Patent Publication Number: US-2004050944-A1

Title: Vehicle air conditioner

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001] This application is related to and claims priority from Japanese Patent Application No. 2002-267363 filed on Sep. 12, 2002, the content of which is hereby incorporated by reference.  
       BACKGROUND OF THE INVENTION  
       [0002] 1. Field of the Invention  
       [0003] The present invention relates to a vehicle air conditioner having a heating heat exchanger for heating air to be blown into a passenger compartment by using hot water (cooling water) heated by a temperature-controlled apparatus such as a fuel cell system.  
       [0004] 2. Description of Related Art  
       [0005] In a vehicle air conditioner disclosed in JP-A-2001-315524, for example, a passenger compartment is heated by using cooling water of a fuel cell system (F/C) as a heat source. The fuel cell system is thermal-controlled to increase its operation efficiency. The vehicle air conditioner includes a heater core, a first cooling-water circuit, a second cooling-water circuit, a switching valve and an auxiliary heater. The heater core mainly heats air to be blown into the passenger compartment, and the auxiliary heater assists the heating operation of the heater core. In the first cooling-water circuit, cooling water of the fuel cell system circulates the fuel cell system and the heater core. In the second cooling-water circuit, the cooling water does not passes through the fuel cell system, but passes through the heater core. The switching valve is provided to switch one of the first and second cooling-water circuits.  
       [0006] When the fuel cell system is stably operated in capable of releasing its thermal energy, the first cooling-water circuit is selected by the switching valve, so that cooling water flows from the fuel cell system into the heater core. In this case, the heater core can heat the blown air. When the blown air cannot be heated to a desired temperature only by using the thermal energy released from the fuel cell system, the auxiliary heater is operated to assist the heating operation of the heater core. On the other hand, when the fuel cell system is unstably operated in incapable of releasing its thermal energy, the second cooling-water circuit is selected by the switching valve, and the auxiliary heater is operated to heat the blown air to the desired temperature.  
       [0007] However, in the above vehicle air conditioner, even when the fuel cell system can release its thermal energy, and even when the blown air is required to be heated by the heater core, the thermal energy, which is unnecessary in the fuel cell system, cannot be used in the heater core in some temperature conditions of the cooling water.  
       SUMMARY OF THE INVENTION  
       [0008] Therefore, it is an object of the present invention to provide a vehicle air conditioner having a heating heat exchanger capable of effectively using an unnecessary thermal energy of a temperature-controlled apparatus.  
       [0009] According to the present invention, in an air conditioner for a vehicle having a temperature-controlled apparatus, a heating heat exchanger is provided for heating air to be blown into a passenger compartment of the vehicle by using cooling water for cooling the temperature-controlled apparatus as a heating source, the cooling water passes through the temperature-controlled apparatus and the heating heat exchanger through a first circuit, the cooling water passes through the heating heat exchanger while bypassing the temperature-controlled apparatus through a second circuit, a switching device is provided for switching a cooling water circuit between the first and second circuits, and a control unit controls the switching device so as to select the first circuit when a cooling water temperature flowing out of the heating heat exchanger is lower than a cooling water temperature flowing out of the temperature-controlled apparatus. Accordingly, the cooling water, flowing out of the heating heat exchanger, is heated by the temperature-controlled apparatus, and is circulated into the heating heat exchanger. Therefore, the heating heat exchanger can effectively heat air by using the unnecessary thermal energy from the temperature-controlled apparatus.  
       [0010] The air conditioner can be provided with an auxiliary heater for heating air to be blown into the passenger compartment by supplying thermal energy to the cooling water to be circulated into the heating heat exchanger. For example, the auxiliary heater is arranged in the first and second circuits to heat the cooling water to be circulated into the heating heat exchanger in the first and second circuits.  
       [0011] Preferably, the control unit calculates the cooling water temperature flowing out of the heating heat exchanger, based on a cooling water temperature flowing into the heating heat exchanger and a heat radiation capacity in the heating heat exchanger. In this case, the switching control of the switching device can be performed without directly detecting the cooling water temperature flowing out of the heating heat exchanger. Alternatively, the control unit calculates the cooling water temperature flowing out of the heating heat exchanger, based on a cooling water temperature flowing into the heating heat exchanger, a flow amount of the cooling water passing through the heating heat exchanger, an air temperature flowing into the heating heat exchanger and an air flow amount passing through the heating heat exchanger. Further, the control unit can control the switching device so as to select one of the first and second circuits based on the cooling water temperature detected by a temperature sensor.  
