JP2006010115A - Hot water supply system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the generation of large undershoot and to prevent the hot water from staying in a hot water storage tank for a long time in a hot water supply system having the hot water storage tank, a mixing valve and an auxiliary heat source. <P>SOLUTION: This exhaust heat recovering hot water supply system comprises an exhaust heat source 11, a heat exchanger 12, the hot water storage tank 20, the mixing valve 30 for mixing the hot water from the hot water storage tank 20 with the water in a water supply passage 50, and a gas water heater 40 (auxiliary heat source). A tank temperature sensor 86 is mounted on a lower position separated from a top end of the hot water storage tank 20 by a specific distance. A control means 70 controls a tapping temperature to remain an intermediate transition layer Wb in the hot water storage tank 20 by using the tank temperature sensor 86, and prevents the undershoot. Further the intermediate transition layer Wb can be diluted by supplying the hot water from the heat exchanger 12 to a side part of the hot water storage tank 20 by switching and controlling a three-way valve 90. When a detection temperature of a tank temperature sensor 87 rises to a threshold value, the three-way valve 90 is switched to supply the hot water of the heat exchanger 12 to a top part of the hot water storage tank 20. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a hot water supply system that uses heat generated from an exhaust heat source (heat generation source) such as a fuel cell, a gas engine, or a solar as heat energy for hot water supply.

  In recent years, an exhaust heat recovery hot water supply system has been developed as a cogeneration system for homes and small-scale offices. This system generates power with a small generator such as a fuel cell, gas engine, solar, etc., and recovers exhaust heat generated by this generator and supplies it to hot water supply, so that energy can be used effectively It is expected to spread.

  As shown in Patent Document 1, an exhaust heat recovery hot water supply system including an exhaust heat source, a heat exchanger, a hot water storage tank, a mixing valve, an auxiliary heat source, and a control means for controlling the mixing valve and the auxiliary heat source. Is known. Also, a hot water supply system having the same components as in Patent Document 1 but having a different arrangement of the mixing valve and the auxiliary heat source is also known. Hereinafter, this latter hot water supply system will be described in detail.

  In the known hot water supply system, the heat exchanger receives heat from the exhaust heat source (heat generation source), heats the water from the bottom of the hot water storage tank with this heat exchanger, and supplies it to the top of the hot water storage tank. It has become. The bottom end of the hot water storage tank is connected to the downstream end of the water supply channel to apply a water supply pressure to the hot water storage tank. The top end of the hot water storage tank is connected to the upstream end of the hot water supply passage. When the hot water tap provided at the downstream end of the hot water supply passage is opened, the hot water in the hot water storage tank is discharged. A mixing valve that mixes hot water from the hot water storage tank with water in the water supply channel and a gas water heater (auxiliary heat source) on the downstream side thereof are provided in the middle of the water supply channel. The control means controls the mixing valve and the gas water heater to discharge hot water having a set temperature.

  The operation of the known hot water supply system will be described. In the hot water storage tank, there is almost no convection, and hot water of the same temperature forms a layer and forms a temperature gradient that decreases from the top to the bottom. More specifically, as shown in FIG. 5, it roughly comprises an upper high temperature layer Wa, an intermediate transition layer Wb, and a lower low temperature layer Wc. Since the hot water temperature from the heat exchanger is substantially constant, the high temperature layer Wa is maintained at a constant temperature Ta (for example, 60 ° C.). The temperature Tc of the low temperature layer Wc is the same as the water supply temperature (for example, 15 ° C.). The intermediate transition layer Wb has a steep temperature gradient from the temperature Ta to Tc.

  In order to make effective use of exhaust heat, the control means basically controls the mixing valve to set the mixing temperature to the set temperature, and stops the gas water heater. In a situation where the hot water temperature cannot be set to the set temperature only by controlling the mixing valve, combustion of the gas water heater is executed to maintain the hot water temperature at the set temperature. Details will be described below.

  When hot water of the high temperature layer Wa is present at the top of the hot water storage tank, as shown in FIG. 6, the temperature Tin of the hot water supplied from the hot water storage tank to the mixing valve (hereinafter referred to as inlet temperature) becomes high temperature Ta. ing. At this time, the mixing valve mixes the hot water from the hot water storage tank with the water from the water supply channel, and the temperature Tmix (hereinafter referred to as the outlet side temperature or mixing temperature) of the hot water coming out of the mixing valve is maintained at the set temperature Ts. The As described above, the high temperature layer Wa has a substantially constant temperature Ta and the feed water temperature Tc is also stable, so that the ratio of hot water from the hot water storage tank is maintained substantially constant. Refer to the period before time t1 'in FIG.

  In the mixing valve used here, the opening on the tank side and the opening on the water supply side are such that when one increases, the other decreases, and the tank side opening indicates the ratio of hot water from the hot water storage tank. There is a one-to-one correspondence. When the tank side opening is fully open, the water supply side opening is fully closed, the ratio of hot water on the hot water storage tank side is 100%, and the ratio of water on the water supply side is 0%. When the tank side opening is fully closed, the water supply side opening is fully open, the ratio of hot water on the hot water storage tank side is 0%, and the ratio of water on the water supply side is 100%. The same applies to a mixing valve used in an embodiment of the present invention described later.

