Vacuum water heater

Abstract

To provide a vacuum type water warmer capable of improving a performance coefficient even in an operational state where a temperature of heat medium water is high, the vacuum type water warmer which heats the heat medium water by a condenser of a heat pump unit.SOLUTION: A vacuum type water warmer includes: an encapsulation container 2 in which heat medium water W is encapsulated and which is held in a state where a pressure is reduced equal to or lower than an atmospheric pressure; a heat exchanger 7 for circulation temperature rise which condenses and liquefies steam generated by heating the heat medium water W through indirect heat exchange with supplied circulation hot water; and a heat pump unit 15 to which an expansion valve 12, an evaporator 13, a compressor 14, a condenser 11 and a subcooler 16 are successively connected and which includes a main circulation path 17 for circulating a cooling medium. The condenser 11 is disposed inside of the encapsulation container 2 in order to heat the heat medium water W and, at an outside of the encapsulation container 2, the subcooler 16 dissipates heat of the cooling medium passing through the condenser 11 through the indirect heat exchange with the circulation hot water.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a vacuum water heater that heats heat transfer water sealed in a sealed container under reduced pressure and in a nearly vacuum state, boils it at a low temperature of 100°C or less, and uses the steam as a heat source to heat water and generate hot water. [Background technology]

[0002] Conventionally, as a vacuum type water heater of this type, for example, one with a structure shown in Figure 5 has been known (Patent Document 1, etc.). The vacuum type water heater 1E shown in Figure 5 includes a sealed container 2, a combustion burner 3, a furnace (combustion chamber) 4, a reduced pressure steam chamber 5, heat transfer water W, heat exchangers 6 and 7, a water tube group 8, an automatic air extraction device 9, etc. The pressure inside the sealed container 2 is reduced to below atmospheric pressure by the automatic air extraction device 9 to create a near-vacuum state, and in this state the heat transfer water W is heated and boiled by the combustion burner 3 to generate steam in the reduced pressure steam chamber 5 that is the same temperature as the heat transfer water W at that time, and the steam condenses on the surfaces of the heat exchangers 6 and 7, heating the water in the heat exchangers 6 and 7 to produce hot water.

[0003] This vacuum water heater 1E has the advantage that the pressure inside the sealed container 2 is reduced, so that hot water at the required temperature can be quickly supplied to the load side even during high-load operation when a large amount of hot water is extracted from the heat exchangers 6 and 7.

[0004] However, in a vacuum water heater in which heat transfer water is heated by a combustion burner 3 as shown in FIG. 5, the thermal efficiency is approximately 80% to 95%, and it is difficult to obtain a thermal efficiency higher than this.

[0005] In order to improve the thermal efficiency, it has been proposed to provide a heat recovery device that recovers the latent heat of the water vapor contained in the combustion exhaust gas (see, for example, Patent Document 2). However, since the heat recovery device is provided separately, the entire device becomes larger, and white smoke is generated as the combustion exhaust gas is cooled by heat exchange. Also, the water vapor in the combustion exhaust gas condenses, resulting in the generation of low-pH condensate, and corrosion countermeasures and a device for neutralizing the condensate are required, which increase the initial cost.

[0006] Therefore, the present inventors have proposed a method of increasing efficiency by heating the heat transfer water W of a vacuum water heater 1F using a refrigerant heat exchanger (hereinafter referred to as "condenser 11") of a heat pump unit 10, as shown in Fig. 6 (Patent Document 3). In Fig. 6, reference numeral 12 denotes an expansion valve, reference numeral 13 denotes an evaporator, and reference numeral 14 denotes a compressor, and the same reference numerals are used for components similar to those in Fig. 5. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 11-337002 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-102906 [Patent Document 3] Patent Publication No. 2021-105491 Summary of the Invention [Problem to be solved by the invention]

