GB2265454A

GB2265454A - Storage heater with twin phial hydraulic charge controller

Info

Publication number: GB2265454A
Application number: GB9204701A
Authority: GB
Inventors: Avtar Singh Bgabra
Original assignee: DIMPLEX
Current assignee: DIMPLEX
Priority date: 1992-03-04
Filing date: 1992-03-04
Publication date: 1993-09-29
Anticipated expiration: 2012-03-04
Also published as: GB9204701D0; GB2265454B

Abstract

A storage heater having a charge controller with two phials 7, 8 connected by capillary tubing 6a, 6b to a chamber 16 which is closed by a diaphragm 14. A bi-metallic contact assembly 10 biases the diaphragm to counteract the combined hydraulic outputs from the two phials. One phial 7 senses core temperature and the other 8 senses room temperature. The room temperature sensing phial is larger than the core temperature sensing phial and there is a predetermined amount of overcompensation. <IMAGE>

Description

STORAGE HEATER WITH TWIN PHIAL HYDRAULIC CHARGE CONTROLLER This invention relates to a storage heater having an hydraulically and thermostatically operated charge controller with two temperature sensing phials.

GB 2 079 712 describes a storage heater which, according to one arrangement, has an hydraulically operated charge controller with a single phial which responds to both core temperature and room temperature in order to provide a single hydraulic output signal which causes the charge controller to switch on and off a supply of current to heating elements within the core. A single temperature sensing phial is used to avoid using a remotely located temperature sensing phial, which needs to be separately installed for sensing external temperature. As only a single phial is used, which responds to both thermal inputs from the core and from the room, the phial must be selectively located to receive these inputs.However, even with this selective location, the operation of the charge controller will depend on finding the best compromise for the two thermal inputs and hence the overall performance will not be optimum. GB 2 079 712 also describes the use of compensation to take account of the effect of heat, received from the core, on the body of the charge controller. However, this does not overcome the disadvantage of using a single phial which responds to both thermal inputs.

GB 1 387 963 discloses a storage heater which uses an hydraulic thermostat having two phials. One phial is located so as to respond to heat received from the core, and the other phial is located in a heated enclosure. The temperature of the enclosure is controlled by a bi-metallic thermostat arrangement having a bi-metal strip for sensing external temperature. This arrangement is more complex and hence more expensive and requires the installation of the external temperature sensing device.

The present invention provides an alternative solution to the problems mentioned above.

More particularly, the present invention provides a storage heater comprising a core made of heat storage medium and containing heating elements for heating the core, an hydraulically and thermostatically operated charge controller for controlling the supply of current to said heating elements, said charge controller including a bimetallic spring contact assembly, a reservoir for hydraulic fluid and first and second phials connected by capillary tubing to the reservoir, said reservoir having a wall in the form of a diaphragm on which a first bias is exerted by said contact assembly, said first phial being located so as to receive heat only from the core and so as to produce a first hydraulic output which represents changes in core temperature, said second phial being located away from the core so that it responds only to air temperature adjacent floor level whereby it produces a second hydraulic output representing changes in said air temperature, said second phial having a substantially larger volumetric capacity than said first phial, said first and second hydraulic outputs exerting a second bias on said diaphragm, the arrangement being such that (a) said first bias counteracts said second bias to compensate for the effect of temperature on the hydraulic fluid in the reservoir, and (b) the first bias causes a predetermined amount of overcompensation, when the core is partially charged, so as to delay switching off a supply of current to the core heating elements, whereby the core will accept more charge during a boost period.

A storage heater embodying the invention provides an inexpensive but more accurate form of charge control and enables more benefit to be gained when off-peak electricity is available during day time or evening "boost" periods.

Thus, a partially discharged storage heater can be recharged or boosted by a greater supplementary charge so as to gain the cost savings of off-peak electricity.

Generally speaking, storage heaters receive their primary or maximum charge during an overnight period.

