GB2265705A - Storage heater - Google Patents

Abstract

A storage heater (1) comprises a core (2) with one or more heating elements (5), thermal insulation (38-41) and a fan (12) for inducing a flow of air through air channels (6) in the core. An external casing (44) has vents (22, 23a, 23b) to enable air to pass into and out of the storage heater. An auxiliary air channel (35), provided between a front panel (44) of the casing and the insulation, carries air, heated by passage through the air channels in the core, before the heated air emerges from one of vents. Auxiliary heating elements (42, 43) can be operated independently. A thermostatic bypass mixes cold air with heated air to reduce the temperature of the emergent air. <IMAGE>

Description

STORAGE HEATER This invention relates to a storage heater having a more flexible performance with regard to periods in which it is charged and/or discharged and also with regard to providing auxiliary heat from direct acting heating elements.

Off-peak electricity is now often available at different times during a 24 hour cycle - although storage heaters are primarily charged overnight, for example, over a continuous period which may last for 5, 6 or 7 hours. The longer overnight period may be reduced to 5 hours or 6 hours, depending on electricity demands, but boost periods of 2-3 hours may be available during the day time or evening.

These variations, together with changes in weather, affect the performance of storage heaters and may lead to inferior thermal performance.

All storage heaters will lose heat, after being fully charged, whether or not heat loss is encouraged by increasing the amount of natural convection, or by using a fan to cause forced convection. This is due to losses through the insulation, since conventional heaters will not retain heat indefinitely. Moreover, when there is a greater demand for heat in cold weather, more heat will be lost at an earlier stage than is normal and then less heat will remain, in the core, to provide adequate room heating at a later stage.

In view of these problems, attempts have been made to incorporate direct acting heating elements in storage heaters in order to supplement the stored heat available in the core. In one known construction, a radial fan is used to draw air through passageways in the core, so as to extract as much heat as possible, either when needed and/or when the core temperature has fallen towards the end of its discharge period. This radial fan also has heating elements, like a fan heater, so that the heating elements can be energised to supplement the heat output when the core temperature has fallen to a low value. However, due to the manner of connection, the fan cannot be operated during a charging period because this was considered to be counter productive to storing of heat in the core.Therefore, storage heaters of the latter type do not offer an adequate solution to the problems noted above.

The present invention seeks to solve these problems by providing a storage heater with a more flexible performance.

In accordance with the invention, a storage heater comprises a core made of heat storage medium with air channels therein, one or more heating elements located in the core for supplying heat to the storage medium during a charging period, thermal insulation for retaining stored heat in the core, a fan for inducing a flow of air through said air channels, and an external casing having vents therein to enable air to pass into and out of the storage heater, an auxiliary air channel being provided between a side panel of the casing and the insulation whereby the air, heated by passage through the air channels in the core, is caused to flow through said auxiliary channel before emerging from one of said vents.

In order to maximise heat storage, the thermal insulation is preferably made thicker than in conventional storage heaters, e.g. two to three times the thickness of conventional insulation. More heat will then be retained for later dissipation due to forced convection by the air flow induced in the air channels in the core. A centrifugal fan is preferably used to force air through the air channels of the core, since a centrifugal fan provides silent running and is better adapted to working against fluidic resistance in the air flow path. Preferably, the fan is independently controlled by a switch which can be operated by a user so that, during a charging period, air can still be induced to flow through the core. An advantage of this arrangement is that direct use can be made of off-peak electricity besides gaining some stored heat in the core.

Preferably, at least one auxiliary heating element is located in the auxiliary air channel, the auxiliary heating element being connected to switching means whereby the auxiliary element can be operated independently of the operating state of the fan. Preferably, an upper vent is located in an upper part of the casing and a lower vent is located in a lower part of the casing, the auxiliary channel communicating with the upper and lower vents so that when the fan is switched off and the auxiliary heating element is switched on, air can flow through the auxiliary channel from the lower to the upper vent, as a result of natural convection. However, when the fan is switched on, the upper and lower vents both serve as outlets for heated air induced to flow through air channels within the core.

Preferably, a thermostatically controlled air flow bypass, responsive to the temperature of air emerging from the storage heater, enables relatively cold inlet air, induced by the fan, to be mixed with air heated by the storage heater, so as to reduce the temperature of the emergent air below a predetermined maximum value. This is advantageous during the early stages of the discharge period when the air temperature is higher due to the higher core temperature. The thermostatic by-pass enables a proportion of cold air to be mixed with this heated air in order to reduce emergent air temperature to a safe or more acceptable level.

In a slim-line storage heater, the side panel which partly defines the auxiliary air channel is the front panel of the heater. When this is heated by the air flowing through the auxiliary channel, the front panel radiates heat into the room and this improves the comfort aspect of the storage heater since this radiant heat can be felt within the vicinity of the front panel.

