JP6766239B2 - Refrigeration cycle equipment - Google Patents

Description

The present invention relates to a refrigeration cycle device such as an air conditioner.

Conventionally, an outdoor unit equipped with a compressor, an outdoor heat exchanger, an outdoor fan, etc. and an indoor unit equipped with an indoor heat exchanger, etc. are connected by a refrigerant pipe to form a refrigeration cycle, and the indoor unit is used for cooling. There are known air conditioners that are designed to perform heating and heating. Since the compressor used in such an air conditioner may break down if a large amount of liquid refrigerant is sucked in, an expansion valve provided in the refrigeration cycle is provided in order to avoid liquid return to the compressor. It is important to control the opening degree of (for example, an electronic expansion valve).

The opening degree of the expansion valve is controlled so that the discharge temperature of the compressor becomes a predetermined value and the degree of superheat of the refrigerant at the outlet of the heat exchanger serving as the evaporator becomes a predetermined value. It is known.

According to Japanese Patent Application Laid-Open No. 2004-225924 (Patent Document 1), the expansion means is controlled so that the outlet superheat degree of the heat exchanger serving as the evaporator is zero and the refrigerant dryness is 1. The evaporation temperature is obtained by converting from the low pressure, and the expansion means is controlled so that this evaporation temperature approaches the target evaporation temperature, and the expansion means is controlled so that the degree of refrigerant superheat on the discharge side of the compressor falls within a predetermined range. What to do is disclosed.

Further, in Japanese Patent Application Laid-Open No. 2002-327950 (Patent Document 2), the opening degree of the indoor expansion valve is controlled so that the degree of superheat of the refrigerant at the evaporator outlet becomes a desired value, and the refrigerant in the evaporator is used. Disclosed is a control method using a dynamic model to improve the mutual control affecting the evaporation temperature and becoming unstable when controlling the capacitance of the compressor so that the evaporation temperature becomes the target temperature. ing.

Japanese Unexamined Patent Publication No. 2004-225924 JP-A-2002-327950

The above-mentioned Patent Document 1 has the following problems.
When the compressor is operated, the compressed refrigerant becomes hot, and the container of the compressor containing the compression mechanism and the motor is heated. Further, the container is also heated by converting a loss such as a mechanical loss of the compression mechanism portion into heat. This amount of heating is large when the air conditioning load is relatively large and the compressor rotation speed is high, but the amount of heat generated is small when the air conditioning load is relatively small.

On the other hand, since the heat capacity of the compressor does not change, the temperature change of the compressor becomes slow when the air conditioning load is small. Therefore, when the air conditioning load is small, the delay in the change in the discharge temperature becomes remarkable with respect to the change in the opening degree of the expansion valve. Therefore, controllability is achieved by controlling the expansion means based on the discharge temperature of the compressor. There is a problem that worsens.

In order to ensure the reliability of the air conditioner, it is important to prevent the liquid from returning to the compressor, but if the controllability deteriorates in this way, the liquid may return depending on the conditions. In particular, when the load is low, the discharge temperature changes slowly as described above, so that there is a problem that sufficient reliability cannot be ensured.

Further, Patent Document 1 also describes that the evaporation temperature of the refrigerant is obtained by converting it from the low pressure in the refrigeration cycle, and the evaporation temperature is controlled so as to approach the target evaporation temperature. The change in evaporation temperature is relatively fast because it is not affected by the heat capacity of the compressor. However, when the evaporation temperature is converted from the low pressure, there is a problem in the estimation accuracy of the evaporation temperature.

That is, the low-pressure pressure near the suction port of the compressor deviates from the evaporation pressure of the indoor unit by the pressure loss corresponding to the connecting pipe (refrigerant pipe) from the indoor unit to the compressor, so that the evaporation temperature is accurate. It is necessary to correct this in order to recognize it.

Further, the pressure loss not only fluctuates depending on the enforcement conditions such as the length of the pipe, but also changes depending on the capacity of the air conditioner, that is, the flow rate of the refrigerant flowing through the connecting pipe, so that the value of the pressure loss is correctly detected. It's difficult to do.
Therefore, it is difficult to estimate the evaporation temperature with high accuracy, and in Patent Document 1, control is performed using the discharge temperature of the compressor, which changes slowly, so that the control has good responsiveness and high accuracy. There was a problem that it was difficult to do. That is, sufficient consideration has not been given to improving controllability while preventing liquid from returning to the compressor.

On the other hand, Patent Document 2 has the following problems.
As described in Patent Document 2, in the case of controlling the degree of superheat of the refrigerant at the outlet of the evaporator, the response is fast because it is not affected by the heat capacity of the compressor, and the control becomes easy even when the air conditioning load is relatively small. .. However, there is a problem that the value of the degree of superheat of the refrigerant becomes 0 degrees regardless of the liquid ratio when the refrigerant at the outlet of the evaporator is not completely gasified, that is, when it flows out in a gas-liquid two-phase state. .. In this case, it is necessary to throttle the expansion valve so that the refrigerant completely evaporates to lower the evaporation temperature, but since the liquid ratio cannot be detected, it is not possible to determine how much the expansion valve should be throttled.

Further, the temperature of the refrigerant rises due to heat exchange with air even after evaporation, but when the air temperature is low, the temperature rise range becomes small, so even when the degree of superheat is large, how much the expansion valve opening degree There is a problem that it is difficult to judge whether to open.

For this reason, even when the degree of superheat deviates significantly from the target value or when the air conditioner is started, even under conditions where there is a large transient change, the expansion valve opening is gradually opened and the control becomes slow, resulting in responsiveness. There is a problem that the controllability is deteriorated.

Further, in the case of Patent Document 2, since the degree of superheat is detected by the low pressure pressure sensor and the suction temperature sensor provided on the suction side of the compressor, the value of the pressure loss can be determined as in Patent Document 1. There is also a problem that it is difficult to detect it correctly and it is difficult to estimate the degree of superheat of the refrigerant at the outlet of the evaporator with high accuracy.

That is, even in Patent Document 2, it is difficult to control with good responsiveness and high accuracy, and sufficient consideration is not given to improving controllability while preventing liquid from returning to the compressor. ..

An object of the present invention is to obtain a refrigerating cycle apparatus capable of improving controllability while preventing liquid from returning to the compressor.

In order to achieve the above object, the present invention comprises a refrigeration cycle apparatus in which a compressor, a heat exchanger serving as a condenser, an expansion valve, and a heat exchanger serving as an evaporator are sequentially connected by a refrigerant pipe to form a refrigeration cycle. It is characterized in that an evaporation temperature sensor is provided between the expansion valve and the heat exchanger serving as the evaporator, and the opening degree of the expansion valve is controlled according to the temperature detected by the evaporation temperature sensor. And.

According to the present invention, there is an effect that it is possible to obtain a refrigeration cycle device capable of improving controllability while preventing liquid from returning to the compressor.

