WO2009123190A1

WO2009123190A1 - Air conditioner

Info

Publication number: WO2009123190A1
Application number: PCT/JP2009/056655
Authority: WO
Inventors: 外囿　圭介; 傑鳩村; 裕之森本
Original assignee: 三菱電機株式会社
Priority date: 2008-03-31
Filing date: 2009-03-31
Publication date: 2009-10-08
Also published as: EP2290304A1; EP2290304A4; WO2009122512A1; JPWO2009123190A1

Abstract

An air conditioner, the COPs of which in both cooling and heating operation are improved. In an air conditioning system in which an outdoor unit (100) and indoor units (301 to 303) are interconnected by a flow dividing controller (200) and a single refrigerating cycle is constructed by using a supercritical fluid, the outdoor unit (100) and the flow dividing controller (200) are interconnected by two lines of piping which are high-pressure piping (400) and low-pressure piping (500), and the flow dividing controller (200) and the indoor units (301 to 303) are interconnected by two lines of piping which are high-pressure piping (700) and low-pressure piping (800). The flow dividing controller (200) has a double tube heat exchanger (240) for exchanging heat between an intermediate pressure two-phase refrigerant and a low-pressure two-phase refrigerant. The intermediate pressure two-phase refrigerant is a refrigerant having a relatively high temperature, and refrigerants from the indoor units and a refrigerant which is generated by diverting a refrigerant from the outdoor unit to the indoor units and reducing this refrigerant in pressure by using a first expansion valve (211) are caused to merge into the intermediate pressure two-phase refrigerant. The low-pressure two-phase refrigerant is a refrigerant having a relatively low temperature and generated by diverting a refrigerant flowing into the indoor units, reducing the pressure of the refrigerant by a second expansion valve (212), and causing the refrigerant to flow out to the outdoor unit.

Description

Air conditioner

The present invention relates to an air conditioner in which an outdoor unit and a plurality of indoor units are connected by a shunt controller, and one refrigeration cycle is configured using a supercritical fluid.

_2. Description of the Related Art Conventionally, a heat recovery type air conditioner that simultaneously cools and warms using a supercritical fluid such as CO ₂ is known. In such an air conditioner, the outdoor unit and the branch kit are mainly connected by three pipes of a high pressure pipe, a low pressure pipe and a high temperature gas pipe. In addition, from the branch kit to the indoor unit is a two-pipe type.

However, since the pressure in the critical region of the supercritical fluid is very high, the wall thickness of the connecting pipe between each unit is significantly increased compared to the case of refrigerants represented by conventional chlorofluorocarbons. For this reason, it is easily anticipated that the material cost increases or the local processing costs such as bending increase enormously.

Therefore, it is conceivable to reduce the number of connection pipes by incorporating a branch kit for each indoor unit in one shunt controller in order to reduce the connection pipes.

On the other hand, as a feature of the air conditioner using a supercritical fluid, it is most effective to lower the temperature of the fluid sent to the cooling operation indoor unit and raise the temperature of the fluid sent to the heating operation indoor unit. Realized with low fluid flow rate. For this reason, efficiency (here, COP: Coefficient of Performance) in which the numerator is the capacity of the air conditioner (unit: kW) and the denominator is power consumption (unit: kW) is improved. Therefore, the inlet temperature of the indoor unit, that is, the outlet temperature of the heat source side heat exchanger is basically low during cooling and high during heating.

However, in an air conditioner that enables simultaneous cooling and heating by a two-pipe system, the following trade-off occurs when the cooling operation indoor unit and the heating operation indoor unit exist (mixed) at the same time.

-It is necessary to lower the outlet temperature of the heat source side heat exchanger in order to supply a low temperature fluid to the cooling operation indoor unit.
-It is necessary to increase the outlet temperature of the heat source side heat exchanger in order to supply a high-temperature fluid to the heating operation indoor unit.

For example, the conventional cooling main operation (refrigeration cycle is simultaneous cooling and heating operation in the cooling cycle) is a heat source side heat exchanger with a certain degree of cooling and heating (for example, a pressure of 10 MPa in the supercritical region, around 40 to 50 ° C. in the Mollier diagram). In order to exert its ability as a result, it must be controlled by the outlet temperature, and the difference in enthalpy is insufficient, which is compensated by increasing the fluid flow rate (increasing the power consumption of the compressor), resulting in a decrease in COP. .