  The hot water of the intermediate transition layer Wb is supplied to the mixing valve from the time when the hot water of the high temperature layer Wa runs out of the hot water storage tank (time point t1 '). Accordingly, the inlet side temperature Tin starts to decrease, and in response to this, the mixing valve increases the tank side opening degree in order to maintain the mixing temperature Tmix at the set temperature Ts. Refer to the period from time t1 'to t2' in FIG.

At the time point t2 ′ when the inlet side temperature Tin decreases and reaches a threshold value (for example, a temperature higher than the set temperature Ts by a predetermined temperature, for example, 2 ° C.), the tank side opening of the mixing valve is rapidly decreased, and at the same time. Ignite the gas water heater and start combustion. The gas water heater can continue combustion only with a minimum supply heat amount to ensure stable combustion, but performs this minimum combustion. The tank side opening of the mixing valve is determined in consideration of the minimum amount of heat supplied by the gas water heater. That is, the opening degree is determined so that the mixing temperature Tmix satisfies the following equation when the minimum amount of heat supplied is Qmin.
Tmix = Ts−Qmin / F (1)
However, F is the flow volume which flows through a water heater.
Therefore, at the ignition time T2 ′, the mixing temperature Tmix is lower than the set temperature Tin by a temperature difference ΔT = Qmin / F. This temperature difference ΔT corresponds to the temperature rise obtained by the minimum combustion of the gas water heater.

  After the ignition time t2 ', the mixing temperature Tmix is maintained at a temperature lower than the set temperature Ts by a temperature difference ΔT by controlling the opening of the mixing valve. Since the temperature of hot water entering the gas water heater, that is, the mixing temperature Tmix is stable in this manner, the temperature control of the hot water by the combustion of the gas water heater can be performed stably.

  As described above, after the ignition time t2 ′, the mixing valve maintains the mixing temperature Tmix obtained by the above equation (1) while the gas water heater is performing the combustion with the minimum amount of heat. Controlled. Since the mixing temperature Tmix in the formula (1) is constant unless the hot water tap is operated or the set temperature Ts is changed, the tank side opening of the mixing valve is reduced in the situation where the inlet temperature Tin is lowered as described above. It will increase. Refer to the period from time t2 'to t3' in FIG.

If the hot water is further continued, the opening of the mixing valve on the tank side continues to increase to satisfy the above formula (1), reaches the full opening at time t3 ′, and thereafter, the opening of the mixing valve on the tank side opens fully. Maintained. The inlet side temperature Tin rapidly decreases in accordance with the temperature gradient of the intermediate transition layer Wb in the hot water storage tank. However, when the opening of the mixing valve on the tank side is fully opened as described above, this temperature decrease is alleviated. It appears as the mixing temperature Tmix as it is. Therefore, in the gas water heater, from the minimum supply heat amount, the supply heat amount is rapidly increased to compensate for the rapid temperature drop of the entry side temperature Tin, and the hot water temperature is maintained at the set temperature Ts. When the hot water is further continued, the inlet side temperature Tin coincides with the feed water temperature Tc and becomes substantially constant. In this situation, the opening of the mixing valve on the tank side is maintained fully open, and the amount of heat supplied to the gas water heater is substantially constant.
JP 2002-364918 A

  However, in the known hot water supply system, since the mixing temperature Tmix, that is, the temperature of hot water entering the gas water heater, rapidly decreases from the time t3 ′ when the opening of the mixing valve on the tank side is fully opened, the gas water heater is However, even if the amount of heat supplied is increased in response to this, there is a drawback that a large undershoot is generated in time. Refer to the tapping temperature after t3 'in FIG.

The present invention has been made to solve the above problems,
(A) a heat generation source;
(B) a heat exchanger that receives heat from the heat generation source;
(C) a hot water storage tank;
(D) a circulation path for circulating water from the bottom of the hot water storage tank to the hot water storage tank through a heat exchanger;
(E) a water supply channel whose downstream end is connected to the bottom of the hot water storage tank;
(F) a hot water supply path whose upstream end is connected to the top of the hot water storage tank;
(G) a mixing valve which is provided in the middle of the hot water supply channel and mixes hot water from the hot water storage tank and water of the water supply channel;
(H) an auxiliary heat source provided on the downstream side of the mixing valve in the hot water supply path;
(I) control means for discharging hot water at a set temperature from the downstream end of the hot water supply path by controlling the mixing valve and the auxiliary heat source;
In the hot water supply system with
The circulation path is branched into a first branch path from the heat exchanger to the top of the hot water storage tank and a second branch path to the side of the hot water storage tank below the first branch path, and the intersection of the first and second branch paths. Switching valve means is provided in the section,
In the hot water storage tank, a high temperature layer made of high temperature hot water from a heat exchanger, a low temperature layer made of water having a feed water temperature, and an intermediate transition layer having a temperature gradient are stored.
The control means controls the mixing valve and the auxiliary heat source so as to leave hot water of the intermediate transition layer in the hot water storage tank, and maintains the hot water temperature at a set temperature,
Further, the control means sets the switching valve means to a first state in which the hot water from the heat exchanger is normally supplied only to the top of the hot water storage tank via the first branch passage, and the heat exchange is performed as necessary. In the second state, at least part of hot water from the vessel is supplied to the second branch passage.