However, auxiliary or "boost" off-peak periods of, for example, two or three hours, may be available in the afternoon and/or evening. Therefore, any extra heat which can be stored, during these auxiliary periods, represents an economy, particularly in colder weather.

In a preferred embodiment of the invention, the hydraulic fluid is liquid over the operating temperatures of the storage heater and therefore has a sufficiently high boiling point to avoid problems due to vapour pressure.

For example, transformer oil is a suitable hydraulic fluid since it has a satisfactory co-efficient of cubical expansion and there is no risk of vaporisation at the highest operating temperatures of the charge controller. On the other hand, xylene which is a liquid which has been used in the past in hydraulic thermostats, has a far lower boiling point and has now been found to create problems when subjected to high operating temperature in storage heaters.

Ideally, the hydraulic fluid has a substantially regular coefficient of cubical expansion so that expansion of the fluid in the temperature sensing phials causes the diaphragm to be moved continuously against the bias of the spring loaded bi-metallic contacts. This provides accurate displacement of switch contacts which supply current to the core heating elements.

The general operation of spring loaded bi-metallic contacts are known to those skilled in the art, i.e. where expansion of a bi-metallic member causes it to deform, against spring bias, to provide a snap-action at a predetermined temperature. However, it was previously thought necessary to cause the bias exerted by the bimetallic spring contact assembly to compensate for the bias exerted by an hydraulic output over the temperature range of operation. In other. words, phial temperature sensing occurs over one given range of temperatures but the charge controller body (including the reservoir and the bi-metallic spring contact assembly) will be subject to a different range of temperatures at similar times. Therefore, overcompensation would normally be unacceptable in this regard.In a particular embodiment of the invention the charge controller has 4-60C overcompensation at 1200C switch head temperature (i.e. temperature of the charge controller body). This level of overcompensation has been found to give particularly good results with the first and second phials having a volumetric capacity ratio of 10:90. This accommodates for the higher temperature of operation of the core temperature sensing phial compared with the lower operating range of the room temperature sensing phial.

This ratio of volumetric capacities may vary in accordance with particular requirements, but the capacity of the room temperature sensing phial remains substantially larger than that of the core temperature sensing phial.

Preferably, the first and second phials are connected in series with the hydraulic fluid reservoir. More preferably, the second phial (for sensing room temperature) is located at the remote end of the capillary tubing and the first phial (for sensing core temperature) is located at a suitable intermediate point between the second phial and the fluid reservoir. However, other arrangements are possible. For example, the first and second phials may both be connected to the reservoir in parallel (instead of in series), or the first phial may be located at a terminal end of the capillary tubing with the second phial between the first phial and the reservoir. In any event, the provision of a separate room sensing phial has the advantage that this can be located more precisely so as to respond to room temperature.

In the preferred embodiment of the invention, the second or room temperature sensing phial is located on a bracket or plate which is attached to the rear external panel of the external casing of the storage heater so that it is located at floor level, adjacent the stream of cold air entering a convection inlet of the heater. The bracket or plate preferably provides a movable anchor point for the second phial so that the second phial can be moved from a storage or shipping position into an optimum operating position close to floor level. Such adjustment also provides a means for tuning the operation of the charge controller.

Preferably, the first phial (for sensing core temperature) is located on a bracket in one of a plurality of positions, its operating position then being selected in accordance with the operating tariff of the local electricity supply. For example, off-peak electricity may be provided over a single 7 hour overnight period, or over a 5 hour overnight period with auxiliary boost periods being available for 2-3 hours during the afternoon and/or evening.

The position of the first phial is then selected in accordance with the local tariff to provide optimum performance.

An example of the invention will now be described with reference to the accompanying drawings in which: Fig. 1 is perspective partially section view of a storage heater showing the location of a charge controller having first and second temperature sensing phials; Fig. 2 is an inset showing a detail of the air temperature sensing phial, Fig. 3 is a schematic diagram of the charge controller, Fig. 4 is a perspective view of a charge controller, and Fig. 5 is a graph illustrating the operating characteristics of a charge controller with 4-60C overcompensation at 1200C switch head temperature.