       [0012] More preferably, the first circuit is selected, only when air to be blown into the passenger compartment is required to be heated by the heating heat exchanger and waste heat from the temperature-controlled apparatus is permitted to be used. Therefore, it can prevent the cooling water circulates in the first circuit when it is unnecessary to heat air by using the heating heat exchanger, or when there is no thermal heat to be radiated from the temperature-controlled apparatus.  
       [0013] According to the present invention, when a fuel cell system is used as the temperature-controlled apparatus, the advantages of the present invention can be effectively improved.  
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0014] Additional objects and advantages of the present invention will be more readily apparent from the following detailed description of preferred embodiments when taken together with the accompanying drawings, in which:  
     [0015]FIG. 1A is a schematic diagram showing a vehicle air conditioner according to a preferred embodiment of the present invention, and FIG. 1B is a block diagram showing a control system of an air-conditioning control unit of the vehicle air conditioner;  
     [0016]FIGS. 2A and 2B are schematic diagrams showing operation of a switching valve according to the preferred embodiment;  
     [0017]FIG. 3 is a flow diagram showing a part of a control process of the air-conditioning control unit according to the preferred embodiment;  
     [0018]FIG. 4 is a flow diagram showing an another part of the control process of the air-conditioning control unit according to the preferred embodiment;  
     [0019]FIG. 5 is a flow diagram showing an another part of the control process of the air-conditioning control unit according to the preferred embodiment;  
     [0020]FIG. 6 is a flow diagram showing a further another part of the control process of the air-conditioning control unit according to the preferred embodiment;  
     [0021]FIG. 7 is a graph showing a control of a blower level (i.e., air blowing amount) according to the preferred embodiment;  
     [0022]FIG. 8 is a graph showing a control of an operation mode according to the preferred embodiment;  
     [0023]FIG. 9A is a graph showing a relationship between a temperature difference (TW−TE) and a reducing temperature T1, and FIG. 9B is a schematic diagram showing a determination of a waste heat usage of a fuel cell system, according to the preferred embodiment;  
     [0024]FIG. 10 is a graph showing a relationship between a target air temperature TEO blown from an evaporator and an outside air temperature Tam, according to the preferred embodiment;  
     [0025]FIG. 11 is a graph showing a relationship between a control value Φ and an air flow amount blown from an air outlet, according to the preferred embodiment;  
     [0026]FIG. 12 is a schematic diagram showing a main part of a vehicle air conditioner according to an another embodiment of the present invention; and  
     [0027]FIG. 13 is a schematic diagram showing a determination of a waste heat usage according to an another embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS  
     [0028] Preferred embodiments of the present invention will be described hereinafter with reference to the appended drawings.  
     [0029] In a preferred embodiment, the present invention is typically applied to an air conditioner for a fuel cell vehicle, as shown in FIG. 1A. A fuel cell system (F/C)  6  is required to be temperature-controlled, and is connected to a cooling water circuit  30  where cooling water is circulated. The cooling water circuit  30  includes a first cooling-water passage  34  at a left side of the fuel cell system  6  in FIG. 1A and a second cooling-water passage  35  at a right side of the fuel cell system  6  in FIG. 1A. In the second cooling-water passage  35 , cooling water is circulated between a heater core  13  and the fuel cell system  6 . A water pump  5  is provided in the fuel cell system  6  to circulate cooling water in the cooling water circuit  30 . The fuel cell system  6  is temperature-controlled with the cooling water in a temperature area (e.g., 72-80° C.) where the power generation efficiency can be effectively improved in the fuel cell system  6 .  
     [0030] Both of upstream and downstream sides of a radiator  32  are connected to the first cooling-water passage  34 , and a thermostat valve  131  is disposed between the radiator  32  and its upstream connection point with the first cooling-water passage  34 . When a temperature of cooling water flowing in the first cooling-water passage  34  becomes equal to or higher than a predetermined temperature (e.g., 80° C.), the thermostat valve  131  is opened, so that cooling water flows into the radiator  32  to be radiated in the radiator  32 . That is, when the temperature of cooling water flowing in the first cooling-water passage  34  becomes equal to or higher than the predetermined temperature, heat of the fuel cell system  6  is radiated from the radiator  32 . Therefore, the temperature of the fuel cell system  6  is not increased to be higher than the temperature area where power generation efficiency can be effectively increased. A vehicle control unit  8  (vehicle ECU) controls the fuel cell system  6 , the water pump  5 , a blower fan (not shown) of the radiator  32  and the like in accordance with a vehicle running state, an environment condition and the like.  
