Hot water production system

Abstract

Provided is a hot water production system with which heat supply to a load facility can be continued more stably even when performing a defrosting operation of an air heat source heat pump, without increasing a facility cost. The hot water production system comprises: a heating device capable of executing a heating operation for heating water using an air heat source heat pump and a defrosting operation for performing defrosting; a water tank that stores heated water; a heat storage correlation value detection means that detects a heat storage correlation value correlated with an amount of stored heat in the water tank; and a control means that controls the air heat source heat pump. The control means includes: a heating operation control unit that controls start and end of the heating operation on the basis of the heat storage correlation value; a defrosting necessity determination unit that determines whether or not the defrosting operation is necessary during execution of the heating operation; and a defrosting operation control unit that starts the defrosting operation when the defrosting operation is determined to be necessary and a predetermined heat storage fulfillment condition based on the heat storage correlation value is satisfied.

Description

Hot water production system

[0001] The present invention relates to a hot water production system for heating water.

[0002] Conventionally, systems that heat water for use in load facilities within a business facility have used air-source heat pumps to heat water. Air-source heat pumps have a refrigerant evaporator that enables heating using the heat of the air, and are known as an excellent heating method that is highly energy efficient and can reduce carbon dioxide emissions.

[0003] However, when an air-source heat pump is used, the heat exchange efficiency decreases as frost builds up on the refrigerant evaporator, so a defrosting operation is performed to melt the frost on the refrigerant evaporator. Patent Document 1 mentions that a defrosting operation is performed in a hot water production system equipped with an air-source heat pump. Known forms of defrosting operation include the reverse cycle defrosting operation disclosed in Patent Document 2 and the hot gas bypass operation disclosed in Patent Document 3.

[0004] JP 2024-014372 A JP 2015-152174 A JP 2012-107836 A

[0005] The frequency of the defrosting operation increases as the difference in heat between the outlet hot water temperature and the outside air temperature increases and as the heating operation time increases, and water heating is not possible during defrosting. Therefore, in order to meet the heat demand during defrosting operation, measures such as installing a large hot water storage tank in advance to store hot water overnight are required, which increases equipment costs.

[0006] In view of the above problems, the present invention aims to provide a hot water production system that can continue to supply heat to load equipment more stably, even when performing defrost operation of an air-source heat pump, without incurring an increase in equipment costs.

[0007] The hot water production system of the present invention is a hot water production system that heats water used in load equipment within a business premises, and includes a heating device that has an air-source heat pump having a refrigerant evaporator and a refrigerant compressor, and is capable of performing a heating operation that heats the water using the air-source heat pump and a defrost operation that defrosts the refrigerant evaporator, a water tank that stores the heated water, a heat storage correlation value detection means that detects a heat storage correlation value that correlates with the amount of heat stored in the water stored in the water tank, and a control means that controls the air-source heat pump, and the control means is configured to include a heating operation control unit that controls the start and end of the heating operation based on the heat storage correlation value, a defrost necessity determination unit that determines whether the defrost operation is necessary while the heating operation is being performed, and a defrost operation control unit that starts the defrost operation when the defrost necessity determination unit determines that the defrost operation is necessary and a predetermined heat storage sufficiency condition based on the heat storage correlation value is satisfied.

[0008] According to this configuration, it is possible to continue to supply heat to the load equipment more stably, without increasing the equipment cost, even when the defrosting operation of the air-source heat pump is performed.

[0009] More specifically, the above configuration may be configured such that the heating operation control unit terminates the heating operation when the heat storage correlation value reaches a predetermined upper threshold, and the heat storage sufficiency condition is a condition that is satisfied when the heat storage correlation value reaches the upper threshold.

[0010] More specifically, the above configuration may be configured such that the heating operation control unit starts the heating operation when the heat storage correlation value drops to a predetermined lower threshold, and ends the heating operation when the heat storage correlation value reaches a predetermined upper threshold, the heat storage sufficiency condition is a condition that is satisfied when the heat storage correlation value reaches a predetermined value, and the predetermined value is equal to or greater than the median of the range from the upper threshold to the lower threshold and is less than the upper threshold.

[0011] More specifically, the above configuration may be a hot water production system having a plurality of heating devices and a control means corresponding to each of the heating devices, and a defrost operation control unit that keeps the number of heating devices that perform the defrost operation at the same time below a specified number, and a priority is assigned to each of the plurality of heating devices, and the defrost operation control unit is configured to start the defrost operation for the excess heating devices in order of priority after the defrost operation that was performed first has finished.

[0012] More specifically, the above configuration may include a water path that allows the water in the water tank to circulate to the heating device, and the heat storage correlation value detection means may be configured to detect the temperature of the water in the water tank as the heat storage correlation value.

[0013] More specifically, the above configuration may include a water path that enables the water in the water tank to circulate to the heating device, the heat storage correlation value detection means detects the temperature of the water in the water tank as the heat storage correlation value, the heating operation control unit controls the refrigerant compressor to reduce its rotation speed as the detected temperature increases, and the heat storage fulfillment condition may be a condition that is fulfilled when the rotation speed falls below a specified number.

[0014] More specifically, the above configuration may include a water path that allows the water sent from a water source to the water tank to flow through the heating device, and the heat storage correlation value detection means may be configured to detect the water level of the water in the water tank as the heat storage correlation value.

