GB2202619A - Electric heating systems - Google Patents

Abstract

A heating system for a building comprises a pipe system (3) for conducting water around the building, a plurality of radiators (1, 2) connected to the pipe system to draw water from and return water to the pipe system, at least one pump (5) for circulating water through the pipe system and heating units each having an electric heating element (12) connected to the pipe system to heat the water. The elements (12) are individually controllable from a single control unit (16). <IMAGE>

Description

HEATING SYSTEM This invention relates to a system for electrically heating buildings. It is applicable to small dwellings and particularly but not exclusively to relative large buildings such as hotels.

Conventional central heating systems using water circulation generally comprise a series of radiators distributed around the building to be heated fed with hot water from a pair of pipes, one for supply of hot water and the pther for recirculation of water discharged from the radiators, the pipes running around the building. Alternatively a single pipe may be used for feeding and discharging from the radiators. A pump is normally provided to propel water around the system and the water is heated by means of a single boiler which may be electrically powered or burn solid fuel, gas or oil. The boiler is normally located at a point in or outside the building, such as in the basement, where it will not be obtrusive.

When used in a large building a system of this type has the disadvantage that when it is switched on the heat provided, originating from a single point, is not conducted immediately to all parts of the building but is intially delivered only to the radiators adjacent to the boiler, which are first supplied with hot water from the supply pipe. The radiators in the building may be provided with their own thermostats so that the feed of hot water to them is stopped when the temperature of the room heated by that radiator reaches 2 desired value, but even then it can take a very long time for heat to be delivered to rooms or corridors of the building which are remote from the boiler. It is then necessary to turn the system on a long time before the heat is actually required, increasing the cost of heating the building considerably.

When a large number of radiators are fed with water from a single boiler it is also necessary to provide relatively large-bore pipes to conduct the necessary volume of hot water from the boiler to all the radiators. Difficulties arise if the rate of transfer of heat is increased by increasing the temperature of the water or by increasing the flow velocity of the water through the pipe beyond a certain value. The use of large-bore pipes increases the volume of water circulating through the system and so increases its thermal inertia.

In a large building it is often desired to heat certain areas of the building, such as particular floors or particular blocks of rooms, while leaving other areas unheated. With a known system of this kind described above, hot water in the pipe is still circulated through all areas of the building and even if the radiators in the unheated areas are turned off some heat is still delivered to those areas, resulting in waste.

According to one aspect of the present invention, there is provided a heating system for a building comprising a pipe system for conducting water around the building, a plurality of radiators connected to the pipe system to draw water from and return water to the pipe system, at least one pump for circulating water through the pipe system and a plurality of heating units each comprising an electric heating element and connected to the pipe system to receive water therefrom, heat the water and return it to the pipe system, the heating units being distributed along the pipe system and individually controllable from a single control unit.

Using the arrangement of the invention, there is no need for a central boiler and the heat required is supplied by the individual heating units which may be distributed around the building. When the system is operated water is pumped through the pipe-system to supply all the radiators and each heating unit can heat the water, thus supplying heat to the radiators between that heating unit and the next heating unit of the system. The heating units may be distributed around the system so that there can be one heating unit for every three radiators approximately and the power required for each heating unit is then quite low, for example 2 KW or less.

When the system is switched on heat is supplied to all parts of the system immediately and, when all the heating units are in operation, the whole of the building may be heated simultaneously thus avoiding the time lag experienced using systems with a single heat source. However there may not be a necessity to heat all parts of the building.

The heating units are indiadslly controllable from a single control unit at a single location so that if, say, one of the floors of the building is to be left unheated the heating units on that floor may be switched off and water will pass through the pipe system on that floor in the cold condition so that no heat is wasted.

As relatively small amounts of heat are supplied to the water at different points of the building there is no need to use a large amount of water in the system. The pipe may be of standard 15 mm or 22 mm diameter and the volume of the water in the radiators in,each area of the building need only be a few litres. The overall thermal inertia of the system may then be very low and the system is capable of very rapid response when turned off or on.

S is preferred that the heating units should be located in the body of one of the radiators. This arrangement reduces the apparent bulk of the system to a minimum and makes it as unobtrusive as possible. The heating unit may be located inside a generally rectangular enclosure of which the front panel is formed of the heat-emitting surface of the radiator and the rectangular enclosure may then visually resemble all the other radiators in the building.

Each of the radiators may be provided with a valve operated by a thermostat in conventional manner so that the heat output of the radiator responds to the temperature of the environment and/or the valve may be operated automatically by the controller which responds to the temperature of the water pumped through the system.

The heating units may all be controlled from a single location, such as the porter's lodge of an hotel or a central location in a dwelling, and individually wired to the control unit. The wiring required is relatively cheap and unobtrusive as the power requirement of each heating unit is quite small. When the building has a polyphase electric supply the different phases may be used to supply the heating units in different areas of the building. All devices required for controlling the system may be located at the single control unit so that the system is easily operated, inspected and maintained.

