Patent Publication Number: US-2011073666-A1

Title: Boiler system having dual heating water tanks

Description:
TECHNICAL FIELD 
     The present invention relates, in general, to a boiler system with dual hot water tanks and, more particularly, to a boiler system with dual hot water tanks, in which high-temperature water in a high-temperature tank is mixed with low-temperature water in a low-temperature tank to supply hot water at a preset temperature to a feedwater heat exchanger, thus always keeping the temperature of the heated water constant. 
     BACKGROUND ART 
     Generally, as shown in  FIG. 1 , a boiler system is constructed so that heating water heated in a boiler  1  is stored in a thermal storage tank  10  having excellent thermo-keeping capacity, and is supplied to a heating pipe  20  of a room or a feedwater heat exchanger  30 , thus heating the room or water. 
     The boiler system is provided with one boiler  1  and one thermal storage tank  10 , and is constructed so that, when a temperature T 0  of thermal storage water supplied from the thermal storage tank to the heating pipe  20  or the feedwater heat exchanger  30  is lower than a preset temperature of heating water, the boiler is operated to reheat the water, and then the water is fed through the thermal storage tank to the heating pipe  20  or the feedwater heat exchanger  30 . 
     However, the conventional boiler system is problematic in that, even when the temperature T 0  of the thermal storage water supplied from the thermal storage tank  10  to the heating pipe  20  or the feedwater heat exchanger  30  is higher than a preset temperature of heating water, the water is supplied without the temperature being controlled, so that a room may be excessively heated above a preset temperature or the temperature T 2  of hot water may become excessively high. 
     Especially, the conventional boiler system is problematic in that heating water supplied through the thermal storage tank  10  does not stay at a constant temperature, so that hot water discharged from the feedwater heat exchanger  30  may momentarily cause a user displeasure and discomfort because of the slight change in the temperature of the hot water. 
     DISCLOSURE 
     Technical Problem 
     Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a boiler system with dual hot water tanks, in which one boiler is accompanied by a high-temperature water tank and a low-temperature water tank, and high-temperature water in the high-temperature water tank and low-temperature water in the low-temperature water tank are mixed at different flow rates by a mixing valve, so that hot water of a preset temperature is supplied to a feedwater heat exchanger, thus keeping the temperature of water heated in the feedwater heat exchanger constant. 
     Technical Solution 
     In order to accomplish the above object, the present invention provides a boiler system with dual hot water tanks, constructed to supply hot water of a boiler to a heating pipe or a feedwater heat exchanger to discharge heated water of a predetermined temperature, the boiler system including a high-temperature water tank storing hot water which is heated in the boiler, a low-temperature water tank storing hot water which is received from the feedwater heat exchanger or the heating pipe and supplying the hot water to the boiler, and a mixing valve mixing the hot water supplied from the high-temperature water tank with the hot water supplied from the low-temperature water tank so as to supply mixed hot water of a predetermined temperature to the feedwater heat exchanger, wherein the mixing valve controls a flow rate of the hot water of the low-temperature water tank which is to be mixed, depending on a temperature of the hot water of the high-temperature water tank, thus supplying the mixed hot water of the predetermined temperature. 
     ADVANTAGEOUS EFFECTS 
     According to the present invention, a boiler system with dual hot water tanks is advantageous in that high-temperature hot water higher than a preset temperature and low-temperature hot water lower than a preset temperature are mixed with each other to provide hot water of a preset temperature, and the hot water of the preset temperature is supplied to a feedwater heat exchanger, thus being capable of always supplying hot water at a temperature which is proper to use, and preventing the temperature of hot water from changing when the hot water is in use so that a user does not feel displeasure or discomfort. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is a view illustrating the construction of a conventional boiler system; 
         FIG. 2  is a view illustrating the construction of a boiler system with dual hot water tanks according to the present invention; and 
         FIG. 3  is a view illustrating the construction of a mixing valve of the boiler system with the dual hot water tanks according to the present invention. 
     
    
    
     MODE FOR INVENTION 
     Hereinafter, the preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. 
       FIG. 2  is a view illustrating the construction of a boiler system with dual hot water tanks according to the present invention, and  FIG. 3  is a view illustrating the construction of a mixing valve of the boiler system with the dual hot water tanks according to the present invention. 