[0015] More specifically, the above configuration may include a water path that allows the water in the water tank to be circulated to the heating device, and the heat storage correlation value detection means may be configured to detect the amount of remaining hot water related to the temperature stratification of the water formed in the water tank as the heat storage correlation value.

[0016] More specifically, the above configuration may include an air temperature detection means for detecting the temperature of the heat source air before heat exchange in the refrigerant evaporator, and a refrigerant temperature detection means for detecting the temperature of the refrigerant after heat exchange in the refrigerant evaporator, and the defrost necessity determination unit may be configured to determine whether or not a defrosting operation is necessary based on the detected temperatures of the air temperature detection means and the refrigerant temperature detection means, respectively.

[0017] More specifically, the above configuration may include a water path that allows the water in the water tank to circulate to the heating device, the heat storage correlation value detection means detects the temperature of the water in the water tank as the heat storage correlation value, and the heating operation control unit terminates the heating operation when the heat storage correlation value reaches a predetermined upper threshold, and if the temperature detected by the air temperature detection means is below a specified temperature, the upper threshold may be changed to a value higher than this.

[0018] According to the hot water production system of the present invention, it is possible to continue to supply heat to load equipment more stably, even when performing defrost operation of the air-source heat pump, without incurring an increase in equipment costs.

[0019] FIG. 1 is a schematic configuration diagram of a hot water production system according to a first embodiment. FIG. 2 is a schematic configuration diagram of an air-source heat pump. FIG. 3 is a flowchart relating to processing performed by a defrost operation control unit. FIG. 4 is an explanatory diagram relating to a hot water production system that supplies water to a hot water supply load. FIG. 5 is an explanatory diagram relating to a hot water production system that detects the water level in a water tank. FIG. 6 is an explanatory diagram relating to a hot water production system that detects the amount of remaining hot water in a water tank. FIG. 7 is a schematic configuration diagram of a hot water production system according to a second embodiment.

[0020] Each embodiment of the present invention will be described below with reference to the drawings.

[0021] 1. First Embodiment Fig. 1 is a schematic configuration diagram of a hot water production system 100 according to a first embodiment. As shown in the figure, the hot water production system 100 includes a heating device 1 having an air-source heat pump 10, a control unit 2 as a control means for the air-source heat pump 10, and a water tank 3 (an open tank in the example shown in Fig. 1) that stores water Wa heated by the heating device 1. The hot water production system 100 serves to heat water Wa to be used in load equipment X within the business (a heat supply load that returns water Wa after heat utilization to the water tank 3 in the example shown in Fig. 1).

[0022] In this context, establishments refer to individual locations where the production of goods or the provision of services is carried out as a business, such as factories, commercial facilities, medical institutions, welfare facilities, accommodation facilities, or research facilities. Service water refers to water used in connection with the production of goods or the provision of services. Heated service water can be used directly as cleaning water or indirectly as heat transfer water.

[0023] If the business establishment is a factory, the load equipment would be production equipment (equipment directly involved in the production of goods) such as food and beverage manufacturing plants, automobile, metal product, and machinery and equipment manufacturing plants. An example of load equipment other than factory production equipment is a steam boiler unit (heat source equipment involved in the operation of production equipment), in which case part of the heated water is used as boiler feed water.

[0024] As shown in Figure 1, the hot water production system 100 includes a first water line L1 that circulates water Wa from the water tank 3 to the heating device 1, a second water line L2 that circulates water Wa from the heating device 1 to the water tank 3, a third water line L3 that circulates water Wa from the water tank 3 to the load equipment X, and a fourth water line L4 that circulates water Wa from the load equipment X to the water tank 3.

[0025] The first water line L1 and the second water line L2 form a water path (a circulation path for the water Wa including the water tank 3 and the heating device 1) that allows the water Wa in the water tank 3 to be circulated to the heating device 1. The third water line L3 and the fourth water line L4 form a water path (a circulation path for the water Wa including the water tank 3 and the load equipment X) that allows the water Wa in the water tank 3 to be circulated to the load equipment X. A pump (not shown) is disposed in each of these water paths, and the water Wa is circulated in the direction indicated by the colored arrows.

[0026] 2 is a schematic diagram of an air-source heat pump 10. As shown in the figure, the air-source heat pump 10 includes a refrigerant compressor 11, a condenser 12, an expansion valve 13, a refrigerant evaporator 14, and a four-way valve 15, which are connected by a refrigerant circulation line Lc. A refrigerant R can be circulated through the refrigerant circulation line Lc.

[0027] The refrigerant compressor 11 has a motor as a drive source, and compresses the refrigerant R received from the upstream side to produce high-temperature, high-pressure refrigerant R, which is then sent downstream. The rotation speed of the refrigerant compressor 11 (the rotation speed of the motor, which can also be considered as the drive frequency) can be controlled by the control unit 2.

[0028] The condenser 12 exchanges heat between the water Wa sent through the first water line L1 and the refrigerant R sent from the refrigerant compressor 11, and condenses the refrigerant R. The water Wa (heated water Wa) that has been heat exchanged in the condenser 12 is sent to the water tank 3 through the second water line L2.

[0029] The expansion valve 13 passes the refrigerant R sent from the condenser 12, thereby reducing the pressure and temperature of the refrigerant R. The refrigerant evaporator 14 exchanges heat between heat source air Ar (outside air) and the refrigerant R sent from the expansion valve 13, and evaporates the refrigerant R by absorbing heat from the heat source air Ar.

