GB2213243A

GB2213243A - Gas-fired hot water boiler

Info

Publication number: GB2213243A
Application number: GB8906486A
Authority: GB
Inventors: Malcolm Kennedy
Original assignee: Glow Worm Ltd
Current assignee: Glow Worm Ltd
Priority date: 1985-11-18
Filing date: 1989-03-21
Publication date: 1989-08-09
Anticipated expiration: 2005-11-18
Also published as: GB8528386D0; GB8906486D0; GB2183016B; GB2183016A; GB2213243B

Abstract

Combustion gases from the burner 4 of a hot water boiler are cooled in a heat exchanger 6. Any condensate produced is collected via a drain 13, and the gases are re-heated as they pass via channel 15 to an outlet 16. An indicator e.g. a light, disposed in the casing will be activated by a temperature sensor 18 when the boiler is operating in a condensing mode. <IMAGE>

Description

Gas-Fired Boilers This invention relates to gas-fired boilers and more particularly to gas-fired condensing hot water boilers.

Gas-fired condensing hot water boilers make use of the principle of cooling the hot combustion products (flue gases) derived from a gas burner to a temperature below the dew point thereof, whereby condensation of the flue gases takes place, the latent heat thereby produced being transferred to the water being heated. In this way the efficiency of the boiler can be significantly increased.

However, when the cooled flue gases are emitted from the boiler, there is a tendency for condensation to collect in the boiler flue duct and/or terminal. This is most undesirable since it can result in condensate, which is usually mildly acidic, dripping from the terminal or running down the wall through which the flue duct may extend.

According to one aspect of the present invention there is provided a gas-fired condensing hot water boiler in which hot combustion products derived from a gas burner thereof are cooled in heat exchanger means to a temperature below the dew point temperature thereof to cause condensate to be produced, means being provided for re-heating the cooled combustion products to a temperature above the dew point temperature thereof before being emitted from said boiler.

Such an arrangement results in a slightly reduced boiler efficiency but the problems of condensate collecting in the boiler flue duct and/or terminal are overcome.

In carrying out the present invention, the cooled combustion products may be re-heated by the heat exchanger means such as by causing them to flow adjacent to a heated surface of the heat exchanger means.

In a preferred arrangement according to the present invention the gas burner will take the form a fully pre-mixed, forced draught, downwardly firing gas burner, the hot combustion products from which are directed downwardly through a heat exchanger in which they are cooled below the dew point temperature thereof to cause condensate to be produced, drain means being provided for draining off excess condensate, the cooled combustion products emanating from the heat exchanger means being directed upwards adjacent a surface heated by the heat exchanger to cause them to be re-heated before being emitted from a flue outlet of said boiler.

In such an arrangement the flue outlet of the boiler will conveniently be disposed above the lowermost part of the heat exchanger.

Condensing boilers can only operate in their condensing mode if the water temperature at the input of the heat exchanger thereof is sufficiently low compared to the dew point of the combustion products. Since the boiler is operating at its most efficient when it is in its condensing mode it is desirable to know when this is the case. Therefore in accordance with another aspect of the present invention there is provided a gas-fired condensing hot water boiler having means, e.g. an indicating light for indicating when condensate is or is likely to be being produced.

In carrying out the invention according to the aforesaid second aspect, the indicating means may include a temperature sensor for sensing the temperature of the cooled combustion products from the heat exchanger thereof and for causing indicator means to be operated when the temperature of said products is below a predetermined temperature.

An exemplary embodiment of the invention will now be described with reference to the accompanying drawings, in which: Figure 1, is a front view of the gas-fired condensing hot water boiler in accordance with the present invention; and Figure 2, is a side view of the boiler of Fig. 1.

The gas-fired condensing hot water boiler shown in the drawings is contained within a casing 19 and comprises a fan 1 which is supplied with air derived from an air inlet duct 2 and gas supplied from a gas feed pipe 3. The gas feed is supplied to the fan 1 upstream thereof whereby the fan 1, in operation, provides a fully pre-mixed, forced draught, gas/air mixture to a burner 4.

The burner 4 is of the downwardly firing, perforated plate type which is provided with ignition electrodes 5 for causing the gas/air mixture supplied to the burner 4 to be ignited on the undersurface thereof.

The hot combustion products thereby produced are directed downwards, in response to the forced draught from the fan 1, through a hot water heat exchanger 6 which consists of thirteen aluminium finned tubes 7 disposed transversely in a 3:2:3:2:3 formation across the path of the combustion products, the finned tubes 7 being carried between opposing aluminium manifolds 8 and 9 which effectively connect the tubes 7 in series.

Water is supplied to the finned tubes 7 via a water inlet feed 10 and a water outlet feed 11.

