(19)
(11) EP 0 762 055 A1

(12) EUROPEAN PATENT APPLICATION

(43) Date of publication:
12.03.1997 Bulletin 1997/11

(21) Application number: 96500124.1

(22) Date of filing: 11.09.1996
(51) International Patent Classification (IPC)6F23N 1/06, F24C 5/18
(84) Designated Contracting States:
BE DE DK FR GR IT NL PT

(30) Priority: 12.09.1995 GB 9518594

(71) Applicant: SATERMIC, S.L.
E-08251 Santpedor (Barcelona) (ES)

(72) Inventor:
  • Casas Salles, Jordi
    08251 Santpedor (Barcelona) (ES)

(74) Representative: Perez Bonal, Bernardo 
C/Explanada 8
28040 Madrid
28040 Madrid (ES)


(56) References cited: : 
   
       


    (54) Forced draught gas-oil heater control device


    (57) A gravity-fed oil-fired furnace for non-industrial heating systems has the combustion process optimised by applying a forced draught to the combustion chamber by means of a motor-driven extractor (6) exhausting the combustion gases through a relatively-narrow flue (10). the speed of the extractor impeller is monitored to derive an output signal which is used as a feedback signal to control the speed of the motor driving the impeller.




    Description

    OBJECT OF THE INVENTION



    [0001] The present invention aims at providing a heater control system for a forced-draught gas-oil heater used to heat individual residential premises, including apartment buildings.

    [0002] In accordance with this invention, a computer receives an extractor-speed signal and compares it with the initial speed selected to get a predetermined draught, and then acts upon the extractor motor voltage regulator through a conventional PID digital regulator in order to cause the extractor motor to reach its design speed.

    BACKGROUND OF THE INVENTION



    [0003] Gas-oil heaters may be split in two main groups, those of the fuel-injection and gravity-fed types.

    [0004] The former have their more extended application in industrial installations, heating up industrial premises, warehouses, etc., competing with liquid fuel nozzles and gas boilers. Their functional characteristics are very similar in all of these cases, in so far as, in one way or another, the fuel drive is pressurised, prior to combustion, by any suitable means.

    [0005] Some gas boilers are known for heating water intermittently, such as are disclosed in US-A-4 519 540, which describes an extraction fan whose speed is regulated depending on the gas that feeds the burner.

    [0006] Another gas boiler is described in EP-B0 279 771, which has an extraction fan whose speed is regulated depending on the combustion air flow.

    [0007] None of these gas boilers has a device to regulate and control a constant draught when external conditions modify the extractor fan speed, and none of these incorporates means for regulating a fuel control valve depending on the operative conditions of the extraction fan.

    [0008] This is not the case in respect of gravity-fed gas-oil combustion heaters. In these heaters the fuel comes, generally, from a reservoir placed laterally and internally to the heater and in an arrangement slightly higher than a fuel feed regulator of the level type that has to incorporate at least an admission valve, a normal float fitted tank, closing fuel passage, plus a filtering unit to filter out fuel impurities, a discharge dosing valve and a flow-indicating device.

    [0009] This regulator discharges, through its lower portion, to a gravity feed conduit leading to the burner admission inlet, arranged below so that the fuel from the reservoir tends to find its own level through communicating pipes, thus feeding the combustion outlet.

    [0010] This specific arrangement and the absence of air injection or extraction fans, arranged prior to the burner, which could cause a considerable number of combustion problems, would cause that the only forced draught would be the very-small one caused by the flues, as a function of their diameter, which impart a low speed to the exhaust gases, so small that the flue draught may stop altogether whenever there is a major temperature difference.

    DESCRIPTION OF THE INVENTION



    [0011] This invention relates to a draught control system, generally for gas-oil combustion heater smoke extraction conduits and, more specifically, for those heaters used to heat up residential premises.

    [0012] These heaters make use of a new burner design, of high combustion performance and high purity in the production of gas residues, thus enabling a different smoke extraction arrangement.

    [0013] The invention consists of a powered regulation system, using a closed chain, to stabilize the draught of a horizontal inlet conduit to an external wall of the building or residential premises to be heated, of a very small diameter of approximately one fifth of that available in conventional outlets, as normally effected through the ceiling of free standing houses, and in the case of apartment blocks, through the various ceiling-floor surfaces all the way up to the roof.

    [0014] This powered system incorporates a heater fuel feed control device made up of an electronically controlled "all-or-nothing" valve fitted in the fuel line leading to the burner.

    [0015] The electronic control system regulates the gas-exhaust means, consisting of a centrifugal extractor with a device that reads its speed using infrared beams, the assembly being then completed through the addition of a metering device and cabling.

    [0016] The main purpose of the centrifugal extractor, of adjustable speed and with a wide range of operating speed grading in respect of its optimum design operating speed, is to maintain a previously fixed and uniform draught. The extractor consists of a centrifugal impeller built so as to reduce its noise level down to values admissible for indoor night-time use.

    [0017] The motor of this fan is connected to an electronic control system, as well as the infrared speed reader acting as a multiple perforation wheel tachometer with an infrared transmitter-receiver that transforms the passage of the perforations and converts them into impulses, that are directed to a regulator to control the speed of the motor-driven fan.

