GB2082761A

GB2082761A - Space Heaters

Info

Publication number: GB2082761A
Application number: GB8122869A
Authority: GB
Original assignee: Colt International Ltd
Current assignee: Colt International Ltd
Priority date: 1980-07-26
Filing date: 1981-07-24
Publication date: 1982-03-10

Abstract

In a gas fired or an oil fired, indirect air heater for space heating. the thermodynamic efficiency of the heater is increased by warming the combustion air passing to the combustion air blower (C) of the heater by heat exchange with the products of combustion from the heater. <IMAGE>

Description

SPECIFICATION Improvements Relating to Air Heaters Gas fired or oil fired indirect air heaters are widely used for space heating.

Increased fuel costs demand an increase in efficiency of such heaters and such increase may, in fact, be enforced by Governmental measures.

An object of the present invention is to provide a simple means of providing such increased efficiency which may readily be applied to existing equipment as well as new equipment.

In accordance with one aspect of the present invention, the combustion air in a gas fired or oil fired indirect air heater is passed in heat exchange relation with the flue gases before being fed to the burner equipment of the heater.

In one arrangement according to the present invention, a combustion air blower of the heater is arranged to draw the combustion air through an air intake duct having an upstream portion which surrounds the heater flue.

In an alternative arrangement according to the present invention, the air intake duct for the combustion air drawn in by a combustion air blower is directed, in part along the inside of the heater flue.

The latter arrangement is useful where it is required to draw the combustion air from outside the space to be heated, the air intake duct entering the exit end of the flue.

In accordance with a further aspect of the present invention, in a gas fired or oil fired indirect air heater space heating air is passed in heat exchange relation with the flue gases before being fed to the air heater.

Specific embodiments of the present invention will now be described by way of example and not by way of limitation, with reference to the accompanying drawings in which: Fig. 1 is a diagrammatic representation of an oil fired indirect air heater according to the present invention, Fig. 2 is a rear view of the heater of Fig. 1, Fig. 3 is a view corresponding to Fig. 2, but shows a modification, Fig. 4 is a diagrammatic representation of a further oil fired indirect air heater according to the present invention, Fig. 5 is a further diagrammatic representation of the heater shown in Fig. 4, Fig. 6 is a perspective view of the heat exchanger included in the air heater shown in Figs. 4 and 5, and Figs. 7 and 8 are diagrammatic representations of still further embodiments of indirect air heaters according to the present invention.

With reference now to the accompanying drawings, the heater illustrated in Figs. 1 and 2 is a floor standing unit having a casing 9 enclosing a heat exchanger E (see Fig. 1) over which air, drawn into the casing 9 from the surrounding space to be heated by the heater, by centrifugal fan F having a scroll casing F' and a centrifugal fan wheel F", is passed by the fan, the heated air re-entering the space to be heated through grilles 10 at the top of the casing 9. A combustion airblower in the form of centrifugal fan C supplies combustion air to a combustion chamber A supplied with oil via a nozzle B. The products of combustion are exhausted up a flue 12 to outside atmosphere (see also Fig. 2).

The thermodynamic efficiency of the heater is increased by warming the combustion air passing to the combustion blower C by passing it in heat exchange relationship with the flue gases passing up the flue. To this end, a sleeve 20 is fitted to the flue adjacent the unit, to define an annular air intake passage 21 having an upper open end 22 through which air is drawn from the space to be heated. At its lower end the sleeve is fitted with a coupling 30 (see Fig. 2) which seals the sleeve with respect to the outside of the flue pipe at the lower end of the sleeve and which directs the warm air into a conduit 24 connected to the normal combustion air intake of the heater unit.

The duct 24 has an insulating covering to minimise heat loss and remove personal hazard.

Fig. 3 shows an alternative arrangement drawing the combustion air from outside the space to be heated, e.g. the outside atmosphere.

In this case, the conduit 24 is continued through the wall of the flue pipe 12 and upwardly along the inside of the flue to emerge through its upper open end, the upper end of the conduit 24 being open and defining a full circular air intake 26 for the combustion air blower.

The flue has, in this case, an annular outlet 28 for the exit of the flue gases and the flue outlet may be sheltered by an annular cowl 32 carried by the conduit 24 which itself has a cowl 36 at its upper, air intake end.

The former arrangement described with reference to Figs. 1 and 2 is preferred since it is more adaptable for reasons which will be explained but the arrangement of Fig. 3 is more efficient and may be adopted where, for example, for safety reasons, due to say a petrol fume laden atmosphere, it is necessary or advisable to draw the combustion air from outside.

Re-circulating waste heat from the flue gases enables the amount of oil or gas fuel used by the heater unit to be reduced to maintain a given room temperature despite the fact that direct room heating by the hot flue is reduced.

