IE49168B1 - 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.

Description

The present invention relates to space heating, and in particular to a method of, and apparatus for, central heating using mains electricity.

When using electricity from the mains a differential 5 tariff system applies whereby electricity used during a predetermined time period of high demand (peak hours) is charged at a higher rate than electricity used during a predetermined time period of lower demand (off peak hours).

A method of heating using mains electricity is known in which a heat storage medium is heated during off-peak hours, and the stored heat is then released from the heat storage medium during peak hours. Thus space heating is achieved during peak hours on the basis of the cheaper electricity tariffs which prevail during off peak hours. Conventional storage heaters are designed to use this method.

Central heating systems employing the above method are also known. Xn such central heating systems, if a heat shortfall arises during peak hours, supplementary heating is then added to the heat storage medium. Thus heating is still achieved and comfort maintained, but at the cost of using some high tariff electricity.

In one such known central heating system, the storage medium is water contained in an insulated storage tank.

To release heat, the water is circulated through radiators. - 3 Two other such central heating systems are described in U.K. Patent Specification No. 1,351,740 (Allied Ironfounders Limited,. The first system is described at page 1, lines 64-87, and is acknowledged as being part of the prior art. The second system is described in the remainder of the specification and comprises an improved version of the first. In these two systems the storage medium is a ceramic heating core. To release heat, air is passed through the heated core to a ducted air system.

In all three of the above described central heating systems, the criterion used in determining whether a heat shortfall has arisen during peak hours is based on the amount of heat still available in store. If less than a certain quantity of heat is available in the heat storage medium, then supplementary heat is added to the storage medium. The quantity is preset, and is fixed.

In the hot water system described above, supplementary heat is added if the temperature of the water in the insulated tank falls below a certain preset level.

In the two ducted air systems described above, supplementary heating is added if the air leaving the heated ceramic core falls below a preset level of 120op (49°C).

A disadvantage of the above described criterion is that supplementary heat is added to the storage medium when the available heat in store falls below a certain level, even when the available heat is in fact sufficient to 9168 - 4 meet the heating demand. Incidental heat gains may arise in the space to be heated due to, for example, direct sunlight, due to other types of heating such as an open fire, or due to occupation of the space by a large number of persons. A reduction in heat loss may arise due to a change in weather conditions. As a result of heat gains or reduced heat loss, the relatively small amount of heat still in store may be sufficient to meet the demand. The incidental heat gains may even be such that no heat at all is required from the store. The above three prior art systems would, nevertheless, add supplementary heating to the store in accordance with the criterion which they employ, which is based on available heat in the store rather than on heating requirements.

The present invention provides a method of electrically heating space, the method employing a central heating system which comprises a heat store for a fluid heat storage medium and a plurality of heat exchangers through which the fluid may be pumped, and comprising the following steps: (a) heating the fluid in the store during off peak hours (b) releasing heat from the store during peak hours, by pumping the fluid through the heat exchangers; and (c) adding supplementary heat to the fluid medium - 5 during peak hours, to meet any heat shortfall which occurs during peak hours; the method being characterized by the fact that supplementary heat is added to the fluid medium during peak hours whenever (1) the temperature of the fluid in the heat exchangers is not sufficient to meet the heat demand on the heat exchangers, and (2) there is insufficient heat in the store to meet the heat demand on the heat exchangers.

Advantageously, the flow of heated fluid from the store to the heat exchangers is controlled so that the temperature of the fluid in the heat exchangers does not exceed a preset maximum value.

The invention also provides a space heating system comprising: (a) a heat store for a fluid heat storage medium; (b, electrical elements for heating the fluid in the store; (c) a plurality of heat exchangers through which the heated fluid may be pumped; (d) input control means for connecting the heating elements to an electricity supply, thereby enabling heat to be supplied to the fluid in the store, during off peak hours; (e) output control means enabling the heated fluid to be pumped from the store through the heat exchangers during peak hours; - 6 (f) further control means enabling the fluid to be electrically heated during peak hours when the temperature of the fluid in the heat exchangers is insufficient to meet the heat demand on the heat exchangers, and there is insufficient heat in the store to meet that demand.

In a preferred embodiment of the invention, the heat 10 store is an insulated water tank or cylinder and the heat exchangers are hot water radiators, and the system comprises two water circuits, namely a primary circuit which includes the water tank and electrical elements and a secondary circuit which includes the radiators, and a mixing valve for mixing heated water from the primary circuit with cooler return water from the secondary circuit.

The further control means may comprise a switch operable by the mixing valve to connect the electrical elements to the mains supply during peak hours only when the mixing valve is in the open position.

Advantageously, the heating system includes a circulating pump in the primary circuit, and the mixing valve is operatively connected to the circulating pump so as to switch off the pump when the mixing valve is in the closed position.

According to a further advantageous feature of the - 7 invention, the heating system is operable to close the mixing valve whenever the temperature of the water being circulated through the secondary circuit exceeds a certain preset value.