Fig. 1 shows a partially sectioned view of a storage heater embodying the invention. It comprises a core 1, made of heat storage medium (such as bricks) containing heating elements 2 for heating the core 1. An hydraulically and thermostatically operated charge controller 2 may be adjusted by a control knob 4 on an upper panel 5 of the storage heater. Charge controller 3 is shown in more detail in Fig 4 and has a generally known construction with the exception of features which will be described below. Therefore, no detailed description of the charge controller will be given. However, its novelty will be apparent from the following description of Fig. 3.

It will also be noted, from Fig. 1, that the body of the charge controller 3 is connected by sections of capillary tubing 6a, 6b to a core temperature sensing phial 7 and a room temperature sensing phial 8. These phials respond to changes in core temperature and room temperature respectively and cause the charge controller to operate electrical switch contacts for switching on and off a supply of electridity to the heating elements 2. As this general function is known, no detailed description will be given.

Referring to Fig. 3, this is not intended to illustrate actual working parts of the charge controller, but merely the principle of operation of its constituent parts. A bimetallic spring contact assembly 10 includes switch contacts 11 (shown open) a spring 12 and a bi-metallic member 13.

As will be known to those skilled in the art, this assembly has a snap-action and the bi-metallic member 13 exerts a bias, on a diaphragm 14, to compensate for the effect of temperature on fluid 15 in diaphragm chamber 16. Diaphragm 14 responds to changes in volume of the hydraulic fluid 15, within chamber 16, and is attached to relatively rigid wall portions 17. Chamber 16 is shown empty, but it would normally be filled with hydraulic fluid, such as transformer oil which does not boil at the highest operating temperatures of the storage heater. Capillary tubing 6a connects chamber 16 to the core temperature sensing phial 7.

Phial 7 is connected by capillary tubing 6b to room temperature sensing phial 8. It will be appreciated that core temperature sensing phial 7 responds to a wider range of temperature than room temperature sensing phial 8. The volumetric capacity of phial 8 is therefore substantially larger than phial 7 and their volumetric capacities, in the ratio of large:small, are preferably about 90:10. Thus, the greater amount of fluid in phial 8 requires less heat to cause an hydraulic output than phial 7. Expansion of the hydraulic fluid 15 within both phials 7 and 8 creates respective hydraulic outputs which are combined, due to the series arrangement. Hence, diaphragm 14 will be biased, by the combined hydraulic output, towards the bi-metallic member 13.

Fig. 2 shows the room temperature sensing phial 8 attached to a slidable plate 18 mounted on a rear panel 19 of the storage heater. Panel 18 is normally slid upwardly for transit (to avoid damaging phial 8) and, during installation, plate 18 is drawn downwardly, to a suitable level, so that phial 8 responds to the temperature of colder air, at floor level, in the room in which the storage heater is installed, which colder air normally enters a convection inlet of the heater.

As shown in Fig. 1, core temperature sensing phial 7 is attached to a bracket 20 which is secured, to insulation 21 above the heat storage brick assembly on the right-hand side of the appliance. Bracket 20 preferably includes clips or a clamp which enables the position of phial 7 to be moved, e.g. further away from the core and its insulation, to suit a different local off-peak electricity supply tariff.

Generally speaking, phial 7 will be moved further away from core 1 when off-peak electricity is supplied over a longer (overnight) period. It is moved closer to the core 1 when a split tariff is used, i.e. when off-peak electricity for boost periods during the day or evening.