[0030] The refrigerant evaporator 14 in this embodiment is, for example, a finned tube heat exchanger, and is configured to use a blower fan 14a to continuously send heat source air Ar to a number of fins provided on the surface of a heat transfer tube (part of the refrigerant circulation line Lc) through which the refrigerant R passes. In addition, a refrigerant temperature sensor 14x (a form of refrigerant temperature detection means) is provided near the outlet of the heat transfer tube in the refrigerant evaporator 14 through which the refrigerant R passes, to detect the temperature of the refrigerant R after heat exchange in the refrigerant evaporator 14, and an air temperature sensor 14y (a form of air temperature detection means) is provided upstream of the fins to detect the temperature of the heat source air Ar before heat exchange in the refrigerant evaporator 14.

[0031] 2, the four-way valve 15 has connection points a to d to which ends of the refrigerant circulation line Lc are connected. The refrigerant circulation line Lc extending from connection point b is connected to connection point d via the condenser 12, expansion valve 13, and refrigerant evaporator 14. On the other hand, the refrigerant circulation line Lc extending from connection point c is connected to connection point a via the refrigerant compressor 11.

[0032] The four-way valve 15 is configured to be switchable between a first state in which the connection points a and b are connected and the connection points c and d are connected, and a second state in which the connection points a and d are connected and the connection points b and c are connected. The switching of the four-way valve 15 between the first state and the second state is controlled by the control unit 2.

[0033] The heating device 1 may have a plurality of air-source heat pumps 10, or may further have a heating means other than the air-source heat pumps 10. The heating device 1 may also be configured to heat the water Wa using a separately provided intermediate heat exchanger, instead of using the condenser 12 to heat the water Wa. In this case, for example, the condenser 12 and the intermediate heat exchanger may be connected by a circulation line for an intermediate medium (water), and heat may be exchanged between the water Wa and the intermediate medium while circulating the intermediate medium.

[0034] The heating device 1 is capable of performing a heating operation in which the service water Wa is heated using the air-source heat pump 10, and a defrosting operation in which the refrigerant evaporator 14 is defrosted. The heating operation can be performed with the four-way valve 15 in a first state, and the defrosting operation can be performed with the four-way valve 15 in a second state.

[0035] That is, when the four-way valve 15 is in the first state, the refrigerant R circulates in the direction shown by the solid arrow in Fig. 2. At this time, the refrigerant R absorbs heat from the heat-source air Ar and vaporizes in the refrigerant evaporator 14, while the refrigerant R condenses by releasing heat to the water Wa in the condenser 12. This achieves heating operation in which the water Wa is heated using the air-source heat pump 10.

[0036] On the other hand, when the four-way valve 15 is in the second state, the refrigerant R circulates in the direction indicated by the dotted arrow in Fig. 2. As a result, the refrigerant R flows in the reverse direction, and the frost adhering to the refrigerant evaporator 14 is melted by the heat generated by the flow, thereby realizing a defrosting operation, i.e., a reverse cycle defrosting operation. Note that the specific form of the defrosting operation is not particularly limited as long as it does not deviate from the spirit of the present invention. For example, the heating device 1 may be configured to be able to perform a hot gas bypass operation, and the hot gas bypass defrosting operation may be performed.

[0037] The water tank 3 is provided with a water temperature sensor 31 that continuously detects the temperature Ta of the water Wa in the water tank 3. Note that the higher the temperature Ta, the higher the amount of heat stored in the water Wa stored in the water tank 3 (hereinafter, sometimes simply referred to as the "heat storage amount HS"). Therefore, the value of the temperature Ta can be seen as a type of heat storage correlation value Z that correlates with the heat storage amount HS, and the water temperature sensor 31 can be seen as a form of heat storage correlation value detection means that detects the heat storage correlation value Z. Note that the heat storage correlation value Z is not limited to the value of the temperature Ta, and other examples of the heat storage correlation value Z will be described later.

[0038] Information on the temperature Ta detected by the water temperature sensor 31 is continuously sent to the control unit 2. When the water Wa is circulated through a path including the heating device 1 and the water tank 3 as in this embodiment, the water temperature sensor 31 may detect the outlet water temperature or inlet water temperature of the heating device 1 instead of detecting the temperature of the hot water stored in the water tank 3.

[0039] The control unit 2 has a heating operation control unit 21 , a defrosting necessity determination unit 22 , and a defrosting operation control unit 23 .

[0040] The heating operation control unit 21 controls the start and end of the heating operation of the heating device 1 based on the heat storage correlation value Z, which is information detected by the heat storage correlation value detection means (the service water temperature sensor 31 in this embodiment). In this embodiment, the heating operation control unit 21 starts the heating operation when the heat storage correlation value Z drops to a predetermined lower threshold PL, and ends the heating operation when the heat storage correlation value Z reaches a predetermined upper threshold PH (a value greater than the lower threshold PL). That is, the heating operation control unit 21 starts the heating operation when the detected temperature Ta drops to a predetermined first set temperature (a temperature corresponding to the lower threshold PL), and ends the heating operation when the detected temperature Ta rises to a second set temperature (a temperature corresponding to the upper threshold PH) that is higher than the first set temperature.

