Patent Publication Number: US-6217320-B1

Title: Space heating appliances

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is a U.S. national application of international application serial No. PCT/GB98/03273 filed Nov. 3, 1998, which claims priority to United Kingdom serial No. 9723394.4 filed Nov. 6, 1997. 
     BACKGROUND AND SUMMARY OF THE INVENTION 
     This invention relates to radiant tube space heating appliances of the kind comprising branched or other radiation ducting, commonly suspended overhead in the space to be heated, an exhaust fan or other pump in a tailpipe of the ducting for drawing a flow of gases there through in use, and a series of inline fluid fuelled burner assemblies, typically gas fired and automatically controlled, upstream of the tailpipe for generating heat carried by said flow. Radiant heat is emitted from the ducting surfaces and this is commonly directed and concentrated, e.g. in a downward direction, by one or more reflectors mounted above or to the side of the ducting. Said appliances are hereinafter referred to as “continuous radiant tube heating appliances”. 
     An example of one known construction of continuous radiant tube heating appliance is described in our GB 2,274,703-A and EP 0606782-A. 
     The object of the invention is to provide a continuous radiant tube heating appliance giving high performance with safety, reliability, and economy of operation. 
     According to the invention there is provided a continuous radiant tube heating appliance as hereinbefore defined including a control damper in the tailpipe selectively operable to throttle the flow of gases induced by the fan or other pump, a power actuator for adjusting the damper, and automatic control means including a temperature sensor responsive to the temperature of gases passing along the tailpipe in use and controlling operation of the actuator so as to reduce the induced flow when said temperature is below a predetermined level as on start-up of the appliance from cold. 
     Typically the appliance will comprise a single branch; or two or more ducting branches acting in parallel and with separate input ends through which individual flows of air are drawn during operation, each branch having a burner assembly or series of burner assemblies spaced along its length and all the branches being connected to a common tallpipe and exhaust fan associated with said control means. 
     A pre-set balancing damper may be included at the downstream end of each said branch upstream of the tailpipe. 
     Preferably the control damper and automatic control means are constructed as a unit to include a section of the tailpipe with the temperature sensor therein in close proximity to the damper providing simple installation by coupling into the other parts of the tailpipe and with an electrically powered actuator merely requiring connection to a power supply. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     An example of the invention is now more particularly described with reference to the accompanying drawings wherein: 
     FIG. 1 is a diagrammatic plan view of an installation of a continuous radiant tube heating appliance, 
     FIG. 2 is a detailed plan view of a control damper and actuator unit of the appliance, 
     FIG. 3 is a side elevation of said unit, and 
     FIG. 4 is a sectional view on line IV—IV of FIG.  3 . 
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     The installation of the appliance shown in FIG. 1 comprises overhead suspended ducting  10  having two spaced parallel branches  12   a ,  12   b  for distribution of heat over the area of workspace or the like defined by walls  14 . 
     Each of the branches  12  is provided with two high thermal input (e.g. 46 kW) gas fuel burner assemblies  16  of known construction. 
     An upstream burner in each branch is adjacent to its input end  18 , said ends opening separately to atmosphere; and the second burner  16  in each branch is approximately halfway along its length. 
     The burners of this example use proportional control (zero governor) so that their heat input to ducting  10  increases in direct proportion to the induced draught along the respective branch. 
     The downstream ends of branches  12  are connected in T formation to a common tailpipe  20  of ducting  10  having a centrifugal exhaust fan  22  at its downstream end vented to a flue  24  discharging externally of the building. 
     To “tune” the appliance on installation, e.g. to balance out differences in flow otherwise present in branches  12 , each branch has a preset balancing damper  26  at its downstream end. These dampers are used for setting up only and will not normally be adjusted subsequently. 
     The fan capacity is selected to provide optimum performance at normal operating temperatures in conjunction with the layout of the installation and its correct setting up and adjustment. However, the performance, i.e. throughput, of fan  22  increases at lower flow temperatures (due to the physical properties of fans) so that excessive flow is induced when handling cold air as on start-up of the appliance. As the burners  16  are self-proportioning they attempt to provide higher thermal input in response to the higher flow rate and this can give rise to problems in initial ignition and flame stabilisation during start-up and warming up. 
