Heating device and method of heating water

Abstract

 Heating device for supplying hot water, comprising a combustion chamber (1) in which a heat exchanger (8) extends; wherein a fuel supply conduit (6), an air inlet pipe (5) and a flue gas outlet pipe (3) are connected to the combustion chamber; wherein a water supply conduit (11) and a water discharge conduit (12) are connected to the heat exchanger and connected at their other outer end to a hot water supply container (10); wherein a fan is placed in the air inlet pipe and/or in the flue gas outlet pipe which can cause a gas flow from the air inlet pipe through the combustion chamber to the flue gas outlet pipe; and wherein a circulation pump (9) is incorporated in the system which can circulate the water through the water supply conduit, the heat exchanger, the water discharge conduit and the hot water supply container; wherein the heating device comprises ventilation control means which are adapted to switch off the fan after the fuel supply conduit has been closed; and wherein the heating device comprises circulation control means which are adapted to switch off the circulation pump after the fuel supply conduit has been closed; wherein the ventilation control means are adapted to switch off the fan after the circulation pump has been switched off such that air flows along the heat exchanger while the water is stationary therein for the purpose of cooling this water.

Description

[0001] The invention relates to a heating device for supplying hot water, comprising a combustion chamber in which a heat exchanger extends; wherein a fuel supply conduit, an air inlet pipe and a flue gas outlet pipe are connected to the combustion chamber; wherein a water supply conduit and a water discharge conduit are connected to the heat exchanger and connected at their other outer end to a hot water supply container; wherein a fan is placed in the air inlet pipe and/or in the flue gas outlet pipe which can cause a gas flow from the air inlet pipe through the combustion chamber to the flue gas outlet pipe; and wherein a circulation pump is incorporated in the system which can circulate the water through the water supply conduit, the heat exchanger, the water discharge conduit and the hot water supply container; wherein the heating device comprises ventilation control means which are adapted to switch off the fan after the fuel supply conduit has been closed; and wherein the heating device comprises circulation control means which are adapted to switch off the circulation pump after the fuel supply conduit has been closed.

[0002] In such a combustion system the combustion air is generally drawn in from the outside atmosphere by means of the built-in fan, and not from the space in which the heating apparatus is set up, while the flue gases are likewise discharged to the outside atmosphere. Such a system requires a casing closed to the environment around the apparatus in order to prevent air being drawn in from the setup area. Closed pipes can also run from the outside atmosphere to the heating apparatus, which pipes are here connected air-tightly to a closed heat exchanger, and pipes which also run to the outside atmosphere, while a fan is arranged at a predetermined location for transport of the combustion air or the flue gases.

[0003] Such systems which are closed relative to the setup area are referred to as closed systems. If deemed desirable however, air can under determined conditions be drawn in from the setup area instead of the air being drawn in from the outside atmosphere.

[0004] The system described here will preferably use as energy carrier fossil fuel in gas form, such as natural gas, propane, butane, or oil converted into gas form (injector) in a burner suitable for this purpose.

[0005] The water is generally heated in the heating device to a temperature lying between 55°C and 70°C. The hot water is stored in the hot water supply container, from which a user can draw it off via a hot water tap. The consumed hot water is replenished with fresh cold water brought to the desired temperature in the heat exchanger. The heating device is also automatically set into operation if the temperature of the water in the container becomes too low. Here the circulation pump and the fan are first started up, whereafter the fuel supply conduit is opened and the fuel is ignited. Once the temperature in the hot water supply container has reached the preset desired level, or if hot water is no longer being demanded, the fuel supply conduit is closed. The fan then continues to operate for a preset short period of time in order to remove possibly non-combusted flue gases from the combustion chamber and fill the chamber with fresh outside air for a subsequent combustion. The circulation pump also continues to pump the water round the system for a preset period of time, generally about five minutes, after the fuel supply conduit has been closed, whereby the temperature of the water in the heat exchanger and in the hot water supply container become the same.

[0006] A problem which can occur in the above described device is that, depending on the hardness of the water, the inner side of the heat exchanger becomes covered in limescale, i.e. calcium present in the water precipitates in the form of flakes, whereby blockage of the heat exchanger can occur.

[0007] The invention has for its object to at least partly resolve the above stated problem.

[0008] For this purpose the ventilation control means are adapted to switch off the fan after the circulation pump has been switched off such that (cold) air flows along the heat exchanger while the water remains stationary therein for the purpose of cooling this water. Limescale occurs particularly at temperatures above about 52°C, wherein it is the case that the higher the temperature of the water, the more calcium is precipitated. The invention ensures that these high temperatures of the water in the heat exchanger occur for as short a time as possible, while the water temperature in the supply container is not reduced.

