Description

CONDENSING BOILER AND METHOD FOR CONTROLLING

HEATING OF BOILER

Technical Field

[1] The present invention relates to a condensing boiler in which the structure of a heat exchanger is improved in order to decrease the difference in the temperature of fluid flowing through a latent heat exchanger and a sensible heat exchanger, thereby minimizing water condensation, and a method for controlling the same. Background Art

[2] Referring to FIG. 1, a conventional condensing boiler includes a fan 1 for forcibly supplying air, a burner 2 for burning fuel using air supplied by the fan 1, a heat exchanger 3 for allowing heat exchange between heating water and the gas produced in the burner 2, and an exhaust duct 4 for discharging exhaust gas, having passed through the heat exchanger 3, to the outside.

[3] The heat exchanger 3 is composed of a sensible heat exchanger 5 and a latent heat exchanger 6, which are sequentially arranged directly below the burner 2.

[4] The sensible heat exchanger 5 is manufactured by welding a plurality of heat conduction fins to a copper pipe so as to improve heat exchange efficiency, and the latent heat exchanger 6 is made of stainless steel so as to be prevented from being corroded by condensed water. Disclosure of Invention Technical Problem

[5] Heating water, which is decreased in temperature by the exchange of heat in a room, is introduced into the latent heat exchanger 6, and the heating water, which is preheated while passing through the latent heat exchanger 6, is introduced into the sensible heat exchanger 5. If the temperature of the heating water introduced into the sensible heat exchanger 5 is too low, water is likely to condense on the sensible heat exchanger 5, by which the useful service life of the sensible heat exchanger 5 may be shortened due to corrosion.

[6] Therefore, in order to prevent heating water having an excessively low temperature from being introduced into the sensible heat exchanger, the heat capacity of the burner must be increased so as to properly control the temperature of heating water. As a result, because the heating water cannot be restored to the latent heat exchanger at a low temperature, the heating efficiency of the condensing boiler can be degraded. Technical Solution

[7] Accordingly, the present invention has been made in an effort to solve the problems

occurring in the related art, and an object of the present invention is to provide a condensing boiler in which a mixing valve is installed between a heating water supply pipe and a point between latent and sensible heat exchangers such that the opening degree of the mixing valve can be proportionally adjusted under the control of a control part depending upon the temperature sensed on the discharge side of the latent heat exchanger, so that the temperature of heating water introduced into the sensible heat exchanger can be maintained at a temperature at which essentially no water condensation occurs, thereby increasing the useful service life of the sensible heat exchanger. [8] Another object of the present invention is to provide a condensing boiler which allows heating water to be recovered at a low temperature, thereby contributing to the improvement of heating efficiency.

Advantageous Effects

[9] Thanks to the features of the present invention, a mixing valve is installed between the discharge side of a sensible heat exchanger and a point between latent and sensible heat exchangers such that the opening degree of the mixing valve can be proportionally adjusted under the control of a control part depending upon the temperature sensed on the discharge side of the latent heat exchanger so that the temperature of heating water introduced into the sensible heat exchanger can be maintained at a temperature at which essentially no water condensation occurs, thereby preventing corrosion of the sensible heat exchanger and increasing the useful service life of the sensible heat exchanger. As a consequence, since heating water can be recovered at a low temperature, the heating efficiency of the condensing boiler can be improved. Brief Description of the Drawings

[10] FIG. 1 is a schematic view illustrating a conventional condensing boiler; and

[11] FIG. 2 is a systematic view illustrating the construction of a condensing boiler in accordance with an embodiment of the present invention, and explaining the method of controlling the same.

Best Mode for Carrying Out the Invention

[12] According to the present invention, there is provided a condensing boiler having a burner for heating water flowing through a latent heat exchanger and a sensible heat exchanger, and a pump for circulating heated water, comprising temperature sensors installed on respective discharge pipes of the latent heat exchanger and the sensible heat exchanger; a communication pipe connected between the heating water supply pipe for the pump and the discharge pipe from the latent heat exchanger; and a mixing valve installed on the communication pipe for returning a portion of the heating water heated through the sensible heat exchanger and having passed through the pump into

the discharge pipe of the latent heat exchanger. Mode for the Invention

[13] FIG. 2 is a systematic view illustrating the construction of a condensing boiler in accordance with an embodiment of the present invention and explaining the method of controlling the same.