     As shown in  FIG. 2 , a boiler system according to an embodiment of the present invention includes a high-temperature water tank  11  which stores hot water heated by and supplied from a boiler  1 , a low-temperature water tank  12  which stores hot water received from a feedwater heat exchanger  30  or a heating pipe  20 , and a mixing valve  50  which mixes hot water supplied from the high-temperature water tank with hot water supplied from the low-temperature water tank so as to supply hot water at a predetermined temperature to the feedwater heat exchanger  30  or the heating pipe  20 . 
     Here, the high-temperature water tank  11  stores hot water heated by the boiler  1 , and is constructed such that the stored hot water stays at a temperature T 0  of 60 to 80° C. 
     The low-temperature water tank  12  stores low-temperature hot water which passes through the feedwater heat exchanger  30  or the heating pipe  20  and then is returned, and is constructed such that the low-temperature hot water stays at a temperature T 3  of 55° C. or less. The low-temperature hot water is re-supplied to the boiler  1  or supplied to the mixing valve  50 . 
     Further, since the low-temperature water of the low-temperature water tank  12  supplied to the mixing valve  50  is used to lower the temperature of the high-temperature water, supplied from the high-temperature water tank  11 , to a preset temperature T 1  of mixed hot water, wherein less of the low-temperature water is used than is the high-temperature water at the time when the low-temperature water is mixed with the high-temperature water. 
     As shown in  FIG. 3 , the mixing valve  50  includes a supply valve disc  51  and a discharge valve disc  52 . The supply valve disc  51  that is fixed is provided with a high-temperature water supply port  51 - 1  and a low-temperature water supply port  51 - 2 , each of which has the shape of a kidney. The discharge valve disc that is rotatable is provided with a discharge port  52 - 1  which has the same shape as the high-temperature water supply port  51 - 1  and the low-temperature water supply port  51 - 2 , namely, the shape of a kidney. 
     Thus, when the high-temperature water of the high-temperature water tank  11  flows through the high-temperature water supply port  51 - 1  into the mixing valve  50  and the low-temperature water of the low-temperature water tank  12  flows through the low-temperature water supply port  51 - 2  into the mixing valve  50 , a predetermined amount of hot water is discharged through the discharge port  52 - 1  of the discharge valve disc  52 , so that the high-temperature water is mixed with the low-temperature water. As the discharge valve disc is rotated, the discharge port overlaps the high-temperature water supply port  51 - 1  and the low-temperature water supply port  51 - 2 . The supply amount of the high-temperature water and the low-temperature water vanes depending on the overlapping area of the discharge port and the high-temperature and low-temperature water supply ports. 
     As for the low-temperature water tank  12 , if the temperature T 0  of the high-temperature water in the high-temperature water tank  11  is lower than the temperature T 1  of the mixed hot water, the low-temperature water is discharged to the boiler  1  and then is re-heated. In contrast, if the temperature T 0  of the high-temperature water is higher than the temperature T 1  of the mixed hot water, the low-temperature water is supplied to the mixing valve  50 . 
     Further, the mixing valve  50  is constructed so that it receives the high-temperature water of the temperature T 0  and the low-temperature water of the temperature T 3  from the high-temperature water tank  11  and the low-temperature water tank  12 , respectively, and mixes the high-temperature water and the low-temperature water so that the mixed hot water has the temperature T 1 , and then supplies the mixed hot water to the feedwater heat exchanger  30  or the heating pipe  20 . 
     For example, if a temperature T 2  of hot water supplied from the feedwater heat exchanger  30  is set to be 55° C., and the boiler  1  is set to start operating when the temperature T 0  of the high-temperature water is 60° C. and stop operating when the temperature T 0  of the high-temperature water is 80° C., the temperature T 0  of the high-temperature water in the high-temperature water tank  11  is maintained within the range of 60 to 80° C., and the temperature T 3  of low-temperature water in the low-temperature water tank  12  is maintained at 55° C. or less. 
     The high-temperature water of 60 to 80° C. is mixed with the low-temperature water of 55° C. or less by the mixing valve  50 , thus supplying mixed hot water having the temperature T 1  of 55 to 60° C. 
     In other words, assuming that the capacity of the boiler  1  is 24,000 Kcal·H, water of 15° C. is supplied from the feedwater heat exchanger  30  at the flow rate of 10 LPM, and hot water of 55° C. is discharged, the quantity of heat required for 60 minutes is as follows: flow rate×change in temperature×time=10 LPM×40° C.×60 minutes=24,000 Kcal·H. 