It is a refrigerating cycle block diagram which shows Example 1 of the refrigerating cycle apparatus of this invention. This is an example of a Ph diagram during the cooling operation of the refrigeration cycle device. Another example of the Ph diagram during the cooling operation of the refrigeration cycle device is a diagram in which the amount of decompression in the expansion valve is insufficient. It is a block diagram explaining the setting method of the control target value of the evaporation temperature in the refrigeration cycle apparatus of this Example 1. It is a figure for demonstrating the effect by this Example, and is a diagram which shows the relationship between the expansion valve opening degree, superheat degree and evaporation temperature. It is a refrigerating cycle block diagram which shows Example 2 of the refrigerating cycle apparatus of this invention. It is a block diagram explaining the setting method of the control target value of the evaporation temperature in the refrigeration cycle apparatus of this Example 2. It is a refrigerating cycle block diagram which shows Example 3 of the refrigerating cycle apparatus of this invention. It is a refrigerating cycle block diagram which shows Example 4 of the refrigerating cycle apparatus of this invention. It is a refrigerating cycle block diagram which shows Example 5 of the refrigerating cycle apparatus of this invention.

Hereinafter, specific examples of the refrigeration cycle apparatus of the present invention will be described with reference to the drawings. In each figure, the parts with the same reference numerals indicate the same or corresponding parts.

Example 1 of the refrigeration cycle apparatus of the present invention will be described with reference to FIGS. 1 to 4. In the first embodiment, an example in which the present invention is applied to an air conditioner as a refrigeration cycle device will be described.
FIG. 1 is a cycle system diagram of the refrigeration cycle apparatus of the first embodiment.

In FIG. 1, 90 is an outdoor unit and 91 is an indoor unit.
The outdoor unit 90 includes a compressor 1 for compressing the refrigerant, a four-way valve 2 for switching the flow direction of the refrigerant between cooling operation and heating operation, and an outdoor heat exchanger for heat exchange between the refrigerant and the outside air (outside air). (Heat exchanger) 3, an outdoor fan 4 for blowing outside air to the outdoor heat exchanger 3, an outdoor expansion valve (expansion valve) 6, and the like are provided. Further, in the outdoor unit 90, an evaporation temperature sensor for detecting the temperature of the outlet of the indoor expansion valve 6 (temperature of the refrigerant pipe) during the heating operation between the outdoor expansion valve 6 and the outdoor heat exchanger 3 is provided. 20 is provided, and an outside air temperature sensor 24 for detecting the temperature of the outside air sucked into the outdoor heat exchanger 3 is also provided.

The indoor unit 91 is provided with an indoor heat exchanger (heat exchanger) 7, an indoor expansion valve (expansion valve) 8, an indoor fan 9 for blowing indoor air to the indoor heat exchanger 7, and the like. An evaporation temperature sensor 21 for detecting the temperature at the outlet of the indoor expansion valve 8 during the cooling operation is provided between the indoor expansion valve 8 and the indoor heat exchanger 7. Further, the indoor unit 91 is also provided with a suction temperature sensor 22 for detecting the temperature of the suction air and a humidity sensor 23 for detecting the humidity.

The outdoor unit 90 and the indoor unit 91 are connected by a gas connecting pipe (refrigerant pipe) 10 through which a gas refrigerant flows and a liquid connecting pipe (refrigerant pipe) 11 through which a liquid refrigerant flows. The outdoor unit 90 is provided with a liquid blocking valve 15 at a portion connected to the liquid connecting pipe 11 and a gas blocking valve 16 at a portion connected to the gas connecting pipe 12.

During the cooling operation, the gas refrigerant compressed by the compressor 1 to a high temperature and high pressure is supplied to the outdoor heat exchanger 3 through the circuit shown by the solid line of the four-way valve 2. In the outdoor heat exchanger 3, the high-temperature and high-pressure gas refrigerant exchanges heat with the outside air supplied by the outdoor fan 4 and dissipates heat to condense and liquefy the refrigerant to become a liquid refrigerant. This liquid refrigerant enters the indoor unit 91 through the liquid connection pipe 11, is decompressed to a predetermined pressure by the indoor expansion valve 8, becomes a low-temperature low-pressure refrigerant, and flows into the indoor heat exchanger 7. In the indoor heat exchanger 7, the refrigerant exchanges heat with the indoor air supplied by the indoor fan 9, takes heat from the indoor air, and cools the room, while the refrigerant itself evaporates and gasifies. After that, the gas refrigerant returns to the outdoor unit 90 through the gas connection pipe 10 and is sucked into the compressor 1 through the four-way valve 4. During the cooling operation, such a refrigeration cycle is repeated.

In the example shown in FIG. 1, a case where only one indoor unit 91 is shown is shown, but as shown in FIG. 9 described later, a plurality of indoor units 91 are often provided in parallel. In this case, The indoor expansion valve 8 not only reduces the pressure of the refrigerant, but also adjusts the flow rate of the refrigerant flowing through each indoor unit 91.

During the heating operation, the four-way valve 2 is switched to the circuit shown by the broken line to perform the operation. The high-temperature and high-pressure gas refrigerant discharged from the compressor 1 flows into the indoor unit 91 through the four-way valve 2 and the gas connection pipe 10, exchanges heat with the indoor air in the indoor heat exchanger 7, dissipates heat, and dissipates heat in the room. As it heats the air, it condenses and liquefies itself. This liquefied liquid refrigerant returns to the outdoor unit 90 through the liquid connection pipe 11, and the refrigerant that has been decompressed by the outdoor expansion valve 6 to a low temperature and low pressure is blown by the outdoor fan in the outdoor heat exchanger 3 with the outside air. After exchanging heat to remove heat from the outside air and evaporating it, it is sucked into the compressor 1 via the four-way valve 4. Such a refrigeration cycle is repeated during the heating operation.

FIG. 2 is an example of a Ph diagram (Morie diagram) during the cooling operation of the refrigeration cycle apparatus, in which the horizontal axis shows the specific enthalpy h (kJ / kg) and the vertical axis shows the pressure P (MPa). There is. The refrigerant sucked by the compressor 1 is compressed from the state a to the state b, and becomes a high-temperature and high-pressure refrigerant. After that, the refrigerant condensed by the outdoor heat exchanger 3 is in the state c, and the pressure is reduced by the indoor expansion valve 6 to be in the state d. The decompressed refrigerant absorbs heat in the indoor heat exchanger 7 and evaporates to the state e. After that, when passing through the connecting pipe or the like from the indoor unit 91 to the outdoor unit 90, the pressure is reduced due to the refrigerant flow pressure loss and the state returns to the state a.

FIG. 3 is another example of the Ph diagram during the cooling operation of the refrigeration cycle apparatus, and is a diagram when the amount of decompression in the expansion valve (for example, the indoor expansion valve 8) is insufficient. In FIG. 3, the broken line indicates the state of FIG. If the amount of decompression in the indoor expansion valve 8 is insufficient, the evaporation temperature rises, so that the temperature difference with the indoor air decreases and the amount of heat exchanged decreases. Therefore, the refrigerant cannot be overheated (superheated) at the outlet of the indoor heat exchanger 7, and the refrigerant returns to the compressor 1 in a state where the liquid phase (liquid refrigerant) is contained.

Since the liquid refrigerant cannot be compressed by the compressor 1, if a large amount of liquid refrigerant returns to the compressor 1, the compressor 1 may fail. Therefore, it is very important to appropriately control the amount of decompression in the indoor expansion valve 8 in order to prevent the liquid from returning to the compressor and to ensure reliability.