In a preferred embodiment of the invention, the interior of the casing is sub-divided into a fan housing, a plenum which communicates with the fan housing, a first core section having air channels communicating with the plenum and in which air is induced to flow in one direction, a second core section having air channels which communicate with the air channels in the first core section and in which air flows in an opposite direction, and an exit chamber which communicates with the auxiliary air channel and with the vents. Suitably, the fan housing is located beneath the first core section on one side of the heater. The fan then delivers air to a plenum beneath the first section so that the air rises through the first section into a second plenum which extends between the upper portions of the first and second core sections.Air flows substantially horizontally through this second plenum before descending through air passages in the second core section on the other side of the heater. This air emerges, via the exit chamber, to a location adjacent the lower vent and the lower portion of the auxiliary air channel. A proportion of the heated air then passes upwardly, through the auxiliary air channel, to emerge from the upper vent, although some heated air will exit from the lower vent due to the forced draught.

Preferably, the thermostatically controlled air flow bypass includes a flap which controls cold air flowing from the plenum beneath the first core section and the exit chamber beneath the second core section. This by-pass arrangement may include a bi-metallic member which responds to the temperature of heated air in the exit chamber.

Preferably, two or more direct acting auxiliary heating elements are provided in the auxiliary air channel. These elements are selectively switched, either manually or in response to sensing means which detects emergent air temperature, so that less auxiliary heating is provided when the core temperature is higher (and therefore capable of raising the air to a higher temperature) and more auxiliary heating is provided when the core temperature is low.

A preferred embodiment of the invention will now be described with reference to the accompanying drawings in which: Figs. 1 and 2 respectively show perspective and side elevational views of a storage heater according to an embodiment of the invention, Figs. 3 and 4 are similar views, but partly cut away or sectioned to show interior components of the storage heater, Figs. 3a and 3b are perspective views showing a detail of a thermostatic air bypass system, Figs. 5-7 show operating stages in the storage heater, Fig. 8 is a schematic circuit diagram of a control circuit, and Fig. 9 is a schematic circuit diagram of an alternative control circuit.

Referring to Figs. 1-4, a storage heater 1 includes a core 2 formed by four brick modules 3, each of which modules consist of four bricks 3a-3d each having a recess 4a in which a portion of one or more heating elements 5 is received and which also help to define an air channel 6 extending vertically upwardly in each module 3. Channel 6 communicates with lower slots 7 and 8 in a plenum 9, part of which communicates, via an air outlet port 10 with centrifugal fan 11, having an axial air inlet 12. The upper regions of air channel 6 communicate with upper slots 13, 14 which allow air into and out of an upper plenum 15.

The interior of the upper plenum 15 extends freely across the tops of the brick modules 3, which form respective right and left hand pairs in the heater 1. However, as shown schematically in Fig. 3, the lower plenum 15 extends across the bottom of the modules 3 but it is divided by a wall 16.

Figs. 3a and 3b show a modification where the lower plenum is partitioned by walls 16a-16d into a cold air chamber 15a and a hot air chamber 15b. Chamber 15b has slots 8a, corresponding to slots 8 in Fig. 3, and a front opening 8c instead of (or in addition to) slots 8b in Fig. 3. A thermostatically controlled flap assembly 17 is mounted in chamber 15b and it is shown, in more detail, in Fig. 3b. It comprises a flap 18 which pivots at points 19 against wall portion 16b for variably restricting passage of air through a triangular aperture 20 which communicates between the cold air chamber 15a and hot air chamber 15b.

A bi-metallic member 21, mounted on a bracket 22, causes flap 18 to move towards and away from opening 20, in accordance with changes in the temperature of air in the hot air portion 9b of plenum 9, whereby the flap 18 acts as a valve which mixes cold inlet air with heated outlet air so as to modify the temperature of the air emerging from vents 22, 23 in an external casing 24 of the heater 1. This will be explained in more detail below.

The external casing 24 has a lower portion which includes a fan housing 25 in which centrifugal fan 11 is mounted. The air inlet port 12 of fan 11 draws air into the heater 1 through vents 23a on the lower colder portion of heater 1. This air is then forced through opening 10 into portion 9a of plenum 9. Arrows 28, 29 show the path of air through channels 6 in the brick modules. Arrows 30 show the subsequent path of air across the upper plenum 15 and into the air channels of brick modules 3 on the lefthand side of the heater 1. Arrows 31, 32 show the subsequent downward flow of air through the modules 3 on the left-hand side and into portion 9b 6r chamber 15b of plenum 9. Arrows 33 and 34 show a subsequent upward flow of air, through an auxiliary air channel 35, best seen in Fig. 4.

