ES2823758T3 - Refrigeration cycle apparatus - Google Patents

Abstract

A refrigerant cycle apparatus comprising: at least one compressor (1), a radiator (2), decompression means (3) capable of changing an opening degree, a heat absorber (4), an internal heat exchanger ( 5) performs heat exchange between a coolant at an outlet of the radiator (2) and the coolant at an outlet of the heat absorber (4), wherein a first temperature sensing means (30) is provided to detect a temperature of coolant between a compressor outlet (1) and a radiator inlet (2) and a second temperature sensing means (31) for detecting the temperature of the coolant between a radiator outlet (2) and a high pressure side inlet of the internal heat exchanger (5), characterized in that a sixth temperature sensing means (33) is provided to detect the temperature of the refrigerant between a low pressure side outlet of the internal heat exchanger (5) and an e input from the compressor (1), the degree of overheating of a suction part is calculated from a saturation temperature of the refrigerant at a detection point of the sixth temperature detection means (33) and a detection temperature by the sixth temperature sensing means (33), and the opening degree of the decompression means (3) is controlled so that the degree of overheating is the target value, and when the degree of overheating becomes the target value, a degree of opening of the decompression means (3) is controlled so that a temperature difference (DT) between a detection temperature by the first temperature detection means (30) and the detection temperature by the second detection means temperature detection (31) become a target value.

Description

DESCRIPTION

Refrigeration cycle apparatus

Technical field

The present invention relates to a refrigeration cycle apparatus using an internal heat exchanger, more particularly a refrigerant control to stably ensure performance.

Background of the technique

US 2003/0061827 A1 describes: In a heat pump water heater with a supercritical refrigerant cycle, a valve opening degree of a decompression valve is controlled to control a refrigerant pressure on the high pressure side , so that a temperature difference between the coolant falling from the water coolant heat exchanger and the water flowing in a water coolant heat exchanger is set in a predetermined temperature range.

JP 2003 176957 A shows: The high pressure of a cycle of a supercritical vapor compression type heat pump is controlled by changing the valve opening degree of a pressure reducing valve so that a temperature difference between an inlet temperature of the hot water flowing to a water coolant heat exchanger and an outlet temperature of the coolant flowing out of an outlet part of the water coolant heat exchanger, is kept within of a constant range Y (for example 102C), so that the high pressure of the refrigerant can be adjusted, and the heat exchange function of the internal heat exchanger can be adjusted within a constant range.

Descriptions of the prior art will be given as follows.

Conventionally, a hot water supply apparatus is proposed as a built-in refrigeration cycle apparatus, such as:

a hot water supply apparatus comprising a refrigeration cycle including a compressor, a hot water supply heat exchanger, an electronic expansion valve, and a heat source side heat exchanger from which the heat source heat is an outdoor air, and a hot water supply cycle that includes a hot water supply heat exchanger and a hot water supply tank,

wherein since a capacity control means using a variable capacity type compressor and controls the capacity of the compressor in response to changes in external environmental conditions of the side heat exchanger of the heat source is set, expansion valve opening degree to control an electronic expansion valve opening degree to make a compressor discharge temperature a target value in response to changes in external environmental conditions (an external temperature, for example ) of the side heat exchanger of the heat source and rotational speed control means for controlling a speed of the compressor rotation to be a target value in response to changes in external environmental conditions of the side heat exchanger of the heat source are fixed, an opening of the electronic expansion valve is controlled in order to make q that the compressor discharge temperature becomes a target value in response to changes in external environmental conditions (an external temperature, for example) of the side heat exchanger of the heat source; and the rotational speed of the compressor is controlled to be a target value in response to changes in the external environmental conditions of the side heat exchanger of the heat source, an optimal operating condition can be obtained in which a supply capacity of hot water and a load of hot water supply are further matched, and a coefficient of performance (COP) can be improved and size reduction of elements such as a heat exchanger becomes possible. (For example, refer to patent document 1)

