JP7485111B1 - Heat pump equipment - Google Patents

Abstract

[Problem] To provide a heat pump device capable of efficient operation while ensuring the reliability of a compressor. [Solution] A heat pump device according to one embodiment of the present invention comprises a compressor, a user-side heat exchanger for exchanging heat between water and a refrigerant, an electronic expansion valve, a heat source-side heat exchanger, and a control means for controlling the rotation speed of the compressor and the opening of the electronic expansion valve. The control means controls the electronic expansion valve based on predetermined upper and lower discharge temperatures, sets the upper discharge temperature according to the magnitude of the load on the compressor, reduces the opening of the electronic expansion valve so that the discharge temperature is equal to or higher than the lower discharge temperature when the discharge temperature is below the lower discharge temperature, increases the opening of the electronic expansion valve so that the discharge temperature is less than the upper discharge temperature when the discharge temperature is equal to or higher than the upper discharge temperature, and controls the opening of the electronic expansion valve so that the subcooling is a target subcooling when the discharge temperature is equal to or higher than the lower discharge temperature but less than the upper discharge temperature. [Selected Figure] Figure 1

Description

The present invention relates to heat pump devices such as heat pump-type hot water heaters.

Known heat pump devices include air conditioners, in which the refrigerant exchanges heat with air, and hot water heaters, in which the refrigerant exchanges heat with water. Hot water heaters have a refrigerant circuit that has a compressor, a user-side heat exchanger, an electronic expansion valve, and a heat source-side heat exchanger, and exchange heat between the high-temperature gas refrigerant compressed by the compressor and water in the user-side heat exchanger, heating the water with the heat released by the refrigerant (see, for example, Patent Document 1).

Hot water heaters can have smaller user-side heat exchangers than air conditioners. This is because water has a higher heat transfer coefficient than air, and the heat transfer area between the refrigerant and water can be made smaller. Heat pump devices used as hot water heaters have a narrow subcooling range in which operation is highly efficient due to the small user-side heat exchanger. Therefore, if the subcooling range is not appropriately adjusted, there is a risk of reduced operation efficiency.
Therefore, in the device described in Patent Document 1, a target subcooling level is calculated from the condensation pressure and the compressor rotation speed, and the opening of the electronic expansion valve is adjusted so that the subcooling level of the refrigerant circuit becomes the target subcooling level. This makes it possible to optimally adjust the subcooling level, enabling efficient operation.

JP 2011-69570 A

However, when the electronic expansion valve is adjusted according to the subcooling level, the state of the suction refrigerant and the discharge temperature are left to their own devices. As a result, the discharge temperature may be too high or too low depending on the installation conditions and variations in the amount of refrigerant charged, which may reduce the reliability of the compressor. Also, depending on the type of refrigerant, the discharge temperature may be more likely to be low or high.

In view of the above circumstances, the object of the present invention is to provide a heat pump device that can operate efficiently while ensuring the reliability of the compressor.

A heat pump device according to one embodiment of the present invention comprises:
a refrigerant circuit in which a compressor, a utilization-side heat exchanger that exchanges heat between water and a refrigerant, an electronic expansion valve, and a heat source-side heat exchanger are connected by piping;
a discharge temperature detection means for detecting a discharge temperature, which is a temperature of the refrigerant discharged from the compressor;
A subcooling detection means for detecting the subcooling of the refrigerant flowing out from the utilization side heat exchanger;
A load detection means for detecting the magnitude of the load on the compressor;
and a control means for controlling the rotation speed of the compressor and the opening degree of the electronic expansion valve.
The control means
Controlling the electronic expansion valve based on a predetermined upper discharge limit temperature and a predetermined lower discharge limit temperature;
setting the upper discharge temperature limit according to the magnitude of the load on the compressor;
When the discharge temperature is lower than the lower limit temperature, the opening degree of the electronic expansion valve is reduced so that the discharge temperature becomes equal to or higher than the lower limit temperature;
When the discharge temperature is equal to or higher than the upper discharge temperature limit, the opening degree of the electronic expansion valve is increased so that the discharge temperature becomes lower than the upper discharge temperature limit;
When the discharge temperature is equal to or higher than the lower discharge limit temperature and lower than the upper discharge limit temperature, the opening degree of the electronic expansion valve is controlled so that the subcooling temperature becomes the target subcooling temperature.

The load detection means may include a discharge pressure detection unit that detects a discharge pressure, which is the pressure of the refrigerant discharged from the compressor, and a suction pressure detection unit that detects a suction pressure, which is the pressure of the refrigerant sucked into the compressor.
The control means may set the upper discharge temperature based on a virtual discharge temperature, which is a discharge temperature when the refrigerant sucked into the compressor is saturated vapor, and is calculated based on at least the discharge pressure and the suction pressure.

The lower limit discharge temperature may be preset based on a predetermined minimum degree of superheat set for the compressor.
The control means may set the upper discharge limit temperature so that the upper discharge limit temperature is higher than the lower discharge limit temperature over the entire load range of the compressor.

Furthermore, the control means may set the upper discharge temperature limit by adding a correction value to the virtual discharge temperature.

Furthermore, the control means may increase the correction value as the load on the compressor decreases.
For example, the heat pump device may further include a memory unit that stores a plurality of temperature values that are preset according to the magnitude of the load on the compressor, and the control means may select the correction value from the plurality of temperature values based on the magnitude of the current load on the compressor.

