JP2001241729A - Cooling water supply system of refrigerating machine for air conditioning - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform stabilized operation even upon variation of load by employing general purpose components in a refrigerating machine supply facility and reducing the amount of materials up to the load side. SOLUTION: Inlet/outlet temperature difference of chilled water in cooling systems 11a, 11b, 11c on the load side is set higher than the inlet/outlet temperature difference of a chilled water supply facility 3 for a refrigerating machine on the chilled water supply side and bypass piping 15 for absorbing the difference in the volume of chilled water between the supply side and the load side is provided. At the time of variation on the load side, the inlet/outlet pressure difference and the return temperature of the chilled water supply facility 3 for the refrigerating machine are varied. In order to sustain stabilized operation regardless of these variations, the bypass piping 15 is provided with a pressure control valve 16 and a controller 21 controls the opening of a flow regulation valve 14 to regulate the flow rate of chilled water flowing through the cooling systems 11a, 11b, 11c on the load side such that the chilled water return temperature of the chilled water supply facility 3 for the refrigerating machine will be constant.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cooling water supply system for an air conditioner.

[0002]

2. Description of the Related Art Conventionally, chilled water equipment for ventilation and air conditioning of a nuclear power plant has been disclosed in Japanese Patent Application Laid-Open No. 64-14542.
This is a system having a refrigerator that supplies a chilled water temperature difference that matches the cooling coil temperature difference on the load side.

Conventional chilled water equipment for ventilation and air conditioning of a nuclear power plant is required for workers at the time of rated operation of the nuclear power plant or at the time of regular inspection of the power plant periodically operating at the nuclear power plant by operating a refrigerator as a standby unit. When the work environment is improved, the cooling water supplied to each load must be supplied using the entire amount of the cooling water supplied to the refrigerator.

If the outside air temperature changes more than expected, the heat exchange of the cooling coil on the load side becomes overloaded, and the temperature of the chilled water circulating from the load side to the refrigerator side is reduced. Exceeds the set inlet temperature to In order to prevent this, Japanese Patent Laid-Open Publication No. 64-14542 discloses a chilled water facility for ventilation and air conditioning at a nuclear power plant. The system has a system that reduces the temperature of the chilled water on the inlet side of the refrigerator by short-passing the side.

[0005]

The above-mentioned prior art is effective as a countermeasure in the event of overload. However, when the cooling coil temperature difference on the load side is to be increased in order to increase the allowable amount on the load side, Similarly, the difference in the chilled water temperature on the refrigerator side also increases,
There is a problem that it cannot be used with the difference in cold water temperature of general-purpose products used in general.

Conversely, when the chiller-side chilled water temperature difference is used as the chilled water temperature difference of a general-purpose product that is generally used, the pipe diameter connecting the supply side and the load side is selected from the reference flow velocity in the pipe. In this case, the diameter of the pipe and the valves and accessories connected to the pipe are increased, which causes a problem of an increase in the amount of material. When such a problem occurs, the amount of the chilled water supply system for the air conditioner becomes large, so that the cost increases.

An object of the present invention is to solve the above-mentioned problems and to reduce the cost of a chilled water supply system for an air conditioner.

[0008]

[MEANS FOR SOLVING THE PROBLEMS] To use the specifications of the chilled water equipment for air conditioning refrigeration equipment in the standard specifications of general-purpose products, and to reduce the diameter of pipes, valves, and accessories that connect the supply side and the load side. Further, a means is provided for expanding the difference between the cooling water temperature at the inlet and outlet of the cooling coil of the cooling device on the load side from the difference between the cooling water temperature on the supply side and absorbing the difference in the amount of chilled water between the supply side and the load side. This allows the chilled water from the chiller chilled water facility and the chilled water returned from the load side to be constantly mixed, so that even if the chilled water temperature difference between the load side cooling coil inlet and outlet is greater than the chilled water temperature difference based on the specifications of the chiller chilled water facility. In addition, the chiller chiller can be used with the chilled water temperature difference of the standard specification of general-purpose products. Also, a part of the whole amount is supplied to the load side from the chiller chilled water equipment, and the remaining chilled water is always bypassed and returned to the chiller chilled water equipment. , The amount of cold water flowing through the accessories is reduced, the pipes and valves connected to the pipes, the diameter of the accessories, and the diameter of the accessories are reduced, and the volume can be reduced. The cost of the chilled water supply system for the air conditioner provided with the cooling device can be reduced.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described.
This will be described with reference to the drawings.