A water heater is also proposed such as: a water heater for heating a hot water supply fluid in a supercritical heat pump cycle where a refrigerant pressure on a high pressure side becomes equal to or greater than the critical pressure of the refrigerant comprising:

a compressor,

a radiator that performs heat exchange between a coolant discharged from the compressor and a hot water supply fluid and is configured so that a coolant flow and a hot water supply fluid flow are opposite,

a decompressor to decompress the coolant flowing out of the radiator, and

an evaporator that makes the refrigerant flowing out of the compressor evaporate, causes the refrigerant to absorb a heat to discharge it on a suction side of the compressor,

wherein a high pressure side coolant pressure is controlled such that a temperature difference (AT) between the coolant flowing out of the radiator and the hot water supply fluid that flows in it becomes a predetermined temperature difference (ATo). (For example, refer to patent document 2). In this example of the prior art, a heat exchange efficiency of the radiator can be improved to improve the efficiency of a heat pump.

[Patent Document 1] Japanese Patent Gazette No. 3601369 (p. 6; Fig. 1)

[Patent Document 2] Japanese Patent Gazette No. 3227651 (pp. 1-3; Fig. 2).

Summary of the invention

Problem to be solved by the invention

Both of the above prior art examples control coolant conditions such that a compressor discharge temperature or temperature difference (AT) between the coolant flowing out of the radiator and the hot water supply fluid flowing in it becomes an objective value to achieve an efficient operation. However, there was a problem that in the vicinity where a refrigeration cycle efficiency (COP) becomes maximum, a control based only on an inlet side (the previous discharge temperature) of the radiator or an outlet side (the temperature difference At above) it is difficult to achieve stable and efficient operating conditions because changes in discharge temperature or temperature difference AT are small. Furthermore, since an operation with an internal heat exchanger in the refrigerant circuit is not being considered, the problem was that it was difficult to control and achieve stable and efficient operating conditions.

The present invention aims to solve the above problems of the prior art. The aim is to obtain a refrigeration cycle apparatus that can stably achieve efficient operating conditions by controlling the operating values based on the standard radiator conditions and the radiator outlet conditions to be a target value.

Means to solve the problem

To solve the above problems, the present invention provides the refrigeration cycle apparatus according to claim 1. Specifically, the characteristics of this apparatus are as follows: It includes, among others, at least one compressor, a radiator, decompression means that It can change a degree of opening, a heat absorber, an internal heat exchanger that performs heat exchange between a refrigerant at an outlet of the radiator and the refrigerant at the outlet of the heat absorber. First temperature sensing means is provided for sensing a coolant temperature between a compressor outlet and a radiator inlet and second temperature sensing means for sensing the coolant temperature between a radiator outlet and a high pressure side inlet of the radiator. internal heat exchanger. Furthermore, a sixth temperature sensing means is provided for sensing the temperature of the refrigerant between a low pressure side outlet of the internal heat exchanger and an inlet of the compressor. Furthermore, the degree of overheating of a suction part of the compressor is calculated from a saturation temperature of the refrigerant at a detection point of the sixth temperature detection means and a detection temperature by the sixth temperature detection means. . Furthermore, the degree of opening of the decompression means is controlled so that the degree of overheating becomes the target value, and when the degree of overheating becomes the target value, an opening degree of the means of decompression is controlled. decompression so that a temperature difference between a detection temperature by the first temperature detection means and the detection temperature by the second temperature detection means is converted into a target value.

Effect of the invention

According to the present invention, the opening degree of the expansion valve is controlled so that the GOP becomes maximum based on standard conditions of the radiator conditions and the coolant conditions of the radiator outlet part, whereby a refrigerant cycle apparatus can be obtained which can stably achieve efficient operation.

Brief description of the drawings

[Fig. 1] Fig. 1 is a diagram showing a configuration of a refrigeration cycle apparatus according to Embodiment 1 of the present invention;

[Fig. 2] Fig. 2 is a diagram showing an operating behavior in a P-h diagram according to Embodiment 1 of the present invention.

