JP2012017945A - Hot water supply apparatus and hot water supply control method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently operate a hot water supply apparatus on boiling water at a high water supply temperature by setting an optimum target pressure on the basis of the water supply temperature and the boiling temperature.SOLUTION: The hot water supply apparatus includes a heat pump including a compressor 10, a water-refrigerant heat exchanger 20, a throttle valve 30 with a controllable opening, and an air-refrigerant heat exchanger 40. A water circulation passage 71 where water to be boiled circulates is connected to a water passage of the water-refrigerant heat exchanger 20. A pressure detector 53 detects a pressure in a high pressure side of the heat pump cycle. A temperature detector 51 detects a water supply temperature in an entrance side of the water passage of the water-refrigerant heat exchanger 20. When the water supply temperature detected by the temperature detector 51 is equal to or higher than a prescribed temperature, a control part 60 sets the higher pressure in a first pressure obtained from the hot water supply temperature and a second pressure obtained from a target boiling temperature and the hot water supply temperature, as a control pressure lower limit, and controls the opening of the throttle valve to maintain a pressure in the high pressure side equal to or higher than the control pressure lower limit.

Description

  The present invention relates to a hot water supply apparatus using a heat pump cycle and a hot water supply control method thereof.

  Conventionally, a hot water supply apparatus has been used in which a compressor, a refrigerant passage of a water refrigerant heat exchanger, an expansion valve, and an air refrigerant heat exchanger are connected in an annular shape to boil the water flowing through the water supply passage of the water refrigerant heat exchanger. Yes. In a conventional hot water supply device, when boiling water with a high feed water temperature, the lower limit of the refrigerant pressure is determined according to the feed water temperature so that the boiling capacity does not drop, so that the refrigerant pressure does not fall below the lower limit value. Is controlled.

JP 2002-206805 A

  However, it is necessary to keep the temperature distribution in the water-refrigerant heat exchanger in a state where the refrigerant temperature is higher than the water temperature. In this case, the lower pressure limit varies depending on the boiling temperature. Therefore, if the refrigerant pressure when the feed water temperature is high is controlled with the lower limit of the refrigerant pressure determined from the feed water temperature as the target, depending on the boiling temperature, efficient operation, that is, boiling with less power cannot be performed. was there.

  An object of the present invention is to set an optimum target pressure based on a feed water temperature and a boiling temperature, and to perform an efficient operation during a boiling operation with a high feed water temperature.

In order to achieve the above object, a water heater of the invention according to claim 1 comprises:
A heat pump cycle having a compressor (10), a water refrigerant heat exchanger (20), a throttle valve (30) whose valve opening is controllable, and an air refrigerant heat exchanger (40);
A water circulation passage (71) connected to the water passage of the water-refrigerant heat exchanger (20) and through which water is circulated;
A pressure detector (53) for detecting a high-pressure side pressure of the heat pump cycle;
A temperature detector (51, 52) for detecting a temperature corresponding to a water supply temperature on the water passage inlet side of the water refrigerant heat exchanger (20);
When the feed water temperature detected by the temperature detector (51, 52) is equal to or higher than a predetermined temperature, a first pressure obtained from the hot water temperature, a target boiling temperature, and a first hot water temperature obtained from the target hot water temperature. A control unit (60) for controlling the opening of the throttle valve so that the higher one of the two pressures is a control pressure lower limit, and the high pressure side pressure is maintained at or above the control pressure lower limit;
Is provided.
Thereby, an efficient driving | operation can be performed at the time of boiling operation with high feed water temperature.

  In the hot water supply apparatus according to the second aspect of the invention, the control pressure lower limit is stored as a pressure map determined in advance from the target boiling temperature and the hot water temperature. Thereby, the process which determines a control pressure minimum can be accelerated.

  In the hot water supply apparatus according to the invention of claim 3, the temperature detector (52) is a refrigerant temperature detector that detects a refrigerant outlet side temperature of the water-refrigerant heat exchanger (20).