[0008] In a typical vacuum water heater, when the outlet temperature is 80°C or when hot water is used in the heating circuit (hot water heat exchanger inlet temperature 55°C, outlet temperature 70°C), the heat transfer water temperature is controlled between 85°C and 90°C. When a vacuum water heater operating at such a heat transfer water temperature is incorporated into a heat pump unit that heats the heat transfer water, as shown in Figure 6, it is desirable to use a refrigerant with a high critical temperature suitable for a high-temperature heat pump cycle. Using R134a, a commercially available pure refrigerant, as an example, and examining the Mollier diagram shown in Figure 7, for example, to provide heat in the condenser to a heat transfer water temperature of 88°C, the refrigerant circulating through the heat pump unit must be compressed to a pressure at which its saturation temperature exceeds the heat transfer water temperature. (If the condenser pinch temperature difference between the 88°C heat transfer water and the 88°C heat transfer water is 2°C, the refrigerant's saturation temperature will be 90°C and its saturation pressure will be 3.2 MPa.) When a compressor is operated at a high compression ratio, the adiabatic efficiency of the compressor generally decreases (the compressor's power increases), which reduces the COP (coefficient of performance) of the heat pump cycle. Furthermore, because the refrigerant in the heat pump unit does not drop below the heat transfer water temperature, even if usable heat remains in the refrigerant, it cannot be used, and the cycle becomes 1' → 2' → 3 → 4 as shown in the Mollier diagram in Figure 7, and the COP further decreases because the amount of heat released from the condenser to the heat transfer water is small.

[0009] SUMMARY OF THE INVENTION Accordingly, a main object of the present invention is to provide a vacuum type water heater that can improve the COP in a vacuum type water heater that heats heat transfer water using a condenser of a heat pump unit. [Means for solving the problem]

[0010] In order to solve the above problems, a vacuum water heater according to one aspect of the present invention includes an airtight container in which heat transfer water is sealed and maintained at a reduced pressure below atmospheric pressure, a circulating heating heat exchanger that condenses and liquefies steam generated by heating the heat transfer water through indirect heat exchange with supplied circulating hot water, and a heat pump unit having a main circulation path for circulating refrigerant in which an expansion valve, an evaporator, a compressor, a condenser, and a supercooler are connected in sequence, wherein the condenser is arranged within the airtight container to heat the heat transfer water, and the supercooler is configured to dissipate heat from the refrigerant that has passed through the condenser through indirect heat exchange with the circulating hot water outside the airtight container.

[0011] In one aspect, the vacuum type water heater includes a bypass passage connected to the main circulation passage and bypassing the subcooler between the condenser and the expansion valve, and a bypass passage extending from an outlet of the expansion valve to the compression machine an internal heat exchanger for dissipating heat from the refrigerant bypassing the subcooler through the bypass passage by indirect heat exchange with the refrigerant flowing through the main circulation passage up to the inlet of the refrigerant bypassing the subcooler through the bypass passage; a flow rate regulator for regulating the flow rate of the refrigerant bypassing the subcooler through the bypass passage; a first temperature detector for detecting the temperature of the refrigerant entering the expansion valve; a pressure detector for detecting the pressure of the refrigerant entering the expansion valve; and a control unit for calculating the degree of subcooling of the refrigerant from the condenser to the expansion valve based on the detection values ​​of the first temperature detector and the pressure detector, and controlling the flow rate regulator so that the calculated degree of subcooling becomes a predetermined degree of subcooling.

[0012] In another aspect, the vacuum water heater further includes a bypass passage connected to the main circulation passage and bypassing the subcooler between the condenser and the expansion valve, and a bypass passage extending from an outlet of the expansion valve to the compression valve. machinean internal heat exchanger for dissipating heat from the refrigerant flowing through the bypass passage by indirect heat exchange with the refrigerant flowing through the main circulation passage up to the inlet of the bypass passage; a flow rate regulator for regulating the flow rate of the refrigerant bypassing the subcooler through the bypass passage; a first temperature detector for detecting the temperature of the refrigerant entering the expansion valve; a second temperature detector for detecting the temperature of the refrigerant leaving the condenser; and a control unit for calculating the degree of subcooling of the refrigerant from the condenser to the expansion valve based on the detection values ​​of the first temperature detector and the second temperature detector, and controlling the flow rate regulator so that the calculated degree of subcooling becomes a predetermined degree of subcooling.

[0013] In one aspect, the circulating heating heat exchanger includes a first circulating heating heat exchanger to which first circulating hot water at a first temperature is supplied, and a second circulating heating heat exchanger to which second circulating hot water at a second temperature lower than the first temperature is supplied, and the supercooler includes a first supercooler and a secondary supercooler connected to the secondary side of the first supercooler, and is configured so that after the first supercooler exchanges heat with the first circulating hot water supplied to the first circulating heating heat exchanger, the secondary supercooler exchanges heat with the second circulating hot water supplied to the second circulating heating heat exchanger.