[Fig. 3] Fig. 3 is a diagram showing a temperature distribution of a refrigerant and water in a water heat exchanger according to Embodiment 1 of the present invention.

[Fig. 4] Fig. 4 is a diagram showing cycle conditions versus expansion valve opening degree according to Embodiment 1 of the present invention.

[Fig. 5] Fig. 5 is a diagram showing the changes in each calculation value, the heating capacity, and the GOP against a degree of opening of the expansion valve according to Embodiment 1 of the present invention.

[Fig. 6] Fig. 6 is a diagram showing the changes in another calculation value, the heating capacity, the arid COP against a degree of opening of the expansion valve according to Embodiment 1 of the present invention.

[Fig. 7] Fig. 7 is a flow chart of the control according to Embodiment 1 of the present invention.

[Fig. 8] Fig. 8 is a diagram showing a refrigeration cycle apparatus according to Embodiment 2.

[Fig. 9] Fig. 9 is a diagram showing an operating behavior in a P-h diagram according to Embodiment 2.

Code and Symbol Descriptions

1 Compressor

2 Radiator (water heat exchanger)

3 Expansion valve

4 Heat absorber (evaporator)

5 Internal heat exchanger

20 Side pump for hot water supply

21 Hot water storage tank

22 Side pump for use

23, 24, 25 On-off valve

29 Fan

30, 31,32, 33, 41,42, 52 Temperature sensing means

35, 51 Pressure sensing means

40 Controller

50 Heat source apparatus

60 Hot water storage device

Best mode of carrying out the invention

Embodiment 1

Descriptions will be given of a refrigerant cycle apparatus of Embodiment 1 according to the present invention.

Fig. 1 shows a configuration diagram of the refrigerant cycle apparatus according to the present embodiment. In the figure, the refrigerant cycle apparatus according to the present embodiment is a hot water supply apparatus using carbon dioxide (hereinafter CO ² ) as a refrigerant, composed of a heat source apparatus 50 , a hot water storage apparatus 60, and a controller 40 to control these. The present embodiment shows an example of the hot water supply apparatus, however, it is not limited thereto. The appliance can be an air conditioner. In the same way, the refrigerant is not limited to carbon dioxide, but an HFC refrigerant can also be used.

The heat source apparatus 50 is composed of a compressor 1 for compressing the refrigerant, a radiator 2 (hereinafter "water heat exchanger") for taking heat out of a compressed refrigerant at high pressure and at high temperature, in the compressor 1, an internal heat exchanger 5 to further cool the refrigerant outlet from the water heat exchanger 2, a decompressor 3 (hereinafter "expansion valve") that decompresses the refrigerant and whose opening degree can be changed , a heat absorber 4 (hereinafter "evaporator") to evaporate the decompressed refrigerant in the expansion valve 3, and an internal heat exchanger 5 to further heat the refrigerant flowing out of the evaporator 4. That is, the Internal heat exchanger 5 is a heat exchanger that exchanges the refrigerant according to the heat at an outlet of the water heat exchanger 2 with the refrigerant at the outlet of the evaporator 4. It is provided ona fan 29 to send air on an outer surface of the evaporator 4. Also provided are first temperature detecting means 30 for detecting a discharge temperature of compressor 1, second temperature detecting means 31 for detecting an outlet temperature of water heat exchanger 2, fifths temperature detecting means 32 for detecting a temperature of the inlet refrigerant of the evaporator 4, and sixth temperature detecting means 33 for detecting a suction temperature of the compressor 1. Furthermore, the first temperature detecting means 30 and the second means temperature detection means 31 correspond to a first refrigerant condition detection means and a second refrigerant condition detection means, respectively, in a control example in Fig. 7 to be described later.

