JP7590935B2 - Heat pump equipment - Google Patents

Description

The present invention relates to a heat pump device that performs expansion valve control.

Conventionally, this type of system has a heat pump circuit in which a compressor, a four-way valve, a user-side exchanger, an expansion valve, and a heat source-side heat exchanger are connected by refrigerant piping, and the refrigerant and heat medium are exchanged in the liquid refrigerant heat exchanger, and the heat medium heated by the heat exchange is used to perform heating operation to heat the conditioned space. During heating operation, depending on conditions such as the outside air temperature and the size of the heating load, frost may form on the heat source-side heat exchanger. When frost forms on the heat source-side heat exchanger, the heat exchange efficiency decreases, making it necessary to defrost the heat source-side heat exchanger. (See, for example, Patent Document 1.)

JP 2019-174001 A

However, with conventional systems, the expansion valve is significantly throttled during the period when the refrigeration cycle stabilizes after heating operation begins, causing the temperature of the heat source heat exchanger, which functions as an evaporator, to drop too low, resulting in frost forming on the heat source heat exchanger shortly after heating begins, reducing the heat exchange efficiency.

In order to solve the above problem, according to claim 1 of the present invention, a heat pump device is provided with a refrigeration cycle in which a compressor, a condenser, an expansion valve, and an evaporator are connected in a ring shape by refrigerant piping, a blower fan that blows air to the evaporator, a refrigerant temperature sensor that is attached to the refrigerant piping between the condenser and the expansion valve and detects the temperature of the refrigerant after passing through the condenser, and a control unit that determines whether the condenser temperature has stabilized based on the temperature of the refrigerant temperature sensor, wherein the heat pump device is operated at a first expansion valve opening that fixes the opening of the expansion valve in a fully open state from the start of operation to a first predetermined time, and when the first predetermined time has elapsed and the rotation speed of the compressor becomes equal to or higher than a predetermined rotation speed, the heat pump device is operated at a second expansion valve opening that fixes the opening of the expansion valve at a predetermined pressure change point that is smaller than the first expansion valve opening and is determined based on an expansion valve opening characteristic, and which is a point at which the pressure change amount of the refrigerant relative to the unit operation amount becomes large if the opening is made smaller than this, and when a second predetermined time has elapsed or when the control unit determines that the condenser temperature has stabilized, the opening of the expansion valve is switched to a third expansion valve opening that is changed according to a load.

In claim 2, a discharge temperature sensor is attached to the refrigerant piping between the compressor and the condenser in the refrigeration cycle to detect the temperature of the refrigerant on the high pressure side, and a target refrigerant discharge temperature determination means is provided to determine the target refrigerant discharge temperature, and the opening degree of the third expansion valve is determined so that the temperature detected by the discharge temperature sensor becomes the target refrigerant discharge temperature.

In addition, in claim 3, the rate of change of the expansion valve opening is set to be slower when switching from the second expansion valve opening to the third expansion valve opening than when switching from the first expansion valve opening to the second expansion valve opening.

According to this invention, the expansion valve opening degree can be set appropriately between the start of operation and the refrigeration cycle becoming stable, and the temperature of the heat source side heat exchanger does not drop too much. As a result, the time from the start of heating until frost forms on the heat source side heat exchanger can be extended, achieving the desired heat exchange efficiency.

FIG. 1 is a diagram showing an overall schematic configuration of a heat pump type temperature control system including an outdoor unit according to an embodiment of the present invention; Diagram showing the external structure of the main remote control unit A schematic diagram of the refrigeration cycle when the outdoor unit is in heating or cooling mode FIG. 1 is a timing chart showing the operation of the expansion valve in a conventional example when heating is started. FIG. 1 is a flowchart showing a control procedure executed by an outdoor unit control unit during heating. FIG. 1 is a timing chart showing the operation of the expansion valve in this embodiment when heating is started.

Next, one embodiment of the present invention will be described with reference to Figures 1 to 6.

<Configuration of an example of a temperature adjustment system>
An overall schematic configuration of a heat pump type temperature control system including a heat pump heat source unit according to this embodiment is shown in Fig. 1. In Fig. 1, this heat pump type temperature control system 100 includes an outdoor unit 1 as a heat pump heat source unit that is disposed outdoors. This heat pump type temperature control system 100 also includes at least one indoor terminal unit (in this example, two units: a hot water panel 51 and a fan coil unit 52) that is connected to the outdoor unit 1 via a hot water supply pipe 2 and a hot water return pipe 3 and disposed indoors.

