GB2335268A

GB2335268A - Gas fired heating unit

Info

Publication number: GB2335268A
Application number: GB9905157A
Authority: GB
Inventors: Martin Searle; David Whittaker
Original assignee: BAXI HEATING Ltd
Current assignee: BAXI HEATING Ltd
Priority date: 1998-03-07
Filing date: 1999-03-08
Publication date: 1999-09-15
Anticipated expiration: 2019-03-08
Also published as: IE990189A1; GB9804790D0; GB9905157D0; GB2335268B

Abstract

A gas fired heating unit for fitting into an open recess defined in a wall of a room incorporates a from section in which an open-fronted gas fire (5) is located and may incorporate a water-heating boiler (1) in a rear section. An exhaust duct (2) is arranged to convey combustion products from the unit to an exhaust outlet external to the room. A combustion air inlet duct (3) is arranged to convey combustion air from an air inlet external to the room to an outlet (10) in the front section of the unit which opens into the adjacent room space. The combustion air outlet may be defined by a vent above the open fire. An air-heating heat exchanger (4) is arranged to transfer heat from combustion products in the exhaust duct (2) to combustion air in the inlet duct (3). Ducts (2) and (3) may be fitted with fans. Combustion air from the room is supplied to the burners in the fire and the boiler via a passage (9). A flow control valve (11) may direct combustion air through an internal passage (12) to the base of the unit. Alternatively, the flow control valve may divert inlet air into the space immediately behind the heating unit.

Description

1 GAS FIRED HEATING UNIT This invention relates to a gas fired heating

unit.

Domestic gas fired heating units or appliances are known which are dimensioned to fit within a standard fire opening of a chimney. These appliances generally incorporate a hot-water boiler arranged to provide domestic space heating through a radiator system and sanitary hot water from a storage cylinder, and an openfronted gas fire giving local space heating and a visual focal point. It is also known however to dispense with the provision of a boiler such that the appliance comprises only an open-fronted gas fire.

Appliances of the above type bum gas with combustion air and produce combustion products which are conveyed to the exterior atmosphere through a suitable flue, for example through a flue lining extending along the length of the existing chimney. Combustion air is drawn from the room in which the appliance is located, and therefore it is neces. sary to ventilate the room to ensure a reliable supply of combustion air. Ventilation generally is provided by inserting at least one air-brick in a wall of the room in which the appliance is located. Air-bricks suffer from the disadvantage that they may cause drafts across the room in which the appliance is situated. As a result it is well known that misguided individuals block air-bricks to prevent such drafts without appreciating the potentially serious consequences in terms of air quality within the room. It is also known for air-bricks to be blocked by for example plant growth with the same potentially disastrous results.

1 2335268 It is an object of the present invention to obviate or mitigate the problems outlined above.

According to the present invention there is provided a gas fired heating unit for fitting into an open recess defined in a wall of a room, comprising a heater which defines a front section of the unit and which in use is located at the front of the recess and serves to heat the adjacent room space, and an exhaust duct arranged to convey combustion products from the heater to an exhaust outlet external to the room, wherein a combustion air inlet duct is arranged to convey combustiori.ah ftom an air 2 inlet external to the room to an outlet in the front section of the unit which opens into the adjacent room space, and an air-heating heat exchanger is arranged to transfer heat from combustion products in the exhaust duct to combustion air in the inlet duct.

In accordance with the present invention, combustion air for operation of the unit is delivered to the room in which the unit is located through the inlet duct and therefore it is not necessary to provide an alternative means of ventilation to the room in which the unit is located. Thus there is no need to provide airbricks which may be deliberately or inadvertently blocked with potential safety implications.

An inlet fan is preferably arranged in the inlet duct, for example at the air inlet end or the heater end of the duct, to pump combustion air through the inlet duct. Similarly, an exhaust fan is preferably arranged in the exhaust duct, for example at the exhaust outlet end or the heater end of the duct, to pump combustion products through the exhaust duct.

Preferably the air outlet is located above the heater which defines the front section of the unit. A flow control valve may be provided to divert combustion air from the inlet duct away from the air outlet located above the heater, for example through a passage extending behind the heater to a passage defined beneath the heater and through which combustion air is delivered to the heater, or into the recess behind the unit. Diversion of the inlet combustion air can be desirable when it is necessary to deliver combustion air to the unit but it is not wished to increase the heat input to the adjacent room by causing heated combustion air to issue into the room from the front section of the unit. For example, circumstances can arise in the summer in which it is desirable to operate the unit but not to deliver heated combustion air to the space in front of the unit.