[0014] In one aspect, the condenser is a condenser that condenses the gaseous refrigerant at a temperature equal to or higher than the saturation temperature of the heat transfer water, thereby releasing latent heat to the heat transfer water, and the supercooler is a supercooler that releases sensible heat to the circulating hot water at a temperature equal to or lower than the heat transfer water.

[0015] In one aspect, the system further includes a hot water supply heat exchanger, and the subcooler is provided only for heat exchange with the circulating hot water circulating through the circulation heating heat exchanger.

[0016] In one embodiment, the heat pump unit is a high-temperature heat pump cycle unit in which the critical temperature of the refrigerant exceeds 92°C.

[0017] In one aspect, the vacuum water heater further includes an auxiliary heating device, which has a furnace and a group of water tubes arranged so as to be submerged in the heat transfer water, and the condenser is arranged above the auxiliary heating device. [Effects of the Invention]

[0018] According to the vacuum type water heater of the present invention, the refrigerant cooled in the condenser dissipates heat to the circulating hot water when passing through the supercooler, thereby improving the COP.

[0019] That is, if the ideal heat pump cycle is treated as a reverse Carnot cycle, the COP can be expressed only by the temperature, as shown in the following equation.

[0020] COP=T2 / (T1-T2) Here, T1 is the temperature of the low temperature part (evaporator), and T2 is the temperature of the high temperature part (condenser).

[0021] The COP improves as the temperature difference between the high-temperature part and the low-temperature part decreases. In the vacuum water heater of Patent Document 3, the temperature of the high-temperature part of the heat pump cannot be made lower than the heat transfer water temperature, so there is a limit to how much the COP can be improved. However, according to the present invention, by providing a supercooler, the average temperature of the high-temperature part decreases, and the temperature difference with the low-temperature part decreases, improving the COP.

[0022] In addition, by dissipating heat from the refrigerant that bypasses the supercooler through indirect heat exchange in an internal heat exchanger installed in the heat cycle unit, the desired degree of supercooling can be obtained even when the degree of supercooling achieved by the supercooler is small. [Brief explanation of the drawings]

[0023] [Figure 1] 1 is a partially omitted vertical sectional front view showing a vacuum type hot water machine according to a first embodiment of the present invention. [Figure 2] FIG. 5 is a partially omitted vertical sectional front view showing a vacuum type hot water machine according to a second embodiment of the present invention. [Figure 3]FIG. 10 is a partially omitted vertical sectional front view showing a vacuum type hot water machine according to a third embodiment of the present invention. [Figure 4] FIG. 10 is a longitudinal sectional front view of a main part showing a vacuum type water heater according to a fourth embodiment of the present invention. [Figure 5] FIG. 1 is a vertical cross-sectional view showing a conventional vacuum type water heater. [Figure 6] FIG. 10 is a vertical cross-sectional view showing another conventional vacuum type water heater. [Figure 7] 1 is a pressure-enthalpy diagram (Mollier diagram) showing the heat cycles of an example of a vacuum water heater according to the present invention and a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0024] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A vacuum water heater according to an embodiment of the present invention will be described with reference to the drawings. In all drawings and embodiments, including the background art, the same or similar components are designated by the same reference numerals.

[0025] First, a vacuum type water heater 1A according to a first embodiment of the present invention will be described with reference to Fig. 1. Referring to Fig. 1, the vacuum type water heater 1A includes an airtight container 2 in which heat transfer water W is sealed and maintained at a reduced pressure below atmospheric pressure, a circulating heating heat exchanger 7 that condenses and liquefies steam generated by heating the heat transfer water W through indirect heat exchange with circulating hot water C, and a heat pump unit 15. The circulating hot water C is condensed by the heat pump unit 15 through an expansion valve 12, an evaporator 13, a compressor 14, and a compressor 15a. machine The refrigerant is circulated through a main circulation path 17, which is connected in this order to the condenser 14, the condenser 11, and the subcooler 16. The condenser 11 is disposed in the sealed container 2 so as to be submerged in the heat transfer water W in order to heat the heat transfer water W.

[0026] The subcooler 16 is configured to subcool the refrigerant that has passed through the condenser 11 by indirect heat exchange with circulating hot water C outside the sealed container 2. The subcooler 16 is incorporated into the inlet side piping 27 of the circulating heating heat exchanger 7.

[0027] The sealed container 2 is evacuated from the top of the sealed container 2 by a known automatic evacuating device 9, and is maintained in a state where the pressure is reduced to a pressure close to a vacuum. The automatic evacuating device 9 can be composed of an evacuating pump, a control valve, etc.