The chilled water supply system for an air conditioner according to the first embodiment shown in FIG. 1 is provided with a chilled water supply system 3 comprising four chillers 1 and four chilled water transfer pumps 2, for example. . A supply-side header pipe 4 for collecting and dispersing the chilled water from the four chillers 1 is provided as an outlet side of the chilled water of the chilled water supply equipment 3 for the chiller, and the cooling devices 11a and 11
A return header pipe 5 for dispersing and flowing the cold water from b and 11c to each refrigerator 1 is provided as a cold water inlet side of the refrigerator cold water supply equipment 3.

The refrigerator 1 and the chilled water transfer pump 2 are connected in a series circuit, and the series circuit is connected in parallel by four circuits between the supply side header tube 4 and the return side header tube 5, and the return side header tube 5
The flows are connected in a unified manner so that cold water is sucked from the side by the cold water transfer pump 2 and flows out through the refrigerator 1 to the supply side header pipe 4 side.

A pipe 15 for bypassing the cold water supplied from the refrigerator cold water supply equipment 3 to the supply header pipe 4 from the supply header pipe 4 to the return header pipe 5 is discharged from the refrigerator cold water supply equipment 3 as the supply side. It is provided as means for absorbing the difference between the amount of chilled water to be used and the amount of chilled water required by the cooling devices 11a, 11b, 11c on the load side.

The chiller chilled water supply equipment 3 is provided with a chilled water passing through the chiller chilled water supply equipment 3 and a deeply cooled refrigerant, for example, R134a, flowing through a cooling water pipe 6 from another cooling equipment. Through 12 ° C. to cool 7 ° C. cold water.

Each of the cooling devices 11a, 11b and 11c comprises a fan 9 and a cooling coil 10 through which cold water flows. The cooling water inlet side of the cooling coil 10 is connected to supply side pipes 7 a, 7 b, 7 c connected to the supply side header pipe 4 via a gate valve 12 and a flange 13. In addition, the cooling water outlet side of the cooling coil 10 is connected to the return pipes 8a, 8b, 8c connected to the return header pipe 5 by flanges 13.
And a flow control valve 14. In this way, each cooling device 11a, 11b, 11c on the load side
Are connected in parallel with each other to the supply pipe and the return pipe.

After the chilled water is cooled by the refrigerator 1, the chilled water enters the supply side header pipe 4, passes through the cooling coils of the cooling devices 11a, 11b, 11c through the supply side pipes 7a, 7b, 7c and is sent by the cooling fan 9. The returned gas is heated by exchanging heat through the surface of the cooling coil, and the return pipes 8a, 8b,
A circulation path is entered through 8c into the return header tube 5 and again into the refrigerator 1. Therefore, the supply side pipes 7a, 7b, 7c and the return side pipes 8a, 8b, 8c are used as pipes for circulation between the cold water refrigerator 1 and the cooling devices 11a, 11b, 11c.

The temperature of the chilled water supplied from the chiller chilled water supply equipment 3 to be supplied to each of the cooling devices 11a, 11b and 11c is output at, for example, a supply temperature of 7 ° C., and the return temperature is, for example, 12 ° C. Use standard specifications with relatively small general-purpose products. On the other hand, each cooling device 11a, 11
The specifications of b and 11c are all assumed to be a temperature difference larger than the temperature difference between the inlet and the outlet of the refrigerator cold water supply equipment 3, for example, the cooling coil inlet side temperature is 7 ° C. and the outlet side temperature is 27 ° C.

On the other hand, 7 ° C. is bypassed from the supply header pipe to the return header pipe through the bypass pipe 15.
Chilled water and 27 ° C. chilled water from each cooling device outlet side merge at the return side header pipe 5, so that the chiller cold water supply equipment 3
Return temperature of standard specification for general-purpose products 12
° C.