    [0018] The elctronic control system also controls an "all-or-nothing" needle type electrically-actuated valve that interrupts gas-oil supply in cases of insufficient or non-existent draught conditions such as, for instance, an obstruction triggering an alarm, as well as due to other normal causes such as lack of electric power supply, incorrect connections, etc,. so that acting upon the fan and upon the cut-off valve would enable the proper operation of the heater in this forced draught arrangement with outlet to small vertical wall orifices.

    [0019] In case of strong winds that may cause the draught to be decreased, and the extraction fan speed to decrease also, the fan speed is automatically regulated by a regulator, after the actual speed signal has been compared with the present speed signal by a microprocessor.

    [0020] If it is not possible to recuperate the initial speed and there is a differential pressure, the fan is activated to its maximum speed.

    [0021] Alternatively to the infrared transmitter-receiver speed variation control, other conventional systems producing a similar effect may also be incorporated or the measuring criteria may also modified, for instance to measure minimal differential pressure but still sufficient to enable the lightest depression caused by obstructions, air turbulence, etc., to activate the gas extraction control.

    DESCRIPTION OF THE DRAWINGS



    [0022] The present invention will now be described by way of example with reference to the accompanying drawings, in which:

    Figure 1 shows a schematic side elevation cut-away view of a heating system of the present invention adjacent to an external wall, and

    Figure 2 is a front elevation view, also cut away, of the heater shown in Fig. 1.


    PREFERRED EMBODIMENT OF THE INVENTION



    [0023] As shown in the drawings, one embodiment of the invention consists of a gas-oil heater forced draught control device, to heat residential premises, of the combustion burner 1 type with a high degree of purity in the production of gas residues, an "all-or-nothing" electrically-actuated valve 2 fitted between the burner 1 and conventional constant level flow regulator 3, fed by fuel from the tank 4, having means to measure the speed of a centrifugal exhaust extraction unit 6, the assembly being completed by a tachometer indicator 8 that indicates extractor speed, and wherein the device incorporates a power-driven system 5 regulated by closed chain configured by a microprocessor that compares the measured speed with the initially selected speed and by a conventional, proportional, integral and derivative (PID) digital regulator acting to the extractor motor voltage regulator, to stabilize combustion gases exhaust draught which are direct to a 80 mm diameter outlet conduit through the vertical wall.

    [0024] The centrifugal extractor 6 is made up of a floating wheel with variable speed between 400 and 2400 rpm, maintaining an operating speed of about 100 rpm and being energised at a voltage defined by the regulator, being designed to withstand high temperatures, as well as reaching draught speed in about three seconds.

    [0025] The infrared reader 7, multi-perforated wheel tachometer with infrared beam transmitter-receiver, transforms the passage of the perforations using an adapter circuit and converts them into impulses, before their transmittal to the microcomputer, so as to regulate the speed of the motor-driven fan.

    [0026] The electronic control system 5 also controls the "all-or-nothing" electrically-operated needle type valve 2 that starts up upon reaching 85% of operating speed and then interrupts gas-oil supply after 30 seconds, because of insufficient or non-existent draught, triggering an alarm condition, as well as due to lack of electric power, incorrect connections, etc., with automatic reconnection before 17 seconds or with a new alarm if air turbulence or any other cause still prevents its operation, deducting an equivalent time to the heater to use up any residual fuel from the electrically-actuated valve 2.

    [0027] It is not necessary to keep the forced draught pipe 9 heated so as to prevent condensation and draught pressure losses, which enables its cooperation in the transmission of radiation energy to the surrounding living area, up to its connection to the extractor 6, which outlet is connected to a small orifice 10 in the vertical wall 11.

    [0028] This description is not extended any further on the understanding that any expert in this subject has sufficient information to understand the invention and the advantages derived therefrom, as well as to be able to reproduce it.


    Claims

    1. A system for controlling forced-draught gas-oil heaters to be used for heating residential premises, including: an "all-or-nothing" electrically-actuated valve fitted between a gas-oil burner and a constant-flow regulator, fed by gas-oil from a reservoir; a motor-driven exhaust extraction unit adapted to generate an output signal dependent upon the speed of rotation of its rotor; a computer for comparing the actual rotor speed with that necessary to produce a desired draught, and a regulator controlling the motor voltage in dependence on the output signal, to stabilize the rate at which combustion gases are exhausted into the atmosphere.
     
    2. A gas-oil heater system as claimed in claim 1, in which the extraction rotor speed is given by the rate at which a beam of radiation is broken by perforations in a disc rotated by the rotor to generate the desired output signal.
     
    3. A gas-oil heater system as claimed in claim 1 or 2, in which the electrically-operated valve is opened when the rotor nears its intended operating speed; in which the valve is closed, to interrupt the gas-oil supply, when the rotor speed falls below a threshold value, with the generation of a primary alarm, with automatic reclosure of the valve after an interval close to half the combustion time of the residual fuel left between the burner and the electrically-actuated valve, followed by a generation of a secondary alarm should air turbulence of any other cause still prevent operation of the exhaust extractor.
     




    Drawing







    Search report