[0028] The circulating heating heat exchanger 7 is disposed in the space above the heat transfer water W in the sealed container 2. In the example shown in FIG. 1, the circulating heating heat exchanger 7 is a hot water heat exchanger for heating, and the temperature of the circulating hot water is about 55°C near the inlet and about 70°C near the outlet. The circulating heating heat exchanger 7 is used to heat circulating hot water for heating, as well as circulating hot water for bathtubs, hot water pools, etc., or circulating hot water for indirect heating of chemical tanks in factories, etc., and other circulating hot water. The temperature (inlet temperature) of the circulating hot water supplied to the circulating heating heat exchanger 7 is preferably higher than 30°C.

[0029] In the illustrated example, the hot water heat exchanger 6 for hot water supply is disposed above the circulation heating heat exchanger 7, and the hot water S for hot water supply heated by the hot water heat exchanger 6 is about 30°C near the inlet and about 65°C near the outlet. In general, the temperature of the supplied water, i.e., the temperature of the water at the inlet of the hot water heat exchanger 6, is 30°C or lower.

[0030] In the heat pump unit 15, the refrigerant flows in the direction of the arrow in the figure. machine After being heated by 14 to a temperature higher than the saturation temperature of the heat transfer water W, it is sent to the refrigerant inlet of the condenser 11.

[0031] The refrigerant circulating through the main circulation path 17 enters the condenser 11 in a gaseous state at a temperature higher than the saturation temperature of the heat transfer water W, where it liquefies by dissipating latent heat to the heat transfer water W, is supercooled in the supercooler 16, is decompressed in the expansion valve 12 to a pressure that makes it easy to evaporate, and is reduced to a temperature that corresponds to that pressure, and then absorbs heat from the air in the evaporator 13 to evaporate (vaporize), and is then compressed again. machine The heat transfer water W is heated to a temperature higher than the saturation temperature at 14 and enters the condenser 11 in a gaseous state.

[0032] The heat transfer surface of the condenser 11 is machine The refrigerant heated by 14 heats the heat transfer water W to a temperature higher than the saturation temperature of the heat transfer water W. When the heat transfer water W is heated by the condenser 11 of the heat pump unit 15, the heat transfer surface reaches a boiling state. On a heat transfer surface in a boiling state, the absorption of latent heat of evaporation when bubbles are formed and the formed bubbles forming a strong local flow when leaving the heat transfer surface cause strong convective heat transfer within the heat transfer water W on the heat transfer surface, resulting in a higher heat transfer efficiency than in a non-boiling state.

[0033] The heat transfer water W generates steam by heating the condenser 11, forming a reduced-pressure steam chamber 5 in a reduced-pressure space above the liquid surface of the heat transfer water W. The steam is cooled and condensed on the surfaces of the circulation heating heat exchanger 7 and the hot water supply heat exchanger 6, which are disposed within the reduced-pressure steam chamber 5, by heat exchange with the circulating hot water supplied to the circulation heating heat exchanger 7 and the feed water supplied to the hot water supply heat exchanger 6, and the condensed liquid drips down as droplets. In this way, the heat transfer water W repeats a cycle of evaporation and condensation. Meanwhile, the circulating hot water supplied to the circulation heating heat exchanger 7 and the feed water supplied to the hot water supply heat exchanger 6 are heated by heat exchange with the steam from the heat transfer water W, and as a result, hot water (circulating hot water and hot water) at the desired temperatures is delivered from the circulation heating heat exchanger 7 and the hot water supply heat exchanger 6, respectively.

[0034] The refrigerant liquefied in the condenser 11 is extracted outside the sealed container 2 and guided to the subcooler 16 incorporated in the inlet piping 27 of the circulation heating heat exchanger 7. In the subcooler 16, the liquid refrigerant dissipates sensible heat to the circulating hot water C supplied to the circulation heating heat exchanger 7, resulting in a cycle shown by 1'->1->2->3->4 on the Mollier diagram of FIG. 7. This increases the amount of heat dissipated from the condenser 11 to the heat transfer water W and the amount of heat dissipated from the subcooler 16 to the circulating hot water C, improving the COP. Furthermore, assuming that the amount of heat dissipated by the refrigerant in the heat pump unit is the same when the subcooler 16 is provided (FIG. 1) and when it is not provided (FIG. 6), the enthalpy difference from 4 to 1 is large as shown in the Mollier diagram of FIG. 7. Therefore, the amount of refrigerant circulating in the heat pump unit can be reduced by providing the subcooler 16. Furthermore, by providing the supercooler 16 outside the sealed vessel 2, the degree of freedom in design increases regardless of the type of heat exchanger.