Further, each of the cooling devices 11a, 11b, 11c
Are all set to a temperature difference larger than the temperature difference of the refrigerator cold water supply equipment 3, the cooling device 11 on the load side
pipes 7a to 7c, 8a to 8 up to a, 11b, 11c
c, and the gate valve 1 at the entrance and exit of each of the cooling devices 11a to 11c
2. The diameters of the flow control valve 14 and the flange 13 can be reduced, which has the effect of reducing the amount of material.

The contents of the reduction described above are shown quantitatively using the following equations. As shown above, supply chilled water temperature 7 ° C,
With a temperature difference of 5 ° C with a return temperature of 12 ° C, for example, a cooling capacity of 100k
When three W refrigerators 1 are operating as one standby unit, the amount of chilled water (m ³ / h) =
[｛Cooling capacity (kW) × 860｝ / ｛Return temperature (° C)-
Supply cold water temperature (° C)}] × 0.001 and enter the actual value {(100 × 860 × 3) / (12-7)} ×
0.001 and a solution value of 51.6 m ³ / h is obtained as a solution. The amount of chilled water of 51.6 m ³ / h is supplied from the chiller chilled water supply equipment 3 to the cooling device 11 on each load side.

In the cooling device 11 having the same inlet / outlet temperature difference of 5 ° C. as that of the conventional refrigerator cold water supply equipment 3, for example, in the case of the same cooling capacity as the refrigerator 1, the amount of cold water 17.2 m ³ equal to the cooling devices 11a, 11b, 11c. / H. That is, the amount of cold water in the pipes 7a and 8a is 51.6 m ³ / h,
The amount of cold water for b and 8b is 34.4 m ³ / h, and the amount of cold water for pipes 7c and 8c is 17.2 m ³ / h.

On the other hand, each of the cooling devices 11a to 11c on the load side
If the cooling water temperature at the inlet of the cooling coil of the cooling device is 7 ° C. and the cooling water temperature at the outlet is 27 ° C. and the cooling capacity is 100 kW, the total amount of the chilled water is ｛(100 ×
860 × 3) / (27-7)｝ × 0.001 to 12.9 m ³
/ H. This conventional pipe 7a, compared to the cold water quantity 51.6m ³ / h at 8a, pipe 7a in the cooling device 11a~11c enlarging the temperature difference, who 8a cold water amount 12.
It is as small as 9 m ³ / h. Further, the pipe 7b, relative to the conventional cold water quantity 34.4m ³ / h also 8b, smaller cold water amount 8.6 m ³ / h in the present embodiment. Furthermore, each pipe 7c, 8c
Similarly, the amount of cold water conventionally can be reduced from 17.2 m ³ / h to 4.3 m ³ / h.

This means that, for example, the reference flow velocity in the pipe is set to 0.
In the case of 5 to 1.5 m / s, the amount of cold water of the conventional method is 51.6.
In m ³ / h, the nominal diameter is 12 as the diameter of each pipe 7a, 8a.
While a pipe of 5A is required, a pipe of nominal diameter 65A is sufficient for the pipes 7a and 8a for the cold water flow rate of 12.9 m ³ / h in the present embodiment, and a pipe of each pipe 7b and 8b is used. In this embodiment, the nominal diameter may be 50A in the present embodiment with respect to the nominal diameter of 100A, and the nominal diameter of the pipes 7c and 8c may be sufficient in the present embodiment with the nominal diameter of 65A in the present embodiment.

It is to be noted that the difference of 38.7 m ³ / h of chilled water is bypassed from the supply header pipe 4 to the return header pipe 5 without being supplied to the cooling devices 11 a to 11 c via the bypass pipe 15. In addition, the balance of heat balance is equal on the supply side and the load side. This is expressed by the following equation, confluence temperature (° C.) = {Cool water amount (m ³ / h) × cold water temperature (° C.)} / {Cool water amount (m ³
/ H) When the return temperature to the refrigerator cold water supply equipment 3 is obtained from｝, {(12.9 × 27) + (38.7 × 7)} / 5
This can be said from the fact that the temperature becomes 12 ° C. from 1.6.

In order to bypass a part of the total chilled water amount of the chiller chilled water supply equipment 3 by the bypass pipe 15,
By selecting the pipe diameter of the bypass pipe 15 based on the reference flow velocity in the pipe, the required amount of cold water can be bypassed.

