GB2567331A

GB2567331A - Heat source system

Info

Publication number: GB2567331A
Application number: GB1819439.9A
Authority: GB
Inventors: Ito Takuya; Okoshi Yasushi; Yamano Yoshio
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 2016-08-04
Filing date: 2016-08-04
Publication date: 2019-04-10
Anticipated expiration: 2036-08-04
Also published as: JPWO2018025382A1; GB201819439D0; WO2018025382A1; JP6639677B2; GB2567331B

Abstract

Disclosed is a heat source system that is provided with a heat source unit that heats and cools a fluid, and a control device that controls the heat source unit. The heat source unit is provided with: a refrigerant circuit wherein a compressor, refrigerant flow channel switch device, air-side heat exchanger, decompression device, and heat medium-side heat exchanger are connected via refrigerant piping; fluid piping, in which the fluid to be subjected to heat exchange with a refrigerant of the refrigerant circuit by means of the heat medium-side heat exchanger flows; a fluid pump, which is provided to the fluid piping, and which supplies the fluid to the heat medium-side heat exchanger; and an inlet temperature sensor that measures the temperature of the fluid flowing into the heat medium-side heat exchanger. The control device is provided with an operation control means that controls the fluid pump so that when defrosting operations, in which the air-side heat exchanger becomes a condenser, and the heat medium-side heat exchanger becomes an evaporator, are being performed, the flow rate of the fluid to be supplied to the heat medium-side heat exchanger changes in accordance with the fluid temperature measured by the inlet temperature sensor.

Description

The present invention relates to a heat source system provided with a heat source unit and for use in, for example, a chilling system for air-conditioning. Background Art [0002]

Generally, chilling systems are known that heat and cool an aqueous medium by causing heat exchange to be performed between refrigerant in a refrigerant circuit and an aqueous medium in a water pipe, in a heat-medium-side heat exchanger. Of the chilling systems, in an air-cooled chilling system, there is a case where frost forms on an air-side heat exchanger functioning as an evaporator during heating. Therefore, in such a chilling system, it is necessary to defrost the air-side heat exchanger. Conventionally, a proposed defrosting operation method is present and applied to an air-cooled chilling system in which a plurality of heat source units are connected by a water pipe (see, for example, Patent Literature 1). Patent Literature 1 discloses a defrosting operation method in which in a heat source system including two or more heat source units, simultaneous defrosting operation of the heat source units is avoided as much as possible to reduce the degree of dropping of a water temperature.

Citation List

Patent Literature [0003]

Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2013-108732

Summary of Invention Technical Problem [0004]

However, in a defrosting control according to Patent Literature 1, water temperature lowers in a single-unit defrosting operation in which only one single heat source unit is operated.

[0005]

The present invention has been made to solve the above problem, and an object of the invention is to provide a heat source system which reduces lowering of water supplied, even during a defrosting operation, regardless of the number of heat source units.

Solution to Problem [0006]

A heat source system according to an embodiment of the present invention includes: a heat source unit which heats and cools fluid; and a controller which controls the heat source unit. The heat source unit includes: a refrigerant circuit in which a compressor, a refrigerant flow switching device, an air-side heat exchanger, a decompressor, and a heat-medium-side heat exchanger are connected by a refrigerant pipe; a fluid pipe through which the fluid flows, the fluid being caused to exchange heat with refrigerant in the refrigerant circuit by the heat-medium-side heat exchanger; a fluid pump provided at the fluid pipe to supply the fluid to the heat-medium-side heat exchanger; and an inlet temperature sensor which measures the temperature of fluid to flow into the heat-medium-side heat exchanger. The controller includes an operation control unit which controls the fluid pump such that during a defrosting operation in which the air-side heat exchanger functions as a condenser and the heat-medium-side heat exchanger functions as an evaporator, the flow rate of fluid to be supplied to the heat-medium-side heat exchanger varies in accordance with the temperature of the fluid which is measured by the inlet temperature sensor.

Advantageous Effects of Invention [0007]

In the heat source system according to an embodiment of the present invention, since the flow rate of fluid to be supplied to a heat-medium-side heat exchanger varies in accordance with the temperature of the fluid, a heat capacity and an outlet temperature also vary. Therefore, even in the case where a single heat source unit is operated, it is possible to restrict dropping of the temperature of hot water to be supplied during a defrosting operation.

Brief Description of Drawings [0008] [Fig. 1] Fig. 1 is a schematic configuration diagram of a heat source system according to embodiment 1 of the present invention at the time of performing a heating operation.

[Fig. 2] Fig. 2 is a schematic configuration diagram of the heat source system according to embodiment 1 of the present invention at the time of performing a defrosting operation.

[Fig. 3] Fig. 3 is a functional block diagram of a controller according to embodiment 1 of the present invention.

[Fig. 4] Fig. 4 is a flowchart of a fluid flow control according to embodiment 1 of the present invention.

[Fig. 5] Fig. 5 is a graph showing a relationship between an inlet temperature and a freezing-evaporating temperature.

[Fig. 6] Fig. 6 is a graph showing a relationship between a water flow rate and the freezing-evaporating temperature.

[Fig. 7] Fig. 7 is a flowchart of a freeze control according to embodiment 1 of the present invention.

[Fig. 8] Fig. 8 is a schematic configuration diagram of a heat source system according to embodiment 2 of the present invention [Fig. 9] Fig. 9 is a flowchart of a fluid flow control according to embodiment 2 of the present invention.

[Fig. 10] Fig. 10 is a flowchart of a control in a conventional apparatus.

Description of embodiments [0009]

A heat source system of the present invention will be described below with reference to the accompanying drawings. The heat source system 100 is an air-cooled chilling system, and is use as, for example, a central heat source for air-conditioning in a building. The heat source system 100 performs a heating operation, a cooling operation or another operation in response to an instruction input by a user. While the heat source system 100 is in operation, heat is exchanged between refrigerant which flows in a refrigerant pipe 11 in a refrigerant circuit 2 and fluid which flows in a fluid pipe 22 to heat or cool the fluid. The fluid heated or cooled in the heat source system 100 is supplied to a load-side apparatus such as an air-conditioning apparatus. The embodiments will be explained by referring to by way of example the case where the fluid is a water heat medium such as antifreeze.