     With the relatively low thermal input burners (typically 30 kW) used in known continuous radiant tube heating appliances the above problem is mitigated to some extent by the use of a long tailpipe, for example in the installation layout shown in FIG. 1 a conventional installation might have a tailpipe extending back from the T connection the full length of the workspace between the branches  12  with the exhaust fan positioned on the opposite wall to its position in FIG. 1, this long tailpipe providing a balancing effect by cooling the exhaust gases to a low temperature before they reach the fan. 
     With an operating temperature of 120° C. in the tailpipe, as might be the typical case with the known lower thermal input burners referred to above and a long tailpipe the depression effected by the fan at optimum heat input taken as 100% would be around 6.2 mbar. On cold start-up, due to the cold flow operated on by the fan, said depression would probably be increased to around 7.5 mbar representing excessive heat input from the burner of around 109.6%. 
     Increasing the operating temperature by use of high thermal input burners, to say, 200° C. in a short tailpipe and with the fan operating at optimum of 100% heat input at that operating temperature, and set up to provide the same depression of 6.2 mbar, will result in a much more disproportionate increase when the fan is handling cold air, in the latter condition the depression will have risen to around 10.0 mbar giving a theoretical excessive heat input of 126.5% which would probably make ignition and warming up impossible or, at best, unstable and unreliable. 
     To avoid these difficulties using the high thermal input burners  16  the appliance described further includes a control damper and actuator unit  28  situated in tailpipe  20  immediately upstream of fan  22  and now described in detail with reference to FIGS. 2-4. 
     Unit  28  comprises a short section  20   a  of tailpipe  20  to be coupled into the ducting run on assembly and having a pivoted butterfly control damper  30  carried on a horizontal cross shaft  32 . An electric (or other) actuator  34  mounted to one side of section  28  and spaced therefrom to insulate it from excessive heat is selectively operable to turn damper  30  for throttling flow in the tailpipe. 
     Unit  28  further includes a temperature sensor responsive to the flow temperature in tailpipe section  20   a , in this example a bimetallic switch  36  mounted on the wall surface of tailpipe section  20   a . It will be appreciated that various forms of temperature sensor could be used mounted on or within tailpipe  20 . 
     Switch  36  operates through a control module  38  of unit  28  to actuate damper  30 , throttling throughflow at lower temperatures. Typically damper  30  will open fully only when the flow temperature in the tailpipe exceeds approximately 50-60° C. 
     The diameter of ducting  10 , including tailpipe  20 , is typically 102 mm (4 inches) or 152 mm (6 inches) nominal diameter. 
     It will be appreciated that an installation may take forms other than that shown, for example there may be more than two branches, or for some applications there night be only a single “branch” or each branch may have one, two or more burner assembles along its length. The branches need not be straight, they could be curved or even of U formation e.g. with one or more burners in each leg. The layout can readily be adapted to suit the shape of the space to be heated and any requirements to concentrate heating in particular areas. 
     The absence of the long tailpipe is an advantage both in economy of manufacture and installation, in making the installation much more readily adaptable to particular requirements, and in providing tidier and neater appearance. 
     However, the use of the Control Damper is not limited to installation having a short tailpipe. It is equally effective in providing lower rate start up condition when a Iona tail pipe is chosen, e.g. for installations in very large buildings where it is necessary to position the fan on a side wall a considerable distance from the burners; or where it is preferred to use a long tail pipe to reduce the exit gas temperature and therefore increase the overall thermal efficiency of the system. 
     As the temperature sensing and consequent flow control is effected in the tailpipe immediately adjacent to the exhaust fan or equivalent the setting and operation of the control damper is unaffected by other features of the installation layout, it is the temperature of the flow acted on by the fan which is being monitored and this is independent of other flow characteristics, e.g. velocity or measured depression, in the tailpipe, or elsewhere in the ducting. Thus the setting up and operation is extremely simple, is easy to check and adjust and requires the minimum of wiring and on-site work to assemble and install. 
     The substantially equable flow rate past the burners, whether hot or cold, ensures their optimal and safe operation on initial ignition from cold, during warming up, and at running temperatures with high thermal output. Effective start up and combustion reduces noxious emissions and may increase fuel economy.