Arrows 36 show air emerging from upper vents 22 and arrows 37 show air emerging from lower vent 23b. As will be apparent from these directions of the air flow path, air is induced to flow upwardly and downwardly through the right and left-hand pairs of brick modules 3 in order to extract heat from the bricks when they have been heated by elements 5 which are supplied with off-peak electricity. This forced discharge of air, which emerges from slots 8b or opening 8c then travels both directly through the lower vent 23b and also, upwardly through air channel 35, to escape from the upper vent 22.

If the fan 11 were switched off, no air would be induced to flow through the channels 6 in the brick modules, but some heat would be lost by the insulated core 2 which would induce a flow of air, by natural convection, upwardly in the auxiliary air channel 35, whereby cold air will enter by lower vent 23b and escape from the upper vent 22.

Consequently, the lower vent 23b can act as both an air outlet and an air inlet.

With further reference to Fig. 4, four bricks 3a, 3b, 3c and 3d can be seen in cross-section. This brick assembly is insulated by thick layers of insulation 38-41.

Compared with conventional storage heaters, the insulation has a substantially greater thickness, for example, two and preferably three times thicker than conventional heaters.

In a particular embodiment, the thickness of the insulation 38, 39 was of the order of 22 millimetres compared with a typical thickness of about 9 millimetres in conventional storage heaters.

This increased thickness of insulation is used to ensure that the core 2 retains as much of its stored heat as possible during a 24 hour charge and discharge cycle. A particular advantage of this increased thickness of insulation is that less heat will be lost, with the passage of time (after charging) when heat losses should be kept to a minimum and therefore, unless the user makes heavy demands on the stored heat over long periods, more heat will be retained towards the end of the discharge period.

Mounted within auxiliary channel 35 are two heating element arrays 42, 43. These may be, for example, socalled hair pin elements mounted between insulated supporting cards extending horizontally across the entire front panel 44 of the heater 1. These are "direct acting" elements which can be supplied with current, independently of the operation of the fan and charging circuitry of the heater, in order to dissipate energy when more heat is required by the user. Thus, elements 42, 43 may be turned on when fan 11 is switched off, or they may be turned on when fan 11 is switched on to supplement heat withdrawn from the core 2 of the heater 1. When elements 42, 43 only supply heat, a natural convection effect will occur, as explained above, where cold air enters lower vent 23b and escapes from upper vent 22.The heating element arrays 42, 43 have been shown only schematically in Figs. 3 and 4.

Figs. 5-7 show operating stages in the heater where solid arrows represent cold air and dotted arrows represent heated air. These figures show the switching states of direct acting elements 42, 43, fan 11 and the elements 5 within the brick modules 3. In view of the versatility of the switching system and the construction of the heater, the user may wish to store heat only, e.g. by turning the fan off and allowing the brick modules to charge, or to make direct use of off-peak electricity, e.g. by turning the fan and/or the direct heating elements 42, 43 on during an offpeak period, or both. The control exercised by the user, and/or by thermostatic controls, will depend on the state of charge of the heater 1 and the weather. Moreover, as the temperature of the emergent air also depends on these factors, the thermostatically controlled air flap 18 will mix various quantities of cold with hot air so that the temperature of the emergent air does not exceed a safe or comfortable exit temperature.

Referring now to Fig. 8, one form of control circuit will now be described. Off-peak supply terminals LN are connected to an off-peak detection circuit 50, in which a relay coil 51 is energised by off-peak current in order to operate contacts 52 which supply current to terminal 53 of a three position (low, off, high) switch SW1. A resistor 55 connects contact 53 to contact 56. Switch SW1 is operated to provide the fan with maximum current (contact 53), minimum current (contact 56), each via a manually resettable cut-out 57, or no current (OFF). Thus the speed of the fan and hence the forced convection heat loss from the heater can be controlled, or the fan can be switched off. Fan 11 is connected to a terminal block 58 including mains LN connections together with connections for timers A and B. The operation of timers in storage heaters is already well-known.Also connected to terminal block 58 is a proprietary electronic room thermostat 59 having a thermistor sensor 60 and a potentiometer adjuster 61 for adjusting the temperature at which thermostat 59 causes fan 11 to operate. Thus, variations in room temperature will automatically bring fan 11 into operation (depending on the operation of the timers).

One of the timers is connected to a direct acting relay 62 having a coil 63 and contacts 64. One of the switched contacts is connected to a manual terminal 65 which is selected, by operating switch 66, to cause current.to be supplied, via a manually resettable cut-out 67, to direct acting heating elements 42, 43. The other switched contact 64 supplies current, via an automatic cut-out 68 to an "automatic" terminal 69. Automatic cut-out 68 is a bimetallic switch located behind the vent 23b and it responds to emergent air temperature so as to control the direct acting elements 42,43. When switch 66 selects "automatic" operation, the direct acting heating elements 42, 43 will be supplied with current when the emergent air temperature falls below a predetermined level and the timer provides an on-phase for room heating.With "manual" operation, the direct acting elements 42, 43 will be supplied immediately with current as soon as the switch 66 is operated.