A hot water storage apparatus 60 is connected with the water heat exchanger 2, which is a radiator, through pipes, which is composed of a heat source side pump 20, a hot water storage tank 21, a side-use pump 22, and on-off valves 23, 24, 25. Here, the on-off valves 23, 24, 25 can be a simple valve to change the operation or a variable valve of opening. When the water level in the hot water storage tank 21 drops, the on-off valves 24, 25 are closed, the on-off valve 23 is opened, and the operation for hot water storage is performed smoothly. that the supplied water is heated to a predetermined temperature. When a loss of heat dissipation is large and the temperature in the hot water storage tank 21 decreases, such as in winter, the on-off valves 23, 25 are closed, the on-off valve 24 is opened, and the circulation heating operation is performed so that the low temperature hot water in the hot water storage tank 21 is boiled again. At the time of using the hot water supply, the on-off valves 23, 24 are closed, the on-off valve 25 is opened, and the use side pump 22 begins to operate to transfer the stored hot water to the side in use. On an inlet side of the water heat exchanger 2, the third temperature sensing means 41 is set to detect an inlet temperature of a medium (water) to be heated. On an outlet side of the water heat exchanger 2, the fourth temperature sensing means 42 are set to detect an outlet temperature of a medium (water) to be heated.

A controller 40 performs calculations using sensed values of the first temperature sensing means 30, second temperature sensing means 31, fifth temperature sensing means 32, sixth temperature sensing means 33, third temperature sensing means 41 and fourth temperature sensing means 42 for controlling an opening degree of the expansion valve 3, a rotational speed of the compressor 1, and the rotational speed of the hot water supply side pump 20, respectively.

Fig. 2 is a Ph diagram describing cycle conditions during hot water storage operation in the refrigeration cycle apparatus shown in Fig. 1. In Fig. 2, solid lines denote refrigerant conditions in a certain degree of expansion valve opening and A, B, C, D, and E denote refrigerant conditions in hot water storage operation. At the time of hot water storage operation, a high temperature high pressure refrigerant (A) discharged from compressor 1 flows into water heat exchanger 2. In water heat exchanger 2, the Refrigerant heats the supplied water while dissipating heat into the water circulating in the hot water storage circuit to lower the temperature itself. A refrigerant (B) flowing out of the water heat exchanger 2 dissipates the heat in the internal heat exchanger 5 to further lower the temperature (C), being decompressed (D) by the expansion valve 3 to become a low temperature and low pressure refrigerant. The low-temperature, low-pressure refrigerant absorbs heat from the air in evaporator 4 to evaporate it (E). The refrigerant flowing out of the evaporator 4 is heated in the internal heat exchanger 5 to become a gas (F) and is sucked in by the compressor 1 to form a refrigeration cycle.

Here, the expansion valve 3 is controlled so that a degree of suction superheat of the compressor 1 becomes a target value (for example, 5 to 10 ° C). Specifically, based on a detection value of the fifth temperature detecting means 32 detecting a temperature of the inlet refrigerant of the evaporator 4, an amount of temperature decrease due to a pressure loss in the evaporator 4 and the internal heat exchanger 5, a suction temperature (ET) is estimated, a degree of suction superheat SHs is calculated by the following formula using a detection value (Ts) of the sixth temperature detection means 33 that detect a temperature compressor suction 1.

SHs = Ts - ET

Using the above formula, an opening degree of expansion valve 3 is controlled so that SHs becomes a target value. An example is given in which an evaporation temperature (ET) is estimated based on the detection value of the fifth temperature detection means 32, however, it is not limited thereto. A pressure sensing means (second pressure sensing means) 51 (refer to Fig. 1) is installed between a low pressure side outlet of the internal heat exchanger 5 and the inlet of the compressor 1, and the sensing value , a saturation temperature of the refrigerant can be obtained. A control of the degree of suction superheat precedes another control of high efficiency operation, since a function to prevent the return of liquid from compressor 1 precedes a function to efficiently operate the water heat exchanger 2 for the purpose to ensure the reliability of the equipment.