     [0031] As shown in FIG. 1A, a water pump  61 , an electric heater  60  as an auxiliary heater, and a water temperature sensor  65  are provided between the fuel cell system  6  and the heater core  13  in the second cooling-water passage  35 . The water temperature sensor  65  detects a temperature TW of cooling water flowing into the heater core  13 , and outputs detected temperature information of cooling water to an air-conditioning control unit (A/C ECU)  7 , as shown in FIG. 1B. A switching valve  40  is disposed in the second cooling-water passage  35  to cross both of a downstream side of the heater core  13  and an upstream side of the water pump  61 , as shown in FIG. 1A. The switching valve  40  switches a stream direction of cooling water flowing out of the heater core  13  between a direction toward the fuel cell system  6  and a direction to the water pump  61 . Further, a water temperature sensor  174 , for detecting a temperature TWFC of cooling water flowing out of the fuel cell system  6 , is disposed in the cooling water circuit  30  downstream of the fuel cell system  6 . The water temperature sensor  174  outputs detected temperature information of cooling water to the A/C control unit  7 , as shown in FIG. 13.  
     [0032] On the other hand, an evaporator  12  is disposed in an air duct  20  so as to cross an entire area of the air duct  20 , and cools air blown by a blower (not shown) disposed upstream of the evaporator  12  in the air duct  20 . The heater core  13  is disposed in the air duct  20  downstream of the evaporator  12  so as to cross substantially half of the air duct  20 , and heats cool air after passing through the evaporator  12 . Further, an air mixing damper  21 , for adjusting a temperature of air to be blown into a passenger compartment, is disposed upstream of the heater core  13 . An air temperature sensor  16 , for detecting a temperature TE of cool air blown immediately from the evaporator  12 , is disposed in the air duct  20  between the evaporator  12  and the air mixing damper  21 . The air temperature sensor  16  outputs detected temperature information of the blown air to the A/C control unit  7 .  
     [0033] An electric compressor  15  of a refrigerant cycle compresses refrigerant to be circulated in a refrigerant cycle (not shown). Then, the refrigerant in the refrigerant cycle after being cooled and decompressed is heat-exchanged with the blown air in the evaporator  12 , thereby cooling the blown air. An air-conditioning inverter (A/C inverter)  9  carries electrical current to the electric compressor  15  and the electric heater  60 , based on output signals from the A/C control unit  7 . The air duct  20  has a defroster air outlet, a face air outlet and a foot air outlet, at downstream positions of the heater core  13 . Conditioned air having been thermal-controlled by the evaporator  12  and the heater core  13  is blown from the defroster air outlet to a windshield, is blown from the face air outlet to the upper half body of a passenger, and is blown from the foot air outlet to the foot portion of the passenger. The defroster air outlet, the face air outlet and the foot air outlet are opened and closed by a mode switching damper to set an air outlet mode. Further, an inside-outside air switching damper (not shown), for adjusting an introduction ratio between inside air and outside air, is disposed upstream of the blower.  
     [0034] An inside air temperature sensor  1  detects air temperature in the passenger compartment, and an outside air temperature sensor  2  detects air temperature outside the vehicle. Further, a sunlight sensor  4  detects solar radiation amount entering the passenger compartment. A temperature setting device  10 , for setting a target blowing temperature TAO of air to be blown into the passenger compartment, is disposed on an operation panel  100 . Signals from the sensors  1 ,  2 ,  4  and the temperature setting device  10  are input to the A/C control unit  7 . The A/C control unit  7  calculates a necessary air-conditioning capacity by using predetermined program and map based on signals from the above sensors  1 ,  2 ,  4 ,  16 ,  65 ,  174  and the temperature setting device  10  and the like. Further, the A/C control unit  7  outputs signals for controlling the electric compressor  15 , the switching valve  40 , the electric heater  60 , the water pump  61  and various actuators for driving dampers and the likes. The A/C control unit  7  outputs information about thermal energy and electric energy required for the air conditioner, to the vehicle control unit  8 .  