[0010]

Embodiment 1.

(Configuration of heat source system 100)

Fig. 1 is a schematic configuration diagram of the heat source system according to embodiment 1 of the present invention at the time of performing a heating operation. Fig. 2 is a schematic configuration diagram of the heat source system according to embodiment 1 of the present invention at the time of performing a defrosting operation. A configuration of the heat source system 100 will be described below with reference to Figs. 1 and 2.

[0011]

The heat source system 100 includes a heat source unit 1 and a controller 50. The heat source unit 1 includes a refrigerant circuit 2, a fluid pipe 22 through which a water heat medium flows, a fluid pump 20 and a pump control device 21. The refrigerant circuit 2 is connected to a compressor 3, a refrigerant flow switching device 4, an air-side heat exchanger 5, a decompressor 7, a heat-medium-side heat exchanger 8 and an accumulator 9 by a refrigerant pipe 11.

[0012]

The compressors sucks low-temperature, low-pressure refrigerant, and compresses the refrigerant to change it into high-temperature, high-pressure refrigerant. For example, as the compressor 3, a capacity-controllable inverter compressor is applied. As the refrigerant flow switching device 4, for example, a four-way valve is applied. The refrigerant flow switching device 4 switches the flow of refrigerant between the flow of the refrigerant during the cooling operation or defrosting operation and that during the heating operation.

[0013]

The decompressor 7 is constituted by, for example, an electronic expansion valve, etc., and decompresses the refrigerant to expand it. The accumulator 9 is provided on a suction side of the compressor 3, and stores condensed liquid refrigerant. The accumulator 9 prevents the liquid refrigerant from being sucked directly into the compressor 3.

[0014]

The air-side heat exchanger 5 causes heat exchange to be performed between air and the refrigerant, and functions as an evaporator during the heating operation and functions as a condenser during the cooling operation or the defrosting operation. In addition, an air-side heat-exchanger fan 6 is attached to the air-side heat exchanger 5. The air-side heat-exchanger fan 6 is constituted by, for example, a propeller fan, and supplies air to the air-side heat exchanger 5.

[0015]

The heat-medium-side heat exchanger 8 causes heat exchange to be performed between the refrigerant and the water heat medium. To be more specific, the heatmedium-side heat exchanger 8 causes heat exchange to be performed between hightemperature, high-pressure refrigerant and the water heat medium during the heating operation, to thereby generate high-temperature water, and also causes heat exchange to be performed between low-temperature, low-pressure refrigerant and the water heat medium during the cooling operation, to thereby generate low-temperature water. [0016]

The fluid pump 20 supplies the water heat medium to the heat-medium-side heat exchanger 8 through the fluid pipe 22. The fluid pump 20 is controlled, for example, in rotation speed, and supplies the water heat medium at a water flow rate FR which can be changed in stages from a maximum flow rate, a high flow rate, a normal flow rate, and a low flow rate in descending order.

[0017]

The pump control device 21 receives a control signal from the controller 50 which will be described later, varies the frequency at which the fluid pump 20 is operated, in response to the control signal, and thereby causes the fluid pump 20 to supply the water heat medium at a water flow rate specified by the controller 50. For example, the pump control device 21 has multiple driving frequencies including a maximum frequency, a high frequency, a normal frequency, a low frequency, etc., and rotates a pump motor at any of these driving frequencies.

[0018]

The heat source unit 1 further includes a group of sensors 12 to 17 including temperature sensors, pressure sensors, etc. A low-pressure sensor 12 is provided at a suction pipe of the compressor 3 to detect a suction pressure at the compressor. A suction-gas temperature sensor 13 is provided on the suction side of the compressor 3, and detects a suction gas temperature of the refrigerant sucked into the compressor. An outside-air temperature sensor 15 detects an outside-air temperature. In addition, an evaporating temperature sensor 14 is provided at an intermediate position of a refrigerant pipe extending in the heat-medium-side heat exchanger 8, and measures a refrigerant temperature (evaporating temperature Te) at the above position.

[0019]

During the heating operation, high-temperature water sent out from the heat source system 100 is sent to a load-side apparatus, and is applied to, for example, heating at the load-side apparatus to change into low-temperature water. The lowtemperature water is supplied to the heat-medium-side heat exchanger 8 of the heat source system 100, and is heated thereby. In such a manner, the water heat medium circulates between the load-side apparatus and the heat source system 100 through the fluid pipe 22.

[0020]

An inlet temperature sensor 16 is provided at the fluid pipe 22 on an inlet side of the heat-medium-side heat exchanger 8, and measures a water temperature (inlet temperature Twi) at its provided positon. An outlet temperature sensor 17 is provided at the fluid pipe 22 on an outlet side of the heat-medium-side heat exchanger 8, and measures a water temperature (outlet temperature Two) at its provided position. [0021]

The controller 50 is constituted by, for example, a microcomputer, etc., and controls the heat source system 100. To be more specific, the controller 50 receives pressure information and temperature information on the refrigerant and temperature information and other information on the water heat medium, from the group of sensors including the low-pressure sensor 12, the suction-gas temperature sensor 13, the evaporating temperature sensor 14, the outside-air temperature sensor 15, the inlet temperature sensor 16, and the outlet temperature sensor 17. The controller 50 performs an operation control based on the information acquired from the group of sensors 12 to 17, operation information regarding the heat source unit 1, and an instruction input by the user. To be more specific, the controller 50 controls the operation and stopping of the compressor or the rotation speed thereof, adjusts the opening degree of the decompressor 7, controls rotation of the air-side heat-exchanger fan 6, and controls the accumulator 9. In addition, during the defrosting operation, the controller 50 varies the water flow rate FR at which the water heat medium is supplied to the heat-medium-side heat exchanger 8 by the fluid pump 20.