[0041] As a result, the heating operation is performed so that the heat storage correlation value Z basically falls within the range from the lower threshold value PL to the upper threshold value PH. From the perspective of the degree of recovery of the heat storage amount HS within this range, when the heat storage correlation value Z is the lower threshold value PL, it can be said that the heat storage amount HS is not recovered at all (the degree of recovery is 0%), and when the heat storage correlation value Z is the upper threshold value PH, it can be said that the heat storage amount HS is completely recovered (100% recovered). Note that if the defrosting operation is being performed when the heat storage correlation value Z drops to the lower threshold value PL (when the heating operation start condition is satisfied), the defrosting operation may be forcibly terminated to give priority to the start of the heating operation.

[0042] The control unit 2 may change the upper threshold value PH (e.g., 60°C) to a higher value (e.g., 65°C) when the temperature detected by the air temperature sensor 14y (which can be considered the outside air temperature) is below a specified temperature (e.g., 10°C). This allows the heat storage amount HS at the start of defrosting operation to be kept higher when the outside air temperature is relatively low. Therefore, even when reverse cycle defrosting operation is performed, for example, it is possible to minimize an excessive decrease in the heat storage amount HS and satisfy the heat demand of the load equipment X.

[0043] During the heating operation, the defrost necessity determination unit 22 determines whether a defrosting operation is required for the refrigerant evaporator 14. In this embodiment, the defrost necessity determination unit 22 determines whether a defrosting operation is required based on the temperatures detected by the air temperature sensor 14y (air temperature detection means) and the refrigerant temperature sensor 14x (refrigerant temperature detection means). More specifically, the defrost necessity determination unit 22 determines that a defrosting operation is required when the difference ΔT between the temperatures detected by the air temperature sensor 14y and the refrigerant temperature sensor 14x exceeds a specified value Ts.

[0044] As the frost layer grows on the heat transfer surface of the refrigerant evaporator 14, thermal resistance and ventilation resistance increase, and the difference ΔT between the temperature detected by the air temperature sensor 14y and the temperature detected by the refrigerant temperature sensor 14x becomes larger. Therefore, when the difference ΔT exceeds a specified value Ts, it is possible to determine that a defrosting operation for the refrigerant evaporator 14 is necessary. The specific value of the specified value Ts may be set appropriately in advance so that the need for a defrosting operation can be appropriately determined. For example, if it is desired to determine the need for a defrosting operation when frost on the heat transfer surface is in the early stages of growth, the specified value Ts is set to a relatively small value. However, if it is desired to determine the need for a defrosting operation when frost is in the advanced growth stage, the specified value Ts is set to a relatively large value.

[0045] In this embodiment, as described above, the necessity of a defrosting operation is determined based on the temperatures detected by the air temperature sensor 14y and the refrigerant temperature sensor 14x, and therefore, it is possible to very accurately determine whether a defrosting operation is necessary. However, the method for determining whether a defrosting operation is necessary is not limited to the method described above, and various methods, including well-known methods, may be used, for example, a method for determining whether a defrosting operation is necessary based on the temperature detected by only one of the air temperature sensor 14y and the refrigerant temperature sensor 14x.

[0046] When the conditions for starting the defrost operation are satisfied, the defrost operation control unit 23 starts the defrost operation of the heating device 1. The flow of main processes performed by the defrost operation control unit 23 will be described with reference to the flowchart shown in FIG.

[0047] The defrost operation control unit 23 continuously monitors whether or not the defrost necessity determination unit 22 has determined that a defrost operation is necessary (step S1). If it has determined that a defrost operation is necessary (Yes in step S1), the defrost operation control unit 23 then continuously monitors whether or not a predetermined heat storage sufficiency condition Q based on the heat storage correlation value Z is satisfied (step S2).

[0048] If the heat storage sufficient condition Q is satisfied (Yes in step S2), the defrost operation control unit 23 determines that the start condition of the defrost operation is satisfied and starts the defrost operation (step S3). Thereafter, the defrost operation control unit 23 continues the defrost operation until the end condition of the defrost operation is satisfied (step S4). When this end condition is satisfied (Yes in step S4), the defrost operation control unit 23 ends the current defrost operation (step S5) and repeats the process of step S1.

[0049] As described above, the defrost operation control unit 23 starts the defrost operation of the heating device 1 when the defrost necessity determination unit 22 determines that a defrost operation is necessary and the heat storage sufficient condition Q is satisfied. Thereafter, the defrost operation control unit 23 continues the defrost operation until the above-described termination condition is satisfied. This termination condition is set as a condition that is satisfied when it is expected that the purpose of the current defrost operation has been achieved. For example, the termination condition may be a condition that is satisfied when the difference between the air temperature (outside air temperature) and the refrigerant temperature (outlet temperature) of the refrigerant evaporator 14 exceeds a required threshold value, or a condition that is satisfied when a predetermined time td has elapsed since the start of the defrost operation.

[0050] The predetermined time td can be set longer as the specified value Ts described above is relatively larger, and shorter as the specified value Ts is relatively smaller. That is, when the specified value Ts is relatively small, it is possible to determine whether or not a defrosting operation is necessary when frost has already formed on the heat transfer surface, as described above. Therefore, complete defrosting is possible even if the defrosting operation is completed in a short time. Furthermore, the predetermined time td can be corrected according to the duration tc of the heating operation after it is determined by any of the determination methods that a defrosting operation is necessary. That is, when the duration tc is relatively long, frost growth is likely to progress, so it is advisable to correct the predetermined time td to be longer.

