GB2049920A - Method and apparatus for electric space heating - Google Patents

Abstract

The invention provides a method of and an apparatus for centrally heating space, using an electricity supply as the primary energy source. Heat is stored in a fluid storage medium e.g. water during a period of time (e.g. at night in the so-called "off- peak" hours) when there is a relatively little demand on the electricity supply. The heated fluid is pumped from the store (11, 12), through heat exchangers (21, 22), during a subsequent period of time (e.g. during the day in the so-called "peak" hours), when there is a relatively high demand on the electricity supply. The heated fluid is pumped through the heat exchangers in response to a heat demand which emanates from the area to be heated. If the demand cannot be met by the heat in store, additional heat is provided by heating the fluid externally of the store (via a heating unit (25)) and pumping the additionally heated fluid directly into the heat exchangers. <IMAGE>

Description

SPECIFICATION Method and apparatus for electric space heating The present invention relates to a method of and apparatus for space heating, using a supply of electricity.

It is known for heat to be stored in a storage medium, by heating the medium when there is relatively little demand on the electricity supply, i.e. at night in the so-called "off-peak" hours, and subsequently releasing the heat during a period of time when there is a relatively high demand on the electricity supply, i.e. during the day in the socalled "peak" hours.

In one known central heating system, the electricity supply is also used during the period of relatively heavy demand, to supplement the heat in the store, whenever the temperature of the storage medium falls below a pre-set level. A major disadvantage of the known system is that the supply of electricity is used during the period of relatively high demand, to maintain the temperature of the storage medium at the pre-set level, irrespective of whether the heat in the storage medium is sufficient to meet the heating requirements of the system.

According to the present invention, there is provided a method of heating space, using a central heating system comprising a heat store for a fluid heat storage medium, and one or more heat exchangers through which the fluid may be passed, said method comprising the following steps: (a) using a supply of electricity to heat the fluid in the store during a period of time, when there is relatively little demand on the supply of electricity.

(b) pumping the heated fluid from the store through the heat exchangers, during a subsequent period of time, when there is a relatively high demand on the electricity supply.

(c) directly heating the fluid, preferably as it passes from the heat store to the heat exchangers, when the temperature of the fluid in the store is insufficient to meet the space heating requirements.

The amount of heat to be stored for subsequent use may be calculated according to a predetermined programme, and the fluid in the store may be heated for a predetermined time period which ends at the end of the period when there is little demand on the electricity supply.

In a preferred method according to the invention, the amount of charge required to heat the fluid directly, during the period of relatively high demand, is also determined according to a predetermined programme, and the amount of heat to be delivered directly to the fluid is provided during a period of reduced demand, within the period of relatively high demand, and is fed into the store for subsequent use. In the preferred method, the flow of heated fluid from the store to the heat exchangers is controlled so that the temperature in the heat exchangers does not exceed a preset maximum value.

The invention also provides space heating apparatus comprising (a) a heat store for a fluid heat storage medium, (b) electrical elements for heating the fluid, (c) one or more heat exchangers through which the heated fluid may be passed, (d) primary control means for connecting the heating elements to an electricity supply, and thereby enabling heat to be supplied to the fluid in the store, during a period when there is relatively little demand on the electricity supply, (e) secondary control means enabling the heated fluid to be pumped from the store through the heat exchangers during a subsequent period of time, when there is a relatively high demand on the electricity supply and (f) further control means enabling the fluid to be heated externally of the store, when the temperature of the fluid in the store is insufficient to meet the requirements of the central heating radiator system.

Advantageously, the primary control means includes a controller which calculates according to a predetermined programme, the amount of the electrical charge required to be supplied during the period of relatively little demand, to meet the heating requirements of the subsequent period of relatively high demand.

The primary control means may be operative to provide the required charge of electricity during a time period which ends at or close to the end of the period when there is relatively little demand on the electricity supply. The primary control means may also be operative, during the period of relatively high demand, to calculate the amount of heat required during that period, and to connect the electricity supply directly to the heating elements during a period of reduced demand, within the period of relatively high demand.

The secondary control means may also control the flow of heated fluid from the store to the heat exchangers in such a manner that the temperature in the heat exchangers does not exceed a pre-set maximum value. For this purpose, the secondary control means may include a mixing valve which is operative to mix hot fluid from the store, with relatively fluid in the heat exchangers.

In a preferred embodiment according to the invention, the apparatus includes a primary fluid circuit which is directly connected to the heat store, and in which the electrical elements are located, and a secondary fluid circuit in which the heat exchangers are located, the mixing valve being positioned between the two fluid circuits so as to transfer fluid from the first fluid circuit into the second fluid circuit.