[0022] (Operation of heat source unit 1 during defrosting)

During the heating operation in which the water heat medium is heated, when it is detected that frost forms on the air-side heat exchanger 5, the controller 50 switches the flow of refrigerant in the refrigerant circuit 2 to melt the frost with the heat of the refrigerant. The formation of frost on the air-side heat exchanger 5 is detected as follows. For example, a temperature sensor is provided at the air-side heat exchanger 5, and is caused to measure the temperature of the refrigerant. When the measured temperature becomes less than or equal to a predetermined threshold temperature, it is determined that the formation of frost is detected. In the defrosting operation, which is performed to defrost the air-side heat exchanger 5, as illustrated in Fig. 2, the air-side heat exchanger 5 functions as a condenser, and the heat-medium-side heat exchanger functions as an evaporator. Therefore, since low-temperature refrigerant flows into the heat-medium-side heat exchanger 8, the water heat medium is cooled in the heat medium side heat exchanger 8.

[0023] (Functions of controller 50)

Fig. 3 is a functional block diagram of the controller according to embodiment 1 of the present invention. The controller 50 will be described with reference to Fig. 3. The controller 50 includes an operation control unit 51, a temperature determination unit

52, a freeze determination unit 53 and a storage unit 54.

[0024]

The operation control unit 51 controls the operation of the refrigerant circuit 2 and the flow rate of the fluid to be supplied by the fluid pump 20, based on temperature information, pressure information, etc., from the group of sensors 12 to 17. To be more specific, the operation control unit 51 adjusts the operation frequency of the compressor 3 such that for example, an outlet temperature Two measured by the outlet temperature sensor 17 is made closer to a set target temperature. In addition, during the defrosting operation to defrost the air-side heat exchanger 5, using the pump control device 21, the operation control unit 51 varies the water flow rate FR of the water heat medium to be supplied to the heat-medium-side heat exchanger 8 by the fluid pump 20. Specifically, the operation control unit 51 transmits a control signal for adjusting the driving frequency of the fluid pump 20 to the pump control device 21. The pump control device 21 varies the driving frequency in response to the control signal, to thereby vary the rotation speed of the fluid pump 20. The operation control unit 51 also transmits current operation information regarding an operation which is being currently performed, to the temperature determination unit 52 and the freeze determination unit

53. Furthermore, the operation control unit 51 varies the water flow rate FR of the water heat medium to be supplied, based on the result of determination by the temperature determination unit 52, and continues or ends the defrosting operation based on the result of determination by the freeze determination unit 53.

[0025]

The temperature determination unit 52 acquires temperature information from the inlet temperature sensor 16, and determines whether the water temperature is high or low. To be more specific, during the defrosting operation, the temperature determination unit 52 determines whether the inlet temperature Twi measured by the inlet temperature sensor 16 is lower than a first set temperature T1 or not, and transmits the result of the above determination to the operation control unit 51. Also, during the defrosting operation, the temperature determination unit 52 determines whether the measured inlet temperature Twi is lower than a second set temperature T2 or not, and transmits the result of this determination to either the operation control unit 51 or the freeze determination unit 53 in accordance with the result of the determination. When temperature determination is requested, the temperature determination unit 52 refers to the first set temperature T1 and the second set temperature T2 which are stored as data in the storage unit 54.

[0026]

The freeze determination unit 53 acquires the inlet temperature Twi from the inlet temperature sensor 16, and acquires the evaporating temperature Te from the evaporating temperature sensor 14. The freeze determination unit 53 also acquires from the operation control unit 51, operation information indicating, for example, which of the heating operation, the cooling operation and the defrosting operation are being performed by the heat source system 100, and which of the water flow rates is applied as the water flow rate at which the fluid pump 20 supplies the water heat medium. Furthermore, during the defrosting operation, when the temperature determination unit 52 determines that the measured inlet temperature Twi is lower than the second set temperature T2, the freeze determination unit 53 performs a freeze determination control to determine whether the heat-medium-side heat exchanger 8 will freeze or not. In the freeze determination control, the freeze determination unit 53 determines whether the heat-medium-side heat exchanger 8 will freeze or not, based on the water flow rate FR of the water heat medium to be supplied to the heat-medium-side heat exchanger 8, the measured inlet temperature Twi, and the measured evaporating temperature Te. To be more specific, based on freeze threshold information T3 stored in the storage unit

54, the freeze determination unit 53 calculates freezing-evaporating temperature Tf according to the measured inlet temperature Twi and the water flow rate FR of the water heat medium to be supplied. In addition, the freeze determination unit 53 compares the measured evaporating temperature Te with the calculated freezing-evaporating temperature Tf. Then, when the measured evaporating temperature Te is lower than the freezing-evaporating temperature Tf, the freeze determination unit 53 determines that the heat-medium-side heat exchanger 8 will freeze. By contrast, when the measured evaporating temperature Te is higher than the freezing-evaporating temperature Tf, the freeze determination unit 53 determines that the heat-medium-side heat exchanger 8 will not freeze. In addition, the freeze determination unit 53 transmits the result of the above determination as the result of a freeze determination to the operation control unit 51. That is, the freeze determination unit 53 can change the timing at which the defrosting operation being performed is ended by the operation control unit 51.

[0027]

The storage unit 54 is constituted by, for example, a memory such as a ROM, and stores as data the first set temperature T1, the second set temperature T2 and the freeze threshold information T3 which are set in advance. The first set temperature T1 is an inlet temperature at a boundary where the water temperature of the water heat medium sent out from the heat source system 100 remarkably drops, for example, when the heat source unit 1 performs the defrosting operation. The first set temperature T1 may be automatically set based on the cooling capacity of the refrigerant circuit, a target outlet temperature, the normal water flow rate, etc. The second set temperature T2 is lower than, for example, the first set temperature, and higher than a normal freezing temperature of the heat-medium-side heat exchanger 8. The freeze threshold information T3 is information on the correspondence between the inlet temperature Twi and the freezing-evaporating temperature and information on the correspondence between the water flow rate FR and the freezing-evaporating temperature, and is referred to when the freeze determination unit 53 calculates the freezing-evaporating temperature Tf. It should be noted that the freeze threshold information T3 may be stored in any form as long as the freezing-evaporating temperature is stored as a value which varies in accordance with the inlet temperature Twi or the water flow rate FR, that is, the freezing-evaporating temperature is associated with the inlet temperature Twi or the water flow rate FR as in a formula or a table.

