GB2283809A

GB2283809A - Electrical storage heater

Info

Publication number: GB2283809A
Application number: GB9323398A
Authority: GB
Inventors: Richard John Lane
Original assignee: Creda Ltd
Current assignee: Creda Ltd
Priority date: 1993-11-12
Filing date: 1993-11-12
Publication date: 1995-05-17
Anticipated expiration: 2013-11-12
Also published as: GB2283809B; GB9323398D0

Abstract

In an electrical storage heater with automatic control of heat input in accordance with ambient conditions the storage heater fails to receive a charge at the start of a charge period only if (a) the ambient temperature is sufficiently high and (b) the store already has a certain amount of charge, in order to prevent erratic operation of the heater. A room temperature sensor 9 is mounted to sense ambient temperature only and not to sense the temperature of the heat store. Changing control means at the upper end of the heater (so as to be adjustable by a manual control), include a component 7 which receive heat from the store. The heat store may be solid or material involving a latent heat of fusion. <IMAGE>

Description

ELECTRICAL STORAGE HEATERS This invention relates to electrical storage heaters.

Such heaters have a heat store and electrical means for heating the heat store.

Typically such heaters are charged during off-peak periods when electricity is available at a cheaper than normal tariff. Some such heaters are provided with charge control means for regulating the flow of current to the electrical means during an off-peak period. In one proposal (GB 2 097 912B), the charge control means includes a pair of contacts which open in response to flexing of the walls of a fluid-containing capsule which is in communication with a fluid-containing temperature sensor.The temperature sensor is arranged to be influenced by a combination of ambient temperature and store temperature, so that while the degree of charge of the store is mainly influenced by the ambient temperature, so called "core depletion" is also avoided: the sensor relies on some heat from the store before the contacts are opened even when the ambient temperature is satisfactory (i.e. no charging is required), to ensure that in normal conditions the store always has a certain residual charge. This prevents erratic charging behaviour from taking place.

In the proposal, the capsule which controls the contacts may be arranged in a position at which the heat input it receives is not appreciable, for otherwise the heat received by the capsule itself would affect the operation of the temperature sensor.

However, it is convenient for the contacts to be mounted in a readily accessible position so that the user can manually operate a control to alter the operating point of the contacts, in order to tailor the operating point to the physical location of the heater (i.e. whether it is positioned in a large room or a small room or on a cold wall and bearing in mind the degree of heating required). One of the most convenient positions is at the top of the heater, where unfortunately the capsule receives an appreciable heat input from the heat store.For this reason, in one version of the proposal, compensation means such as a bimetallic element is provided, so that the tendency of the contacts to be operated at too low a temperature of the sensor due to the heat input of the capsule from the heat store is counteracted by deflection of the bimetallic element, also as a result of heat input from the heat store.

In another proposal, the sensor associated with the charge control means is in two parts in communication with each other, one part being mounted so as to be influenced mainly or wholly by ambient temperature, and the other being mounted to be influenced by store temperature, the latter being provided again to avoid core depletion. However, the operating contacts and capsule are again mounted at the top of the heater for convenience, and it is similarly necessary to provide compensation means to compensate for the effect on the operating point of the contacts due to the heating of the capsule by the store.

The invention provides an electrical storage heater comprising a heat store, electrical means for heating the heat store, charge control means for regulating the flow of current to the electrical means during an off-peak period, the charge control means including a pair of contacts operable in response to flexing of the walls of a fluid-containing capsule which is in communication with a fluid-containing temperature sensor arranged to be influenced by ambient temperature but not to be influenced by changes in store temperature, the capsule being mounted in a region in which its temperature is responsive to the temperature of the heat store but no means is provided to compensate for the effect of the temperature of the heat store on the operation of the contacts.

The Applicants have realised that the compensation means can be dispensed with while the capsule is mounted in a convenient position by making the sensor responsive to ambient temperature only: the operating point of the contacts remains affected by both ambient temperature and store temperature thereby avoiding core depletion.

The principle of using the heat in the vicinity of the charge control means to provide a temperature signal related to store temperature, especially if a manual control for adjusting the operating point of the charge control means is provided, may be extended to heaters using electronic temperature sensors.