[14] Referring to FIG. 2, a condensing boiler in accordance with an embodiment of the present invention includes a burner for heating water flowing through a heat exchanger 10, a pump 20 for circulating heated water, and a control part 60 for proportionally controlling the operation of the condensing boiler.

[15] The heat exchanger 10 is composed of a latent heat exchanger 11 and a sensible heat exchanger 12, and has a conventional structure.

[16] Temperature sensors T2 and T3 are installed on the discharge sides of the latent heat exchanger 11 and the sensible heat exchanger 12, respectively. A heating water recovery pipe 50 is connected to the latent heat exchanger 11, and a temperature sensor Tl is installed on the heating water recovery pipe 50.

[17] A pump 20 is installed on the discharge pipe 13 of the sensible heat exchanger 12, and a heating water supply pipe 40 for supplying heating water under pressure is connected to the discharge side of the pump 20.

[18] A communication pipe 31 is connected between the heating water supply pipe 40, which extends from the pump 20, and the discharge pipe 13 of the latent heat exchanger 11.

[19] A mixing valve 30 is installed between the communication pipe 31 and the heating water supply pipe 40. The mixing valve 30 functions to return a portion of the heating water, having passed through the sensible heat exchanger 12 and the pump 20, to the discharge pipe 13 of the latent heat exchanger 11, and to supply the remaining portion of the heating water for the purpose of heating a room.

[20] The mixing valve 30 is driven by a stepping motor, a DC motor or an AC motor.

Therefore, a predetermined amount of heating water, discharged under pressure from the pump 20, is directed to the discharge side of the latent heat exchanger 11 through adjustment of the opening degree of the mixing valve 30.

[21] In the present invention, if the temperature of heating water recovered through the heating water recovery pipe 50, which is sensed by the temperature sensor Tl, is below a predetermined temperature, the control part 60 senses this situation and operates the pump to circulate the heating water which has finished exchanging heat. The heating water circulated in this way is heated to a predefined temperature while passing through the latent heat exchanger 11 and the sensible heat exchanger 12. The temperatures of the heating water that has passed through the latent heat exchanger 11 and

the heating water that has passed through the sensible heat exchanger 12 are sensed by the temperature sensors T2 and T3 at the discharge pipes 13 of the latent heat exchanger 11 and the sensible heat exchanger 12. The sensed temperatures are transmitted to a PID (proportional-integral-derivative) controller 70, where the sensed temperatures from the temperature sensors T2 and T3 are compared with preset temperatures. As a result of the comparison, the control part 60 outputs a signal to the mixing valve 30, and the mixing valve 30 returns a portion of the heating water, which has passed through the sensible heat exchanger 12 and the pump 20, to the discharge side of the latent heat exchanger 11. The heating water mixed at the discharge side of the latent heat exchanger 11 is supplied to the sensible heat exchanger 12 at an appropriate temperature, at which water does not condense.

[22] That is to say, heating water is circulated through the operation of the pump 20.

Then, the temperature of heating water, which is introduced into the sensible heat exchanger 12, is sensed by the temperature sensor T2 which is installed on the discharge side of the latent heat exchanger 11, and the temperature of heating water, which is supplied into the heating water supply pipe 40, is sensed by the temperature sensor T3 installed on the discharge side of the sensible heat exchanger 12. The difference between the temperatures sensed by the temperature sensors T2 and T3 is processed as data under the control of the PID controller 70, and as a result, the control part 60 can proportionally control the opening degree of the mixing valve 30.

[23] In greater detail, assuming that water does not condense in the sensible heat exchanger 12 at a temperature of 45 ⁰ C, the temperature sensor installed on the heating water recovery pipe 50 is Tl, the temperature sensor installed on the discharge side of the latent heat exchanger 11 is T2, and the temperature sensor installed on the discharge side of the sensible heat exchanger 12 is T3, the control part 60 first receives the temperature sensed by the temperature sensor T3. When the temperature sensed by the temperature sensor T3 is below a predetermined temperature, the control part 60 operates the burner and the pump 20. Then, as the heating water is circulated, heating water is heated by the burner while it passes through the latent heat exchanger 11 and the sensible heat exchanger 12.