Referring to Fig. 5, this shows the overcompensation characteristics of the charge controller 3. The Y axis of the graph represents the temperature of the room sensing phial 8. The X axis of the graph represents the temperature of the core sensing phial 7. The graph was plotted by inserting the body of the charge controller 3 (including the reservoir and bi-metallic contact assembly), together with phial 7, in an oven whilst phial 8 was heated in a water bath. The points plotted on the graph represent the temperatures at which the contacts of the charge controller opened. Thus, the line of the graph corresponds to points at which the contacts have opened, the phials 7 and 8 being at different temperatures. With overcompensation, the line of the graph is not linear but curved. Without overcompensation, the line of the graph would be linear (as shown by the broken line in Fig. 5).

In this particular embodiment, when the charge controller body was at 1200C, the room sensing phial was at 310C when the contacts opened due to about 60C of overcompensation. With no overcompensation, the contacts would have opened at a lower room temperature e.g. of about 25C (phial 8) at the same charge controller temperature of 1200C (phial 7). Thus, with no overcompensation, the room temperature sensing phial 8 responds at a lower temperature and cuts off the supply of off-peak electricity at an earlier stage when the storage heater is boosted by an auxiliary charge. The preferred embodiment of the invention therefore exploits an overcompensation in the range of from 4-60e with the volumetric phial ratios of 90:10 mentioned above. Such an amount of overcompensation would have been considered as a disadvantage with conventional charge controllers.

By way of an example of the operation of the preferred embodiment of the invention, the contacts of the charge controller would be closed at the start of an auxiliary or boost period so that off-peak electricity is supplied to the core heating elements as soon as it became available. As the core then heats up, opening of the contacts would be delayed, due to overcompensation. Thus, the room temperature sensing phial would need to reach a higher temperature before the combined hydraulic outputs of the phials 7 and 8 sufficiently counteracted the bias due to the bi-metallic spring contact assembly to open the contacts.

Thus, more heat would be stored in an off-peak period than would otherwise be the case, particularly in colder weather.

This represents a significant economy to the user.

Clearly, the graph in Fig. 5 represents an example of one kind of operation, since different degrees of overcompensation will be required to suit different circumstances.

In addition, the advantage of using a separate room temperature sensing phial is that it can be located more precisely and also dimensioned, with respect to the core sensing phial, so as to produce an optimum effect.

Claims

CLAIMS:

1. A storage heater comprising a core made of heat storage medium and containing heating elements for heating the core, an hydraulically and thermostatically operated charge controller for controlling the supply of current to said heating elements, said charge controller including a bimetallic spring contact assembly, a reservoir for hydraulic fluid and first and second phials connected by capillary tubing to the reservoir, said reservoir having a wall in the form of a diaphragm on which a first bias is exerted by said contact assembly, said first phial being located so as to receive heat only from the core and so as to produce a first hydraulic output which represents changes in core temperature, said second phial being located away from the core so that it responds only to air temperature adjacent floor level whereby it produces a second hydraulic output representing changes in said air temperature, said second phial having a substantially larger volumetric capacity than said first phial, said first and second hydraulic outputs exerting a second bias on said diaphragm, the arrangement being such that (a) said first bias counteracts said second bias to compensate for the effect of temperature on the hydraulic fluid in the reservoir, and (b) the first bias causes a predetermined amount of overcompensation, when the core is partially charged, so as to delay switching off a supply of current to the core heating elements, whereby the core will accept more charge during a boost period.

2. A storage heater according to Claim 1 in which the hydraulic fluid is an oil having a boiling point significantly above the highest operating temperature of the charge controller.

3. A storage heater according to Claim 1 or 2 in which the charge controller has 4-60C overcompensation when the reservoir is at 1200C.

4. A storage heater according to any of the preceding Claims in which the volumetric ratios of the core temperature sensing and room temperature sensing phials is about 10:90.

5. A storage heater according to any of the preceding Claims in which provision is made for mounting said first phial in one of a plurality of selectable positions in accordance with local off-peak electricity tariffs.

6. A storage heater according to any of the preceding Claims in which the second phial is mounted on a movable support to enable it to be positioned, adjacent floor level, for sensing room temperature.