[0035] The COP of a heat pump is expressed by the following formula: COP=Q2 / W=Q2 / (Q2-Q1) where: Q1: Amount of heat absorbed by the refrigerant in the evaporator (3-2 in Figure 7) Q2: Amount of heat released by the refrigerant in the condenser (4-1 in Figure 7) W: Compressor power is.

[0036] Taking the heat cycle in Figure 7 as an example, the refrigerant pressure and flow rate actually differ depending on the operating conditions of the heat pump, but assuming that the compressor workload (4-3 in Figure 7) is the same, the predicted COP value is calculated as follows, and it can be seen that the COP value of the example is larger than that of the comparative example.

[0037] Without a subcooler (comparison example): COP = (4-1') / (4-3) = (455-339) / (455-407) = 2.4 With a subcooler (example): COP = (4-1) / (4-3) = (455 - 301) / (455 - 407) = 3.2 To boil the heat transfer water W under reduced pressure, the degree of superheat (the difference between the heat transfer surface temperature and the saturation temperature) must be greater than under atmospheric pressure. The condenser 11 of the heat pump unit 15 cannot achieve a very high degree of superheat. For example, the critical temperature of the refrigerant R134a is 101°C, while the typical heat transfer water temperature setting for a vacuum water heater is 90°C. Therefore, the boiling bubbles on the heat transfer surface of the condenser 11 are in a partial nucleate boiling state, and the heat transfer coefficient does not increase significantly. Furthermore, when boiling under reduced pressure, bubbles grow larger on the heat transfer surface than under atmospheric pressure, and the bubble separation period becomes longer, which can result in a decrease in the heat transfer coefficient.

[0038] Therefore, it is conceivable to design the heat transfer area of ​​the condenser 11 to be large, but this would result in an increase in the size of the device. Therefore, it is preferable to provide an auxiliary heating device in the sealed vessel 2. The auxiliary heating device can include a furnace 4 and a group of water tubes 8 that are provided so as to be submerged in the heat transfer water.

[0039] A combustion burner 3 is installed in the furnace 4. The amount of fuel supplied to the combustion burner 3 is controlled by a known control device (not shown). Combustion air in the furnace 4 passes through gaps in the water tube group 8, and then passes through a smoke chamber 18 and an exhaust stack 19 before being discharged to the outside as exhaust gas. Heat transfer water W flows inside the water tubes of the water tube group 8 while being heated.

[0040] The condenser 11 can be disposed above the auxiliary heating device (furnace 4 and / or water tube group 8). As a result, the heat transfer surfaces of the furnace 4 and / or water tube group 8 are heated by the high-temperature combustion gas from the combustion burner 3, resulting in developed nucleate boiling, and large bubbles are repeatedly formed and detached on the heat transfer surfaces. The detachment and rising of these bubbles creates a large flow of heat transfer water above the furnace 4 and / or water tube group 8. Placing the condenser 11 in this flow significantly increases the heat transfer coefficient. Furthermore, the refrigerant side of the condenser 11 is responsible for dissipating the latent heat of condensation from gas to liquid, so the heat exchanger can be designed specifically for latent heat, allowing the heat exchanger to be made even more compact.

[0041] 1, the hot water supply heat exchanger 6 does not have a subcooler installed in its water supply pipe because the supply water temperature (for example, 30°C or less) is too low. The present invention is suitable for use in high-temperature heat pump cycles (heat-rising type heat pumps with small heat load temperature differences), so it is not suitable for use in circuits where the heat load inlet temperature is extremely low, such as for hot water supply.

[0042] In a typical vacuum water heater, the set temperature of the heat transfer water is controlled to an upper limit of 90° C. and not to exceed 92° C. in order to keep the pressure of the heat transfer water below atmospheric pressure. Therefore, a refrigerant with a high critical temperature is preferred for the heat pump unit 15, and a refrigerant with a critical temperature exceeding 92° C. is preferably used.

[0043] In the vacuum water heater 1A according to the first embodiment, under operating conditions where the hot water supply heat exchanger 6, which is not provided with a subcooler, is under load and the circulating heating heat exchanger 7 for heating, which is provided with the subcooler 16, is under load, the refrigerant cannot dissipate heat in the subcooler 16, the degree of subcooling decreases, and the refrigerant may enter a two-phase state at the inlet of the expansion valve 12. This may increase the pressure loss of the expansion valve 12, causing a problem of reduced heating capacity.