In the above configuration, the hot water of the intermediate transition layer is controlled so that it remains in the hot water storage tank without being supplied to the mixing valve, thereby preventing a sudden drop in the hot water from the mixing valve and avoiding an undershoot of the tapping temperature. Can do.
In the above control, when the hot water from the heat exchanger is replenished to the top of the hot water storage tank, the intermediate transition layer moves downward. At the time of re-heating, only this hot water is supplied to the mixing valve, and the intermediate transition layer remains. By repeating this, hot water in the intermediate transition layer may stay in the hot water storage tank for a long time. Therefore, the switching valve means is operated to supply hot hot water from the heat exchanger to the side of the hot water storage tank via the second branch path, thereby causing convection in the hot water storage tank. As a result, it is possible to avoid a relatively narrow intermediate transition layer from being diffused and diluted in a wide area and staying in the hot water storage tank for a long time.

(A) a heat generation source;
(B) a heat exchanger that receives heat from the heat generation source;
(C) a hot water storage tank;
(D) a circulation path for circulating water from the bottom of the hot water storage tank to the hot water storage tank through a heat exchanger;
(E) a water supply channel whose downstream end is connected to the bottom of the hot water storage tank;
(F) a hot water supply path whose upstream end is connected to the top of the hot water storage tank;
(G) a mixing valve which is provided in the middle of the hot water supply channel and mixes hot water from the hot water storage tank and water of the water supply channel;
(H) an auxiliary heat source provided on the downstream side of the mixing valve in the hot water supply path;
(I) control means for discharging hot water at a set temperature from the downstream end of the hot water supply path by controlling the mixing valve and the auxiliary heat source;
In the hot water supply system with
A tank temperature sensor for measuring the temperature of the hot water in the hot water storage tank is provided at a position below a predetermined distance from the top end of the hot water storage tank, and the circulation path is a first branch path from the heat exchanger to the top of the hot water storage tank. Branched to a second branch path toward the side of the lower hot water storage tank, and switching valve means is provided at the intersection of these first and second branch paths,
The control means includes
(A) In the situation where the detected temperature of the tank temperature sensor is higher than the threshold value, the temperature of the mixed hot water from the mixing valve is maintained at the set temperature by controlling the mixing valve while the auxiliary heat source is stopped.
(B) When the detected temperature decreases and reaches a threshold value, the auxiliary heat source is started to supply a minimum amount of heat, and the hot water from the hot water storage tank is supplied in response to the minimum amount of heat supply. By controlling the mixing valve to reduce the rate, the tapping temperature is maintained at the set temperature,
(C) The ratio of hot water from the hot water storage tank by the mixing valve is gradually reduced from the value reduced at the start of operation of the auxiliary heat source to substantially zero, and the temperature of the mixed hot water from the mixing valve is reduced. Compensating by increasing the amount of heat supplied from the auxiliary heat source, maintaining the tapping temperature at the set temperature,
(D) The switching valve means is normally set to a first state in which hot water from the heat exchanger is supplied only to the top of the hot water storage tank via the first branch passage, and the mixing valve is used to supply hot water from the hot water storage tank. After the ratio is substantially zero, the second state in which at least a part of the hot water from the heat exchanger is supplied to the second branch path is set.

In the above configuration, after the operation of the auxiliary heat source is started, the ratio of hot water from the hot water storage tank by the mixing valve is gradually reduced, the temperature of the hot water from the mixing valve is gradually brought closer to the water supply temperature, and the amount of heat supplied from the auxiliary heat source is gradually increased. By increasing and compensating for the drop in the temperature of the hot water from the mixing valve, the hot water temperature is maintained at the set temperature. In this way, the temperature of the mixed hot water generated after the mixing valve has made the ratio of hot water from the hot water storage tank 100% as in the known hot water supply system does not occur, and a large undershoot occurs in the tapping temperature. Can be avoided.
In the above control, the hot water in the intermediate transition layer remains in the hot water storage tank without being supplied to the mixing valve. When hot water from the heat exchanger is replenished to the top of the hot water storage tank, this intermediate transition layer moves downward. At the time of re-heating, only this hot water is supplied to the mixing valve, and the intermediate transition layer remains. By repeating this, hot water in the intermediate transition layer may stay in the hot water storage tank for a long time. Therefore, after the ratio of hot water from the hot water storage tank is made substantially zero by the mixing valve as described above, the switching valve means is operated to supply hot hot water from the heat exchanger via the second branch passage. Supply to the side of the tank to cause convection in the hot water storage tank. As a result, it is possible to avoid a relatively narrow intermediate transition layer from being diffused and diluted in a wide area and staying in the hot water storage tank for a long time.

