EP1777471A1

EP1777471A1 - Heat pump-type hot-water supply device

Info

Publication number: EP1777471A1
Application number: EP05765649A
Authority: EP
Inventors: Jouji Kuroki; Hisayoshi Sakakibara; Teruhiko Taira; Susumu Kawamura; Masato Murayama
Original assignee: Denso Corp
Current assignee: Denso Corp
Priority date: 2004-07-12
Filing date: 2005-07-12
Publication date: 2007-04-25
Also published as: JP4337880B2; WO2006006578A1; JPWO2006006578A1

Abstract

At least at the time of starting of a heat pump cycle, a target high pressure Pt on a high-pressure side is set, a refrigerant pressure on the high-pressure side is controlled so as to approach the target high pressure Pt. Furthermore, a temperature difference ΔT1 between a target temperature difference ΔTt and an actual temperature difference ΔT is calculated, and the target high pressure Pt is corrected to make the temperature difference ΔT1 equal to or less than a predetermined value. Accordingly, stability of the cycle relative to a variation in the heat pump cycle, which is caused by external factors, can be improved by directly controlling pressure reducing means 3, 30 based on a high pressure value detected by a pressure sensor having a good response or the like. Since the pressure sensor involves a large dispersion in detection values, it is difficult to obtain a target COP. However, the target COP can be obtained by correcting the target high pressure Pt on the basis of an actual temperature difference ΔT detected by a temperature sensor, which involves less dispersion.

Description

Technical Field

The present invention relates to a heat pump type water heater using a heat pump cycle as a heating means for heating water for hot-water supply, and more particular, relative to a method of controlling a pressure reducing means at the time of a boiling-up operation.

Background Art

The applicant of the present application discloses a technology shown in JP-A-2000-213806 as a related art. In the technology, in order to improve a coefficient of performance (referred below to as COP) in a heat pump type water heater, a pressure reducing means controls pressure of a refrigerant on a high-pressure side so that a temperature difference ΔT between temperature of a refrigerant flowing from a gas cooler (radiator), which heats water for hot-water supply, and temperature of water for hot-water supply, flowing into the gas cooler becomes a predetermined temperature difference ΔTo.
However, a change may occur in a heat pump cycle due to external factors such as frosting in an evaporator during operation, variations in an amount of water circulating through a heat pump due to a using of hot water from a hot-water storage tank by a user, or the like. In this case, there is caused a problem that a delay in response of a thermistor for detection of temperature generates a delay in control of the pressure reducing means, thereby damaging stability of the cycle and increasing a possibility of an error stop.
The invention has been thought of in view of the problem and has an object to provide a heat pump type water heater, in which stability of a cycle relative to external factors is high.

Disclosure of the Invention

In order to obtain the object, the invention adopts technical means according to claims 1 to 4. That is, in the invention of claim 1, a heat pump type water heater is for heating water for hot-water supply in a vapor-compression type heat pump cycle in which heat on a low-temperature side is transferred to a high-temperature side. The heat pump type water heater includes a compressor (1) that sucks and compresses refrigerant; a radiator (2) constructed such that heat exchange is performed between refrigerant discharged from the compressor (1) and water for hot-water supply and a flow of refrigerant and a flow of water for hot-water supply are opposed to each other; pressure reducing means (3, 30) that reduces pressure of refrigerant flowing from the radiator (2); and an evaporator (4), in which refrigerant flowing from the pressure reducing means (3, 30) is evaporated by absorbing heat and refrigerant is discharged to flow to a suction side of the compressor (1). In this heat pump type water heater, a refrigerant pressure on a high-pressure side is controlled such that when refrigerant pressure on the high-pressure side is less than a predetermined pressure, an actual temperature difference (ΔT) between a refrigerant temperature flowing from the radiator (2) and a water temperature flowing into the radiator (2) becomes a predetermined target temperature difference (ΔTt). Furthermore, the heat pump type water heater is characterized in that:

at least at the time of starting of the heat pump cycle, a target pressure (Pt) on the high-pressure side is set, and the refrigerant pressure on the high-pressure side is controlled so as to approach the target pressure (Pt); and a temperature difference (ΔT1) between the target temperature difference (ΔTt) and the actual temperature difference (ΔT) is calculated, and the target pressure (Pt) is corrected to make the temperature difference (ΔT1) equal to or less than a predetermined value.

According to the invention of claim 1, stability of the cycle relative to a variation in the heat pump cycle, which is caused by external factors, can be improved by directly controlling the pressure reducing means (3, 30) based on a high pressure value detected by a pressure sensor having a good response or the like.
Further, since the pressure sensor involves a large dispersion in detection values, it is difficult to obtain a target COP. However, the target COP can be obtained by correcting the target pressure (Pt) on the basis of an actual temperature difference (ΔT) detected by the temperature sensor, which is small in dispersion. Since a control of the pressure reducing valve is made possible even when either of the pressure sensor and the temperature sensor is abnormal, reliability of a system can be improved on a user's side.
In the invention described in claim 2, a heat pump type water heater is for heating water for hot-water supply in a vapor-compression type heat pump cycle in which heat on a low-temperature side is transferred to a high-temperature side. The heat pump type water heater includes: a compressor (1) that sucks and compresses refrigerant; a radiator (2) constructed such that heat exchange is performed between refrigerant discharged from the compressor (1) and water for hot-water supply and a flow of refrigerant and a flow of water for hot-water supply are opposed to each other; pressure reducing means (3, 30) that reduces pressure of refrigerant flowing from the radiator (2); and an evaporator (4), in which refrigerant flowing from the pressure reducing means (3, 30) is evaporated by absorbing heat and refrigerant is discharged to flow to a suction side of the compressor (1) . In this heat pump type water heater, a refrigerant pressure on a high-pressure side is controlled such that when the refrigerant pressure on the high-pressure side is less than a predetermined pressure, an actual temperature difference (ΔT) between a refrigerant temperature flowing from the radiator (2) and a water temperature flowing into the radiator (2) becomes a predetermined target temperature difference (ΔTt). Furthermore, the heat pump type water heater is characterized in that:

at least at the time of starting of the heat pump cycle, a target pressure (Pt) on the high-pressure side is set, and the refrigerant pressure on the high-pressure side is controlled so as to approach the target pressure (Pt); and a target discharge temperature (Tt) of refrigerant discharged from the compressor (1) is set, a temperature difference (ΔT2) between the target discharge temperature (Tt) and an actual discharge temperature (T) is calculated, and the target pressure (Pt) is corrected to make the temperature difference (ΔT2) equal to or less than a predetermined value.

