IES970657A2 - Fan flue unit for twin burner cookers - Google Patents

Abstract

A fan flue unit incorporating a flue fan used with a multi burner cooker delivering air to the burners and venting gases produced by combustion. The unit incorporates a controller that senses the burner status and controls operation of the flue fan accordingly. <Fig. 1>

Description

Fan Flue Unit for Twin Burner Cookers The present invention relates to a fan flue unit for twin burner cookers. Twin burner cookers are high output cooking and water heating appliances which are powered by two burners which are either oil burners or gas burners. Each burner is provided with its own fan for providing air to the burner for combustion and for providing the pressure differences to operate the fan flue unit of the cookers so as to exhaust the products of the combustion.

Fan flue units in use to date were designed for cookers with one oil or gas burner. The unit allows the cooker to be situated on an outside wall where a chimney would be impractical or impossible. The fan is attached to an insulated stainless steel extension pipe which is in turn fitted to a cast iron pipe. This typically 150mm diameter cast iron pipe comprises a 90° bend and a straight run of 200mm and has the effect of exiting the flue gases straight back from the top of the cooker. The exit point through the wall is at 1065mm from floor level.

The fan switches on and off at the same time as the burner. Draught control is achieved using an air dilution slot which introduces fresh air from outside. The introduction of this cold air serves two purposes: 1. To limit the volume of gases pulled through the cooker by the fan hence enabling a constant draught level to be set. 2. To cool the flue gases before they pass through the fan.

As the fan switches off at the same time as the burner, a volume of flue gases remains within the cooker. If wind conditions outside are unfavourable, these fumes can enter the room when the burner switches off.

S80797 2 IE 970657 When connected to a fan flue unit, cookers generally take their air for combustion from outside the intake point being approximately lm below the fan exhaust. In certain locations this can lead to a re-circulation of products of combustion. As there is a very low oxygen content in the products of combustion, a burner supplied with air mixed with burnt flue gases cannot operate effectively, the main symptoms being a loud rumbling noise and dirty combustion.

The present invention provides a cooker with a plurality of burners and having a fan flue unit, the fan flue unit having a variable speed fan which is variable to give different outputs depending on the flue requirements for the output of the burners.

Advantageously, the speed of the flue fan is varied by the voltage loading of the fan changing in line with the power requirements of the burners.

Although the invention is described in relation to twin burner cookers, it could also be applied to cookers during more than two burners In cases where the fan stops, the fan exit is obstructed or strong prolonged gusts of wind prevent the fan from exhausting sufficiently, a differential pressure switch causes the burner fuel solenoid to close thus sending the burner into lock-out mode. This safety feature will not allow the burner to fire again until the problem has been solved.

Twin burner cookers have two independent burners operating at different input levels. The cooker can be operated with either burner running on its own or with both burners running together. The burners are firstly controlled by two independent channels on a programmable controller and secondly by their respective control thermostats.

A single speed fan is controlled from the timer channels via a relay which ensures that the fan runs when either or both channels are energised. The fan will run as long as either channel is energised and will stop when the channel is de-energised either manually or by IE 970657 -3 the timer. In this way, the instance where the fan stops as the burner stops is greatly reduced.

As the burners have different inputs, the volume of flue gases passing through the system is different for the three possible modes of operation i.e. boiler mode, cooker mode and both burners running. This results in the need for different draught levels for each mode to ensure the appliance runs at maximum efficiency.

A single speed fan does not have the facility for changing draught levels as the different modes of operation are activated.

The problem of flue gas re-circulation is increased with a single speed fan due to the extra volume of the flue gases passing through the system when on boiler mode and with both burners running.

The pressure switch safety system is operated in the same manner as for the single burner cooker by means of an additional relay.

The fan flue unit of the invention uses voltage control to give a separate fan speed for each mode of operation. A constant level of air dilution is used to further control the draught along with cooling the gases before entry to the fan.

The invention will hereinafter be more particularly described with reference to the accompanying drawing, which shows by way of example only, a waring diagram showing a fan flue unit according to the invention fitted to a twin burner cooker.

The unit is controlled by an electronic control which uses three independent potentiometers to vary the voltage to the fan depending on which mode of operation of the cooker is chosen. Each fan speed can be adjusted on site to suit the extraction requirements in different cooker locations.

IE 970657 -4An example of the burner combination to fan speed relationship is as follows: Cooker burner only Slow speed #1 135VAC Boiler burner only Medium speed #2 145VAC 5 Both burners High speed #3 190VAC Startup/post-purge 15 secs Max speed #4 220VAC When the cooker is initially powered up, the fan runs for 15 sec at maximum speed to prove the pressure switch.