Accordingly, the invention also provides an electrical storage heater comprising a heat store, electrical means for heating the heat store, charge control means for regulating the flow of current to the electrical means during an off-peak period, the charge control means being operable in response to an electronic temperature sensor, an electrical parameter of which is responsive to temperature, the sensor being arranged to be influenced by ambient temperature but not to be influenced by changes in store temperature, the charge control means being mounted in a region in which its temperature is responsive to the temperature of the heat store and the point of interruption of current being dependent on its temperature.

An electrical storage heater constructed in accordance with the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a front view in schematic form of a storage heater; and Figure 2 shows part of a thermostatic charge control means on an enlarged scale.

The storage heater is usually mounted against the wall of a room and consists of a metal casing 1 housing a heat store in the form of bricks 2 surrounded by insulation 3. The heater is mounted on supports 4. The bricks are relatively thin in the vertical plane (i.e. the plane of Figure 1). A heating element 5, only one of which is shown, is arranged between four bricks, a pair of bricks arranged in a vertical stack behind the element and a similar pair in front of the element. The facing surfaces of the bricks are recessed so that the element lies in a vertically-extending channel, which also has an opening at the lower end and at the upper end to allow for upward passage of air past the heating element 5 between the pairs of bricks 2. The illustrated heater has three such heating elements, each arranged between four bricks.

A damper (not shown) controls the opening into which the openings from the pairs of bricks are channelled in order to provide a means of varying the heat output of the storage heater.

The heat input is thermostatically controlled by charge control means. Referring to Figure 2, this includes a pair of contacts 6 in one of the leads from the mains to the heating elements 5, which are arranged in series. The contacts have an over-centre mechanism, and are opened by flexing of the walls of a capsule in the form of bellows 7. The bellows is connected by means of a thin tube to a tubular room temperature sensor 9, and the space thus enclosed contains a fluid which expands when heated.

Flexing of the walls of the bellows due to expansion of the fluid causes the switch contacts to be opened.

The upper switch contact is mounted upon a carrier 10 which is mounted on a deflectable arm 11, so that the carrier may be deflected upwardly or downwardly by rotation of a thermostatic control knob 12. When it is desired to set the heater at a higher heat input the knob is turned to move the upper contact 6 upwardly so that more expansion of the bellows is required before charging current is interrupted, and vice versa.

In a heater such as is described in the Applicants' prior patent number 2 097 912, the thermostatically controlled charge control means also includes a bimetallic element. This is provided because the bellows itself receives a significant heat input being mounted as it is at the top of the casing, and this is sufficient to alter the operating point of the switch contacts 6 compared to if the bellows was not heated.

The bimetallic element deflects the bellows marginally away from the switch contacts in response to heating in order to compensate for the slightly premature opening of the contacts caused by the bellows itself being heated. The room temperature sensor 9 is positioned in a space beneath the insulation 3 but within the casing 1 so that it not only senses ambient air temperature, but also senses some heat from the heat store via the insulation 3. This serves to avoid so called "core depletion". Consider the position at the start of a charging period. The contacts are only opened when (a) there is sufficient heat input to the room temperature sensor 9 from the ambient air to make charging unnecessary and, (b), there is also a contribution to the heat input of the room temperature sensor 9 from the heat from the store.If the ambient temperature is such that charging is unnecessary, but the heat store is totally depleted, the contacts will not open until a certain small charge has been provided.

This prevents erratic operation of the heater.

In accordance with the invention, the bimetallic element which compensates for the heat received by the bellows itself by virtue of its position at the top of the casing is dispensed with, and the room temperature sensor 9 is positioned in thermal isolation from the heat store, for example, on a plastic plate 13 which extends from the lower end of the casing. In the latter position, the room temperature sensor 9 receives substantially no heat from the heat store, and senses ambient temperature only.

Core depletion is nevertheless avoided. This is because the contacts 6 are opened (a) when the ambient temperature is sufficient to warrant no charging and, (b), when the bellows 7 has received a certain amount of heat from the store. Thus, if at the start of a charging period, the room temperature is sufficiently high for no charging of the heat store, only when the bellows has received a certain heat input from the store will the charging contacts be opened i.e. a certain small charge will be received while the bellows is being heated.