The installation cost of the system will generally be very low as only a single narrow-bore pipe is required for supplying water to the radiators, there is no central boiler required, and the wires feeding electricity to the heating units are required to conduct only a modest current.

Each of the heating units may be provided with a thermostat or a temperature-sensitive control device operable to turn the respective heating element on and off in response to the temperature of the water flowing through the heating unit or pipe system. Each heating element may be controlled by a respective control device situated at or near said control unit. In one arrangement each heating element is remotely controlled by a control unit programmed to control all the heating units of the system as required to maintain a presetable temperature in the system in such a manner that each heating element is turned on or off at a preselectable time or time interval. The control unit and heating units may be connected by direct wire connections or other means using appropriate coded signals.

Heating systems according to embodiments of the invention will now be described with reference to the accompanying drawings in which Figure 1 is a schematic diagram of a serial-feed heating system.

Figure 2 is a schematic diagram of a parallel-feed heating system.

Figure 3 is a schematic diagram of a control arrangement for the heating system of Figure 1 or 2.

The system shown in Figure 1 comprises a series of radiators 1 and 2 which are arranged on two floors of a building.

Each radiator receives water through inlet 7 of pipe 3, the water circulates through the radiator and is discharged at outlet 8 of pipe 3. Six radiators are shown in the drawings but any number of radiators, arranged on any number of floors or separate areas of the building, may be used.

The radiators are connected to a single pipe 3 made of standard 15, 22 or 28 mm copper tubing which feeds water to and drains it from the radiators in conventional manner.

A known type of top-up tank 4 is provided to replenish the system with water as necessary.

Water is circulated through pipe 3 by electrically driven pump 5 in known manner. Additional pumps to circulate the water may be provided if necessary; one such additional pump 6 is shown on the drawing. The pump or pumps may be located at any point of the water circuit formed by pipe 3.

Radiators 2 are of the conventional type but radiators 1 are provided with electric heaters for heating the water passing through them.

Between inlet 7 and valve 9 in radiators 1, the water passes through pipe 11 which contains an electric heating element 12 of 2 KW power or less. The heating element is associated with a manually resetable thermal cut-out 13 arranged to switch the element off when the temperature of the water exceeds a preset safe value, such as 180 degrees F. The radiator is provided with a short-circuit pipe 14 to return water to outlet 8, thus water may pass through pipe 11 even when valve 9 is closed.

Radiators 2 are of similar construction to radiators 1 except that they are not provided with element 12 or thermal cutout 13.

Electric current is fed to elements 12 by individual power circuits (not shown) from control unit 16, which contains devices for operating these circuits independently of each other. Control unit 16 also comprises circuitry for controlling pumps 5 and 6 and circuitry for controlling the water temperature to a preset value. The control unit is operated by push-button console 17 which may be located at a convenient position in the building, for example at the reception desk of an hotel or a convenient location in a dwelling. The console and control unit are provided with facilities for activating the power circuits to the radiators all together, individually, or in groups as desired and also with a programmed time switch facility to allow automatic operation.

As shown in the drawing, the electromagnetic valve of each radiator may be turned on and off individually by control unit 16. In addition to valve 9, each radiator has a thermostatic valve to turn the radiator on and off in response to the temperature of the room in which the radiator is situated.

The control unit may be operated manually or according to a pre-set programme from console 17.

The control unit 16 incorporates control devices for each radiator power circuit, together with a master switch for controlling the main power supply to the system, and ancillary equipment for circuit protection such as circuitbreakers. In a preferred arrangement the control unit 16 is fed by a 3-phase power supply and each radiator power circuit is supplied using one of the phases.

The system described above is cheap and easy to install in a building, has a short start-up time and is capable of reducing the electric power wasted virtually to zero. The system described uses water as the heat transfer fluid but it could be adapted to use other liquids if desired.

The system shown in Figure 2 is generally similar to that of Figure 1 and similar components are denoted by the same numerals. However in the arrangement of Fig.2, instead of fluid being drawn from pipe 3 and returned to pipe 3 at closely adjacent points for each radiator a "two-pipe" system is used in which pipe 3 runs past each radiator twice, hot water is drawn from one of the pipe sections and the cooled water is discharged to the other pipe section by each radiator.

The hot water feed for each radiator is thus separated from the cold water discharge.

In the arrangement in Figure 2 different groups of radiators, located on different floors of a building, are fed by different branches of pipe 3.

If desired, these branches may be isolated from the remainder of pipe 3 by suitably located electrically operated valves (not shown in the drawing). In this arrangement also, extra pumps 6 may be arranged at different points along the pipe 3 as required and one such pump 6 is shown in Figure 2.