[0044] Therefore, as shown in FIG. 2, the vacuum type water heater 1B according to the second embodiment of the present invention includes a bypass passage 22 connected to the main circulation passage 17 and bypassing the subcooler 16 between the condenser 11 and the expansion valve 12, and a compression passage 23 connected to the outlet of the expansion valve 12. machine The refrigerant cooling system includes an internal heat exchanger 23 for dissipating heat from the refrigerant flowing through the bypass passage 22 by indirect heat exchange with the refrigerant flowing through the main circulation passage 17 up to the inlet of the condenser 14, a flow rate regulator 24 for regulating the flow rate of the refrigerant bypassing the subcooler 16 through the bypass passage 22, a first temperature detector 20 for detecting the temperature of the refrigerant entering the expansion valve 12, a pressure detector 21 for detecting the pressure of the refrigerant entering the expansion valve 12, and a control unit 25 for calculating the degree of subcooling of the refrigerant from the condenser 11 to the expansion valve 12 based on the detection values ​​of the first temperature detector 20 and the pressure detector 20, and for controlling the flow rate regulator 24 so that the calculated degree of subcooling becomes a preset degree of subcooling. A second embodiment will now be described.

[0045] The first temperature detector 20 is provided near the inlet of the expansion valve 12. Specifically, the first temperature detector 20 is provided in the main circulation path 17 downstream of the connection point of the bypass path 22 between the outlet of the subcooler 16 and the inlet of the expansion valve 12.

[0046] The pressure detector 21 is provided near the inlet of the expansion valve 12. Specifically, the pressure detector 21 is provided in the main circulation path 17 downstream of the connection point of the bypass path 22 between the outlet of the subcooler 16 and the inlet of the expansion valve 12. Note that the pressure of the refrigerant flowing from the outlet of the condenser 11 to the inlet of the expansion valve 12 (including the bypass path 22) is almost constant, so the pressure detector used to measure the degree of subcooling may be located between the outlet of the condenser 11 and the inlet of the expansion valve 12, but is preferably located near the inlet of the expansion valve 12.

[0047] The internal heat exchanger 23 connects the outlet of the evaporator 13 with the compressor machine The bypass passage 22 is disposed in the main circulation passage 17 between the outlet of the expansion valve 12 and the inlet of the evaporator 13. However, it may also be disposed in the main circulation passage 17 between the outlet of the expansion valve 12 and the inlet of the evaporator 13. The main circulation passage 17 is shown with a thicker line than the bypass passage 22.

[0048] The flow rate regulator 24 is a three-way valve controllable by the control unit 25, which is interposed at the branch point between the main circulation path 17 and the bypass path 22, and can adjust the flow rate of the refrigerant flowing into the bypass path 22 by adjusting the opening degree of the three-way valve. By adjusting the flow rate of the refrigerant flowing into the bypass path 22, the flow rate of the refrigerant flowing toward the subcooler 16 is also adjusted. The flow rate regulator 24 can also be another control valve, for example, a two-way valve provided in the bypass path 22.

[0049] The control unit 25 regards the detected pressure value of the pressure detector 21 as the saturation pressure, calculates the difference between the saturation temperature at that detected pressure value and the temperature detection value of the first temperature detector 20 as the degree of subcooling, and controls the flow rate regulator 24 so that the calculated degree of subcooling becomes a predetermined degree of subcooling.

[0050] For example, when there is a load on the circulating heating heat exchanger 7 and sufficient subcooling is being achieved in the subcooler 16, the flow rate to the bypass path 22 is limited by the control of the flow rate regulator 24, and when the load on the circulating heating heat exchanger 7 decreases or disappears and the calculated degree of subcooling falls below a preset degree of subcooling, the flow rate regulator 24 increases the amount of refrigerant flowing into the bypass path 22, and controls the flow rate of refrigerant flowing into the bypass path 22 by the flow rate regulator 24 so that the calculated value of the degree of subcooling becomes the set value of the degree of subcooling. In this case, the flow rate regulator 24 may be a directional control valve that switches the flow of refrigerant to either the bypass path 22 or the main circulation path 17.