[0051] It is also preferable to provide a required interval time (e.g., an interlock time of about 0.5 to 1 hour) between the end of a defrosting operation and the start of the next defrosting operation. By providing an interval time, the ratio of the defrosting operation time to the total operation time can be reduced, thereby suppressing a decrease in the coefficient of performance (COP) of the heat pump.

[0052] The heat storage sufficiency condition Q is set so as to enable appropriate and continuous heat supply from the water tank 3 to the load equipment X. Note that the stricter the heat storage sufficiency condition Q, the more stable the heat supply becomes, but the timing of the start of the defrosting operation tends to be delayed accordingly. Therefore, it is preferable to set the heat storage sufficiency condition Q to an appropriate condition, taking into consideration the application and usage conditions of the hot water production system 100.

[0053] As an example, the heat storage sufficient condition Q may be a condition that is satisfied when the heat storage correlation value Z reaches the upper threshold value PH (hereinafter, for convenience, this condition may be referred to as the "first heat storage sufficient condition Q1"). As a result, the defrosting operation is performed when the heat storage amount HS is fully (100%) restored. Therefore, even if a heat demand occurs in the load equipment X during the defrosting operation, the heat supply from the water tank 3 to the load equipment X can be continued as stably as possible.

[0054] Alternatively, the heat storage sufficient condition Q may be set to a predetermined value equal to or greater than the median value in the range from the upper threshold PH to the lower threshold PL and less than the upper threshold PH, and the condition Q is satisfied when the heat storage correlation value Z reaches this predetermined value (hereinafter, for convenience, this condition may be referred to as the "second heat storage sufficient condition Q2"). In this way, the defrosting operation is performed when the heat storage amount HS is restored to more than half (50% or more and less than 100%). Therefore, even if a heat demand occurs in the load equipment X during the defrosting operation, the heat supply from the water tank 3 to the load equipment X can continue without causing any problems. For example, if the lower threshold PL (the starting temperature of the heating operation) is set to 55°C and the upper threshold PH (the ending temperature of the heating operation) is set to 65°C, the second heat storage sufficient condition Q2 is satisfied when the temperature Ta, which is the heat storage correlation value Z, reaches the predetermined reference value, which is equal to or greater than 60°C and less than 65°C.

[0055] The heating operation control unit 21 may control the rotation speed of the refrigerant compressor 11 to decrease stepwise or continuously as the temperature Ta detected by the service water temperature sensor 31 increases. In this case, the thermal storage sufficient condition Q may be a condition that is satisfied when the rotation speed of the refrigerant compressor 11 falls below a specified value (hereinafter, for convenience, this condition may be referred to as the "third thermal storage sufficient condition Q3"). This makes it possible to start the defrosting operation at an appropriate timing based on the rotation speed. Note that the rotation speed is related to the value of the temperature Ta, which is the thermal storage correlation value Z, so the third thermal storage sufficient condition Q3 can be considered one form of a condition based on the thermal storage correlation value Z.

[0056] According to the hot water production system 100 described above, the water Wa heated by the heating device 1 is stored in the water tank 3, and this stored heated water Wa can be supplied to the load equipment X to meet the heat demand.

[0057] Various changes can be made to the specific configuration of the hot water production system 100 without departing from the spirit of the present invention. For example, as shown in Figure 4, the hot water production system 100 may be configured to supply water Wa to a hot water supply load (load equipment X that consumes water Wa and does not return the water Wa to the water tank 3) instead of a heat supply load.

[0058] In the hot water production system 100 shown in Figure 4, the water Wa supplied from the water tank 3 via the third water line L3 to the load equipment X is consumed by the load equipment X. Therefore, the installation of the fourth water line L4 (a path for circulating the water Wa from the load equipment X to the water tank 3) is omitted. In addition, the amount of water Wa reduced by the supply to the load equipment X is replenished to the water tank 3 from the water supply source Y via the fifth water line L5.

[0059] Furthermore, in this embodiment, the value of the temperature Ta is used as the heat storage correlation value Z, but it is also possible to use another value correlated with the heat storage amount HS as the heat storage correlation value Z. For example, since the higher the water level of the water Wa in the water tank 3, the higher the heat storage amount HS, this water level value may be used as the heat storage correlation value Z. In this case, as shown in FIG. 5 , a water level sensor 32 may be provided that continuously detects the water level WL of the water Wa in the water tank 3, and information on the water level WL detected by the water level sensor 32 may be continuously sent to the control unit 2. The water level sensor 32 may be considered as one form of heat storage correlation value detection means that detects the heat storage correlation value Z.

[0060] Even when the water level WL is used as the heat storage correlation value Z in this way, the heating operation control unit 21 starts the heating operation when the heat storage correlation value Z drops to a predetermined lower threshold PL, and ends the heating operation when the heat storage correlation value Z reaches a predetermined upper threshold PH (a value greater than the lower threshold PL). That is, the heating operation control unit 21 starts the heating operation when the detected water level WL drops to a predetermined first set water level (a water level corresponding to the lower threshold PL), and ends the heating operation when the detected water level WL rises to a second set water level (a water level corresponding to the upper threshold PH) that is higher than the first set water level.