The hot water panel 51 uses hot water heated by the outdoor unit 1 to dissipate heat to the air in the room, thereby heating the room.

The fan coil unit 52 includes a heat exchanger (not shown), a blower fan (not shown), and a thermal valve V3. The fan coil unit 52 also includes an indoor temperature sensor (not shown) that detects the indoor temperature, a water temperature sensor (not shown) that detects the temperature of the hot water circulating inside the fan coil unit 52, and a terminal control unit 29. The terminal control unit 29 receives a signal from the indoor temperature sensor inside the fan coil unit 52 and a signal from a terminal remote control device RC (described later), and controls the operation of the blower fan and the thermal valve V3. As a result, the fan coil unit 52 passes the hot water heated by the outdoor unit 1 through the internal heat exchanger and drives the blower fan to exchange heat with the indoor air, thereby heating the room.

The hot water panel 51 is located in room A, and the fan coil unit 52 is located in room B, of the rooms A and B provided in the living room. A single forward header 91 is provided in the hot water forward pipe 2 extending from the outdoor unit 1, and the portion of the hot water forward pipe 2 upstream of the forward header 91 is configured as a single common forward pipe 2A, to which hot water from the outdoor unit 1 is supplied. The portion 2B of the hot water forward pipe 2 downstream of the forward header 91 is connected to the forward header 91 in a manner that branches into multiple forward pipes (two in this example), namely, a forward pipe 2B1 to the hot water panel 51 and a forward pipe 2B2 to the fan coil unit 52.

Similarly, one return header 92 is provided in the hot water return pipe 3 extending to the outdoor unit 1. Furthermore, the upstream portion 3B of the hot water return pipe 3 from the return header 92 is divided into multiple return pipes (two in this example), namely, the return pipe 3B1 from the hot water panel 51 and the return pipe 3B2 from the fan coil unit 52. The downstream portion of the hot water return pipe 3 from the return header 92 is configured as one common return pipe 3A. In other words, the branched return pipes 3B1 and 3B2 are connected to the return header 92 in a manner that they converge on the upstream side of the common return pipe 3A. The hot water introduced through the return pipes 3B1 and 3B2 is returned to the outdoor unit 1.

The supply pipe 2B1 to the hot water panel 51 is provided with a thermal valve V1 that can open and close the supply pipe 2B1 in response to a drive signal from a thermal valve controller CV.

In this example, a main remote control device RM is provided in room A for operating the indoor terminal devices (hot water panel 51 and fan coil unit 52 in this example) for heating and cooling. In addition, a terminal remote control device RA is provided for operating the hot water panel 51 for heating and cooling. Also, in this example, a wireless terminal remote control device RC is provided in room B for remotely controlling the fan coil unit 52.

The terminal remote control device RA may be provided with the same functions as the main remote control device RM, and the main remote control device RM may be omitted.

The main remote control device RM outputs a control signal SS1 in response to a user's operation. This control signal SS1 is input to an outdoor unit control unit CU (described later) that controls the outdoor unit 1. This controls the flow rate and temperature of the hot water supplied to the common supply pipe 2A. In response to this, a control signal SS2 is output from the outdoor unit control unit CU to the thermal valve controller CV, and the opening and closing operation of the thermal valve V1 can be controlled by a control signal S1 output from the thermal valve controller CV in response to this. In addition, a control signal Sa output in response to an operation on the terminal remote control device RA is input to the thermal valve controller CV, and the opening and closing operation of the thermal valve V1 can be controlled by a control signal S1 output from the thermal valve controller CV in response to this.

On the other hand, a return temperature sensor 54 is provided in the return pipe 3B1 from the hot water panel 51. This return temperature sensor 54 detects the temperature (return temperature) of the hot water in the corresponding return pipe 3B1, and outputs a detection signal indicating the detection result to the thermal valve controller CV.

The thermal valve controller CV responds to the operation of the main remote control device RM and the terminal remote control device RA, and controls the opening and closing of the thermal valve V1 based on the return temperature detected by the return temperature sensor 54. This allows the user to control the operating state of the hot water panel 51 and the fan coil unit 52 by appropriately operating the remote control devices RM and RA.

The terminal remote control device RC is equipped with a heating switch 24 as a heating instruction means for causing the fan coil unit 52 to perform heating operation to heat the room. Furthermore, the terminal remote control device RC is equipped with a stop switch 26 for stopping the operation of the fan coil unit 52, an indoor temperature setting switch 27 for setting the indoor temperature, and a display unit 28 for displaying the indoor set temperature and the operating status. The terminal remote control device RC is also connected to the terminal control unit 29 so as to be able to communicate with it.