[0028] (Pump control during defrosting)

Fig. 4 is a flowchart of a fluid flow control according to embodiment 1 of the present invention. During the defrosting operation, the refrigerant flows in the same direction as during the cooling operation, and the outlet temperature Two thus drops with respect to the inlet temperature Twi. Thus, during the defrosting operation, there is a possibility that for example, the temperature of the water heat medium to be supplied from the heat source system 100 will drop, and the heat-medium-side heat exchanger 8 will freeze. By contrast, in the fluid flow control as indicated in Fig. 4, the water flow rate FR is varied by varying the driving frequency of the fluid pump 20. The cooling capacity of the refrigerant circuit 2 is defined by the product of the water flow rate FR and the difference between the inlet temperature Twi and the outlet temperature Two. Therefore, in the case where the cooling capacity and the inlet temperature Twi are constant, when the water flow rate FR is high, the degree of dropping of the outlet temperature Two is more greatly reduced than when the water flow rate FR is low. [0029]

In the heat source system 100, for example, when the heating operation of the heat source unit 1 is started, the controller 50 starts the fluid flow control as indicated in Fig. 4 over the heat source unit 1. First, the operation control unit 51 determines whether the heat source unit 1 is in the defrosting operation or (step ST 101). When the heat source unit 1 is not in the defrosting operation (NO in step ST101), the operation control unit 51 performs control such that the water flow rate FR of the water heat medium to be supplied by the fluid pump 20 is set to the normal flow rate (step ST104). To be more specific, the operation control unit 51 transmits a control signal to the pump control device 21, and the pump control device 21 rotates the fluid pump 20 at a normal frequency (e.g., 40 Hz) in response to the control signal.

On the other hand, when the heat source unit 1 is in the defrosting operation (YES in step ST101), the operation control unit 51 sends a notice to the temperature determination unit 52. Upon reception of the notice from the operation control unit 51, the temperature determination unit 52 acquires information on the inlet temperature Twi from the inlet temperature sensor 16 of the heat source unit 1, and acquires the first set temperature T1 from the storage unit 54. Then, the temperature determination unit 52 determines whether the acquired inlet temperature Twi is lower than or equal to the first set temperature T1 or not (step ST102). The first set threshold is a predetermined water temperature, and is set at, for example, 30 degrees C in this case. The temperature determination unit 52 sends a notification indicating the result of the above determination to the operation control unit 51. Upon reception of the notice from the temperature determination unit 52, the operation control unit 51 increases the water flow rate FR of the water heat medium to be supplied (step ST103), when the inlet temperature Twi is lower than or equal to the first set temperature T1 (YES in step T102). Specifically, the operation control unit 51 increases the rotation speed of the fluid pump 20 to “maximum” (for example, 60 Hz) using the pump control device 21 to reduce dropping of the outlet temperature Two with respect to the inlet temperature Twi. On the other hand, when the inlet temperature Twi is higher than the first set temperature T1, the operation control unit 51 sets the above water flow rate FR to the normal water flow rate (step ST 104). After step ST 103 or ST 104 is carried out, the operation control unit 51 returns to step ST101 and repeats the fluid flow control of steps ST101 to ST104. When the heating operation is ended, the operation control unit 51 ends the fluid flow control.

[0030] (Freezing-evaporating temperature Tf)

It should be noted that increasing of the amount of water restricts not only dropping of the outlet temperature Two, but freezing of the heat-medium-side heat exchanger 8. Fig. 5 is a graph indicating a relationship between the inlet temperature and the freezing-evaporating temperature. The freezing-evaporating temperature drops as the inlet temperature Twi raises, while the freezing-evaporating temperature raises as the inlet temperature Twi drops. For example, in the case where the water flow rate FR and the evaporating temperature Te that corresponds to the cooling capacity of the refrigerant circuit 2 are constant, when the inlet temperature Twi of the water heat medium is low, the outlet temperature Two easily drops accordingly, and as a result freezing can easily occurs.

[0031]

Fig. 6 is a graph indicating a relationship between the water flow rate and the freezing-evaporating temperature. The freezing-evaporating temperature drops as the water flow rate FR of the water heat medium to be supplied to the heat-medium-side heat exchanger 8 increases, while the freezing-evaporating temperature raises as the water flow rate FR decreases. For example, in the case where the water flow rate FR is high, even when the inlet temperature Twi and the evaporating temperature Te are constant, the heat capacity of the water heat medium flowing in the heat-medium-side heat exchanger 8 increases, and the degree of dropping of the outlet temperature Two is thus reduced, as a result of which the heat-medium-side heat exchanger 8 does not easily freeze.

[0032]

Furthermore, in consideration of the relationship between the inlet temperature Twi and the freezing-evaporating temperature and the relationship between the water flow rate FR and the freezing-evaporating temperature, it is also possible to restrict freezing of the heat-medium-side heat exchanger 8 based on the evaporating temperature Te. In the heat source system 100 in which the water flow rate FR varies, the heat capacity varies in accordance with variation of the water flow rate FR. Therefore, in detection of freezing of the heat-medium-side heat exchanger 8 during the defrosting operation to defrost the air-side heat exchanger 5, in the case where a control is performed such that as in a conventional technique, the defrosting operation is ended when it is detected that the inlet temperature Twi or outlet temperature Two drops, it is necessary to set a threshold for freeze detection at a high temperature for safety's sake.

[0033]

Fig. 7 is a flowchart of a freeze control according to embodiment 1 of the present invention. When the inlet temperature Twi falls below a predetermined temperature, the controller 50 compares the evaporating temperature Te with the freezingevaporating temperature Tf in relation to the inlet temperature Twi and the water flow rate FR, for detection of freezing.