Furthermore, the efficiency of the air conditioner has been evaluated only with respect to 100% load by using the coefficient called COP described above. However, in recent years, for example, loads in general offices have been accompanied by the development of OA equipment and the improvement of the insulation performance of buildings, and cooling loads have also occurred in the heating season, and the frequency of simultaneous cooling and heating increases throughout the year. It is coming. Therefore, the trend of improving the efficiency including the COP in the simultaneous cooling and heating operation is increasing rather than evaluating only with the COP of 100% load.

As described above, the conventional air conditioner has a problem that COP is lowered when it is operated so as to satisfy both the cooling and heating conditions.

The present invention has been made in view of the above points, and an object thereof is to obtain an air conditioner that can improve COP in simultaneous cooling and heating operations.

The air conditioning apparatus according to the present invention is an air conditioning system in which an outdoor unit and a plurality of indoor units are connected by a shunt controller, and a single refrigeration cycle is configured using a supercritical fluid. The outdoor unit, the shunt controller, Are connected by two pipes of a high pressure pipe and a low pressure pipe, and are connected between the branch flow controller and the plurality of indoor units by two pipes of a high pressure pipe and a low pressure pipe, and the branch flow controller is connected to the outdoor unit. The refrigerant from the indoor unit to the indoor unit is branched and the refrigerant decompressed by the first expansion valve and the refrigerant from the indoor unit merge and flow into the indoor unit. And a double pipe heat exchanger for exchanging heat with a relatively low-temperature, low-pressure two-phase refrigerant that is branched and decompressed by a second expansion valve to flow out to the outdoor unit.

According to this invention, the number of connecting pipes between the outdoor unit and the branch flow controller and between the branch flow controller and each indoor unit can be greatly reduced, and a large enthalpy difference on the cooling operation indoor unit side can be secured. COP in simultaneous cooling and heating is also improved.

It is a refrigerant circuit figure at the time of the cooling main operation | movement of the air conditioning apparatus which concerns on Embodiment 1 of this invention. It is a Mollier diagram used for description of the air conditioning apparatus which concerns on Embodiment 1 of this invention. It is a refrigerant circuit figure at the time of heating main operation | movement of the air conditioning apparatus which concerns on Embodiment 1 of this invention. It is a control flowchart of the 1st expansion valve 211 at the time of the cold main operation | movement in the air conditioning apparatus which concerns on Embodiment 2 of this invention. It is a control flowchart of the 1st expansion valve 211 at the time of the full warm and warm main operation | movement in the air conditioning apparatus which concerns on Embodiment 2 of this invention. It is a control flowchart of the 2nd expansion valve 212 at the time of the total cooling in the air conditioning apparatus which concerns on Embodiment 3 of this invention, and cold main operation. It is a control flowchart of the 2nd expansion valve 212 at the time of the warm main operation | movement in the air conditioning apparatus which concerns on Embodiment 3 of this invention. It is a Mollier diagram used for description of the air conditioning apparatus which concerns on Embodiment 3 of this invention.

Embodiment 1 FIG.
FIG. 1 is a refrigerant circuit diagram at the time of cooling main operation of the air-conditioning apparatus according to Embodiment 1 of the present invention. In the air conditioner shown in FIG. 1, an outdoor unit 100 and a plurality of indoor units 301 to 303 are connected by a shunt controller 200 to constitute one refrigeration cycle using a supercritical fluid. The outdoor unit 100 mainly includes a compressor 110, a four-way valve 120, a heat source unit side heat exchanger 130, and check valves 141 to 147. The indoor units 301 to 303 include use side (load side) heat exchangers 311 to 313 and expansion valves 321 to 323 as expansion devices. Further, the flow dividing controller 200 mainly includes a first expansion valve 211, a second expansion valve 212, check valves 231 to 233, flow path switching valves 221 to 223, and a double pipe heat exchanger 240. The double tube heat exchanger 240 may be a plate heat exchanger or a microchannel heat exchanger.