<Main remote control device>
Next, the main remote control device RM shown in FIG. 1 will be described in detail.

2 shows the external appearance of the main remote control device RM. The main remote control device RM is provided with a display unit 250. The main remote control device RM is also provided with an "ON/OFF" button 253 for instructing the outdoor unit 1 and the indoor terminal device (the hot water panel 51 and the hot water panel 51 of the fan coil unit 52) to start and stop operation. The main remote control device RM is also provided with a "TIMER" button 254 for instructing the indoor terminal device to operate using a timer. The main remote control device RM is also provided with an "OPERATION SWITCH" button 255 for instructing the indoor terminal device to switch between operating modes (cooling/heating, normal mode/save mode, etc.) and a "BACK" button 257 for returning the screen display to the previous screen. The main remote control device RM is also provided with a "MENU/ENTER" button 258 and a cross key 259 for up, down, left and right directions. In this description, the "On/Off" button 253, the "Timer" button 254, the "Operation Switch" button 255, the "Back" button 257, and the "Menu/Enter" button 258 will hereinafter be referred to simply as the "operation buttons 253, etc." Furthermore, in this description, these operation buttons 253, etc. and the cross key 259 will be collectively referred to simply as the "operation unit 259, etc." Although not shown in the figure, the main remote control device RM has a built-in CPU, memory as a storage means, and the like.

The display unit 250 can switch between various screens under the control of the CPU. In the illustrated example, the display unit 250 displays a setting screen 200 for making settings related to the entire temperature adjustment system 100 shown in FIG. 1 or 2, including hot water temperature setting and cooling/heating switching. This setting screen 200 is centrally located and has an operating status display area 200A that indicates the operating status of the entire temperature adjustment system 100, and is located at the right end. In addition, this setting screen 200 has a temperature setting display area 200B that displays the set temperature of the hot water supplied from the outdoor unit 1 to the entire temperature adjustment system 100 (which can be set by the user using the operation unit 259, etc.).

In the illustrated example, the operation status display area 200A displays "Hot water heating in operation," which indicates that hot water is being supplied from the outdoor unit 1 and the temperature control system 100 as a whole is performing heating operation. The temperature setting display area 200B also displays the hot water setting temperature "40°C" that the user has previously (variably) set for heating.

<Outdoor unit configuration>
Next, a schematic system configuration of the outdoor unit 1 is shown in Fig. 3. In Fig. 3, the outdoor unit 1 includes a refrigerant circulation circuit 21 that circulates a synthetic compound gas such as HFC as a refrigerant and absorbs and releases heat outdoors. The outdoor unit 1 also includes a hot water circulation circuit 22 (comprising a hot water supply pipe 2 and a hot water return pipe 3) that circulates, for example, antifreeze as the hot water and absorbs and releases heat at the indoor terminal units (two units, a hot water panel 51 and a fan coil unit 52). The outdoor unit 1 is a heat pump type heat source unit that exchanges heat between the refrigerant circulation circuit 21 and the hot water circulation circuit 22.

That is, the refrigerant circulation circuit 21 includes a four-way valve 6 for switching the circulation direction of the refrigerant, a compressor 7 for compressing the refrigerant, and a heat source side heat exchanger 8, which is an air heat exchanger for exchanging heat between the refrigerant and the outside air, which are provided in the outdoor unit 1. In addition, the refrigerant circulation circuit 21 includes an expansion valve 9 for decompressing and expanding the refrigerant, and a water-refrigerant heat exchanger 11 for exchanging heat between the refrigerant and the hot water circulating through the hot water supply pipe 2 and the hot water return pipe 3. Furthermore, the refrigerant circulation circuit 21 is formed by connecting the above-mentioned components with a refrigerant pipe 15. The four-way valve 6, compressor 7, heat source side heat exchanger 8, and expansion valve 9, which are connected to each other by the refrigerant pipe 15, constitute a heat pump device. In addition, an outdoor fan 10 for blowing air to the heat source side heat exchanger 8 is also provided.

The four-way valve 6 is a valve with four ports, and switches between connecting each of the two ports for the main refrigerant path 15a (which constitutes part of the refrigerant piping 15) to one of the two ports for the other sub-refrigerant path 15b (which constitutes part of the refrigerant piping 15). The two ports for the sub-refrigerant path 15b are connected to each other by the sub-refrigerant path 15b arranged in a loop, and the compressor 7 is provided on this sub-refrigerant path 15b.