The arrangement of Fig. 1 is readily fitted to existing equipment. Tests on the Applicants' existing equipment have shown that within useful ranges of efficiency increase, the added resistance to combustion air flow to a combustion blower of the centrifugal fan type imposed by the sleeve 20 and/or the conduit 24 does not impair the ability of the usual combustion airblower C to deliver the combustion air requirements of the burner.

However, the length of the sleeve 12 is readily adjusted in accordance with the ability of an existing blower C to overcome the added resistance in any existing equipment and deliver the combustion air requirement. The size of the annular passage 21 also plays a part in determining the effectiveness of the energy saving arrangements being described and the resistance added to the combustion air flow path to the combustion blower. Some latitude is therefore offered with respect to existing equipment by varying also the diameter of the sleeve.

Tests have shown that for an existing oil fired unit modified as described with reference to Fig. 1 and having a flue 12 of 7 inches in diameter, a sleeve 20 of 12 feet in length and having a diameter of 8 inches, makes no appreciable difference to the volume of air delivered by the blower C and yet increases the thermal efficiency of the unit from 80% to 84%.

An existing oil fired unit modified as described with reference to Fig. 3 and having 30 feet of 5 inch diameter conduit 24 concentrically disposed inside a flue pipe 1 2 of 8 inches in diameter achieved a thermal efficiency increase of 7% but gave rise to some condensation of water in the flue.

Far higher thermal efficiencies can be achieved by using a higher pressure centrifugal fan C for blowing the combustion air to the burner. There is some practical limit to the increase, however, unless some means is provided for removing condensates, since over cooling of the flue gases, particularly when using oil fuel, gives rise to condensation of water in the flue pipe, which leads to corrosion problems. There is also a faster build up of solids in the flue if the flue gases are unduly cooled.

However, tests on the Applicants' existing equipment have shown that an increase of 5% in thermal efficiency using gaseous fuel is readily achieved by the heaters described with reference to Figs. 1 to 3 without practical problems occurring.

With reference now to Figs. 4 to 6 in which the same reference numerals and letters are used to indicate parts corresponding with parts in figs. 1 to 3 which parts will not be further described except in so far as is necessary to explain the construction and operation of the present embodiment, the combustion products of the combustion chamber A pass into the primary heat exchanger chamber 39 of the heat exchanger E and, after circulating therein, downwardly through four hollow support legs 40 of the heat exchanger into bottom collector boxes 41 of which two are provided one associated with a pair of the legs 40 on the two sides of the heat exchanger respectively.The boxes 41 communicate with a top collector box or secondary heat exchanger compartment 42 via a series of vertical heat exchange tubes 43 grouped on the same two sides of the heat exchanger, the top collector box 42 communicating centrally with a conduit 44 which conducts the flue gases into a pressure relief box 46 which in turn communicates at its upper end with the lower end of the flue 1 2. The pressure relief box communicates also with the interior of the primary heat exchanger chamber 39 through a pressure relief door 48.

The combustion air in the present example is drawn by the combustion air blower C through a combustion air duct 50 which passes through the top collector box 42 and centrally through the conduit 44 and through the pressure relief box centrally below the lower end of the flue 1 2 to open into the space being heated. The hot flue gases thus pass in heat exchange relation with the combustion air in the top collector box 42, and along the conduit 44, and in the pressure relief box before actually entering the flue and the thermodynamic efficiency of the heater is increased by more rapidly warming the combustion air passing to the combustion blower C due to the somewhat higher temperature of the flue gases in the regions indicated compared with the previous embodiments.Also, since a full circular, relatively short combustion air duct 50 is used in the present embodiment, the added resistance to combustion air flow to the combustion blower does not impair the ability of the usual blower C to deliver the combustion air requirement of the burner and the arrangement may be fitted with little difficulty to existing equipment.

It is to be understood that Figs. 4 and 5 are partially diagrammatic in that the pressure relief box and the combustion air blower are housed at the back of the outer casing 9 of the heater unit, the former outside the casing and the latter inside the casing. The combustion air duct is also housed inside the casing, except at its entry portion inside the pressure relief box, and the duct passes forwardly through the top collector box and then downwardly and rearwardly to the combustion air blower, portions of the combustion air duct being made flexible to allow for the passage of the duct through the casing of the unit to the blower.