Preferably, the control for gradually reducing the ratio of the hot water from the hot water storage tank is a control of a mixing valve that manages the temperature of the mixed hot water and gradually lowers the temperature of the mixed hot water over time. As a result, the temperature of the mixed hot water, that is, the temperature of the hot water supplied to the auxiliary heat source can be managed without being affected by the amount of the hot water, so that stable control of the amount of heat supplied by the auxiliary heat source can be ensured, and the hot water temperature can be further stabilized. Can be
Preferably, the control means controls the mixing valve so as to maintain the temperature of the mixed hot water after the ratio of hot water in the hot water storage tank by the mixing valve is reduced at the start of operation of the auxiliary heat source, and the mixed hot water. The mixing valve is controlled so as to gradually lower the temperature of the mixed hot water when the temperature of the water reaches the temperature detected by the tank temperature sensor. Thereby, stable control of the auxiliary heat source immediately after the operation of the auxiliary heat source can be secured, and the tapping temperature can be further stabilized.
Preferably, an electromagnetic on-off valve is provided on the upstream side of the mixing valve in the hot water supply path, and the control means has the electromagnetic on-off valve when the mixing valve makes the ratio of hot water from the hot water storage tank substantially zero. Close. Thereby, the supply of hot water from the hot water storage tank to the auxiliary heat source can be reliably shut off.

In one aspect, the switching valve means is a three-way valve, and the second state is a state in which hot water from the heat exchanger is supplied only to the second branch passage. In this case, the dilution effect can be maximized and the structure is simple.
In another aspect, the switching valve means is another mixing valve, and the second state is a state in which hot water from the heat exchanger is supplied to both the first and second branch paths. In this case, the above-described dilution effect can be obtained, and it is possible to quickly reach a state where the hot water in the hot water storage tank can be supplied to the mixing valve, and the heat energy from the heat exchanger can be effectively utilized.

Preferably, the hot water storage tank includes another tank temperature sensor that measures the temperature of hot water in the hot water storage tank below the tank temperature sensor, and the temperature detected by the other temperature sensor is lower than the threshold value. When the threshold value is exceeded, the control means returns the switching valve means from the second state to the first state. Thereby, it can be detected that the staying layer has been sufficiently diluted, and the heat energy from the heat exchanger can be effectively utilized by switching to supplying the hot water from the heat exchanger to the top of the hot water storage tank.
Preferably, the heat generation source is an exhaust heat source, and the auxiliary heat source is a gas water heater. Thereby, thermal energy can be used effectively.

  According to the present invention, in a hot water supply system having a mixing valve for mixing hot water from a hot water storage tank and water in a water supply channel and an auxiliary heat source downstream thereof, it is possible to avoid occurrence of a large undershoot in the hot water temperature. it can. Moreover, it is possible to avoid the staying layer from remaining in the hot water storage tank for a long time.

  Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. As shown in FIG. 1, the hot water supply system includes a generator 10 such as a fuel cell, a hot water storage tank 20, a mixing valve 30, and a gas water heater 40 (auxiliary heat source) as main components.

  The generator 10 is unitized in a housing 10a with an exhaust heat source 11 (heat generation source), a heat exchanger 12, a heat medium circulation path 13, and two pumps 14 and 15. . The heat medium circulation path 13 passes through the exhaust heat source 11 and the heat exchanger 12, and the heat medium (for example, water) is driven by the pump 14 provided in the heat medium circulation path 13 so that the heat medium (for example, water). Circulates between and.

  A water circulation path 25 is connected between the bottom wall 20 a (bottom end) and the top wall 20 b (top end) of the hot water storage tank 20. The water circulation path 25 passes through the heat exchanger 12, and the water at the bottom end 20 a of the hot water storage tank 20 passes through the heat exchanger 12 by the driving of the pump 15 provided in the water circulation path 25. Hot water is received from the heat medium flowing through the heat exchanger 12 and is supplied to the top end 20 b of the hot water storage tank 20. In the present specification, the bottom of the hot water storage tank 20 refers to the bottom wall 20a or the vicinity thereof, and the top refers to the top wall 20b or the vicinity thereof.

  As described above, there is almost no convection in the hot water storage tank 20, and it has an upper high temperature layer Wa, an intermediate transition layer Wb, and a lower low temperature layer Wc. Since the hot water temperature from the heat exchanger 12 is substantially constant, the high temperature layer Wa is maintained at a constant temperature Ta (for example, 60 ° C.). The temperature Tc of the low temperature layer Wc is the same as the water supply temperature (for example, 15 ° C.). The intermediate transition layer Wb has a steep temperature gradient from the temperature Ta to Tc.

  The bottom wall 20a of the hot water storage tank 20 is connected to the downstream end of the water supply channel 50 so that a constant water supply pressure is applied. An upstream end of the hot water supply path 60 is connected to the top wall 20 b of the hot water storage tank 20, and a hot water supply tap 61 is provided at the downstream end of the hot water supply path 60. When the hot water tap 61 is opened, the hot water stored in the hot water storage tank 20 receives the above-mentioned water supply pressure and is discharged from the hot water tap 61.

