Air-conditioning apparatus with primary and secondary heat exchange cycles

1. An air-conditioning apparatus comprising:

a primary-side cycle including a compressor, a heat source side heat exchanger, a first expansion device, a second expansion device, a third expansion device, a fourth expansion device, a first intermediate heat exchanger, a second intermediate heat exchanger, a first flow switching valve and a second flow switching valve, all of which are connected in a closed loop allowing a primary-side heat transfer medium to circulate; and

a secondary-side cycle including a variable capacity pump configured to vary a flow rate of a secondary-side heat transfer medium continuously, a plurality of use side heat exchangers, the first intermediate heat exchanger and the second intermediate heat exchanger, all of which are connected in a closed loop allowing the secondary-side heat transfer medium to circulate, wherein the secondary-side heat transfer medium is different from the primary-side heat transfer medium, and contains at least either one of brine and water,

the first and the second intermediate heat exchangers exchanging heat between the primary-side heat transfer medium and the secondary-side heat transfer medium,

wherein the plurality of use side heat exchangers are connected to a single outdoor unit, an operation mode of each of the use side heat exchangers being freely selectable between cooling and heating,

the compressor and the heat source side heat exchanger are provided in the outdoor unit,

the plurality of use side heat exchangers are provided in a plurality of indoor units, respectively,

a control valve controlling the flow rate of the secondary-side heat transfer medium supplied to the first and second intermediate heat exchangers and the plurality of indoor units is provided in a relay unit, the relay unit being a separate enclosure from the indoor units and the outdoor unit,

heat transport from the outdoor unit to the relay unit is performed using the primary-side heat transfer medium and heat transport from the relay unit to the indoor units is performed using the secondary-side heat transfer medium,

wherein the secondary-side cycle further comprises a first temperature detector and a second temperature detector of the secondary-side heat transfer medium provided before and after each of the first and second intermediate heat exchangers, respectively,

wherein a passage of the primary-side heat transfer medium provided to the relay unit includes a first branch portion branching the primary-side heat transfer medium at high pressure, a second branch portion branching the primary-side heat transfer medium at low pressure and a third branch portion branching the primary-side heat transfer medium at intermediate pressure, the intermediate pressure being lower than the high pressure,

wherein the third expansion device connects the first branch portion and the third branch portion, and the fourth expansion device connects the third branch portion and the second branch portion,

wherein a first end of the first intermediate heat exchanger is connected to the first flow switching valve and a second end of the first intermediate heat exchanger is connected to the first expansion device, the first flow switching valve selectively connects the first end of the first intermediate heat exchanger to the first branch portion and to the second branch portion,

wherein a first end of the second intermediate heat exchanger is connected to the second flow switching valve and a second end of the second intermediate heat exchanger is connected to the second expansion device, the second flow switching valve selectively connects the first end of the second intermediate heat exchanger to the first branch portion and to the second branch portion,

wherein during a cooling mode, the primary-side heat transfer medium flows in an order of the first branch portion, the third expansion device and the third branch portion, then is divided into a first stream and a second stream, the first stream flows in an order of the first expansion device, the first intermediate heat exchanger, and the first flow switching valve, the second stream flows, in parallel with the first stream, in an order of the second expansion device, the second intermediate heat exchanger, and the second flow switching valve, and then the first stream and the second stream merge and flow out from the relay unit via the second branch portion,

wherein during a heating mode, the primary-side heat transfer medium flows into the first branch portion, then is divided into a third stream and a fourth stream, the third stream flows in an order of the first flow switching valve, the first intermediate heat exchanger, and the first expansion device, and the fourth stream flows, in parallel with the third stream, in an order of the second flow switching valve, the second intermediate heat exchanger, the second expansion device, and then the third stream and the fourth stream merge at the third branch portion, flow through the fourth expansion device and flow out from the relay unit via the second branch portion,

the air-conditioning apparatus further comprises a controller for setting a target value of the difference between the temperatures of the secondary-side heat transfer medium at a position before and at a position after the first and second intermediate heat exchangers based on whether the operation mode is the heating mode or the cooling mode, and for controlling the flow rate of the secondary-side heat transfer medium flowing in the first and second intermediate heat exchangers such that the difference between the temperatures of the secondary-side heat transfer medium at the position before and at the position after the first and second intermediate heat exchangers detected by the first temperature detector and the second temperature detector will correspond to the target values in both the heating and cooling operations, by adjusting the capacity of the pump,

wherein the controller

sets the target value of the difference between the temperatures of the secondary-side heat transfer medium at the position before and at the position after the first and second intermediate heat exchangers during a rated operation in the heating operation so as to have a larger magnitude than the target value of the difference between the temperatures of the secondary-side heat transfer medium at the position before and at the position after the first and second intermediate heat exchangers during a rated operation in the cooling operation.