[0034]

In the heat source system 100, for example, when the heating operation of the heat source unit 1 is started, the controller 50 starts the freeze control as indicated in Fig. 7 over the heat source unit 1. First, the operation control unit 51 determines whether the heat source unit 1 is in the defrosting operation or not (step ST111). When the heat source unit 1 is in the defrosting operation (YES in step ST111), the operation control unit 51 sends a notice to the temperature determination unit 52. By contrast, when the heat source unit 1 is not in the defrosting operation (NO in step ST101), the operation control unit 51 returns to step ST111, and monitors whether the defrosting operation is started during the heating operation. Then, upon reception of the notice from the operation control unit 51, the temperature determination unit 52 acquires temperature information on the inlet temperature Twi from the inlet temperature sensor 16 of the heat source unit 1, and acquires the second set temperature T2 from the storage unit 54. The temperature determination unit 52 determines whether the acquired inlet temperature Twi is lower than or equal to the second set temperature (step ST112). The second set temperature T2 is a predetermined water temperature, and is, for example, 15 degrees C in this case. When the operation control unit 51 determines that the inlet temperature Twi is lower than or equal to the second set temperature T2 (YES in step ST112), the temperature determination unit 52 sends a notice to the freeze determination unit 53. By contrast, when the inlet temperature Twi is higher than the second set temperature T2 (NO in step ST 112), the temperature determination unit 52 sends a notice to the operation control unit 51. Upon reception of the notice from the temperature determination unit 52, the operation control unit 51 continues the defrosting operation (step ST115). On the other hand, upon reception of the notice from the temperature determination unit 52, the freeze determination unit 53 acquires temperature information from the evaporating temperature sensor 14 and the inlet temperature sensor 16. The freeze determination unit 53 also acquires from the operation control unit 51, operation information on the water flow rate which is set at the fluid pump 20. Then, based on the freeze threshold information T3 in the storage unit 54, the freeze determination unit 53 calculates the freezing-evaporating temperature Tf which accords to the evaporating temperature Te, the inlet temperature Twi and the water flow rate FR. In addition, the freeze determination unit 53 determines whether the acquired evaporating temperature Te is lower than or equal to the calculated freezing-evaporating temperature Tf (step ST 113). The freeze determination unit 53 notifies the operation control unit 51 of the result of the freeze determination. When the evaporating temperature Te is lower than or equal to the freezing-evaporating temperature Tf (YES in step ST113), the operation control unit 51 ends the defrosting operation (step ST114). That is, when the water heat medium having the set inlet temperature Twi and supplied at the set water flow rate FR passes through the heatmedium-side heat exchanger 8 in which the evaporating temperature Te is measured, if the water temperature drops such that freezing occurs at the outlet temperature, the defrosting operation is ended, thus reducing freezing. By contrast, when the evaporating temperature Te is higher than the freezing-evaporating temperature Tf (NO in step ST113), the operation control unit 51 determines that the heat-medium-side heat exchanger 8 will not freeze, and continues the defrosting operation (step ST115). After ending or continuing the defrosting operation in step ST114 or ST115, the operation control unit returns to step ST111 and repeats the freeze control. When the heating operation is ended, the operation control unit ends the freeze control.

[0035]

The freeze control is advantageous in the heat source system 100 in which the water flow rate FR of the water heat medium to be supplied by the fluid pump 20 to the heat-medium-side heat exchanger 8 varies, since it is determined whether or not freezing occurs also in consideration of the variation of the water flow rate FR. The controller 50 can perform both the freeze control as indicated in Fig. 7 and the flow control as indicated in Fig. 4.

[0036]

As described above, in embodiment 1, the heat source system 100 includes: the heat source unit 1 which heats and cools fluid; and the controller 50 which controls the heat source unit 1. The heat source unit 1 includes: the refrigerant circuit 2 in which the compressor 3, the refrigerant flow switching device 4, the air-side heat exchanger 5, the decompressor 7 and the heat-medium-side heat exchanger 8 are connected by the refrigerant pipe 11, the fluid pipe 22 through which the fluid flows, the fluid being caused to exchange heat with refrigerant in the refrigerant circuit 2 by the heat-medium-side heat exchanger 8, the fluid pump 20 provided at the fluid pipe 22 to supply the fluid to the heat-medium-side heat exchanger 8, and the inlet temperature sensor 16 which measures the temperature of the fluid flowing into the heat-medium-side heat exchanger 8. The controller 50 includes the operation control unit 51 which controls the fluid pump 20 such that during the defrosting operation in which the air-side heat exchanger 5 functions as a condenser and the heat-medium-side heat exchanger 8 function as an evaporator, the flow rate of the fluid to be supplied to the heat-mediumside heat exchanger 8 varies in accordance with the fluid temperature Twi measured by the inlet temperature sensor 16.

[0037]

Thereby, during the defrosting operation, the degree of dropping of the temperature of the water heat medium to be supplied from the heat source system 100 can be reduced regardless of whether the heat source system 100 is made up of a single heat source unit 1 or a plurality of heat source units 1.

[0038]

The controller 50 further includes the temperature determination unit 52 which determines, during the defrosting operation, whether the measured fluid temperature Twi is lower than the first set temperature T1 or not, and during the defrosting operation, when it is determined that the measured fluid temperature Twi is lower than the first set temperature T1, the operation control unit 51 causes the fluid flow rate FR of the water heat medium to be supplied to be higher than the normal flow rate.

[0039]

Thereby, during the defrosting operation, when the fluid temperature Two at an inlet to the heat-medium-side heat exchanger 8 is low, the water flow rate FR of the water heat medium to be supplied is increased, thus restricting dropping of the water heat medium to be supplied from the heat source system 100. Freezing of the heatmedium-side heat exchanger 8 is also restricted.

[0040]

The heat source unit 1 further includes the evaporating temperature sensor 14 which measures the evaporating temperature of the refrigerant. The controller 50 further includes the freeze determination unit 53 which determines during the defrosting operation whether the heat-medium-side heat exchanger 8 will freeze, based on the flow rate FR of the water heat medium to be supplied, the measured fluid temperature Twi and the evaporating temperature Te measured by the evaporating temperature sensor 14. The operation control unit 51 continues the defrosting operation when it is determined that the heat-medium-side heat exchanger 8 will not freeze.