In operation of the boiler thus far described, the hot combustion products from the burner 4 will be cooled by the finned tubes 7 of the heat exchanger 6, thereby causing the water in the heat exchanger 6 to be heated.

Providing the temperature of the water inlet feed is sufficiently below the dew point temperature (e.g. 550C) of the hot combustion products, the combustion products will be cooled to a temperature below the dew point thereof, and water vapour in the condense on the finned tubes 7 and the resulting latent heat will be imparted to the water in the finned tubes 7. In this way the efficiency of the boiler can be greatly improved relative to a conventional non-condensing boiler.

The condensate produced on the finned tube 7 falls onto a rearwardly and downwardly inclined collecting tray 12 on which the condensate, which is mildly acidic, collects, and excess condensate is removed from the boiler via a condensate drain pipe 13.

The hot combustion products from the heat burner 4, after passage through the heat exchanger 6 are directed, via an outlet 14 at the bottom of the heat exchanger 6, upwards along rearward passageway 15 to a flue gas outlet duct 16. In passing through the passageway 15, the flue gases from the heat exchanger, which may be at a temperature below the dew point thereof, are caused to be re-heated due to the passageway 15 being directly adjacent the heat exchanger 6, so that when they are emitted from the oulet duct 16, they are at a temperature (e.g. 800C) which is above their dew point temperature. In this way the problem of condensate forming or collecting in the outlet duct 16 or on any terminal connected thereto is obviated.

Preferably it is arranged that the collecting tray 12 and the rear-wall 17 of the passageway 15 are formed integrally with one another.

As has already been stated, condensing boilers can only operate in their condensing mode if the water temperature at the inlet of the heat exchanger is sufficiently low compared to the dew point temperature of the hot combustion products. Since the boiler is operating at its most efficient when it is operating in its condensing mode it is desirable to know when this is the case. In the boiler depicted in the accompanying drawings this is achieved by providing a temperature sensor 18 in the bottom part of the passageway 15 for sensing the temperature of the flue gases at that point.

When the temperature of the flue gas as sensed by the temperature sensor 18 is below a predetermined temperature (e.g. 550C) it can be assumed that the boiler is operating in its condensing mode and the temperature sensor 18 output is used to cause an indicator 19, which may take the form of an indicating light, disposed in the casing 19 of the boiler to be operated.

Although described with reference to a specific type of condensing boiler, it should be appreicated that the feature of re-heating the cooled combustion products from the heat exchanger before they are emitted from a flue outlet may be applied to any form of condensing boiler, and also the re-heating may be effected by the heat exchanger as described above or by any other suitable means.

Claims

1. A gas-fired condensing hot water boiler in which hot combustion products derived from a gas burner thereof are cooled in heat exchanger means to a temperature below the dew point temperature thereof to cause condesate to be produced, means being provided for re-heating the cooled combustion products to a temperature above the dew point temperature thereof being emitted from said boiler.

2. A boiler as claimed in claim 1, in which the cooled combustion products are re-heated by the heat exchanger means.

3. A boiler as claimed in claim 2, in which the cooled combustion products are re-heated by the heat exchanger means by causing them to flow adjacent a surface heated by the heat exchanger means.

4. A boiler as claimed in any preceding claims, in which the gas burner takes the form of a fully pre-mixed, forced draught, downwardly firing gas burner.

5. A boiler as claimed in claim 4, in which the hot combustion products from the gas burner are directed downwardly through a heat exchanger in which they are cooled below the dew point temperature thereof to cause condensate to be produced.

6. A boiler as claimed in claim 5, comprising drain means for draining off excess condensate.

7. A boiler as claimed in claim 5 or claim 6, in which the cooled combustion products emenating from the heat exchanger are directed upwards adjacent a surface heated by the heat exchanger to cause them to be re-heated before being emitted from a flue outlet of said boiler.

8. A boiler as claimed in claim 7, in which the flue outlet of said boiler is disposed above the lowermost part of the heat exchanger.

9. A boiler as claimed in any preceding claim, comprising indicating means for indicating when the boiler is operating in its condensing mode.

10. A boiler as claimed in claim 9, in which the indicating means includes a temperature sensor for sensing the temperature of the cooled combustion products from the heat exchanger thereof and for causing indicator means to be opera Led when the temperature of said products is below a predetermined temperature.

11. A gas-fired condensing hot water boiler in which hot combustion products derived from a gas burner thereof are cooled in heat exchanger means to a temperature below the dew point temperature thereof to cause condensate to be produced, and means for indicating when condensate is being so-produced.

12. A boiler as claimed in claim 11, in which the indicating means includes a temperature sensor for sensing the temperature of the cooled combustion products from the heat exchanger means and for causing indicator means to be operated when the temperature of said products is below a predetermined temperature.

13. A gas-fired condensing hot water boiler substantially as hereinbefore described with reference to the accompanying drawings.