In order to rescue usage of direct electrical energy, the apparatus advantageously includes a switch which is normally open, but which is adapted to close, thereby connecting the supply of electricity to the electrical heating elements or other energy source, when the mixing valve is in the position in which the secondary fluid circuit calls for the maximum heat available from the primary fluid circuit. Furthermore, the secondary fluid circuit is adapted to be shut down, when the mixing valve is in a position such that no fluid is being exchanged between the primary and secondary fluid circuits. The mixing valve may also be operable so as to allow circulation of fluid in the secondary circuit, whenever the temperature of the fluid in the primary circuit exceeds a predetermined value.

Advantageously, heating elements are located outside the store, within a control unit, which also contains the mixing valve, primary and secondary pumps and pipe connections for the primary and secondary fluid circuits.

The invention will hereinafter be described more particularly with reference to the accompanying drawings, which illustrate, by way of example only, a preferred embodiment of the invention. In the drawings, Figure 1 is a schematic diagram of a central heating system, including a control unit, constructed in accordance with the invention, Figure 2 shows the control unit to an enlarged scale, Figure 3 shows the construction of a storage cylinder, and Figure 4 is an electrical circuit diagram.

Referring to the drawings, and initially to Figure 1, the central heating system includes water storage tanks 11 and 1 2 which are interconnected by pipe 13 and connected to a control unit 19 by pipes 14 and 15. The control unit 19 is connected, by pipes 16, 17 and 18, to radiator systems designated by radiators 21 and 22.

The control unit 19, which is also shown in Figure 2, includes a heating unit 25 containing heating elements 26. The heating unit 25 is connected to a primary pump 27, enabling water heated in the heating unit 25 to be pumped into the storage tanks 11 and 12.

A secondary pump 31 enables water to be pumped from the storage tanks 11 and 12, through the heating unit 25 and into the radiators 21 and 22.

The primary pump 27 is located in a primary circuit in which are also located the storage tanks 11 and 12, the heating elements 26, and the heating unit 25, and the secondary pump 31 is located in a secondary circuit in which are also located the radiators 21 and 22.

The control unit 1 9 also includes a modulating motorized mixing valve 32, heating unit thermostats 33 and 34, a water 38, temperature sensor 35, a thermostat 36, a valve 37 in a by pass pipe a non-return valve 41, and a vent outlet 42. The mixing valve 32 enables water from the primary circuit to be mixed with water in the secondary circuit.

As shown diagrammatically in Figure 1, the electrical connections to the control unit 1 9 include connections 44 from the off-peak electricity supply, connections 45 from the mains electricity supply, connections 46 from an outdoor temperature sensor, connections 47 from an indoor temperature sensor, and electrical connections 48 for controlling the supply of hot water to the radiator 22.

A reservoir 51 is connected by pipe 52 to the pipe 14, and the vent outlet 42 is connected by pipe 53 to the reservoir 51. In the pipe 52 is a lock shield valve. Storage tanks 11 and 12 have automatic air vents 54 and storage tank 12 may be provided with a vent pipe 55 connecting the storage tank 12 to the reservoir 51.

Eachofthepipes14,15,16,17and18hasa valve 64, 65, 66, 67 and 68 respectively, by means of which the flow of water through the respective pipes may be interrupted.

When the off-peak electricity supply becomes available, the outdoor temperature, and the temperature of the water in the storage cylinders 11 and 12, are measured by the outdoor and water temperature sensors. The heat which must be stored during the time when the off-peak electricity supply is available, to meet the requirements of the time when only the peak electricity supply is available, is determined using the results of these two measurements.

For this purpose the system includes a controller of the kind commercially available under the trade mark PACTROL.

The PACTROL controller normally operates according to a predetermined programme which, utilizing the results of the outdoor and water temperature measurements, calculates the heating requirements, and in consequence, the duration of the electrical charge, required to meet the subsequent demand. The PACTROL controller then connects the off-peak supply to the electrical heating elements 26 and to the primary pump 27, resulting in heat being transferred to the storage cylinders 11 and 12. The duration of the charge is determined by the PACTROL controller, but the charging period terminatesatthe end of the period during which the off-peak supply is available.The electricity supply to the heating elements 26 is cut off when the temperature of the water in the storage cylinders 11 and 12 reaches a predetermined temperature (e.g.

1 000C), or at the end of the period of availability of the off-peak supply.

The heating elements 26 may also be provided with an electrical supply during a subsequent peak period, should the heat stored during the off-peak period be insufficient to meet the demands of the subsequent peak period. The peak demand period is divided according to the present invention into sub-periods of (a) moderately high demand and (b) very high demand. A very high demand sub-period could be, for example, between 17.00 and 20.00 hours every day. For this purpose, the PACTROL controller as marketed is modified to provide a programme according to which the anticipated heat requirements of the very high demand subperiod are fulfilled during the moderately high demand sub-period.

The transfer of load from peak demand periods to off-peak demand periods results in a saving to the consumer due to the reduced tariff available, and thereby provides direct benefits to the consumer.