The control means may determine that the load on the compressor is greater as the differential pressure between the discharge pressure and the suction pressure increases.

The refrigerant sealed in the refrigerant circuit is typically a refrigerant whose specific heat ratio in saturated vapor form at 10°C is less than 1.25.

The present invention provides a heat pump device that can operate efficiently while ensuring the reliability of the compressor.

1 is a refrigerant circuit diagram of a heat pump device according to an embodiment of the present invention. FIG. 13 is a diagram showing a comparison of a hot water heater (black circles in the figure) and an air conditioner (black squares in the figure) with respect to the relationship between subcooling and COP when the outside air temperature is 7° C. 2 is a block diagram showing a configuration of a control device in the heat pump device. FIG. FIG. 13 is a diagram showing an example of a target subcool table. FIG. 13 is a conceptual diagram illustrating a method for extracting a target subcool. 6 is a conceptual diagram illustrating a method for determining a discharge upper limit temperature correction value. FIG. FIG. 4 is a diagram showing an example of a discharge upper limit temperature and a discharge lower limit temperature under two conditions of different refrigerants and different operating states. 5 is a flowchart showing an example of a processing procedure executed in the control device.

The following describes an embodiment of the present invention with reference to the drawings.

[Basic configuration of heat pump device]
1 is a refrigerant circuit diagram of a heat pump device 100 according to one embodiment of the present invention. The heat pump device 100 of this embodiment is a heat pump type floor heating device (hot water heater).

The heat pump device 100 includes a refrigerant circuit 10 in which a compressor 11, a four-way valve 12, a user-side heat exchanger 13, an electronic expansion valve 14, and a heat source-side heat exchanger 15, which is an outdoor heat exchanger, are connected in sequence by piping, and a control device 20 as a control means.

The type of refrigerant filled in the refrigerant circuit 10 is not particularly limited, and for example, natural refrigerants such as hydrocarbon refrigerants and fluorocarbon refrigerants can be used. In particular, in this embodiment, as described later, a refrigerant that may cause a reversal of the lower limit temperature (hereinafter also referred to as the discharge lower limit temperature) and the upper limit temperature (hereinafter also referred to as the discharge upper limit temperature) of the discharge temperature, which is the temperature of the refrigerant discharged from the compressor 11, is used, more specifically, a refrigerant whose specific heat ratio γ (the ratio of constant pressure molar specific heat Cp to constant volume molar specific heat Cv: Cp/Cv) in saturated vapor at 10°C is less than 1.25. Examples of this type of refrigerant include R290 (specific heat ratio γ: 1.24), R1234yf (specific heat ratio γ: 1.17), and R454C (specific heat ratio γ: 1.24).

The compressor 11 is a variable capacity compressor that compresses a low-temperature, low-pressure refrigerant and discharges a high-temperature, high-pressure refrigerant. The high-temperature, high-pressure refrigerant discharged from the compressor 11 is supplied to port a of the four-way valve 12 via piping 91.

The four-way valve 12 is a flow path switching valve having ports a, b, c, and d. Based on a command from the control device 20, the four-way valve 12 is switched to either a first state in which ports a and b communicate with each other and ports c and d communicate with each other as shown by solid lines in FIG. 1, or a second state in which ports a and d communicate with each other and ports b and c communicate with each other as shown by dashed lines in FIG. 1. The four-way valve 12 is switched to the first state when performing heating operation, and is switched to the second state when performing defrosting operation of the heat source side heat exchanger 15. When the four-way valve 12 is switched to the first state, the refrigerant circulates through the refrigerant circuit 10 in the direction shown by the arrow in FIG. 1.

Port b of the four-way valve 12 is connected to the utilization side heat exchanger 13 via piping 92. Port c of the four-way valve 12 is connected to the intake port of the compressor 11 via piping 95. Port d of the four-way valve 12 is connected to the heat source side heat exchanger 15 via piping 94.

The user-side heat exchanger 13 is a radiator (condenser) that exchanges heat between the high-temperature, high-pressure refrigerant discharged from the compressor 11 and the water passing through the floor heating panel 18. The user-side heat exchanger 13 can be any type of heat exchanger capable of exchanging heat between water and the refrigerant, such as a plate-type heat exchanger, a double-tube heat exchanger, or a multi-tube heat exchanger. The refrigerant that has exchanged heat with the water in the user-side heat exchanger 13 is supplied in sequence to the electronic expansion valve 14 and the heat source-side heat exchanger 15 via piping 93.

The heat pump device 100 further includes a hot water circuit 96 formed by sequentially connecting the utilization side heat exchanger 13, the floor heating panel 18, and the hot water pump 19. In the hot water circuit 96, water (hot water) that has been heat exchanged with the refrigerant in the utilization side heat exchanger 13 circulates. The hot water circulates through the hot water circuit 96 in the direction indicated by the arrow in FIG. 1. The hot water circuit 96 has a serpentine passage 96a provided in the floor heating panel 18, and the floor heating panel 18 is heated by the hot water flowing through the serpentine passage 96a.

The electronic expansion valve 14 is a pressure reducer for reducing the pressure of the refrigerant that flows out from the user-side heat exchanger 13 through the pipe 93. The opening of the electronic expansion valve 14 is controlled based on a command from the control device 20.

