GB2189314A - Radiant heating systems - Google Patents

Abstract

A radiant heating system comprises a tube 1, a burner 5 for supplying combustion products to the tube, a fan for drawing the combustion products through the tube, and at least one swirler (or heat transfer plate) within the tube, the burner being connected to its fuel supply through a dual aperture valve 12, (Fig. 2, not shown) whereby, during operation of the burner, the first aperture provides on/off fuel supply to the burner, and the second aperture controls the rate of fuel supply to the burner. Preferably the fan is of variable speed to maximise combustion efficiency. <IMAGE>

Description

SPECIFICATION Radiant heating systems The present invention relates to heating systems comprising at least one tube, a burnerforsupplying combustion products to the tube, and a fan for drawing the combustion products through the tube.

The combustion products heatthe tubes to a temperature at which they radiate infra-red energy.

Originally infra-red radiant devices were only used in industrial appliances such as ovens. Such devices radiated energy in the upper infra-red regions. At this stage domestic or industrial space heating devices generally relied on conduction or convection and utilized very little, if any, radiation for heating.

Recently, efficient space heating has been achieved using devices which radiate infra-red energy. Such devices are energy efficient in that they heat directly the objects on which the radiation impinges with little loss of energy to the air between the device and the object two be heated. The object may absorb the radiated energy, conduct itto other objects to be heated, or re-radiate it onto other objects.

Use of infra-red radiating devices can be very energy-efficient, since it can minimise heat losses to the surrounding air, especially roof spaces, and can reduce the creation of draughts.

At its simplest, an infra-red radiant heating system comprises a single tube having atone end a burner and at its other end a fan. The fan draws the combustion products from the burner along the tube, which is thereby heated to a temperature at which it radiates infra-red energy. Generally, a reflectorwill be mounted adjacent the tube for directing the radiant energy to the area it is desired to heat.

A more compact system can be provided by use of a U-shape tube. This enables the fan and the burner to be located at the same endow the device, with the bend of the tube at the opposite end. Such an arrangement is shown, for example, in GB-A-1 315 685. Itis also possible to mountthefan and the burner in a single assembly.

Use of singletubes, whetherstraight or U-shape, can be relatively inefficient, since it requires a numberof devices to heat a large area. This in turn requires the use of a numberoffans, and associated connections and controls.

This drawback can be avoided by the use of a connected system oftubes, for instance of the type described in GB-A-2 102555. In such a system, a numberoftubes are connected to a single fan for drawing combustion products therethrough. The problem within a connected system is that it requires a number of burners in the tubes to ensurethatall the tubes are heated to the necessarytemperature.

To ensure that the fuel is properly combusted in each burner it is necessary to include in the tubes various dampers two regulate the effect ofthefan and to ensure that sufficient air is supplied to each burner.

Since combustion efficiency depends on matching airflow rate and fuel supply rate with heater dimensions, it has not previously been possible to modulate continuously the fuel supply rate to match the desired radiant heat output and maintain combustion efficiency.

Therefore most radiant heating systems operate on an on/off basis. This will be inefficient when demand is less than the maximum heat output.

During the operation of such systems as shown in GB-A-2 102555, the burners always operate at a predetermined single heat output.

It is therefore an aim of the present invention to provide a radiant heating system which preferably has an automatically adjustable heat output.

The present invention provides a radiant heating system comprising a tube, a burner for supplying combustion products to the tube, and a fan for drawing the combustion products through the tube, and at least one swirler (or heat transfer piate) within the tu be, the bu rner being con nected to its fuel supplythrough a dual aperture valve, whereby, during operation ofthe burner, the first aperture provides on/offfuel supply to the burner, and the second aperture controls the rate offuel supply to the burner Preferably the fan is of variable speed to maximise combustion efficiency.

The fuel supply may be variable stepwise, for instance in a high/lowfashion, or continuously between zero and a predetermined maximum, by the operation ofthesecond aperture.

It is believed that the present system operates on the following principle, although the Applicants do not wish to be limited bythefollowing explanation.

It is well known that the amount of energy radiated by a body is related to the fourth power of its temperature, i.e. Q= kT, where Q is the amount of energy, K is a constant and T isthe absolute temperature of the body. lfthetemperature is relatively low, there is very little heat radiated. If the temperature is relatively high, the material from which the body is made may begin to degrade. It can thus be seen that there is only a relatively narrow operated with a preset fuel supply which maintains the band oftemperatures in which a radiant heater will produce sufficient radiant heat to be effective in space heating without destroying the material of which the body is formed.