According to the invention of claim 2, stability of the cycle relative to a variation in the heat pump cycle, which is caused by external factors, can be improved by directly controlling pressure reducing means (3, 30) based on a high pressure value detected by a pressure sensor having a good response or the like.
The pressure sensor involves a large dispersion in detection values and is difficult to obtain a target COP. However, the target COP can be obtained by correcting a target pressure (Pt) on the basis of an actual discharge temperature (T) detected by the temperature sensor, which is small in dispersion. Since a control of the pressure reducing valve is made possible even when either of the pressure sensor and the temperature sensor is abnormal, reliability of a system can be improved on a user's side.
In the invention of claim 3, a control of setting the target pressure (Pt), controlling the refrigerant pressure on the high-pressure side to approach the target pressure (Pt), calculating the temperature difference (ΔT1) between the target temperature difference (ΔTt) and the actual temperature difference (ΔT), and correcting the target pressure (Pt) to make the temperature difference (ΔT1) equal to or less than a predetermined value is performed when at least one of an outside air temperature, an inlet refrigerant temperature of the evaporator (4), and an outlet refrigerant temperature of the evaporator (4) is less than a predetermined value.
When an optimum high-pressure F/B pressure reducing valve control for obtaining an optimum COP is to be performed in the case where an operating environment is low in outside air temperature (for example, an outside air temperature is 0°C or lower), delay in detection of temperature is generated in the temperature sensor such as a thermistor or the like in association with the heat capacity of functional parts and the heat pump cycle, so that it becomes difficult to control the pressure reducing means (3, 30) in real time and it becomes necessary to ensure stability to variation in the heat pump cycle.
According to the invention of claim 3, stability of the cycle can be improved by performing the high-pressure F/B pressure reducing valve control with the use of the pressure sensor at the time of low temperature when at least one of the outside air temperature, the inlet refrigerant temperature of the evaporator (4), and the outlet refrigerant temperature of the evaporator (4) is lower than a predetermined value (for example, 0°C or lower). The boiling-up operation is performed by the high-pressure F/B pressure reducing valve control corresponding to a target COP at the time of high temperature when at least one of the outside air temperature, the inlet refrigerant temperature of the evaporator (4), and the outlet refrigerant temperature of the evaporator (4) is higher than the predetermined value (for example, over 0°C).
Accordingly, when the outside air temperature is low, a value of the pressure sensor is used to give priority to the stability of the cycle, and a stable heating capacity can be ensured to eliminate abnormal stop of the system. In contrast, when the outside air temperature is high, the target COP can be obtained by the high-pressure F/B pressure reducing valve control that uses a value of the temperature sensor.
In the invention of claim 4, a control of setting the target pressure (Pt), controlling the refrigerant pressure on the high-pressure side to approach the target pressure (Pt), setting the target discharge temperature (Tt) of refrigerant discharged from the compressor (1), calculating a temperature difference (ΔT2) between the target discharge temperature (Tt) and the actual discharge temperature (T), and correcting the target pressure (Pt) to make the temperature difference (ΔT2) equal to or less than a predetermined value is performed when at least one of an outside air temperature, an inlet refrigerant temperature of the evaporator (4), and an outlet refrigerant temperature of the evaporator (4) is less than a predetermined value.
In the case where the operating environment is low in outside air temperature (for example, an outside air temperature is 0°C or lower), a delay in detection of temperature is generated in the temperature sensor such as a thermistor or the like in association with the heat capacity of functional parts and the heat pump cycle. Accordingly, there is a possibility that it becomes difficult to control the pressure reducing means (3, 30) in real time, and so it becomes necessary to ensure stability to variation in the heat pump cycle.
According to the invention of claim 4, stability of the cycle can be improved by performing the high-pressure F/B pressure reducing valve control with the use of the pressure sensor at the time of low temperature (for example, 0°C or lower) when at least one of the outside air temperature, the inlet refrigerant temperature of the evaporator (4), and the outlet refrigerant temperature of the evaporator (4) is lower than a predetermined value. The boiling-up operation is performed by the high-pressure F/B pressure reducing valve control corresponding to the target COP at the time of high temperature when at least one of the outside air temperature, the inlet refrigerant temperature of the evaporator (4), and the outlet refrigerant temperature of the evaporator (4) is higher than the predetermined value (for example, over 0°C).
Accordingly, at the time of low outside air temperature, a value of the pressure sensor is used to give priority to stability of the cycle, and a stable heating capacity can be ensured to eliminate abnormal stop of the system. In contrast, at the time of high outside air temperature, a target COP can be obtained by the high-pressure F/B pressure reducing valve control that uses a value of the temperature sensor.
Further, in the invention of claim 5, a pressure sensor (10) is provided between a refrigerant flow downstream side of the radiator (2) and the pressure reducing means (3, 30), or on a refrigerant flow upstream side of the radiator (2), to detect the refrigerant pressure on the high-pressure side. According to the invention of claim 5, a cycle stability relative to a variation in the heat pump cycle, which is caused by external factors, can be improved by using the pressure sensor (10) having a good response as means that detects high pressures.
In the invention of claim 6, a heat pump type water heater includes: a compressor (1) that sucks and compresses refrigerant; a radiator (2) constructed such that heat exchange is performed between refrigerant discharged from the compressor (1) and water for hot-water supply and a flow of refrigerant and a flow of water for hot-water supply are opposed to each other; pressure reducing means (3, 30) that reduces pressure of refrigerant flowing from the radiator (2); and an evaporator (4), in which refrigerant flowing from the pressure reducing means (3, 30) is evaporated and from which refrigerant flows toward a suction side of the compressor (1). In the heat pump type water heater, a refrigerant pressure on a high-pressure side is controlled such that when the refrigerant pressure on the high-pressure side is less than a predetermined pressure, an actual temperature difference (ΔT) between a refrigerant temperature flowing from the radiator (2) and a water temperature flowing into the radiator (2) becomes a predetermined target temperature difference (ΔTt).
Furthermore, the heater pump type water heater is characterized in that: a discharge temperature sensor (8) for detecting a discharge temperature of refrigerant discharged from the compressor (1) is provided; and
at least at the time of starting of the heat pump cycle, a target discharge temperature (Tt) of refrigerant discharged from the compressor (1) is set, a temperature difference (ΔT2) between the target discharge temperature (Tt) and an actual discharge temperature (T) is calculated, and the target discharge temperature (Tt) is corrected to make the temperature difference (ΔT2) equal to or less than a predetermined value.
According to the invention of claim 6, a refrigerant state on the high-pressure side can be detected by the use of the temperature sensor (8), which involves less dispersion in detection values as compared with the pressure sensor (10). Therefore, it becomes possible to further surely obtain the target COP.
In the invention described in claim 7, a control of correcting the target discharge temperature (Tt) to make the temperature difference (ΔT2) between the target discharge temperature (Tt) and the actual discharge temperature (T) equal to or less than a predetermined value is performed when at least one of an outside air temperature, an inlet refrigerant temperature of the evaporator (4), and an outlet refrigerant temperature of the evaporator (4) is less than a predetermined value.
According to the invention of claim 7, at the time of low outside air temperature, a value of the pressure sensor is used to give priority to stability of the cycle, a stable heating capacity can be ensured to eliminate abnormal stop of the system. In contrast, at the time of high outside air temperature, the target COP can be obtained by the high-pressure F/B pressure reducing valve control that uses a value of the temperature sensor.
Incidentally, the reference numerals in parentheses of the respective means serve as examples representative of the corresponding relationship with specific means described in embodiments described later.