In the hot water supply apparatus according to the invention according to claim 4,
When the feed water temperature detected by the temperature detector (51, 52) is lower than a predetermined temperature, the refrigerant outlet side temperature of the water refrigerant heat exchanger (20) and the water passage inlet of the water refrigerant heat exchanger (20) The opening degree of the expansion valve is controlled so that the temperature difference from the supply water temperature on the side becomes the target temperature difference.
Thereby, an efficient driving | operation can be performed at the time of the boiling operation with low feed water temperature.

  In the hot water supply apparatus according to the invention of claim 5, the throttle valves (30, 33) are expansion valves (30).

  In the hot water supply device according to the invention of claim 6, the throttle valves (30, 33) are ejectors (33).

In the hot water supply control method according to the invention of claim 7,
A heat pump cycle having a compressor (10), a water refrigerant heat exchanger (20), throttle valves (30, 33) whose valve opening degree can be controlled, and an air refrigerant heat exchanger (40);
A water circulation passage (71) connected to the water passage of the water-refrigerant heat exchanger (20) and through which water is circulated;
A pressure detector (53) for detecting a high-pressure side pressure of the heat pump cycle;
A temperature detector (51, 52) for detecting a temperature corresponding to a water supply temperature on the water passage inlet side of the water refrigerant heat exchanger (20);
A hot water supply control method in a hot water supply apparatus comprising:
When the feed water temperature detected by the temperature detector (51, 52) is equal to or higher than a predetermined temperature, a first pressure obtained from the hot water temperature, a target boiling temperature, and a first hot water temperature obtained from the target hot water temperature. The higher pressure of the two pressures is taken as the control pressure lower limit,
The opening degree of the throttle valves (30, 33) is controlled so as to maintain the high-pressure side pressure at or above the control pressure lower limit.
Thereby, the control which performs efficient operation at the time of boiling operation with high feed water temperature can be performed.

In the hot water supply control method according to the invention according to claim 8,
When the feed water temperature detected by the temperature detector (51, 52) is lower than a predetermined temperature, the refrigerant outlet side temperature of the water refrigerant heat exchanger (20) and the water passage inlet of the water refrigerant heat exchanger (20) The opening degree of the throttle valves (30, 33) is controlled so that the temperature difference with the side water supply temperature becomes the target temperature difference.
Thereby, the control which performs an efficient driving | operation at the time of the boiling operation with low feed water temperature can be performed.

It is a figure which shows an example of the heat pump type hot water supply apparatus by one Embodiment of this invention. (a) (b) is a figure explaining the optimal high voltage | pressure determined from feed water temperature, (a) is the figure which described the refrigerating cycle of feed water temperature 40 degreeC on Ph curve, (b), It is a figure which shows the relationship between COP (A / B) and the high voltage | pressure P about the refrigerating cycle of (a). It is a Th diagram which shows the relationship between the refrigerant | coolant temperature at the time of boiling temperature of 65 degreeC, and feed water temperature. It is a Th diagram which shows the relationship between the refrigerant | coolant temperature at the time of boiling temperature of 80 degreeC, and feed water temperature. It is a figure which shows an example of the control flow of the hot water supply apparatus of this embodiment. (A) (b) is a figure which shows an example of the target pressure minimum in case boiling temperature differs. (A) (b) is a figure which shows the heat pump cycle which has an ejector used by other embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram illustrating an example of a heat pump type hot water supply apparatus according to the present embodiment. Hot water in the hot water storage tank 70 circulates in the water circulation passage 71 by an electric pump 72 disposed between the water outlet of the hot water storage tank 70 and the water inlet of the water refrigerant heat exchanger 20. The hot water is heated by heat exchange when passing through the water passage in the water refrigerant exchanger 20 disposed in the water circulation passage 71.

  The heat pump hot water supply apparatus includes a heat pump cycle including an annular circuit having a compressor 10, a water refrigerant heat exchanger 20, an expansion valve 30, and an air refrigerant heat exchanger 40. In the heat pump cycle, the refrigerant is sucked and discharged by the compressor 1 and circulates in the circuit. The heat pump hot water supply device heats up the water supply by supplying heat supply to the water supply via the water / refrigerant heat exchanger 20 with an amount of heat absorbed from the outside air and the amount of compression work of the compressor 1. As the refrigerant used in the present embodiment, for example, a refrigerant mainly composed of carbon dioxide can be used. In the heat pump cycle of the present embodiment, the expansion valve 30 is used, but a pressure reducing valve or an ejector having a similar function can also be used.