[0009] The heating device preferably comprises at least two temperature sensors which can measure the temperature at least at two different locations of the heat exchanger, the water supply conduit, the water discharge conduit and the hot water supply container, or of the water situated therein at these locations, wherein the circulation control means are adapted to switch off the circulation pump when the measured difference in temperature between the two temperature sensors is less than a preset threshold value. The set threshold value of the temperature difference for the circulation control means is preferably lower than 5°C, more preferably lower than 2°C. The purpose of this control is that the circulation pump does not operate any longer than is necessary in order to cause the temperature of the water in the heat exchanger to become about the same as the temperature of the water in the hot water supply container, so that cooling of the heat exchanger can begin as quickly as possible.

[0010] The ventilation control means are preferably adapted to switch off the fan when the measured temperature at, in and/or close to the heat exchanger is less than a preset threshold value. The set threshold value of the temperature for the ventilation control means preferably lies between 45°C and 55°C, more preferably between 51°C and 54°C. The ventilation control means are also preferably adapted to control the rotation speed of the fan subject to the measured temperature at, in and/or close to the heat exchanger, wherein a higher measured temperature results in a higher rotation speed of the fan. In this way the fan is not used any longer than necessary, is used at an efficient power and unnecessary noise nuisance is prevented.

[0011] The water supply conduit and/or the water discharge conduit is preferably provided with a valve which prevents water flowing through the conduits when the circulation pump is switched off. Due to thermal flow hot water could otherwise still flow out of the supply container into the heat exchanger. The valve can be a non-return valve which is closed here by for instance its own weight or by a spring.

[0012] The invention also relates to a method of heating water by means of a heating device, wherein a fuel is burned in a combustion chamber in which a heat exchanger extends; wherein a fuel supply conduit, an air inlet pipe and a flue gas outlet pipe are connected to the combustion chamber; wherein a water supply conduit and a water discharge conduit are connected to the heat exchanger and connected at their other outer end to a hot water supply container; wherein a fan is placed in the air inlet pipe and/or in the flue gas outlet pipe which causes a gas flow from the air inlet pipe through the combustion chamber to the flue gas outlet pipe; and wherein a circulation pump is incorporated in the system which circulates the water through the water supply conduit, the heat exchanger, the water discharge conduit and the hot water supply container; wherein the fan and the circulation pump are switched off after the fuel supply conduit has been closed; and wherein the fan is switched off after the circulation pump has been switched off such that air flows along the heat exchanger while the water is stationary therein for the purpose of cooling this water.

[0013] Further features, aspects, advantages and possibilities relating to the invention are described hereinbelow on the basis of an exemplary embodiment and with reference to the figure, in which a heating device is shown schematically.

[0014] The heating apparatus according to the figure is provided with a combustion space 1 in which is situated a heat exchanger 8 and in which is situated a burner 2 which is connected by means of a gas/air mixture inlet pipe 7 to an air inlet pipe 5 and a gas inlet pipe 6. Air inlet pipe 5 comprises a pipe part which is present in the device and to which an external pipe of a desired length can be connected. The gas and the air are mixed in a correct ratio and fed to burner 2 by means of a fan 4. The gas/air mixture is converted into thermal energy by means of a burner 2. This energy is carried along the heat exchanger, wherein the resulting heat is relinquished to the water for heating. The temperature of the water is hereby increased, whereafter the combustion gases, the temperature of which has decreased due to this exchange, are carried via a pipe system 3 to the outside atmosphere. The flue gas outlet pipe system 3 comprises a pipe part which is present in the device and to which an external pipe of a desired length can be connected.

[0015] Depending on the construction and the intended efficiency, the heat exchanger will provide an amount of resistance to throughflow of the flue gases. This resistance can be overcome by applying a fan 4 with a correct pressure increase adjusted to the resistance such that sufficient pressure still remains, and such that the flue gases which have left heat exchanger 8 can be displaced through pipe system 3 to the outside atmosphere.

[0016] The water is pumped by a circulation pump 9 from a hot water supply container 10 via a water supply conduit 11 to heat exchanger 8, whereafter it flows back again into hot water supply container 10 via a water discharge conduit 12. Hot water supply container 10 is provided with a hot water discharge conduit (not shown) whereby a user can draw off the hot water, and there is a cold water supply conduit (not shown) connected to heat exchanger 8 through which the drained water can be replenished.