Here, the outdoor unit 100 and the branch flow controller 200 are connected by two pipes, a high pressure pipe 400 and a low pressure pipe 500, and the high pressure pipe 700 and the low pressure pipe 200 are similarly connected between the branch flow controller 200 and each of the indoor units 301 to 303. Two pipes 800 are connected to each other. Here, the cooling operation is mainly performed, and a cooling-main operation (hereinafter abbreviated as a cooling main operation) of a part of the heating operation is described, but the heating main operation (hereinafter abbreviated as a warm main operation) is described as a four-way valve 120, The flow path is switched by check valves 141 to 147.

In FIG. 1, a high pressure detection means 281, an intermediate pressure detection means 282, a first temperature detection means 291, and a second temperature detection means 292 are shown in the shunt controller 200. Is unnecessary, and is used in Embodiment 2 to be described later.

First, the flow in the refrigerant circuit in the cold main operation will be described with reference to FIG. Here, the case where CO ₂ is used as the supercritical fluid will be described. The high-pressure and high-temperature fluid compressed by the compressor 110 is heat-exchanged with the surrounding air through the four-way valve 120 in the heat source unit-side heat exchanger 130 and cooled to a temperature that does not reach the ambient air temperature. The degree of dryness of the Mollier diagram (pressure p-enthalpy h) shown in FIG. 2 is cooled to a temperature in the vicinity of 0.5 (point B in FIG. 2), and the outlet of the heat source side heat exchanger 130 is in a high pressure / intermediate temperature state. . The fluid that has exited the heat source unit side heat exchanger 130 flows into the diversion controller 200 via the high-pressure pipe 400, and the cooling operation

indoor units

302 and 303 and the heating operation chamber are flown at the flow path switching valves 221 to 223, respectively. Branch to machine 301.

As for the refrigerant to the heating operation indoor unit 301 side, the high-pressure / medium-temperature fluid that has flowed into the load-side heat exchanger 311 from the branch port via the flow path switching valve 223 further exchanges heat with room temperature. The temperature becomes medium (point C in FIG. 2), and the pressure is reduced by the expansion valve 321 (point D in FIG. 2). The refrigerant that has exited the heating operation indoor unit 301 via the low-pressure pipe 800 passes between the first expansion valve 211 and the double-pipe heat exchanger 240 via the check valve 231 in the shunt controller 200 in a state of intermediate pressure and intermediate temperature. Join at.

On the other hand, the refrigerant toward the cooling operation

indoor units

302 and 303 is reduced from the branch port to the intermediate pressure in the supercritical region slightly lower than the high pressure by the first expansion valve 211 (point E in FIG. 2). It flows into the middle temperature side in the double-pipe heat exchanger 240 in the middle temperature state. Furthermore, the medium-pressure / medium-temperature fluid decompressed by the expansion valve 321 of the heating operation indoor unit 301 joins here and flows into the middle temperature side of the double-pipe heat exchanger 240. Here, the partial fluid that has come out from the middle temperature side of the double-pipe heat exchanger 240 is further branched at the branch port, and is further depressurized by the second expansion valve 212 to become a gas-liquid two-phase low-pressure low-temperature (I in FIG. 2). Point) and flows into the low temperature side in the double-tube heat exchanger 240.

By exchanging heat with the medium-pressure medium-temperature fluid at the medium-temperature side in the double-tube heat exchanger 240, the low-pressure low-temperature fluid at the low-temperature side becomes a state of low pressure and medium-temperature dryness (point H in FIG. 2). On the other hand, the medium-pressure medium-temperature fluid on the medium-temperature side is further cooled to become a medium-pressure medium-temperature fluid (point D in FIG. 2) in a low enthalpy state. The further cooled medium pressure medium temperature fluid (point D in FIG. 2) is further depressurized by the

expansion valves

322 and 323 on the load side to become a gas-liquid two-phase low pressure and low temperature (point G in FIG. 2). By flowing into the

heat exchangers

322 and 323 on the load side, heat exchange with room temperature occurs, and the dryness at low pressure and intermediate temperature is high (point H in FIG. 2). Finally, the low pressure / medium temperature fluid exiting the low temperature side of the double pipe heat exchanger 240 and the low pressure / medium temperature fluid exiting the load

side heat exchangers

322 and 323 merge, and the outdoor unit is connected via the low pressure pipe 500. Return to the 100 side.