The transfer of loads from very high peak demand sub-periods to moderately high peak demand sub-periods does not result in any monetary saving to the consumer but it avoids excessive peak demands; and thereby provides indirect benefits for the consumer.

The heat output from the storage cylinders 11 and 12 to the radiators 21 and 22 will now be described.

The modulating motorized mixing valve 32 is used for mixing hot water from the storage cylinders 11 and 12 with water in circulation in the radiators, to provide the flow temperature necessary to maintain comfort. The valve 32 is incorporated in a controller of the kind manufactured by the The Sachwell Company and commercially available under the trade mark TRIOTRONIC.

The TRIOTRONIC controller, as marketed, provides automatic control of hot water central heating systems by adjusting the heat output, in response to changes in both external weather conditions and room temperature. The TRIOTRONIC controller consists of three basic components, namely an outside temperature sensor, a room temperature sensor, and an electronic controller in combination with a flow temperature sensor and a motorized mixing valve.

The required room temperature is maintained by a flow water temperature which is variable from a maximum of approximately 600C when the outside temperature is at --1 OC, to a minimum of approximately 450C, when the outside temperature is at 1 60C.

An automatic temperature reduction is incorporated, to reduce the room temperature by 50C below the normal daytime level. The automatic temperature reduction is brought into and out of operation by a time switch. The room sensor is left at its normal setting which becomes operative when the time switch, governing the temperature reduction, opens.

In operation, the external temperature, as signalled by the outside temperature sensor, is used to calculate the heat losses from the house.

Any increase in outside temperature above the basic minimum design conditions causes a proportionate reduction in the flow temperature of water in the heating system. The ratio of change of water temperature to change of outside temperature is set on the TRIOTRONIC controller.

The room temperature sensor signais to the TRIOTRONIC controller any incidental heat gains or losses from sunshine, lighting, occupants, fires, open doors or strong winds. The TRIOTRONIC controller varies the flow water temperature in response to the signal, thereby reducing variations in room temperature due to such incidental heat gains or losses. The required temperature comfort level is selected on the room temperature sensor.

The outside temperature sensor is situated on an exterior shaded wall, preferably facing north, and is positioned away from warm air outlets. The room temperature sensor can be fitted in any room normally maintained at full comfort during the day.

When there is a demand for heat, the room temperature sensor automatically causes an increase in flow water temperature until the temperature in a space to be heated has reached its normal desired value.

The TRIOTRONIC controller, as marketed, has been modified to suit the conditions of the present invention.

In q first modification, a micro switch which, when open, interrupts the supply to the electrical heating elements, is incorporated in the mixing valve 32 and remains open except when the valve is in its maximum heat calling position i.e. the electrical heating elements are disconnected by the micro switch at all times except when the maximum amount of hot water from the storage cylinders 11 and 12 is being called for, and when the temperature of the hot water in the storage cylinders 11 and 12 is not sufficient to provide the flow water temperature required to meet the space heating requirements. When the mixing valve 32 is in the maximum heat calling position, the micro switch is closed, and the electrical heating elements 26 are switched on.This modification ensures that direct energy is used only when called for by the controller and that no unnecessary "topping-up" of the storage cylinders 11 and 12 takes place in mind weather, as occurs In the known system, when the temperature in the store falls below the predetermined level.

With the first modification, maximum advantage is taken of solar and other incidental heat gains and the temperature of the water in the storage cylinders 11 and 12 may drop to as low as 400C.

A second modification is that when the motor on the TRIOTRONIC controller is driven so that the mixing valve 32 is in such a position that no water is being taken from the storage cylinders 11 and 12, and the water in the radiators 21 and/or 22 is being completely recirculated, the secondary pump 31 is switched off.

A third modification is that the thermostat 36, which senses the flow water temperature, causes the motor to drive in the reverse direction when the flow water temperature exceeds a pre-set value. This action closes the motorized mixing valve and allows recirculation. The third modification has been introduced in order to maintain the temperature in the radiators 21 and 22 at a safe level.

The system may be used in conjunction with a back boiler or other system which could inject heat intp the water storage cylinders.

Water heated by the system may also be used in the domestic hot water supply system.

Instead of using the micro switch to connect the electrical elements directly to heat the water during the period of very high demand on the electrical supply, the micro switch may be used to switch on an alternative energy source, such as, for example, an oil fired burner, directly to heat the water during that period.

Claims (25)

1. A method of heating space, using a central heating system comprising a heat store for a fluid heat storage medium, and one or more heat exchangers through which the fluid may be passed, said method comprising the following steps: (a) using a supply of electricity to heat the fluid in the store during a specified period of time, when there is relatively little demand on the supply of electricity.

(b) pumping the heated fluid from the store through the heat exchangers, during a subsequent period of time, when there is a relatively high demand on the electricity supply.