As described above, according to this embodiment, even when a general-purpose product having a relatively small temperature difference of 5 ° C. between the inlet and outlet is used for the refrigerator cold water supply equipment 3, the supply-side header pipe 4 to the return-side header pipe 5 can be used. A bypass pipe 1 of a length equivalent to about one refrigerator 1
5, the pipes 7a, 7b, 7 connecting the supply side and the load side, which are longer than the bypass pipe 15,
c, 8a, 8b, 8c and cooling devices 11a, 11b, 1
The diameter of each of the gate valve 12, the flow control valve 14, and the flange 13 on the entrance / exit side of 1c can be reduced, the physical quantity can be reduced, and the cost of the chilled water supply system for the air conditioner can be reduced.

FIGS. 2 and 3 show the configuration of a chilled water supply system for an air conditioning refrigerator according to a second embodiment of the present invention. Reference numerals 1 to 15 in FIGS. 2 and 3 are the same as those in FIG. 1 of the first embodiment. Reference numeral 16 shown in FIG.
And a pressure control valve for controlling the pressure difference between the return side header pipe 5 and the pressure control valve 16 provided in the bypass pipe 15.

A pipe 17 for transmitting pressure to a pressure detector 18 is connected to the supply header pipe 4 and the return header pipe 5. The pressure detector 18 detects the pressure of the chilled water in the supply header pipe 4 and the return header pipe 5 through the pipe 17, and obtains the pressure difference between the supply header pipe 4 and the return header pipe 5. The obtained pressure difference is used as a signal as a pressure control valve 16.
Is sent to the control device 19 for the valve opening. The control device 19
Then, the preset pressure difference is compared with the pressure difference obtained by the pressure detector 18, and when the preset pressure difference exceeds the pressure difference obtained by the pressure detector 18, the control device Reference numeral 19 issues a control signal to a driving device for opening and closing the pressure control valve 16 so as to drive the valve in a direction to open the valve.

Upon receiving the control signal, the pressure control valve 16 is driven to open the valve more than it is, and the pressure difference between the cold water of the supply header pipe 4 and the return water of the return header pipe 5 is reduced to the above-mentioned predetermined pressure. It works to get back to the difference. During this time, the flow rate of the cold water passing through the bypass pipe 15 increases.

Conversely, if the pressure difference determined by the pressure detector 18 is smaller than the preset pressure difference, the control device 19 closes the pressure control valve 16 by a driving device that controls the opening and closing of the valve. A control signal is issued to drive the valve in the direction.

Upon receiving the control signal, the pressure control valve 16 is driven so as to close the valve further, and the pressure difference between the chilled water of the supply header pipe 4 and the return water of the return header pipe 5 is reduced to the above-mentioned predetermined pressure. It works to get back to the difference. During this time, the flow rate of the cold water passing through the bypass pipe 15 decreases, but the flow rate does not disappear.

In the second embodiment shown in FIG. 2, since the pressure control valve 16 shown above is provided, the cooling device 11a for cooling the outside air of the same specification for cooling the outside air supplied to the building is provided.
For example, when the outside air temperature changes (load fluctuation) between daytime and evening in the day, the cooling device 11 cools the outside air.
a to 11c (the cooling devices 11a to 11c).
c), the supply side pressure and the return side of the chiller chilled water supply equipment 3 can be changed even when the amount of chilled water changes due to adjusting the valve opening of the flow control valve 14 in order to make the temperature constant. The pressure difference between the pressures can be automatically maintained at a constant pressure difference.

The pressure in the header pipes 4 and 5 is monitored by a pressure detector so that the pressure control valve 16 performs an opening and closing operation similar to the opening and closing control of the pressure control valve 16 described above.
It may be operated manually. In this case, the control device 1
9 becomes unnecessary.

FIG. 3 shows, for example, cooling devices 11a and 11a.
A plurality of cooling devices having different specifications on each load side and different uses, such as an outside air cooling device for cooling the outside air supplied to the building by c, and a recirculation cooling device for cooling the specific room by the cooling device 11b. Similarly, in the configuration having 11a, 11b, and 11c, the pressure difference between the supply side pressure and the return side pressure of the refrigerator cold water supply equipment 3, that is, the difference between the pressures in the header pipes 4 and 5 is set to a constant pressure. The difference can be maintained. Other configurations and operations are the same as those of the first embodiment shown in FIG.

