GB2068529A - Central heating system - Google Patents

Abstract

A space heating system, in which radiators (1-6), are connected in a common hot water circuit, is supplied with hot water from a storage tank (7) in which the water is heated electrically, e.g. by immersion heaters (8). The capacity of the tank is preferably large enough to enable only an "off-peak" tariff to be used. Domestic hot water is heated in a direct-heating cylinder (20) submerged in the storage tank and deriving its heat from the main body of water in the latter. <IMAGE>

Description

SPECIFICATION Space heating systems This invention relates to space heating systems of the kind comprising a plurality of hot-water radiators, a vessel for containing water, pipework connecting the 'water vessel in a closed circuit with the radiators and heating means for heating the water in the water vessel. Such a space heating system will be referred to herein as a "wet central heating system".

Wet central heating systems are distinguished from "dry" central and other space heating systems in that the latter do not employ hot water, but rely on heat transmission using air or solid bodies as the medium. One example of a dry central heating system is a ducted warm-air system in which air is heated by electricity or by combustion of mineral fuel (gas or oil), heat being transferred to the air in an indirect heat exchanger and the heated air then being circulated through ducting by a fan or blower. Examples of other kinds of dry space heating systems include night storage heating, using individual and unconnected electric storage heaters in different parts of the building; and various electrical systems such as underfloor heating, and skirting or wall panels containing oil which is heated by electric elements.All these systems are susceptible to thermostatic control so that they can provide heat as and when required in response to ambient temperature in the building being heated.

Nevertheless, dry space heating systems have all been found to display certain disadvantages. In warm-air systems the air tends to be dry and presents problems of smell, whilst with nightstorage heating the heaters tend to be bulky, and often inconvenient for that reason, besides being relatively inefficient in that satisfactory control of output can be difficult to achieve. Underfloor heating and other electrical systems built into the structure of a room, such as skirting, wall or ceiling panel heating, have on the whole proved unpopular. They are expensive to instal and access for repairs, in the event of failure, is difficult or impossible without major damage to the parts of the room concealing the heating elements. Oilfilled radiators are expensive in first cost.

Electrical space heating systems, with the exception of those employing ducted warm air, are generally confined to those in which each room is heated by its own individual heat source, supplied with power separately from those elsewhere in the building. This militates against economy in first cost, apart from the other disadvantages of such arrangements. Another disadvantage is that separate means has to be provided for heating domestic hot water Electric space heating systems do on the other hand offer certain advantages, among which are the convenience and cleanliness of electricity. One important advantage, however, is that if (as in night storage heaters), the heat produced can be stored until required for use, advantage can be taken of "offpeak" tariffs, so reducing running costs considerably.

A true "central" heating system is one in which a medium is heated at a single location and is then distributed to the various parts of the building.

Apart from electrically heated ducted warm-air systems, central heating systems fall into the categories of oil- or gas-fired ducted warm air systems, solar-heated hot water ("wet") systems, and lastly the most widespread conventional kind of central heating system, viz. hot water or wet systems fired by gas, oil or solid fuel.

Wet central heating in itself offers a number of advantages, in that the humidity or smell of the air in a heated room is not unduly affected thereby; the system is usually relatively inexpensive in first cost and installation cost; and there is considerable flexibility possible in design due to the different sizes of radiator available and the fact that these may be positioned whenever most convenient or effective. Again, conventional wet central heating is well-tried and generally reliable.

It can if desired be adapted for quite precise individual control of temperatures in different rooms by the use of local radiator valves controlled by room thermostats, which may be incorporated in the valve units themselves. Even without thermostatically-controlled radiator valves, room temperature can be effectively controlled by operation of manual radiator valves, usually in conjunction with a single air thermostat, arranged centrally in the building, which controls the minimum temperature above which a circulating pump passes more hot water through the radiators.

However, conventional wet central heating systems also suffer, nowadays, for disadvantages which tend to be different according to what source of heat is used. Gas-fired systems are not possible where there is no main gas supply, unless bottled liquid petroleum gas (L.P.G.) is used which is extremely expensive. The alternatives, if a "wet" system is required, are to use an oil-fired or solid fuel boiler, or solar energy. Solar heating systems so far available are expensive in first cost, and relatively inefficient. Furthermore, it is not possible (as it is with other kinds of wet central heating systems) to heat domestic hot water from the same heat source as the water for central heating.

Fuel oil, coke, gas is convenient but has now become very expensive. Solid fuel is inconvenient to handle and occupies much storage space.