     [0035] Next, the structure of the switching valve  40  will be described with reference to FIGS. 2A, 2B. The switching valve  40  has a F/C side inlet  41 , a heater-core side outlet  42 , a heater-core side inlet  43  and a F/C side outlet  44 . Cooling water, flowing from the fuel cell system  6 , flows from the F/C side inlet  41  into the switching valve  40 . The cooling water, flowing into the switching valve  40 , flows from the heater-core side outlet  42  toward the heater core  13 . The cooling water, flowing out of the heater core  13 , flows from the heater-core side inlet  43  into the switching valve  40 . The cooling water, flowing from the heater-core side inlet  43  into the switching valve  40 , flows from the F/C side outlet  44  toward the fuel cell system  6 . The switching valve  40  includes a valve body  45  that is movable in an up-down direction in FIGS. 2A, 2B, and the valve body  45  has first and second valve bodies  45   a ,  45   b  at its both ends. Further, the switching valve  40  includes a first valve seat  46  on which the first valve body  45   a  water-tightly contacts, and a second valve seat  47  on which the second valve body  45   b  water-tightly contacts. As shown in FIG. 2A, when no electric current is supplied to the valve body  45 , the valve body  45  is placed at the uppermost position in its movable area. In this case, the first valve body  45   a  water-tightly contacts the first valve seat  46 , and the second valve body  45   b  is separated from the second valve seat  47 . As shown in FIG. 2B, when electric current is supplied to the valve body  45 , the valve body  45  is placed at the lowermost position in its movable area. In this case, the first valve body  45   a  is separated from the first valve seat  46 , and the second valve body  45   b  water-tightly contacts the second valve seat  47 .  
     [0036] The switching valve  40  has therein a first water passage  50 , a second water passage  51  and a third water passage  52 . Cooling water, flowing from the heater-core side inlet  43  into the switching valve  40 , flows to the heater-core side outlet  42  through the first water passage  50 . The cooling water, flowing from the F/C side inlet  41  into the switching valve  40 , flows to the heater-core side outlet  42  through the second water passage  51 . The cooling water, flowing from the heater-core side inlet  43  into the switching valve  40 , flows to the F/C side outlet  44  through the third water passage  52 . The first and second water passages  50 ,  51  are opened and closed by the first and second valve bodies  45   a ,  45   b , respectively, and the third water passage  52  is always opened.  
     [0037] When cooling water circulates in the second cooling-water passage  35  shown in FIG. 1A so as to pass through the fuel cell system  6  and the heater core  13 , the valve body  45  is moved to the uppermost position in its movable area as shown in FIG. 2A. On the other hand, when cooling water circulates in the second cooling-water passage  35  so as to pass through the heater core  13  while bypassing the fuel cell system  6 , the valve body  45  is moved to the lower most position in its movable area as shown in FIG. 2B. The switching valve  40  includes a control device  48  having a solenoid. The valve body  45  is controlled by the control device  48 , and is moved by using electromagnetic force of the solenoid in the up-down direction as shown in FIGS. 2A, 2B. In this control, the valve body  45  is placed at the uppermost position in its movable area when no electrical current is applied to the switching valve  40 , and the valve body  45  is placed at the lowermost position when electrical current is applied to the switching valve  40 .  
     [0038] Accordingly, a first circuit of the present invention is constructed with the second cooling-water passage  35  including the second and third water passages  51 ,  52  of the switching valve  40 . Further, a second circuit of the present invention is constructed with a water passage  35   a  of the second cooling-water passage  35  and the first water passage  50  of the switching valve  40 . Specifically, the water passage  35   a  is provided at a side of the heater core  13  (in the right side in FIG. 1A) with respect to the switching valve  40 .  
     [0039] Next, control operation of the vehicle air conditioner according to the present embodiment will be described with reference to FIGS.  3 - 11 . When the vehicle air conditioner is in an ON state, the A/C control unit  7  performs initialization of various data and the likes at step S 1  in FIG. 3. Next, at step S 2 , the A/C control unit  7  reads various signals from the inside air temperature sensor  1 ,the outside air temperature sensor  2 , the sunlight sensor  4 , the temperature setting device  10 , the temperature sensors  16 ,  65 ,  174  and the like, as shown in FIG. 3. Then, at step S 3 , a target blowing temperature TAO of air to be blown into the passenger compartment is calculated based on the input signals of step S 2 .  
     [0040] Specifically, the target blowing temperature TAO is calculated by using the following formula (1).  
       TAO=Kset×Tset−Kr×Tr−Kam×Tam−Ks×Ts+C    (1)  
     [0041] wherein, Tr is an inside air temperature detected by the inside air temperature sensor  1 , Tam is an outside air temperature detected by the outside air temperature sensor  2 , Ts is a solar radiation amount detected by the sunlight sensor  4 , Tset is a set temperature set by the temperature setting device  4 , Kset, Kr, Kam and Ks are gain values, and C is a correction constant.  