The heat source side heat exchanger 15 is an evaporator that exchanges heat between the refrigerant flowing out from the electronic expansion valve 14 and outside air. The type of heat source side heat exchanger 15 is not particularly limited, and various types of heat exchangers can be used, such as a parallel flow type heat exchanger that can exchange heat between air and refrigerant, a fin tube type heat exchanger, and a plate fin type heat exchanger. A blower fan (not shown) may be placed near the heat source side heat exchanger 15.

The refrigerant that has exchanged heat with the outside air in the heat source side heat exchanger 15 is returned to the compressor 11 via the pipe 94, the four-way valve 12 in the first state, and the pipe 95. The pipe 95 may be provided with an accumulator (not shown) for separating the liquid phase refrigerant from the refrigerant that is returned to the compressor 11 through the pipe 95.

The piping 91 is provided with a discharge temperature sensor 31 as a discharge temperature detection means for detecting the discharge temperature, which is the temperature of the refrigerant discharged from the compressor 11, and a discharge pressure sensor 32 as a discharge pressure detection unit for detecting the discharge pressure, which is the pressure of the refrigerant discharged from the compressor 11. The piping 93 between the user-side heat exchanger 13 and the electronic expansion valve 14 is provided with a refrigerant temperature sensor 33 for detecting the temperature of the refrigerant flowing out from the user-side heat exchanger 13. The piping 95 is provided with a suction pressure sensor 34 as a suction pressure detection unit for detecting the suction pressure, which is the pressure of the refrigerant sucked into the compressor 11. The hot water circulation path 96 is provided at the outlet side of the user-side heat exchanger 13 with an outlet temperature sensor 35 for detecting the outlet temperature.

The control device 20 is a computer including a CPU, memory, etc., and controls the overall operation of the heat pump device 100. More specifically, the control device 20 outputs signals instructing the rotation speed of the compressor 11 and the opening degree of the electronic expansion valve 14, etc., based on the detection values of the discharge temperature sensor 31, the discharge pressure sensor 32, the refrigerant temperature sensor 33, the suction pressure sensor 34, the outlet hot water temperature sensor 35, etc., and controls each of them.

For example, the control device 20 rotates the compressor 11 so that the current hot water outlet temperature detected by the hot water outlet temperature sensor 34, i.e., the temperature of the water heated by the user-side heat exchanger 13, becomes a preset target temperature (target hot water outlet temperature).

The control device 20 also calculates the subcooling (degree of supercooling) of the refrigerant flowing out of the user-side heat exchanger 13 based on the detection value of the discharge pressure sensor 32 and the detection value of the refrigerant temperature sensor 33, and controls the opening of the electronic expansion valve 14 so that this calculation result becomes a target value. The discharge pressure sensor 32 and the refrigerant temperature sensor 33 correspond to a subcooling detection means that detects the subcooling of the refrigerant.

In general, hot water heaters can have smaller user-side heat exchangers than air conditioners. This is because water has a higher heat transfer coefficient than air, and the heat transfer area between the refrigerant and water can be made smaller. Heat pump devices used as hot water heaters have a narrower subcooling range at which high operating efficiency can be achieved due to the small user-side heat exchanger. In other words, in terms of the relationship between subcooling and the coefficient of performance (COP), which represents operating efficiency, changes in subcooling have a greater impact on the COP in hot water heaters than in air conditioners, and if the subcooling is not strictly controlled to maintain it within a narrow range, the COP may deteriorate and the operation may become inefficient.

For example, Figure 2 compares the relationship between subcooling and COP for a hot water heater (black circle in the figure) and an air conditioner (black square in the figure) when the outside air temperature is 7°C. As shown in Figure 2, the COP of a hot water heater is significantly lower when the subcooling is 5°C or higher than that of an air conditioner, and it can be seen that changes in subcooling have a large impact on the COP. Water has a higher heat transfer coefficient than air, but in the subcooling region, the heat transfer coefficient of the refrigerant side drops significantly and there is no large difference in the heat transfer coefficient (the heat transfer coefficient is the reciprocal of the sum of the thermal resistances, so the areas with high thermal resistance are dominant). Therefore, the proportion of the two-phase region in the entire heat exchanger when the subcooling is increased decreases more rapidly in the hot water heater. The sudden decrease in the area of the two-phase region with high heat transfer coefficient increases the discharge pressure, and the COP drops rapidly as the subcooling increases. In this way, in a hot water heater, if the subcooling is not adjusted to be maintained within an appropriate range, the operating efficiency will drop rapidly.

Therefore, subcooling control is known, which calculates a target subcooling from the condensation pressure and compressor rotation speed, and controls the opening of the electronic expansion valve so that the subcooling of the refrigerant circuit becomes the target subcooling (see, for example, Patent Document 1). Subcooling control subtracts the target subcooling from the current subcooling, and when the result of the subtraction is positive, the opening of the electronic expansion valve is increased in response to the value of the subtraction result, and when the result of the subtraction is negative, the opening of the electronic expansion valve is decreased in response to the value of the subtraction result. This allows the subcooling to be optimally adjusted, enabling efficient operation.

However, when the electronic expansion valve is adjusted according to the subcooling, unlike when the opening of the electronic expansion valve is controlled based on the target discharge temperature, the state of the refrigerant sucked into the compressor and the discharge temperature are left to chance. For this reason, the discharge temperature may be too high or too low due to influences such as variations in the length of pipes 92 and 93 and the amount of refrigerant charged, which may reduce the reliability of the compressor.