[0051] 3 shows a vacuum type water heater 1C according to a third embodiment of the present invention. In the third embodiment, in order to measure the degree of subcooling of the refrigerant from the time it leaves the condenser 11 until it enters the expansion valve 12, a second temperature detector 26 that detects the temperature of the refrigerant leaving the condenser 11 is provided instead of the pressure detector 21 of the second embodiment, and the degree of subcooling is calculated by finding the difference between the detection value of the first temperature detector 20 and the detection value of the second temperature detector 26, and the flow rate regulator 24 is controlled so that the calculated degree of subcooling becomes a preset degree of subcooling. The other configurations of the third embodiment are the same as those of the second embodiment.

[0052] Next, a vacuum type water heater according to a fourth embodiment of the present invention will be described with reference to Fig. 2. The fourth embodiment shown in Fig. 2 is a modified example of the first embodiment, and mainly illustrates parts that differ from the first embodiment, with parts that are not illustrated being similar in configuration to the first embodiment or the second and third embodiments.

[0053] A typical vacuum water heater has one to three heat exchanger circuits with different capacities in the reduced pressure steam chamber, producing hot water at different temperature ranges depending on the application.

[0054] 4, a vacuum type water heater 1D includes a first circulation heating heat exchanger 7A to which first circulating hot water at a first temperature is supplied, and a second circulation heating heat exchanger 7B to which second circulating hot water at a second temperature lower than the first temperature is supplied. The fourth embodiment shown in FIG. 4 does not include a hot water supply heat exchanger, but it may also include one.

[0055] In the fourth embodiment, the first temperature, i.e., the temperature of the first circulating hot water near the inlet of the first circulation heating heat exchanger 7A, is approximately 55°C, and the second temperature, i.e., the temperature of the second circulating hot water near the inlet of the second circulation heating heat exchanger 7B, is approximately 40°C. In the illustrated example, the temperature of the first circulating hot water near the outlet of the first circulation heating heat exchanger 7A is approximately 70°C, and the temperature of the second circulating hot water near the outlet of the second circulation heating heat exchanger 7B is approximately 60°C. The first circulation heating heat exchanger 7A is used, for example, for heating, and the second circulation heating heat exchanger 7B is used, for example, for circulating water in a bathtub.

[0056] In the fourth embodiment, there are two subcoolers, and a secondary subcooler 16B is connected in series to the secondary side of a primary subcooler 16A. The primary subcooler 16A is incorporated into the inlet pipe 27 of the first circulation heating heat exchanger 7A, and the secondary subcooler 16B is incorporated into the inlet pipe 28 of the second circulation heating heat exchanger 7B.

[0057] The primary supercooler 16A is configured to exchange heat with the first circulating hot water supplied to the first circulation heating heat exchanger 7A, and then the secondary supercooler 16B is configured to exchange heat with the second circulating hot water supplied to the second circulation heating heat exchanger 7B.

[0058] The refrigerant liquefied in the condenser 11 dissipates heat in a primary subcooler 16A incorporated in the inlet side of the first circulation heating heat exchanger 7A, then dissipates heat in a secondary subcooler 16B incorporated in the inlet side of the second circulation heating heat exchanger 7B, and reaches the expansion valve 12.

[0059] Figure 2 shows an example of a case where the circulating heating heat exchanger has two circuits, but even if the circulating heating heat exchanger has three circuits, the heat can be dissipated in the order of highest temperature of the circulating hot water from the primary, secondary, and tertiary subcoolers.

[0060] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the present invention.

[0061] In the above embodiment, a furnace and a group of water tubes are used as examples of the auxiliary heating device, but other known heat sources such as an electric heater can also be used. The auxiliary heating device can be driven only when a large amount of heat transfer water W needs to be heated rapidly, such as when the hot water load is high or when the heat transfer water W needs to be heated quickly when the vacuum water heater 1 is started, thereby reducing energy consumption, running costs, and CO2 emissions. Therefore, it is preferable that the auxiliary heating device has a high heating capacity greater than the output of the condenser 11 and can quickly heat a large amount of heat transfer water W.