  The hot water supply path 60 is provided with the mixing valve 30 and the hot water heater 40 in order from the upstream side to the downstream side. The mixing valve 30 adjusts the mixing ratio of hot water that has passed through the hot water supply path 60 from the hot water storage tank 20 and water from the branch portion 51 of the water supply path 50. An electromagnetic opening / closing valve 35 is provided on the upstream side of the mixing valve 30 in the hot water supply path 60.

  The gas water heater 40 includes a gas combustion unit 41 and a heat exchanger 42 positioned thereon, and the hot water supply path 60 passes through the heat exchanger 42, and hot water or water in the hot water supply path 60 is supplied. When passing through the heat exchanger 42, the combustion heat in the gas combustion section 41 is received.

  The hot water supply system further includes a control unit 70 (control means) and various sensors. More specifically, an inlet-side temperature sensor 81 that detects the temperature of hot water entering the mixing valve 30 from the hot water storage tank 20 is provided upstream of the mixing valve 30 and downstream of the electromagnetic opening / closing valve 35. In addition, a water supply temperature sensor 82 that detects a water supply temperature is provided at the branch portion 51 of the water supply passage 50 located on the upstream side of the mixing valve 30.

  A mixing temperature sensor 83 that detects the temperature of the hot water mixed by the mixing valve 30 is provided downstream of the mixing valve 30 and upstream of the gas water heater 40 in the hot water supply path 60. The hot water supply path 60 is provided with a hot water temperature sensor 84 located on the downstream side of the heat exchanger 42 of the gas water heater 40. Further, the hot water supply path 60 is provided with a flow sensor 85 for detecting the flow rate between the mixing valve 30 and the gas water heater 40.

  The above-described configuration is almost the same as a known hot water supply system. In the present embodiment, a tank temperature sensor 86 is newly provided on the top side wall of the hot water storage tank 20. The tank temperature sensor 86 detects the temperature of the hot water in the hot water storage tank 20 located below the top wall 20b of the hot water storage tank 20 by a predetermined distance D. This distance D is set so that, for example, about 10 liters of hot water can be stored between the installation position of the sensor 86 and the top wall 20b. Another tank temperature sensor 87 is provided on the side wall of the hot water storage tank 20 below the tank temperature sensor 86 by a predetermined distance.

  The circulation path 25 is bifurcated from the heat exchanger 12 toward the hot water storage tank 20, and the first branch path 25a is connected to the top end 20b of the hot water storage tank 20 as described above, and the second branch path 25b. Is connected to the side wall of the hot water storage tank 20 at an intermediate height position. The connection position of the second branch path 25b may be sufficiently separated from the connection position of the first branch path 25a and the bottom end 20a in the vertical direction. Preferably, it is at a position lower than the tank temperature sensor 86 by a predetermined distance and higher than the center of the hot water storage tank 20, and substantially at the same height as the tank temperature sensor 87.

  An electromagnetic three-way valve 90 is provided at the intersection of the first and second branch paths 25a and 25b. The three-way valve 90 can be switched between a first state in which hot water from the heat exchanger 12 is supplied only to the first branch 25a and a second state in which only the second branch 25b is supplied.

  Based on the detection information of the sensors 81 to 86, the control unit 70 sets the mixing valve 30, the on-off valve 35, and the gas water heater 40 so that the hot water temperature from the hot water tap 61 becomes a temperature set by the user. Take control. Details will be described below.

  The mixing valve 30 is in a standby state in which the tank side opening is fully closed and the water supply side is fully opened when hot water is stopped. When the hot-water tap 61 is opened, this is detected by the flow sensor 85, and the control unit 70 determines whether the detected temperature Td at the tank temperature sensor 86 is equal to or higher than a threshold value in response to this detection signal. The threshold is set to a temperature that is higher by a predetermined temperature, for example, 2 ° C. than the set temperature. This threshold is usually in the temperature range of the intermediate transition layer Wb.

  When the control unit 70 determines that the detected temperature Td is equal to or higher than the threshold value, the control unit 70 executes the first control routine. In this case, since the tank temperature sensor 86 is located below the top wall 20b of the hot water storage tank 20 by a distance D, the temperature of the hot water on the top wall 20b is equal to or higher than the threshold value. Usually, hot water of the high temperature layer Wa is stored at the top of the hot water storage tank 20. Taking the case where the detected temperature is the hot water temperature Ta of the high temperature layer Wa as an example, the first control routine will be described with reference to FIG.

  The gas water heater 30 is maintained in a stopped state. The mixing valve 30 mixes the hot water from the hot water storage tank 20 and the water from the water supply channel 50 and performs control so that the mixing temperature Tmix becomes the set temperature Ts. More specifically, the hot water temperature Tin of the hot water storage tank 20 detected by the inlet temperature sensor 81, the feed water temperature Tc detected by the feed water temperature sensor 82, the flow rate detected by the flow sensor 85, and the set temperature Ts. Based on the feedforward control, feedback control is performed based on the mixing temperature Tmix detected by the mixing temperature sensor 83 and the set temperature Ts. Therefore, the mixed hot water that has reached the set temperature Ts by the mixing valve 30 is not heated by the gas water heater 30 and is discharged from the hot water tap 61. Since the hot water temperature Ta of the high temperature layer Wa is substantially constant, the mixing ratio in the mixing valve 30 is substantially constant as long as the set temperature Ts does not change and the amount of discharged hot water does not change. Refer to the period before time t1 in FIG.

