Radiant plaque heater

Abstract: A radiant plaque heater has a casing (1) a burner (4) and a plaque element (3) arranged within the casing so as to be heated by the burner and produce a radiant heat output. An air flow means (5) is provided and is operable to induce a flow of air into the casing in order to create an over-pressure therein which inhibits air flow from the exterior into the casing adjacent the plaque. A heat exchanger (7) may be provided for extracting heat from the burner exhaust gases and returning the extracted heat to the plaque element (3).

Description: This invention relates to a radiant plaque heater of the kind having a burner arranged to heat a plaque element from which radiant heat is emitted into a space to be heated, such as a factory working area. US-A-4524753 discloses a radiant plaque heater in which a plaque element is arranged within the casing so as to be heated by a burner, and air flow means induces a flow of air into the casing creating an over-pressure therein which inhibits air flow from the exterior into the casing adjacent the plaque. The efficiency of some conventional plaque heaters is relatively low, typically less than 30%, because much of the heat produced by the burner is carried away in the burner exhaust gases. An object of the invention is to provide an improved radiant plaque heater of relatively increased efficiency. According to the present invention, a radiant plaque heater comprises a casing, a burner, a plaque element arranged within the casing so as to be heated by the burner and produce a radiant heat output, and air flow means operable to induce a flow of air into the casing in order to create an over-pressure therein which inhibits air flow from the exterior into the casing adjacent the plaque, and a heat exchanger arranged to receive burner exhaust gas and said air flow in heat exchange relationship in respective separate flow paths therein, an outlet of the heat exchanger being arranged to introduce heated air emitted therefrom into a location from which the heated air serves to transmit heat to the plaque element to assist in raising the temperature of the latter. Conveniently, the air flow induced into the heater passes through a flow distributor which controls the induced air flow, preferably in a variable manner, and thereby the over-pressure in the casing. The invention will now be described, by way of example, with reference to the accompanying drawings in which:- Figure 1 is a diagrammatic side elevation of one form of the radiant plaque heater of the invention; Figure 2 is a view of the heater of Figure 1 from the opposite side, and Figure 3 is an end view of the heater of Figures 1 and 2. The radiant plaque heater illustrated in the drawings includes an outer hollow casing 1 which supports, adjacent to an open end 2 thereof, a radiant plaque element 3 and a burner 4 arranged to direct burning fuel, such as gas, over and/or into the interior of the plaque to heat the latter. The heated plaque radiates heat outwardly through the open end 2 of the casing. The open end of the casing is flared outwardly by the provision of an oblique peripheral surface 2A which acts as a reflector to direct radiant heat from the plaque downwards and thereby minimise sideways heat loss The flared casing portion also forms a space beneath the plaque within which a slight positive air pressure may exist. Air flow means, illustrated as a fan 5, is mounted on the casing and, although conveniently shown at the top of the casing, could be disposed at any convenient location. The fan, when operating, draws in air and injects this under a small pressure into the interior of the casing 1, the air flow being controlled by means of a flow distributor, illustrated as a perforated plate 6 which may be adjusted to vary the flow rate of the air entering the casing. As will be seen more clearly from Figure 3, the casing in this embodiment of the plaque heater contains a heat exchanger, illustrated diagrammatically and in a general manner at 7. The heat exchanger contains a first convoluted flow path, branches of which are illustrated at A and a second convoluted flow path having branches B, the paths A and B being separated in fluid tight manner by partitions 8. An outlet from the path B communicates with an exhaust port 9 of the casing (fig 2) and the flow of exhaust gas through the heat exchanger to the exhaust port is represented by the arrows B in Figure 2. The path A of the heat exchanger communicates with a region 10 adjacent the burner for introduction of gas flow on to the plaque 3, as illustrated by the arrows A in Figure 1. In operation, the plaque 3 is heated by the burner 4 and radiates heat through the open end 2 of the casing 2 as mentioned previously. The exhaust gases from the burner, represented by the arrows E rise within the casing into the exhaust flow path B within the heat exchanger. Operation of the fan 5 produces an inflow of air to the casing 1 through the flow control plate 6, which is adjusted to provide the desired air flow. The inflow of air enters the path A of the heat exchanger and, in flowing along this path, extracts heat from the exhaust gases in path B and is thereby heated. The heated air is then introduced at a relatively high temperature into the aforesaid region 10 and assists in raising the temperature of the radiant plaque 3. The action of the fan 5 creates within the housing 1 a slight over-pressure, the magnitude of which can be optimised by adjustment of the plate 6 and/or the fan speed. Because of the flared casing end portion, the aforesaid over-pressure exists beneath the plaque and inhibits any tendency for air to be drawn inwardly through the open end 2 of the casing and thereby substantially prevents the radiant plaque 3 from being contacted by an upward inflow of cool air which would have the effect of cooling the plaque and lessening the efficiency of the heater. Tests have shown that the heater of the invention in the form described incorporating a heat exchanger can achieve an efficiency approaching 50% of the energy input, measured as radiant heat output, in comparison with an efficiency of less than 30% obtained in many conventional radiant plaque heaters. The heat exchanger may be demountable, or in the form of an add-on module which may be attached, when required, to an existing radiant plaque heater. It will be understood that the various components such as the radiant plaque, fan and heat exchanger may be of any appropriate type and arranged in ways possibly differing from the particular arrangement illustrated.

Claims: A radiant plaque heater comprising a casing (1) a burner (4), a plaque element (3) arranged within the casing so as to be heated by the burner and produce a radiant heat output, and air flow means (5) operable to induce a flow of air into the casing in order to create an over-pressure therein which inhibits air flow from the exterior into the casing adjacent the plaque, characterised by a heat exchanger (7) arranged to receive burner exhaust gas and said air flow in heat exchange relationship in respective separate flow paths (A, B) therein, an outlet of the heat exchanger being arranged to introduce heated air emitted therefrom into a location (10) from which the heated air serves to transmit heat to the plaque element (3) to assist in raising the temperature of the latter. A heater according to Claim 1, characterised in that the air flow induced into the casing (1) passes through a flow distributor (6) which controls the induced air flow and thereby the over-pressure in the casing. A heater according to Claim 2, characterised in that the flow distributor (6) is operable to vary the induced air flow. A heater according to Claim 2 or Claim 3, characterised in that a mouth (2) of the casing through which the radiant heat output is directed is provided with a divergent peripheral surface (2A) which acts as an inward deflector for the radiant heat. A heater according to Claim 1, characterised in that one of the heat exchanger paths (B) receives exhaust gases from the burner (4) and has an outlet which communicates with an exhaust port (9) of the casing, the other path (A) having an inlet for air from said air flow means (5) and an outlet from which emerging heated air is directed onto or into the plaque element (3) to assist in raising the temperature of the latter. A heater according to any one of the preceding claims, characterised in that the casing (1) is provided with an exhaust port (9) for egress of burner exhaust gases.

Inventors: JONES DAVID MERVIN, MAUND JOHN KEITH, JONES, DAVID MERVIN, MAUND, JOHN KEITH
Applicants: ADVENTEC LTD, ADVENTEC LIMITED
Application year: 1990
Main classification: F24H3
IPC codes: F24C1