Next, the operation in the Ph diagram, when the opening degree of the expansion valve 3 becomes smaller, is represented by dashed lines in Fig. 2. When the opening degree of the expansion valve 3 becomes smaller, the amount of refrigerant flow flowing from the expansion valve 3 to the evaporator 4 decreases and the superheat suction degree of the compressor 1 increases temporarily. Also, as the high pressure side refrigerant changes, the pressure on the high pressure side increases and a discharge temperature becomes high. At the same time, an outlet temperature of the water heat exchanger decreases so that a temperature difference in it becomes constant. When the outlet temperature of the water heat exchanger decreases, an amount of heat exchange in the internal heat exchanger 5 decreases, and as a result, the degree of suction superheat becomes almost the same state as before that the degree of opening of the expansion valve 3 was made smaller to indicate a constant value. That is, a change in the degree of opening of the expansion valve 3 is absorbed by the amount of heat exchange of the internal heat exchanger 5 (the amount of heat exchange varies in response to the degree of opening of the expansion valve 3) to make the change in suction superheat degree small. Accordingly, the control of the suction superheat degree of the compressor 1 alone cannot ensure the heating capacity in the water heat exchanger 2, and the efficiency decreases. Therefore, a new control is required in order to ensure heating capacity and improve operating efficiency.

In the following, descriptions will be given as to why a local maximum value occurs in performance (COP) using a temperature distribution in the water heat exchanger shown in Fig. 3.

Fig. 3 shows a distribution of the temperature of the refrigerant and water in the water heat exchanger 2. In the figure, the thick solid lines show a change in the temperature of the refrigerant, and the thin solid lines denote a change in the water's temperature. AT1 denotes a temperature difference between the water heat exchanger inlet temperature and the water outlet temperature, and AT2 denotes a temperature difference between the water heat exchanger outlet temperature and the water inlet temperature . A Tp is a temperature difference at a peak point, where the temperature difference between a refrigerant and the water in the water heat exchanger 2 becomes minimal. A T denotes a temperature difference between the inlet temperature of the water heat exchanger and the outlet temperature of the water heat exchanger. As shown by a cycle state versus the expansion valve opening degree in Fig. 4, when a discharge temperature is increased by decreasing the expansion valve 3 opening degree, as long as the heating capacity in the water heat exchanger 2 is almost constant, the outlet temperature of the water heat exchanger 2 decreases so that an average temperature difference of the refrigerant and water in the water heat exchanger 2 can be maintained, and the temperature difference A Tp at the peak point also decreases. Also, as the amount of refrigerant is shifted to the high pressure side, a discharge pressure rises to increase an input and the COP is reduced. On the contrary, when the opening degree of the expansion valve 3 becomes large and the discharge temperature is lowered, the outlet temperature of the water heat exchanger 2 increases so that an average temperature difference is maintained between the refrigerant and water in water heat exchanger 2. The temperature difference ATp at the peak point also increases, however, the ratio of heating capacity becomes smaller and the COP decreases. Consequently, as shown by the dashed lines in the figure, there is a suitable expansion opening degree that causes the COP to reach its maximum value.

Next, Fig. 5 shows the changes in the operating values obtained from the temperature of each part, when the opening degree of the expansion valve 3 changes. In Fig. 5; the horizontal axis represents the degree of opening (%) of the expansion valve 3, and the vertical axis represents the degree of suction superheat, the discharge temperature, temperature difference A T2 between the outlet temperature of the heat exchanger of water and the water inlet temperature, the heating capacity ratio and the COP ratio. Heating capacity ratio and COP ratio show ratio when set maximum value against expansion valve opening degree as 100%, respectively. Faced with the changes in the opening degree of the expansion valve 3, the changes in the suction superheat degree can be considered as practically a constant value, so that it is understood that the changes in the proportion of heating capacity and The proportion of COP cannot be judged by the degree of suction superheat. By controlling the COP to be maximum based on the temperature difference AT2 between the discharge temperature and the water heat exchanger outlet temperature and the water inlet temperature, changes in the discharge temperature and the AT2 temperature differences are small in the vicinity of the expansion valve opening degree when the COP reaches the maximum as shown by a dashed line in the figure, so it was found that a high precision temperature measurement is required to control the COP to be maximum.