As a result, the number of connecting pipes between the outdoor unit 100 and the shunt controller 200 and between the shunt controller 200 and each of the indoor units 301 to 303 can be greatly reduced, and the cooling operation

indoor units

302 and 303 side can be reduced. By ensuring a large enthalpy difference, COP during simultaneous cooling and heating is improved.

Next, FIG. 3 is a refrigerant circuit diagram at the time of heating main operation of the air-conditioning apparatus according to Embodiment 1 of the present invention. The air conditioning apparatus shown in FIG. 3 has the same configuration as that of the first embodiment shown in FIG.

FIG. 3 explains the flow in the refrigerant circuit during the warm main operation. The high-pressure and high-temperature fluid compressed by the compressor 110 flows into the shunt controller 200 via the four-way valve 120, the check valve 145 and the high-pressure pipe 400. Further, the high-pressure and high-temperature fluid branches to the cooling operation indoor units 303 and the heating operation

indoor units

301 and 302 at the flow path switching valves 221 to 223 in the flow dividing controller 200, respectively. Further, the flow of the first expansion valve 211 is interrupted in a fully closed state.

Refrigerant to the heating operation

indoor units

301 and 302 side flows into the load-

side heat exchangers

311 and 312 from the branch port in the diversion controller 200 via the flow

path switching valves

222 and 223 and the high-pressure pipe 700, and the high-pressure intermediate temperature. The fluid further exchanges heat with room temperature, and becomes a high pressure / intermediate temperature substantially equal to the room temperature (point C in FIG. 2). Then, the refrigerant depressurized by the

expansion valves

321 and 322 flows into the diversion controller 200 via the low-pressure pipe 800 and exchanges heat with the first expansion valve 211 and the double pipe via the

check valves

231 and 232. The medium 240 is joined at a medium pressure and intermediate temperature state.

On the other hand, the refrigerant to the cooling operation indoor unit 303 side flows into the load side expansion valve 323 through the following path. The fluid that has flowed from the heating operation

indoor units

301 and 302 to the medium pressure / medium temperature side of the double-pipe heat exchanger 240 through the low-pressure pipe 800 and the

check valves

231 and 232 is further branched at the branch port, and a part of the flow rate Is further reduced in pressure by the second expansion valve 212 to become a low pressure and low temperature (point I in FIG. 2), and flows into the low temperature side in the double pipe heat exchanger 240. Then, the low-temperature low-pressure low-temperature fluid is in a low-pressure / medium-temperature dryness state (point H in FIG. 2) by exchanging heat with the medium-temperature medium-pressure medium-temperature fluid in the double-tube heat exchanger 240. Thus, the medium-pressure medium-temperature fluid at the medium-temperature side is further cooled to become a medium-pressure medium-temperature fluid (point D in FIG. 2) in a low enthalpy state.

The further cooled medium-pressure medium-temperature fluid (point D in FIG. 2) is further depressurized by the load-side expansion valve 323 to become low-pressure and low-temperature, and flows into the load-side heat exchanger 313, thereby As a result, heat is exchanged and the dryness of the low pressure medium temperature is large (point H in FIG. 2). Finally, the low pressure / medium temperature fluid exiting the low temperature side of the double-pipe heat exchanger 240 and the low pressure / medium temperature fluid exiting the load side heat exchanger 313 merge to form a low pressure pipe 500, a heat source machine side heat exchanger. 130, Return to the outdoor unit 100 side through the four-way valve 120.

Therefore, according to the first embodiment, one outdoor unit 100 and one shunt controller 200 are connected by two pipes, and the shunt controller 200 and a plurality of indoor units 301 to 303 are connected by two pipes. Therefore, the number of connecting pipes from the shunt controller 200 to each of the indoor units 301 to 303 can be greatly reduced, and a large enthalpy difference on the cooling operation

indoor units

302 and 303 side can be secured, thereby improving COP in simultaneous cooling and heating operations. To do. In addition, an energy saving operation can be realized in a cooling main operation in which the cooling main operation is partly heating operation.

Embodiment 2. FIG.
In the second embodiment, the same configuration as that of the first embodiment shown in FIGS. 1 and 3 is provided. Further, in FIG. 1 and FIG. 3, the high pressure detection means 281, the intermediate pressure detection means 282, the first temperature detection means 291, and the second temperature detection means that are not required in the first embodiment are included in the shunt controller 200. 292 is provided.