  If the hot water in the hot water storage tank 20 continues to be consumed, the intermediate transition layer Wb eventually reaches the tank temperature sensor 86, and the temperature Td detected by the tank temperature sensor 86 begins to decrease. However, since the tank temperature sensor 86 is located below the top end 20b of the hot water storage tank 20 by a predetermined distance D, the temperature of the hot water coming out of the hot water storage tank 20, that is, the temperature Tin of the hot water entering the mixing valve 30 (inlet temperature) is still present. High temperature Ta is maintained.

  At a time t1 when the detected temperature Td of the tank temperature sensor 86 further decreases and reaches a threshold value, the gas water heater 40 is ignited to supply the minimum supply heat amount Qmin to the hot water, and the mixing valve 30 is opened on the tank side. Decrease rapidly. The tank side opening of the mixing valve 30 is determined so that the mixing temperature Tmix satisfies the above-described equation (1). Therefore, at the ignition time t1, the mixing temperature Tmix is lower than the set temperature Ts by a temperature difference ΔT = Qmin / F.

  The mixing temperature Tmix rapidly decreased at the ignition time t1 is maintained as it is, that is, at a temperature lower by the temperature difference ΔT than the set temperature Ts, and is continued until the detected temperature Td reaches the mixing temperature Tmix. The control of the mixing valve 30 at this time is executed by feedforward control and feedback control as described above. It should be noted that the tank temperature sensor 86 is positioned below the top wall 20b by a predetermined distance D, and at the time t1 when the detected temperature Td reaches the threshold value and the gas water heater 40 is ignited, the hot water tank 20 still has the high temperature layer Wa. Since the inlet temperature Tin is still maintained at the high temperature Ta, in the control for maintaining the mixing temperature Tmix at a constant level, the opening of the mixing valve 30 is maintained at a substantially constant level only by fine adjustment. It will be. Thus, since the mixing temperature Tmix is maintained constant, the control immediately after ignition in the gas water heater 40 can be stably performed. Refer to the period from time t1 to time t2 in FIG.

  At the time t2 when the detected temperature Td reaches the mixing temperature Tmix, the mixing valve 30 is controlled so that the mixing temperature Tmix gradually decreases as time passes. Along with this, the tank side opening of the mixing valve 30 gradually decreases. In the gas water heater 40, feedforward control based on the detected temperature Tmix and set temperature Ts of the mixed temperature sensor 83 and the detected flow rate of the flow sensor 85, and feedback control based on the detected temperature of the hot water temperature sensor 84 and the set temperature Ts, The amount of heat supplied is controlled to maintain the tapping temperature at the set temperature Ts. The amount of heat supplied increases as the mixing temperature Tmix decreases. Since the mixing temperature Tmix gradually decreases, the increase in the amount of heat supplied by the gas water heater 40 can be followed well, and a large undershoot does not occur. In addition, since the temperature of the mixing temperature Tmix is decreased as time elapses, the gas water heater 40 can be stably controlled without being affected by an excessive flow rate. Refer to the period of time t2 to t3 in FIG.

  If the hot water is further continued, the tank side opening of the mixing valve 30 is substantially fully closed at time t3. At the same time, the electromagnetic opening / closing valve 35 is closed. At this time t3, the opening on the water supply side of the mixing valve 30 is fully opened, and the mixing temperature Tmix from the mixing valve 30 coincides with the water supply temperature Tc. Thereafter, the hot water supply at the set temperature is maintained by giving the heat supplied from the gas water heater 40 to the water from the water supply channel 50 while the supply of hot water from the hot water storage tank 20 is stopped.

  As described above, since the mixing temperature Tmix from the mixing valve 30 is gradually decreased to the feed water temperature Tc, the mixing temperature Tmix does not rapidly decrease as in the known hot water supply system. The increase in the amount of heat supplied by the water heater 40 does not catch up with the phenomenon of undershooting in the hot water temperature.

  When hot water is stopped by tightening the hot-water tap 61, the flow sensor 85 detects this, and in response to this detection signal, the combustion of the gas water heater 40 is stopped. See time t4 in FIG. In this first control routine, when the hot water supply is stopped during the period from the time point t1 to the time point t3, the combustion of the gas water heater 40 is stopped, and the mixing valve 30 is fully closed and the water supply side opening is opened. The degree is controlled to be fully open. When the hot water supply is stopped before time t1, the mixing valve 30 is controlled so that the tank side opening is fully closed and the water supply side opening is fully open.

  When it is determined that the temperature Td detected by the tank temperature sensor 86 is less than the threshold at the start of hot water supply, the control unit 70 executes a second control routine. That is, while the opening of the mixing valve 30 on the tank side is fully closed and the solenoid valve 35 is closed, the water from the water supply passage 50 is heated by the gas water heater 40 without using the hot water from the hot water storage tank 20, and the set temperature is reached. Maintaining hot spring water.