[0041]

Thereby, freeze control is performed also in consideration of variation of the freezing-evaporating temperature Tf, which is caused by variation of the water flow rate FR. Even when the water temperature is low, there is a case where the defrosting operation for defrosting the air-side heat exchanger 5 can be continued without freezing of the heat-medium-side heat exchanger 8. Whether it can be or not depends on the water flow rate FR. Furthermore, in the case where the freeze control is set such that the flow rate is increased for the freeze control, even if the temperature is lower, the defrosting operation can be continued. Therefore, in the case where defrosting is incomplete, it is possible to prevent the defrosting operation from being stopped to prevent freezing of the heat-medium-side heat exchanger 8.

[0042]

The controller 50 further includes the temperature determination unit 52 which determines during the defrosting operation whether the measured fluid temperature Twi is lower than the second set temperature T2, and during the defrosting operation, when it is determined that the measured fluid temperature Twi is lower than the second set temperature T2, the freeze determination unit 53 determines whether the heat-mediumside heat exchanger 8 will freeze. Thereby, the controller 50 can set a threshold for the fluid temperature, and use the threshold as a requirement for causing the freeze determination unit 53 to start freeze determination.

[0043]

In addition, the freeze determination unit 53 calculates a freezing-evaporating temperature Tf according to the flow rate FR of the fluid to be supplied and the measured fluid temperature Twi, and determines, when the measured evaporating temperature Te is lower than the calculated freezing-evaporating temperature Tf, that freezing will occur, and determines, when the measured evaporating temperature Te is higher than the calculated freezing-evaporating temperature Tf, that freezing will not occur.

[0044]

Thereby, the threshold (freezing-evaporating temperature Tf) is calculated based on the inlet temperature Twi and the water flow rate FR, as a result of which freeze determination is made with a high accuracy. Therefore, for example, when the inlet temperature Twi is high or the water flow rate FR is high, the heat source system 100 can perform the defrosting operation for a longer time period than in the case where the defrosting operation is performed based on a conventional freeze determination.

[0045]

The operation control unit 51 varies the water flow rate FR by adjusting the driving frequency of the appropriate fluid pump 20. To be more specific, the operation control unit 51 increases the driving frequency of the fluid pump 20 in order to increase the water flow rate FR, and decreases the driving frequency of the fluid pump 20 in order to decrease the water flow rate FR. Thereby, once the driving frequency of the fluid pump 20 is synchronized with the water flow rate FR, the controller 50 can vary the water flow rate FR in multiple stages by transmitting a control signal according to a target water flow rate.

[0046]

Embodiment 2

According to embodiment 2, the heat source system 100 includes a plurality of heat source units 1a to 1c which have the same configuration as the heat source unit 1 of embodiment 1. In the plural heat source units 1 a to 1 c, fluid pipes 22a to 22c are connected in parallel with each other in such a way as to join each other on an upstream side and downstream side of heat-medium-side heat exchangers 8a to 8c. The water heat medium supplied from a hot-water storage tank to the heat source system 100 branches off into water heat mediums at a joining point on the upstream side, and the water heat mediums flow into the heat source units 1a to 1c. Then, after heated or cooled in the heat-medium-side heat exchangers 8a to 8c, the water heat mediums join each other at a joining point on the downstream side, thus changing back to a single water heat medium. Then, the water heat medium is sent from the heat source system 100, and returns to the hot-water storage tank. The following description is made by referring to the case where during the heating operation of the heat source system 100, only the heat source unit 1a of the heat source units 1a to 1c is in the defrosting operation, and the others are not in the defrosting operation.

[0047]

Fig. 9 is a flowchart of the fluid flow control according to embodiment 2 of the present invention. Although not illustrated in Fig. 9, each of the heat source unit 1a to 1c includes the same refrigerant circuit as or a similar refrigerant circuit to that of embodiment 1. In embodiment 2, it is assumed that the controller 50 collectively controls the heat source units 1a to 1c, and can also manage them in distinction from each other, and control them individually.

[0048] (Pump control during defrosting)

In embodiment 2, when the inlet temperature Twi of the heat source unit 1a in the defrosting operation is higher than a predetermined temperature, the controller 50 reduces the water flow rate FRa of a water heat medium to be supplied by a fluid pump 20a of the heat source unit 1 a to the heat-medium-side heat exchanger 8a. Thereby, the flow rate of a water heat medium cooled is reduced, and dropping of the temperature of the water heat medium to be sent to the hot-water storage tank is restricted. In the heat source system 100 made up of the plurality of heat source units 1a to 1c, since the heat source units 1b and 1c which are not in the defrosting operation can supply hot water, the water flow rate FRa of the water heat medium to be supplied by the heat source unit 1a which is in the defrosting operation can be reduced until the temperature drops to a lower temperature than in a heat source system provided with only one heat source unit.

[0049]

