EP2577172B1

EP2577172B1 - Heat storage cooker

Info

Publication number: EP2577172B1
Application number: EP11726931.6A
Authority: EP
Inventors: Patrick Collins
Original assignee: AGA Rangemaster Ltd
Current assignee: AGA Rangemaster Ltd
Priority date: 2010-05-24
Filing date: 2011-05-24
Publication date: 2018-10-31
Anticipated expiration: 2031-05-24
Also published as: WO2011148170A2; CN103261795B; US20130168378A1; EP2577172A2; WO2011148170A3; GB201008608D0; CN103261795A

Description

This invention relates to domestic cookers of the heat-storage type.
It is known to provide cookers including at least one oven compartment which comprises a box of relatively thin steel sheets surrounded by thermal insulation or air. A heating element may be provided within the box, such as a gas burner, or within the walls themselves, such as thin electric heating elements. To help ensure that the oven is at the same elevated temperature at all locations a fan is often provided which blows air around inside the compartment. The walls of the oven store very little heat and so the cavity can be warmed up to full operating temperature from cold very quickly. Conversely when the heat source is turned off they cool down very quickly as well.
It is also known to provide domestic cookers which are known as heat-storage type cookers. Perhaps the most well known and loved are the applicants own Aga and Rayburn Ranges of heat storage cookers. These cookers differ from the pressed steel type because the oven walls are formed of a thick material with high specific heat capacity so that the walls have a relatively high thermal mass. The cavity does not contain a heating element, and the walls also are not provided with a direct heating element. Instead the one or more ovens are in thermal contact with a system of ducts communicating with a combustion chamber which serves as heat source.
The combustion chamber is fed with a solid fuel, or, and more commonly nowadays, with fuels such as kerosene, natural gas or propane. By making the shell from cast iron, heat from the heat source is stored residually allowing the device to provide constant high temperatures with heat source constantly topping it up if heat is lost (for instance by opening a door to the oven).
It is also known to provide a heat storage stove with the heat exchange chamber containing one or more resistance heating elements. Two types of electric heat store stoves have been proposed. In the first the heat store is "charged" with heat to a high level using a high power heating element rated at 30 amps at 240 volts. This charging can be performed overnight when electricity is cheaper and then released from the store during the day as required to keep the stove at its operating temperature.
Because it takes a long time to heat up the cookers are usually left on for extended periods so they are ready to use at meal times. This style of cooking is very different to cooking with a sheet steel cooker, and many people feel that food cooked in a range cooker is preferable. A beneficial side effect of the heat stored in the cast iron is that a gentle background heat is emitted constantly which gives the room in which it is located a cosy warm feel. A potential disadvantage of this type of cooker over the pressed steel cookers is the long warm up cycle for the ovens.
Prior art documents CH101787 and CH205478 disclose such ovens comprising a cavity made from cast iron.
According to a first aspect the invention provides a heat storage cooker comprising a least one oven cavity formed by walls of high thermal mass, such as cast iron, and at least one electric radiant heating element which is embedded in at least one of the walls such that in use the electric radiant heating element transfers heat energy to the wall which subsequently radiates at least part of that heat energy in to the oven cavity.
By walls of high thermal mass we mean walls which are made of cast iron or similar and are relatively thick so that they retain heat in the manner of a traditional heat storage oven for gradual release over an extended period of time. For instance using cast iron for the walls of the oven cavity it is ensured that the ovens cook using radiant heat in the same manner as a traditional heat storage cooker. However, because the total amount of thermal mass is lower than a traditional cooker of that type and heat is applied directly to each oven using a radiant heating element thermally connected to a wall of the oven rather than a single heat source connected to all the ovens through a series of ducts the warm up time is much reduced, and an increase in efficiency may be attained. At the same time the traditional comforting effect of gentle heat radiated out of the cooker from the heat stored in the cast iron walls is retained compared with a steel walled cooker.
The or each radiant heating element may comprise a radiant hot plate. Each element comprises a generally flat plate of ceramic or glass ceramic covering a coil of electrical resistive heating element. A spacer may be provided to make the ceramic plate stand proud of the heating element, and a backing plate- perhaps of thin pressed steel, may be provided to enclose the heating element. An optional thermal insulated may be provided between the coil and the backing plate. One or more holes may be provided through which bolts can pass to bolt the heat source to a wall of the oven cavity. A thermocouple may be provided within the element which may output a signal that can be used to help control the temperature of the element.
More preferably each radiant heating element may comprise a commercial grade solid element hot plate or radiant heating element in which the electrical heating element- either a coil or ribbon- is embedded in a plate like cast iron body. This arrangement ensures excellent even radiate heat distribution and also enables high levels of heat transfer from the body to the wall which it is secured to. A seal may be provided between the element and the body. The cast iron body effectively forms a part of the wall of the oven cavity so that the heating element is embedded in the wall, causing the iron to heat up and store the heat.
The hot plate may be located inside the cavity in thermal contact with an inner face of the wall. In this way it will radiate heat directly into the cavity, some of which will heat the walls of the cavity, and also heat the wall it contacts through conduction.
Where it is located inside the cavity, the hot plate may be located in a recess in respective wall of the oven cavity so that the surface of the hot plate may be substantially flush with the surrounding surface of the wall.
The area of the hot plate may be at least 50 percent of the area of the associated oven wall.
The wall may have a thickness of at least 3mm, and preferably at least 5mm, and may be of cast iron. The or each wall may form part of a cast iron frame which defines more than one oven cavity.