  The water refrigerant heat exchanger 20 is a high-pressure heat exchanger that heats hot water by exchanging heat between the high-temperature refrigerant discharged from the compressor 10 and hot water flowing through the water circulation passage.

  The expansion valve 30 expands the liquid-phase refrigerant or the like flowing out from the water refrigerant exchanger 20 by decompressing it in an enthalpy manner. The expansion valve 30 of the present embodiment is an electronic expansion valve, and the amount of refrigerant can be adjusted by adjusting the opening degree.

  The air refrigerant heat exchanger 40 evaporates the low-pressure refrigerant that has absorbed heat from the outside air blown by a blower (not shown) and has flowed out of the expansion valve 30. Note that a gas-liquid separator that separates the refrigerant flowing out from the air refrigerant heat exchanger 40 into a liquid-phase refrigerant and a gas-phase refrigerant, stores excess refrigerant, and supplies the gas-phase refrigerant to the compressor 10 may be provided. Good.

  The control unit 60 that controls the hot water supply apparatus includes a computer control circuit including a processor (CPU), a memory (RAM), a nonvolatile memory (ROM), and the like. Various sensors 51 to 53 are arranged for boiling control in the present embodiment. The temperature sensor 51 is disposed on the inlet side of the water supply passage of the water-refrigerant heat exchanger 20 and detects the water supply temperature. The temperature sensor 52 is disposed on the refrigerant outlet side of the water-refrigerant heat exchanger 20 and detects the temperature of the refrigerant. The pressure sensor 53 is disposed on the refrigerant outlet side of the water-refrigerant heat exchanger 20 and detects the high-pressure side pressure. The location of the pressure sensor 53 that detects the high-pressure side pressure is not limited to the refrigerant outlet side of the water-refrigerant heat exchange device 20. It can be disposed anywhere in the range from the discharge side of the compressor 10 to the inlet side of the expansion valve 30.

  FIGS. 2-4 is a figure for demonstrating the control of this embodiment for boiling high temperature feed water, FIG. 2 (a) (b) is a figure which shows the optimal high pressure determined from feed water temperature, 3 and 4 are diagrams showing a high pressure determined from the feed water temperature and the boiling temperature.

  FIG. 2A shows a refrigeration cycle having a feed water temperature of 40 ° C. on a Ph curve illustrating the relationship between high pressure and enthalpy. In Fig.2 (a), A shows the heating capability which boils feed water, B shows compressor power or the power consumption of a compressor. The COP indicating the efficiency or performance is represented by A / B. In order to increase the COP, the heating capacity A may be increased or the power consumption B may be decreased.

  In Fig.2 (a), the heating capability A and the power consumption B are shown about the cycle (1). Regarding cycles (2) and (3), the heating capacity A and the power consumption B can be similarly shown. As can be seen from FIG. 2A, when the high pressure is increased as in the cycle (1), the heating ability A represented by the difference in the high pressure side enthalpy can be increased. However, the power consumption B of the compressor also increases. Further, when the high pressure is lowered as in the cycle (3), the power consumption B of the compressor is reduced, but the heating capacity A represented by the difference in the high pressure side enthalpy is also reduced. If COP is given by A / B and considering the slope of the 40 ° C. isotherm, it can be seen that cycle (2) gives the pressure that gives the maximum efficiency, ie the optimum pressure, depending on the feed water temperature.

  FIG. 2B shows the relationship between COP (A / B) and high pressure P for cycles (1) to (3) in FIG. When the feed water temperature is 40 ° C., the high pressure at the point indicated by (2) is the pressure at which the COP is maximum. Therefore, it is considered that the most efficient operation is to control the high pressure of the refrigeration cycle to the value indicated by (2) in FIG.