Of course, variations may be made without departing from the scope of the invention. Thus, the illustrated storage heater may be modified to replace the hydraulic temperature by an electronic temperature sensor, in which an electronic parameter (for example, resistance) is responsive to temperature. The temperature sensor could be a thermistor thermally isolated from the heater casing, to sense ambient temperature only (and replacing bulb 9). The thermistor could control operation of the contacts 6 by affecting the heating applied to a bimetal element (as in Figure 4 of the prior proposal GB 2 097 912 B) referred to. Once again, instead of providing compensation means (as in the prior proposal) to counteract the heating effect of the bimetal element, one could positively use this signal to ensure that the contacts are not opened until some charge has been received by the store.Opening of the contacts would require (a) a sufficiently high ambient temperature and (b) a sufficiently high temperature of the bimetal element responsible for opening the contacts indicating a predetermined charge of the store. Indeed, there is no need to provide mechanical contacts, and these may be replaced by a solid state switch. In such a case, a bimetal element would not be used to control its operation, but the temperature of the charge control means employing such a solid state switch could be used to affect some electrical parameter which controlled operation of the switch.

The room temperature sensor may be positioned in other places provided it is thermally isolated from the heater casing and the effects of conduction/radiation from the heat store. The invention is also applicable to heat stores of the kind involving a material which stores heat as the latent heat of fusion of the material. In such a case, the arrangement described in prior patent number 2 097 912 would be unsuitable, since typical phase change materials have a much lower temperature of operation than heat storage bricks, and a heat sensing element 9 positioned in a space at the lower end of the casing would receive little if any heat from the store. In contrast, by relying on the heat input to the charge control means which is arranged above the store, a sufficiently strong signal from phase change material can be provided. Since the temperature of operation of phase change materials is so much less than that of the heat storage bricks, it may be necessary to arrange the charge control means directly in the path of convection air currents rising through the heater, whereas the charge control means is not positioned in the path of convection currents passing directly through the heat storage bricks in the described embodiment because too great a signal from the heat store would then be provided. The thermostatically controlled charge control means is, in the described embodiment, positioned in an upper region of the casing which only receives convection air which has passed around the insulation on the outside of the bricks.

Claims

1. An electrical storage heater comprising a heat store, electrical means for heating the heat store, charge control means for regulating the flow of current to the electrical means during an off-peak period, the charge control means including a pair of contacts operable in response to flexing of the walls of a fluid-containing capsule which is in communication with a fluid-containing temperature sensor arranged to be influenced by ambient temperature but not to be influenced by changes in store temperature, the capsule being mounted in a region in which its temperature is responsive to the temperature of the heat store but no means is provided to compensate for the effect of the temperature of the heat store on the operation of the contacts.

2. An electrical storage heater as claimed in claim 1, including a manual control for adjusting the operating point of the contacts, the manual control being positioned in the vicinity of the capsule.

3. An electrical storage heater as claimed in claim 2, in which the manual control is positioned at the top of the storage heater.

4. An electrical storage heater as claimed in any one of claims 1 to 3, in which the temperature sensor is arranged below and spaced apart from the casing of the heater.

5. An electrical storage heater as claimed in any one of claims 1 to 4, in which the heat store is a material which absorbs heat as latent heat of fusion.

6. An electrical storage heater comprising a heat store, electrical means for heating the heat store, charge control means for regulating the flow of current to the electrical means during an off-peak period, the charge control means being operable in response to an electronic temperature sensor, an electrical parameter of which is responsive to temperature, the sensor being arranged to be influenced by ambient temperature but not to be influenced by changes in store temperature, the charge control means being mounted in a region in which its temperature is responsive to the temperature of the heat store and the point of interruption of current being dependent on its temperature.

7. An electrical storage heater substantially as herein described with reference to the accompanying drawings.

Amendments to the claims have been filed as follows 1. An electrical storage heater comprising a heat store, electrical means for heating the heat store, charge control means for regulating the flow of current to the electrical means during an off-peak period, the charge control means including a pair of contacts operable in response to flexing of the walls of a fluid-containing capsule which is in communication with a fluid-containing temperature sensor arranged to be influenced by ambient temperature but not to be influenced by changes in store temperature, the capsule being mounted in a region in which its temperature is responsive to the temperature of the heat store to such an extent that the charge control means is responsive to a combination of ambient temperature and store temperature, no means being provided to compensate for the effect of the temperature of the heat store on the operation of the contacts 2. An electrical storage heater as claimed in claim 1, including a manual control for adjusting the operating point of the contacts, the manual control being positioned in the vicinity of the capsule.