On the other hand, when the amount of decompression in the indoor expansion valve 8 becomes excessive, the degree of superheat at the outlet of the indoor heat exchanger 7 serving as an evaporator increases, and the temperature of the refrigerant sucked into the compressor rises. Further, since the suction pressure becomes low, the discharge temperature of the theoretical compressor 1 determined from the physical properties of the refrigerant further rises.
Since the discharge temperature of the compressor 1 rises due to these factors, the temperature of the compressor 1 may become too high depending on the conditions, and the reliability thereof may be impaired.

Further, since the refrigerant that has become overheated gas inside the indoor heat exchanger 7 has low heat transfer performance with air, the heat transfer performance (heat exchange efficiency) of the heat exchanger deteriorates as the area of the overheated gas becomes wider. There are also challenges. Therefore, since the efficiency of the air conditioner is also lowered, it is not desirable that the amount of decompression in the indoor expansion valve 8 becomes excessive.

As described above, not only from the viewpoint of ensuring the reliability of the compressor 1, but also from the viewpoint of efficiency as an air conditioner, the opening degree of the indoor expansion valve 8 is appropriately controlled to control the degree of superheat at the evaporator outlet. It is important to keep it properly. The discharge temperature of the compressor 1 has a characteristic that it decreases when the amount of decompression is insufficient and liquid returns, and conversely it rises when the amount of decompression becomes excessive. Therefore, it is reliable to maintain the discharge temperature of the compressor 1 properly. It is possible to secure to some extent.

However, since the discharge temperature of the compressor 1 changes slowly by the amount of the heat capacity of the compressor 1 with respect to the change of the state of the refrigerant, it is inferior in followability to a sudden change of the state of the refrigerant (control response). There is a problem (bad sex). This problem becomes particularly remarkable under the condition that the compressor rotation speed is low and the heat loss in the compressor 1 is reduced, and the influence of changes such as the rotation speed of the compressor 1 and the opening degree of the indoor expansion valve 8 appears in the discharge temperature. It takes time.

Therefore, for example, assuming that the opening degree of the indoor expansion valve 8 is opened because the discharge temperature is higher than the target, the discharge temperature does not easily decrease even if the opening degree of the indoor expansion valve 8 is increased. A situation may occur in which the opening degree is made too large and the liquid returns to the compressor 1. As described above, in the control for maintaining the discharge temperature of the compressor 1 appropriately, the controllability may be deteriorated and the reliability of the air conditioner may be impaired.

Further, when the connecting pipes (refrigerant pipes) 10 and 11 between the outdoor unit 90 and the indoor unit 91 are long, the heat capacity of the connecting pipes 10 and 11 is greatly affected, so that the change in the opening degree of the indoor expansion valve 8 has an effect. It will take more time before it appears at the discharge temperature of the compressor. Therefore, the controllability is further deteriorated.

Examples of the present invention for solving the above problems will be described below. In this embodiment, the refrigerant pipe between the expansion valve outlet and the heat exchanger serving as the evaporator, that is, between the indoor expansion valve 8 and the indoor heat exchanger 7 serving as the evaporator during cooling operation, is used. An evaporation temperature sensor 21 that detects the evaporation temperature is installed, and the indoor expansion valve 8 is controlled so that the detected temperature becomes a control target value.

The outlet of the indoor expansion valve 8 is a place where the temperature first changes when the opening degree of the indoor expansion valve 8 is changed or the rotation speed of the compressor 1 is changed, and the response to the change in the control state is It is characterized by being fast. In this embodiment, the evaporation temperature sensor 21 is arranged at the outlet of the indoor expansion valve 8, and the temperature (evaporation temperature) detected by the evaporation temperature sensor 21 is used to control the indoor expansion valve 8. The expansion valve 8 can be controlled by quickly detecting the change in the state of the evaporator with respect to the change in the state. Further, in this embodiment, since the evaporation temperature is directly detected by the evaporation temperature sensor 21, there is no possibility that an error will occur in the estimation of the evaporation temperature due to the pressure loss in the gas connection pipe 10 or the like as in the conventional case.

Therefore, according to the present embodiment, controllability such as opening degree control of the indoor expansion valve 8 can be improved, and as a result, liquid return to the compressor 1 can be prevented and reliability can be improved. .. Further, in this embodiment, not only the control with good responsiveness becomes possible, but also the evaporation temperature can be detected with high accuracy, so that the superheat degree control at the outlet of the evaporator can be performed with high accuracy. As a result, it becomes possible to easily control the degree of superheat, so that the heat exchange efficiency in the air conditioner can also be improved. Therefore, according to the present embodiment, it is possible to obtain an efficient air conditioner with improved controllability while preventing the liquid from returning to the compressor.

In particular, in this embodiment, since the heat capacity of the compressor 1 and the gas connection pipe 10 and the pressure loss in the gas connection pipe 10 are not affected, the air conditioning load is small and the rotation speed of the compressor 1 is low. However, since the evaporation temperature can be detected quickly with high accuracy and the controllability can be improved, the controllable capacity range of the air conditioner can be expanded to the low load side.

When the load of the air conditioner is low, if the number of revolutions of the compressor is reduced in order to reduce the capacity of the air conditioner while keeping the degree of superheat in the evaporator constant, the suction pressure of the compressor will increase and the difference required for the compressor. There is a risk that the pressure and pressure ratio cannot be secured. If the rotation speed of the compressor is not reduced, the air conditioning capacity becomes excessive, so that the compressor needs to be operated intermittently, and energy saving is deteriorated.

On the other hand, in this embodiment, since the controllable capacity range of the air conditioner can be expanded to the low load side, the intermittent operation of the compressor under low load conditions can be suppressed, and the power consumption increases due to the intermittent operation of the compressor. Can be suppressed. Therefore, from this point as well, it is possible to obtain an air conditioner with low power consumption and high efficiency.

Further, in the conventional method of estimating the evaporation temperature from the low pressure on the suction side of the compressor 1, when a plurality of indoor units 91 are provided in parallel, the respective states of the indoor units 91 cannot be detected. On the other hand, in this embodiment, even when a plurality of indoor units 91 are installed in parallel, the change in the evaporation temperature in each indoor unit 91 can be correctly detected, so that the change in each indoor unit can be detected. It also has the effect of enabling appropriate control.

Next, the setting of the control target value of the evaporation temperature in the refrigeration cycle apparatus of the first embodiment will be described with reference to FIG. FIG. 4 is a block diagram illustrating a method of setting a control target value of the evaporation temperature in the first embodiment.

The control target value of the evaporation temperature can be determined by various methods, but in this embodiment, as shown in FIG. 4, the temperature of the suction air to the indoor heat exchanger 7 is determined by the suction temperature sensor 22 to determine the humidity. It is provided with an evaporation temperature estimation unit 50 that estimates the evaporation temperature from these values and the air volume to the indoor heat exchanger 7 and the exchange heat amount 31 according to the air volume set value 30 detected by the humidity sensor 23. Here, the exchange heat amount 31 of the indoor heat exchanger 7 can be estimated from the evaporation temperature detected by the evaporation temperature sensor 21 and the rotation speed of the compressor 1. Further, the air volume set value 30 is a set value of the air volume supplied to the indoor heat exchanger 7 by the indoor fan 9.