For example, a lower limit discharge temperature and an upper limit discharge temperature are set for the discharge temperature. The lower limit discharge temperature is set in advance based on a predetermined minimum degree of superheat set for the compressor 11. The predetermined minimum degree of superheat is the minimum degree of superheat required to ensure lubrication of the compressor, for example, the minimum required discharge SH set as a specification for the compressor 11. For this reason, if subcooling control is performed when the discharge temperature is below the lower limit discharge temperature, there is a risk that the humidity of the refrigerant sucked into the compressor will become excessively high. On the other hand, the upper limit discharge temperature is set for the purpose of protecting the compressor. Therefore, if subcooling control is performed when the discharge temperature is equal to or higher than the upper limit discharge temperature, there is a risk that the discharge temperature will rise excessively.

In addition, the lower and upper limit discharge temperatures vary depending on the type of refrigerant and the operating state of the compressor, so the discharge temperature may tend to be low or high depending on the type of refrigerant used.

To solve such problems, the control device 20 controls the opening degree of the electronic expansion valve 14 based on the upper limit discharge temperature and the lower limit discharge temperature (also called the predetermined temperature range) that are preset according to the type of refrigerant. The control device 20 sets the upper limit discharge temperature according to the magnitude of the load on the compressor 11. For example, when the discharge temperature is outside the predetermined temperature range, the control device 20 controls the opening degree of the electronic expansion valve 14 so that the discharge temperature falls within the predetermined temperature range. When the discharge temperature is within the predetermined temperature range, the control device 20 controls the opening degree of the electronic expansion valve 14 so that the subcooling is the target value. Specifically, when the discharge temperature is less than the lower limit discharge temperature, the control device 20 reduces the opening degree of the electronic expansion valve 14 so that the discharge temperature is equal to or greater than the lower limit discharge temperature, when the discharge temperature is equal to or greater than the upper limit discharge temperature, the control device 20 increases the opening degree of the electronic expansion valve 14 so that the discharge temperature is less than the upper limit discharge temperature, and when the discharge temperature is equal to or greater than the lower limit discharge temperature and less than the upper limit discharge temperature, the control device 20 controls the opening degree of the electronic expansion valve 14 so that the subcooling is the target subcooling.

[Control device details]
The following describes the details of the control device 20. FIG 3 is a block diagram showing the configuration of the control device 20.

As shown in FIG. 3, the control device 20 has a target subcool extraction unit 21, a load determination unit 22, a discharge upper limit temperature setting unit 23, a discharge temperature determination unit 24, and a memory unit 25. The target subcool extraction unit 21, the load determination unit 22, the discharge upper limit temperature setting unit 23, and the discharge temperature determination unit 24 are functional blocks of the CPU of the control device 20, and the memory unit 25 is a semiconductor memory or other storage device.

(Target subcooling extraction part)
The target subcool extracting unit 21 extracts a target subcool based on the rotation speed instructed by the control device 20 to the compressor 11 and the detection value of the discharge pressure sensor 32. The memory unit 25 stores a target subcool table that is calculated in advance based on the condensation pressure state of the refrigerant in the user side heat exchanger 13 and the rotation speed of the compressor 11. The target subcool extracting unit 21 extracts a target subcool from the target subcool table stored in the memory unit 25 based on the rotation speed instructed by the control device 20 to the compressor 11 and the discharge pressure sensor 32. The control device 20 controls the opening of the electronic expansion valve 14 so that the current subcool calculated based on the detection values of the discharge pressure sensor 32 and the refrigerant temperature sensor 33 becomes the target subcool. The current subcool is calculated by subtracting the detection value of the refrigerant temperature sensor 33 from a value obtained by converting the detection value of the discharge pressure sensor 32 into a saturation temperature.

Figure 4 shows an example of a target subcooling table. Here, the left side of the target subcooling table shows the items, which are, from top to bottom, "condensation pressure state," "condensation pressure threshold (MPaG)," and "rotation speed (rps (rotations per second))."

The "condensation pressure state" distinguishes whether the condensation pressure is rising or falling. In practice, when the detection value of the discharge pressure sensor 32 acquired by the control device 20 at a predetermined interval changes from below to above the previous detection value, it is judged as "rising," and when it changes from above to below the previous detection value, it is judged as "falling."

The "rotation speed" is divided into three zones (70 rps or more, 40 rps or more but less than 70 rps, and less than 40 rps). The "condensation pressure threshold" is divided into three zones as shown in Figure 5, and a target subcooling is set for each zone. The condensation pressure threshold that separates these three zones has hysteresis in response to the rise/fall of the condensation pressure to reduce hunting in the control.

For example, when the rotation speed of the compressor 11 is 40 rps or more and less than 70 rps, when the pressure is on an upward trend, the condensation pressure threshold is divided into zones of less than 3.0 MPaG, 3.0 MPaG or more and less than 3.6 MPaG, and 3.6 MPaG or more, and the target subcooling is set to 10°C, 8°C, and 6°C, respectively, starting from the lowest pressure zone. Conversely, when the pressure is on a downward trend, the condensation pressure threshold is divided into zones of less than 2.8 MPaG, 2.8 MPaG or more and less than 3.4 MPaG, and 3.4 MPaG or more, and the target subcooling is set to 10°C, 8°C, and 6°C, respectively, starting from the lowest pressure zone. The target subcooling is determined to be the subcooling that maximizes the COP for each condensing pressure and the rotation speed of the compressor 11, so even if the condensing pressure changes, by switching the target subcooling accordingly, strict subcooling control that can maintain a high COP even if the condensing pressure changes can be performed.