  The electromagnetic opening / closing valve 35 is closed when the opening of the mixing valve 30 on the tank side is fully closed, but is also closed when the mixed hot water temperature sensor 83 fails, and the supply of hot water from the hot water storage tank 20 is stopped. It is forbidden to be supplied from the hot water tap 61.

  The control unit 70 controls the three-way valve 90 in addition to the hot water temperature control. Normally, the three-way valve 90 is maintained in the state shown in FIG. 1 (first state). In this state, hot water from the heat exchanger 12 is supplied to the top of the hot water storage tank 20 via the first branch path 25a. Therefore, it is possible to effectively use high-temperature hot water and reduce the opportunity to use the gas water heater 40.

  As described above, when the first control routine shown in FIG. 3 is executed and the time point t3 is reached, the three-way valve 90 is moved to the state shown in FIG. 2 state). In this state, hot water from the heat exchanger 12 is supplied to the side of the hot water storage tank 20 via the second branch path 25b. As described above, since the top of the hot water storage tank 20 is the intermediate transition layer Wb, the intermediate transition layer Wb or the low temperature layer Wc is formed at the connection position of the second branch path 25b. Therefore, the hot water supplied to the second branch 25b rises in the hot water storage tank 20, and heat is taken away in the process. Due to this convection, the intermediate transition layer Wb is widened and diluted with fresh water from the bottom of the hot water storage tank 20 via the heat exchanger 12. As a result, the hot water belonging to the intermediate transition layer Wb can be prevented from staying in the hot water storage tank 20 for a long time without being replaced.

  The second state of the three-way valve 90 is continued until the temperature detected by the lower tank temperature sensor 87 reaches a threshold value. This threshold value is set to a predetermined temperature, for example, 5 ° C. higher than the water supply temperature, and is lower than the threshold value for the tank temperature sensor 86 during hot water control. When the tank temperature sensor 87 reaches this threshold, the three-way valve 90 is switched from the second state to the first state. Thereby, the hot water from the heat exchanger 12 can be supplied again to the top of the hot water storage tank 20 via the first branch passage 25a, and the hot water can be effectively utilized. Note that the electromagnetic on-off valve 35 is opened at the time of switching.

Next, a second embodiment of the present invention will be described with reference to FIG. In this embodiment, a mixing valve 91 is used instead of the three-way valve 90 of the first embodiment. The mixing valve 91 supplies the hot water of the heat exchanger 12 only to the first branch 25a in the first state, and supplies the hot water of the heat exchanger 12 to the first branch 25a and the second branch 25b in the second state. Supply to both. In this case, the above-described dilution effect can be obtained, and it is possible to quickly reach a state where the hot water in the hot water storage tank 20 can be supplied to the mixing valve 30, and the thermal energy from the heat exchanger 12 can be effectively utilized.
The distribution ratio to the branch paths 25a and 25b may be fixed or variable. In the case of being variable, the distribution ratio to the first branch 25a may be increased as time passes or the temperature detected by the tank temperature sensor 87 increases. Since other control is the same as that of the first embodiment, description thereof is omitted.

  The present invention is not limited to the above-described embodiments, and various aspects are possible. The hot water temperature control can be any control as long as the hot water temperature does not cause an undershoot while leaving the intermediate transition layer.

It is the schematic of the waste heat recovery hot water supply system which makes one Embodiment of this invention, and shows the state which supplies the hot water from a heat exchanger to the top part of a hot water storage tank. It is principal part schematic of the system, and is principal part schematic which shows the state which supplies the hot water of a heat exchanger to the side part of a hot water storage tank. It is a time chart which shows the hot water control in the system. It is a principal part schematic of the hot water supply system which shows other embodiment of this invention. It is a figure which shows the temperature gradient in the hot water storage tank of this invention and a well-known system. It is a figure which shows the time chart of the control in the conventional hot water supply system.

Explanation of symbols

10 Generator 11 Waste heat source (Heat generation source)
12 Heat exchanger 20 Hot water storage tank 30 Mixing valve 40 Gas water heater (auxiliary heat source)
50 Water supply path 60 Hot water supply path 70 Control unit (control means)
86 Tank temperature sensor 87 Other tank temperature sensor 90 Three-way valve (switching valve means)
91 Other mixing valves (switching valve means)

Claims (9)

