GB2087064A - Heating apparatus - Google Patents

Abstract

Heating apparatus for reclaiming heat from flue gases passing along a flue pipe (11) comprises a cylindrical enclosure (10) surrounding the flue pipe (11) and having diametrically opposed inlet (13) and outlet (17) which extend parallel with the flue pipe (11) over the full length of the enclosure (10). A fan (16) controlled in response to an enclosure wall temperature sensor (19) causes an airflow through a diverging passageway (14) to the inlet (13), through the enclosure (10) and out of the divergent outlet (17) to ducting (18) leading to a location to be heated. The flue pipe (11) is provided with outer fins (12) and an internal spiral guide (20) to increase heat conduction from the flue gases to the airflow. <IMAGE>

Description

SPECIFICATION Heating apparatus This invention relates to heating apparatus and in particular to apparatus for reclaiming heat from flue gases which would otherwise pass to waste.

Since the cost of fuel for use in heating homes and the like is ever increasing and the stocks of such natural fuels are diminishing it is of increasing importance to use fuel as efficiently as possible. in this context it has long been realised that flue gases issuing from heating appliances carry a considerable amount of heat to waste and several proposals have been made for reclaiming such heat. Such proposals have included ducting the flue gases to areas requiring heating or passing the flue gases through heat exchangers.

However, such proposals have not been very effective in practice and particularly in the former case give rise to objections on the grounds of safety.

It is also known to pass cold air in the case of air conditioning systems, or fuel/air mixtures in the case of engines, around a hot flue pipe or exhaust manifold respectively so as to heat the air or fuel/air mixture. The achieved temperature rise of the air or fuel/air mixture is sufficient only to prevent substantial cooling of the premises in the former cases and to improve the efficiency of the combustion process in the latter case. In all of the aforementioned cases the proportion of the available heat which is removed from the flue or exhaust gases is relatively small, and it is an object of the present invention to provide apparatus which will reclaim a substantial proportion of the available heat from the flue gases such as will provide heating for a part of the premises not heated directly by the heating appliance from which the flue gases emanate.

The invention provides heating apparatus for reclaiming heat from the flue gases of a heating appliance having a flue pipe extending therefrom, said apparatus comprising an enclosure through which said flue pipe passes, said enclosure having an inlet extending substantially parallel with said flue pipe, said inlet being at the downstream end of a divergent passageway, airflow generating means adapted to generate an airflow along said passageway, and through said inlet into said enclosure, and a converging outlet in said enclosure diametrically opposed to said inlet.

Preferably said outlet is connected to ducting through which air, heated in said enclosure, may be passed to a location or locations to be heated.

In this respect the invention is seen as having particular application to the reclaiming of heat from the flue gases of a solid fuel heating appliance, which appliance is provided for heating the downstairs rooms of a domestic premises, and the heated air from the apparatus may then be utilized for heating the upstairs rooms of that premises.

Said airflow generating means is preferably a fan. Means may be provided for sensing the temperature of a wall of said enclosure and control means may be provided for switching on or off said fan in response to a predetermined temperature or temperatures sensed by said sensing means.

Fins may be provided on the outside of said flue pipe to increase the surface area thereof to be contacted by airflow through said enclosure. Said fins may be in the form of a star in planform.

A spiral guide may be provided within said flue pipe so as to direct flue gases flowing therethrough outwardly towards said flue pipe.

One embodiment of apparatus in accordance with the invention will now be described with reference to the accompanying drawings in which: Fig. 1 is a sectional elevation; Fig. 2 is a sectional plan view.

Referring now to the figures there is shown a cylindrical enclosure 10 through which a flue pipe 11 passes. The flue pipe 11 has a vitreous coating 1 a within a steepl pipe 1 b so as to be impervious to flame produced by a solid fuel heating appliance (not shown) to which the flue pipe 11 is connected. Fins 12 are attached to the flue pipe 11 so as to increase the outer surface area thereof which can be contacted by air passing through the enclosure 10.

An inlet 13 is provided in the enclosure 10, and extends parallel with the flue pipe 11 throughout the length of the enclosure 10. A divergent passageway 14 leads to the inlet 13 from a housing 1 5 in which is mounted a fan 1 6. The fan 1 6 is driven by a motor (not shown).

Diametrically opposite inlet 13 there is provided in the enclosure 10 an outlet 1 7. The outlet 1 7 extends over substantially the whole axial extent of the enclosure 10 and a passageway 1 8 converges away from the outlet 1 7 and enclosure 1 0. This arrangement has the effect of allowing air from around the whole length of the flue pipe 11 within the enclosure 10 to be throttled down and be delivered through passageway 1 8 to ducting (not shown). Such ducting may lead heated air to a room or rooms of premises in which the apparatus is installed.

Since flue gas is ducted to waste and not ducted to rooms there is no danger associated with the arrangement hereindescribed.