Brief Description of the Drawings

Fig. 1 is a schematic view showing the construction of a heat pump type water heater according to a first embodiment of the invention.
Fig. 2 is a flowchart illustrating an example of control performed by a control device 16 in the embodiment of Fig. 1.
Fig. 3 is a graph illustrating an example of control characteristics of a high-pressure F/B pressure reducing valve control in the flowchart in Fig. 2.
Fig. 4 is a graph illustrating an example of correction characteristics of a high pressure correction in the flowchart in Fig. 2.
Fig. 5 is a flowchart illustrating an example of control performed by a control device 16 in a second embodiment of the invention.
Fig. 6 illustrates an example of a map for calculation of a target discharge temperature Tt in the flowchart of Fig. 5.
Fig. 7 shows a graph illustrating an example of correction characteristics of a high-pressure correction in the flowchart of Fig. 5.
Fig. 8 is a flowchart illustrating an example of control performed by a control device 16 in a third embodiment of the invention.
Fig. 9 is a graph illustrating an example of control characteristics of a temperature difference F/B pressure reducing valve control in the flowchart in Fig. 8.
Fig. 10 is a flowchart illustrating an example of control performed by a control device 16 in a fourth embodiment of the invention.
Fig. 11 is a graph illustrating an example of control characteristics of a discharge-temperature difference F/B pressure reducing valve control in the flowchart in Fig. 10.
Fig. 12 is a schematic view showing the construction of a heat pump type water heater according to a further embodiment of the invention.

Best Mode for Carrying Out the Invention

Embodiments of the invention will be described below with reference to the drawings.

(First Embodiment)