     [0042] At step S 4 , a blower level, that is, an amount of air blown by the blower (not shown) is determined based on the calculated TAO as shown in FIG. 7, and an air outlet mode is determined based on the calculated TAO. At steps S 5 , S 6 , as shown in FIG. 8, an operation mode is determined based on the calculated TAO and a temperature TIN of air sucked into the air duct  20  of the air conditioner. Specifically, at step S 5 , it is determined whether or not the operation mode is a cooling mode, by using the relationship shown in FIG. 8, based on a difference between the target blowing temperature TAO and the air suction temperature TIN. When it is determined at step S 5  that the operation mode is the cooling mode, the control program proceeds to step S 7  shown in FIG. 4. When it is determined at step S 5  that the cooling mode is not set, it is determined at step S 6  by using the relationship shown in FIG. 8 whether or not the operation mode is a dehumidifying mode. When it is determined at step S 6  that the dehumidifying mode is set, the control program proceeds to step S 21  shown in FIG. 5. When it is determined at step S 6  that the dehumidifying mode is not set, it is determined that a heating mode is set, and the control program proceeds to step S 35  shown in FIG. 6.  
     [0043] When it is determined at step S 5  that the cooling mode is set, the control program proceeds to step S 7 . At step S 7  in FIG. 4, it is determined whether the unnecessary waste heat of the fuel cell system  6  is permitted to be used. Specifically, the A/C control unit  7  outputs a waste-heat requirement signal to the vehicle control unit  8 , and receives a waste-heat permission signal from the vehicle control unit  8 . When the waste-heat usage is permitted, that is, when the waste heat from the fuel cell system  6  is in a usable state, it is determined whether or not a cooling water temperature TWFC detected by the temperature sensor  174  is higher than a cooling water temperature TWout flowing from the heater core  13 . When the cooling water temperature TWFC detected by the temperature sensor  174  is higher than the cooling water temperature Twout flowing from the heater core  13 , it is determined that the waste heat of the fuel cell system  6  is in the usable state.  
     [0044] In the present embodiment, since a temperature sensor for detecting the cooling water temperature TWout flowing from the heater core  13  is not provided, the A/C control unit  7  estimates the cooling water temperature TWout based on other detection values. The temperature TWout can be estimated based on a cooling water temperature TW flowing into the heater core  13 , detected by the temperature sensor  65 , and heat radiation capacity in the heater core  13 . In the present embodiment, the cooling water temperature TWout is estimated based on the cooling water temperature TW detected by the water temperature sensor  65 , an air temperature TE (i.e., air temperature to flow into the heater core  13 ) blown from the evaporator  12 , a cooling water flow amount passing through the heater core  13  and an air flow amount passing through the heater core  13 . As shown in FIG. 9A, when the cooling water flow amount and the air flow amount passing through the heater core  13  are constant, a relationship between a temperature difference (TW−TE) and a reducing temperature T1 of cooling water while passing through the heater core  13  is linear as shown in FIG. 9A. This relationship has been found by the present inventors. When the cooling water flow amount and the air flow amount change, a gradient of this linear relationship is changed. Therefore, the cooling water temperature TWout flowing out of the heater core  13  can be readily estimated, based on the cooling water temperature TW flowing into the heater core  13 , the air temperature TE from the evaporator  12 , the cooling water amount passing through the heater core  13  and the air amount passing through the heater core  13 .  
     [0045] By using the cooling water temperature TWout estimated in this way, it is determined whether or not the cooling water temperature TWFC detected by the water temperature sensor  174  is higher than the cooling water temperature TWout. Specifically, as shown in FIG. 9B, hysteresis is provided in a change direction of the temperature difference of (TWFC−TWout), and the waste heat using state is switched in accordance with the temperature difference of (TWFC−TWout). At step S 7 , when the waste heat usage is permitted by the vehicle control unit  8 , and when it is determined that the cooling water temperature TWFC of the fuel cell system  6  is higher than the cooling water temperature Twout flowing out of the heater core  13 , it is determined that the waste heat of the fuel cell system  6  can be used. Then, no electrical current is applied to the switching valve (SW valve)  40  at step S 8 , and the water pump (W/P)  61  is driven at step S 9 .  