The information from the humidity sensor 23 shown in FIG. 4 is not always necessary, and for example, the humidity may be estimated and used instead of using the value detected from the humidity sensor 23. Further, for the air volume setting value 30, the rotation speed of the indoor fan 9 may be used.

Further, the evaporation temperature control target value setting unit 51 for setting the evaporation temperature control target value from the evaporation temperature estimated by the evaporation temperature estimation unit 50 is provided. The functions of the evaporation temperature estimation unit 30 and the evaporation temperature control target value setting unit 51 may be provided in a control device (not shown) provided in the air conditioner. The evaporation temperature control target value set by the evaporation temperature estimation unit 50 and the evaporation temperature control target value setting unit 51 is preferably configured to be corrected for each predetermined control cycle.

The indoor expansion valve 8 is controlled by the control device so that the temperature detected by the evaporation temperature sensor 21 becomes the control target value of the evaporation temperature set by the control target value setting unit 51 of the evaporation temperature. To. In this embodiment, since the control target value of the evaporation temperature can be held as an absolute value, evaporation provided at the outlet of the indoor expansion valve 8 even when the degree of superheat is excessive or liquid return occurs, for example. The opening degree of the indoor expansion valve 8 can be controlled so that the value of the temperature sensor 21 becomes the control target value of the evaporation temperature.

For example, if the indoor expansion valve 8 is slightly throttled to prevent liquid return when the air conditioner is started, the evaporation pressure is excessively lowered, the cooling capacity of the air conditioner is difficult to obtain, and the cooling capacity is lowered. .. If the cooling capacity is low, the rate of increase in the discharge temperature of the compressor 1 becomes slow and it takes time.
For this reason, in the case where the outdoor expansion valve is controlled by using the conventional discharge temperature, it takes time until the operation of opening the opening of the indoor expansion valve is performed, and the state where the cooling capacity is low continues for a while. As a result, the cooling capacity at startup tends to be insufficient.

Further, in the conventional one in which the indoor expansion valve is controlled so that the degree of superheat of the refrigerant at the outlet of the evaporator becomes a desired value, when the indoor expansion valve is slightly throttled when the air conditioner is started, the evaporator The degree of superheat at the outlet is secured and rises relatively early, but it is difficult to determine how much the indoor expansion valve should be opened in order to make the degree of superheat an appropriate value, and liquid return is required. In order to prevent it and ensure reliability, the indoor expansion valve had to be gradually opened over time.
As described above, the conventional one has a problem that the cooling capacity of the air conditioner is difficult to obtain.

On the other hand, in this embodiment, the control target value of the evaporation temperature is set as an absolute value, and the indoor expansion valve 8 is controlled so that the detection temperature of the evaporation temperature sensor 21 becomes the control target value. Therefore, the opening degree of the indoor expansion valve 8 can be maintained at an appropriate opening degree without being excessively reduced or increased.

Further, even if the indoor expansion valve 8 is in a state of being over-throttled, the deviation between the detection temperature of the evaporation temperature sensor 21 and the control target value of the evaporation temperature can be known. It is possible to determine whether to change the opening degree of. Therefore, it is possible to prevent the evaporation pressure from becoming excessively low when the air conditioner is started and the cooling capacity from being insufficient, and it is also possible to shorten the time until the sufficient cooling capacity can be exhibited. It can also improve the comfort of the air conditioner.

Further, when the pressure change in the indoor heat exchanger 7 serving as the evaporator is abrupt, the opening of the indoor expansion valve 8 may be over-throttled or the liquid may return to the compressor, but the conventional discharge temperature and degree of superheat may occur. In the control using, it may not be possible to determine how much the opening degree of the indoor expansion valve should be changed.

On the other hand, in the case of this embodiment, since the control target value of the evaporation temperature is provided as an absolute value, the deviation between the detection temperature of the evaporation temperature sensor 21 and the control target value can be detected, and the compression can be performed. Even when the liquid returns to the machine or the degree of superheat is excessive, the required change amount of the indoor expansion valve 8 opening can be estimated. Therefore, the reliability of the air conditioner can be improved.

The above will be described with reference to FIG. FIG. 5 is a diagram for explaining the effect of the present embodiment, and is a diagram showing the relationship between the expansion valve opening degree, the degree of superheat, and the evaporation temperature.

In the case of the conventional example of controlling the degree of refrigerant superheat at the evaporator outlet, as shown in FIG. 5A, the degree of refrigerant superheat is when the refrigerant at the evaporator outlet is not completely gasified (in a gas-liquid two-phase state). The value of the degree of superheat becomes 0 degrees regardless of whether the liquid ratio is high (in the case of point A) or low (in the case of point B). In this case, it is necessary to throttle the expansion valve so that the refrigerant completely evaporates to lower the evaporation temperature, but since the liquid ratio cannot be detected, it is not possible to determine how much the expansion valve should be throttled.

Further, the temperature of the refrigerant rises due to heat exchange with air even after evaporation, but when the air temperature is low, the temperature rise range becomes small, so when the degree of superheat is large (in the case of points D and E). However, it is difficult to determine how much the expansion valve opening should be opened.
That is, assuming that the expansion valve opening degree is appropriate at point C, the degree of superheat at points A and B is equal to 0 degrees. Therefore, when looking only at the degree of superheat, the expansion valve opening degree is increased to point C. When changing, it is difficult to judge how much the opening should be reduced.

Also, when the expansion valve is throttled too much, the evaporation temperature drops according to the expansion valve opening, but the degree of superheat is almost the same at points D and E, so how much is it to control to point C? It is difficult to determine whether to open the expansion valve.
For this reason, the conventional one in which the degree of superheat of the refrigerant at the outlet of the evaporator is controlled has a drawback that the opening degree is gradually changed for safety and the control is delayed.

On the other hand, in this embodiment, the evaporation temperature sensor 21 is installed between the indoor expansion valve 8 and the indoor heat exchanger 7 serving as an evaporator, and the indoor expansion valve 8 is set so that the detected temperature becomes the control target value. As shown in FIG. 5 (b), the magnitude of the difference between the control target value (point C) of the evaporation temperature and the detected evaporation temperature becomes clear, and the expansion valve is opened. It becomes easier to determine how much the temperature should be narrowed down or opened.

That is, the degree of superheat at points A and B is equal to 0 degrees, but when looking at the evaporation temperature, the difference between the evaporation temperatures at points A and B with respect to the control target value at point C is different, so it depends on each difference. Therefore, by adjusting the throttle amount as X _A and X _B , the expansion valve opening can be corrected appropriately and quickly.
Even when the expansion valve is throttled too much, the degree of superheat is almost the same at points D and E, but the evaporation temperature decreases according to the opening degree of the expansion valve, so that the points D and E differ greatly. Therefore, even in this case, the expansion valve opening can be corrected appropriately and quickly by adjusting the opening amount as X _D , X _E according to the difference from each control target value (point C). .. Therefore, according to this embodiment, since it is possible to grasp the appropriate opening control amount of the expansion valve, it is possible to control the evaporation temperature to approach the control target value quickly and accurately, and the refrigeration cycle with good controllability. You can get the device.