(A) a heat generation source;
(B) a heat exchanger that receives heat from the heat generation source;
(C) a hot water storage tank;
(D) a circulation path for circulating water from the bottom of the hot water storage tank to the hot water storage tank through a heat exchanger;
(E) a water supply channel whose downstream end is connected to the bottom of the hot water storage tank;
(F) a hot water supply path whose upstream end is connected to the top of the hot water storage tank;
(G) a mixing valve provided in the middle of the hot water supply channel for mixing hot water from the hot water storage tank and water of the water supply channel;
(H) an auxiliary heat source provided on the downstream side of the mixing valve in the hot water supply path;
(I) control means for discharging hot water at a set temperature from the downstream end of the hot water supply path by controlling the mixing valve and the auxiliary heat source;
In the hot water supply system with
The circulation path is branched into a first branch path from the heat exchanger to the top of the hot water storage tank and a second branch path to the side of the hot water storage tank below the first branch path, and the intersection of the first and second branch paths. Switching valve means is provided in the section,
In the hot water storage tank, a high temperature layer made of high temperature hot water from a heat exchanger, a low temperature layer made of water having a feed water temperature, and an intermediate transition layer having a temperature gradient are stored.
The control means controls the mixing valve and the auxiliary heat source so as to leave hot water of the intermediate transition layer in the hot water storage tank, and maintains the hot water temperature at a set temperature,
Further, the control means sets the switching valve means to a first state in which hot water from the heat exchanger is normally supplied only to the top of the hot water storage tank via the first branch passage, and the heat exchange is performed as necessary. A hot water supply system, wherein a second state is set in which at least a part of hot water from the vessel is supplied to the second branch passage. (A) a heat generation source;
(B) a heat exchanger that receives heat from the heat generation source;
(C) a hot water storage tank;
(D) a circulation path for circulating water from the bottom of the hot water storage tank to the hot water storage tank through a heat exchanger;
(E) a water supply channel whose downstream end is connected to the bottom of the hot water storage tank;
(F) a hot water supply path whose upstream end is connected to the top of the hot water storage tank;
(G) a mixing valve which is provided in the middle of the hot water supply channel and mixes hot water from the hot water storage tank and water of the water supply channel;
(H) an auxiliary heat source provided on the downstream side of the mixing valve in the hot water supply path;
(I) control means for discharging hot water at a set temperature from the downstream end of the hot water supply path by controlling the mixing valve and the auxiliary heat source;
In the hot water supply system with
A tank temperature sensor for measuring the temperature of the hot water in the hot water storage tank is provided at a position below the top end of the hot water storage tank by a predetermined distance, and the circulation path is a first branch path from the heat exchanger to the top of the hot water storage tank. Branched to a second branch path toward the side of the lower hot water storage tank, and switching valve means is provided at the intersection of these first and second branch paths,
The control means includes
(A) In the situation where the temperature detected by the tank temperature sensor is higher than the threshold value, the temperature of the mixed hot water from the mixing valve is maintained at the set temperature by controlling the mixing valve while the auxiliary heat source is stopped.
(A) When the detected temperature decreases and reaches a threshold value, the auxiliary heat source is started to supply a minimum amount of heat, and hot water from the hot water storage tank is supplied corresponding to the minimum amount of heat supply. By controlling the mixing valve to reduce the rate, the tapping temperature is maintained at the set temperature,
(C) The ratio of hot water from the hot water storage tank by the mixing valve is gradually reduced from the value reduced at the start of operation of the auxiliary heat source to substantially zero, and the temperature of the mixed hot water from the mixing valve is reduced. Compensating by increasing the amount of heat supplied from the auxiliary heat source, maintaining the tapping temperature at the set temperature,
(D) The switching valve means is in a first state in which hot water from the heat exchanger is normally supplied only to the top of the hot water storage tank via the first branch passage, and the mixing valve is used to supply hot water from the hot water storage tank. After the ratio is substantially zero, the hot water supply system is in a second state in which at least part of the hot water from the heat exchanger is supplied to the second branch passage.   The control for gradually reducing the ratio of the hot water from the hot water storage tank is a mixing valve control for managing the temperature of the mixed hot water and gradually lowering the temperature of the mixed hot water over time. Item 3. A hot water supply system according to item 2.   The control means controls the mixing valve so that the temperature of the mixed hot water is kept constant after the ratio of hot water in the hot water storage tank by the mixing valve is reduced at the start of operation of the auxiliary heat source, and the temperature of the mixed hot water is controlled. 4. The hot water supply system according to claim 3, wherein the mixing valve is controlled so as to gradually lower the temperature of the mixed hot water when it coincides with the temperature detected by the tank temperature sensor.   An electromagnetic on-off valve is provided on the upstream side of the mixing valve in the hot water supply path, and the control means closes the electromagnetic on-off valve when the mixing valve makes the ratio of hot water from the hot water storage tank substantially zero. The hot water supply system according to any one of claims 2 to 4.   The switching valve means is a three-way valve, and the second state is a state in which hot water from the heat exchanger is supplied only to the second branch passage. The hot water supply system described.   3. The switching valve means is another mixing valve, and the second state is a state in which hot water from the heat exchanger is supplied to both the first and second branch passages. The hot water supply system in any one of -5.   The hot water storage tank is provided with another tank temperature sensor for measuring the temperature of hot water in the hot water storage tank below the tank temperature sensor, and the temperature detected by the other temperature sensor exceeds another threshold value lower than the threshold value. The hot water supply system according to any one of claims 2 to 7, wherein the control means returns the switching valve means from the second state to the first state.   The hot water supply system according to any one of claims 1 to 8, wherein the heat generation source is an exhaust heat source, and the auxiliary heat source is a gas water heater.

Images