The unit may incorporate a further heater which defines a rear section of the unit and which in use is located within the recess behind the front section. A water heating heat exchanger may be arranged to be heated by the further heater, combustion products from the further heater being conveyed to the exhaust duct through the air-heating heat exchanger. The further heater may be required to deliver hot water even in circumstances in which no room heating is required and in such 1 3 circumstances it is important to be able to divert the combustion air directly to the further heater rather than through the room in which the unit is located. Combustion air may be conveyed to the further heater through a lower portion of the front section of the unit to which the flow of combustion air from the inlet duct may be diverted by the above- mentioned control valve.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a schematic part-sectional side view of a domestic gas appliance in accordance with a first embodiment of the present invention and in a first operational configuration; Figure 2 is a schematic view similar to that of Figure 1 showing the appliance in a second operational configuration; Figure 3 is a schematic view similar to that of Figure 1 but showing the appliance in a third operational configuration; Figure 4 is a schematic sectional side view of a second embodiment of the present invention which is similar to the embodiment of Figures 1 to 3 but incorporate only one heater; Figure 5 is a schematic view from above as a third embodiment of the present invention on which inlet and exhaust inlet and exhaust fans are directly mounted. and Fiaure 6 is a schematic illustration of a fourth embodiment of the present invention.

Referring to Figures 1 to-3, the illustrated domestic gas appliance comprises a boiler 1, an exhaust duct 2, an air inlet duct 3, a heat recovery heat exchanger 4, and an open-fronted gas fire 5. The appliance is located within a recess located below a chimney space or flue 6.

The arrows in the Figures indicate the direction of flow of air and combustion products during operation of the unit. The unit comprises gas burners (not shown in detail) located in a lower portion 7 of the gas fire 5 and further gas burners (nor shown in detail) in a lower portion 8 of the boiler 1. Combustion air is supplied to the two sets of gas burners through a passage 9 which extends beneath the gas fire 5. Products t -- 4 of combustion from both the boiler 1 and the fire 5 are passed through the heat recovery heat exchanger 4 and then through the exhaust duct 2. Air is taken in through the inlet duct 3) and is passed through the heat recovery heat exchanger 4, where it is warmed by heat from the combustion products. The warmed air passes through a vent 10 to ventilate and to provide space heating to a room in which the appliance is located. The boiler 1 incorporates a water-filled heat exchanger (not shown in detail) to enable water to be heated for circulation to a network of radiators (not shown).

The heat exchanger 4 is provided with a first surface area of relatively large extent which is heated by the passage of the combustion products and a second surface area of relatively large extent across which combustion air supplied through the inlet duct 3 passes and is as a result warmed. The heat exchanger may be made up of a number of moulded high temperature-resistant polymer sheets stacked together to form alternate flow paths for the combustion products and the air, the moulded surfaces providing the necessary extensive surface areas. Alternatively, the heat recovery heat exchanger may be metallic, and may be constructed for example from plates of aluminium, cast iron, copper or stainless steel, or may be constructed from finned tubes. - The air inlet duct 3) and the exhaust duct 2 are fitted with fans (not shown).

These fans may be fitted adjacent the boiler 1 or may be fitted at the ends of the ducts 2 and 3 remote form the boiler, for example by being fitted into an outlet (not shown) from the exhaust duct 2 and an inlet (not shown) to the air inlet 3). If the fans are fitted at the boiler, the fans may be located in part of the space occupied by the heat exchanger in the arrangement as illustrated in Figure 1. The necessary space may be obtained by positioning all or a major proportion of the heat exchanger immediately behind the vent 10. Space is- then available immediately above the boiler 1 to accommodate the fans which are coupled to the ducts 2, 3.

It will be appreciated that the outlet end of the exhaust duct 2 and the inlet end of the inlet duct 3 should be positioned such that combustion products from the exhaust duct 2 cannot be drawn into the inlet duct 3. The ducts 2 and 3 may extend to suitable terminations (not shown) at the top of the flue 6, but preferably the ducts 2 and 3 will extend to the nearest adjacent exterior wall so as to limit the length of the ducts and to make access easier. For example, the ducts 2 and 3 can extend to a common termination unit mounted in a vertical wall with the inlet to the duct-3 spaced from and located beneath the outlet from the duct 2.

The unit incorporates a flow control valve 11 which may be positioned as shown in Figure 1 to direct combustion air from the inlet duct 3 to the vent 10, or as shown in Figure 2 to direct combustion air through an internal passage 12 to the base of the unit.