Therefore more than one cavity may be provided, each one comprising walls of high thermal mass, and at least one radiant heating element (such as an electric hot plate) which is in thermal contact with at least one of the walls to form an integral part of the wall such that in use the electric hot plate transfers heat energy to the wall which subsequently radiates at least part of that heat energy in to the oven cavity.
There may preferably be two oven cavities or three cavities. One of the ovens may be provided with more radiant heat elements than the other to enable it to attain a higher temperature than the other. For instance one may include two elements and the others only one.
Each wall of a cavity may be separate from any other wall and secured so that it is in thermal contact with at least one other wall of the cavity. Alternatively two or more walls may be integrally formed. If cast iron is used, two or more walls may be formed as part of a single casting.
A hot plate may be secured to a wall of a cavity using one or more bolts or screws. A thermal matching paste may be provided between the hot plate and the wall.
Each hot plate may be arranged to radiate heat substantially evenly over the whole of its surface, by which we mean all points radiate at a temperate within 20 percent, or 10 percent, or 5 percent of the temperature of any other point on the surface. This ensures heat is radiated evenly into the cavity (where it is located inside) and also into the cast iron wall avoiding undesirable hot spots.
Each hot plate may be constructed generally of the same material as the wall it is secured to, typically cast iron, so that when a steady state temperature is reached in the oven the walls and hot plate will be generally at the same temperature. When the oven is switched off and allowed to cool it will do so slowly due to the high thermal mass of the walls and also the hot plate. To further help retain heat in the cavities an amount of thermal insulation may be packed around the cavities.
A controller may be provided which controls the heating of the heating elements. Where two oven cavities are present, the controller may include a setting which maintains a first one of the ovens at a first set temperature when the cooker is switched on a second one of the ovens at a second set temperature when the cooker is switched on, the second temperature being lower than the first. The controller may include a preset strategy which raises the ovens to these temperatures and maintains them there at a single command from a user. These temperatures may be permanently stored in a memory associated with the controller. A button, rotary knob, switch or other input may be provided which a user can operate to initiate this strategy or to turn off the oven when heating is not needed.
Providing two preset temperatures allows the cooker to mimic the different temperatures of a traditional cast iron heat storage range cooker, in which a single heat source is provided that heats all the ovens and so does not allow independent control.
Where three ovens are provided, three different preset temperatures may be stored in the memory of the controller. One of these may be a temperature far below the other two to allow the oven to be used as a warming oven. The three preset temperatures are preferably approximately 240ºC, 180ºC & 120ºC.
The controller may receive input signals from a thermocouple associated with the or each heating element associated with a cavity, the or each thermocouple providing an output indicative of the temperature of a heating element, and also from a thermocouple that measures the overall temperature inside an oven cavity.
The controller may allow the user to override the preset temperatures so that individual control of the temperature of each oven may be achieved. A separate switch, button, rotary knob or other input may be provided which a user can operate to provide an indication of the desired temperature of an oven to the controller, for example to choose one of three preset temperatures.
The controller may, for instance, include or otherwise be compatible with a controller of the kind disclosed in GB2447777 , in which a programmable timer is provided for control of the operation of a traditional heat storage oven. The principles disclosed there for the control of a set of ovens from a common heat source apply equally to the control of the individual heat elements of the present invention.
Hot plates are well known for use as a heated surface on which to cook food items, often forming part of the hob of a cooker. It is not known to use them to heat an oven cavity and not known to use them to heat a cast iron wall of an oven to provide an effect similar to traditional heat storage cooker. There are a wide variety of different types available, and the preferred type for use in this invention comprises a sandwich construction with two layers of cast iron or ceramic material (or indeed any other material of high thermal mass) surrounding one or more flat electrical heating elements.
The cooker may include a hob which is provided with at least two hot plates, each one covered by an insulated lid. The hot plates may be circular to enable the hot plate to be styled in the manner of a traditional heat storage cooker.
The cooker may be absent any form of central heat source, traditionally a heating barrel, and as such may also be absent the ducts that would otherwise be needed to take the heat from the central heat source to each oven cavity. The controller may be located in the space that would traditionally have been occupied by the central heat source.
According to a second aspect the invention provides a heat storage cooker comprising at least two oven cavities, each one formed from a plurality of walls having a high thermal mass and each one being provided with a respective heat source which is adapted to heat the walls of the oven cavity which in turn heat the interior of the cavity by radiating heat.
Each oven cavity may be heated independently of the other. The walls of one of the oven cavities may be insulated from the walls of the other cavity, or one or more walls of one cavity may be in good thermal contact with one or more walls of the other cavity.
Each oven may function independently as a heat storage device, meaning that the thermal mass of the walls of the oven is sufficient that it retains heat for an extended period of time to continue to heat the oven cavity.
The heat source of each oven may comprise a hot plate or other electrical heating element in thermal contact with at least one wall of the oven cavity. The heat source may comprise a hot plate. The walls may comprise cast iron components.
A controller may be provided, which may operate according to the principles set out for the controller of the first aspect of the invention. Indeed, any of the features of the first aspect of the invention may be incorporated into the second aspect of the invention.
There will now be described, by way of example only, one embodiment of the present invention with reference to the accompanying drawings of which:

Figure 1 is a general view of an embodiment of a domestic heat storage cooker in accordance with the present invention;
Figure 2 is an exploded view of the parts of one of the oven cavities of the cooker;
Figure 3 is a schematic view of the control circuit and heating elements of the cooker of Figures 1 and 2; and
Figure 4 is a view of the user interface device that forms part of a controller for the cooker.

A range cooker 1 for domestic use is shown in Figure 1 of the drawings. It comprises a shell comprising front, side, rear and base panels (although only the front is shown) bolted and screwed to a support frame (not shown). The front panel 2 is about 120cm wide in this example, although it may be wider or narrower, and is located above a plinth 3. It can be styled in a variety of different manners depending on whether a traditional or contemporize effect is required, and also can be provided in a range of different colours. It is provided with three openings which are covered by respective hinged insulated doors 4, 5, 6. Each door is provided with a handle 4a, 5a, 6a to enable the door to be opened and closed. The top panel 7 forms a hob, and is inset with two circular hot plates. Each hot plate is covered by a hinged insulated lid 8,9, again each hinged lid being provided with a grab handle. When lowered, the lids 8,9 retain heat in the hot plates when they are switched off. Each hot plate is supplied with electricity through wires connected to respective outputs of a controller, as described later.
Inside the frame are three oven cavities. The doors of Figure 1 show the general location of the three oven cavities and their general construction. A view of the walls of one of the cavities (the other is to be understood to be of similar construction) is provided in Figure 2 of the drawings. Each cavity comprises a base, a rear wall, two side walls and a top wall. The front wall of each cavity is open and aligned with a respective opening in the front panel of the range cooker, allowing access to the cavities through the doors 4,5,6.
The walls (including the top and bottom walls) of each oven comprise cast iron plates of around 5mm thickness, giving them a high thermal mass. The walls meet one another in such a manner that each oven cavity defines a closed spaced when the doors are shut and that heat can readily conduct from one wall into the adjacent wall or walls. Indeed if preferred the walls may be cast as one part, with two or more walls being integrally connected. Each oven is individually insulated. Thermal insulation is provided between the walls and the shell to stop the shell from becoming too hot to comfortably touch but also to minimise unwanted heat loss from the cast iron walls, ensuring they cool down only slowly.
The upper right oven cavity, when viewed from the front, is intended for use as a roasting and baking oven and as such operates at higher temperature than the bottom right oven cavity. In this embodiment all of the ovens are the same size.
Secured to at least one wall of each oven is a rectangular or square hot plate or radiant heating element 20 as shown in Figure 2 which is in thermal contact with the cast iron wall. A matching paste may be provided between them to improve conductivity from one to the other. The hot plate is located on the side of the oven wall that is internal to the oven cavity, although it could be located on the other side of the wall. In this example five such hot plates are used, two for the hob and one in each oven. There are five fixed temperature cooking zones on the cooker-three ovens and two hotplates.