In addition, when the rotation speed of the compressor 11 is less than 40 rps, the target subcooling is specified as 6°C, 5°C, and 4°C, starting from the zone with the lowest condensing pressure, and when the rotation speed of the compressor 11 is 70 rps or more, the target subcooling is specified as 12°C, 10°C, and 7°C, starting from the zone with the lowest condensing pressure.

Note that the condensation pressure threshold, rotation speed, and target subcooling values in Figure 4 are merely examples and can be changed as desired depending on the type of refrigerant, installation conditions, operating conditions, etc.

(Load Determination Unit)
The load determining unit 22 determines the magnitude of the load on the compressor 11. In this embodiment, the load determining unit 22 calculates the load on the compressor 11 based on the differential pressure between the discharge pressure (high pressure) and the suction pressure (low pressure), and determines to which of a plurality of preset zones the calculated load magnitude belongs. The discharge pressure sensor 32 and the suction pressure sensor 34 correspond to a load detecting means for detecting the magnitude of the load on the compressor 11.

Figure 6 is a conceptual diagram explaining the above-mentioned multiple regions, and shows a method for determining the discharge upper limit temperature correction value selected according to the magnitude of the load on the compressor 11. Here, as shown in Figure 6, it is divided into three zones, and a discharge upper limit temperature correction value is set for each zone. The differential pressure that divides these three zones has hysteresis corresponding to the rise/fall of the differential pressure in order to reduce hunting in the control.

The discharge upper limit temperature correction value is set to a higher temperature value as the load (differential pressure) of the compressor 11 is smaller. For example, when the differential pressure is on the rise, the pressure threshold is divided into zones of less than 1.5 MPa, 1.5 MPa to less than 2.3 MPa, and 2.3 MPa or more, and the discharge upper limit temperature correction values are specified as 30°C, 15°C, and 0°C, respectively, starting from the lowest pressure zone. Conversely, when the differential pressure is on the decrease, the pressure threshold is divided into zones of less than 1.3 MPa, 1.3 MPa to less than 2.1 MPa, and 2.1 MPa or more, and the discharge upper limit temperature correction values are specified as 30°C, 15°C, and 0°C, respectively, starting from the lowest pressure zone. The discharge upper limit temperature correction value and pressure threshold can be set arbitrarily according to the type of refrigerant, and are determined in advance by performing experiments, etc., and stored in the memory unit 25.

In this way, the memory unit 25 stores a number of temperature values (30°C, 15°C, and 0°C in the example of FIG. 6) that are preset according to the magnitude of the load on the compressor 11, and the load determination unit 22 selects the discharge upper limit temperature correction value from the above-mentioned number of temperature values based on the magnitude of the current load on the compressor 11. Note that when the differential pressure is equal to or greater than a predetermined threshold value (2.3 MPa (when the differential pressure is increasing) or 2.1 MPa (when the differential pressure is decreasing)), the temperature value (discharge upper limit temperature correction value) is 0°C, so when the differential pressure is equal to or greater than the threshold value, the discharge upper limit temperature is not corrected, and the virtual discharge temperature stored in the memory unit 25 is treated as the discharge upper limit temperature.

(Upper discharge temperature setting unit)
The discharge upper limit temperature setting unit 23 sets the discharge upper limit temperature according to the magnitude of the load on the compressor 11. The discharge upper limit temperature is set by adding a discharge upper limit temperature correction value (see FIG. 6 ) determined according to the magnitude of the load on the compressor 11 to the virtual discharge temperature stored in the storage unit 25.

The virtual discharge temperature is the discharge temperature calculated based on the discharge pressure and suction pressure when the refrigerant drawn into the compressor 11 is saturated vapor (with a dryness of 1), and refers to the discharge temperature when adjusted to an ideal refrigeration cycle. The calculation parameters for the virtual discharge temperature may include the rotation speed of the compressor 11 in addition to the discharge pressure and suction pressure.

The smaller the specific heat ratio γ of the refrigerant used, the lower the virtual discharge temperature. Therefore, for example, with a refrigerant with a small specific heat ratio γ, such as R290, there is a risk of a reversal of the discharge upper limit temperature and the discharge lower limit temperature (discharge upper limit temperature < discharge lower limit temperature) occurring depending on the operating state (load) of the compressor 11. In such a case, the reversal makes it impossible to stably perform the desired subcooling control. In this embodiment, a discharge upper limit temperature correction value determined depending on the load of the compressor 11 is added to the virtual discharge temperature to prevent a reversal of the discharge upper limit temperature and the discharge lower limit temperature, thereby achieving appropriate subcooling control and maintaining a high COP.

Figure 7 shows an example of the upper and lower discharge temperatures when R290 is used as the refrigerant, in comparison with a refrigerant for which the upper and lower discharge temperatures are relatively unlikely to reverse (R32 (specific heat ratio γ at saturated vapor at 10°C: 1.53)). For example, in an operating state (state 1) when the evaporation temperature is 0°C and the condensation temperature is 37°C, if the refrigerant is R32 (minimum degree of superheat: 15°C), the lower discharge temperature is 52°C and the upper discharge temperature is 73.5°C, and there is a temperature difference of 20°C or more between these. In contrast, in the same operating state (state 1), if the refrigerant is R290 (minimum degree of superheat: 10°C), the lower discharge temperature is 47°C and the upper discharge temperature is 46.7°C, and the upper and lower discharge temperatures are reversed.