Fig. 1 is a schematic view showing the construction of a heat pump type water heater according to the first embodiment of the invention. The heat pump type water heater according to the embodiment includes a hot-water storage tank 6 that stores water for hot-water supply, water flowing pipes C, H connected to the hot-water storage tank 6, a water pump 7 that circulates water for hot-water supply to the water flowing pipes C, H, a heat pump unit HU of a supercritical heat-pump cycle, described later, which makes a heating means for water for hot-water supply, a control device 16 that controls an operation of the heat pump type water heater, and the like.
The hot-water storage tank 6 is formed from a metal (for example, stainless steel) having an excellent corrosion resistance and structured in thermal insulation to be able to keep high-temperature water for hot-water supply warm over a long time. The water for hot-water supply stored in the hot-water storage tank 6 mixes with cold water in use to be adjusted to temperature and then used in a kitchen and a bath, however, can also be made use of as a heat source for floor heating, indoor air conditioning, or the like in addition to hot-water supply.
The water flowing pipes C, H includes a cold-water pipe C and a hot-water pipe H, which connect the hot-water storage tank 6 and a water heat exchanger (radiator) 2 described later. The cold-water pipe C is connected at one end thereof to a cold-water outlet 6a provided at a lower portion of the hot-water storage tank 6 and at the other end thereof to an inlet of a water passage (not shown) provided in the water heat exchanger 2. The hot-water pipe H is connected at one end thereof to an outlet of the water passage (not shown) provided in the water heat exchanger 2 and at the other end thereof to a hot-water inlet 6b provided on an upper portion of the hot-water storage tank 6.
The water pump 7 produces a water flow so that water for hot-water supply stored in the hot-water storage tank 6 flows from the cold-water outlet 6a to pass through the cold-water pipe C → the water passage of the water heat exchanger → the hot-water pipe H, and to return to the hot-water storage tank 6 through the hot-water inlet 6b, as indicated by arrows in Fig. 1. The water pump 7 can adjust an amount of water based on a rotating speed of a motor mounted therein (not shown), and is controlled in electrification by the control device 16.
The supercritical heat-pump cycle includes, as shown in Fig. 1, a compressor 1, the water heat exchanger 2, a variable expansion valve 3 as a pressure reducing means, an air heat exchanger (evaporator) 4, an accumulator 5, a refrigerant piping (a high-pressure piping Hi and a low-pressure piping Lo) for connection of these equipments, and the like, and is filled with carbon dioxide (abbreviated below to CO2), which serves as a refrigerant having a low critical temperature.
The compressor 1 is driven by a motor mounted therein (not shown). The compressor 1 compresses a drawn gas refrigerant to a critical pressure or higher and discharges the compressed refrigerant. An amount of the refrigerant discharged from the compressor 1 is variable according to the rotating speed of the motor.
The water heat exchanger 2 performs heat exchange between a gas refrigerant having a high temperature and high pressure pressurized in the compressor 1 and water for hot-water supply fed from the hot-water storage tank 6. The water heat exchanger 2 is provided with a refrigerant passage, which is adjacent to the water passage described above (not shown), and is constructed such that a direction, in which refrigerant flows through the refrigerant passage, and a direction, in which water for hot-water supply flows through the water passage, are opposed to each other.
The variable expansion valve 3 is provided between the water heat exchanger 2 and the air heat exchanger 4 to reduce pressure of the refrigerant cooled by the water heat exchanger 2 to feed the reduced refrigerant to the air heat exchanger 4. The variable expansion valve 3 is constructed to be electrically adjustable in valve opening degree, and controlled in electrification by the control device 16.
The air heat exchanger 4 receives air blown by an outside air fan 4a so that refrigerant, pressure of which is reduced by the variable expansion valve 3, is evaporated by heat exchange with outside air. The accumulator 5 performs vapor-liquid separation of the refrigerant evaporated in the air heat exchanger 4 so that a surplus refrigerant in the cycle is stored therein and only gas refrigerant is drawn into the compressor 1.
Subsequently, sensors arranged in respective portions of the heat pump type water heater will be described. The reference numeral 8 denotes a discharge temperature sensor that detects a discharge temperature of the refrigerant discharged from the compressor 1, and the reference numeral 9 denotes an outlet refrigerant temperature sensor that detects a temperature of the refrigerant flowing out from the water heat exchanger 2. The reference numeral 10 denotes a pressure sensor provided on an inlet side or an outlet side of the water heat exchanger 2 to detect a high pressure of the high-pressure piping Hi.
The reference numeral 11 denotes a refrigerant temperature sensor at an inlet of the air heat exchanger 4, and the reference numeral 12 denotes a refrigerant temperature sensor at an outlet of the air heat exchanger 4. The reference numeral 13 denotes an outside air temperature sensor that detects an outside air temperature. The reference numeral 14 denotes a water temperature sensor that detects an inlet temperature of water flowing into the water heat exchanger 2, and the reference numeral 15 denotes a boiling-up temperature sensor that detects a temperature of heated water for hot-water supply. All signals detected by a group of these sensors 8 to 15 are input into the control device 16, and electric control of the compressor 1, the variable expansion valve 3, the outside air fan 4a, the water pump 7, etc. is performed according to a flowchart described later.
Next, a normal boiling-up operation will be explained. The refrigerant is pressurized by the compressor 1 to become a high-temperature and high-pressure refrigerant, and radiates heat to water for hot-water supply in the water heat exchanger 2 to be cooled. The refrigerant from the water heat exchanger 2 is decompressed in the variable expansion valve 3 based on an opening degree of the variable expansion valve 3. Then, the refrigerant having a low temperature and low pressure decompressed in the variable expansion valve 3 absorbs heat from outside air in the air heat exchanger 4 (the outside air fan 4a: operated) to be evaporated, and is separated into gas refrigerant and liquid refrigerant in the accumulator 5. Thereafter, only the separated gas refrigerant is drawn into the compressor 1, so as to repeat a cycle operation.