     Here, when the flow rate of the mixed hot water supplied from the mixing valve  50  is 20 LPM, the temperature T 1  of the mixed hot water is 60° C., and the temperature T 3  at which the mixed hot water passes through the feedwater heat exchanger  30  and is returned to the low-temperature water tank  12  is 40° C., the quantity of heat supplied to the feedwater heat exchanger for 60 minutes is calculated as follows. That is, flow rate×change in temperature×time=20 LPM×20° C.×60 minutes=24,000 Kcal·H. It can be seen from this equation that the quantity of heat supplied to the feedwater heat exchanger is equal to the quantity of heat required when heating water and supplying hot water. 
     To this end, the boiler  1  supplies 24,000 Kcal·H corresponding to the capacity of the boiler to heat the low-temperature water of 40° C. such that it is changed into the high-temperature water of 60 to 80° C. 
     Here, if the flow rate of water of 15° C. which is supplied from the feedwater heat exchanger  30  at the flow rate of 10 LPM is reduced to 5 LPM, the water of 5 LPM is heated with the heat quantity of 24,000 Kcal·H. Thus, water is momentarily heated at 55° C. or more and supplied. However, according to the present invention, the heat quantity supplied to the feedwater heat exchanger can be controlled to be reduced to a proper heat quantity, that is, flow rate×change in temperature×time=5 LPM×40° C.×60 minutes=12,000 Kcal·H. 
     In other words, if the flow rate of supplied water is reduced and the temperature T 2  of heated water is increased to a preset temperature or more, the temperature T 1  of the mixed hot water is lowered in the mixing valve  50 . When the discharge valve disc  52  is rotated so that the discharge port  52 - 1  moves to the low-temperature water supply port  51 - 2  of the supply valve disc  51 , the inflow amount of the low-temperature water of the low-temperature water tank  12  is increased, and the supply amount of the high-temperature water of the high-temperature water tank  11  is reduced, thus reducing the temperature T 1  of the mixed hot water. 
     Therefore, while the flow rate of the low-temperature water supplied from the low-temperature water tank  12  to the mixing valve  50  is increased, the flow rate of the low-temperature water supplied to the boiler  1  is reduced. Simultaneously, while the flow rate of the high-temperature water supplied from the high-temperature water tank  11  to the mixing valve is reduced, the temperature T 0  of the high-temperature water is increased. Thereby, the heat quantity supplied from the boiler is reduced from 24,000 Kcal·H to 12,000 Kcal·H, namely, by 50%. 
     Further, if the flow rate of the water of 15° C. supplied to the feedwater heat exchanger  30  is reduced to 2 LPM, the heat quantity of 4,800 Kcal·H is required to obtain the heated water of 55° C. Thus, a boiler  1  having a capacity of 24,000 Kcal·H is controlled to be operated only at 20% capacity. 
     In the case where the operating range of a burner of the boiler  1  is variable and is continuously operated at 40%˜100% of capacity, if the operating rate of the boiler is reduced to 20% of the capacity as described above, it deviates from the variable range of the burner, thus triggering the On/Off operation. 
     When hot water stops being used, the discharge valve disc  52  is rotated in the mixing valve  50  so that the discharge port  52 - 1  is moved to the low-temperature water supply port  51 - 2  of the supply valve disc  51 . Thereby, the inflow amount of the low-temperature water of the low-temperature water tank  12  is increased, and the supply amount of the high-temperature water of the high-temperature water tank  11  is reduced in proportion to the increased inflow amount, so that the temperature T 1  of the mixed hot water is controlled to be lowered up to 55° C. Since the heat quantity is never lost while the mixed hot water passes through the feedwater heat exchanger  30  and returns to the low-temperature water tank  12 , the temperature T 3  of the low-temperature water of the low-temperature water tank is abruptly increased up to 55° C. In this case, the operation of the boiler  1  is immediately halted. 
     In brief, the present invention controls the supply flow rate when the low-temperature water of the low-temperature water tank having relatively irregular temperature T 3  is supplied to the mixing valve  50 , so that the temperature T 1  of mixed hot water can be rapidly and precisely controlled to a preset temperature, thus always keeping the temperature T 2  of hot water discharged from the feedwater heat exchanger  30  constant. 
     Although the preferred embodiment of the present invention has been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims. 
     INDUSTRIAL APPLICABILITY 
     The present invention is applied to a boiler system, thus always supplying hot water at a temperature which is proper to use, and preventing the temperature of hot water from changing when the hot water is in use so that a user does not feel displeasure or discomfort, therefore having high industrial applicability.