Next, Fig. 6 shows changes in other operating values obtained from the temperatures of each part when the opening degree of expansion valve 3 is changed. In Fig. 6, the horizontal axis represents the degree of expansion valve opening (%) 3. The vertical axis represents a temperature difference A Thx of the outlet / inlet of the internal heat exchanger, a temperature difference AT between a discharge temperature and an outlet temperature of the exchanger of heat of water, a total temperature difference £ AT from the above AT1 and AT2, the heating capacity, and the proportion of COP, respectively. The characteristics of Fig. 6 show that the operation can be performed in the vicinity where the COP becomes maximum, either by controlling a heat exchange amount of the internal heat exchanger 5 based on the temperature difference Thx A between the outlet and inlet of the internal heat exchanger or by controlling the amount of heat exchange of the water heat exchanger 2 based on the total temperature difference £ AT of ATI and AT2 of the water heat exchanger 2. In addition, the AT temperature difference between the discharge temperature and the outlet temperature of the water heat exchanger changes significantly in the vicinity of the expansion valve opening degree at which the COP becomes maximum, by which it is understood that a deviation from the maximum value of the COP could be controlled to be small based on the temperature difference A T. Only the case of the difference is shown here. However, the same effect can be expected by controlling based on the difference (AT 1 - AT2) of the temperature differences ATI and AT2.

Therefore, it is possible to achieve an operation in the vicinity of maximum efficiency by adopting a high pressure side outlet temperature of the internal heat exchanger 5 for A Thx, the discharge temperature for AT, and the discharge temperature and the temperatures side water inlet / outlet for £ AT.

As understood from Fig. 6, a total temperature difference of £ AT of the temperature difference AT1 between the inlet temperature of the water heat exchanger and the outlet temperature of water and the temperature difference AT2 between the water heat exchanger outlet temperature and the water inlet temperature becomes a minimum. Control based on such an index has a physical meaning and is reasonable. However, high precision temperature detection is required, because the change in temperature is small in the vicinity where the COP becomes a maximum compared to the temperature difference A T. Also, in Fig. 3, It is considered that when the COP becomes a maximum value, a temperature difference A Tp at a peak point is almost the same as that of AT2 between the water heat exchanger outlet temperature and the water inlet temperature. This is because maximum performance is displayed when two temperature differences that become minimal in the water heat exchanger 2 become equal without being partial to either of them when considering the characteristics of the heat exchanger. Accordingly, it is permissible to control the expansion valve 3 in order to make A Tp and A T2 equal.

Next, descriptions will be given of an example of a control operation of the refrigeration cycle apparatus of Fig. 1 in which an opening degree of the expansion valve is controlled in order to achieve a suction superheat degree and that the temperature difference AT above converges to target values.

Fig. 7 is a flow chart showing a control operation of the refrigeration cycle apparatus. With the present invention, in order to give priority to the reliability of the products, the control of the degree of suction superheat (SHs) of the compressor 1 precedes the control of the temperature difference AT to ensure the heating capacity.

First, when the suction superheat degree (SHs) is less than a target value (SHm) by a preset ASH convergence range or less (S101), the expansion valve opening degree is reduced until the degree of suction superheat (SHs) converges. Therefore, when the degree of suction superheat (SHs) is ensured, the temperature difference AT is converged to the target value. Specifically, when the temperature difference AT is less than a target value (ATm) by a preset convergence range 8 T or less (S102), the expansion opening degree is lowered and AT is converged. Therefore, the lower limit values of the degree of suction superheat (SHs) and the temperature difference AT can be suppressed.

Then, when the suction superheat degree (SHs) is greater than the target value (SHm) by a preset convergence range A SH or more (S103), the expansion valve opening degree is increased until the degree of suction superheat (SHs) converges. Therefore, when the degree of suction superheat (SHs) is converged, the temperature difference T A is converged to the target value. Therefore, when the degree of suction superheat (SHs) is converged, the temperature difference AT is converged to the target value. Specifically, when the temperature difference A T is greater than the target value (ATm) by a preset convergence range 8 T or more (S104), the expansion opening degree is increased and AT is converged. Therefore, the upper limit values of the suction superheat degree (SHs) and the temperature difference AT can be suppressed. An example is shown in which a priority is given to control the degree of suction superheat, however, it is not limited thereto when using a compressor that is resistant to back-flow of liquids. The same effect can be expected even when the order of priority is changed. Through the above control, the degree of suction superheat (SHs) and the temperature difference AT are made to converge on the target values.