As described above, the pressure difference between the header tubes 4 and 5 can be maintained at a predetermined constant pressure difference, so that not only the cost of the system is reduced, but also the safety of the system and the load side are reduced. Cooling devices 11a, 11b, 11
The effect of maintaining the normalization of the function of the system with respect to the load fluctuation of c can be obtained.

FIG. 4 shows a configuration of a chilled water supply system for an air conditioning refrigerator according to a third embodiment of the present invention. 4 denote the same items as in FIG. 4 is a thermo-sensitive element for detecting the return temperature of the chilled water of the return-side header tube 5, and 21 is a sensor for reading the return temperature of the chilled water from the thermo-sensitive element 20 and performing cooling based on the returned temperature of the chilled water. Apparatus 1
This is a control device that prompts the first flow control valve 14 to adjust the valve opening.

In this embodiment, the return temperature of the chilled water supply equipment 3 is made more constant by adjusting the opening of the chilled water control valve 14 described above. Cooling device 11 as shown in the second embodiment
Even when the load fluctuations of a, 11b, and 11c are abrupt or slow, the amount of chilled water is automatically and easily controlled to return the return temperature of the chiller chilled water supply equipment 3 (standard temperature of 12 ° C.). Temperature).

The temperature sensing element 20 detects the temperature of the cold water in the header pipe on the return side, and if the detected value is lower than a preset 12 degrees Celsius, the control device receives the detection signal of the temperature sensing element. 21 sends a signal to the flow control valve 14 to open the valve any more, and the flow control valve 14 receives the signal and is driven to open the valve. Conversely, the temperature sensing element 20 detects the temperature of the chilled water in the return header pipe, and if the detected value is higher than a preset 12 degrees Celsius, the control device receives the detection signal of the temperature sensing element 20 and receives the detection signal. 21 sends a signal to the flow control valve 14 to close the valve any more, and the flow control valve 14 receives the signal and is driven in a direction to close the valve.

The present embodiment will be described below quantitatively. The operating conditions during the rated operation of the present embodiment are, for example, the same as those of the first embodiment and FIG. Here, for example, the load of each cooling device 11a, 11b, 11c on the load side fluctuates,
Assume that the power has been reduced from kW to 90 kW.

If the flow control valve 14 does not have the control device 21 for prompting the valve opening adjustment, the same amount of chilled water flows through the cooling devices 11a, 11b, and 11c before and after the load change. The outlet cold water temperature of the cooling devices 11a, 11b, 11c is ｛(90 × 860 × 0.001) / 4.
25 ° C. from 3｝ +7. Therefore, the return temperature to the refrigerator cold water supply equipment 3 is ｛(12.9 × 25) + (38.7)
× 7) It becomes 11.5 ° C from｝ /51.6.

On the other hand, according to the embodiment shown in FIG. 4 of the present invention, each cooling device 11a, 1
When the load of 1b, 11c decreases, control is performed to keep the return temperature of the chilled water to the chiller chilled water supply equipment 3 constant, and therefore, each flow control valve 14 connected to each of the cooling devices 11a, 11b, 11c. Can be opened from the rated state.

Therefore, according to the embodiment shown in FIG. 4 of the present invention, each cooling device 11a, 11b, 11c is provided with a reduced load by lowering the air temperature on the outlet side.
a, 11b, 11c. For example, the flow rate adjustment for connecting each cooling device 11a, 11b, the cold water of 11c from 4.3 m ³ / h with the load variation 8.6 m ³ / h so that each cooling device 11a, 11b, and 11c When the valve 14 is opened, each cooling device 11a, 11b, 11
The load of c is 100
kW, and therefore each of the cooling devices 11a, 11b, 11c
Outlet cold water temperature is ｛(100 × 860 × 0.001)
/8.6｝+7, the temperature becomes 17 ° C., and the decrease in pressure difference between the header pipes 4 and 5 due to the flow of a large amount of chilled water to the load side is caused by adjusting the valve opening of the pressure control valve 16 (this In the case of the example, the valve is adjusted in a direction to close), so that when these are used to calculate the temperature of the chilled water returning to the refrigerator cold water supply facility 3, that is, the return temperature to the refrigerator cold water supply facility 3,
{(8.6 × 3 × 17) + (25.8 × 7)} / 51.6
12 ° C.