  By the way, in the water-refrigerant heat exchanger, heat exchange is not performed unless the refrigerant temperature is kept equal to or higher than the feed water temperature, so a high pressure equal to or higher than a predetermined pressure is required. FIG. 3 is a Th diagram showing the relationship between the refrigerant and the feed water in the water-refrigerant heat exchanger when the feed water temperature is 40 ° C. and the boiling temperature is 65 ° C. In FIG. 3, the feed water temperature is represented by a solid line, and the refrigerant temperature is represented by a broken line. As can be seen from FIG. 3, when the high pressure is set to 10 MPa, the refrigerant temperature ≧ the feed water temperature can always be maintained when the feed water temperature is raised from 40 ° C. to 65 ° C. Therefore, it can be said that the minimum pressure when boiling from a feed water temperature of 40 ° C. to 65 ° C. is 10 MPa.

  However, if the boiling temperature is raised to 80 degrees with the pressure kept at 10 MPa, the feed water temperature is required to rise as shown by the one-dot chain line in FIG. 3, but the rise in the refrigerant temperature is determined by the high pressure. It can be seen that there is a region where the refrigerant temperature is lower than the feed water temperature. Actually, in this region, the refrigerant temperature and the feed water temperature are equal in the water refrigerant heat exchanger. Accordingly, the water refrigerant heat exchange performance cannot be exhibited in this region.

  FIG. 4 is a Th diagram showing the relationship between the refrigerant and water in the water-refrigerant heat exchanger when the high pressure is 12 MPa and the water is heated from 40 ° C. to the boiling temperature of 80 ° C. In FIG. 4, from 40 ° C. to 80 ° C., the temperature of the refrigerant is always higher than the temperature of the feed water. Thus, in order to boil from the feed water temperature of 40 ° C. to the boiling temperature of 80 ° C., it can be said that the lower limit value of the high pressure is 12 MPa.

  As described above, in order to efficiently boil high-temperature feed water to the desired boiling temperature, the high pressure is controlled by the larger of the optimum value of the high pressure determined by the feed water temperature and the lower limit of the high pressure determined by the boiling temperature. It is necessary to do.

  FIG. 5 is a diagram illustrating an example of a control flow of the hot water supply apparatus of the present embodiment. When the boiling operation of the hot water supply apparatus is started, normal control similar to the conventional one is performed in step S1. The normal control in step S1 is control performed when the feed water temperature is lower than a predetermined temperature such as 30 ° C., for example, and the refrigerant temperature on the refrigerant outlet side of the water refrigerant heat exchanger 20 and water refrigerant heat exchange. The opening degree of the expansion valve (30) is controlled so that the temperature difference from the water supply temperature on the water inlet side of the vessel 20 becomes a predetermined target value. This control increases the operating efficiency in the case of low temperature water supply. The refrigerant temperature on the refrigerant outlet side of the water-refrigerant heat exchange device 20 is detected by the temperature sensor 52, and the water supply temperature in the water supply passage of the water-refrigerant heat exchange device 20 is detected by the water supply temperature sensor 51.

  In step S <b> 2, it is determined whether or not the feed water temperature is 30 ° C. or higher based on a signal from a feed water temperature sensor 51 disposed on the inlet side of the feed water passage of the water / refrigerant heat exchange device 20. The feed water temperature can also be obtained by a signal from a temperature sensor 52 that is disposed on the refrigerant outlet side of the water refrigerant heat exchange device 20 and detects the refrigerant temperature.

  In step S2, based on the signal from the feed water temperature sensor 51, if the feed water temperature is less than 30 ° C., the process returns to step S1 and normal control is continued. If it is determined in step S2 that the feed water temperature is 30 ° C. or higher, steps S3 and S4 are executed. In Step S3, for example, based on a Ph diagram as shown in FIG. In step S4, for example, a second lower limit Pmin2 of the target pressure determined from the feed water temperature and the target boiling temperature is obtained based on the Th diagram shown in FIGS. The optimum pressure determined from the feed water temperature and the target pressure determined from the feed water temperature and the target boiling temperature can all be stored in the memory of the control unit 60 as a table or a map.

  Next, in step S5, a larger value Max (Pmin1, Pmin2) is set as the target pressure lower limit Pmin compared to the first lower limit Pmin1 and the second lower limit Pmin2. The target pressure lower limit Pmin can be calculated in advance from the feed water temperature and the target boiling temperature and stored in the memory of the control unit 60 as a pressure map.