2. The air-conditioning apparatus of claim 1 , wherein in the heating operation, a target value of a degree of supercooling of the primary-side heat transfer medium at an outlet of the first and second intermediate heat exchangers is set to be equal to or lower than the difference in magnitude between the inlet and outlet temperatures of the secondary-side heat transfer medium at the position before and at the position after the first and second intermediate heat exchangers,

and the expansion devices are controlled based on a degree of supercooling of the primary-side heat transfer medium at an outlet of the first and second intermediate heat exchangers and the target value of the degree of supercooling.

3. The air-conditioning apparatus of claim 1 , wherein the target value of the difference in magnitude between the temperatures of the secondary-side heat transfer medium at the position before and at the position after the first and second intermediate heat exchangers is set according to the magnitude of a load on the use side heat exchanger.

4. The air-conditioning apparatus of claim 3 , wherein the target value of the difference in magnitude between the temperatures of the secondary-side heat transfer medium in a case where a load on the use side heat exchanger is equal to or lower than a predetermined load is set so as to be equal to or lower than a target value of the difference in magnitude between the temperatures of the secondary-side heat transfer medium in a case where the load on the use-side heat exchanger is larger than the predetermined load.

5. The air-conditioning apparatus of claim 1 , further comprising:

an outdoor unit side control device that controls each device accommodated in the outdoor unit; and

a relay unit control device that controls respective devices accommodated in the relay unit and that is capable of communicating with the outdoor unit side control device, wherein

a control signal including data on load information of the indoor units and/or a target value of the difference in magnitude between the temperatures of the secondary-side heat transfer medium and/or a target value of the degree of supercooling of the primary-side heat transfer medium at an outlet of the first and second intermediate heat exchangers or an adjustment value of the control target value is transmitted from the relay unit control device to the outdoor unit side control device or from the outdoor unit side control device to the relay unit control device.

6. The air-conditioning apparatus of claim 1 , wherein

each of the intermediate heat exchangers is installed in series with respect to the flow of the primary-side heat transfer medium and in parallel with respect to the flow of the secondary-side heat transfer medium,

the differences in magnitude between the inlet and outlet temperatures of the secondary-side heat transfer medium in the respective intermediate heat exchangers are controlled to be identical at the time of a cooling operation, and

the difference in magnitude between the inlet and outlet temperatures of the secondary-side heat transfer medium in the first and second intermediate heat exchangers on the upstream side with respect to the flow of the primary-side heat transfer medium is controlled to be equal to or larger than the difference in magnitude between the inlet and outlet temperatures of the secondary-side heat transfer medium in the first and second intermediate heat exchangers on the downstream side with respect to the flow of the primary-side heat transfer medium at the time of a heating operation.

7. The air conditioning apparatus of claim 1 , wherein

the first and second intermediate heat exchangers are used as a condenser of the primary-side heat transfer medium, and

the primary-side heat transfer medium and the secondary-side heat transfer medium flowing in the first and second intermediate heat exchangers flow in a counter-flow manner.

8. The air-conditioning apparatus of claim 1 , wherein a heat medium having a critical temperature of 50 degrees C. or lower is used as the primary-side heat transfer medium.

9. The air-conditioning apparatus of claim 1 , wherein the target value of the difference between the temperatures of the secondary-side transfer medium in a case where a distance from the pump to the use-side heat exchanger is not longer than 10 m is set in a range of 3 through 7 degrees C. at the time of a cooling operation or 5 through 15 degrees C. at the time of a heating operation.

10. The air-conditioning apparatus of claim 1 , wherein the target value of the difference between the temperatures of the secondary-side transfer medium in a case where a distance from the pump to the use-side heat exchanger is 40 m or longer is set in a range of 7 through 9 degrees C. at the time of a cooling operation or 10 through 20 degrees C. at the time of a heating operation.

11. The air-conditioning apparatus of claim 1 , wherein, the primary-side cycle and the secondary-side cycle are configured so that,

at the time of cooling operation, the primary-side heat transfer medium and secondary-side heat transfer medium flow through the first and second intermediate heat exchangers in a parallel-flow manner or a counter-flow manner and

at the time of the heating operation, the primary-side heat transfer medium and secondary-side heat transfer medium flow through the first and second intermediate heat exchangers in the counter-flow manner.

12. The air-conditioning apparatus of claim 1 , wherein,

during a simultaneous cooling and heating operation in which at least one indoor unit operates in the cooling mode and another at least one indoor unit operates in the heating mode, the primary-side heat transfer medium flows into the first branch portion, then flows in an order of the second flow switching valve, the second intermediate heat exchanger and the second expansion device to heat the secondary-side heat transfer medium at the second intermediate heat exchanger, then flows in an order of the third branch portion, the first expansion device, the first intermediate heat exchanger and the first flow switching valve to cool the secondary-side heat transfer medium at the first intermediate heat exchanger and then flows out from the relay unit via the second branch portion,

the controller is configured to set the target value of the difference between the temperatures of the secondary-side heat transfer medium at the position before and at the position after the intermediate heat exchangers connected to the indoor unit operating in the heating mode so as to have a larger magnitude than the target value of the difference between the temperatures of the secondary-side heat transfer medium at the position before and at the position after the intermediate heat exchangers connected to the indoor unit operating in the cooling mode.