In the second embodiment, the refrigerant flow is the same as in the first embodiment. Hereinafter, a method for controlling the first expansion valve 211 will be described. First, Table 1 shows an outline of control in each control mode (full cooling, cooling main, total warming, warm main).

When all the indoor units 301 to 303 are in a cooling only operation (hereinafter, abbreviated as “fully cooled”), the first expansion valve 211 is fully opened, and the expansion valves of the indoor units 301 to 303 Only 321 to 323 performs flow control according to the load.

In FIG. 1,

temperature sensors

311a, 312a, and 313a for detecting temperature are provided above the load side heat exchangers 311 to 313. Between the load-side heat exchangers 311 to 313 and the load-side expansion valves 321 to 323,

temperature sensors

311b, 312b and 313b for detecting temperature and

pressure sensors

311c, 312c and 313c for detecting pressure are provided. ing.

In the case of the total cooling operation, the temperature difference between the

temperature sensors

311a, 312a, and 313a and the

temperature sensors

311b, 312b, and 313b is calculated, and the calculation result is defined as a superheat degree (superheat), and the superheat degree is a predetermined value, for example, The opening degree of the

expansion valves

321, 322, and 323 on the load side is adjusted so as to be about 2 ° C.

In the case of a “cooling main” operation in which cooling and heating are performed simultaneously in the cooling cycle state, differential pressure control, which will be described later, using the differential pressures of the high pressure detection means 281 and the intermediate pressure detection means 282 is performed. Even in the cold main operation, when the load-side heat exchanger acts as an evaporator, the load-side expansion valve opening is adjusted to a predetermined degree of superheat while detecting the degree of superheat described above.

When all the indoor units 301 to 303 are in a heating operation that is a heating operation (hereinafter abbreviated as “fully warm”), the first expansion valve 211 is basically in a fully closed state, The flow rate control according to the load is performed only by the expansion valves 321 to 323 of the machine, and the differential pressure control described later using the differential pressure of the high pressure detecting means 281 and the intermediate pressure detecting means 282 is performed.

Between the load-side heat exchangers 311 to 313 and the load-side expansion valves 321 to 323,

temperature sensors

311b, 312b and 313b for detecting temperature and

pressure sensors

311c, 312c and 313c for detecting pressure are provided. Yes.

In the case of the full warm operation, the saturation temperature T _sc is calculated from the pressure values detected by the

pressure sensors

311c, 312c, and 313c. The calculated saturation temperature is defined as a condensation temperature _Tc . It is necessary to prepare a relational expression between the saturation temperature T _sc and the pressure P as shown in the formula (1) in advance.
T _sc = f (P) (1)

As shown in FIG. 8 to be described later, when carbon dioxide is used as a refrigerant, the high pressure side operates at a critical point or higher, so that no phase change occurs. That is, there is no saturation temperature T _sc . Therefore, an experiment of the refrigeration cycle is performed, and a virtual saturation temperature is set from the pressure to be balanced and the intake air temperature. For example, the saturation temperature is 45 ° C. when the pressure is 100 kgf / cm ² . Expression (1) in the present embodiment is an arithmetic expression for calculating a virtual saturation temperature T _sc .

A virtual condensing temperature T _c is calculated from the pressure values obtained from the

pressure sensors

311b, 312b, and 313b using the equation (1). A difference (T _c −T _L ) between the temperature T _L obtained from the

temperature sensors

311b, 312b, and 313b and the virtual condensing temperature T _c is obtained, and this value is set as the degree of supercooling SC (subcool). The opening degree of the

expansion valves

321, 322, and 323 on the load side is adjusted so that the degree of supercooling SC becomes a predetermined value, for example, about 5 ° C.

In the case of the “warm main” operation in which the cooling and heating operations are performed simultaneously in the heating cycle state, basically, as in the case of full warming, the fully closed state is basically set, and the differential pressure between the high pressure detection means 281 and the intermediate pressure detection means 282 is changed. The differential pressure control used later is performed.