     [0046] Then, at step S 10 , a target air temperature TEO blown out of the evaporator  12  is calculated. Specifically, as shown in FIG. 10, the target air temperature TEO blown out of the evaporator  12  is calculated in accordance with the outside air temperature Tam to perform dehumidification and the like. At step S 11 , a target opening degree SW of the air mixing damper  21  is calculated. Specifically, the target opening degree SW is calculated by using the following formula (2).  
       SW =( TAO−TE )/( TW−TE )×100%   (2)  
     [0047] Wherein, TE is the detected temperature of air flowing from the evaporator  12 , TW is the detected temperature of water flowing into the heater core  13 , and TAO is the target blowing temperature of air to be blown into the passenger compartment.  
     [0048] At step S 12 , the air mixing damper (A/M damper)  21  is driven so that its opening degree is set at the calculated target opening degree SW.  
     [0049] When it is determined at step S 7  that the waste heat usage is not permitted by the vehicle control unit  8 , or when it is determined that the cooling water temperature TWFC is equal to or lower than the cooling water temperature TWout, that is, when it is determined that the waste heat of the fuel cell system  6  cannot be used, no electrical current is applied to the switching valve  40  at step S 13 , and the operation of the water pump  61  is stopped at step S 14 . Then, at step S 15 , the target air temperature TEO blown out of the evaporator  12  is calculated, and the target blowing temperature TAO is set at the target air temperature TEO. At step S 16 , the air mixing damper (A/M damper)  21  is operated to its maximum cooling position.  
     [0050] After step S 12  is performed, or after step S 16  is performed based on the target air temperature TEO calculated at step S 10 , a target rotational speed IVO of the electric compressor  15  is calculated at step S 17 . Then, at step S 18 , the A/C control unit  7  transmits an electric-energy requirement signal, indicating electric energy required by the air conditioner, to the vehicle control unit  8 . At step S 19 , the A/C control unit  7  receives an electric-energy permission signal, indicating electric energy usable in the air conditioner, from the vehicle control unit  8 . At step S 20 , the electric compressor  15  is driven by the A/C control unit  7  through the A/C inverter  9  so that the rotational speed of the electric compressor  15  approaches the target rotational speed IVO, calculated at step S 17 . Then, the control program returns to step S 2  shown in FIG. 3.  
     [0051] When it is determined at step S 6  that the dehumidifying mode is set, the control program proceeds to step S 21  shown in FIG. 5, where a target water temperature TWO (e.g., 50° C. at step S 21 ) of cooling water to flow into the heater core  13  is calculated. Then, the target air temperature TEO blown from the evaporator  12  is calculated at step S 22 , and the target opening degree SW of the air mixing damper  21  is calculated by using the formula (2) at step S 23 . At step S 24 , the air mixing damper  21  is driven so that its opening degree approaches the target opening degree SW. Then, at step S 25 , it is determined whether the waste heat usage is permitted by the vehicle control unit  8  as in step S 7 . When it is determined at step S 25  that the waste heat usage is permitted, no electric current is applied to the switching valve  40  at step S 26 . On the other hand, when it is determined at step S 25  that the waste heat usage is not permitted, electrical current is applied to the switching valve  40  at step S 27 .  
     [0052] After one of steps S 26 , S 27  is performed, the water pump  61  is driven at step S 28 . Then, at step S 29 , a target heater power IHO to be supplied to the electric heater  60  is calculated based on the target water temperature TWO calculated at step S 21  and the cooling water temperature TWFC detected by the temperature sensor  174 . At step S 30 , the target rotational speed IVO of the electric compressor  15  is calculated based on the target air temperature TEO calculated at step S 22 . Then, the A/C control unit  7  transmits the electric-energy requirement signal to the vehicle control unit  8  at step S 31 , and receives the electric-energy permission signal from the vehicle control unit  8 , at step S 32 .  
     [0053] At step S 33 , electric power is supplied to the electric heater  60  through the A/C inverter  9  so that the target heater power IHO calculated at step S 29  is supplied to the electric heater  60  in the permitted electric energy. Further, at step S 34 , the electric compressor  15  is driven so that its rotational speed becomes the target rotational speed IVO calculated at step S 30  in the permitted electric energy. When both target values IHO, IVO cannot be satisfied in the permitted electric energy, the electric compressor  15  is driven in preference to the electric heater  60 , and electric current supplied to the electric heater  60  is adjusted based on the consumed electric power in the compressor  15  and the permitted electric energy. That is, the control at steps S 33 , S 34  is performed so that a dehumidifying operation is considered in preference to an air temperature controlling operation. Thereafter, the control program returns to step S 2  shown in FIG. 3.  