[0017] The heating apparatus comprises two temperature sensors 13, 14 which can measure the temperature of the water supply conduit and the water discharge conduit. A control means (not shown) switches off circulation pump 9 when the measured difference in temperature between the two temperature sensors is less than a preset threshold value of for instance 1°C.

[0018] Another control means (not shown) switches off fan 4 after circulation pump 9 has been switched off such that cold air flows through pipes 5, 7 along heat exchanger 8 while the water is stationary therein, for the purpose of cooling this water. The control means only switches off fan 4 when the temperature in sensor 14, which is situated close to the heat exchanger, is lower than 52°C. The rotation speed of fan 4 is variable and the control means ensures that fan 4 operates at a higher rotation speed at higher measured temperatures of sensor 14.

[0019] Supply conduit 11 is provided with a non-return valve (not shown) in order to prevent hot water flowing out of supply container 10 to heat exchanger 8 when pump 9 is not in operation.

Claims

1. Heating device for supplying hot water, comprising a combustion chamber in which a heat exchanger extends;
wherein a fuel supply conduit, an air inlet pipe and a flue gas outlet pipe are connected to the combustion chamber;
wherein a water supply conduit and a water discharge conduit are connected to the heat exchanger and connected at their other outer end to a hot water supply container;
wherein a fan is placed in the air inlet pipe and/or in the flue gas outlet pipe which can cause a gas flow from the air inlet pipe through the combustion chamber to the flue gas outlet pipe; and
wherein a circulation pump is incorporated in the system which can circulate the water through the water supply conduit, the heat exchanger, the water discharge conduit and the hot water supply container;
wherein the heating device comprises ventilation control means which are adapted to switch off the fan after the fuel supply conduit has been closed; and
wherein the heating device comprises circulation control means which are adapted to switch off the circulation pump after the fuel supply conduit has been closed;
characterized in that
the ventilation control means are adapted to switch off the fan after the circulation pump has been switched off such that air flows along the heat exchanger while the water is stationary therein for the purpose of cooling this water.

2. Heating device as claimed in claim 1, wherein the heating device comprises at least two temperature sensors which can measure the temperature at least at two different locations of the heat exchanger, the water supply conduit, the water discharge conduit and the hot water supply container, or of the water situated therein at these locations,
wherein the circulation control means are adapted to switch off the circulation pump when the measured difference in temperature between the two temperature sensors is less than a preset threshold value.

3. Heating device as claimed in claim 2, wherein the set threshold value of the temperature difference for the circulation control means is lower than 5°C, preferably lower than 2°C.

4. Heating device as claimed in claim 1, 2 or 3,
wherein the heating device comprises at least one temperature sensor which can measure the temperature at the heat exchanger or at the water supply conduit or the water discharge conduit close to the heat exchanger, or of the water situated therein at this location, wherein the ventilation control means are adapted to switch off the fan when the measured temperature is less than a preset threshold value.

5. Heating device as claimed in claim 4, wherein the set threshold value of the temperature for the ventilation control means lies between 45°C and 55°C, preferably between 51°C and 54°C.

6. Heating device as claimed in claim 4 or 5, wherein the ventilation control means are adapted to control the rotation speed of the fan subject to the measured temperature at, in and/or close to the heat exchanger, wherein a higher measured temperature results in a higher rotation speed of the fan.

7. Heating device as claimed in any of the foregoing claims 1-6, wherein the water supply conduit and/or the water discharge conduit is provided with a valve which prevents the water flowing through the conduits when the circulation pump is switched off.

8. Method of heating water by means of a heating device, wherein a fuel is burned in a combustion chamber in which a heat exchanger extends;
wherein a fuel supply conduit, an air inlet pipe and a flue gas outlet pipe are connected to the combustion chamber;
wherein a water supply conduit and a water discharge conduit are connected to the heat exchanger and connected at their other outer end to a hot water supply container;
wherein a fan is placed in the air inlet pipe and/or in the flue gas outlet pipe which causes a gas flow from the air inlet pipe through the combustion chamber to the flue gas outlet pipe; and
wherein a circulation pump is incorporated in the system which circulates the water through the water supply conduit, the heat exchanger, the water discharge conduit and the hot water supply container;
wherein the fan is switched off after the fuel supply conduit has been closed; and
wherein the circulation pump is switched off after the fuel supply conduit has been closed;
characterized in that
the fan is switched off after the circulation pump has been switched off such that air flows along the heat exchanger while the water is stationary therein for the purpose of cooling this water.

Drawing