In addition, in the operating state (state 2) when the evaporation temperature is 2°C and the condensation temperature is 57°C, if the refrigerant is R32, the lower discharge limit temperature is 72°C and the upper discharge limit temperature is 110.8°C, with a temperature difference of approximately 40°C between them, whereas in the same operating state (state 2) when the refrigerant is R290, the lower discharge limit temperature is 67°C and the upper discharge limit temperature is 69.7°C, with the upper discharge limit temperature approaching the lower discharge limit temperature, making it difficult to maintain the temperature difference between them.

When the load on the compressor 11 is large, the upper and lower discharge temperature do not invert, and the upper and lower discharge temperature do not approach each other. However, in an operating state where the load on the compressor 11 is relatively small, such as in state 1 and state 2 shown in FIG. 7, such inversions and approaches do occur. Therefore, in this embodiment, the smaller the load on the compressor 11, the larger the temperature correction value (30°C in this example) is added to the virtual discharge temperature to increase the upper discharge temperature, thereby preventing the upper and lower discharge temperature from inverting.

In addition, by setting multiple discharge upper limit temperature correction values according to the load on the compressor 11, it is possible to achieve subcooling control that is adapted to the operating conditions of the compressor 11, which change from moment to moment.

The memory unit 25 stores the target subcool table (Figure 4), the upper discharge temperature correction value (Figure 6), the virtual discharge temperature, and the lower discharge temperature. The upper discharge temperature setting unit 23 sets the upper discharge temperature so that the upper discharge temperature is higher than the lower discharge temperature across the entire load range of the compressor 11.

(Discharge temperature determination unit)
The discharge temperature determination unit 24 compares the temperature (discharge temperature) of the refrigerant discharged from the compressor 11 with the discharge lower limit temperature and the discharge upper limit temperature stored in the memory unit 25, and determines whether the discharge temperature is greater than or equal to the discharge lower limit temperature and less than the discharge upper limit temperature.

When the discharge temperature is less than the lower discharge limit temperature, the control device 20 reduces the opening of the electronic expansion valve 14 so that the discharge temperature is equal to or greater than the lower discharge limit temperature. When the discharge temperature is equal to or greater than the upper discharge limit temperature, the control device 20 increases the opening of the electronic expansion valve 14 so that the discharge temperature is less than the upper discharge limit temperature. When the discharge temperature is equal to or greater than the lower discharge limit temperature but less than the upper discharge limit temperature, the control device 20 controls the opening of the electronic expansion valve 14 so that the subcooling is the target subcooling.

[Operation of heat pump device]
Next, a specific control procedure executed by the control device 20 will be described together with the operation of the heat pump device 100. FIG.

First, the control device 20 starts the operation of the hot water pump 19 to circulate water (hot water) through the hot water circuit 96, and switches the four-way valve 12 to the first state shown in FIG. 1. The control device 20 then operates the heat pump device 100 by determining the rotation speed of the compressor 11 and starting it so that the detection value of the hot water outlet temperature sensor 35 becomes the preset target hot water outlet temperature (ST101).

After a predetermined time has elapsed until the circulation of the refrigerant in the refrigerant circuit 10 becomes stable, the control device 20 acquires the pressure of the refrigerant discharged from the compressor 11 (discharge pressure) and the pressure of the refrigerant sucked into the compressor (suction pressure) (ST102). The discharge pressure is acquired from the discharge pressure sensor 32, and the suction pressure is acquired from the suction pressure sensor 34.

The control device 20 (load determination unit 22) calculates the magnitude of the load (differential pressure) of the compressor 11 based on the acquired discharge pressure and suction pressure, and determines whether this is equal to or greater than a predetermined threshold value set in advance (ST103).

The predetermined threshold is a pressure value (differential pressure between discharge pressure and suction pressure) for determining whether or not a predetermined correction value (Figure 6) should be added to the discharge upper limit temperature, and in the example of Figure 6, it is 2.3 MPa (when the differential pressure increases) or 2.1 MPa (when the differential pressure decreases). When the differential pressure is less than the predetermined threshold (No in ST103), the control device 20 (discharge upper limit temperature setting unit 23) corrects the discharge upper limit temperature (ST104).

The upper discharge temperature limit is corrected by adding a discharge upper temperature limit correction value to the virtual discharge temperature. The discharge upper temperature limit correction value is a temperature value that is preset in stages according to the magnitude of the pressure difference between the discharge pressure and the suction pressure, as shown in FIG. 6. As a result, the smaller the load (pressure difference) on the compressor 11, the higher the discharge upper temperature limit is set relative to the virtual discharge temperature.

When the load on the compressor 11 is equal to or greater than a predetermined threshold (Yes in ST103), the discharge upper limit temperature is not corrected and the virtual discharge temperature previously stored in the memory unit 25 continues to be used as the discharge upper limit temperature.

Then, the control device 20 (discharge temperature determination unit 24) determines whether the discharge temperature is less than the discharge lower limit temperature (ST105). The discharge temperature is acquired from the discharge temperature sensor 31. When the discharge temperature is less than the discharge lower limit temperature (Yes in ST105), the control device 20 reduces the opening of the electronic expansion valve 14 so that the discharge temperature is equal to or greater than the discharge lower limit temperature (ST106) and returns the process to ST102. When the discharge temperature is equal to or greater than the discharge lower limit temperature (No in ST105), the process proceeds to ST107 without controlling the opening of the electronic expansion valve 14.