When the heating operation is started in the heat source system 100, the controller 50 starts the fluid flow control as indicated in Fig. 9. First, the operation control unit 51 determines whether any of the heat source units 1a to 1c is in the defrosting operation (step ST201). When none of these heat source units is in the defrosting operation (NO in step ST201), the operation control unit 51 sets each of water flow rates FRa to FRc of water heat mediums to be supplied by fluid pumps 20a to 20c, respectively, to a normal water flow rate (step ST207). To be more specific, the operation control unit 51 transmits control signals to the pump control devices 21a to 21c to cause the fluid pumps 20a to 20c to rotate at a normal frequency (e.g., 40 Hz). On the other hand, in the case where the heat source unit 1a is in the defrosting operation (YES in step ST201), the operation control unit 51 sends a notice to the temperature determination unit 52. Upon reception of the notice from the operation control unit 51, the temperature determination unit 52 acquires temperature information on the inlet temperature Twi from an inlet temperature sensor 16a of the heat source unit 1a being in the defrosting operation, and also acquires the first set temperature T1 from the storage unit 54. Then, the temperature determination unit 52 determines whether the acquired inlet temperature Twi is lower than or equal to the first set temperature T1 (step ST202). It is assumed that the first set temperature T1 is a predetermined water temperature, and set at, for example, 30 degrees C. The temperature determination unit 52 sends a notice indicating the result of the above determination to the operation control unit 51. Upon receiving the notice from the temperature determination unit 52, the operation control unit 51 sets the water flow rate FRa of the water heat medium to be supplied by the heat source unit 1a being in the defrosting operation to a maximum water flow rate (step ST203), when the inlet temperature Twi is lower than or equal to the first set temperature T1 (YES in step T202). To be more specific, the operation control unit 51 sets the driving frequency of the fluid pump 20a to a maximum (e.g., 60 Hz). The operation control unit 51 also sets water flow rates FRb and FRc of the water heat medium to be supplied by the heat source units 1b and 1c, respectively, that are not in the defrosting operation, to the normal water flow rate (step ST204). On the other hand, when the acquired inlet temperature Twi is higher than the first set temperature T1 (NO in step ST202), the operation control unit 51 sets the water flow rate FRa of the water heat medium to be supplied by the heat source unit 1 a being in the defrosting operation to a low water flow rate (step ST205). Specifically, the operation control unit 51 sets the driving frequency of the fluid pump 20a to a low driving frequency (e.g., 30 Hz). The operation control unit 51 also sets each of the water flow rates FRb and FRc of the water heat mediums to be supplied by the heat source units 1 b and 1 c which are not in the defrosting operation to a high flow rate (step ST206). Specifically, the operation control unit 51 sets each of the driving frequencies of the fluid pumps 20b and 20c to a high driving frequency (e.g., 50 Hz). After setting the flow rates of the water heat mediums to be supplied by the fluid pumps in step ST204, ST206, or ST207, the operation control unit 51 returns to step ST201 and repeats the fluid flow control. When the heating operation is ended, the operation control unit 51 ends the fluid flow control.

[0050]

Therefore, when the inlet temperature Twi is higher than the first set temperature T1, reduction of the flow rate of the water heat medium to be supplied by the heat source unit 1a being in the defrosting operation is compensated for by increasing of the water flow rates FRb and FRc of the water heat mediums to be supplied by the heat source units 1b and 1c not being in the defrosting operation, as a result of which reduction of the flow rate of water supplied from the heat source system 100 are restricted.

[0051]

In order that outlet temperatures Two associated with the heat source units 1a to 1c reach target water temperatures, the controller 50 controls the frequencies of respective compressors 3. In step ST206, in the heat source units 1b and 1c not being in the defrosting operation, since the flow rates are higher than the normal flow rate, raising of the outlet temperatures Two is restricted, and the outlet temperatures may thus be lower than the target water temperatures. However, in a configuration in which the frequencies of the compressors 3 are controlled, the frequencies thereof in the heat source units 1b and 1c not being in the defrosting operation are increased, and the heating capacity is increased, thus compensating for reduction of the water temperature, which is caused by reduction of the flow rate of the water heat medium to be supplied by the heat source unit 1a being in the defrosting operation.

[0052]

Although it is described above that in step ST204, the operation control unit 51 sets the water flow rates FRb and FRc of water to be supplied by the heat source units 1b and 1c not being in the defrosting operation to the normal water flow rate, this is not restrictive, that is, setting of the flow rates is not limited to such setting. For example, if the water flow rates FRb and FRc are set to a high water flow rate, the heat source unit 1a can be backed up. It should be noted that in the heat source unit 1a also, the flow rate is set to the maximum water flow rate in step ST203, and thus in the case where the heat source units 1b and 1c are operated to supply the water heat mediums at the high water flow rate, the total flow rate may be high. Therefore, the operation control unit 51 may be configured to set the water flow rates FRb and FRc of the water heat mediums to be supplied by the heat source units 1 b and 1 c to a low water flow rate in step ST204.

[0053]

In embodiment 2, the heat source system 100 includes the plurality of heat source units 1a to 1c in which the fluid pipes 22a to 22c are connected in parallel to each other. In the case where the first heat source unit 1 a of the heat source units 1 a to 1c is in the defrosting operation, and the second heat source units 1b and 1c are not in the defrosting operation, when it is determined that the measured fluid temperature

Twi of the first heat source unit 1 a is higher than the first set temperature T1, the operation control unit 51 sets the flow rate Fra of the water heat medium to be supplied by the first heat source unit 1a to a flow rate lower than the normal flow rate, and sets the flow rates of the supplied fluid FRb and FRc of the water heat mediums to be supplied by the second heat source units 1b and 1c to flow rates higher than the normal flow rate.

[0054]

Thus, since the heat source system 100 includes the heat source units 1a to 1c, when the fluid temperature Twi is higher than the first set temperature T1, the flow rate of the water heat medium to be cooled in the heat source unit 1a being in the defrosting operation can be reduced, and the water flow rate and temperature of the water heat medium to be supplied can be compensated for those in the other heat source units 1 b and 1c, that is, it can be backed up as the entire system.

[0055]

The heat source units 1a to 1c further include respective outlet temperature sensors 17a to 17c which measure outlet temperatures of fluid flowing out of the heatmedium-side heat exchangers 8a to 8c, and the operation control unit 51 adjusts the frequencies of the compressors 3 of the second heat source units 1b and 1c such that the outlet temperatures Two measured at the second heat source units 1b and 1c are made closer to set target temperatures.

[0056]

Therefore, even when the water flow rates FRb and FRc of water to be supplied by the other heat source units 1b and 1c are high, the heating capacity is increased, as a result of which dropping of the temperature of water to be supplied from the heat source system 100 is restricted even if the heat source unit 1a is in the defrosting operation.

[0057]

It should be noted that the embodiments of the present invention are not limited to those described above, and can be variously modified. For example, the above description is made by referring to the case where in the heat source system 100 including the heat source units 1a to 1c, the single controller 50 controls the plurality of heat source units 1 a to 1 c. However, for example, the heat source units 1 a to 1 c may be provided with respective controllers 50a to 50c. In this case, for example, it suffices that the controller 50a can acquire operation information, etc., from the heat source units 1b and 1c, perform the fluid flow control as indicated in Fig. 9, and send information on, for example, changing of the water flow rate to the other controllers 50b and 50c.