When the boiler burner control thermostat signals for heat input, the fan starts and runs at full speed for the initial 15 sec when the fan exit pressure is checked. After 15 sec, the voltage to the fan drops to 145V to maintain a draught of 0.06 water gauge. When the thermostat temperature is reached, the burner is turned off but the fan runs on at maximum speed for 15 sec to remove all products of combustion from the flue passages. After the 15 sec post-purge, the fan remains off until the boiler stat calls for heat again.

The same sequence is followed when the oven burner thermostat signals for heat input. However the fan runs at 135V to maintain a draught of 0.06 water gauge.

When both burners are activated, the fan runs at 190V to maintain a draught of 0.06 water gauge. During this sequence, each burner will run for some period on its own in which case the controller reverts back to the relevant speed for each mode.

A +0.4mbar differential pressure transducer mounted in the exit of the fan to determine the positive pressure created by the fan relative to ambient atmospheric drives a micro-switch closed when the +0.4mbar level is achieved. If the pressure falls below the level for more than 23sec at one time, the controller will close both burner fuel solenoids causing the system lo shut down. This feature safeguards against a faulty fan, blocked fan exit and sustained strong gusts of wind while eliminating the occurrences of nuisance lock-outs caused by intermittently strong gusts of wind. -5IE 970657 The fan is attached to a steel fan plate which is mounted on a wall plate. The fan plate is mounted on the wall plate such that a 10mm gap exists between them. Dilution air is introduced at this point, the amount entering the fan being determined by the area of the fan inlet that is not covered. This is achieved by placing an adhesive gasket around ’/< of the circumference of the fan inlet.

This wall plate is permanently attached to a stainless steel twin walled insulated flue pipe 400mm long.

The fan is mounted such that it exits to either the left or right hand side, depending on the installation. This will eliminate the problem of re-circulation of products of combustion.

The fan unit will be covered with a coated steel cover box which will allow for exits to the left and right hand sides, the exit hole which is not in use is covered with a blanking plate.

The control system is linked to the fan with a 4 core cable.

The control PCB is mounted in the cooker base with an 8 way connector supplying power and burner selection information.

Once the fan has been mounted in the wall and the control PCB has been installed, both burners must be run for at least one hour before adjusting the fan speed and hence the draught. This measure is to allow for expansion of the flue gases as the temperature rises. Once an hour has elapsed, a balance potentiometer in the speed regulator will allow for final site adjustments to ensure draught levels between 0.04 and 0.07 weight gauge for each mode.

It will of course be understood that the invention is not limited to the specific details described herein, which are given by way of example only, and that various modifications -6IE 970657 and alterations are possible within the scope of the invention as defined in the appended claims.

Claims (3)

Claims

1. A fan flue unit incorporating a flue fan for use with a cooker having at least two burners, the unit having:5 means for supplying air for combustion to each burner; means for venting gases produced by said combustion; and 10 a controller for sensing burner status and for controlling operation of the flue fan in response to sensed burner status.

2. A fan flue unit as claimed in claim 1 wherein:15 the controller is adapted to conduct real time estimation of burner power requirements; optionally in which the controller is adapted to control operation of the flue fan using a voltage loading speed controller; optionally in which the controller includes a fan monitor for detecting incorrect flue fan operation and lockout means for closing a burner fuel solenoid; 25 optionally in which the lockout means comprises a differential pressure switch; and optionally in which the controller incorporates level calibration means for setting a base operating level. IE 970657 -8Λ cooker having two or more independently operable burners, at least one burner being controlled by an independent channel of a programmable controller optionally wherein the programmable controller incorporates means for a control thermostat associated with the controlled burner; optionally in which the cooker has a flue fan unit incorporating a single speed flue fan; optionally in which the single speed flue fan is controlled by a timer channel of the programmable controller; optionally in which the controller is operable to vent products of combustion in a variety of operation modes. A method for venting gases from a cooker of the type having a burner connected to a flue fan unit having a fan and controller comprising the steps of;detecting an initialisation signal at the controller; generating a fan test signal from the controller to operate the fan at maximum speed; receiving a heat input signal to the controller and generating a fan run signal to operate the fan at full speed for a specified time period; and periodically sensing exit pressure from the flue fan unit and generating an appropriate controlled fan run signal to operate the fan at a desired level responsive to the sensed exit pressure, the method optionally further comprising the steps of:-9ΙΕ 970657 detecting a temperature reached signal from a thermostat; generating a burner off signal from the controller; and 5 generating a fan run signal to operate the fan at full speed for a specified time period.

3. 5. A fan flue unit or a cooker or a method substantially as herein described with io reference to the accompanying drawing.