     [0054] When it is determined at step S 6  that the dehumidifying mode is not set, that is, that the heating mode is set, the control program proceeds to step S 35  shown in FIG. 6. The target water temperature TWO is calculated at step S 35 , and the target air temperature TEO blown from the evaporator  12  is calculated at step S 36 . Specifically, at step S 35 , the target water temperature TWO is calculated by using the following formula (3) based on a control value Φ that is set in accordance with an air flow amount from the air outlet, as shown in FIG. 11.  
       TWO =( TAO−TE )/Φ+ TE    (3)  
     [0055] At step S 36 , the target air temperature TEO is set at 10° C. when the outside air temperature Tam is higher than 10° C., and the target air temperature TEO is set at a higher temperature among the outside air temperature Tam and 5° C., when the outside air temperature Tam is equal to or lower than 10° C. Then, as in step S 7 , it is determined at step S 37  whether the waste heat usage is permitted by the vehicle control unit  8 . When it is determined at step S 37  that the waste heat usage is permitted by the vehicle control unit  8 , no electric current is carried to the switching valve  40  at step S 38 , and the water pump  61  is driven at step S 39 . Then, it is determined at step S 40  whether the cooling water temperature TWFC detected by the temperature sensor  174  is higher than the target water temperature TWO calculated at step S 35  or not. When it is determined at step S 40  that the cooling water temperature TWFC is higher than the target water temperature TWO, the target opening degree SW of the air mixing damper  21  is calculated by using the formula (2) at step S 41 . At step S 42 , the air mixing damper is driven so that its opening degree becomes the target opening degree SW. At step S 43 , the target rotational speed IVO of the electric compressor  15  is calculated based on the target air temperature TEO calculated at step S 36 .  
     [0056] Then, the A/C control unit  7  transmits the electric-energy requirement signal to the vehicle control unit  8  at step S 44 , and receives the electric-energy permission signal from the vehicle control unit  8  at step S 45 . At step S 46 , the electric compressor  15  is driven through the A/C inverter  9  so that its rotational speed approaches the target rotational speed IVO calculated at step S 43  in the permitted electric energy. Thereafter, the control step returns to step S 2  shown in FIG. 3. When it is determined at step S 37  that the waste heat usage is not permitted by the vehicle control unit  8 , electrical current is applied to the switching valve at step S 47 , and the water pump  61  is driven at step S 48 . Alternatively, when it is determined at step S 40  that the cooling water temperature TWFC is equal to or lower than the target water temperature TWO, the air mixing damper  21  is operated so that its opening degree is in a maximum heating state (maxhot) at step S 49 .  
     [0057] Then, at step S 50 , the target heater power IHO is calculated based on the target water temperature TWO calculated at step S 35  and the cooling water temperature TWFC detected by the temperature sensor  174 . At step S 51 , the target rotational speed IVO is calculated based on the target air temperature TEO calculated at step S 36 . Then, the A/C control unit  7  transmits the electric-energy requirement signal to the vehicle control unit  8  at step S 52 , and receives the electric-energy permission signal from the vehicle control unit  8  at step S 53 . At step S 54 , electric current is applied to the electric heater  60  through the A/C inverter  9  so that the target heater power IHO is applied thereto in the permitted electric energy. Then, at step S 55 , the electric compressor  15  is driven so that its rotational speed becomes the target rotational speed IVO in the permitted electric energy. When both of the target values IHO, IVO cannot be satisfied in the permitted electric energy, the electric compressor  15  is driven in preference to the electric heater  60 , and the electric current carried to the electric heater  60  is adjusted. Thereafter, the control program returns to step S 2  shown in FIG. 3.  
     [0058] In this embodiment, in a case where the blown air is required to be heated by the heater core  13 , when the waste heat of the fuel cell system  6  is in the usable state and when the cooling water temperature TWFC detected by the temperature sensor  174  is higher than the cooling water temperature TWout from the heater core  13 , no electric current is applied to the switching valve  40 , thereby forming the cooling water circuit where cooling water is circulated from the heater core  13  into the fuel cell system  6 . That is, when the cooling water temperature Twout from the heater core  13  is lower than the cooling water temperature TWFC from the fuel cell system  6 , cooling water circulates between the heater core  13  and the fuel cell system  6 . Accordingly, cooling water from the heater core  13  can be heated by the fuel cell system  6  having a temperature higher than the cooling water from the heater core  13 , and is circulated to the heater core  13 . In this way, the heater core  13  effectively uses thermal energy which is unnecessary in the fuel cell system  6 .  