For this reason, the expansion valve opening can be controlled quickly and accurately even under conditions where the transient change is large, such as when the degree of superheat deviates significantly from the target value or when the air conditioner is started, so that the control response is good. Therefore, controllability can be improved.

By the way, in a refrigeration cycle apparatus, usually, when the air conditioning load, that is, the amount of heat exchanged becomes small, the temperature difference between the refrigerant and the indoor air in the indoor unit 91 becomes small, so that the evaporation temperature becomes high. As a result, the suction pressure of the compressor 1 becomes high, so that the difference between the suction pressure and the discharge pressure becomes small, which may deviate from the operable range of the compressor 1. Therefore, an excessive increase in the evaporation temperature is not desirable in order to ensure the reliability of the compressor 1.

Therefore, in this embodiment, an upper limit value is set for the control target value of the evaporation temperature. At the outlet of the indoor expansion valve 8, the refrigerant is in a gas-liquid two-phase state, and the saturation pressure is determined according to the refrigerant temperature. Therefore, since the evaporation pressure does not rise above the saturation pressure of this evaporation temperature, the evaporation pressure can be limited by setting an upper limit value for the control target value of the evaporation temperature.
Since the suction pressure of the compressor 1 is lower by the pressure loss of the gas connection pipe 10, the suction pressure of the compressor 1 is set to be higher than the evaporation pressure of the indoor heat exchanger 7 serving as the evaporator by setting a limit on the evaporation pressure. It can be surely kept low. Therefore, since the increase in the suction pressure can be suppressed, the reliability of the compressor 1 can be ensured.

It is conceivable to prevent an increase in the suction pressure of the compressor 1 by increasing the number of revolutions of the compressor 1, that is, increasing the cooling capacity, but in this case, the cooling capacity is excessive with respect to the air conditioning load. Therefore, the compressor 1 is operated intermittently, and the power consumption increases. On the other hand, in the present embodiment, since the increase in the suction pressure can be suppressed without increasing the rotation speed of the compressor 1, it is possible to suppress the intermittent operation of the compressor 1 and continuously operate the compressor 1, resulting in an increase in power consumption. It is possible to obtain an air conditioner with high energy saving.

Although the above description is for the cooling operation, the present invention can be similarly performed even during the heating operation. This will be described with reference to FIG. During the heating operation, the four-way valve 2 is switched so that the refrigerant flows to the broken line side, the high-temperature and high-pressure gas refrigerant discharged from the compressor 1 flows to the indoor heat exchanger 7, and the liquid refrigerant condensed here is connected for liquid. It flows into the outdoor unit 90 through the pipe 11.
At this time, the indoor expansion valve 8 is fully opened, and the refrigerant is depressurized by the outdoor expansion valve 6.

Further, an evaporation temperature sensor 20 is installed in the refrigerant pipe between the outdoor expansion valve 6 and the outdoor heat exchanger 3, and the evaporation temperature detected by the evaporation temperature sensor 20 becomes a predetermined temperature (control target value). As described above, the opening degree of the outdoor expansion valve 6 is controlled. By holding the control target value of the evaporation temperature as an absolute value even during the heating operation, the outdoor expansion valve 6 can be controlled stably, so that the operation can prevent the liquid from returning to the compressor 1. , Reliability can be improved.

Further, even under conditions where the evaporation pressure tends to be high, such as when the outside air temperature is high, the evaporation pressure can be limited by setting an upper limit value for the control target value of the evaporation temperature. Therefore, it is possible to prevent the suction pressure of the compressor from becoming excessively high, so that the reliability of the compressor 1 can be ensured and the reliability of the air conditioner can be improved.

Next, Example 2 of the present invention will be described with reference to FIGS. 6 and 7. FIG. 6 is a refrigeration cycle configuration diagram showing the second embodiment of the refrigeration cycle apparatus of the present invention, and FIG. 7 is a block diagram illustrating a method of setting a control target value of evaporation temperature in the refrigeration cycle apparatus of the second embodiment.

In FIGS. 6 and 7, the parts having the same reference numerals as those in FIGS. 1 and 4 are the same or corresponding parts, and the points different from those in FIG. 1 will be mainly described. In the second embodiment, the outlet temperature sensor 25 is provided on the side opposite to the indoor expansion valve 8 side of the indoor heat exchanger 7 in the indoor unit 91, and further, the outdoor expansion valve 6 side of the outdoor heat exchanger 3 in the outdoor unit 90. It is different from the first embodiment in that the outlet temperature sensor 26 is installed on the opposite side to the above. In the second embodiment, the suction temperature sensor 22 and the humidity sensor 23 in the first embodiment are not installed, but the sensors 22 and 23 are also installed in the same manner as in the first embodiment. It may be configured to perform the same control as above.

In the second embodiment as well, similarly to the first embodiment, the opening degree of the indoor expansion valve 8 is set so that the temperature detected by the evaporation temperature sensor 21 becomes the target temperature (control target value of the evaporation temperature) during the cooling operation. To control. Here, unlike the first embodiment, the control target value of the evaporation temperature is not fixed, and the evaporator outlet temperature and the evaporation temperature sensor 21 detected by the outlet temperature sensor 25 installed at the outlet of the indoor heat exchanger 7 are used. The control target value of the evaporation temperature is sequentially corrected so that the difference from the detected evaporation temperature becomes a desired value. The control target value of the evaporation temperature is corrected for each predetermined control cycle.

Since the difference between the evaporator outlet temperature and the evaporation temperature corresponds to the degree of superheat at the evaporator outlet, the evaporation temperature is sequentially corrected so that the degree of superheat becomes a desired value. By sequentially correcting the control target value of the evaporation temperature according to the degree of superheat, even if the evaporation temperature estimated by the evaporation temperature estimation unit 50 shown in FIG. 7 is incorrect, indoor heat exchange serving as an evaporator By ensuring the degree of superheat at the outlet of the vessel 7, not only the reliability of the compressor 1 can be improved, but also the efficient operation of the air conditioner becomes possible.

The effect of maintaining the evaporator outlet superheat degree is the same as that of the conventional superheat degree control, but in the second embodiment, since the absolute value of the evaporation temperature is set as the control target value, the superheat degree is excessive or zero. Even in this case, as in the first embodiment, the deviation between the control target value and the evaporation temperature detected by the evaporation temperature sensor 21 can be grasped, and the opening degree of the indoor expansion valve 8 can be determined. Stable control can be realized because the control amount of the expansion valve opening degree is clarified as to whether the degree should be changed.

By the way, the temperature detected by the outlet temperature sensor 25 is stable when the degree of superheat is sufficiently high, but fluctuates when the degree of superheat is small. This is because when the degree of superheat at the outlet of the heat exchanger is sufficiently large, the refrigerant completely evaporates and vaporizes, so the temperature is stable, but when the degree of superheat is small, the refrigerant completely evaporates and the temperature rises. This is because a state in which the refrigerant is in a mixed state and a state in which a low-temperature liquid-phase refrigerant that cannot be completely vaporized are mixed alternately occur, and the temperature fluctuates according to the movement.