The configuration of the appliance illustrated in Figure 1 allows simultaneous operation of the boiler 1 and the fire 5 and this will be the normal winter configuration. Combustion air is drawn in through the passage 9 beneath the fire 5 to both the fire 5 and the boiler 1. Combustion products pass from the fire 5 and the boiler 1 to the exhaust duct 2 through the heat exchanger 4. Combustion air in the room in front of the unit is replenished by the flow of air through the duct 3, past the valve 11 and through the vent 10. Combustion products from both the fire 5 and the boiler 1 thus contribute to heating the combustion air flowing through the heat exchanger 4. As the supply of combustion air is provided via the duct 3, it is not necessary to provide alternative ventilation via for example air-bricks to the room in which the unit is fitted.

In the configuration of Figure 2, it is assumed that the fire 5 is not operational but the boiler 1 is operational to provide for example hot water. Such a configuration would be appropriate in for example the summer when hot water may be required but there is no space heating requirement. In the configuration of Figure 2, the valve 11 is switched to the position shown so as to divert the flow of combustion air from the duct J3) through the passage 12 to the passage 9, the combustion air flowing from the passage 9 to the boiler 1. The combustion air is heated as it passes through the heat exchanger 4 but is not delivered directly into the room in which the appliance is fitted although the passage 9 does open into the room. Of course if low level background

6 heating was required the valve 11 could be opened so that the heated combustion air would be introduced directly into the room.

The configuration shown in Figure 3 corresponds to circumstances in which neither the fire 5 or the boiler 1 is operational. The unit operates as a simple ventilator, drawing ventilation air in through the duct 3 and expelling air from the room through the duct 2. It would of course be possible to arrange for the unit when operating in the configuration shown in Figure 3 to operate in conjunction with a full house mechanical ventilation system and in addition could provide some cooling if linked to appropriate air conditioning equipment.

Referring to Figure 4, this shows an alternative embodiment of the invention in which the space behind the fire 5 is empty. This is in contrast to the arrangement of Figure 1 where a boiler is provided behind the fire 5. It will be appreciated that in some circumstances it is not necessary to provide a boiler to deliver hot water for space heating or sanitary purposes, and the embodiment of Figure 4 can be used in such circumstances. In the arrangement of Figure 4, during normal operation of the fire combustion products pass from the fire 5 through the heat exchanger 4 to the exhaust duct 2 and combustion air is delivered to the room in front of the appliance via the duct ") and the vent 10. Closure of the valve 11 would divert the flow of combustion air through the passage 12 but this would still be a safe configuration given that the combustion air would be made available to the fire 5 from the passage 9. Generally one would expect the valve 11 to be positioned as shown in Figure 4 so as to enhance the total heating efficiency of the unit.

It will be appreciated that conventional designs for the fire 5, boiler 1 and associated gas burners and control equipment may be used. The unit may bum any suitable gas, for example Natural Gas, LPG or Town Gas. The gas fire 5 may be of any appropriate type, for example radiant, and may be designed to fit within the recess as shown in the drawings (an inset configuration) or to project outwards from the recess (an outset configuration).

As explained above, the inlet and outlet fans may be positioned at any convenient location. The embodiment of the invention illustrated in Figure 5 shows 7 one arrangement for mounting air inlet and exhaust outlet fans directly behind the heating unit.

Referring to Figure 5, the illustrated heating unit has a heat exchanger 13 from a front side 14 of which inlet combustion air is issued as indicated by arrows 15. The inlet combustion air is delivered from an air inlet duct 16 via a centrifugal fan 17 directly mounted on a rear wall 18 defined by the heat exchanger. A centrifugal exhaust fan 19 is directly mounted on a rear wall 20 of the heat exchanger 13 and draws combustion products from the heat exchanger in the directions indicated by arrows 2 1. An outlet of the fan 19 is connected to an exhaust gas outlet duct 22.

It will be appreciated that the heat exchanger 13 is made up from a series of parallel plates each of which is parallel to the plane of Figure 5 so as to define a series of passageways. The passageway on one side of each plate is open at the front side 14 of the heat exchanger and carries inlet air, whereas the passageway on the other side of each plate is closed at the front side 14 of the heat exchanger but is open to receive combustion products from gas burning units located beneath the heat exchanger.

An arrangement such as that illustrated in Figure 5 in which inlet and exhaust fans are directly mounted on the heating unit is advantageous from the installers point of view and from the point of view of routine servicing as all the active components of the device are readily accessible adjacent the heating unit.

Referring now to Figure 6, this schematically illustrates a fourth embodiment of the invention in which an inlet air diversion valve is arranged in a manner different from the arrangement illustrated in Figures 1 to 4 in which an inlet air diversion valve 11 is arranged to divert inlet air through a passageway within the heating unit to the air inlet of burner units.