Conventional radiant heating systems have been operated with a preset fuel supply, which maintains the temperature ofthe majority ofthe tube within the useful radiating range. However, any attempts to modulate this fuel supply resulted in the temperature of the majority of the tube falling below the useful radiating range. Hence these systems were operated on the on/off principle.

It is believed that in the system of the present invention, when operating at a lowfuel supply rate, the combustion of the fuel, in conjunction with the effects ofthe or each swirler/or heat transfer plate maintains the temperature ofthe majority of the tube in the useful radiating range, while the high rate of fuel supply can be used to raise the tubetemperature a desired amount without raising itabovethe useful radiating range.

In a preferred embodiment,thedual aperturevalve is electrically or electronically controlled. For instance, the opening of both the apertures may be linked to the operation of the fan, whereby they may only be opened when the fan is operating. Their opening may also be linked to a flame detector, whereby they may only be opened when the pilot flame is burning.

The opening ofthe second aperture may be linked to a thermostat. In one embodiment, the second aperture may be open when the thermostat temperature is below a preset limit and closed when it is above this limit. Thus, the second aperture may be opened to allow enhanced heating atan initial stage, which is then switched to a iower degree of heating atthe presettemperature.

In an alternative em bodiment, the opening ofthe second aperture is variable and is linked to the thermostat whereby its degree of opening is inversely related to temperature within the area to be heated.

The present invention may be applied to straight tube, U-shape tube or continuous tube type radiant heating systems, and maythereforeinclude any of the features, in particularthe safety features, used in such systems. Typically the system of the present invention will include at least one reflectorfor directing heat to the desired area.

The burnerofthe present system mayoperateon liquid or gaseous fuel, but preferably operates on gaseous fuel, such as natural gas or bottled gas.

A subjective measurement of the efficiency of a heating system is the "comfort level". This is a combination of many features, such as radiant heat received, airtemperature, and amount of draughts.

The system ofthe present invention allows a reasonable comfort level to be obtained at much lower airtemperatures than is usual for convection or conduction systems.

For instance, a factory space may be at a temperature of between 0 and 10 "C atthe beginning of a working day. Once the radiant heating system of the presentinvention issetgoing,with both apertures open, the amount of radiant heat received will be high, the airtemperature will be low and the amount of draughts will be low, leading to an acceptable comfort level.

Once the airtemperature has reached,for instance, 1 0 C the second aperture may close, thus reducing the amount of radiated heat received, which may be becoming less than acceptable to a person in the area. However, the reduction will only occurwith the increase in air temperature, and thus maintainence of the desired comfort level will be achieved.

The maintainence ofthe comfort level can be more readily achieved by use of a continuously variable second aperture, and, if desired, could be manually adjustable.

One embodiment of a radiant heating system according to the present invention is now described, by way of example only, with reference to the accompanying drawings, in which: Figure ishowsthesystemdiagrammatically; and Figure2 shows an enlarged view of part ofthe system shown in Figure 1.

Referring nowto Figure 1,thesystem ofthe present invention comprises a U-shape steel tube 1.

At one end of the tube lisa fan 3 which causes a flow of gas in the direction marked by the arrows in the tube. Atthe other end ofthetube lisa burner 5. The tube 1 has a reflector (not shown) around itfor directing radiant heat to a desired location and a swirler (not shown) for maximising radiant efficiency.

TheburnerSincludesa pilotburner,whichis supplied with gas along line 7, and an electronic ignition therefor. The burner5 also includes a main burner, airsuppliesforthe pilot burner and the main burner, and a flame detector for detecting the pilot flame. These are conventional items and are not described in detail.

The burner 5 is provided with line 9 for supplying gas to the main burner. The lines7 and 9 pass through electrically controlled valves 11 and 12 respectively.

The system includes one or more a thermostats 14, the fan 3, the electronic ignition, the flame detector and the valves 11 and 12, all operatively connected to a microprocessor control unit 17.

The electrically controlled valve 12 is shown in more detail in Figure 2,to which reference is now also made.