[0061] In the hot water production system 100 shown in Fig. 5, the first water line L1 is a water path that circulates water Wa from an external water supply Y to the heating device 1. The water Wa that flows into the heating device 1 through this first water line L1 is heated in the condenser 12, as in the example shown in Fig. 2, and then flows into the water tank 3 via the second water line L2.

[0062] 5 includes a water path that allows the water Wa sent from the water supply source Y to the water tank 3 to flow through the heating device 1. In addition, in the hot water production system 100 shown in Fig. 5, a hot water supply load is used as the load equipment X, and the installation of the fourth water line L4 (a path that circulates the water Wa from the load equipment X to the water tank 3) is omitted, as in the example shown in Fig. 4.

[0063] Furthermore, particularly when a sealed tank is used as the water tank 3, the greater the amount of remaining hot water associated with the temperature stratification of the water Wa formed in the water tank 3, the higher the heat storage amount HS, and so the value of this remaining hot water amount may be used as the heat storage correlation value Z. In this case, as illustrated in FIG. 6 , a group of temperature sensors 33 may be provided to detect the remaining hot water amount WV associated with the temperature stratification of the water Wa formed in the water tank 3 (sealed tank), and the detection information of the remaining hot water amount WV by the group of temperature sensors 33 may be continuously sent to the control unit 2. The group of temperature sensors 33 is a plurality of temperature sensors arranged in a vertical direction (the direction in which temperature stratification is formed) within the water tank 3. The group of temperature sensors 33 may be considered to be one form of heat storage correlation value detection means for detecting the heat storage correlation value Z.

[0064] Even when the remaining hot water amount WV is used as the heat storage correlation value Z in this way, the heating operation control unit 21 starts the heating operation when the heat storage correlation value Z falls to a predetermined lower threshold value PL, and ends the heating operation when the heat storage correlation value Z reaches a predetermined upper threshold value PH (a value greater than the lower threshold value PL). That is, the heating operation control unit 21 starts the heating operation when the detected remaining hot water amount WV falls to a predetermined first set remaining hot water amount (a water level corresponding to the lower threshold value PL), and ends the heating operation when the detected remaining hot water amount WV increases to a second set remaining hot water amount (a water level corresponding to the upper threshold value PH) that is higher than the first set remaining hot water amount.

[0065] In the hot water production system 100 shown in Figure 6, a hot water supply load is also used as the load equipment X, and the installation of the fourth water line L4 (a path for circulating the water Wa from the load equipment X to the water tank 3) is omitted, as in the example shown in Figure 4. The water Wa that is reduced by the supply to the load equipment X is replenished near the bottom of the water tank 3 from the water supply source Y via the fifth water line L5.

[0066] The first water line L1 and the second water line L2 shown in Figure 6 form a water path (a circulation path for the water Wa that includes the water tank 3 and the heating device 1) that allows the water Wa in the water tank 3 to be circulated to the heating device 1. Furthermore, the first water line L1 is connected near the bottom end of the water tank 3, and the second water line L2 is connected near the top end. This makes it possible to supply the relatively low-temperature water Wa in the water tank 3 to the heating device 1, and to return the water Wa after heating in the heating device 1 to the top end of the water tank 3. Furthermore, the third water line L3 is connected near the top end of the water tank 3, making it possible to supply high-temperature water Wa (the water Wa in the top layer of the temperature stratification) to the load equipment X.

[0067] 2. Second Embodiment Next, a second embodiment will be described. In the description of the second embodiment, emphasis will be placed on the differences from the first embodiment, and descriptions of the commonalities with the first embodiment may be omitted.

[0068] FIG. 7 is a schematic diagram of a hot water production system 100 according to a second embodiment. As shown in this figure, the hot water production system 100 includes a plurality of heating devices 1a-1c (three in the example of FIG. 7 ), each having an air-source heat pump 10 (hereinafter, these may be collectively referred to as "heating devices 1"); a plurality of control units 2a-2c (hereinafter, these may be collectively referred to as "control units 2") corresponding to the heating devices 1a-1c; a water tank 3 for storing water Wa heated by each heating device 1a-1c; and a central control unit 4 for centrally controlling the control units 2a-2c. The central control unit 4 corresponds to a system controller that centralizes the control units 2a-2c (local controllers) and may correspond to a master unit in this control system.

[0069] 7, in the hot water production system 100, the first water line L1 is a path for circulating the water Wa from the water tank 3 to each of the heating devices 1a to 1c, and the second water line L2 is a path for circulating the water Wa from each of the heating devices 1a to 1c to the water tank 3. The first water line L1 and the second water line L2 form a water path (a water Wa circulation path that includes the water tank 3 and each of the heating devices 1a to 1c arranged in parallel) that enables the water Wa in the water tank 3 to be circulated to each of the heating devices 1a to 1c. A pump (not shown) is disposed in this water path, and the water Wa is circulated in the direction indicated by the colored arrow.

[0070] According to the hot water production system 100, the hot water Wa can be heated using a plurality of heating devices 1a to 1c, which makes it possible to more stably ensure the heat storage amount HS. Also, in the hot water production system 100, the heat storage satisfaction condition Q can be, for example, the first to third heat storage satisfaction conditions Q1 to Q3 described above.