This temperature fluctuation may be as large as 5 ° C depending on the conditions, but the cause of the temperature change is either the effect of the change in operating conditions or the effect of such fluctuation based on the information on the degree of superheat. It is difficult to judge whether it is. In such a case, in order to ensure reliability, it is conceivable to control the expansion valve to keep the degree of superheat high, but if the control keeps the degree of superheat large, the total heat transfer area of the heat exchanger is effective. The power consumption of the air conditioner increases because the heat transfer performance is reduced.

On the other hand, in this embodiment, since the opening degree of the indoor expansion valve 8 is controlled so that the temperature detected by the evaporation temperature sensor 21 becomes the target temperature, the degree of superheat is small and the evaporator outlet temperature fluctuates. Even in this case, since the evaporation temperature at the inlet of the evaporator is stable, problems such as false detection of temperature due to temperature fluctuation at the outlet of the evaporator can be avoided. Therefore, it is possible to obtain an effect that stable control can be realized without being affected by erroneous detection.

Further, when the operating state of the constituent devices such as the compressor 1 and the outdoor fan 4 does not change and the cycle is relatively stable, the appropriate evaporation temperature is also stable, so that the degree of superheat at the evaporator outlet (evaporator outlet superheat) ( Or even if there is a change in the outlet temperature), the change in the control target value of the evaporation temperature may be small. Therefore, even under the condition that the degree of superheat is relatively small and the degree of superheat fluctuates, the fluctuation of the evaporation temperature, which is the control target value, is small and the control becomes easy. Therefore, the heat exchanger performance by increasing the degree of superheat can be improved. It is possible to suppress the decrease and perform efficient operation with a small degree of overheating. That is, according to this embodiment, it is possible to obtain an efficient air conditioner with low power consumption.

Further, if the upper limit value and the lower limit value are set in the control target value of the evaporation temperature, it is possible to prevent an extreme increase or decrease in the evaporation pressure, so that the reliability of the compressor 1 can be ensured. The upper limit value and the lower limit value of the control target value of the evaporation temperature may be set according to the air temperature flowing into the heat exchanger 7 serving as the evaporator, and the control target value may be set according to the air volume, humidity and the like. May be changed. For example, when the air volume is small, the evaporation temperature becomes low, so it is preferable to lower the lower limit value.

By the way, when the air conditioning load fluctuates abruptly and the rotation speed of the compressor 1 also fluctuates, the evaporation temperature also changes abruptly. If the target value of the evaporation temperature is not changed, the degree of superheat at the outlet of the evaporator may become excessive or liquid return may occur. On the other hand, in this embodiment, as shown in FIG. 7, the evaporation temperature estimation unit 50 is provided with a function of correcting the control target value 51 of the evaporation temperature according to the amount of change in the compressor rotation speed 32. Therefore, even when the air conditioning load fluctuates, the control target value 51 of the evaporation temperature can be optimized and the opening degree of the indoor expansion valve 8 can be controlled toward the control target value, so that the degree of superheat is excessive. It is possible to avoid problems such as becoming liquid and causing liquid return.

Further, since the evaporation temperature suddenly changes even when the air volume of the indoor fan 9 is changed, such as when the user changes the air volume setting value 30 of the indoor unit 91 during the cooling operation, the evaporation temperature estimation unit is described in this embodiment. The 50 has a function of estimating a change in evaporation temperature when the air volume set value 30 changes. As a result, by changing the control target value of the evaporation temperature in advance as in the case where the air conditioning load fluctuates, it is possible to avoid a problem that the degree of superheat at the evaporator outlet becomes excessive or liquid returns. ..

By the way, a discharge temperature sensor (not shown) for detecting the discharge temperature is provided in the discharge pipe of the compressor or the closed container of the compressor, and the discharge temperature is controlled by detecting the discharge temperature and controlling the discharge temperature to a target value. When doing so, it is relatively easy to control the degree of superheat at the outlet of the compressor to be small. On the other hand, in the superheat degree control using the evaporation temperature, the target superheat degree cannot be set to 0 degree, so it is necessary to keep the target superheat degree to some extent. When the degree of superheat is increased, a large superheated gas region is formed near the outlet of the heat exchanger that serves as an evaporator, and the heat transfer performance of this superheated gas region is lower than that of the two-phase region. Therefore, the heat transfer performance of the heat exchanger as a whole deteriorates. Therefore, in order to operate the air conditioner efficiently, the above-mentioned discharge temperature control is preferable to the superheat control using the evaporation temperature.

However, when the discharge temperature is controlled in the low load region, the change in the discharge temperature becomes slow and the controllability deteriorates. Therefore, in the low load region, the superheat degree control using the evaporation temperature is more efficient.
Therefore, in this embodiment, the evaporation temperature control that controls the evaporation temperature to be the control target value is adopted in the low load region, while the discharge temperature is set to the target value in the high load region where the compressor rotation speed is high. It is possible to switch to controlled discharge temperature control for operation. That is, in addition to the evaporation temperature control function that controls the opening degree of the indoor expansion valve 8 so that the evaporation temperature detected by the evaporation temperature sensor 21 becomes the control target value of the evaporation temperature, the discharge temperature of the compressor is Further equipped with a discharge temperature control function for controlling to reach a target value, the evaporation temperature control function is selected and operated in a low load region, and the discharge temperature control function is selected and operated in a high load region. It is equipped with a control device (not shown) that switches and controls the temperature. This control device may also be provided in the control device that controls the air conditioner.

Therefore, in the high load region, the discharge temperature control can maintain an appropriate discharge temperature and realize highly energy-saving operation, while in the low load region, the evaporation temperature control makes the evaporation temperature appropriate. By controlling the indoor expansion valve 8, stable expansion valve control with good responsiveness can be realized, and by continuously operating the compressor 1, an air conditioner with high energy saving can be realized. As a result, an air conditioner with low power consumption can be obtained throughout the year, and energy saving can be improved especially in a high load region, so that an effect of reducing peak power consumption can also be obtained.

In the second embodiment, the operation is switched to the discharge temperature control in the high load region, but the evaporation temperature control is maintained even in the high load region, and instead, the evaporation temperature is controlled in the high load region. The same effect can be obtained by using the discharge temperature to calculate the target value.

Further, in the second embodiment as well, the above-mentioned control can be similarly performed during the heating operation as in the first embodiment. That is, during the heating operation, the evaporation temperature sensor 20 sequentially corrects the control target value of the evaporation temperature so that the difference between the evaporation temperature sensor 20 provided in the outdoor unit 90 and the outlet temperature sensor 26 becomes a predetermined temperature. The opening degree of the outdoor expansion valve 6 is controlled so that the detected evaporation temperature becomes the control target value. By controlling the opening degree of the outdoor expansion valve 6 not by the degree of superheat but by the control target value (absolute value) of the evaporation temperature, the same effect as in the cooling operation can be obtained.

Example 3 of the present invention will be described with reference to FIG. FIG. 8 is a refrigeration cycle configuration diagram showing Example 3 of the refrigeration cycle apparatus of the present invention. In FIG. 8, the portions having the same reference numerals as those in FIGS. 1 and 6 are the same or corresponding portions, and the points different from those in FIGS. 1 and 6 will be mainly described.