According to the invention, in a wet central heating system (as hereinbefore defined) the heating means is electrical.

Preferably the water vessel has a storage capacity whose volume is at least as great as that of the radiators and pipework together, whereby water heated in the vessel over one period of time can be used in the system at a later period. The capacity of the water vessel in any particular installation is preferably, in fact, large enough to enable the water in it, if heated only during the period in which an "off-peak" tariff operates, to be adequate for all heat demands during the remainder of the 24 hours until the next "off peak" period.

The water vessel is thermally insulated and is preferably in the form of a simple storage tank. It is indeed preferably made of a strong insulating material such as a glass-reinforced hightemperature plastics resin.

The heating means preferably comprises at least one immersion heater in the water vessel.

As thus described, it will be seen that a central heating system according to the invention combines the advantages of a wet system with the economy resulting from ability to use off-peak electricity supplies, i.e. the economic advantage, already stated, of stored-heat systems.

Furthermore, it can be used where no gas is available, and yet avoids the disadvantages, discussed above, of gas-fired and other conventional wet central heating systems whilst retaining their advantages. Among these latter is the ability to be arranged for precise and efficient control of ambient temperature in rooms heated by the system.

To this end, and in order to ensure the greatest possible simplification of the pipework commensurate therewith, the preferred arrangement provides that the radiators are connected in loops of the pipework between a flow main and a return main, each loop having a thermostatically-controlled local valve responsive to ambient temperature for admitting hot water from the flow main and through the loop to the return main, the flow and return mains being connected.to the water vessel.

In some applications, circulation of water through the system may be achievable by simple convection. More usually, however, there is provided a circulating pump arranged in the pipework for circulating water through the system.

The pump is preferably arranged to be energised whenever the thermostat associated with any one of the said local valves (where the latter are themselves provided) opens the said valve. Thus the pump will only run when there is a call for heat. Loss of heat from the system is minimised by correct use of adequate insulation, particularly around the water storage tank.

One very important advantage shared by a system according to the invention with wet central heating systems of the gas-fired, oil-fired or solid fuel types is the ability to heat domestic hot water from the same energy source as for the central heating itself. Conventionally, however, a fossilfuelled boiler has a separate outlet and inlet connected with a hot water cylinder, usually located at a position remote from the boiler. Such a cylinder has to be cf the indirect-heating kind, in which the domestic hot water passes through a coil within the cylinder. Such cylinders are expensive in first cost, and tend to be subject to failure due to corrosion of the coil, particularly in hard-water areas.

According to a preferred feature of the invention, the central heating system is combined with a domestic hot water system comprising a hot-water cylinder, a source of feed water to said cylinder, and at least one hot water tap connected with an outlet of the cylinder, the cylinder being within the water vessel so that water in the cylinder is heated by indirect heat exchange with the electrically-heated water in the vessel. It will be appreciated that the cylinder is of the simple direct kind, not having a coil. This arrangement provides a source of constant domestic water at minimal cost.

Economic operation of the system according to the invention is envisaged by maintaining the central heating system in use at all times. That is to say that, if the individual room thermostats are all set to a minimum predetermined temperature, no electrical energy is used unless the local temperature falls below that value. On this basis, no time clock is necessary, and the only adjustment needed by the user is when the temperature in a room is desired to be increased above the minimum temperature at which it is normally set.

The arrangement of the pipework and radiators may take any desired form, there being no more constraints on freedom of design with the system of the present invention that with conventional wet central heating systems. In this connection, it should be made clear that the water vessel with its electrical heating means constitute an electrically-powered hot water boiler, which may be substituted in other heating systems for other kinds of boiler.

One embodiment of the invention will now be described, by way of example only, with reference to the drawings hereof, in which: Figure 1 is a diagram showing the circuit and principal components of a typical wet central heating system according to the invention; Figure 2 is a circuit diagram illustrating an electrical control circuit for the circulating pump of the same system; Figure 3 is a simplified sectional elevation, taken on the line Ill-Ill in Figure 4, showing the electrical hot water boiler unit of the system shown in Figure 1; and Figure 4 is a simplified sectional plan view, taken on the line IV-lV in Figure 3.

Referring to Figure 1, the wet central heating system shown therein is installed in a small house having five rooms and two domestic hot-water taps. It will however be understood that there may be any number of rooms, any or all of which may be heated by the system; and there may be any number of domestic hot-water outlets. The small size of the system here described is chosen merely for simplicity.