[0071] When the second heat storage sufficiency condition Q2 is adopted as the heat storage sufficiency condition Q, the heat storage amount HS is said to be partially restored when this condition is satisfied. Therefore, when the second heat storage sufficiency condition Q2 is adopted in an embodiment in which a plurality of heating devices 1 are installed, as in the present embodiment, even if a large number of heating devices 1 that should perform the defrost operation appear at the same time, it is preferable to have the defrost operation performed in sequence, for example, one or two devices at a time, so as to minimize the shortage of heat supply from the heating devices 1.

[0072] Therefore, in this embodiment, a priority is assigned to each of the multiple heating devices 1a to 1c, and the central control unit 4 (defrost operation control unit) keeps the number of heating devices 1 that perform defrost operation at the same time below a specified number. More specifically, when the number of heating devices 1 that perform defrost operation at the same time exceeds the specified number, the central control unit 4 starts the defrost operation of the excess heating devices 1 in order of priority, after the defrost operation that was previously performed has finished.

[0073] That is, when the number of heating devices 1 currently performing defrosting operation has not reached the specified number, if a heating device 1 that should perform defrosting operation (a heating device 1 that satisfies the conditions for starting defrosting operation) appears, the central control unit 4 permits the execution of defrosting operation for that heating device 1. On the other hand, when the number of heating devices 1 currently performing defrosting operation has reached the specified number, even if a heating device 1 that should perform defrosting operation appears, the central control unit 4 suspends the execution of defrosting operation for that heating device 1 until the number of heating devices 1 currently performing defrosting operation does not reach the specified number. Furthermore, when the number of heating devices 1 currently performing defrosting operation has not reached the specified number and the execution of defrosting operation for multiple heating devices 1 is suspended, the defrosting operation of the heating device 1 with the highest priority is started first.

[0074] For example, assume that the specified number of units is set to "1 unit" and that, while heating device 1a is performing a defrosting operation, heating devices 1b and 1c also need to perform a defrosting operation (the conditions for starting a defrosting operation are met). However, under these circumstances, if defrosting operation of heating device 1b or heating device 1c were to be started, the number of heating devices performing a defrosting operation at the same time would exceed the specified number. Therefore, the central control unit 4 postpones the start of defrosting operation of the other heating devices 1b and 1c until the defrosting operation of heating device 1a is completed. Then, after the defrosting operation of heating device 1a is completed, the central control unit 4 starts the defrosting operation of heating device 1b or heating device 1c, whichever has the higher priority.

[0075] In this embodiment, since the multiple heating devices 1 are defrosted in turn, even if the heat storage capacity HS is partially restored, heat supply can be continued using the heating devices 1 waiting for defrosting. Furthermore, even if a configuration is adopted in which the water Wa is heated by circulating the water through each of the heating devices 1a to 1c and the water tank 3, and a configuration in which defrosting operation is performed by reverse cycle defrosting, it is possible to suppress a decrease in the heat storage capacity HS of the water tank 3.

[0076] When the first heat storage fulfillment condition Q1 is adopted as the heat storage fulfillment condition Q, it is assumed that the heat demand of the load equipment X is low when this condition is fulfilled (i.e., when the heating operation termination condition is fulfilled). Therefore, in this case, there is no limit to the number of heating devices 1 that perform the defrost operation at the same time, and the defrost operation may be performed immediately in any heating device 1 as soon as the defrost operation start condition is fulfilled.

[0077] 3. Others As described above, the hot water production system 100 of each embodiment heats the service water Wa to be used in the load equipment X within a business premises, and includes a heating device 1 (a device having an air-source heat pump 10 having a refrigerant evaporator 14 and a refrigerant compressor 11, and capable of performing a heating operation to heat the service water Wa using the air-source heat pump 10 and a defrost operation to defrost the refrigerant evaporator 14), a service water tank 3 to store the heated service water Wa, heat storage correlation value detection means for detecting a heat storage correlation value Z that correlates with the amount of heat stored in the service water Wa stored in the service water tank 3, and a control unit 2 to control the air-source heat pump 10.

[0078] Furthermore, the control unit 2 includes a heating operation control unit 21 that controls the start and end of the heating operation based on the heat storage correlation value Z, a defrost necessity determination unit 22 that determines whether the defrosting operation is necessary while the heating operation is being performed, and a defrost operation control unit 23 that starts defrost operation when the defrost necessity determination unit 22 determines that the defrosting operation is necessary and the heat storage sufficiency condition Q based on the heat storage correlation value Z is satisfied.

[0079] Therefore, in the hot water production system 100, it is possible to perform the defrosting operation of the air-source heat pump 10 when the heat storage capacity HS has been sufficiently or to some extent restored. This makes it possible to continue to supply heat to the load equipment X more stably, without incurring an increase in equipment costs, even when the defrosting operation of the air-source heat pump 10 is performed.

[0080] The heating operation in this embodiment includes either a circulation heating operation of service water Wa (reservoir water) as in the example of Fig. 1 or a once-through heating operation of service water Wa (make-up water) as in the example of Fig. 5. Furthermore, the end of the heating operation in this embodiment means the end of the corresponding heating operation in a heating device 1 configured to perform only one of the once-through heating operation and the circulation heating operation, and means the end of both heating operations in a heating device 1 configured to perform both.

[0081] It should be noted that the above-described embodiments are illustrative in all respects and should not be considered limiting. The technical scope of the present invention is defined by the claims, not by the description of the above-described embodiments, and should be understood to include all modifications that fall within the meaning and scope of the claims.