Next, details of the control method will be described with reference to the control flowcharts shown in FIGS. First, in the “fully-cooled” operation, the first expansion valve 211 is always in a fully opened state, and the flow rate control corresponding to the load is performed only by the expansion valves 321 to 323 of the indoor units.

For the “cold main” operation, as shown in FIG. 4, starting from the compressor 110 or the like as a trigger, the operation is started from a preset initial opening degree L0 (step S41), and a predetermined time from the start. After a lapse of U (step S42), according to the comparison between the differential pressure ΔP of the detected value of the high pressure detecting means 281 and the intermediate pressure detecting means 282 and the preset set values P1, P2 (P1 <P2) The opening degree of the 1 expansion valve 211 is controlled.

For example, when ΔP> P2, the first expansion valve 211 is increased by a predetermined opening degree set in advance (steps S43 → S44), and when P1 ≦ ΔP ≦ P2, the first expansion valve 211 is opened at the current opening degree. (Step S43 → S45 → S46), and when P1 <ΔP, the first expansion valve 211 is lowered by a predetermined opening degree (steps S43 → S45 → S47 → S48).

By the above control, a necessary differential pressure sufficient to flow the refrigerant flow corresponding to the load on the heating operation indoor unit side is secured, and an excessive pressure difference is applied, resulting in a decrease in low pressure, resulting in COP. It can suppress that it falls.

In the “fully warm” operation, the first expansion valve 211 is always in a fully closed state, and the flow rate is controlled according to the load only with the expansion valves 321 to 323 of the indoor unit.

Then, as shown in FIG. 5, the “warm main” operation starts from the fully closed state of the first expansion valve 211 with the start of the compressor 110 as a trigger (step S51), and starts a predetermined time U from the start. After the elapse (step S52), the first expansion is performed in accordance with the comparison between the differential pressure ΔP between the detection values of the high pressure detection means 281 and the intermediate pressure detection means 282 and preset values P1, P2 (P1 <P2). The opening degree of the valve 211 is controlled.

For example, when ΔP> P2, the first expansion valve 211 is increased by a predetermined opening degree set in advance (steps S53 → S54), and when P1 ≦ ΔP ≦ P2, the first expansion valve 211 is currently opened. (Step S53 → S55 → S56), and if P1 <ΔP, the first expansion valve 211 is lowered by a predetermined opening degree (steps S53 → S55 → S57 → S58).

The above control ensures the necessary differential pressure to flow the refrigerant flow according to the load on the heating operation indoor unit side, and applies the differential pressure more than necessary, thereby reducing the inlet pressure of the cooling operation indoor unit. As a result, the necessary differential pressure sufficient to allow the refrigerant flow rate corresponding to the load to flow in the cooling operation indoor unit can be secured, and as a result, it is possible to suppress a COP decrease. Moreover, a change in pressure can be suppressed, and the refrigerant can be stably sent to the indoor unit, so that energy saving operation and comfort can be realized.

Embodiment 3 FIG.
In the third embodiment, the same configuration as the configuration of the first embodiment shown in FIG. 1 and FIG. Further, in FIG. 1 and FIG. 3, the high pressure detection means 281, the intermediate pressure detection means 282, the first temperature detection means 291, and the second temperature detection means that are not required in the first embodiment are included in the shunt controller 200. 292 is provided.

In the third embodiment, the refrigerant flow is the same as in the first embodiment. Hereinafter, a method for controlling the second expansion valve 212 will be described. First, Table 1 shows an outline of control in each control mode (full cooling, cool main, full warm, warm main).

When all the indoor units 301 to 303 are in the “cooling” operation, which is a cooling operation, the second expansion valve 212 uses the first temperature detection means 291 and the second temperature detection means 292, which will be described later. Superheat) control is performed, and on the indoor units 301 to 303 side, the expansion valves 321 to 323 perform flow rate control according to the load. The “cooling main” operation in which the cooling and heating operations are performed simultaneously in the cooling cycle state is the same as “full cooling”.

When all the indoor units 301 to 303 are in the “fully warm” operation, which is a heating operation, the second expansion valve 212 is kept fully open, and the flow rate corresponding to the load is set by the expansion valves 321 to 323 of the indoor units. The refrigerant that has been controlled and exchanged heat with the load side flows into the outdoor unit low-pressure line via the second expansion valve 212.