The compressor 7 pressurizes the refrigerant in a low-pressure gas state to a high-pressure gas state, and also functions as a pump that circulates the refrigerant throughout the refrigerant piping 15 in the outdoor unit 1. A discharge temperature sensor 55 (corresponding to a discharge temperature detection means) is provided in the refrigerant sub-path 15b on the discharge side of the compressor 7. A refrigerant temperature sensor 57 is provided in the main refrigerant path 15a between the expansion valve 9 and the water-refrigerant heat exchanger 11. Furthermore, an outside air temperature sensor 58 (corresponding to an outside air temperature detection means) that detects the outside air temperature is provided in or near the heat source side heat exchanger 8.

The two ports for the main refrigerant path 15a of the four-way valve 6 are connected to each other by the main refrigerant path 15a arranged in a loop. The heat source side heat exchanger 8, the expansion valve 9, and the water-refrigerant heat exchanger 11 are arranged in this main refrigerant path 15a in this order (in the example shown in FIG. 3, in the counterclockwise order of the main refrigerant path 15a).

When the temperature of the liquid refrigerant passing through the heat source side heat exchanger 8 is lower than the outdoor air temperature, the heat source side heat exchanger 8 functions as an evaporator that absorbs the heat of the outdoor air into the refrigerant and evaporates it into a gas state.

The outdoor fan 10 blows air toward the heat source side heat exchanger 8, improving the performance of the heat source side heat exchanger 8.

The expansion valve 9 functions to reduce the pressure of the refrigerant from a high-pressure liquid state and expand it to a low-pressure liquid state.

As described above, the water-refrigerant heat exchanger 11 is connected to the main refrigerant path 15a and passes refrigerant through it, and is also connected to the hot water supply pipe 2 and the hot water return pipe 3 and passes hot water through it. When the temperature of the gaseous refrigerant passing through the water-refrigerant heat exchanger 11 is higher than the temperature of the hot water, it functions as a condenser that transfers heat from the refrigerant to the hot water and condenses it into a liquid state.

The hot water circulation circuit 22, on the other hand, comprises a water-refrigerant heat exchanger 11, a circulation pump 12 that applies circulation pressure to the hot water, and a cistern tank 13, all of which are provided in the outdoor unit 1, as well as indoor terminal units (two units: a hot water panel 51 and a fan coil unit 52). Furthermore, the hot water circulation circuit 22 is formed by connecting the aforementioned components with a hot water supply pipe 2 (specifically, a common supply pipe 2A) and a hot water return pipe 3 (specifically, a common return pipe 3A).

The water-refrigerant heat exchanger 11 is connected to a hot water supply pipe 2 and a hot water return pipe 3, and a cistern tank 13 and a circulation pump 12 are provided on the hot water return pipe 3.

The cistern tank 13 separates air bubbles generated in the hot water due to cavitation, etc. (air-water separation function), and absorbs the expanded hot water in the hot water circulation circuit 22 and replenishes the hot water.

The circulation pump 12 functions to circulate hot water throughout the hot water supply pipe 2 and the hot water return pipe 3.

In this example, a return temperature sensor 56B is provided in the hot water return pipe 3 (more specifically, the common return pipe 3A) on the inlet side (inflow side) of the water-refrigerant heat exchanger 11. The return temperature sensor 56B detects the temperature of the hot water in the common return pipe 3A (hereinafter referred to as the "actual return temperature") and outputs a detection signal indicating the detection result to the outdoor unit control unit CU, which will be described later.

The outdoor unit 1 is equipped with an outdoor unit control unit CU that controls the outdoor unit 1. This outdoor unit control unit CU is mainly composed of a microcomputer equipped with a CPU, ROM, RAM, etc. The outdoor unit control unit CU and the main remote control device RM are connected by a two-way communication line, allowing signals to be exchanged between them (see Figure 1). As a result, the outdoor unit control unit CU controls the entire outdoor unit 1 based on a control signal SS1 from the main remote control device RM as shown in Figure 1 (details will be described later), and outputs a corresponding control signal SS2 to the thermal valve controller CV.