In the third embodiment, the indoor unit 91 is not provided with an expansion valve (indoor expansion valve 8 shown in FIGS. 1 and 6), and the outdoor expansion valve 6 is used even during the cooling operation as in the heating operation. I try to reduce the pressure. Further, in this embodiment, by providing the suction temperature sensor 27 in the suction pipe of the compressor 1, the outlet temperature of the evaporator outlet can be determined by using the suction temperature sensor 27 during both the cooling operation and the heating operation. The outlet temperature sensors 25 and 26 shown in 6 are not required. Further, in the first and second embodiments, the evaporation temperature sensor 21 provided in the indoor unit 91 is provided on the indoor heat exchanger 7 side of the outdoor expansion valve 6 in the outdoor unit 90. These points are different from Examples 1 and 2 above.
In this embodiment, during the cooling operation, the control target value of the evaporation temperature is sequentially corrected so that the difference between the suction temperature sensor 27 and the evaporation temperature sensor 21 becomes a desired value, and is detected by the evaporation temperature sensor 21. The outdoor expansion valve 6 is controlled so that the temperature is the control target value. Further, during the heating operation, the control target value of the evaporation temperature is sequentially corrected so that the difference between the suction temperature sensor 27 and the evaporation temperature sensor 20 becomes a desired value, and the temperature detected by the evaporation temperature sensor 21 is set. The outdoor expansion valve 6 is controlled so as to have this control target value.

In the third embodiment, by configuring and controlling as described above, those having almost the same functions as those in the first and second embodiments can be obtained, and the number of expansion valves and outlet temperature sensors can be reduced, so that the cost is high. It can be reduced. In addition, since the number of parts is reduced, equipment failure is less likely to occur, so that a more reliable air conditioner can be obtained.

Next, Example 4 of the present invention will be described with reference to FIG. FIG. 9 is a refrigeration cycle configuration diagram showing Example 4 of the refrigeration cycle apparatus of the present invention. In FIG. 9, the parts having the same reference numerals as those in FIGS. 1 and 6 are the same or corresponding parts, and the points different from those in FIGS. 1 and 6 will be mainly described.

The fourth embodiment is different from the above-described embodiment in that a plurality of indoor units 91 are connected in parallel to the outdoor unit 90.
During the cooling operation, the refrigerant condensed by the outdoor heat exchanger 3 passes through the liquid connection pipe 11 and branches and flows to the plurality of indoor units 91a and 91b connected in parallel at the portion F. At the other ends of the indoor units 91a and 91b, the branched refrigerants rejoin at the G portion, pass through the gas connection pipe 10, and return to the outdoor unit 90.

Here, the refrigerant flowing to the indoor units 91a and 91b is flow-distributed so that the pressure loss from the branch portion of F to the confluence portion of G is equal. The indoor units 91a and 91b are provided with indoor expansion valves 8a and 8b, respectively, and the evaporation temperature for detecting the refrigerant temperature is between the indoor expansion valves 8a and 8b and the indoor heat exchangers 7a and 7b. Sensors 21a and 21b are installed. Further, outlet temperature sensors 25a and 25b are installed on the opposite sides of the indoor heat exchangers 7a and 7b of the indoor units 91a and 91b from the indoor expansion valves 8a and 8b. Reference numerals 9a and 9b are indoor fans provided in the indoor units 91a and 91b.

When the evaporation temperature in each of the indoor heat exchangers 7a and 7b is estimated from the suction side pressure of the compressor 1 as in the conventional case, the evaporation temperature in each of the indoor heat exchangers 7a and 7b cannot be detected individually. , It is not possible to determine how to control the indoor expansion valves 8a and 8b. On the other hand, in this embodiment, since the evaporation temperature sensor 21 is provided in each indoor unit 91a, 91b, the outlet temperature (evaporation temperature) of each indoor expansion valve 8a, 8b is provided for each indoor unit 91a, 91b. Can be detected.

Therefore, similarly to the first and second embodiments, the control target value of the evaporation temperature can be set, and the opening degree of the indoor expansion valve 8 can be controlled so as to reach the evaporation temperature. In the fourth embodiment as well, as in the above embodiment, even when the degree of superheat at the outlet of the evaporator becomes 0 degree and the liquid returns, the control target value of the evaporation temperature and the evaporation temperature sensors 21a and 21b are used. Since the deviation can be detected, the opening degrees of the indoor expansion valves 8a and 8b may be changed according to the deviation, and an air conditioner having good responsiveness and high controllability can be obtained.

Further, among the plurality of indoor units 91a and 91b, when some of the indoor units 91a are in operation and the other indoor units 91b are stopped, or when the indoor unit 91b is started from the stopped state, the indoor unit The number of operating units changes from one to two. Under such transient conditions, the degree of superheat of the indoor unit 91a that continues to operate may not be stable, but since the operating state of the indoor unit 91a basically does not change, the control target value of the evaporation temperature is set. There is no need to change. Since the control target value of the evaporation temperature is given as an absolute value in this way, stable control of the indoor expansion valve 8a can be realized even when the degree of superheat at the outlet of the evaporator fluctuates transiently.

Further, the control target value of the evaporation temperature in the indoor unit 91b that starts operation needs to be estimated because it is not in operation. In the fourth embodiment, the control target value of the evaporation temperature of the indoor unit 91a that continues to operate is used to determine the control target value of the evaporation temperature of the indoor unit 91b that starts the operation.

Since the pressure at the confluence (G) on the outlet side of the indoor heat exchangers 7a and 7b is the same for the plurality of indoor units 91a and 91b, the pressure loss in the piping from the indoor heat exchangers 7a and 7b to the confluence can be excluded. For example, the evaporation temperatures in the indoor units 91a and 91b are equal. Therefore, according to this embodiment in which the control target value of the evaporation temperature of the indoor unit 91b that starts the operation is determined by using the evaporation temperature of the indoor unit 91a that is continuing the operation, the estimation accuracy of the evaporation temperature is relatively high. High and reliable control is possible. The control as described in the fourth embodiment described above is particularly effective when the indoor units 91a and 91b are installed in the same air-conditioned space.

Further, when the room temperature rises and the operation of the indoor unit that has been stopped is restarted after the room temperature drops and the operation of the indoor units 91a and 91b is temporarily stopped, the evaporation temperature before the stop is controlled. It is advisable to retain the target value information and reuse the control target value. In this case, since the control target value of the evaporation temperature set according to the condition of the space where the indoor units 91a and 91b are installed can be used, the estimation accuracy of the control target value can be improved. Therefore, it is possible to avoid problems such as liquid return and excessive increase in the degree of superheat, and it is possible to obtain a highly reliable air conditioner.

Such control for retaining the information before the stop is effective even in a situation where the indoor units 91a and 91b are installed in different air-conditioned spaces, and only one indoor unit is operating. This is also effective in the case where only one indoor unit is connected as in the case of the first embodiment.

Example 5 of the present invention will be described with reference to FIG. FIG. 10 is a refrigeration cycle configuration diagram showing Example 5 of the refrigeration cycle apparatus of the present invention. In FIG. 10, the parts having the same reference numerals as those in FIGS. 1 and 6 are the same or corresponding parts, and the points different from those in FIGS. 1 and 6 will be mainly described.