In the case of the “warm main” operation in which the cooling and heating operation is performed simultaneously in the heating cycle state, basically, as will be described later, the differential pressure between the high pressure detection means 281 and the intermediate pressure detection means 282 is used as the fully closed state. Perform differential pressure control.

Next, details of the control method will be described with reference to control flowcharts shown in FIGS. First, as shown in FIG. 6, the “all-cooling” operation starts from the initial opening L0 set in advance by using the start of the compressor 110 as a trigger (step S61), and starts for a predetermined time from the start. After the elapse of U (step S62), the temperature difference ΔT (superheat) of the detected values is calculated using the first temperature detecting means 291 and the second temperature detecting means 292, and the temperature difference ΔT is set to T1, which is set in advance. The opening degree of the second expansion valve 212 is controlled according to the comparison with T2 (T1 <T2).

For example, when ΔT> T2, the second expansion valve 212 is increased by a predetermined opening degree set in advance (steps S63 → S64), and when T1 ≦ ΔT ≦ T2, the second expansion valve 212 is currently opened. (Step S63 → S65 → S66), and when T1 <ΔT, the second expansion valve 212 is lowered by a predetermined opening degree (steps S63 → S65 → S67 → S68).

With the above control, the refrigerant temperature at the cooling operation indoor unit side inlet is cooled, and a necessary enthalpy difference sufficient to satisfy the performance can be secured, so that it is possible to suppress the decrease in COP. Further, even in the cooling main operation in which the cooling main operation is a partial heating operation, a lower temperature refrigerant can be sent to the cooling operation indoor unit, and an energy saving operation can be realized.

In the “fully warm” operation, the second expansion valve 212 is always fully opened, the flow rate is controlled according to the load by the expansion valves 321 to 323 of the indoor units, and the refrigerant exchanging heat with the load side is It flows into the outdoor unit low pressure line through the second expansion valve 212.

As shown in FIG. 7, the “warm main” operation starts from the fully closed state triggered by the start of the compressor 110 (step S71), and after a predetermined time U has elapsed from the start (step S72). The opening degree of the second expansion valve 212 is determined in accordance with a comparison between the pressure difference ΔP detected by the high pressure detection means 281 and the intermediate pressure detection means 282 and preset values P1, P2 (P1 <P2). To control.

For example, if ΔP> P2, the second expansion valve 212 is lowered by a predetermined opening degree set in advance (steps S73 → S74), and if P1 ≦ ΔP ≦ P2, the second expansion valve 212 is currently opened. (Step S73 → S75 → S76), and when P1 <ΔP, the second expansion valve 212 is increased by a predetermined opening degree (steps S73 → S75 → S77 → S78).

By the above control, the necessary differential pressure that allows the refrigerant flow rate to flow according to the load on the heating operation indoor unit side is secured, and the differential pressure more than necessary is applied (the intermediate pressure approaches low pressure), thereby cooling the system. The inlet pressure of the operating indoor unit approaches a low pressure, and the required differential pressure sufficient to flow the refrigerant flow rate corresponding to the load cannot be secured in the cooling operation indoor unit, and as a result, it is possible to suppress a COP decrease.

During the cold main operation, the heat source machine side heat exchanger 130 acts with a condenser (heat radiator). In the cooling main operation, since the cooling load is higher than the heating load, it is necessary to radiate a part of the heat radiation capability with the heat source unit side heat exchanger 130. For that purpose, it is necessary to divide the fan speed and the heat source device side heat exchanger 130 to increase or decrease the heat exchanger capacity.

In the present invention, a method for adjusting the heat radiation capacity without dividing the heat source apparatus side heat exchanger 130 will be described. In the present embodiment, carbon dioxide is used as the refrigerant. As shown in FIGS. 2 and 8, this refrigerant operates on the high pressure side above the critical point. If this characteristic is used, the heat radiation capacity can be easily adjusted.

As shown in FIG. 3, a pressure sensor 900 and a temperature sensor 901 are provided between the heat source device side heat exchanger 130 and the check valve 141, and a temperature sensor 902 is provided at the inlet of the heat source device side heat exchanger 130. . In supercritical, if temperature and pressure are determined, enthalpy is uniquely determined.