[0082] <Contribution to the United Nations-led Sustainable Development Goals (SDGs)> The hot water production system according to the present disclosure uses an air-source heat pump that heats water using electricity and does not use fossil fuels. Therefore, by promoting the reduction of carbon dioxide emissions, it can contribute to the realization of Goal 13 of the Sustainable Development Goals (SDGs), "Take urgent action to combat climate change."

[0083] The present invention can be used in a hot water production system for heating water.

[0084] REFERENCE SIGNS LIST 1, 1a to 1c Heating device 2, 2a to 2c Control unit 3 Water tank 4 General control unit 10 Air source heat pump 11 Refrigerant compressor 12 Condenser 13 Expansion valve 14 Refrigerant evaporator 14x Refrigerant temperature sensor 14y Air temperature sensor 15 Four-way valve 21 Heating operation control unit 22 Defrost necessity determination unit 23 Defrost operation control unit 31 Water temperature sensor 32 Water level sensor 33 Temperature sensor group 100 Hot water production system L1 First water line L2 Second water line L3 Third water line L4 Fourth water line L5 Fifth water line Lc Refrigerant circulation line R Refrigerant Wa Water X Load equipment Y Water supply source

Claims

1. A hot water production system that heats water used in load equipment within a business, the hot water production system comprising: a heating device having an air-source heat pump with a refrigerant evaporator and a refrigerant compressor, and capable of performing a heating operation that heats the water using the air-source heat pump, and a defrost operation that defrosts the refrigerant evaporator; a water tank that stores the heated water; a heat storage correlation value detection means that detects a heat storage correlation value that correlates with the amount of heat stored in the water stored in the water tank; and a control means that controls the air-source heat pump, the control means including: a heating operation control unit that controls the start and end of the heating operation based on the heat storage correlation value; a defrost necessity determination unit that determines whether the defrost operation is necessary while the heating operation is being performed; and a defrost operation control unit that starts the defrost operation when the defrost necessity determination unit determines that the defrost operation is necessary and a predetermined heat storage sufficiency condition based on the heat storage correlation value is satisfied.

2. The hot water production system of claim 1, wherein the heating operation control unit terminates the heating operation when the heat storage correlation value reaches a predetermined upper threshold, and the heat storage sufficiency condition is a condition that is satisfied when the heat storage correlation value reaches the upper threshold.

3. The hot water production system of claim 1, wherein the heating operation control unit starts the heating operation when the heat storage correlation value drops to a predetermined lower threshold and ends the heating operation when the heat storage correlation value reaches a predetermined upper threshold, and the heat storage sufficiency condition is a condition that is met when the heat storage correlation value reaches a predetermined value, and the predetermined value is a value that is equal to or greater than the median of the range from the upper threshold to the lower threshold and is less than the upper threshold.

4. A hot water production system as described in claim 3, comprising a plurality of heating devices and a control means corresponding to each of the heating devices, and further comprising a defrost operation control unit that keeps the number of heating devices that are simultaneously executing the defrost operation below a specified number, and a priority is assigned to each of the plurality of heating devices, and the defrost operation control unit is configured so that when the number of heating devices that are simultaneously executing the defrost operation exceeds the specified number, the defrost operation of the excess heating devices is started in order of the heating devices with the highest priority after the defrost operation that was executed first has finished.

5. A hot water production system as described in claim 2 or claim 3, further comprising a water path that enables the water in the water tank to be circulated to the heating device, and wherein the heat storage correlation value detection means detects the temperature of the water in the water tank as the heat storage correlation value.

6. A hot water production system as described in claim 1, further comprising a water path that enables the water in the water tank to be circulated to the heating device, wherein the heat storage correlation value detection means detects the temperature of the water in the water tank as the heat storage correlation value, and the heating operation control unit controls the refrigerant compressor to reduce its rotation speed as the detected temperature increases, and the heat storage sufficiency condition is a condition that is satisfied when the rotation speed falls below a specified number.

7. A hot water production system as described in claim 2 or claim 3, which is provided with a water path that allows the water sent from a water source to the water tank to flow through the heating device, and the heat storage correlation value detection means detects the water level of the water in the water tank as the heat storage correlation value.

8. A hot water production system as described in claim 2 or claim 3, which is provided with a water path that enables the water in the water tank to be circulated to the heating device, and the heat storage correlation value detection means detects the amount of remaining hot water related to the temperature stratification of the water formed in the water tank as the heat storage correlation value.

9. A hot water production system as described in any one of claims 1 to 3, comprising an air temperature detection means for detecting the temperature of the heat source air before heat exchange in the refrigerant evaporator, and a refrigerant temperature detection means for detecting the temperature of the refrigerant after heat exchange in the refrigerant evaporator, wherein the defrost necessity determination unit determines whether or not the defrosting operation is necessary based on the temperatures detected by the air temperature detection means and the refrigerant temperature detection means, respectively.

10. A hot water production system as described in claim 9, further comprising a water path that enables the water in the water tank to be circulated to the heating device, wherein the heat storage correlation value detection means detects the temperature of the water in the water tank as the heat storage correlation value, and the heating operation control unit terminates the heating operation when the heat storage correlation value reaches a predetermined upper threshold value, and when the temperature detected by the air temperature detection means is below a specified temperature, changes the upper threshold value to a value higher than that.

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