In other respects the manner of construction and operation of the system shown in Figure 2 is the same as that in Drawing Figure 1.

typical arrangement of control unit 16 and console 17 is shown diagrammatically in Figure 3. The console is provide with clock 21 controlling a time switch so that the whole system may be turned on and off automatically at preset times; console 17 also has a switch for turning the system on and off manually. Console 17 has push-buttons or similar devices 22 for selecting individual radiators, or groups of radiators, to be operated as required. Devices 22 control feed of power to the solenoids of radiator valves 9 through respective contact devices 23 and lines 24 (only one of which is shown in the drawing).

Mains power is fed to the system through line 25, through thermal cut-out 26 which disconnects the power supply to the heaters in the event of a rise in temperature above a preset safety limit by means of contact devices 27 controlling feed of power to the heater elements through lines 28 (only one of which is shown).

The temperature at different points of the system is sensed by appropriately located temperature sensors and the signals received, amplified as required, are converted to digital form by an analogue/digital converter 29 and compared with preset values, which may be varied by means of system control unit 30, by means of a comparator. The control system supplies power to the individual heating elements through lines 28, and also feeds power to the pumps through lines 31 controlled.by contact devices 32, as required to maintain the preset temperatures at different points in the pipe system. The circuits feeding power to the pumps are provided with an over-run delay device 33 to allow the pumps to operate for a predetermined time after the heating units are switched off in order to dissipate residual heat in the system.

The system described above may be used as the only source of heat for a building, alternatively it may be used to supplement, or be integrated with, an additional system which may use a solid fuel, gas or oil-fired boiler or a heat storage unit using cheap off-peak electricity. With a solid fuel system or heat storage unit the heat output of the additional system will generally vary according to the time of day. For example, with a conventional solid fuel fire heating a back boiler the heat output of the fire falls during the night and increases when the fire is stoked up in the morning. The heat output from an electric storage heater generally falls as the stored heat becomes exhausted, N during a full-tariff period when electric current is nof - - supplied to the unit. The system of the present invention may be used to supplement such a known heating system and it may be arranged to sense the heat output of the additional system, or the ambient temperature, and to supply additional heat when the heat output or temperature falls below a given value.

The system of the invention may also be used in conjunction with a known type of oil or gas-fired system, which may have a higher capacity and hence a higher running cost than the system of the invention. The oil or gas-fired system may supply hot water through the same pipes as the electric system of the invention and the oil or gas system may be used when a high heat output is required, for example during the day, and the system of the invention may be used during the night when the heat output required is lower and cheap electricity is available at off-peak rates.

Claims (16)

1. A heating system for a building, comprising a pipesystem for conducting water around the building, a plurality of radiators connected to the pipe-system to draw water from and return water to the pipe-system, at least one pump for circulating water through the pipe-system, and a plurality of heating units each comprising an electric heating element and connected to the pipe-system to receive water therefrom, heat the water and return it to the pipe-system, the heating units being distributed along the pipe-system and individually controllable from a single control unit.

2. A system according to claim 1, in which each heating unit comprises a vessel containing the electric heating element positioned within the body of one of the radiators.

3. A system according to claim 1 or 2, in which each heating unit has a heating power of about 2 KW or less.

4. A system according to claim 1, 2 or 3, in which each heating unit is provided with a thermostat or a temperature sensitive control device operable to turn the respective heating element on and off in response to the temperature of the water flowing through the heating unit or pipe-system.

5. A system according to one of claims 1 through 4, in which each heating element is controlled by a respective control device situated at or near said control unit.

6. A system according to one of claims 1 through 5, in which each heating element is remotely controlled by a control unit programmed to control all heating units in the system as required to maintain a presetable temperature in the system, in such a manner that each heating element is turned on or off at a preselectable time or time interval.

7. A system according to any preceding claim, in which each radiator is provided with a thermostat controlling a valve for regulating the flow of the water through the radiator.

8. A system according to any preceding claim, in which said pipe-system comprises piping of external diameter of 15, 22 or 28 mm.

9. A system according to any preceding claim, in which the number of radiators exceeds the number of heating units and/or heating units distributed along the pipe-system at intervals, each heating unit being associated with one of the radiators but not necessarily contributing heat to the associated radiator.

10. A system according to any preceding claim, in which different heating units or groups of heating units are supplied with electric current from different phases of a multiphase supply.

11. A system according to any preceding claim, in which the control unit is arranged so that the said heating units or groups of heating units may be turned on and off independently of the others.

12. A combination comprising an electric heating system as claimed in any preceding claim integrated with an additional heating system in which heat is supplied by a boiler or electric heat storage unit.

13. A combination according to claim 12, in which said additional heating system generates heat by burning solid fuel or stores heat generated by off-peak electricity.

14. A combination according to claim 12 or 13, in which said electric heating system is adapted to detect the heat output of said additional heating system, or the ambient temperature, and to vary its own heat output according to the heat output of the additional system or according to the ambient temperature.

15. A combination according to claim 12, 13 or 14,in which the electric heating system is adapted to operate only on off-peak rate electricity.

16. A heating system, substantially as hereinbefore described with reference to Figure 1 or Figure 2 of-the accompanying drawings.