[0058]

Furthermore, the fluid pump 20 has only to vary the water flow rate FR of the water heat medium to be supplied, in multiple steps, and the pump may be configured to obtain kinetic energy for circulating the fluid, using a reciprocating motion in place of a rotary motion, to obtain kinetic energy for circulating the fluid.

[0059]

In the heat source system 100 of embodiment 2, with respect to each of the plurality of heat source units 1a to 1c, the timing of ending of the defrosting operation may be controlled based on the freeze determination as in embodiment 1. [0060]

Although the above description is made on the assumption that the load-side apparatus is an air-conditioning apparatus, the load-side apparatus may be, for example, a floor heating system, a hot-water supply system, or the like. Furthermore, it may be set as a configuration that a hot-water storage tank is provided between the heat source system and the load-side apparatus, and the water heat medium is circulated between the heat source system and the hot-water storage tank, or between the hot-water storage tank and the load-side apparatus.

Reference Signs List [0061]

1,1a-1c heat source unit refrigerant circuit compressor 4 refrigerant flow switching device air-side heat exchanger 6 air-side heatexchanger fan decompressor

8, 8a - 8c heat-medium-side heat exchanger accumulator refrigerant pipe low-pressure suction-gas temperature sensor outside-air temperature sensor 16,

17, 17a -17c outlet temperature sensor pump control device 22, sensor sensor sensor

21,21a-21c controller 51 operation control unit freeze determination unit source system T1 first set temperature freeze threshold information FR, FRa - FRc evaporating temperature 16a -16c inlet temperature

20, 20a - 20c fluid pump

22a - 22c fluid pipe 50 temperature determination unit storage unit 100 heat

T2 second set temperature T3 water flow rate (fluid flow rate) Twi fluid temperature (inlet temperature)

Two outlet temperature Te evaporating temperature

Tf freezing-evaporating temperature

Claims

A heat source system comprising a heat source unit configured to heat and cool fluid; and a controller configured to control the heat source unit, wherein the heat source unit includes:

a refrigerant circuit in which a compressor, a refrigerant flow switching device, an air-side heat exchanger, a decompressor, and a heat-medium-side heat exchanger are connected by a refrigerant pipe, a fluid pipe through which the fluid flows, the fluid being caused to exchange heat with refrigerant in the refrigerant circuit by the heat-medium-side heat exchanger, a fluid pump provided at the fluid pipe, and configured to supply the fluid to the heat-medium-side heat exchanger, and an inlet temperature sensor configured to measure a temperature of fluid to flow into the heat-medium-side heat exchanger, and the controller includes an operation control unit configured to control the fluid pump such that during a defrosting operation in which the air-side heat exchanger functions as a condenser and the heat-medium-side heat exchanger functions as an evaporator, a flow rate of fluid to be supplied to the heat-medium-side heat exchanger varies in accordance with the temperature of the fluid which is measured by the inlet temperature sensor.
[Claim 2]

The heat source system of claim 1, wherein:

the controller further includes a temperature determination unit configured to determine, during the defrosting operation, whether the measured temperature of the fluid is lower than a first set temperature or not; and when it is determined during the defrosting operation that the measured temperature of the fluid is lower than the first set temperature, the operation control unit sets the flow rate of the fluid to be supplied to a flow rate higher than a normal flow rate. [Claim 3]

The heat source system of claim 2, comprising a plurality of heat source unit including the heat source unit, and including fluid pipes including the fluid pipe that are connected in parallel, wherein in a case where of the plurality of heat source units, a first heat source unit is in the defrosting operation and a second heat source unit is not in the defrosting operation, when it is determined that a measured temperature of fluid in the first heat source unit is higher than the first set temperature, the operation control unit sets a flow rate of fluid to be supplied by the first heat source unit to a flow rate lower than the normal flow rate, and sets a flow rate of fluid to be supplied by the second heat source unit to a flow rate higher than the normal flow rate.

[Claim 4]

The heat source system of claim 3, wherein:

each of the heat source units further includes an outlet temperature sensor configured to measure an outlet temperature of fluid which flows out of the heatmedium-side heat exchanger; and the operation control unit adjusts a frequency of a compressor in the second heat source unit such that an outlet temperature measured in the second heat source unit is made closer to a set target temperature.

[Claim 5]

The heat source system of any one of claims 1 to 4, wherein:

each heat source unit further includes an evaporating temperature sensor configured to measure an evaporating temperature of the refrigerant;

the controller further includes a freeze determination unit configured to determine, during the defrosting operation, whether the heat-medium-side heat exchanger will freeze, based on the flow rate of the fluid to be supplied, the measured temperature of the fluid, and the measured evaporating temperature; and the operation control unit continues the defrosting operation when it is determined that the heat-medium-side heat exchanger will not freeze.

[Claim 6]

The heat source system of claim 5, wherein:

the controller further includes a temperature determination unit configured to determine, during the defrosting operation, whether the measured temperature of the fluid is lower than the second set temperature or not; and during the defrosting operation, when it is determined that the measured temperature of the fluid is lower than the second set temperature, the freeze determination unit determines whether the heat-medium-side heat exchanger will freeze.

[Claim 7]

The heat source system of claim 5 or 6, wherein the freeze determination unit calculates a freezing-evaporating temperature according to the flow rate of the fluid to be supplied and the measured temperature of the fluid, and determines, when the measured evaporating temperature is lower than the calculated freezing-evaporating temperature, that freezing will occur, and determines, when the measured evaporating temperature is higher than the calculated freezing-evaporating temperature, that freezing will not occur.

[Claim 8]

The heat source system of any one of claims 1 to 7, wherein the operation control unit varies the flow rate of the fluid to be supplied, by adjusting a driving frequency of an associated fluid pump, increases the driving frequency of the fluid pump when the flow rate of the fluid to be supplied is required to be increased, and decreases the driving frequency of the fluid pump when the flow rate of the fluid to be supplied is required to be decreased.