Direct acting element 43 is connected to a "1/2 heat cut-out" 80 which is a bi-metallic switch located adjacent the upper vent 22. This switch cuts off the supply of current to element 43 when the emergent air temperature exceeds a predetermined value and supplies this current again when the temperature falls below a predetermined value. Thus, both automatic cut-outs 68 and 80 detect the temperature of emergent air leaving the vents so as to avoid excess temperatures.

A conventional charge controller 70 is connected via a manually resettable cut-out 71, to core elements 5a, 5b ....

the number of elements depending on the size of heater 1.

Alternatively, the charge controller 70 may be of the kind described in our co-pending Application entitled "Storage Heater with Twin Phial Hydraulic Charge Controller".

Fig. 9 is a wiring diagram of the circuit shown in Fig. 8.

The brick modules 3 may be conventional or alternatively they may be in accordance with the arrangement described in our co-pending Application entitled "Storage Heater with Heating Elements Adapted for Local Tariff Electricity Supplies.

Claims (12)

CLAIMS:

1. A storage heater comprising a core made of heat storage medium with air channels therein, one or more heating elements located in the core for supplying heat to the storage medium during a charging period, thermal insulation for retaining stored heat in the core, a fan for inducing a flow of air through said air channels, and an external casing having vents therein to enable air to pass into and out of the storage heater, an auxiliary air channel being provided between a side panel of the casing and the insulation whereby the air, heated by passage through the air channels in the core, is caused to flow through said auxiliary channel before emerging from one of said vents.

2. A storage heater according to Claim 1 wherein said the thermal insulation is substantially thicker than in conventional storage heaters, e.g. two to three times the thickness of conventional insulation.

3. A storage heater according to Claim 1 or 2 wherein said fan is a centrifugal fan.

4. A storage heater according to Claim 3 wherein the fan is independently controlled by a switch which can be operated by a user so that, during a charging period, air can still be induced to flow through the core.

5. A storage heater according to any of the preceding Claims-wherein at least one auxiliary heating element is located in the auxiliary air channel, the auxiliary heating element being connected to switching means whereby the auxiliary element can be operated independently of the operating state of the fan.

6. A storage heater according to Claim 5 wherein an upper vent is located in an upper part of the casing and a lower vent is located in a lower part of the casing, the auxiliary channel communicating with the upper and lower vents so that when the fan is switched off and the auxiliary heating element is switched on, air can flow through the auxiliary channel from the lower to the upper vent, as a result of natural convection and so that when the fan is switched on, the upper and lower vents both serve as outlets for heated air induced to flow through air channels within the core.

7. A storage heater according to any of the preceding Claims wherein a thermostatically controlled air flow bypass, responsive to the temperature of air emerging from the storage heater, enables relatively cold inlet air, induced by the fan, to be mixed with air heated by the storage heater, so as to reduce the temperature of the emergent air below a predetermined maximum value.

8. A storage heater according to any of the preceding Claims wherein said side panel is a front panel of the heater which, when heated by the air flowing through the auxiliary channel, radiates heat.

9. A storage heater according to any of the preceding Claims wherein the interior of the casing is sub-divided into a fan housing, a plenum which communicates with the fan housing, a first core section having air channels communicating with the plenum and in which air is induced to flow in one direction, a second core section having air channels which communicate with the air channels in the first core section and in which air flows in an opposite direction, and an exit chamber which communicates with the auxiliary air channel and with the vents.

10. A storage heater according to Claim 9 wherein the fan housing is located beneath the first core section on one side of the heater so that air delivered by the fan to the plenum beneath the first section then rises through the first section into a second plenum which extends between the upper portions of the first and second core sections, the air flowing substantially horizontally through this second plenum before descending through air passages in the second core section on the other side of the heater, heated air emerging via the exit chamber, to a location adjacent the lower vent and the lower portion of the auxiliary air channel.

11. A storage heater according to Claim 9, when dependent on Claim 7, wherein said by-pass includes a flap which controls cold air flowing from the plenum beneath the first core section and the exit chamber beneath the second core section, and a bi-metallic member which responds to the temperature of heated air in the exit chamber to control the position of the flap.

12. A storage heater according to any of the preceding Claims wherein two or more direct acting auxiliary heating elements are provided in the auxiliary air channel, which elements are selectively switched, either manually or in response to sensing means which respond to emergent air temperature, so that less auxiliary heating is provided when the core temperature is higher (and therefore capable of raising the air to a higher temperature) and more auxiliary heating is provided when the core temperature is low.