Then, the control device 20 determines whether the discharge temperature is equal to or higher than the upper discharge limit temperature (ST107). If the discharge temperature is equal to or higher than the upper discharge limit temperature (Yes in ST107), the control device 20 increases the opening of the electronic expansion valve 14 so that the discharge temperature is less than the upper discharge limit temperature (ST108) and returns the process to ST102. If the discharge temperature is less than the upper discharge limit temperature (No in ST107), the control device 20 proceeds to ST109 without controlling the opening of the electronic expansion valve 14.

ST105-108 control the opening of the electronic expansion valve 14 so that the discharge temperature is equal to or higher than the lower discharge limit temperature and lower than the upper discharge limit temperature. In this state, the control device 20 executes subcool control (ST109). Note that the subcool control in ST109 is the above-mentioned control based on the target subcool and the current subcool.

That is, the control device 20 (target subcool extraction unit 21) extracts the target subcool from the target subcool table (Figure 4) stored in the memory unit 25 based on the rotation speed of the compressor 11 and the condensation pressure of the refrigerant in the user-side heat exchanger 13. The condensation pressure can be calculated based on the detection value of the discharge pressure sensor 32, for example.

Then, the control device 20 calculates the current subcool based on the detection values of the discharge pressure sensor 32 and the refrigerant temperature sensor 33, compares this calculated subcool with the target subcool extracted from the target subcool table (Figure 4), and adjusts the opening of the electronic expansion valve 14 based on this difference. In other words, the control device 20 subtracts the target subcool from the current subcool, and when the result of this subtraction is positive, it controls the opening of the electronic expansion valve 14 to be larger in accordance with the value of the subtraction result, and when the result of this subtraction is negative, it controls the opening of the electronic expansion valve 14 to be smaller in accordance with the value of the subtraction result. By controlling in this way, the current subcool is always controlled to be the target subcool value, and as a result, the COP is maintained at a high level.

The control device 20 repeatedly executes the processes of ST102 to ST109 at a predetermined cycle, thereby performing subcool control while maintaining the discharge temperature at or above a predetermined discharge lower limit temperature and below a discharge upper limit temperature.

According to this embodiment, the discharge temperature can be maintained above the lower discharge limit temperature, so that excessive intake of wet refrigerant vapor into the compressor 11 can be avoided. In addition, the upper discharge limit temperature is set according to the magnitude of the load on the compressor 11, and the discharge temperature is maintained below the upper discharge limit temperature, so that an excessive increase in the discharge temperature can be avoided. This allows the desired subcooling control to be performed stably, so that the COP of the heat pump device 100 can be maintained at a high level while ensuring the reliability of the compressor 11.

In addition, according to this embodiment, the upper discharge temperature limit is set based on the virtual discharge temperature calculated based on at least the discharge pressure and the suction pressure. This allows the upper discharge temperature limit to be determined based on the discharge temperature when adjusted to an ideal refrigeration cycle, and therefore allows the discharge temperature to be set to an appropriate upper limit value according to the magnitude of the load on the compressor 11.

In addition, according to this embodiment, the upper discharge limit temperature is set so that it is higher than the lower discharge limit temperature across the entire load range of the compressor 11. Therefore, even when a refrigerant that is prone to reverse between the upper and lower discharge limits is used, the desired subcooling control can be stably performed without causing a control failure due to the reversal.

In addition, according to this embodiment, the upper discharge temperature limit is set by adding a correction value to the virtual discharge temperature, so that the upper discharge temperature limit can be set appropriately even when the load on the compressor 11 changes from moment to moment.

In addition, according to this embodiment, the lower the load on the compressor 11, the larger the correction value is set, so that the discharge upper limit temperature can be set appropriately according to the load on the compressor 11.

In addition, according to this embodiment, the correction value is selected from multiple temperature values based on the current load on the compressor 11, which simplifies control and reduces system construction costs compared to when the correction value is calculated using complex calculation processing.

Furthermore, according to this embodiment, the greater the differential pressure between the discharge pressure and the suction pressure, the greater the load on the compressor 11 is determined to be. Therefore, the magnitude of the load on the compressor 11 can be determined using an existing sensor without requiring additional parameters required to determine the load on the compressor 11.

The above describes an embodiment of the present invention, but the present invention is not limited to the above embodiment and can of course be modified in various ways.

For example, in the above embodiment, the differential pressure between the discharge pressure and the suction pressure is used to determine the magnitude of the load on the compressor 11, but this is not limited to the above. For example, the magnitude of the load on the compressor 11 may be determined by referring to only the discharge pressure or the discharge temperature. Furthermore, the magnitude of the load on the compressor 11 may be determined by referring to the rotation speed of the compressor 11, the current value of the motor that drives the compressor 11, etc.

In the above embodiment, the upper discharge temperature is changed according to the load on the compressor 11 in order to avoid a control failure due to a reversal of the upper discharge temperature and the lower discharge temperature, but this is not limited to this. For example, in a low load state of the compressor 11 where the above-mentioned reversal may occur, the upper discharge temperature may be ignored and the processes of ST107 and ST108 in FIG. 8 may not be performed, or a lower limit may be set for the upper discharge temperature so that the above-mentioned reversal does not occur even in the low load state.