In the configuration example shown in FIG. 1, the outdoor unit control unit CU and the terminal control unit 29 of the fan coil unit 52 are connected by a terminal control line (so-called E-con communication line) that transmits a signal from the terminal control unit 29 in one direction (see FIG. 1). For example, when the user operates the heating switch 24 of the terminal remote control device RC to instruct the start of operation, the terminal control unit 29 receives the instruction signal. In response to the received instruction signal, the terminal control unit 29 outputs a hot water request signal SC related to the heating operation to the outdoor unit control unit CU (see the imaginary line in FIG. 3). In addition, when stopping the heating operation after the operation has started, the user performs an appropriate stop instruction operation (for example, the heating switch 24 is pressed again, or the separately provided stop switch 26 is pressed, etc.). As a result, the terminal control unit 29 outputs a heating operation stop request signal (not shown) to the outdoor unit control unit CU.

In the configuration example shown in FIG. 1, when the fan coil unit 52 is provided as described above, the fan coil unit 52 is not limited to being operated by the terminal remote control device RC. In other words, the fan coil unit 52 may be provided with a switch or display unit having the same function as the switch of the terminal remote control device RC, and the terminal remote control device RC may be omitted. In this case, when a user operates a switch or the like of the fan coil unit 52 to instruct the start of operation, the terminal control unit 29 receives the instruction signal and outputs a hot water request signal SC to the outdoor unit control unit CU. Similarly, when a user operates the switch or the like of the fan coil unit 52 to instruct the operation to stop, the terminal control unit 29 outputs the stop request signal for the heating operation to the outdoor unit control unit CU.

In the refrigerant circulation circuit 21 configured as above, the compressor 7 circulates the refrigerant in one direction on the refrigerant sub-path 15b, and the direction of circulation of the refrigerant on the refrigerant main path 15a is controlled by switching the four-way valve 6. FIG. 3 shows the circulation direction during heating operation in the configuration example shown in FIG. 1, and the refrigerant discharged from the compressor 7 flows in the order of the water-refrigerant heat exchanger 11, the expansion valve 9, and the heat source side heat exchanger 8. As a result, the refrigerant in a gas state sucked in at low temperature and low pressure is compressed by the compressor 7 to become a high temperature and high pressure gas, and then changes to a high pressure liquid in the water-refrigerant heat exchanger 11 (functioning as a condenser) while releasing heat to the hot water from the hot water return pipe 3. The refrigerant that has become liquid in this way is decompressed by the expansion valve 9 to become a low pressure liquid, and becomes in a state that is easy to evaporate. After that, the low pressure liquid evaporates in the heat source side heat exchanger 8 (functioning as an evaporator) and changes to a gas, absorbing heat from the outside air. The refrigerant then returns to the compressor 7 again as a low temperature and low pressure gas.

At this time, the hot water heated in the water-refrigerant heat exchanger 11 as described above is supplied from the hot water supply pipe 2 to the indoor terminal units (the hot water panel 51 and the fan coil unit 52) and dissipates heat to the indoor air to heat the room. The hot water then passes through the cistern tank 13 and returns to the circulation pump 12. Heat exchange between the refrigeration cycle of the refrigerant circulation circuit 21 and the hot water circulation circuit 22 as described above performs a heating operation to raise the temperature of the indoor air.

Next, a conventional example will be described with reference to FIG. 4. In the outdoor unit 1 having the circuit configuration shown in FIG. 3, in the comparative example shown in FIG. 4, in order to increase the heating output in a short time when the heating operation starts, the valve opening of the expansion valve 9 is greatly narrowed in the time period from the compressor 7 starting to t1. By operating the expansion valve 9 at a small valve opening, the heating capacity increases and the time until the desired heating output is reached is shortened. However, in the time period from the start of the heating operation to t1, the refrigeration cycle is not stable, and the valve opening of the expansion valve 9 is small relative to the rotation speed of the compressor 7. As a result, the refrigerant pressure rises rapidly and the temperature of the heat source side heat exchanger 8 drops significantly, which may cause frost to form on the heat source side heat exchanger 8 in a short time after the heating operation starts.

When frost forms on the heat source side heat exchanger 8, the heat exchange in the heat source side heat exchanger 8 becomes insufficient at t3, and the heating output decreases. Therefore, when frost forms on the heat source side heat exchanger 8, it is necessary to provide a defrosting means for removing the frost formed on the heat source side heat exchanger 8 and to execute the defrosting means.