[24] At this time, the temperature on the introduction side of the latent heat exchanger 11 is sensed by the temperature sensor Tl, the temperature on the introduction side of the sensible heat exchanger 12 is sensed by the temperature sensor T2, and the temperature on the discharge side of the sensible heat exchanger 12 is sensed by the temperature sensor T3. If the temperature sensed by the temperature sensor T2 is below 45 ⁰ C, the control part 60 starts to control the mixing valve 30. In order to maintain the target temperature sensed by the temperature sensor T2 at 55 ⁰ C, the PID controller 70 executes an operation of referring to the temperature sensed by the temperature sensor

T3, and transmits the operation result to the control part 60. Here, it is to be understood that the target temperature of 55 ⁰ C can be changed depending upon the characteristic of the burner, etc.

[25] As the operation result from the PID controller 70 is transmitted to the control part

60, the control part 60 controls the opening and closing of the mixing valve 30 so that the predetermined amount of heating water can be supplied to the discharge side of the latent heat exchanger 11 through the communication pipe 31. Therefore, as heating water having the temperature sensed by the temperature sensor T3 on the discharge side of the sensible heat exchanger 12 and heating water having the temperature sensed by the temperature sensor T2 on the discharge side of the latent heat exchanger 11 are mixed with each other, heating water having an appropriate temperature (for example, 45 ⁰ C) on the discharge side of the latent heat exchanger 11 can be introduced into the sensible heat exchanger 12.

[26] The remaining heating water discharged from the pump 20 is circulated through the heating water supply pipe 40 and is introduced into the latent heat exchanger 11 through the heating water recovery pipe 50. The temperature of the heating water which passes through the heating water recovery pipe 50 is sensed by the temperature sensor Tl. Then, the temperature of the heating water which has passed through the latent heat exchanger 11 is sensed by the temperature sensor T2. The control part 60 opens and closes the mixing valve 30 depending upon the temperature sensed by the temperature sensor T2. While the heating water is circulated, as the temperature at the temperature sensor T2 rises, the opening degree of the mixing valve 30 is gradually decreased.

[27] Thus, depending upon the opening degree of the mixing valve 30, the amount of heating water to be supplied through the communication pipe 31 is adjusted. Because the heating water having the temperature sensed by the temperature sensor T3 on the discharge side of the sensible heat exchanger 12 and the heating water having the temperature sensed by the temperature sensor T2 on the discharge side of the latent heat exchanger 11 are mixed with each other, heating water having an appropriate temperature can be introduced into the sensible heat exchanger 12 through the discharge side of the latent heat exchanger 11.

[28] Therefore, as the condensing boiler is operated, the temperatures of heating water passing through the latent heat exchanger 11 and the sensible heat exchanger 12 are sensed, and the control part 60 adjusts the opening degree of the mixing valve 30 to proportionally control the amount of heating water supplied to the discharge side of the latent heat exchanger 11.

[29] Then, when the temperature sensed by the temperature sensor T2 on the discharge side of the latent heat exchanger 11 reaches an appropriate temperature, at which water

does not condense, the control part 60 interrupts the operation of the mixing valve 30.

[30] In the condensing boiler and the method for controlling the same according to the present invention, even when heating water is recovered to the latent heat exchanger 11 at a low temperature, water condensation at the sensible heat exchanger 12 is minimized, and the useful service life of the sensible heat exchanger 12 is thus extended. Therefore, since heating water can be recovered at a temperature that is as low as possible, the heating efficiency of the condensing boiler can be improved. Industrial Applicability

[31] As is apparent from the above description, the condensing boiler constructed as mentioned above and the method for controlling the same according to the present invention provide advantages in that a mixing valve is installed between the discharge side of a sensible heat exchanger and a point between latent and sensible heat exchangers. Therefore, the opening degree of the mixing valve can be proportionally adjusted under the control of a control part depending upon the temperature sensed on the discharge side of the latent heat exchanger so that the temperature of the heating water introduced into the sensible heat exchanger can be maintained at a temperature at which essentially no water condensation occurs, whereby corrosion of the sensible heat exchanger can be prevented and the useful service life of the sensible heat exchanger can be increased. As a consequence, since heating water can be recovered at a low temperature, the heating efficiency of the condensing boiler can be improved.