The water for hot-water supply is pressurized by the water pump 7, absorbs heat from the refrigerant in the water heat exchanger 2 to become a hot water, and is fed to the hot-water storage tank 6 to be stored therein. For a boiling-up temperature, hot-water temperature is detected by the boiling-up temperature sensor 15, a circulating flow rate is adjusted by the water pump 7, and water temperature control is performed. When the water temperature sensor 14 detects a state in which all the water in the hot-water storage tank 6 becomes a hot water and water supplied from the cold-water pipe C becomes high in temperature, the circulation of the refrigerant and the circulation of water for hot-water supply are stopped.
Subsequently, an explanation will be given to an operation of the heat pump type water heater 1, according to the invention, at the time of a boiling-up operation. Fig. 2 is a flowchart illustrating an example of control performed by the control device 16 in the embodiment of Fig. 1. Fig. 3 is a graph illustrating an example of control characteristics of a high-pressure F/B pressure reducing valve control in the flowchart in Fig. 2, and Fig. 4 is a graph illustrating an example of correction characteristics of high pressure correction in the flowchart in Fig. 2.
The heat pump type water heater 1 according to the invention makes substantially a system, in which a target high pressure Pt is first provisionally set at the time of starting of a heat pump, a control is performed by the variable expansion valve 3 to provide for a target high pressure Pt while high pressure is detected by the pressure sensor 10, an actual temperature difference ΔT between an inlet water temperature and an outlet refrigerant temperature of the water heat exchanger 2 is detected, and the set target high pressure Pt is corrected to a value for obtaining a target COP (i.e., an optimum value, at which COP becomes highest, in the embodiment).
When a boiling-up operation of the heat pump system is started by an operation command from the control device 16, high pressure at the time of stabilization of the cycle, determined by an outside air temperature, an inlet water temperature of the water heat exchanger 2, and a target boiling-up temperature, is estimated, and a target high pressure Pt is set provisionally in step S1 shown in Fig. 2.
In the next step S2, respective cycle functional parts such as the compressor 1, the outside air fan 4a, the water pump 7, etc. are operated. Furthermore, while an actual pressure is detected by the pressure sensor 10, an opening degree of the variable expansion valve 3 is controlled (high-pressure F/B pressure reducing valve control) so as to obtain the target high pressure Pt. Fig. 3 illustrates an example of control characteristics of the variable expansion valve 3. In the characteristics, the expansion valve 3 is throttled when an actual high pressure is low relative to a target high pressure, and the expansion valve 3 is opened when an actual high pressure is high relative to a target high pressure. As the actual high pressure approaches the target high pressure, the expansion valve 3 is reduced in opening degree to improve the heat-pump cycle in stability.
In the next step S3, it is determined whether the target high pressure has been reached. When the determination is NO and the actual high pressure is not reached to the target high pressure, a high-pressure F/B pressure reducing valve control in step S2 is continued. When the actual high pressure does not reach the target high pressure and the determination in step S3 is YES, the procedure proceeds to step S4 and an actual temperature difference ΔT between an inlet water temperature and an outlet refrigerant temperature of the water heat exchanger 2 is detected. In step S5, a temperature difference ΔT1 between a target temperature difference ΔTt for obtaining an optimum COP, and the actual temperature difference ΔT is calculated. The target temperature difference ΔTt may be a predetermined value (for example, 10 °C), or may be calculated according to the map.
In the next step S6, it is determined whether an absolute value of the temperature difference ΔT1 calculated in step S5 is equal to or less than a predetermined value (3 °C in this example). When the determination in step S6 is NO and the absolute value of the temperature difference ΔT1 is equal to or larger than the predetermined value, the procedure proceeds to step S7 to correct the target high pressure Pt and repeats again the high-pressure F/B pressure reducing valve control in step S2. Fig. 4 illustrates an example of correction characteristics of high-pressure correction. In the characteristics, when the temperature difference ΔT1 calculated in step S5 is positive (an actual temperature difference ΔT is short of the target temperature difference ΔTt), the target high pressure Pt is positive-corrected. Furthermore, when the temperature difference is negative (an actual temperature difference ΔT is over the target temperature difference ΔTt), the target high pressure Pt is negative-corrected.
When the absolute value of the temperature difference ΔT1 becomes equal to or less than the predetermined value and the determination in step S6 is YES, the procedure proceeds to step S8 without performing correction of the target high pressure, and subsequently shifts to an optimum high-pressure F/B pressure reducing valve control. In step S9, it is determined whether an operation shutdown command has been input. When the determination of step S9 is NO and any operation shutdown command is not input, the optimum high-pressure F/B pressure reducing valve control in step S8 is continued. Thereafter, when an operation shutdown command is input and results of the determination in step S9 is YES, the boiling-up operation is ended.
Subsequently, features and effects in this embodiment will be now described. At least, when the heat pump cycle is started, a target high pressure Pt on a high-pressure side is set, and a refrigerant pressure on the high-pressure side is controlled so as to become the target high pressure Pt. Furthermore, the temperature difference ΔT1 between the target temperature difference ΔTt and the actual temperature difference ΔT is calculated, and the target high pressure Pt is corrected so as to make the temperature difference ΔT1 equal to or less than a predetermined value.
Accordingly, stability of the cycle relative to a variation in the heat pump cycle, which is caused by external factors, can be improved by directly controlling the variable expansion valve 3 based on a high pressure value detected by a pressure sensor having a good response.
The pressure sensor involves a large dispersion in detection values and it is difficult to obtain a target COP. However, the target COP can be obtained by correcting the target high pressure Pt on the basis of an actual temperature difference ΔT detected by the temperature sensor, which involves less dispersion. Since control of the pressure reducing valve is made possible even when either of the pressure sensor and the temperature sensor is abnormal, reliability of the system can be improved on a user's side.