Here, the defrosting means stops the operation of the circulation pump 12 that applies circulation pressure to the hot water circulating through the hot water circulation circuit 22, or operates it at a pressure lower than the circulation pressure during heating operation. In this way, the defrosting means makes it difficult for the water-refrigerant heat exchanger 11 (functioning as a condenser) to release the heat of the refrigerant circulating through the refrigerant pipe 15 to the hot water circulating through the hot water circulation circuit 22. Furthermore, the defrosting means makes it difficult for the heat of the refrigerant circulating through the refrigerant pipe 15 to be released to the hot water circulating through the hot water circulation circuit 22 by fully opening the expansion valve 9 and keeping the pressure of the refrigerant passing through the water-refrigerant heat exchanger 11 (functioning as a condenser) low. As a result, the refrigerant circulating through the refrigerant pipe 15 circulates while retaining its heat, and the heat is used to perform positive cycle defrosting that melts the frost on the heat source side heat exchanger 8.

The defrosting means is not limited to the forward cycle defrosting, but may be a reverse cycle defrosting in which the refrigerant circulating through the refrigerant pipe 15 is circulated in the opposite direction to the forward cycle defrosting. The reverse cycle defrosting uses the water-refrigerant heat exchanger 11 as an evaporator and the heat source side heat exchanger 8 as a condenser to melt the frost on the heat source side heat exchanger 8.

The above-mentioned defrosting means requires stopping the heating operation or reducing the heating output. Furthermore, if frost forms on the heat source side heat exchanger 8 shortly after the start of the heating operation, the time from the start of the heating operation to t3, at which the heat exchange of the heat source side heat exchanger 8 becomes insufficient, becomes shorter. This increases the frequency with which the defrosting means for removing the frost formed on the heat source side heat exchanger 8 is executed, and it takes time to bring the temperature of the indoor air to the desired temperature. Not only that, it becomes difficult to bring the temperature of the indoor air to the desired temperature.

Therefore, in this embodiment, from the start of heating operation in step ST1 shown in FIG. 5 until the first predetermined time T1 when the rotation of the compressor 7 reaches the desired rotation speed, the expansion valve 9 is operated at a first expansion valve opening EV1 fixed to full opening as shown in step ST2. Thereafter, when both of the following two conditions are satisfied: the first predetermined time has elapsed as shown in step ST31, and the rotation speed of the compressor 7 has reached a predetermined rotation speed or higher as shown in step ST32, the outdoor unit control unit CU determines that the rotation speed of the compressor 7 has reached the desired rotation speed. When the outdoor unit control unit CU determines that the rotation speed of the compressor 7 has reached the desired rotation speed, the expansion valve 9 is switched to a fixed second expansion valve opening EV2 at an opening smaller than the first expansion valve opening EV1 as shown in step ST4 and operated. The second expansion valve opening EV2 is determined based on the expansion valve opening characteristic, and is set so that it is the pressure change point at which the pressure change amount for the unit operation amount increases if the opening is reduced any further. In step ST5, the outdoor unit control unit CU determines that the refrigeration cycle has stabilized when at least one of the two conditions is met: when a second predetermined time has elapsed, or when the temperature of the water-refrigerant heat exchanger 11 has reached a predetermined temperature. When the outdoor unit control unit CU determines that the refrigeration cycle has stabilized, it switches the opening of the expansion valve 9 to a third expansion valve opening EV3, which is changed according to the load, regardless of the openings of the first expansion valve opening EV1 and the second expansion valve opening EV2, as shown in step ST6.

The third expansion valve opening EV3 is attached to the refrigerant piping 15 between the compressor 7 and the water-refrigerant heat exchanger 11 in the refrigeration cycle, and includes a discharge temperature sensor 55 that detects the temperature of the refrigerant on the high pressure side, and a target refrigerant discharge temperature determination means that determines the target refrigerant discharge temperature. The third expansion valve opening EV3 is determined so that the high pressure side refrigerant temperature detected by the discharge temperature sensor 55 becomes the target refrigerant discharge temperature.

Although not shown, the rate of change of the expansion valve opening of the expansion valve 9 is set to be slower when switching from the second expansion valve opening EV2 to the third expansion valve opening EV3 than when switching from the first expansion valve opening EV1 to the second expansion valve opening EV2.

As a result, the expansion valve opening is fixed at a large first expansion valve opening EV1 during the first predetermined time T1 from the start of heating operation until the rotation speed of the compressor 7 reaches the desired rotation speed, as shown in FIG. 6. This makes it possible to maintain a low refrigerant pressure and also prevents a sudden drop in the refrigerant evaporation temperature, thereby suppressing frost formation on the heat source side heat exchanger 8.

The outdoor unit control unit CU switches from the first expansion valve opening degree EV1 to the second expansion valve opening degree EV2 at the first predetermined time T1, but operates by switching the second expansion valve opening degree EV2 to a fixed second expansion valve opening degree EV2 that is smaller than the first expansion valve opening degree EV1.