  6A and 6B are diagrams showing examples of the target pressure lower limit when the boiling temperatures are different, and show an example of the processing result of step S5. 6 (a) and 6 (b), the feed water temperature is 40 ° C., (i) shows the optimum pressure determined from the Ph diagram, and (ii) shows the minimum pressure determined from the Th diagram. Show. Here, (ii) (80 ° C.) is the minimum pressure determined from the Th diagram when the boiling temperature is 80 ° C., and (ii) (65 ° C.) is the T pressure when the boiling temperature is 65 ° C. -Minimum pressure determined from the h diagram. (Ii) (80 ° C.) and (ii) (65 ° C.) are represented as two straight lines having a substantially constant slope.

  FIG. 6A shows a line indicating the minimum pressure when the target boiling temperature is 65 ° C. by a solid line. The optimum pressure (i) determined from the Ph diagram and the minimum pressure (ii) (65 ° C.) determined from the Th diagram are compared, and the larger pressure is adopted as the target pressure. Up to a certain temperature, the first lower limit Pmin1 is the target pressure, and when the temperature is exceeded, the second lower limit Pmin2 is the target pressure.

  FIG. 6B shows a line indicating the minimum pressure when the target boiling temperature is 80 ° C. by a solid line. The optimum pressure (i) determined from the Ph diagram and the minimum pressure (ii) (80 ° C.) determined from the Th diagram are compared, and the larger pressure is adopted as the target pressure. Up to a certain temperature, the first lower limit Pmin1 is the target pressure, and when the temperature is exceeded, the second lower limit Pmin2 is the target pressure.

  Returning to the flow of FIG. 5, when the target pressure lower limit Pmin is determined in step S5, the target pressure of the refrigeration cycle is compared with the target pressure lower limit Pmin in step S6. If the target pressure is less than the target pressure lower limit Pmin, the target pressure lower limit Pmin is set as the target pressure in step S7, and the opening of the expansion valve 30 is determined in step S8 as the target pressure lower limit Pmin. And the opening degree of the expansion valve 30 is controlled so that the opening degree of the expansion valve 30 becomes the determined opening degree.

  If the target pressure is greater than or equal to the target pressure lower limit Pmin in step S6, the opening of the expansion valve 30 is determined for this target pressure in step S8 without changing the target pressure. And the opening degree of the expansion valve 30 is controlled so that the opening degree of the expansion valve 30 becomes the determined opening degree.

  In the above-described embodiment, a heat pump cycle including an expansion valve is used, but the present invention can also be applied to a heat pump cycle using an ejector.

  FIGS. 7A and 7B are views showing a heat pump cycle having an ejector used in another embodiment of the present invention.

  7A includes a compressor 10, a water refrigerant heat exchanger 20, an ejector 33, a circuit that circulates the gas-liquid separator 80, an air refrigerant heat exchanger 41, an ejector 33, and a gas-liquid. A circuit for circulating the separator 80 is provided. The ejector 33 has a function of sucking the gaseous refrigerant circulating in the air refrigerant heat exchanger 41 and a function of increasing the suction pressure of the compressor 10. That is, the ejector 33 works as a pump, and the power of the compressor 10 can be reduced. The gas-liquid separator 80 separates the gas phase and the liquid phase, and flows only the liquid refrigerant to the air refrigerant heat exchanger 41.

  The nozzle of the ejector 33 is a variable nozzle that can adjust the nozzle opening, and can adjust the nozzle opening, that is, the ejector opening. When the present invention is applied, the ejector opening is adjusted according to the target pressure.

  The heat pump cycle shown in FIG. 7B is branched from the outlet side of the water-refrigerant heat exchanger 20 to the drive side of the ejector 33, and the suction side of the ejector 33 via the fixed throttle or the expansion valve 35. The air refrigerant heat exchanger 43 has a branch passage leading to the inlet side. An air refrigerant heat exchanger 45 is disposed on the outflow side of the ejector 33, and the air refrigerant heat exchanger 45 and the air refrigerant heat exchanger 43 constitute a two-stage air refrigerant heat exchanger. Also in the heat pump cycle of FIG.7 (b), when applying this invention, an ejector opening degree is adjusted according to target pressure.