Figs. 7 and 8 show still further embodiments of gas fired or oil fired indirect air heaters in which, again, the same reference numerals and letters are used to indicate parts corresponding with parts in Figs. 1 to 6 which will not be further described except in so far as is necessary to explain the construction and operation of these further embodiments. These still further embodiments suppose that the centrifugal fan C has insufficient capacity to deliver the full requirement of combustion air to the burner equipment against the upstream resistance imposed by the preheating arrangements for the combustion air, in this case, preheating arrangements as hereinbefore described with reference to Fig. 2 or Fig. 3. However, these preheating arrangements may be as hereinbefore described with reference to Figs. 4 to 6 if desired.

Accordingly, the conduit 24 is branched and the branch conduit 24' is connected with the space inside the casing 9 and opens into the casing 9 through a nozzle N (see Fig. 8), having its longitudinal axis coincident with the rotational axis of the fan wheel F". In this way, the main fan F is made to assist by increasing the volume flow of air through the conduit 24.

As shown in Fig. 7, instead of branching the conduit 24, the conduit 24 may be connected instead with the space inside the casing 9 to relieve the combustion air blower entirely of added resistance to air flow upstream of the blower.

Claims

1. A gas fired or an oil fired indirect air heater in which the combustion air is passed in heat exchange relation with the flue gases of the air heater before being fed to the burner equipment of the heater.

2. A gas fired or an oil fired indirect air heater as claimed in claim 1 in which a combustion air blower of the heater is arranged to draw the combustion air through an air intake duct having an upstream portion which surrounds the heater flue.

3. A gas fired or an oil fired indirect air heater as claimed in claim 1 in which a combustion air blower of the heater is arranged to draw the combustion air through an air intake duct directed, in part, along the inside of the heater flue.

4. A gas fired or an oil fired indirect air heater as claimed in claim 1 in which a combustion air blower of the heater is arranged to draw the combustion air through an air intake duct which passes through a heat exchanger compartment of the heater which receives the products of combustion of the heater.

5. A gas fired or an oil fired indirect air heater as claimed in claim 4 in which said heat exchanger compartment is a secondary heat exchanger compartment which discharges into a pressure relief box immediately upstream of the flue.

6. A gas fired or an oil fired indirect air heater as claimed in claim 5 in which the air intake duct opens to the outside of the heater through the wall of the pressure relief box.

7. A gas fired or an oil fired indirect air heater as claimed in any one of claims 2 to 6 in which said air intake duct is branched and the branch duct is connected with a space inside the heater casing from which space heating air is drawn by a main fan of the heater and directed over a heat exchanger of the heater.

8. A gas fired or an oil fired indirect air heater as claimed in claim 7 in which the main fan is a centrifugal fan.

9. A gas fired or an oil fired indirect air heater as claimed in any one of claims 2 to 8 in which the combustion air blower is a centrifugal fan.

10. A gas fired or an oil fired indirect air heater in which space heating air is passed in heat exchange relation with the flue gases before being fed to the heater for space heating.

11. A gas fired or an oil fired indirect air heater as claimed in claim 10 in which a main fan of the heater is positioned in a heater casing and arranged to draw space heating air into the heater casing through an air intake duct having an upstream portion which surrounds the heater flue.

12. A gas fired or an oil fired indirect air heater as claimed in claim 10 in which a main fan of the heater is positioned in a heater casing and is arranged to draw space heating air into the heater casing through an air intake duct directed, in part, along the inside of the heater flue.

13. A gas fired or an oil fired indirect air heater as claimed in claim 10 in which a main fan of the heater is positioned in a heater casing and is arranged to draw space heating air through an intake duct which passes through a compartment of a heat exchanger of the heater which receives the products of combustion of the heater and over which space heating air is directed by said fan.

14. A gas fired or an oil fired indirect air heater as claimed in claim 13 in which said heat exchanger compartment is a secondary heat exchanger compartment which discharges into a pressure relief box immediately upstream of the flue.

1 5. A gas fired or an oil fired indirect air heater as claimed in claim 14 in which the intake duct opens to the outside of the heater through the wall of the pressure relief box.

1 6. A gas fired or an oil fired indirect air heater as claimed in any one of claims 11 to 1S in which the main fan is a centrifugal fan and said air intake duct opens into said casing through a nozzle directed towards the main fan wheel and having its longitudinal axis coincident with the rotational axis of the main fan wheel.

1 7. A gas fired or an oil fired indirect air heater substantially as hereinbefore described with reference to Figs. 1 to 3 of the accompanying drawings.

1 8. A gas fired or an oil fired indirect air heater substantially as hereinbefore described with reference to Figs. 4 to 6 of the accompanying drawings.

19. A gas fired or an oil fired indirect air heater substantially as hereinbefore described with reference to Fig. 7 of the accompanying drawings.

20. A gas fired or an oil fired indirect air heater substantially as hereinbefore described with reference to Fig. 8 of the accompanying drawings.