(Second Embodiment)

Fig. 5 is a flowchart illustrating an example of control performed by the control device 16 in the second embodiment. Fig. 6 illustrates an example of a map for calculation of a target discharge temperature Tt in the flowchart of Fig. 5, and Fig. 7 shows a graph illustrating an example of correction characteristics of high-pressure correction in the flowchart of Fig. 5. A heat pump type water heater is the same in construction as that in the first embodiment. In the second embodiment, a target high pressure Pt is corrected while performing a high-pressure F/B pressure reducing valve control on the basis of a temperature difference in the same manner as in the first embodiment. However, in the second embodiment, the temperature difference is calculated by the use of a discharge temperature of the refrigerant discharged from the compressor 1.
When a boiling-up operation of the heat pump system is started by an operation command from the control device 16, high pressure at the time of stabilization of the cycle, determined by an outside air temperature, an inlet water temperature of the water heat exchanger 2, and a target boiling-up temperature, is estimated, and a target high pressure Pt is set provisionally in step S11 shown in Fig. 5.
In the next step S12, respective cycle functional parts such as the compressor 1, the outside air fan 4a, the water pump 7, etc. are operated. Furthermore, while an actual pressure is detected by the pressure sensor 10, an opening degree of the variable expansion valve 3 is controlled (i.e., high-pressure F/B pressure reducing valve control) so as to obtain the target high pressure Pt. Fig. 3 illustrates an example of control characteristics of the variable expansion valve 3. In the characteristics, the expansion valve 3 is throttled when an actual high pressure is low relative to a target high pressure, and the expansion valve 3 is opened when an actual pressure is high relative to a target high pressure. As an actual high pressure approximates to the target high pressure, the expansion valve is reduced in opening degree to improve the stability of the heat-pump cycle.
In the next step S13, it is determined whether the target high pressure has been reached. When the determination of step S13 is NO and the target high pressure is not reached, the high-pressure F/B pressure reducing valve control in step S12 is continued. When the actual high temperature reaches to the target high pressure and the determination in step S13 is YES, the procedure proceeds to step S14 and a target discharge temperature Tt is calculated from an outside air temperature and a target boiling-up temperature based on the map (or calculating formula) in Fig. 6. In step S15, a temperature difference ΔT2 between the target discharge temperature Tt for obtaining an optimum COP, and an actual discharge temperature T is calculated.
In the next step S16, it is determined whether an absolute value of the temperature difference ΔT2 calculated in step S15 is equal to or less than a predetermined value (3°C in this example). When the determination of step S16 is NO and the absolute value of the temperature difference ΔT2 is equal to or more than the predetermined value, the procedure proceeds to step S17 to correct the target high pressure Pt and repeats again the high-pressure F/B pressure reducing valve control in step S12. Fig. 7 illustrates an example of correction characteristics of high-pressure correction. In the characteristics of Fig. 7, when the temperature difference ΔT2 calculated in step S15 is positive (an actual discharge temperature T is short of the target discharge temperature Tt), the target high pressure Pt is positive-corrected. Furthermore, when the temperature difference ΔT2 is negative (an actual discharge temperature T is over the target discharge temperature Tt), the target high pressure Pt is negative-corrected.
When the absolute value of the temperature difference ΔT2 becomes equal to or less than the predetermined value and the determination of step S16 is YES, the procedure proceeds to step S18 without performing correction of the target high pressure, and subsequently shifts to the optimum high-pressure F/B pressure reducing valve control. In step S19, it is determined whether an operation shutdown command has been input. When the determination of step S19 is NO and any operation shutdown command is not input, the optimum high-pressure F/B pressure reducing valve control in step S18 is continued. In contrast, when an operation shutdown command is input and the determination of step S19 is YES, the boiling-up operation is ended.
Subsequently, features and effects in this embodiment will be described. At least, when the heat pump cycle is started, the target high pressure Pt on a high-pressure side is set, the refrigerant pressure on the high-pressure side is controlled so as to become the target high pressure Pt, the target discharge temperature Tt of the refrigerant discharged from the compressor 1 is set, the temperature difference ΔT2 between the target discharge temperature Tt and an actual discharge temperature T is calculated, and the target high pressure Pt is corrected so as to make the temperature difference ΔT2 equal to or less than a predetermined value.
Accordingly, stability of the cycle relative to a variation in the heat pump cycle, which is caused by external factors, can be improved by directly controlling the variable expansion valve 3 based on a high pressure value detected by a pressure sensor having a good response.
Since the pressure sensor involves a large dispersion in detection values, it is difficult to obtain a target COP. However, the target COP can be obtained by correcting the target high pressure Pt on the basis of an actual discharge temperature T detected by the temperature sensor, which involves less dispersion. Since control of the pressure reducing valve 3 is made possible even when either of the pressure sensor and the temperature sensor is abnormal, reliability of the system can be improved on a user's side.

(Third embodiment)

Fig. 8 is a flowchart illustrating an example of control performed by the control device 16 in the third embodiment of the invention. The invention provides a system, in which a high-pressure F/B pressure reducing valve control and a temperature difference F/B pressure reducing valve control are switched based on an outside air temperature detected by the outside air temperature sensor 13. In step S21, it is determined whether the outside air temperature is equal to or higher than a predetermined value (0°C in the embodiment). When the determination of step S21 is YES and the outside air temperature is equal to or higher than 0°C, the procedure proceeds to step S22 to set a target temperature difference ΔTt for obtaining an optimum COP.
In step S23, an actual temperature difference ΔT between an inlet water temperature and an outlet refrigerant temperature of the water heat exchanger 2 is detected, and the temperature difference F/B pressure reducing valve control for control of the variable expansion valve 3 is performed so as to obtain a target temperature difference ΔTt. Fig. 9 is a graph illustrating an example of control characteristics of the temperature difference F/B pressure reducing valve control in the flowchart in Fig. 8. In the characteristics, when a temperature difference ΔT1 is positive (an actual temperature difference ΔT is short of the target temperature difference ΔTt), the expansion valve 3 is throttled. In contrast, when the temperature difference is negative (an actual temperature difference AT is over the target temperature difference ΔTt), the expansion valve 3 is opened. The target temperature difference ΔTt may be a predetermined value (for example, 10°C), or may be calculated according to the map.
The high-pressure F/B pressure reducing valve control is performed such that the determination in step S21 is NO and an outside air temperature is lower than 0°C, the procedure proceeds to step S24 to first set a target high pressure Pt provisionally. Then, control operation is performed in the next step S25 by the variable expansion valve 3 so as to obtain the target high pressure Pt while detecting a high pressure by means of the pressure sensor 10. Furthermore, an actual temperature difference ΔT between an inlet water temperature and an outlet refrigerant temperature of the water heat exchanger 2 is detected, and the target high pressure Pt thus set is corrected to an optimum value, at which COP becomes highest.
Subsequently, features and effects in this embodiment will be explained. In this embodiment, the target high pressure Pt is set, the refrigerant pressure on the high-pressure side is controlled so as to become the target high pressure Pt, and a temperature difference ΔT1 between the target temperature difference ΔTt and an actual temperature difference ΔT is calculated. Furthermore, control operation that corrects the target high pressure Pt so as to make the temperature difference ΔT1 equal to or less than a predetermined value is performed, in the case where at least one of the outside air temperature, the inlet refrigerant temperature of the air heat exchanger 4, and the outlet refrigerant temperature of the air heat exchanger 4 is less than the predetermined value.
When an optimum high-pressure F/B pressure reducing valve control for obtaining an optimum COP is to be performed in the case where the operating environment is low in outside air temperature (for example, an outside air temperature is 0°C or lower), delay in detection of temperature is generated in the temperature sensor such as a thermistor or the like in association with the heat capacity of functional parts, the heat pump cycle or the like. In this case, it becomes difficult to control the variable expansion valve 3 in real time and it becomes necessary to ensure stability to variation in the heat pump cycle.
However, stability of the cycle can be improved by performing the high-pressure F/B pressure reducing valve control with the use of the pressure sensor at the time of low temperature when at least one of the outside air temperature, the inlet refrigerant temperature of the air heat exchanger 4, and the outlet refrigerant temperature of the air heat exchanger 4 is less than a predetermined value (for example, 0°C or lower). The boiling-up operation is performed by the high-pressure F/B pressure reducing valve control corresponding to a target COP, in a high temperature state where at least one of the outside air temperature, the inlet refrigerant temperature of the air heat exchanger 4, and the outlet refrigerant temperature of the air heat exchanger 4 is higher than the predetermined value (for example, over 0°C).
Accordingly, an operation is made possible, in which at the time of a low outside air temperature, a value of the pressure sensor is used to give priority to stability of the cycle, and a stable heating capacity can be ensured to eliminate abnormal stop of the system. Furthermore, at the time of a high outside air temperature, a target COP can be obtained by the high-pressure F/B pressure reducing valve control that uses a value of the temperature sensor.