DESCRIPTION OF SYMBOLS 10 Compressor 20 Water refrigerant heat exchanger 30 Expansion valve 33 Ejector 40 Air refrigerant heat exchanger 41 (Suction side) Air refrigerant heat exchanger 43 (Suction side) Air refrigerant heat exchanger 45 (Outflow side) Air refrigerant heat exchanger 51, 52 Temperature sensor 53 Pressure sensor 60 Control unit 70 Hot water storage tank 71 Water circulation passage 72 Electric pump 80 Gas-liquid separator

Claims (8)

A heat pump cycle having a compressor (10), a water refrigerant heat exchanger (20), a throttle valve (30) whose valve opening is controllable, and an air refrigerant heat exchanger (40);
A water circulation passage (71) connected to the water passage of the water-refrigerant heat exchanger (20) and through which water is circulated;
A pressure detector (53) for detecting a high-pressure side pressure of the heat pump cycle;
A temperature detector (51, 52) for detecting a temperature corresponding to a water supply temperature on the water passage inlet side of the water refrigerant heat exchanger (20);
When the feed water temperature detected by the temperature detector (51, 52) is equal to or higher than a predetermined temperature, a first pressure obtained from the hot water temperature, a target boiling temperature, and a first hot water temperature obtained from the target hot water temperature. A control unit (60) for controlling the opening of the throttle valve so that the higher one of the two pressures is a control pressure lower limit, and the high pressure side pressure is maintained at or above the control pressure lower limit;
A hot water supply device comprising:   The hot water supply apparatus according to claim 1, wherein the control pressure lower limit is stored as a pressure map determined in advance from the target boiling temperature and the hot water temperature.   The hot water supply apparatus according to claim 1 or 2, wherein the temperature detector (52) is a refrigerant temperature detector that detects a refrigerant outlet side temperature of the water-refrigerant heat exchanger (20).   When the feed water temperature detected by the temperature detector (51, 52) is lower than a predetermined temperature, the refrigerant outlet side temperature of the water refrigerant heat exchanger (20) and the water passage inlet of the water refrigerant heat exchanger (20) The hot-water supply apparatus of Claim 1 or Claim 2 which controls the opening degree of an expansion valve so that a temperature difference with the water supply temperature of a side turns into a target temperature difference.   The hot water supply device according to any one of claims 1 to 4, wherein the throttle valve (30, 33) is an expansion valve (30).   The hot water supply device according to any one of claims 1 to 4, wherein the throttle valve (30, 33) is an ejector (33). A heat pump cycle having a compressor (10), a water refrigerant heat exchanger (20), throttle valves (30, 33) whose valve opening degree can be controlled, and an air refrigerant heat exchanger (40);
A water circulation passage (71) connected to the water passage of the water-refrigerant heat exchanger (20) and through which water is circulated;
A pressure detector (53) for detecting a high-pressure side pressure of the heat pump cycle;
A temperature detector (51, 52) for detecting a temperature corresponding to a water supply temperature on the water passage inlet side of the water refrigerant heat exchanger (20);
A hot water supply control method in a hot water supply apparatus comprising:
When the feed water temperature detected by the temperature detector (51, 52) is equal to or higher than a predetermined temperature, a first pressure obtained from the hot water temperature, a target boiling temperature, and a first hot water temperature obtained from the target hot water temperature. The higher pressure of the two pressures is taken as the control pressure lower limit,
A hot water supply control method for controlling an opening degree of the throttle valve (30, 33) so as to maintain the high-pressure side pressure at or above the lower limit of the control pressure.   When the feed water temperature detected by the temperature detector (51, 52) is lower than a predetermined temperature, the refrigerant outlet side temperature of the water refrigerant heat exchanger (20) and the water passage inlet of the water refrigerant heat exchanger (20) The hot water supply control method according to claim 7, wherein the opening degree of the throttle valve (30, 33) is controlled so that a temperature difference with a side water supply temperature becomes a target temperature difference.

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