In addition, in the above embodiment, the discharge pressure sensor 32 for detecting the discharge pressure is installed on the pipe 91 between the discharge port of the compressor 11 and the four-way valve 12, but the installation location of the discharge pressure sensor 32 is not particularly limited as long as it is between the discharge port of the compressor 11 and the electronic expansion valve 14. In addition, a heat exchanger temperature sensor may be installed in the user side heat exchanger 13, and the discharge pressure may be calculated based on the detected value (condensation temperature).

Similarly, the suction pressure sensor 34 for detecting the suction pressure is installed on the pipe 95 between the four-way valve 12 and the suction port of the compressor 11, but the location of the suction pressure sensor 34 is not particularly limited as long as it is between the electronic expansion valve 14 and the suction port of the compressor 11. Also, a heat exchanger temperature sensor may be installed in the heat source side heat exchanger 15, and the suction pressure may be calculated based on the detected value (evaporation temperature).

Furthermore, in the above embodiment, a hot water heater (floor heating device) has been described as an example of the heat pump device 100, but the present invention is not limited to this and can also be applied to a heat pump type hot water supply device, etc.

REFRIGERATION SYSTEM AND METHOD FOR USE OF REFRIGERATION SYSTEM 10 REFRIGERANIUM CIRCUIT 11 COMPRESSOR 12 FOUR-WAY VALVE 13 USING-SIDE HEAT EXCHANGER 14 ELECTRONIC EXPANSION VALVE 15 HEAT SOURCE-SIDE HEAT EXCHANGER 20 CONTROL DEVICE 21 TARGET SUB-COOL EXTRACTION UNIT 22 LOAD DETECTION UNIT 23 DISCHARGE UPPER TEMPERATURE SETTING UNIT 24 DISCHARGE TEMPERATURE DETECTION UNIT 25 MEMORY UNIT 31 DISCHARGE TEMPERATURE SENSOR 32 DISCHARGE PRESSURE SENSOR 33 REFRIGERANIUM TEMPERATURE SENSOR 34 SUCTION PRESSURE SENSOR 100 HEAT PUMP APPARATUS

Claims (8)

a refrigerant circuit in which a compressor, a utilization-side heat exchanger that exchanges heat between water and a refrigerant, an electronic expansion valve, and a heat source-side heat exchanger are connected by piping;
a discharge temperature detection means for detecting a discharge temperature, which is a temperature of the refrigerant discharged from the compressor;
A subcooling detection means for detecting the subcooling of the refrigerant flowing out from the utilization side heat exchanger;
A load detection means for detecting the magnitude of the load on the compressor;
a control means for controlling the rotation speed of the compressor and the opening degree of the electronic expansion valve;
The control means
Controlling the electronic expansion valve based on a predetermined upper discharge limit temperature and a predetermined lower discharge limit temperature;
setting the upper discharge temperature limit according to the magnitude of the load on the compressor;
When the discharge temperature is lower than the lower limit temperature, the opening degree of the electronic expansion valve is reduced so that the discharge temperature becomes equal to or higher than the lower limit temperature;
When the discharge temperature is equal to or higher than the upper discharge temperature limit, the opening degree of the electronic expansion valve is increased so that the discharge temperature becomes lower than the upper discharge temperature limit;
the heat pump device controls the opening degree of the electronic expansion valve so that the subcooling temperature becomes a target subcooling temperature when the discharge temperature is equal to or higher than the lower discharge limit temperature and lower than the upper discharge limit temperature. The heat pump apparatus according to claim 1,
the load detection means includes a discharge pressure detection unit that detects a discharge pressure, which is a pressure of the refrigerant discharged from the compressor, and a suction pressure detection unit that detects a suction pressure, which is a pressure of the refrigerant sucked into the compressor;
The control means sets the discharge upper limit temperature based on a virtual discharge temperature which is a discharge temperature when the refrigerant sucked into the compressor is saturated vapor, the virtual discharge temperature being calculated based on at least the discharge pressure and the suction pressure. The heat pump apparatus according to claim 2,
The discharge lower limit temperature is preset based on a predetermined minimum degree of superheat set for the compressor,
The control means sets the upper discharge limit temperature so that the upper discharge limit temperature is higher than the lower discharge limit temperature over an entire load range of the compressor. The heat pump apparatus according to claim 3,
The control means sets the upper discharge limit temperature by adding a correction value to the virtual discharge temperature. The heat pump apparatus according to claim 4,
The control means increases the correction value as the load on the compressor decreases. The heat pump apparatus according to claim 5,
A storage unit that stores a plurality of temperature values that are preset according to the magnitude of the load of the compressor,
The control means selects the correction value from the plurality of temperature values based on the magnitude of a current load on the compressor. The heat pump apparatus according to claim 1,
the load detection means includes a discharge pressure detection unit that detects a discharge pressure, which is a pressure of the refrigerant discharged from the compressor, and a suction pressure detection unit that detects a suction pressure, which is a pressure of the refrigerant sucked into the compressor;
The control means determines that the load on the compressor is greater as a pressure difference between the discharge pressure and the suction pressure increases. The heat pump device according to any one of claims 1 to 6,
The refrigerant sealed in the refrigerant circuit has a specific heat ratio of less than 1.25 when saturated vapor at 10°C.

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