In the above, descriptions are given for an example where the degree of suction superheat (SHs) and the temperature difference AT are controlled to converge on the target values (SHm, A Tm), however, it is permissible that, instead of the temperature difference AT, a total temperature difference £ AT of AT1 and AT2, a difference between AT 1 and AT2 (AT 1 - A T2) can be used, or AThx to control them so that they converge on a target value , respectively. Using £ AT and (AT1 - A T2), these are obtained by calculating the temperatures in the first media temperature detection means 30, second temperature detection means 31, third temperature detection means 41, and fourth temperature detection means 42. When using Thx A, temperature detection means are coupled at the outlet of the heat exchanger internal 52 (see Fig. 1) between a high pressure side outlet of the internal heat exchanger 5 and an inlet of the expansion valve 3, the temperature difference AThx is obtained from a sensing temperature in the second means temperature detection device 31 and the internal heat exchanger outlet temperature detection means 52.

Since, in the present embodiment, in addition to controlling the degree of suction superheat of the compressor, the opening degree of the expansion valve is made to be controlled so that the COP becomes maximum based on a temperature difference. AT (or £ AT, AT1 - AT2, AThx) between the discharge temperature and the outlet temperature of the water heat exchanger, and a high-efficiency refrigeration cycle apparatus can be obtained.

A saturation temperature of the refrigerant (ET) is obtained based on an output from the fifth temperature sensing means 32 or pressure sensing means, the degree of suction superheat (SHs) is obtained by the sensing temperature (Ts ) of the sixth temperature sensing means and the saturation temperature of the refrigerant (ET), and the opening degree of the expansion valve is controlled so that the suction superheat degree (SHs) becomes a target value , so that the degree of overheating of the suction part of the compressor 1 is ensured, the return of liquid to the compressor 1 is prevented, and reliability can be ensured. In the example of Fig. 1, descriptions are given for an example in which the fifth temperature sensing means 32 is arranged between the expansion valve 3 and the evaporator 4, it can be arranged at any position between the evaporator inlet 4 and a low pressure side inlet of the internal heat exchanger 5.

In the present embodiment, by controlling the degree of overheating and the above temperature differences (AT, £ A T, AT 1 - AT2, AThx), the control of the degree of overheating precedes the control of the above temperature differences. From this point, the reliability of the compressor 1 is assured.

In the present embodiment, the radiator is composed of the water heat exchanger, so that a high-efficiency hot water supply apparatus can be obtained.

Embodiment 2

Descriptions of a refrigeration cycle apparatus according to Embodiment 2 will be given as follows. Embodiment 2 is not an embodiment of the present invention, but is helpful in understanding certain aspects of it.

Fig. 8 is a drawing showing a configuration of the refrigeration cycle apparatus according to the present invention. What is different from Embodiment 1 is that a first pressure sensing means 35 is provided instead of the first temperature sensing means 30, to detect the discharge temperature of the compressor 1. Based on the first pressure sensing means pressure 35, a virtual saturation temperature is obtained, which is a standard condition of the water heat exchanger 2. The pressure sensing means 35, can be shared with a pressure sensor, which is provided, for example, to avoid an abnormal rise in high blood pressure. Descriptions of an operating behavior will be omitted as they are the same as in Embodiment 1.

In the present embodiment, like a conventional HFC refrigerant, a degree of virtual superheating of the outlet of the water heat exchanger 2 is calculated, to control its cooling conditions. Specifically, from the first pressure sensing means 35 provided instead of the first temperature sensing means 30, a virtual saturation temperature is calculated as a standard condition of the water heat exchanger 2, and from the difference between a virtual saturation temperature, Tsat, and the outlet temperature, Tcount, of the water heat exchanger 2, detected by the second temperature means 31, a virtual superheat degree SC is obtained from the following formula.