     [0059] In the present embodiment, the electric heater  60  as the auxiliary heater is provided upstream of the heater core  13  in the second cooling-water passage  35  in a water flow direction. Therefore, even when unnecessary thermal energy from the fuel cell system  6  is small, the electric heater  60  can heat cooling water before flowing into the heater core  13 . In the present embodiment, because the electric heater  60  is provided upstream of the heater core  13  in the second cooling-water passage  35 , a cooling water temperature flowing into the fuel cell system  6  can be readily reduced as compared with a case where the electric heater  60  is provided downstream of the heater core  13 . Therefore, the thermal energy, which is unnecessary in the fuel cell system  6 , can be further effectively used. Further, even when the switching valve  40  forms a closed circuit (corresponding to the second circuit in the present invention) where cooling water is not circulated to the fuel cell system  6 , the electric heater  60  can heat cooling water before flowing into the heater core  13 . In the present embodiment, the cooling water temperature TWout flowing out of the heater core  13  is calculated based on the cooling water temperature flowing into the heater core  13 , the cooling water amount passing through the heater core  13 , the air temperature TE flowing into the heater core  13  and the air flow amount passing through the heater core  13 . Therefore, a temperature sensor, for directly detecting the cooling water temperature Twout flowing out of the heater core  13 , is not required to be provided.  
     [0060] Although the present invention has been fully described in connection with the preferred embodiment thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications will become apparent to those skilled in the art.  
     [0061] For example, in the above-described embodiment, the cooling water temperature TWout flowing from the heater core  13  is calculated and estimated. For example, a temperature sensor  165 , for directly detecting the cooling water temperature TWout, may be provided downstream of the heater core  13  in the second cooling-water passage  35  as shown in FIG. 12. In this case, the cooling water temperature TWout can be more accurately detected.  
     [0062] In the above-described embodiment, the A/C control unit  7  calculates and estimates the cooling water temperature TWout based on the cooling water temperature TW to flow into the heater core  13 , the cooling water flow amount passing through the heater core  13 , the air temperature TE flowing from the evaporator  12  into the heater core  13 , and the air flow amount passing through the heater core  13 . Then, the switching control of the switching valve  40  is performed by using the calculated TWout. However, the switching control is not limited to this manner. For example, as shown by a slant line in FIG. 13, a limit value of a rising temperature Δt of the cooling water heated by the electric heater  60 , in which the TWFC becomes the TWout, is obtained based on the cooling water temperature TWFC, the air temperature TE, the cooling water flow amount and the like. The switching control of the switching valve  40  can be performed based on the limit value (limit line). Specifically, when the rising temperature Δt becomes a value lower than the limit line in FIG. 13 by 2° C., the switching valve  40  is switched to a state shown in FIG. 2A. When the rising temperature Δt becomes a value lower than the limit line in FIG. 13 by 1° C., the switching valve  40  is switched to a state shown in FIG. 2B. Preferably, this switching control is performed with a hysteresis.  
     [0063] In the above embodiment, the electric heater  60  as the auxiliary heater is provided in the second cooling-water passage  35 . However,the electric heater  60  may be provided at a downstream air side of the heater core so as to directly heat the blown air. In the above embodiment, when it is determined that the waste heat of the fuel cell system  6  is in the using state (usable state), the water pump  61  is controlled to be driven at steps S 9 , S 28 , S 39 . However, when cooling water can be suitably circulated in the second cooling-water passage  35  by operation of the water pump  5  at the vehicle side, the water pump  61  may be not required to be driven.  
     [0064] Further, for example, a three-way valve, or two two-way valves may be adopted to switch the cooling water circuit between the first circuit and the second circuit, without being limited to the switching valve  40  in the above embodiment. Further, the energization control to the electric heater  60  may be performed by an electromagnetic relay and the like, without being limited to the A/C inverter  9  in the above embodiment. Further, plural electric heaters may be used as the electric heater  60  in the second cooling-water passage  35  without being limited to the single electric heater  60  in the above embodiment. In this way, a peak current carried to the plural electric heaters can be reduced. Further, a real value such as 72° C. and 80° C. in the above embodiment is shown as an example, but can be suitably set in accordance with characteristics of the fuel cell system  6  and the likes.  
     [0065] Such changes and modifications are to be understood as being within the scope of the present invention as defined by the appended claims.