Here, if the second expansion valve opening EV2 is greater than the pressure change point, the refrigerant pressure is kept low when switching from the first expansion valve opening EV1 to the second expansion valve opening EV2, so the refrigerant pressure does not overshoot. However, since the third expansion valve opening EV3 during stability is an opening that changes depending on the load, the third expansion valve opening EV3 may be a small opening. In that case, if the second expansion valve opening EV2 is greater than the pressure change point, the difference between the second expansion valve opening EV2 and the third expansion valve opening EV3 is large, and the expansion valve opening is reduced too much in a short time when switching from the second expansion valve opening EV2 to the third expansion valve opening EV3. As a result, the refrigerant pressure rises suddenly and it is not possible to prevent the refrigerant pressure from overshooting, and the refrigerant evaporation temperature drops suddenly, which may cause frosting on the heat source side heat exchanger 8.

On the other hand, if the second expansion valve opening EV2 is smaller than the pressure change point, the difference between the first expansion valve opening EV1 and the second expansion valve opening EV2 is large, and when switching from the first expansion valve opening EV1 to the second expansion valve opening EV2, the expansion valve opening is reduced too much in a short time. This causes the refrigerant pressure to rise suddenly, making it impossible to prevent refrigerant pressure overshoot, and the refrigerant evaporation temperature to drop suddenly, which may result in frost formation on the heat source side heat exchanger 8.

That is, according to this embodiment, the second expansion valve opening EV2 is set to be the pressure change point. As a result, the second expansion valve opening EV2 does not reduce the expansion valve opening too much in a short time, even when switching from the first expansion valve opening EV1 to the second expansion valve opening EV2, or when switching from the second expansion valve opening EV2 to the third expansion valve opening EV3. Therefore, the second expansion valve opening EV2 can prevent the refrigerant pressure from overshooting, and the refrigerant evaporation temperature does not drop suddenly, so frost formation on the heat source side heat exchanger 8 can be suppressed.

The outdoor unit control unit CU determines that the refrigeration cycle has stabilized when at least one of the two conditions is met: when a second specified time has elapsed after the first specified time T1, or when the condenser temperature has reached a specified temperature. If the outdoor unit control unit CU determines that the refrigeration cycle has stabilized, at the second specified time T2, the opening of the expansion valve 9 is switched to the third expansion valve opening EV3, which is changed according to the load, regardless of the openings of the first expansion valve opening EV1 and the second expansion valve opening EV2. This makes it possible to determine that the refrigeration cycle is stable, and then transition to expansion valve control that is changed according to the load.

In addition, by switching the expansion valve 9 from the second expansion valve opening EV2, which is closer to the third expansion valve opening EV3 in stable conditions than the first expansion valve opening EV1, to the third expansion valve opening EV3 in stable conditions, the expansion valve opening is suddenly reduced and the refrigerant pressure does not increase excessively. Furthermore, since the refrigerant evaporation temperature does not suddenly decrease, frost formation on the heat source side heat exchanger 8 can be suppressed.

The third expansion valve opening EV3 is attached to the refrigerant piping 15 between the compressor 7 and the water-refrigerant heat exchanger 11 in the refrigeration cycle, and is equipped with a discharge temperature sensor 55 that detects the temperature of the refrigerant on the high-pressure side, and a target refrigerant discharge temperature determination means that determines the target refrigerant discharge temperature. The third expansion valve opening EV3 is determined to be the target refrigerant discharge temperature. This allows the expansion valve opening to be optimal for the state of the refrigeration cycle, so that the refrigerant pressure does not increase excessively and the refrigerant evaporation temperature does not drop suddenly, thereby suppressing frost formation on the heat source side heat exchanger 8.

The rate of change of the expansion valve opening of the expansion valve 9 is set slower when switching from the second expansion valve opening EV2 to the third expansion valve opening EV3 at the second specified time T2 than when switching from the first expansion valve opening EV1 to the second expansion valve opening EV2 at the first specified time T1. This allows the refrigeration cycle to be stabilized in the minimum time possible at the first specified time T1 from the start of operation. At the same time, it is possible to prevent the expansion valve opening from being suddenly reduced at the second specified time T2, so that the refrigerant pressure does not rise excessively and the refrigerant evaporation temperature does not drop suddenly, thereby suppressing frost formation on the heat source side heat exchanger 8.