As described above, according to the present embodiment, the temperature sensing element 20 is provided in the return header tube 5, and the temperature of the cold water returning from the temperature sensing element 20 to the refrigerator cold water supply facility 3, that is, the temperature of the cold water supply facility 3 The return temperature is read and each cooling device 11a, 11b, 1
By providing the control device 21 for prompting the adjustment of the opening degree of each flow control valve 14 connected to the flow control valve 1c, stable chiller chilled water supply not affected by load fluctuations of the load side cooling devices 11a, 11b, 11c. Effective for operation of equipment. In this embodiment as well, the opening degree of the valve may be manually adjusted in the same manner as in the embodiment of FIG. 1 while checking the pressure difference between the pressures in the header pipes 4 and 5 using the pressure control valve 16.

[0043]

As described above, according to the chilled water supply system for an air conditioner of the present invention, the cooling device on the load side having an inlet / outlet temperature difference larger than the inlet / outlet temperature difference of the chiller chilled water supply equipment is provided. Since it is possible to use and a difference between the amount of chilled water to the cooling device on the load side and the amount of chilled water supplied to the chiller chilled water supply equipment as described above, application of a general-purpose chiller chilled water supply equipment, and By reducing the amount of water including the piping by reducing the amount of cooling water passing through between the cooling water supply equipment for the refrigerator and the cooling device on the load side, there is an effect of reducing the cost of the cooling water supply system for the air conditioning refrigerator.

[Brief description of the drawings]

FIG. 1 is a system diagram of a chilled water supply system for an air conditioning refrigerator according to a first embodiment of the present invention.

FIG. 2 is a system diagram of a chilled water supply system for an air conditioner according to a second embodiment of the present invention.

FIG. 3 is a system diagram of an air-conditioning chiller chilled water supply system when a load side is different in a second embodiment of the present invention.

FIG. 4 is a system diagram of a chilled water supply system for an air conditioner according to a third embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Refrigerator, 2 ... Cold water conveyance pump, 3 ... Refrigerator cold water supply equipment, 4 ... Supply side header pipe, 5 ... Return side header pipe, 6 ...
Cooling water piping, 7a, 7b, 7c ... supply side piping, 8a, 8
b, 8c: return side pipe, 9: fan, 10: cooling coil, 11a, 11b, 11c: cooling device, 12: gate valve, 13: flange, 14: flow control valve, 15: bypass pipe, 16: pressure control Valves, 17 ... Piping for detecting pressure, 18 ... Pressure detector, 19 ... Control device for adjusting valve opening of pressure control valve, 20 ... Temperature sensing element, 21 ... Adjusting valve opening of flow control valve Control device.

Claims (4)

[Claims] 1. A refrigerator chilled water supply system, a cooling device in which the temperature difference between the incoming and outgoing chilled water is larger than the temperature difference between the incoming and outgoing chilled water of the refrigerator cold water supplying device, and the chiller chilled water supply device And a cooling device, and a bypass pipe for communicating the cooling water so that the cold water circulates, and a bypass pipe for bypassing the cooling device and returning cold water from an outlet side of the refrigerator cold water supply facility to an inlet side. Refrigerator cold water supply system. 2. The chilled water supply system for an air conditioner according to claim 1, further comprising a pressure control valve in a bypass pipe. 3. The pressure control valve according to claim 2, wherein the pressure difference is larger than a set pressure difference based on a pressure difference between the outlet side and the inlet side of the refrigerator cold water supply equipment. In such a case, the pressure control valve is driven so that the valve opening is increased, and conversely, if the pressure is small, the pressure control valve is driven so that the valve opening is reduced. Air conditioner chiller water supply system comprising: 4. The refrigeration system according to claim 1, further comprising the cooling device, a pipe for circulating cold water from the cooling device to the chilled water supply equipment for the refrigerator, and a flow control valve. Based on the temperature of the chilled water on the inlet side of the chilled water of the machine chilled water supply equipment, when the temperature is higher than a set temperature, the flow rate control valve is driven such that the valve opening of the flow rate control valve is reduced, Conversely, when the temperature is low, the flow control valve is driven so that the valve opening of the flow control valve is increased, and the control means for controlling the valve opening of the flow control valve is provided.