(c) directly heating the fluid as it passes from the heat store to the heat exchangers, when the temperature of the fluid in the store is insufficient to meet the requirements of the central heating system.

2. A method according to Claim 1, wherein the amount of heat to be stored for subsequent use is calculated according to a predetermined programme.

3. A method according to Claim 2, wherein the fluid in the store is heated for a predetermined time period which ends at the end of the period when there is relatively little demand on the electricity supply,

4. A method as claimed in any one of the preceding claims, wherein the amount of charge required to heat the fluid, during the period of relatively high demand, is also determined according to a predetermined programme.

5. A method as claimed in Claim 4, in which the amount of heat to be delivered directly to the fluid is provided during a period of reduced demand, within the period of relatively high demand, and is fed into the store for subsequent use.

6. A method as claimed in any one of the preceding claims, in which the flow of heated fluid from the store to the heat exchangers, is controlled so that the temperature in the heat exchangers does not exceed a preset maximum value.

7. Space heating apparatus comprising: (a) a heat store for a fluid heat storage medium (b) electrical elements for heating the fluid (c) one or more heat exchangers through which the heated fluid may be passed (d) primary control means for connecting the heating elements to an electricity supply, and thereby enabling heat to be supplied to the fluid in the store, during a period when there is relatively little demand on the electricity supply (e) secondary control means enabling the heated fluid to be pumped from the store through the heat exchangers during a subsequent period of time, when there is a relatively high demand on the electricity supply, and (f) further control means enabling the fluid to be heated externally of the store, when the temperature of the fluid in the store is insufficient to meet the space heating requirements.

8. Space heating apparatus as claimed in Claim 7, in which the primary control means includes a controller which calculates according to a predetermined programme, the amount of the electrical charge required to be supplied during the period of relatively little demand, to meet the heating requirements of the subsequent period of relatively high demand.

9. Apparatus as claimed in Claim 8, in which the primary control means is operative to provide the required charge of electricity during a time period which ends at or close to the end of the period when there is relatively little demand on the electricity supply.

10. Apparatus as claimed in any of Claims 7 to 9, in which the primary control means is also operative, during the period of relatively high demand, to calculate the amount of heat required duririgthat period, and to connect the electricity supply directly to the heating elements during a period of reduced demand, within the period of relatively high demand.

11. Apparatus as claimed in any of Claims 7 to 10, in which the secondary control means is operative to control the flow of heated fluid from the store to the heat exchangers in such a manner that the temperature in the heat exchangers does not exceed a pre-set maximum value.

12. Apparatus as claimed in Claim 1 in which the secondary control means includes a mixing valve which is operative to mix hot fluid from the store, with relatively cold fluid in the heat exchangers.

13. Apparatus as claimed in Claim 12, in which there are two fluid circuits, a primary fluid circuit which is directly connected to the heat store, and in which the electrical elements are located, and a secondary fluid circuit in which the heat exchangers are located, the mixing valve being positioned between the two fluid circuits.

1 4.Apparatus as claimed in either of Claims 12 or 13, including a switch which is normally open but which is adapted to close, thereby connecting the supply of electricity to the electrical heating elements or other energy source, when the mixing valve is in the position in which the secondary fluid circuit calls for the maximum heat available from the primary fluid circuit.

1 5. Apparatus as claimed in either of Claims 13 or 14, in which the secondary fluid circuit is adapted to be shut down when the mixing valve is in a position such that no fluid is being exchanged between the primary and secondary fluid circuits.

1 6. Apparatus as claimed in any one of Claims 12 to 1 5 inclusive, in which the mixing valve is operable so as to allow circulation of fluid in the secondary circuit, whenever the temperature of the fluid in the primary circuit exceeds a predetermined valve.

17. Apparatus as claimed in any one of the preceding Claims 7 to 16, in which the heating elements are located outside the heat store.

1 8. Apparatus as claimed in Claim 17, including a control unit which contains the heating elements, the mixing valve, primary and secondary pumps and pipe connections for the primary and secondary fluid circuits.

1 9. Apparatus as claimed in any one of Claims 7 to 18, in which the primary control means is a controller of the kind sold under the trade mark PACTROL.

20. Apparatus as claimed in any one of Claims 7 to 19, in which the secondary control means is a controller of the kind sold under the trade mark TRIOTRONIC.

21. Apparatus as claimed in any one of Claims 8 to 20, in which the heat store includes one or more water storage cylinders.

22. Apparatus as claimed in any one of Claims 8 to 21, in which each heat exchanger is a central heating radiator.

23. Apparatus as claimed in Claim 22, in which there are two radiators circuits in parallel, each circuit being independently controllable.

24. A method of heating space, substantially as described.

25. Apparatus for heating space, substantially as hereinbefore described with reference to, and as illustrated in the accompanying drawings.