The third predetermined time T3 shown in FIG. 6 of this embodiment indicates the same time as t3, which is the time from the start of operation to the insufficient heat exchange of the heat source side heat exchanger 8 due to frost formation on the heat source side heat exchanger 8, shown in FIG. 4 of the conventional example. According to this embodiment, frost formation on the heat source side heat exchanger 8 is sufficiently prevented when heating starts, so that the third predetermined time T3 does not result in insufficient heat exchange on the heat source side heat exchanger 8, and it is possible to extend the time from the start of operation to defrosting.

Note that the present invention is not limited to the above embodiment, and various modifications are possible within the scope of the invention. For example, in the above embodiment, a return temperature sensor 56B is provided in the hot water return pipe 3 (specifically, the common return pipe 3A) on the inlet side (inlet side) of the water-refrigerant heat exchanger 11. The outdoor unit control unit CU performs so-called return temperature control, which controls the rotation speed of the compressor 7 according to the actual return temperature of the hot water detected by the return temperature sensor 56B. Instead, the outdoor unit 1 is provided with a forward temperature sensor 56A (see the two-dot chain line in FIG. 3) in the hot water forward pipe 2 (specifically, the common forward pipe 2A) on the outlet side (outlet side) of the water-refrigerant heat exchanger 11. Using this, the outdoor unit control unit CU may perform so-called forward temperature control, which controls the rotation speed of the compressor 7 according to the return temperature of the hot water detected by the forward temperature sensor 56A.

In the above, an example has been described in which a hot water panel 51 and a fan coil unit 52 are connected as heat exchange terminals. However, the present invention may be applied to cases in which the heat exchange terminal is connected to other terminals (heat absorption/dissipation terminals) that have at least one or both of a cooling and heating function, such as a hot/cold water panel, a floor heating panel, a radiator, a convector, etc. Also, in the above embodiment, an example has been described in which two heat exchange terminals are connected, but this is not limited to the above. In other words, a configuration in which three or more heat exchange terminals or only one heat exchange terminal is connected may also be used.

In the above, the condenser uses a water heat exchanger, and a heater that uses hot water has been described as an example, but the invention is not limited to this. The condenser may be equipped with an air heat exchanger, and the invention may be applied to a room heating device that does not use hot water, for example, the refrigeration cycle of an air conditioner.

In the above, the condenser uses a water heat exchanger, and a heater that uses hot water has been described as an example, but the present invention is not limited to this, and may be applied to a refrigeration cycle of a heat pump water heater, for example, that uses the generated hot water to supply hot water.

In addition, in the above, a heater that uses a water heat exchanger as a condenser and uses hot water has been described as an example, but the present invention may be applied to appliances that can provide cooling or not.

7 Compressor 8 Heat source side heat exchanger 9 Expansion valve EV1 First expansion valve opening EV2 Second expansion valve opening EV3 Third expansion valve opening T1 First predetermined time T2 Second predetermined time

Claims (3)

a control unit that determines whether a condenser temperature has stabilized based on the temperature of the refrigerant temperature sensor; and a control unit that determines whether a condenser temperature has stabilized based on the temperature of the refrigerant temperature sensor. The heat pump apparatus is characterized in that: from a start of operation to a first predetermined time, the heat pump apparatus is operated with a first expansion valve opening that fixes the opening of the expansion valve in a fully open state; when the first predetermined time has elapsed and the compressor rotation speed becomes equal to or higher than a predetermined rotation speed, the heat pump apparatus is operated with a second expansion valve opening that fixes the opening of the expansion valve to a second expansion valve opening that is smaller than the first expansion valve opening and is determined based on an expansion valve opening characteristic, and that is a predetermined pressure change point that is a point at which a pressure change amount of the refrigerant relative to a unit operation amount becomes large if the opening is made any smaller ; and when a second predetermined time has elapsed or the control unit determines that the condenser temperature has stabilized, the heat pump apparatus is characterized in that The heat pump device according to claim 1, characterized in that a discharge temperature sensor is attached to the refrigerant piping between the compressor and the condenser in the refrigeration cycle to detect the temperature of the refrigerant on the high pressure side, and a target refrigerant discharge temperature determination means is provided to determine a target refrigerant discharge temperature, and the opening degree of the third expansion valve is determined so that the temperature detected by the discharge temperature sensor becomes the target refrigerant discharge temperature. The heat pump device according to claim 1 or 2, characterized in that the rate of change in the expansion valve opening when switching from the second expansion valve opening to the third expansion valve opening is slower than the rate of change in the expansion valve opening when switching from the first expansion valve opening to the second expansion valve opening.

Images