Referring to Figure 6, a gas burning unit 23 produces combustion products which pass through a heat exchanger 24 to an exhaust outlet duct 25. The outlet duct 25 may incorporate a temperature sensor 26 which will be incorporated in a control system (not illustrated). An air inlet duct 27 incorporates a diverter valve having a flap which is normally in the position indicated by full line 28 but is displaceable to the position shown by broken line 29. When the valve is in the position indicated by line 28, inlet area is forced through the heat exchanger 24 and issues from the heat exchanger via an outlet 30 provided in the front of the heat exchanger 24. The overall mode of operation is thus the same as in the case of the first embodiment as described with reference to Figure 1.

In circumstances in which it is not desired to deliver heated air through the outlet 30, for example when the burner unit 23) is operating but the ambient temperature is relatively high, the air inlet valve can be moved to the position shown by line 29. When the valve is so positioned, the inlet air is diverted into the space immediately behind the heating unit, that is into a recess in a wall within which the heating unit is positioned. Air for combustion will be drawn from this recess to the burner unit 23. Thus in contrast to the embodiments of Figures 1 to 4 in which a passageway 12 is provided within the body of the heating unit to carry diverted air, in the arrangement schematically represented in Figure 6 no such passageway is required as inlet air is simply diverted into the space within which the heatina unit is located.

W When the burner unit is fired up, it is desirable to heat up the exhaust duct 25 quickly thereby to limit the formation of condensation. To avoid cooling of combustion products in the heat exchanger during start-up, the temperature sensor 26 and the associated control system can be arranged to switch the valve to the position indicated by line 29 until the temperature sensed by the sensor 26 reaches a predetermined limited, whereafter the valve is switched to the position indicated by line 28.

In addition to the advantage of obviating the need for air-bricks in a room in which the unit is fitted, the heat recovery heat exchanger provided in accordance with the present invention improves overall efficiency. The flexibility afforded by the provision of both combustion air inlet and exhaust gas outlet ducts in terms of the siting of flue terminations makes it possible to use the unit in many different circumstances and. generally in an economical manner given that the lining of existing chimneys and the provision of flue terminals at the top of existing chimneys can be avoided. In addition, mechanical ventilation can be provided throughout the year in a manner which enables some heat recovery when this is appropriate.

9

Claims

1 A gas fired heating unit for fitting into an open recess defined in a wall of a room, comprising a heater which defines a front section of the unit and which in use is located at the front of the recess and serves to heat the adjacent room space, and an exhaust duct arranged to convey combustion products from the heater to an exhaust outlet external to the room, wherein a combustion air inlet duct is arranged to convey combustion air from an air inlet external to the room to an outlet in the front section of the unit which opens into the adjacent room space, and an air-heating heat exchanger is arranged to transfer heat from combustion products in the exhaust duct to combustion air in the inlet duct.

2. A heating unit according to claim 1, wherein an inlet fan is arranged in the inlet duct to pump combustion air through the inlet duct.

3. A heating unit according to claim 2, wherein the inlet fan is inlet.

located in the air

4. A heating unit according to claim 2, wherein the inlet fan is located at the heater end of the inlet duct.

5. A heating unit according to any preceding claim, wherein an exhaust fan is arranged in the exhaust duct to pump combustion products through the exhaust duct.

6. A heating unit according to claim 5, wherein the exhaust fan is located in the exhaust outlet.

7. A heating unit according to claim 5, wherein the exhaust fan is located at the heater end of the exhaust duct.

8. A heating unit according to any preceding claim, wherein the air outlet is located above the heater in the first section of the unit.

9. A heating unit according to claim 8, wherein a flow control valve is provided which may be controlled to divert combustion air from the inlet duct away from the outlet in the front section of the unit.

10. A heating unit according to claim 9, wherein the flow control valve is located in the front section of the unit and may be controlled to direct combustion air from the inlet duct through a passage extending behind the heater to a passage defined beneath the heater and through which combustion air is delivered to the heater.

11. A heating unit according to claim 10, wherein the flow control valve is located 1 in the air inlet duct and may be controlled to divert combustion air into the recess behind the unit.

12. A heating unit according to any preceding claim, comprising a further heater which defines a rear section of the unit and which in use is located within the recess behind the front section, and a water-heating heat exchanger which in use is filled with water and is arranged to be heated by the further heater, combustion products from the further heater being conveyed to the exhaust duct through the air-heating heat exchanger.

- 1

13. A heating unit according to claim 12, wherein combustion air is conveyed to the further heater through a lower portion of the front section of the unit.

14. A heating -unit substantially as hereinbefore described with reference to Figures 1 to 3, Figure 4, Figure 5 or Figure 6 of the accompanying drawings.