Space heating appliances

Space heating appliance of the radiant tube type has sheet metal or other shield formations mounted in the tube to extend downstream of fan induced gas flow from side edges of the mouth of a fluid fueled burner head which projects into the tube to feed hot gases into the flow so as initially to separate that infeed from the general flow along the tube.

This invention relates to radiant tube space heating appliances of the kind 
comprising a radiation tube or duct, commonly suspended overhead in the 
space to be heated, a fan or other pump for inducing flow of gases along 
the duct in use, and one or more fluid fuelled burner assemblies, 
typically gas fired and automatically controlled, for feeding hot gases 
into the flow. Radiant heat is emitted from the duct surface and this is 
commonly directed and concentrated, e.g. in a downward direction, by 
reflectors mounted adjacent to the duct. Such appliances are hereinafter 
referred to as "radiant tube heating appliances". 
BACKGROUND OF THE INVENTION 
Examples of known constructions of radiant tube heating appliance are 
described in EP-A-0248629 and in EP-A-2102555 and also in our co-pending 
application GB 9300612.0 filed 14 Jan. 1993. 
The object of the invention is to provide improvements in radiant tube 
heating appliances giving better efficiency, more reliable operation, and, 
in particular, substantially reduced levels of noxious emissions. 
SUMMARY OF THE INVENTION 
According to the invention there is provided a radiant tube heating 
appliance as hereinbefore defined including a burner head mounted in use 
to project laterally inwardly of the radiation duct into the path of flow 
therethrough and having a burner mouth at the front of the head facing 
downstream of said path of flow whereby fuel mix is operatively discharged 
along said flow for combustion in the duct immediately downstream of the 
head; A shield formation or formations are operatively mounted within the 
radiation duct with its or their upstream end or ends adjoining or in 
close proximity to at least each side of the burner mouth and extending 
downstream therefrom at least in a substantial part of the zone in which 
are said combustion takes place in use whereby the flow of gases along the 
duct past the head is substantially separated from the flow of fuel mix 
issuing from the duct in the zone. 
Conveniently, where the burner mount is straight sided, for example as 
described in our application 9300612.0, a pair of substantially 
rectangular flat sheet shield formations made typically of stainless 
steel, are mounted in spaced parallel relationship to extend downstream 
from the side edges of the burner mouth. 
In a radiation duct of circular cross section where the burner head depends 
vertically into the duct the formations will lie on spaced vertical chords 
of the cross section leaving segmental through passages to either side. 
However, it is to be understood that other forms and shapes of shield 
formation or formations may be used e.g. to suit particular shapes of 
burner head or mouth. Thus a burner head having a circular mouth could be 
provided with a cylindrical shield formation i.e. the latter may take the 
form of a burner tube mounted within the radiation duct.

DETAILED DESCRIPTION 
The radiant tube space heating appliance of this example is an installation 
for heating a large space such as a factory building or public hall: the 
overall installation is generally of conventional type comprising branched 
or other runs of circular section radiation tube 10 through which hot 
gases provided by burner assemblies 14 are drawn by an exhaust fan leading 
to a discharge flue. The fan and each burner assembly is controlled 
automatically in known manner. 
This example includes burner assemblies 14 as described in detail in our 
co-pending application 9300612.0 which gives details of their construction 
and operation. Briefly each assembly comprises a control unit 20 mounted 
externally above tube 10 and a burner head 22 which depends downwardly 
through a top opening in the tube and has a rectangular burner mouth 24 on 
a vertical diametral plane of tube 10 and directed downstream of the 
direction of flow through tube 10 (from right to left as viewed in FIG. 
1). The longer axis of mouth 24 is vertical leaving substantial segmental 
spaces each side of head 22 for passage of said flow but, in this example, 
the lower horizontal edge of mouth 24 is in close proximity to the bottom 
of the tube. 
In use a mix of gas fuel and air is projected from mouth 24 for combustion 
within tube 10, burning taking place as a flame directed downstream and 
approximately in the zone indicated by the wavy broken lines 26 in FIG. 1. 
In known constructions, for example as in our above co-pending application, 
problems arise due to reduced efficiency and over-production of noxious 
emissions, notably CO due to chilling of the flame arising from its direct 
contact with the passing through flow of gases along tube 10 which will be 
relatively cool by the time they reach the respective burner head 22. The 
first burner head at the upstream end of a particular run or leg of tube 
10 will be subjected to cold carrier air admitted at the end vent and 
burner heads downstream along the line are subjected to gases which have 
been heated by the upstream burner or burners but which have then been 
substantially cooled in their passage along tube 10 as the whole object is 
to emit maximum heat into the surrounding space. 
The chilling of the flame by this direct contact has an adverse effect on 
combustion, rendering it much less efficient than is possible in theory 
and giving much higher CO emission than would otherwise be the case. Much 
higher standards aimed at reduction of atmospheric pollution are now being 
imposed by law in many countries for equipment of this type and many of 
the known designs of radiant tube heating appliance are incapable of 
operation to meet these new standards often due to the problem of flame 
chilling. 
In the present example the assembly includes a pair of shield formations 
30. Each formation is a flat metal plate, substantially rectangular in 
shape, typically of stainless steel and provided with a return flange 32 
along an upper extension which projects into a collar 28 of tube 10 on 
which the burner assembly 14 is mounted, said flange being secured by 
bolts 34 or other appropriate fastening means to the collar structure. 
The formations 30 are disposed in spaced parallel relationship with their 
upstream edges positioned close to the side faces of the burner mouth 
walls leaving only a small gap, and extending forwardly in the downstream 
direction along tube 10 over substantially the full zone in which 
combustion takes place. The upper and lower edges of each formation are in 
close proximity to the wall of tube 10 so that they define segmental 
passages 36 (FIG. 2) on either side containing the through flow along tube 
10. This flow can only mix with the products of combustion issuing from 
head 22 downstream of said combustion zone. As the formations 30 are 
themselves heated by the flame there is little or no chilling effect in 
the combustion zone so providing much more efficient operation, improved 
flame stability, and, more importantly, a very substantial reduction in 
noxious emissions notably CO bringing the latter well below the maximum 
allowable under the most exacting standards presently contemplated. 
The increased efficiency gives improved heat output and hence more 
economical operation. 
The shield formations 30 are simple to manufacture and easy to instal, they 
can readily be adapted to existing patterns of burner assemblies and 
heating appliances and the preferred method of their mounting and 
attachment as described above simplifies assembly and maintenance. The 
burner assembly 14 can be simple mounted and dismounted as before, the 
front face of head 22, i.e. the structure surrounding mouth 24 being 
simply slotted vertically between the pair of formations 30 which are 
attached to the tube structure. The formations themselves can readily be 
dismounted for repair or replacement. 
It is contemplated that the performance of existing installations may be 
substantially improved by fitting a shield formation or formations of the 
invention and the latter further contemplates a method of improving 
performance and reducing noxious emissions and pollutants in a radiant 
tube space heating appliance by providing a shield formation or formations 
described above.