The system comprises seven hot-water radiators 1, 1A and 2 to 6, for space heating; a water-containing vessel 7 in the form of a thermally-insulated storage tank; pipework connecting the tank 7 in a closed circuit with the radiators 1 to 6; and electrical heating means, in the form of an immersion heater 8 mounted in the wall of the tank 7 for heating the water in the tank.

The tank 7 and heater 8 form part of an electrical hot-water boiler unit 27.

The pipework of the central heating system includes a flow main 9 leading away from the storage tank 7, and a return main 10 leading back into the storage tank. The radiators 1 and 1A are both in one room and are connected in series with each other. Each- of the radiators 2 to 6 is in a separate room. The radiator or radiators of each room are connected between the flow main 9 and return main 10 in a respective one of five loops of pipework 11. At the junction of each loop 11 with the flow main 9, there is a solenoid valve, S1 to S6 respectively. There is thus one solenoid valve for each room, each of these valves being controlled by a corresponding room thermostat T1 to T6 respectively (which are not shown in Figure 1 but whose electrical contacts are indicated in Figure 2).The room thermostats are adjustable manually, so as to enable the minimum valve to which the temperature in the room is to be allowed to fall to be preset at will. When the temperature falls to or just below this valve, the thermostat contacts close,' so energising the solenoid of the corresponding local valve S1 to S6 and causing the latter to open so that hot water circulates through the radiator or radiators in that room.

A circulating pump 12 is arranged in the flow main 9 upstream of the radiator loops 1 for circulating water through the system. The pump 12 is arranged to be energised whenever the thermostat T associated with any one of the local valves S causes that valve to open, in the following manner.

Referring to figure 2, the control circuit shown therein is a low-voltage (15 volt) circuit in which it can be seen that each pair of thermostat contacts is connected in series with the corresponding solenoid valve in a separate loop of the circuit, with each of these loops in parallel with each other. Each loop is connected with a respective one of six inputs of a NOR gate 13, whose output is connected through an inverter 14 to the coil 1 5 of a starting relay of the circulating pump 12. The pump relay has contacts (not shown) which serve as the circuit breaker of the pump, so that the pump operates only whilst the relay coil 1 5 is energised. It will be seen that the NOR gate 1 3 operates to energise the coil 1 5 whenever any one or more of the thermostat contacts T1 to T6 is closed.

Referring once again to Figure 1, the central heating system itself is combined with a domestic hot water system for supplying hot water to the two taps indicated at 1 6. The domestic hot water system includes a conventional cold water tank 1 7 supplied from the main supply 1 8 and connected by a feed-water downpipe 1 9 to a hot-water cylinder 20 of the direct type. The hot-water cylinder 20 is mounted within the storage tank 7 of the central heating system and has an outlet pipe 21 leading to the hot water taps 16.

Make-up water for the storage tank 7 (to compensate for loss through inadvertent leakage etc. from the central heating system) is supplied through a downpipe 24 from a header tank 22, to which the return main 10 is vented via a vent pipe 23 in the usual way. Supply of make-up water is controlled by a valve 25 in the downpipe 24, the valve 25 being arranged to be opened when the water level falls below its correct value as indicated by a suitable device 26.

Figures 3 and 4 show in greater detail the construction of the electrical hot water boiler unit 27. The storage tank 7 is made of thermally insulating material, which in this example is a high-temperature plastics resin reinforced with glass fibre. Techniques for making such a tank of this material are well known and need not be described here. The tank 7 may be of any suitable shape, for example cylindrical or spherical, or in the form of a domed cylinder. In this example, however, it is in the form of a rectangle in plan, having a shallow domed roof 30 and a flat floor 31. The domestic hot water cylinder 20 is mounted on its side on cradles 32 fixed to the floor 31 of the storage tank. The central heating return main 10 is connected into the tank 7 by two return ports 33 in the floor of the tank.These ports may number one or more; two are shown in this example so as to give more even distribution of the cooled returning water, within the mass of water in the tank, than if there was only one return port. Also the return port or ports may if desired be in any other wall or walls of the storage tank, The central heating flow main 9 is led out from a wall of the storage tank 7, from a flow port 34.

Again, there may be more than one such flow port, any of the flow port or ports can be in any convenient wall or walls of the tank.

The feed pipe 1 9 and domestic hot water flow pipe 21, connected with the hot water cylinder 20, are led through appropriate walls of the tank 7.

