temperature is low, the refrigerant circulation flow rate is increased by setting the target degree of superheat low. This makes it possible to increase the amount of heat recovered even if the heat source fluid is low-temperature heat source water W5. By setting the lower limit of the target degree of superheat to, for example, 5°C, it is possible to prevent damage to the compressor 11 due to liquid compression. Furthermore, by setting the upper limit of the target degree of superheat to, for example, 10°C, it is possible to maintain the refrigerant circulation flow rate at or above a predetermined flow rate and prevent a decrease in the amount of heat recovered.

[0126] (2C) The control means of the feedwater heating system 1 of this embodiment increases the target degree of superheat when it is determined that the fluctuation in the temperature detected by the heat source temperature sensor is large. This allows the heat pump circuit 10 to operate stably even if a situation in which the temperature of the heat source fluid changes suddenly is confirmed. For example, even if the temperature of the heat source fluid drops suddenly, the refrigerant can be reliably vaporized in the evaporator 14 by setting the target superheat degree to a high value, thereby preventing damage to the compressor 11 due to liquid compression.

[0127] (3C) The control means of the feedwater heating system 1 of this embodiment decreases the target degree of superheat when it is determined that the temperature detected by the heat source temperature sensor is stable. As a result, when the temperature of the heat source fluid is stable, the target degree of superheat can be set to a low value to increase the refrigerant circulation flow rate, thereby increasing the amount of heat recovered in the evaporator 14.

[0128] (4C) The water supply heating system 1 of this embodiment is equipped with a suction temperature sensor 17 that detects the suction temperature of the gas refrigerant R flowing into the compressor 11, and a vapor pressure sensor 18 that detects the vapor pressure of the gas refrigerant R flowing out from the evaporator 14, and the control means determines the evaporation temperature of the liquid refrigerant R from the pressure detected by the vapor pressure sensor 18, and calculates the degree of superheat of the gas refrigerant R by subtracting the evaporation temperature from the temperature detected by the suction temperature sensor 17, and controls the refrigerant flow rate adjustment means so that the calculated degree of superheat becomes a target degree of superheat. In this way, by accurately calculating the degree of superheat of the gas refrigerant R and keeping this value constant, the heat output of the condenser 12 to the preheated feed water W1 is stabilized, thereby reducing fluctuations in the hot water flow rate.

[0129] (5C) The water supply heating system 1 of this embodiment is equipped with a water supply flow rate adjustment means for adjusting the water supply flow rate flowing through the condenser 12, and an outlet water temperature sensor 27 for detecting the outlet water temperature of the water supply W1 flowing out from the condenser 12, and the control means controls the water supply flow rate adjustment means so that the detected temperature of the outlet water temperature sensor 27 becomes the target outlet water temperature. This allows the water W1 to always be heated to a desired temperature and dispensed.

[0130] (6C) The water supply heating system 1 of this embodiment is equipped with a water supply temperature sensor that detects the temperature of the water supply W1 before it flows into the condenser 12, and the control means sets the target hot water outlet temperature according to the temperature detected by the water supply temperature sensor. In this way, by setting an appropriate target hot water outlet temperature according to the temperature of the supply water W1, it is possible to prevent insufficient supercooling in the condenser 12, an excessive supply water flow rate, and the like.

[0131] (7C) The water supply heating system 1 of this embodiment is equipped with a water supply temperature sensor that detects the temperature of the water supply W1 before it flows into the condenser 12, and the target outlet temperature can be set to a value between an upper limit and a lower limit, and the lower limit is a value obtained by adding a predetermined value to the temperature detected by the water supply temperature sensor, and the higher the detected temperature of the water supply temperature sensor, the higher the value. In this way, by setting the lower limit of the range of target hot water outlet temperatures that can be set according to the feed water temperature, it is possible to reliably prevent insufficient supercooling in condenser 12 and stabilize the amount of heat recovered in evaporator 14. In addition, it is possible to prevent the feed water flow rate from becoming excessive and suppress deterioration of feed water pump 21 due to overload.

[0132] Although a preferred embodiment of the supply water heating system of the present invention has been described above, the present invention is not limited to the above-described embodiment and can be modified as appropriate. [Explanation of symbols]