Zone 1 _ hot spot _ 330°C_ single plate 2.5kW
Zone 2 _ simmer spot _ 220°C_single plate 2.5kW
Zone 3 _ roast oven _ 240°C_ dual plates 2.5kW each (run at 2:1 power ratio top element to bottom element)
Zone 4 _ baking oven _ 185°C_ dual plates 2.5kW each (run at 2:1 power ratio top element to bottom element)
Zone 5 _ simmer oven _ 120°C_single plate 2.5kW (run at a maximum of 50% power - i.e. 1.25kW)

Each one receives electricity from the controller. Each one comprises a heating element embedded in a thermal compound within a plate of cast iron material. The arrangement ensures that the element radiates heat evenly preventing hot spots forming in the oven. Also because the material of the hot plate matches that of the walls once it has been heated to a steady state temperature the hot plate and walls will generally all be at a similar temperature, and when switched off will all cool at the same rate and remain at the same temperature.
Located behind a door 11 at the upper left front of the cooker is a controller 10 which includes a user interface panel with a set of buttons which enable the hot plates on the hob to be turned on and off and to be set at different heat outputs. The buttons also turn on and off the ovens. Each button is connected to the controller which responds to changes in the position of the knobs. This panel can be seen in Figure 4 of the drawings and is described in more detail later.
The electrical diagram for the cooker is shown schematically in Figure 3 of the accompanying drawings. The control system can be separated into three parts. It comprises a Main power board which is provided with high power electrical switches, in this example relays and triacs, for selectively connecting each heat element to the mains electricity supply.
The switches are controlled by a secondary printed circuit board in the form of a control panel which contains switches allowing the user to choose between auto and manual operation, selecting the required cook zones and operate the oven vent fan. This may be located behind the top left door of the cooker. The panel also receives inputs from thermocouples associated with each cooking zone. The secondary printed circuit board carries the controller that determines the switch states required and is connected to a memory in which is stored a preset temperature for the top oven and the bottom oven. The preset temperature for the top oven is higher than for the bottom oven.
Starting with all the ovens turned off, all the switches are arranged so that all the radiant heat elements are isolated from the mains supply. As soon as the ovens are turned on by movement of the associated button the controller applies full power to all the hotplates that form a part of the oven walls by changing the state of the switches to connect the hotplates to the mains supply. This causes the ovens to rapidly heat, all the while raising the temperature of the cast iron that forms the walls. The walls and the hotplates radiate an even heat into the oven cavities.
If all five zones were to be switched on simultaneously the total load demand would exceed 60A; therefore the controls limit total current demand in some way to a maximum of 30A. This 30A limit will allow installation of the cooker using the normal 6mm² cooker circuits available in many homes in the UK. The limit is achieved by 'power sharing' between elements during heating up periods. The priority for 'power sharing' between zones follows the zone numbers, i.e. zone 1 has top priority; zone 2 has second call on power, then zone 3 and so on.
A power de-rating technique is used to maintain the correct temperature in the hotplates. PID control varies the power to the element as it heats up or cools down from its target temperature.
A more complicated de-rating technique is used to control the cooking performance of the ovens. Full power is provided until 20°C below target temperature is achieved; beyond this point electrical power to the element is limited to a maximum of 20% Top -10% Bottom (2:1 ratio) with PID control varying this between 20% and 0% as the oven temperature approaches the target temperature. The Simmering oven has a single 2.5kW element which uses a maximum power level of 50% during warm up and varies between 25% and 0% during PID control.
The cooker may also include a vent fan to extract moisture and cooking smells from the oven cavities. The vent fan motor requires a pre-set variable supply of 12 to 24v dc, capable of a continuous output of 5W, provided by an electronic circuit on the main power board. The output voltage to the vent fan is set by the installation engineer using a potentiometer situated on the power board.
Once an oven reaches close to it's set point temperature the power drops to a pre-determined de-rated power, typically 20% (top element) and 10% (bottom element) of full power, preventing aggressive temperature over shoot with in the oven. Once at the desired set point, the temperature is maintained with PID feed back monitoring and controlled power burst creating a cycling temperature range of 2°C. The ovens are therefore held at the preset temperatures stored in the memory until the ovens are turned off.
The ovens are therefore heated by radiant heat from the cast iron walls, as supplied by the hot plates.
The third part is an optional remote control may be provided which enables the ovens to be switched on or off remotely. Hand held remote control (HHC) provides the user with timing functions to switch the cooker on and off up to twice a day (Auto modes) and display information such as time/date. The HHC transmits time/event settings via RF to a small 'piggyback' board which stores the Auto programmes. The 'piggyback' board is connected to the power board via a communication link.
The controller can cause the cooker to function in a wide range of different ways but the following sets out a preferred control logic that may be implemented.
If all five zones were to be switched on simultaneously the total load demand would exceed 60A; therefore the controls limit total current demand in some way to a maximum of 30A. This 30A limit will allow installation of the cooker using the normal 6mm² cooker circuits available in many homes in the UK. The limit is achieved by 'power sharing' between elements during heating up periods. The priority for 'power sharing' between zones follows the zone numbers, i.e. zone 1 has top priority; zone 2 has second call on power, then zone 3 and so on.
The user can switch the vent fan on or off manually using a dedicated vent fan button on the UIB/touch panel.
The user interface board contains piezoelectric touch sensitive switches or buttons with LED status indication and audible confirmation of operation. There are eight switches as shown in Figure 4 of the drawings. Each switch performs one of the following functions:

Standby/on
Mode - Manual, Slumber, Auto, Auto/Slumber selection
Boil (hotspot) -on/off
Simmer (simmerspot) -on/off
Fan (oven vent fan) -on/off
Roast (oven) -on/off or selected for auto
Bake (baking oven) -on/off or selected for auto
Simmer (oven) -on/off or selected for auto

In addition to these switches the hand held controller can be used to control the cooker. The hand held remote control displays the time, date and Auto event settings. Programming is via eight push buttons.
Information is displayed via a backlit LCD screen. Refer to Appendix 3 for screen layouts.
The controller may cause the cooker to operate in one of several different modes as described hereinafter.
Modes can only be selected or active when the standby button status is 'on' (green LED). If the standby button status is set to 'standby' then zones cannot be switched on/off or selected/de-selected. 'Auto' and 'Auto/Slumber' mode 'Events' will not be activated in 'standby' status (indicated by no LED).
Manual - Each zone of the cooker can be operated individually when in manual mode. The corresponding zone button is pressed once to operate (switch on) and once more to de-select (switch off) the zone. While in manual mode any zone selected will remain on indefinitely until de-selected (switched off).
Slumber - In this mode all three oven zones (3, 4 & 5) are active, preset to 120°C, this is termed being in 'slumber'. No oven zone can be 'off'. Any oven zone can be switched from 'slumber' to 'full temperature' as if in manual mode by one press of the zone button. Pressing the zone button once more returns that zone back to 'slumber'.
Auto/Slumber - Each of the oven zones, ( zones 3, 4 & 5) of the cooker can be selected to operate once or twice each day, each operation is termed an 'event'. The start and finish time, and therefore the duration of each 'event' is chosen by the user. For the time between the 'events', the ovens will maintain a temperature of 120°C, this is termed being in 'slumber'.
Auto- Each of the oven zones, ( zones 3, 4 & 5) of the cooker can be selected to operate as in 'Auto/Slumber' mode, however during the time between 'events' the ovens are switched off and allowed to cool.
The five cooking zones are split into two groups, hotplates and ovens. Hotplates (zones 1 & 2) are always manually controlled, while the ovens ( zones 3, 4 & 5) can be individually switched 'on' in Manual and Slumber modes or pre-selected to be 'on' during 'event times' in the Auto modes. There are two 'Auto' modes; one can be selected with 'slumber' heating between events and the other with no heating between the 'events'. Selection of the modes is via the 'Manual, Slumber, Auto, Auto/Slumber' mode button on the UIB/touch panel.
When in either Auto mode, using the handheld remote control, each day of the week can be programmed independently for the number of events (0, 1, or 2 events) and each event start/stop time. Oven zones are selected on the UIB/touch panel and not stored on the remote, so oven selection cannot be changed within the daily program and the 'Auto' zone selection will carry over from one day to the next.
When the cooker is under manual operation the following statements apply:

The Hand Held Remote Control is not used.
Manual mode is selected via the 'mode' button on the UIB/touch panel. Each time the mode button is pressed it steps to the next mode and indicates the selected mode using one of four LEDs.
Each time manual mode is selected all zones are included and are switched to 'off' as a default operation.
Once in manual mode each zone can be switched on or off by pressing the corresponding zone button on the UIB/touch panel. Confirmation of the button press is by an audible tone, 'zone on' is indicated by the associated zone LED being lit. The zone LED will flash green while the zone is heating and become constant when the zone is at or close to operating temperature.
Once 'on' then each zone will remain 'on' indefinitely until switched 'off' using its own zone button or by selection of one of the other modes using the mode button (when the rules of that mode will apply to each zone) or by switching the TC to standby.
During Manual mode operation any 'on or off event commands from the auto program are ignored.

When the cooker is in Slumber operation the following statements apply:

The Hand Held Remote Control is not used.
Slumber mode is selected via the 'Mode' button on the UIB/touch panel, each time the button is pressed it steps to the next mode and indicates the selected mode using one of four LEDs
Each time 'slumber' mode is selected, all oven zones default to their respective 'slumber' set point (120°C) this. No oven zone can be switched 'off' from the 'slumber' mode.
When 'Slumber' mode is selected the hotplate zones default to off.
Hotplate zones are not included in 'slumber' mode they work as in 'Manual' mode.
When in 'Slumber' mode any oven zone can be switched from its 'slumber temperature' to 'full temperature' by one press of the zone button, the selected oven setpoint is changed from 'slumber' to 'full'. The corresponding oven zone button LED changes colour to indicate which status the zone is in (No LED for 'slumber' mode, green LED for 'full temperature').
During 'slumber' mode operation any 'on or off event commands from the auto program are ignored.
To achieve the slumber set point of 120°C in the Roast oven and Baking Oven the same de-rating technique will be used as for the normal set point i.e. full power is provided until a zone temperature of 100°C; beyond this point electrical power to the element is limited to a maximum of 20% Top -10% Bottom (2:1 ratio) with PID control varying this between 20% and 0% as the oven temperature approaches the target temperature.

When in Auto operation the following statements apply:

The Hand Held Remote Control is used to program the Auto operation.
Auto mode is selected via the 'Mode' button on the user interface board; each time the button is pressed it steps to the next mode and indicates the selected mode using one of four LEDs.
Each time Auto mode is selected all oven zones are switched to 'off' as a default operation unless the real time corresponds with an 'event' time, in which case the selected zones will be turned on.
When 'Auto' mode is selected the hotplate zones default to off.
Hotplate zones are not included in 'Auto' mode, they work as in 'Manual' mode
Once in Auto mode each oven zone can be selected or de-selected for auto operation by pressing the zone button on the UIB/touch panel.
. 'Zone selected' is indicated by the associated zone LED being lit yellow. The zone LED will flash green while the oven is heating and become constant green when the oven is close to operating temperature during its event period.
Once 'selected' then each zone will remain 'selected' indefinitely until de-selected using its own zone button. The 'Auto' oven zone selection is stored and remembered so that returning to Auto from non-auto modes (slumber and manual) does not require resetting of the oven zone selection.
During the time between events the ovens are switched off.
The 'events' are programmed by the handset and are stored by a 'piggy back' board connected to the power board. Confirmation of receipt of the program settings transmitted from the HHC to the 'piggyback board' is required. ('message sent ok' is briefly displayed on the handset)

When in Auto/Slumber operation the following statements apply:

The Hand Held Remote Control is used to program the Auto/Slumber operation.
Auto/Slumber mode is selected via the 'Mode' button on the UIB/touch panel; each time the button is pressed it steps to the next mode and indicates the selected mode using one of four LEDs.
Each time Auto/Slumber mode is selected all oven zones are switched to 'slumber' as a default operation unless the real time corresponds with an 'event' time, in which case the selected zones will be turned on to 'full'.
When 'Auto/Slumber' mode is selected Hotplate zones default to 'off'.
Hotplates are not included in 'Auto/Slumber' mode, they work as in 'Manual' mode
Once in Auto/Slumber mode each oven zone can be selected or de-selected for auto operation by pressing the zone button on the UIB/touch panel.. 'Zone selected' is indicated by the associated zone LED being lit yellow. The zone LED will flash green while the oven is heating and become constant green when the oven is close to operating temperature during its event period
Once 'selected' then each oven zone will remain 'selected' indefinitely until de-selected using its own zone button. The 'Auto/Slumber' oven zone selection is stored and remembered so that returning to Auto/Slumber from Manual mode does not require resetting of the oven zone selection.
During the time between events the ovens are switched to Slumber, this means the selected ovens maintain a temperature of 120°C, using the same de-rating techniques as the Slumber mode set points. The 'events' are programmed by the handset and are stored by a 'piggy back' board connected to the power board. Confirmation of receipt of the program settings transmitted from the HHC to the 'piggyback board' is required.

Claims

A heat storage cooker (1) comprising a least one oven cavity formed by walls of cast iron, and at least one electric radiant heating element (20) which is in thermal contact with at least one wall such that in use the electric radiant heating element (20) transfers heat energy to the walls which in use store the heat energy and subsequently radiate at least part of that heat energy in to the oven cavity, wherein said at least one wall is in turn in thermal contact with at least one other wall of the oven cavity, characterised in that the at least one radiant heating element (20) comprises a generally flat plate of ceramic or glass ceramic covering a coil of electrical resistive heating element.
A heat storage cooker (1) according to claim 1 in which at least one oven cavity includes a radiant hot plate which comprises a cast iron body forming a part of the at least one wall and an electrical resistive heating element embedded in the cast iron body.
A heat storage cooker (1) according to claim 1 or 2 in which the electric radiant heating element (20) is located inside the cavity in thermal contact with an inner face of a respective wall.
A heat storage cooker (1) according to claim 3 in which the electric radiant heating element (20) is located in a recess in a respective wall of the oven cavity so that the surface of said heating element (20) is substantially flush with the surrounding surface of the wall.
A heat storage cooker (1) according to any preceding claim in which the at least one wall and other wall are formed as part of a single casting which is in thermal contact with the electric radiant heating element (20).
A heat storage cooker (1) according to any preceding claim in which a controller (10) is provided which controls the heating of the electric radiant heating elements (20).
A heat storage cooker (1) according to claim 6 in which two oven cavities are present, each cavity having at least one electric radiant heating element (20) which is in thermal contact with at least one wall to form an integral part of the wall such that in use the electric radiant heating element (20) transfers heat energy to the wall which subsequently radiates at least part of that heat energy in to the oven cavity and the controller (10) includes a setting which in use causes the heating elements to maintain a first one of the ovens at a first set temperature when the cooker (1) is switched on a second one of the ovens at a second set temperature when the cooker (1) is switched on, the second temperature being lower than the first.
A heat storage cooker (1) according to claim 6 or claim 7 in which the controller (10) is operable to implement the setting at a single command from a user, the temperatures being stored in a memory associated with the controller (10).
A heat storage cooker (1) according to claim 7 or claim 8 in which a third oven cavity is provided which has at least one electric radiant heating element (20) which is in thermal contact with at least one wall to form an integral part of the wall such that in use the electric radiant heating element (20) transfers heat energy to the wall which subsequently radiates at least part of that heat energy in to the oven cavity, and the controller (100) setting in use maintains the third oven at a third set temperature when the oven is switched on, the third temperature being different from the first and second temperatures.
A heat storage cooker (1) according to claim 9 in which the three preset temperatures are approximately 240ºC, 180ºC & 120ºC.
A heat storage cooker (1) according to any one of claims 6 to 10 in which the controller (10) receives input signals from a thermocouple associated with the or each heating element associated with a cavity, the or each thermocouple providing an output indicative of the temperature of a heating element, and also from a thermocouple that measures the overall temperature inside an oven cavity.
A heat storage cooker (1) according to any preceding claim which is absent any form of central heat source, traditionally a heating barrel, and absent the ducts that would otherwise be needed to take the heat from the central heat source to each oven cavity.