The valve 12 comprises a housing 21 having in it an inlet 23 for connection to a gas supply line 25 and an outlet 27 for connection to line 9. The inlet 23 is separated from the outlet by a valve block 29 in which are provided two apertures 31 and 33.

The aperture 31 is closed by valve disc 35 and is normally held closed by spring action but can be opened by solenoid 39 operatively connected to the microprocessor 17 byline43 Aperture 33 includes a web 45. In normal use, to provide a low flow rate, the aperture 33 is closed by valve disc 37 and is held closed by spring action.

However, in this "closed" position gas is able to weep through an orifice 47 in the web atthe lowflow rate. To provide the high flow rate, the valve disc 37 is moved against the spring action by solenoid 41 which is operatively connected to the microprocessor 17 by line 43.

Avalve ofthis type is commercially available as a "Series 24 Double Valve" from Tenknigas Ltd, of Charleswoods Place, East Grinstead." To set the system in operation,the microprocessor 17 is activated to settle fan 3 going. Once the fan 3 is determined to be operating correctly, the pilotvalve 11 and the electronic ignition are activated. If after a predetermined time the flame detector does not detect the existence of a pilot flame in the pilot burner, the system shuts down. Otherwise, the microprocessor 17 causes both the apertures 31 and 33 inthevalve 12to open. Gas isthereforedrawn into the main burner wherein it is ignited by the pilot flame (or, if no pilot valve is used, by direct electric spark).

The main burner thus produces a stream of combustion products at a temperature of about 1000 C, These are swept through the tube 1 and heat the tube to the temperatures indicated thereon. At thesetemperatures,the majority ofthetube 1 emits effective quantities of thermal energy as infra-red radiation.

The cooled combustion products are exhausted by the fan 3 and may be used, for instance, for heating water or for preheating the air being fed to the burner 5.

Once the thermostat 14 indicates that the air temperature has reached a preset level, the microprocessor 17 operates to close the second aperture 33. This reduces the amount of gas supplied to the main burner, which therefore produces less heat. The temperature of the tube 1 will therefore decrease slightly, but not sufficiently to reduce the efficiency ofthe radiation in heating the area to which it is directed.

The system described above may be changed to a continuously variable system by replacing the valve disc 37 by a tapered memberwhich will allowthe degreeofopeningoftheapertureto bevaried continuously in accordance with control signals from the microprocessor.

It will be appreciated that the present invention has been described above by way of example only, and that modifications can be made within the scope of the invention. In particular, the above described system can readily be adapted for use with straight or continuous tu be systems.

Claims (12)

1. A radiant heating system comprising a tube, a burnerfor supplying combustion products to the tube, a fan for drawing the combustion products through thetube, and at leastoneswirler (or heat transfer plate) within the tube, the burner being connected to its fuel supplyithrough a dual aperture valve, whereby, during operation of the burner, the first aperture provideson/offfuel supply to the burner, and the second aperture controls the rate of the fuel supplytothe burner.

2. The system of claim 1, wherein the fan is of variable speed to maximise combustion efficiency.

3. Thesystemofclaim 1 orclaim2,whereinthe fuel supply is variable stepwise by the operation of the second aperture.

4. The system of claim 1 orclaim2,whereinthe fuel supply is variable continuously between zero and a predetermined maximum by the operation of the second aperture.

5. The system ofanyoneofclaims 1 to4,wherein the dual aperture valve is electrically or electronically controlled.

6. The system of any one of claims 1 to 5, wherein the opening of both the apertures is linked to the operation of the fan, wherebythey may only be opened when the fan is operating.

7. The system of any one of claims 1 to 6, wherein the opening of both apertures is iinked to a flame detector, whereby they may only be opened when the pilot flame is burning.

8. The system of any one of claims 1 to 7, wherein the opening ofthe second aperture is linked to a thermostat.

9. The system of claim 8, wherein the second aperture is open when thethermostattemperature is below a preset limit and closed when it is above this limit.

10. The system of claim 8,wherein the opening of the second aperture is variable and is linked to the thermostatwhereby its degree of opening is inversely related to the temperature within the area to be heated.

11. The system of any one ofclams 1 to 10, which includes at least one reflector for directing heat to the desired area.

12. A radiant heating system, substantially as hereinbefore described with reference to the accompanying drawings.