[0133] 1. Water heating system 10 Heat pump circuit 11 Compressor 12 Condenser 12A Condenser 12B Supercooler 13 Expansion valve (refrigerant flow rate control means) 14 Evaporator 17 Intake temperature sensor 18 Steam pressure sensor 21 Water supply pump (water supply flow rate adjustment means, water flow mode switching means) 24 1st supply water temperature sensor (supply water temperature sensor before entering heat exchanger, supply water temperature sensor) 25 Three-way valve (preheat mode switching means) 26 Second supply water temperature sensor (supply water temperature sensor) 27 Outlet water temperature sensor 31 Circulation pump (supply water flow rate adjustment means, water flow mode switching means) 40 Heat recovery heat exchanger 50 Heat source water tank 53 Heat source supply pump 54 First heat source temperature sensor (heat source temperature sensor before flowing into heat exchanger, heat source temperature sensor) 55 Second heat source temperature sensor (heat source temperature sensor) 60 Hot Water Tank 61 Hot water temperature sensor 62 Water level detector 63 Hot water supply pump 70 Water Supply Tank 100 Control section 111 Target superheat degree setting section 112 Superheat degree calculation section 113 Refrigerant flow control unit 121 Target outlet hot water temperature setting range determination unit 122 Target outlet water temperature setting section 123 Water supply flow control unit 130 Water flow mode switching control unit 140 Preheating mode switching control unit 150 Signal input section 151 First signal input section 152 Second signal input section L1 Water supply line L2 Reflux line L3 Bypass Line L4 Hot water supply line L5 Heat source fluid line L9 Refrigerant circulation line R refrigerant (gas refrigerant, liquid refrigerant) W Make-up water W1 Water supply W2 Hot water W5 Heat source water (heat source fluid)

Claims

1. a vapor compression heat pump circuit in which a compressor, a condenser, an expansion valve, and an evaporator are connected in a ring shape by a refrigerant circulation line, and heat is extracted by the condenser when the compressor is driven; a water supply line for circulating water to the condenser; a heat source fluid line for passing a heat source fluid through the evaporator; a heat source temperature sensor that detects the temperature of the heat source fluid before it flows into the evaporator; A control means for feedback-controlling a valve opening degree of the expansion valve so that the superheat degree of the refrigerant flowing into the compressor becomes a target superheat degree, The control means Setting the target superheat degree to an upper limit value and starting the system; After the system is started, the target degree of superheat is set within the range from the upper limit value to the lower limit value according to the temperature detected by the heat source temperature sensor; During operation with the target degree of superheat set in the range from the upper limit value to the lower limit value, when it is determined that the fluctuation in the detected temperature of the heat source temperature sensor is large, the target degree of superheat is set to the upper limit value, During operation with the target degree of superheat set to the upper limit value, if it is determined that the detected temperature of the heat source temperature sensor is stable, the target degree of superheat is set in a range from the upper limit value to the lower limit value according to the detected temperature of the heat source temperature sensor; The target superheat degree is set to be lower as the detected temperature of the heat source temperature sensor becomes lower, The lower limit is a value that can prevent liquid compression in the compressor. Water heating system.

2. A vapor compression heat pump circuit in which a compressor, a condenser, an expansion valve, and an evaporator are connected in a ring shape by a refrigerant circulation line, and heat is extracted by the condenser when the compressor is driven; a water supply line for circulating water to the condenser; a heat source fluid line for passing a heat source fluid through the evaporator; a heat source temperature sensor that detects the temperature of the heat source fluid before it flows into the evaporator; A control means for feedback-controlling a valve opening degree of the expansion valve so that the superheat degree of the refrigerant flowing into the compressor becomes a target superheat degree, The control means Setting the target superheat degree to an upper limit value and starting the system; After the system is started, the target degree of superheat is set within the range from the upper limit value to the lower limit value according to the temperature detected by the heat source temperature sensor; During operation with the target degree of superheat set in the range from the upper limit value to the lower limit value, when it is determined that the fluctuation in the detected temperature of the heat source temperature sensor is large, the target degree of superheat is set to the upper limit value, During operation with the target degree of superheat set to the upper limit value, when it is determined that the temperature detected by the heat source temperature sensor is stable, the target degree of superheat is set in a range from the upper limit value to the lower limit value according to the temperature detected by the heat source temperature sensor. Water heating system.

3. A suction temperature sensor that detects a suction temperature of the gas refrigerant flowing into the compressor; A vapor pressure sensor that detects the vapor pressure of the gas refrigerant flowing out from the evaporator; Equipped with The control means 3. The supply water heating system according to claim 1 or 2, wherein an evaporation temperature of the liquid refrigerant is calculated from the pressure detected by the steam pressure sensor, and a degree of superheat of the gas refrigerant is calculated by subtracting the evaporation temperature from the temperature detected by the suction temperature sensor to set the degree of superheat as a feedback value, and an operation amount of the expansion valve is calculated by a PID calculation algorithm so that the calculated degree of superheat becomes a target degree of superheat.

4. Further comprising a heat exchanger for heat recovery; The water supply line is configured to pass the water through the heat recovery heat exchanger and the condenser in this order, The heat source fluid line is configured to pass a heat source fluid through the heat recovery heat exchanger and the evaporator in this order, 3. The supply water heating system according to claim 1, wherein the heat source temperature sensor is disposed in the heat source fluid line so as to detect a temperature of the heat source fluid flowing out from the heat recovery heat exchanger.

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