A temperature sensor 1 9 is provided on the enclosure 10 and control means (not shown) is adapted to control operation of the aforementioned fan motor in response to predetermined values of temperature sensed by sensor 1 9.

A spiral guide 20 is located within the flue pipe 11 so as to cause the flue gases passing therethrough to spin outwardly and in contact with the wall of the flue pipe to ensure good heat conduction thereto. The guide 20 is mounted so as to be easily removable for cleaning purposes both of itself and of the flue pipe 11.

The operation of the apparatus is as follows. As a consequence of hot flue gases passing through the flue pipe 11 the outer steel wall 11 b becomes heated. The air within the enclosure 10, which air is static at this stage, becomes heated and in turn the wall of enclosure 10 becomes heated. When a predetermined temperature of the enclosure 10 has been reached, for example 1 350F, (570C) as sensed by the temperature sensor 1 9 the fan 1 6 is caused to operate. Air is then blown by the fan 1 6 along divergent passageway 14 and into the enclosure 10 in which the airflow will be turbulent by virtue of the large angle of divergence of the passageway 14 and the sudden changes of air flow direction as the air enters the enclosure 1 0.

The turbulent airflow within enclosure 10 provides for the maximum heat transfer from the outside of the flue pipe 11 to the air, and the fins 12 on the flue pipe 11 further facilitate such maximum heat transfer by increasing the surface area of flue pipe 11 for contact by the air. The inlet 13 and outlet 17 extend substantially the full length of the enclosure 10 to ensure that the airflow through the enclosure 10 utilizes the total extent thereof without relatively static air regions at the upper and lower ends of the enclosure. Also this configuration of inlet 13 and outlet 1 7 ensures that a small portion of the flue pipe 11 is not overcooled due to a high speed narrow jet of air passing therearound as would occur if the apparatus comprised a small inlet and a small outlet.The throttling of the air as it passes along convergent passageway 18 provides that there is an appropriate static pressure within the system to preclude a high speed throughflow of air which would overcool the flue pipe and render the apparatus ineffective. The characteristics of ducting to the room or rooms to be heated the dimensions of the passageways 14, 1 8 and the size and speed of the fan 16 are chosen so as to provide desired turbulence and speed of airflow within enclosure 10 to give optimum heating effect to the ducted air. In order that the airflow through enclosure 10 does not cool the flue pipe 11 excessively and render the apparatus ineffective the control of the fan 16 may be arranged so that the fan is switched off if the temperature sensed by sensor 1 9 falls below a predetermined figure, for example 1 000 F (3 8 OC).

The fan 1 6 may be switched off at a predetermined high temperature if so desired and also may be provided with a control-overriding manually operated switch.

Claims (14)

1. Heating apparatus for reclaiming heat from the flue gases of a heating appliance having a flue pipe extending therefrom, said apparatus comprising an enclosure through which said flue pipe passes and having an inlet and an outlet communicating with a space in said enclosure surrounding said flue pipe, said inlet being disposed at a downstream end of an inlet passageway, and airflow generating means adapted to generate an airflow along said passageway, through said inlet, said space and said outlet.

2. Heating apparatus according to claim 1 wherein said outlet is connected to ducting along which said airflow is caused to pass.

3. Heating apparatus according to claim 1 or claim 2 wherein said airflow generating means comprises a fan.

4. Heating apparatus according to claim 3 comprising temperature sensing means adapted to sense the temperature of a wall of said enclosure and control means adapted to switch on or off said fan in response to a predetermined temperature or temperatures being sensed by said sensing means.

5. Heating apparatus according to claim 4 further comprising a manual override switch for said fan.

6. Heating apparatus according to any one of claims 1 to 5 wherein said enclosure is cylindrical and said flue pipe extends therethrough substantially axially thereof.

7. Heating apparatus according to claim 6 wherein said inlet and said outlet are elongate and extend in directions substantially parallel with said flue pipe.

8. Heating apparatus according to claim 7 wherein said inlet and said outlet extend over substantially the full axial extent of said enclosure.

9. Heating apparatus according to any one of claims 1 to 8 wherein said inlet passageway diverges towards said inlet.

10. Heating apparatus according to any one of claims 1 to 9 wherein said outlet converges away from said enclosure.

11. Heating apparatus according to any one of claims 1 to 10 wherein said inlet and said outlet are at diametrically opposed sides of said enclosure.

12. Heating apparatus according to any one of claims 1 to 11 wherein fins are provided on the outer surface of said flue pipe within said enclosure.

13. Heating apparatus according to claim 12 wherein said fins are in the form of a star in planform.

14. Heating apparatus according to any one of claims 1 to 1 3 wherein a spiral guide is provided within said flue pipe in the region of said enclosure.

1 5. Heating apparatus substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.