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 12 which are inter-connected 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 - 8 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 19 also includes a modulating motorized mixing valve 32, heating unit thermostats 33 and 34, a water temperature sensor 35, an indoor air temperature sensor, a thermostat 36, a valve 37 in a bypass 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 19 include connections 44 from the electricity supply, connections 45 to receive the off-peak signal, connections 46 from an outdoor temperature sensor for the input control means, connections 47 from an outdoor temperature sensor for the output control means, connections 48 from an indoor air sensor for the output control means for controlling the supply of hot water to the radiator 22, and connections 49, from a store water temperature sensor, to the input control means.

A reservoir 51 is connected by pipe 52 to the pipe 14, and the vent outlet 42 is connected by pipe 53 to the - 9 reservoir 51. Xn 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.

Each of the pipes 14, 15, 16, 17 and 18 has a 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, 10 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 an input controller of the kind commercially available under the trade mark PACTROL.

The input 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 input controller then connects the off-peak supply to the electrical heating - 10 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 input controller, but the charging period terminates at the 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. 100°C), or at the end of the period of availability of the off-peak supply.

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 15 with water in circulation in the radiators 21 and 22, to provide the flow temperature necessary to maintain comfort. The valve 32 is incorporated in an output controller of the kind manufactured by the The Sachwell Company and commercially available under the trade mark TRIOTRONIC.

The output 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 output controller consists of three basic components, namely an outside temperature sensor, a room temperature sensor, and an electronic controller in - 11 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 60°C when the outside temperature is at 1°C, to a minimum of approximately 45oc, when the outside tenperature is at 16°C.

An automatic temperature reduction is incorporated, to reduce the room temperature by 5°C 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 output controller. The room temperature sensor signals to the output controller any incidental heat gains or losses from sunshine, lighting, occupants, fires, open doors or strong winds. The output controller varies the flow water temperature in response to the signal, thereby reducing variations in room - 12 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 5 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 signals the output control means to increase the flow water temperature until the temperature in the space to be heated has reached its normal desired value.

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

In a first modification, a micro switch which, when open during peak hours, 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 - 13 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 mild weather, as occurs in the known systems, when the temperature in the store falls below the predetermined level.

A second modification is that when the motor on the output 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 primary pump 27 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 or partially closes the motorized mixing valve until the flow water temperature drops.

The third modification has been introduced in order to maintain the temperature in the radiators 21 and 22 at a safe level.

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

Claims (9)

1. A method of electrically heating space, the method employing a central heating system which comprises a heat store for a fluid heat storage medium and a plurality of heat exchangers through which the fluid may be pumped, and comprising the following steps : (a) heating the fluid medium in the store during off peak hours; (b) releasing heat from the store during peak hours by pumping the fluid medium through the heat exchangers; and (c) adding supplementary heat to the fluid medium during peak hours, to meet any heat shortfall which occurs during peak hours; the method being characterised by the fact that supplementary heat is added to the fluid medium during peak hours whenever (1) the temperature of the fluid in the heat exchangers is not sufficient to meet the heat demand on the heat exchangers, and (2) there is insufficient heat in the store to meet the heat demand on the heat exchangers.

2. A method as claimed in Claim 1, in which the flow 25 of heated fluid from the store to the heat exchangers is controlled so that the temperature of the fluid in the heat exchangers does not exceed a preset maximum value.

3. A space heating system comprising: - 15 (a) a heat store for a fluid heat storage medium; (b) electrical elements for heating the fluid in the store; (c) a plurality of heat exchangers through which the heated fluid may be pumped; (d) input control means for connecting the heating elements to an electricity supply, thereby enabling heat to be supplied to the fluid in the store, during off peak hours; (e) output control means enabling the heated fluid to be pumped from the store through the heat exchangers during peak hours; (f) further control means enabling the fluid to be electrically heated during peak hours when the temperature of the fluid in the heat exchangers is insufficient to meet the heat demand on the heat exchangers, and there is insufficient heat in the store to meet that demand.

4. A space heating system according to Claim 3, in which the heat store is an insulated water tank or cylinder and the heat exchangers are hot water radiators, the system comprising two water circuits, namely a primary circuit which includes the water tank and the electrical elements, and a secondary circuit which includes the radiators, and a mixing valve for mixing heated water from the primary circuit with cooler - 16 return water from the secondary circuit.

5. A space heating system according to Claim 4, in which the further control means comprises a switch operable by the mixing valve to connect the electrical 5 elements to the mains supply during peak hours only when the mixing valve is in the open position.

6. A space heating system according to Claim 4 or 5, including a circulating pump in the primary circuit, in which the mixing valve is operatively connected to the 10 circulating pump so as to switch off the pump when the mixing valve is in the closed position.

7. A space heating system according to Claim 4, 5 or 6, operable to close the mixing valve whenever the temperature of the water being circulated through the 15 secondary circuit exceeds a certain preset valve.

8. A method of space heating substantially as herein described with reference to the drawings.

9. A space heating system substantially as herein described with reference to and as shown in the 20 accompanying drawings.