Stoves and furnaces – Stoves – Heating
Reexamination Certificate
1999-12-23
2001-09-11
Price, Carl D. (Department: 3743)
Stoves and furnaces
Stoves
Heating
C126S09200C, C126S089000, C126S11600A
Reexamination Certificate
active
06286500
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to heaters and in particular space heaters of the type intended to heat large buildings such as warehouses, factories, hangars etcetera.
Space heaters are known from inter alia, WO-A-96/10720, GB-A-2 145 218, EP-A-0 408 396, EP-A-0 408 397, and EP-A-0 410 707. The heaters disclosed in EP-A-0 408 396 comprise a housing, an elongate combustion tube, a burner at one end of the tube and a fan at the other end of the tube for drawing combustion gases through the tube. The housing is open at its lower end to permit radiant heat from the combustion tube to be directed downwardly from the heater towards the ground. In addition to providing radiant heating, the heater disclosed in EP-A-0 408 396 is also arranged to provide blown warm air heating. This is achieved by providing an air duct which passes along the interior of the housing such that the air inside is warmed as it moves along the air duct, apertures in the air duct allowing the warm air to escape in a downwards direction. In addition, at the air inlet a proportion of the air can be diverted by deflector plates such that the air impinges directly onto the combustion tube thereby providing a faster rate of heating of the air before it passes out through the bottom of the heater towards the ground. The positions of the deflector plates can be varied so as to divert more or less air directly on to the combustion tube so as to achieve a desired balance between the radiant heat and the convected heat emitted by the heater.
One consequence of directing air on to the combustion tube directly is that it cools the tube which can lead to loss of radiant efficiency and can also cause the formation of soot and condensation within the combustion tube. A further potential disadvantage of the heater disclosed in EP-A-0 408 396 is that there is only a single centrifugal fan at one end of the heater and hence it is difficult to ensure that the output of heated fan-assisted convected air from the heater remains at a useful and constant level along the length of the heater; particularly in heaters of longer length.
SUMMARY OF THE INVENTION
The present invention overcomes the aforesaid problems by providing one or more fans located on top of the heater housing and arranged to draw external air down through the heater housing. In order to prevent the air from cooling the burner tubes with the attendant problems described above, the upper surfaces of the tubes are surrounded by thermal radiation-absorbing plates or heat exchangers which are heated by radiation from the upper halves of the tubes. The air driven through the heater by the fans on top of the heater housing is thus heated as it comes into contact with the heat exchanger plates before passing out through the lower end of the heater towards the ground.
Accordingly, in a first aspect, the invention provides a space heater capable of providing both radiant and blown warm air heating to a space beneath the heater; the heater comprising a housing, the underside of which is recessed to define a channel in which a combustion tube is mounted; the heater having a burner communicating with a first end of the tube; and first fan means communicating with the tube for moving combustion gases along the tube from the first end to a second end thereof; the housing having an aperture in an upper surface thereof, the aperture being linked to second fan means for directing air into the channel within the housing; and a heat exchanger plate mounted between the tube and the aperture, the heat exchanger plate being shaped so as to surround the upper surface of the tube so as to absorb radiation therefrom and to prevent air from the aperture from impinging directly onto the tube; whereby the air is heated by the heat exchanger plate before passing out downwardly through the lower end of the channel.
The recessed underside of the housing can have only one combustion tube mounted therein, or it can have a plurality of combustion tubes mounted therein, for example, two, three or four combustion tubes. Where there is a plurality of combustion tubes, the tubes can be mounted, for example, in a side by side manner.
In one particular embodiment of the invention, there is only a single combustion tube.
The or each combustion tube can comprise two or more limbs, a main first limb being connected at one end to the burner and being connected at an end remote from the burner to one or more return limbs which is or are substantially parallel to the main first limb. In one preferred embodiment, the combustion tube comprises a main first limb and a pair of return limbs each linked to the main first limb at an end remote from the burner, the two return limbs being arranged either side of the main first limb.
Where there is more than one return limb, the main first limb is typically of greater cross-sectional area than the return limbs. For example, where there are two return limbs, the volume of the main first limb can be approximately twice that of the individual return limbs.
The return limb or limbs can each have a fan, for example a centrifugal fan, attached thereto for drawing combustion gases along the first limb and into the or each return limb.
The second fan means preferably comprises a fan mounted on top of the housing. The second fan means can comprise a plurality of fans mounted at spaced apart locations along the top of the housing. The fans advantageously are axial fans. The air directed by the second fan means into the channel typically is air from the exterior of the housing. Advantageously, the air drawn into the housing by the second fan means can be preheated, for example by passing it through a heat exchanger to remove heat from the exhaust gases arising from the combustion process. This can be accomplished for example by using a balanced flue system.
The housing can comprise inner and outer skins, the inner skin defining the walls of the channel and the outer skin defining the upper surface of the housing, the space between the inner and outer skins being at least partially filled with thermal insulating material. The thermal insulating material is preferably one which is capable of resisting temperatures in excess of 500° C., and in particular temperatures above 600° C.
The inner surface of the channel within the housing, e.g. the inner skin, preferably has a reflective surface so as to reflect thermal radiation from the combustion tubes in a downwards direction, or to reflect any thermal radiation from the heat exchanger plates back onto the plates. In order to improve the reflective efficiency of the reflective surfaces of the channel, the reflective surfaces are preferably surfaces which have been treated to reduce surface porosity and unevenness and improve reflectance. For example, the surfaces may be of anodised aluminium, and in particular may be formed of a coloured anodised aluminium, most preferably a gold coloured anodised aluminium. Gold coloured anodised aluminium is considered to be particularly efficient at reflecting radiation in the context of the heaters of the present invention.
By contrast, the under surface of the heat exchanger plate, and preferably also the upper surface, is usually substantially non-reflective, and can advantageously be treated to improve its radiation-absorbing properties. For example, the under surface can be blackened. Alternatively, or additionally, the surfaces of the heat exchangers can be treated to increase their surface area, for example by shot or bead blasting to create craters and pits in the surface.
The radiation emitted by a hot body is related to the temperature of that body by a power law and if follows that increased efficiency can be obtained from a radiant heater by running it such that the heating element, i.e. the combustion tube, is as hot as possible. One limiting factor, however, on the efficiency of the heater, is the formation of “hot spots” on the surface of the heater, where the flame comes into direct contact with the wall of the tube. If the combustible mix is adjusted to provide a
Jones Philomena Joan
Lahive & Cockfield LLP
Price Carl D.
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