SC = Tsat - Tcount

In the present embodiment, the degree of opening of the expansion valve 3 is controlled in the same way as in the flow chart of Fig. 7 so that the SC obtained by the above formula is converted into a target value (SCm ) whose efficiency is maximum.

Now, how to get the virtual saturation temperature will be explained.

Fig. 9 is a diagram showing an operating behavior of the refrigeration cycle apparatus according to the present invention in a Ph diagram. The virtual saturation temperature can be freely defined by demonstrating a definition such as a pseudo-critical temperature path that connects bending points of isothermal lines as a dashed line a and a vertical line as a dotted line p extended with an enthalpy to a critical point being a constant. However, to operate the refrigeration cycle apparatus stably and at maximum efficiency, a virtual saturation temperature must be selected below which the Temperature difference becomes larger in the vicinity of maximum efficiency, as mentioned above. Then, the virtual saturation temperature can be obtained as an intersection of a constant pressure line with a pressure at a point B, which is a detection value by the first detection means 35, and the dashed line a, or as a intersection of a constant pressure line at a point B, which is a detection value by the first pressure detection means 35 and the dotted line p.

In the present embodiment, since the virtual saturation temperature is used instead of the discharge temperature of the compressor 1, the first temperature sensing means 30 in Fig. 1 can be omitted and low cost can be achieved. As the conventional HFC refrigerant, the degree of overheating of the outlet of the water heat exchanger 2 is controlled, therefore, the expansion valve control as-is, which has been conventionally used, can be applied.

Claims (6)

1. A refrigerant cycle apparatus comprising: at least one compressor (1), a radiator (2), decompression means (3) capable of changing an opening degree, a heat absorber (4), an internal heat exchanger (5) performs the heat exchange between a coolant at an outlet of the radiator (2) and the coolant at an outlet of the heat absorber (4), where First temperature sensing means (30) are provided to detect a refrigerant temperature between an outlet of the compressor (1) and an inlet of the radiator (2) and a second temperature sensing means (31) to detect the temperature of the coolant between a radiator outlet (2) and a high pressure side inlet of the internal heat exchanger (5), characterized because A sixth temperature sensing means (33) is provided to detect the temperature of the refrigerant between a low pressure side outlet of the internal heat exchanger (5) and an inlet of the compressor (1), The degree of overheating of a suction part is calculated from a saturation temperature of the refrigerant at a detection point of the sixth temperature detection means (33) and a detection temperature by the sixth temperature detection means ( 33), and the degree of opening of the decompression means (3) is controlled so that the degree of overheating is the target value, and When the degree of overheating becomes the target value, an opening degree of the decompression means (3) is controlled so that a temperature difference (DT) between a detection temperature by the first temperature detection means ( 30) and the detection temperature by the second temperature detection means (31) is converted to a target value. 2. The refrigerant cycle apparatus of claim 1, wherein a second pressure sensing means (51) is provided between the low pressure side outlet of the internal heat exchanger (5) and the compressor inlet (1) and the saturation temperature of the refrigerant is calculated based on a detection value of the second pressure detection means (51). 3. The refrigerant cycle apparatus of claim 1, wherein A fifth temperature sensing means (32) is provided between the inlet of the heat absorber (4) and the low pressure side inlet of the internal heat exchanger (5) and the saturation temperature of the refrigerant is calculated based on the detection temperature of the fifth temperature detection means (32). The refrigerant cycle apparatus of any one of claims 1 to 3, wherein a priority is given to controlling the degree of superheat versus the temperature difference. The refrigerant cycle apparatus of any one of claims 1 to 4, wherein the radiator (2) is a heat exchanger that exchanges heat with water. 6. The refrigerant cycle apparatus of any of claims 1 to 5, wherein carbon dioxide is used as a refrigerant.