(Fourth Embodiment)

Fig. 10 is a flowchart illustrating an example of control performed by the control device 16 in the fourth embodiment of the invention. The invention provides a system, in which a high-pressure F/B pressure reducing valve control and a discharge-temperature difference F/B pressure reducing valve control are switched over according to the outside air temperature detected by the outside air temperature sensor 13. In step S31, it is determined whether an outside air temperature is equal to or higher than a predetermined value (0°C in the embodiment). When the determination of step S31 is YES and the outside air temperature is equal to or higher than 0°C, the procedure proceeds to step S32 to set a target discharge temperature Tt for obtaining an optimum COP.
In step S33, an actual discharge temperature T of the compressor 1 is detected, and the discharge-temperature difference F/B pressure reducing valve control for control of the variable expansion valve 3 is performed so as to obtain a target discharge temperature Tt. Fig. 11 is a graph illustrating an example of control characteristics of the discharge-temperature difference F/B pressure reducing valve control in the flowchart in Fig. 10. In the characteristics, when a temperature difference ΔT2 is positive (an actual discharge temperature T is short of the target discharge temperature Tt), the expansion valve 3 is throttled. In contrast, when the temperature difference is negative (an actual discharge temperature T is over the target discharge temperature Tt), the expansion valve 3 is opened.
The high-pressure F/B pressure reducing valve control is performed such that when the determination in step S31 is NO and the outside air temperature is lower than 0°C, the procedure proceeds to step S34 to first set a target high pressure Pt provisionally. Furthermore, the control is performed in the next step S35 by the variable expansion valve 3 so as to obtain the target high pressure Pt while detecting a high pressure by means of the pressure sensor 10. In addition, the actual temperature difference ΔT between the inlet water temperature and the outlet refrigerant temperature of the water heat exchanger 2 is detected, and the target high pressure Pt thus set is corrected to an optimum value, at which COP becomes highest.
Subsequently, features and effects in the embodiment will be described. In this embodiment, a target high pressure Pt is set, a refrigerant pressure on a high-pressure side is controlled so as to become the target high pressure Pt, and a target discharge temperature Tt of the refrigerant discharged from the compressor 1 is set. Furthermore, the temperature difference ΔT2 between the target discharge temperature Tt and an actual discharge temperature T is calculated. In addition, a control that corrects the target high pressure Pt so as to make the temperature difference ΔT2 equal to or less than a predetermined value is performed, in the case where at least one of the outside air temperature, the inlet refrigerant temperature of the air heat exchanger 4, and the outlet refrigerant temperature of the air heat exchanger 4 is less than a predetermined value.
In the case where the operating environment is low in outside air temperature (for example, an outside air temperature is 0°C or lower), delay in detection of temperature is generated in the temperature sensor such as a thermistor or the like in association with the heat capacity of functional parts, the heat pump cycle and the like. In this case, there is a possibility that it becomes difficult to control the variable expansion valve 3 in real time, and it becomes necessary to ensure stability to variation in the heat pump cycle.
According to the embodiment described above, because a value of the pressure sensor is used at the time of low outside air temperature to give priority to stability of the cycle, a stable heating capacity can be ensured to eliminate abnormal stop of the system. Furthermore, a target COP can be obtained by the high-pressure F/B pressure reducing valve control that uses a value of the temperature sensor at the time of high outside air temperature.

(Other Embodiment)

Fig. 12 is a schematic view showing a structure of a heat pump type water heater according to another embodiment of the invention. The variable expansion valve 3 is used as a pressure reducing means in the above embodiments. However, the invention is not limited to the embodiments but a heat pump cycle, in which an ejector 30 is used as the pressure reducing means, will be used as shown in Fig. 12. Even in this case, the same effect can be obtained.
In the embodiments described above, the target high pressure Pt on the high-pressure side is set at the time of starting of the heat pump cycle. However, the same effect can also be obtained by performing a control, in which a target discharge temperature Tt of a refrigerant discharged from the compressor 1 is set in place of the target high pressure Pt on the high-pressure side, and a target temperature difference Tt is corrected so that a temperature difference ΔT2 between the target discharge temperature Tt and an actual discharge temperature T becomes equal to or less than a predetermined value.