The fifth embodiment is an example when the present invention is applied to a heat pump type water heater, and the present invention is not limited to an air conditioner, but is also applied to a water heater, a refrigerator, and the like if it is a refrigeration cycle device. Is possible. An embodiment in the case where the present invention is applied to a water heater as a refrigeration cycle device will be described with reference to FIG.

In FIG. 10, reference numeral 40 denotes a water tank constituting the water heater, and the water in the water tank is heated by the water heat exchanger 5. The compressor 1, the water heat exchanger 5, the outdoor expansion valve 6, and the outdoor heat exchanger 3 are cyclically connected by the gas connection pipe 10 and the liquid connection pipe 11 to form a refrigeration cycle. In the water heat exchanger 5, the water in the water tank 40 is heated by heat exchange between the high-temperature and high-pressure refrigerant discharged from the compressor 1 and flowing in the heat exchanger and the water in the water tank 40. It is configured in. The outdoor heat exchanger 3 is configured to exchange heat between the low-temperature low-pressure refrigerant that is decompressed by the outdoor expansion valve 6 and flows through the heat exchanger, and the outdoor air that is blown by the outdoor fan 4.

When the hot water supply operation is performed, the high-temperature and high-pressure refrigerant compressed by the compressor 1 flows to the heat exchanger 5 and dissipates heat to the water in the water tank to raise the water temperature. The refrigerant condensed by the water heat exchanger 5 is depressurized by the expansion valve 6, and then the refrigerant evaporated and gasified by the outdoor heat exchanger 3 returns to the compressor 1 and is compressed again.

During this hot water supply operation, the opening degree of the outdoor expansion valve 6 is such that the evaporation temperature detected by the evaporation temperature sensor 20 installed between the outdoor expansion valve 6 and the outdoor heat exchanger 3 is the control target temperature. It is adjusted to be. The control target value of the evaporation temperature is a predetermined temperature difference between the outlet temperature of the outdoor heat exchanger (evaporator) 3 detected by the outlet temperature sensor 26 and the evaporation temperature detected by the evaporation temperature sensor 20. It is corrected sequentially so as to be.

Even in such a heat pump type water heater, under the condition that the hot water supply load is small and the rotation speed of the compressor 1 is small, the change in the discharge temperature becomes slow and the controllability deteriorates. On the other hand, in the fifth embodiment, since the opening degree of the outdoor expansion valve 6 is controlled by using the evaporation temperature detected by the evaporation temperature sensor 20, highly responsive control is possible and the hot water supply load is increased. Even if it is small, stable control can be realized.

Further, even under operating conditions with a small degree of superheat such that the evaporator outlet temperature detected by the outlet temperature sensor 26 fluctuates, the evaporation temperature detected by the evaporation temperature sensor 20 does not fluctuate.
Therefore, by controlling the evaporation temperature detected by the evaporation temperature sensor 20 so as to be a control target value, stable control becomes possible, and further, compared with the conventional one that controls the degree of superheat of the refrigerant at the outlet of the evaporator. Therefore, it is also possible to determine the control target value of the evaporation temperature by using the one in which the value of the degree of superheat is set smaller. As a result, the heat transfer area of the outdoor heat exchanger 3 can be effectively utilized to improve the heat transfer performance, so that a water heater with low power consumption can be obtained.

Further, also in this embodiment, as in each of the above-described embodiments, the appropriate opening control amount of the expansion valve can be grasped, so that the outdoor expansion valve 6 can be controlled even when a transient change is large such as at the time of starting. By optimizing and suppressing excessive throttle, the hot water supply capacity at startup can be improved and the power consumption can be reduced.

Further, even when the hot water supply load fluctuates, the evaporation temperature control target is the same as that described with reference to FIG. 7, in response to the change in the rotation speed of the compressor 1 which changes in accordance with the load fluctuation. By changing the value, it is possible to improve the followability to load fluctuations.

As described above, in the fifth embodiment as well, it is possible to realize highly responsive and highly stable control not only during normal operation but also during low load and transient, so that the hot water supply is highly reliable. A machine (refrigeration cycle device) can be obtained.

According to each embodiment of the present invention described above, an evaporation temperature sensor is provided at the outlet of the expansion valve, and the expansion valve opening degree is controlled so that the evaporation temperature becomes a desired temperature (control target value of the evaporation temperature). Therefore, it is possible to control the evaporation temperature with good responsiveness, and it is possible to obtain an appropriate evaporation temperature. Therefore, the degree of superheat can be reliably ensured to prevent the liquid from returning to the compressor, and the degree of superheat can be controlled appropriately, and the heat exchange efficiency can be improved. That is, according to this embodiment, it is possible to obtain a refrigerating cycle apparatus having good controllability capable of quick response and stable control while preventing liquid return and improving reliability. Further, according to the present embodiment, since it is possible to accurately control the appropriate degree of superheat, the heat exchange efficiency can be improved, and there is an effect that stable opening control of the expansion valve can be performed even in a low load region.

The present invention is not limited to the above-described examples, and includes various modifications.
Further, it is possible to replace a part of the configuration of a certain embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of a certain embodiment.
Further, the above-described embodiment has been described in detail in order to explain the present invention in an easy-to-understand manner, and is not necessarily limited to those having all the described configurations.

1: Compressor, 2: Four-way valve, 3: Outdoor heat exchanger (heat exchanger), 4: Outdoor fan,
5: Water heat exchanger, 6: Outdoor expansion valve (expansion valve),
7 (7a, 7b): Indoor heat exchanger (heat exchanger),
8 (8a, 8b): Indoor expansion valve (expansion valve),
9 (9a, 9b): Indoor fan,
10, 11: Refrigerant piping (10: Gas connection piping, 11: Liquid connection piping),
15: Liquid blocking valve, 16: Gas blocking valve,
20, 21: Evaporation temperature sensor, 22: Suction temperature sensor, 23: Humidity sensor,
24: Outside air temperature sensor, 25 (25a, 25b), 26: Outlet temperature sensor,
27: Suction temperature sensor,
30: Air volume set value, 32: Compressor rotation speed,
40: Water tank,
50: Evaporation temperature estimation unit, 51: Evaporation temperature control target value setting unit,
90: Outdoor unit, 91 (91a, 91b): Indoor unit.

Claims (1)

It is a refrigeration cycle device that constitutes a refrigeration cycle by sequentially connecting a compressor, a heat exchanger that serves as a condenser, an expansion valve, and a heat exchanger that serves as an evaporator with a refrigerant pipe.
An evaporation temperature sensor is provided between the expansion valve and the heat exchanger serving as the evaporator, and the opening degree of the expansion valve is controlled according to the temperature detected by the evaporation temperature sensor.
In addition to the evaporation temperature control function that controls the opening degree of the expansion valve so that the evaporation temperature detected by the evaporation temperature sensor becomes the control target value of the evaporation temperature, the discharge temperature of the compressor becomes the target value. It is further provided with a discharge temperature control function to control the temperature, and in a low load region, the evaporation temperature control function is selected and operated, and in a high load region, the discharge temperature control function is selected and operated. A refrigeration cycle device characterized by being provided with the device .

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