The water level in the tank is indicated at 35, and is of course such that the flow port 34, return ports 33 and hot-water cylinder 20 are completely submerged at all times.

Four immersion heaters 8 are shown. There may be any number of such heaters, chosen according to the heating requirements for the system. At least one of the immersion heaters has a thermostat 36, which serves as a boiler thermostat, such that the heaters are energised whenever the water temperature in the storage tank 7 is below a predetermined value at a time when there is a power supply available to the immersion heaters. If any one or more of the immersion heaters has no thermostat (as in this example), it is connected electrically so as to be controlled by the boiler thermostat, or one of the boiler thermostats, that are provided, so that all of the immersion heaters are energised simultaneously.

The storage tank 7 is encased in a thick jacket 37 of thermal insulating material such as glass fibre or other suitable material, within an outer casing 38. The number of interruptions in the outer casing and insulating jacket is kept to a minimum, to ensure the greatest possible effectiveness of insulation. Access holes 39, provided with thermally insulating removable plugs 40, are however provided to enable access to be gained to the immersion heaters 8. If access is required to the hot water cylinder 20 or other parts of the interior of the storage tank 7, the latter can if desired be made with, say, its roof 30 removable, the outer casing 38 and insulation jacket 37 being correspondingly provided with removable portions.

The water level indicating device 36 is, with a view to minimising the need for maintenance or replacement, preferably a simple float valve or the like operating an electrical switch, the valve 25 (Figure 1) being a solenoid valve opened by the closing of such switch. Any other suitable known type of device, for controlling the ingress of makeup water to maintain the water level 35 constant, may however be employed.

In operation, the central heating radiators 1 to 6 operate in the manner already described, hot water being circulated by the pump 12 from and back to the storage tank 7. The storage capacity of the latter is at least as great as that of the radiators and the pipework 9, 10, 11 together; and is preferably large enough to satisfy all the demands for heat by both the central heating and domestic hot water systems likely to be made during the period of the day when "off-peak" tariffs are not in operation. For this reason the tank 7 as shown in Figures 3 and 4 is comparatively large. Thus when the off-peak electricity becomes available, the immersion heaters 8 will be energised if and when the temperature of the water in the storage tank 7 is below the value to which the heater thermostat 36 is set.

The water capacity of the tank 7 should be such that, under normal conditions, the water therein is always sufficiently hot to enable domestic hot water to be available at all times at the taps 1 6.

The water in the cylinder 20 is heated by simple heat transfer, through the wall of the cylinder, from the main body of water in the tank 7.

The boiler 27 may be arranged in any convenient attitude or position, for example in an upright position so as to occupy as little floor or ground space as possible. The hot water cylinder 20 may be arranged vertically instead of horizontally. Provided the insulation 37 is adequate and satisfactory weatherproofing is provided, the boiler may be mounted outside the building.

Claims (9)

1. A wet central heating system (as hereinbefore defined), wherein the heating means is electrical.

2. A central heating system according to Claim 1, wherein the water vessel has a storage capacity whose volume is at least as great as that of the radiators and pipework together, whereby water heated in the vessel over one period of time can be used in the system at a later period.

3. A central heating system according to Claim 1 or Claim 2, wherein the water vessel is a thermally-insulated storage tank.

4. A central heating system according to any one of the preceding claims, wherein the heating means comprises at least one immersion heater in the water vessel.

5. A central heating system according to any one of the preceding claims, wherein the radiators are connected in loops of the pipework between a flow main and a return main, each loop having a thermostatically-controlled local valve responsive to ambient temperature for admitting hot water from the flow main and through the loop to the return main, the flow and return mains being connected to the water vessel.

6. A central heating system according to any one of the preceding claims, including a circulating pump arranged in the pipework for circulating water through the system.

7. A central heating system according to Claim 5, including a circulating pump arranged in the pipework for circulating water through the system, the pump being arranged to be energised whenever the thermostat associated with any one of the said local valves causes the said valve to open.

8. A central heating system according to any one of the preceding claims, in combination with a domestic hot water system comprising a hotwater cylinder, a source of feed water to said cylinder, and at least one hot water tap connected with an outlet of the cylinder, the cylinder being within the water vessel so that water in the cylinder is heated by indirect heat exchange with the electrically-heated water in the vessel.

9. A wet central heating system (as hereinbefore defined), constructed, arranged and adapted to operate substantially as hereinbefore described with reference to, and as illustrated in, the drawings hereof.