In FIG. 8, a is the enthalpy H ₁ at the inlet of the heat source machine side heat exchanger 130, b is the enthalpy H _{2 at the} outlet of the heat source machine side heat exchanger 130 (inlet of the load side heat exchanger in the heating operation), c Is the enthalpy H ₃ at the inlet of the heat source machine side heat exchanger 130.

The load on the heating side can be determined from the number of heating operations and the capacity of the connected indoor units. Let this heating load be Q _c . Further, the refrigerant flow rate G _r can be obtained from the discharge pressure and suction pressure of the compressor. The enthalpy difference ΔH necessary to cover the heating load can be obtained from the equation (2).
Q _c / G _r = ΔH = H ₂ −H ₃ (2)

Further, the enthalpy H ₃ at the load side heat exchanger (heating) outlet can be obtained from the pressure sensor 311c and the temperature sensor 311b at the load side heat exchanger outlet. Equation (2) can be rewritten as Equation (3).
H ₂ = Q _c / G _r + H ₃ (3)

That is, the enthalpy H _{2 at the} outlet of the heat source device side heat exchanger is determined. The enthalpy at the heat source side heat exchanger outlet can be obtained from the pressure sensor 900 and the temperature sensor 901. The enthalpy obtained from the equation (3) is set as the target enthalpy H _2m .

Further, the enthalpy measured by the pressure sensor 900 and the temperature sensor 901 is assumed to be H _2s . The difference (H _2m -H _2s ) between the target enthalpy H _2m and the measured enthalpy H _2s is calculated to be H _2m -H _2s = ΔH _s .

And, -epsH ₂ <ΔH _s <epsH ₂ (where -epsH ₂ and epsH ₂ indicate the lower limit value and the upper limit value of the error range) to be a predetermined value by the control means by the heat source side fan (blower) Increase or decrease the rotation of. When -epsH ₂ > ΔH _s , the fan speed is increased, and when ΔH _s > epsH ₂ , the fan speed is decreased.

In addition, in order to obtain enthalpy H, it is necessary to create a physical property formula of Formula (4) in advance.
H = f (P, T) (4)
P: Pressure, T: Temperature

Claims

In an air conditioning system in which an outdoor unit and a plurality of indoor units are connected by a shunt controller and one refrigeration cycle is configured using a supercritical fluid,
Between the outdoor unit and the diversion controller are connected by two pipes, a high pressure pipe and a low pressure pipe,
Between the shunt controller and the plurality of indoor units is connected by two pipes, a high pressure pipe and a low pressure pipe,
The shunt controller is
A relatively high-temperature intermediate-pressure two-phase refrigerant into which the refrigerant branched from the outdoor unit to the indoor unit and depressurized by the first expansion valve and the refrigerant from the indoor unit are combined and flowed; A double pipe heat exchanger for branching the refrigerant flowing out to the machine, reducing the pressure by the second expansion valve, and exchanging heat with the relatively low-temperature low-pressure two-phase refrigerant flowing out to the outdoor unit, Air conditioner to do.
In the air conditioning apparatus according to claim 1,
The air conditioner characterized in that the double pipe heat exchanger is a plate heat exchanger or a microchannel heat exchanger.
In the air conditioning apparatus according to claim 1,
Pressure detecting means are provided at the inlet and outlet of the first expansion valve,
The opening degree of the first expansion valve is controlled such that the differential pressure between the two pressure detection values of the pressure detection means is constant.
In the air conditioning apparatus according to claim 1,
Temperature detection means are provided at the outlet of the second expansion valve and the low pressure side outlet of the double pipe heat exchanger,
The opening degree of the second expansion valve is controlled so that the difference between the two temperature detection values of the temperature detection means is constant.
In the air conditioning apparatus according to claim 1,
Pressure detecting means are provided at the inlet and outlet of the first expansion valve,
The opening degree of the second expansion valve is controlled such that the differential pressure between the two pressure detection values of the pressure detection means is constant.
In the air conditioning apparatus according to claim 1,
At the outlet of the heat source machine side heat exchanger, a pressure detection means and a temperature detection means, and a control means for calculating an enthalpy from the value of the pressure detection means and the value of the temperature detection means are provided so as to achieve a target enthalpy. The air conditioner characterized by increasing or decreasing the rotational speed of the fan on the heat source side.