Claims

A heat pump type water heater for heating water for hot-water supply in a vapor-compression type heat pump cycle in which heat on a low-temperature side is transferred to a high-temperature side, the heat pump type water heater comprising:
a compressor (1) that sucks and compresses refrigerant;

a radiator (2) constructed such that heat exchange is performed between refrigerant discharged from the compressor (1) and water for hot-water supply and a flow of refrigerant and a flow of water for hot-water supply are opposed to each other;

pressure reducing means (3, 30) that reduces pressure of refrigerant flowing from the radiator (2); and

an evaporator (4), in which refrigerant flowing from the pressure reducing means (3, 30) is evaporated by absorbing heat and refrigerant is discharged to flow to a suction side of the compressor (1),
wherein a refrigerant pressure on a high-pressure side is controlled such that when refrigerant pressure on the high-pressure side is less than a predetermined pressure, an actual temperature difference (ΔT) between a refrigerant temperature flowing from the radiator (2) and a water temperature flowing into the radiator (2) becomes a predetermined target temperature difference (ΔTt), characterized in that:
at least at the time of starting of the heat pump cycle, a target pressure (Pt) on the high-pressure side is set, and the refrigerant pressure on the high-pressure side is controlled so as to approach the target pressure (Pt); and

a temperature difference (ΔT1) between the target temperature difference (ΔTt) and the actual temperature difference (ΔT) is calculated, and the target pressure (Pt) is corrected to make the temperature difference (ΔT1) equal to or less than a predetermined value.
A heat pump type water heater for heating water for hot-water supply in a vapor-compression type heat pump cycle in which heat on a low-temperature side is transferred to a high-temperature side, the heat pump type water heater comprising:
a compressor (1) that sucks and compresses refrigerant;

a radiator (2) constructed such that heat exchange is performed between refrigerant discharged from the compressor (1) and water for hot-water supply and a flow of refrigerant and a flow of water for hot-water supply are opposed to each other;

pressure reducing means (3, 30) that reduces pressure of refrigerant flowing from the radiator (2); and

an evaporator (4), in which refrigerant flowing from the pressure reducing means (3, 30) is evaporated by absorbing heat and refrigerant is discharged to flow to a suction side of the compressor (1),
wherein a refrigerant pressure on a high-pressure side is controlled such that when refrigerant pressure on the high-pressure side is less than a predetermined pressure, an actual temperature difference (ΔT) between a refrigerant temperature flowing from the radiator (2) and a water temperature flowing into the radiator (2) becomes a predetermined target temperature difference (ΔTt), characterized in that:
at least at the time of starting of the heat pump cycle, a target pressure (Pt) on the high-pressure side is set, and the refrigerant pressure on the high-pressure side is controlled so as to approach the target pressure (Pt); and

a target discharge temperature (Tt) of refrigerant discharged from the compressor (1) is set, a temperature difference (ΔT2) between the target discharge temperature (Tt) and an actual discharge temperature (T) is calculated, and the target pressure (Pt) is corrected to make the temperature difference (ΔT2) equal to or less than a predetermined value.
The heat pump type water heater according to claim 1 , wherein a control of setting the target pressure (Pt), controlling the refrigerant pressure on the high-pressure side to approach the target pressure (Pt), calculating the temperature difference (ΔT1) between the target temperature difference (ΔTt) and the actual temperature difference (ΔT), and correcting the target pressure (Pt) to make the temperature difference (ΔT1) equal to or less than a predetermined value is performed when at least one of an outside air temperature, an inlet refrigerant temperature of the evaporator (4), and an outlet refrigerant temperature of the evaporator (4) is less than a predetermined value.
The heat pump type water heater according to claim 2, wherein a control of setting the target pressure (Pt), controlling the refrigerant pressure on the high-pressure side to approach the target pressure (Pt), setting the target discharge temperature (Tt) of refrigerant discharged from the compressor (1), calculating a temperature difference (ΔT2) between the target discharge temperature (Tt) and the actual discharge temperature (T), and correcting the target pressure (Pt) to make the temperature difference (ΔT2) equal to or less than a predetermined value is performed when at least one of an outside air temperature, an inlet refrigerant temperature of the evaporator (4), and an outlet refrigerant temperature of the evaporator (4) is less than a predetermined value.
The heat pump type water heater according to any one of claims 1 to 4, further comprising a pressure sensor (10) provided between a refrigerant flow downstream side of the radiator (2) and the pressure reducing means (3, 30), or on a refrigerant flow upstream side of the radiator (2) to detect the refrigerant pressure on the high-pressure side.
A heat pump type water heater comprising:
a compressor (1) that sucks and compresses refrigerant;

a radiator (2) constructed such that heat exchange is performed between refrigerant discharged from the compressor (1) and water for hot-water supply and a flow of refrigerant and a flow of water for hot-water supply are opposed to each other;

pressure reducing means (3, 30) that reduces pressure of refrigerant flowing from the radiator (2); and

an evaporator (4), in which refrigerant flowing from the pressure reducing means (3, 30) is evaporated and from which refrigerant flows toward a suction side of the compressor (1),
wherein a refrigerant pressure on a high-pressure side is controlled such that when the refrigerant pressure on the high-pressure side is less than a predetermined pressure, an actual temperature difference (ΔT) between a refrigerant temperature flowing from the radiator (2) and a water temperature flowing into the radiator (2) becomes a predetermined target temperature difference (ΔTt), characterized in that:
the heat pump type water heater further comprising a discharge temperature sensor (8) that detects a discharge temperature of refrigerant discharged from the compressor (1),
wherein at least at the time of starting of the heat pump cycle, a target discharge temperature (Tt) of refrigerant discharged from the compressor (1) is set, a temperature difference (ΔT2) between the target discharge temperature (Tt) and an actual discharge temperature (T) is calculated, and the target discharge temperature (Tt) is corrected to make the temperature difference (ΔT2) equal to or less than a predetermined value.
The heat pump type water heater according to claim 6, wherein a control of correcting the target discharge temperature (Tt) to make the temperature difference (ΔT2) between the target discharge temperature (Tt) and the actual discharge temperature (T) equal to or less than a predetermined value is performed when at least one of an outside air temperature, an inlet refrigerant temperature of the evaporator (4), and an outlet refrigerant temperature of the evaporator (4) is less than a predetermined value.