[0062] Furthermore, as disclosed in Patent No. 4139827, by incorporating a hybrid hot water supply system in which a heat pump specialized for hot water supply is connected to a hot water storage tank, further efficiency improvements and CO2 reduction effects can be achieved. [Explanation of symbols]

[0063] 1A,1B,1C,1D Vacuum water heater 2. Airtight containers 3 Combustion burner 4 Furnace 5. Decompression steam chamber 6. Hot water heat exchanger 7. Circulating heat exchanger 7A 1st circulation heating heat exchanger 7B Second circulation heating heat exchanger 8 Water pipe group 11 Condenser 12 Expansion valve 13 Evaporator 14 Compressor 15 Heat pump unit 16 Supercooler 16A primary subcooler 16B Secondary subcooler 17 Main circulation path 20 First temperature detector 21 Pressure detector 22 Bypass Road 23 Internal heat exchanger 24 Flow regulator 25 Control Unit 26 Second temperature detector

Claims

1. a sealed container in which heat transfer water is sealed and maintained at a reduced pressure below atmospheric pressure; a circulation heating heat exchanger that condenses and liquefies the steam generated by heating the heat transfer water through indirect heat exchange with the supplied circulating hot water; a heat pump unit having a main circulation path for circulating a refrigerant, in which an expansion valve, an evaporator, a compressor, a condenser, and a subcooler are connected in sequence, the condenser is disposed in the sealed container to heat the heat transfer water; The subcooler is configured to dissipate heat from the refrigerant that has passed through the condenser by indirect heat exchange with the circulating hot water outside the sealed container. Vacuum water heater.

2. a bypass passage connected to the main circulation passage and bypassing the subcooler between the condenser and the expansion valve; an internal heat exchanger for dissipating heat from the refrigerant bypassing the subcooler through the bypass passage by indirect heat exchange with the refrigerant flowing through the main circulation passage from the outlet of the expansion valve to the inlet of the compressor; a flow rate regulator that regulates the flow rate of the refrigerant that bypasses the subcooler through the bypass path; a first temperature detector for detecting the temperature of the refrigerant entering the expansion valve; a pressure detector for detecting the pressure of the refrigerant entering the expansion valve; a control unit that calculates a degree of subcooling of the refrigerant from the condenser to the expansion valve based on the detected value of the first temperature detector and the detected value of the pressure detector, and controls the flow rate regulator so that the calculated degree of subcooling becomes a predetermined degree of subcooling; The vacuum water heater according to claim 1 , comprising:

3. a bypass passage connected to the main circulation passage and bypassing the subcooler between the condenser and the expansion valve; an internal heat exchanger for dissipating heat from the refrigerant flowing through the bypass passage by indirect heat exchange with the refrigerant flowing through the main circulation passage from the outlet of the expansion valve to the inlet of the compressor; a flow rate regulator that regulates the flow rate of the refrigerant that bypasses the subcooler through the bypass path; a first temperature detector for detecting the temperature of the refrigerant entering the expansion valve; a second temperature detector for detecting the temperature of the refrigerant exiting the condenser; a control unit that calculates a degree of subcooling of the refrigerant from the condenser to the expansion valve based on the detected value of the first temperature detector and the detected value of the second temperature detector, and controls the flow rate regulator so that the calculated degree of subcooling becomes a predetermined degree of subcooling; The vacuum water heater according to claim 1 , comprising:

4. the circulating heating heat exchanger includes a first circulating heating heat exchanger to which first circulating hot water at a first temperature is supplied, and a second circulating heating heat exchanger to which second circulating hot water at a second temperature lower than the first temperature is supplied, the subcooler includes a primary subcooler and a secondary subcooler connected to the secondary side of the primary subcooler; A vacuum water heater according to any one of claims 1 to 3, wherein the primary supercooler exchanges heat with the first circulating hot water supplied to the first circulation heating heat exchanger, and then the secondary supercooler exchanges heat with the second circulating hot water supplied to the second circulation heating heat exchanger.

5. the condenser is a condenser that condenses the gaseous refrigerant at a temperature equal to or higher than a saturation temperature of the heat transfer water to release latent heat to the heat transfer water, 5. The vacuum water heater according to claim 1, wherein the supercooler is a supercooler that radiates sensible heat to the circulating hot water having a temperature equal to or lower than the temperature of the heat transfer water.

6. Further provided with a hot water heat exchanger, The subcooler is provided only for heat exchange with the circulating hot water circulating through the circulating heating heat exchanger. A vacuum water heater according to any one of claims 1 to 5.

7. 7. The vacuum water heater according to claim 1, wherein the heat pump unit is a high-temperature heat pump cycle unit in which the critical temperature of the refrigerant exceeds 92°C.

8. Further comprising an auxiliary heating device; The auxiliary heating device has a furnace and a group of water tubes arranged so as to be submerged in the heat transfer water, 8. The vacuum water heater according to claim 1, wherein the condenser is disposed above the auxiliary heating device.

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