GB2129581A

GB2129581A - Central heating systems

Info

Publication number: GB2129581A
Application number: GB08327485A
Authority: GB
Inventors: Barrington James Waring
Original assignee: Bass PLC
Current assignee: Bass PLC
Priority date: 1982-10-13
Filing date: 1983-10-13
Publication date: 1984-05-16
Also published as: GB8327485D0

Abstract

A central heating system includes a water heater (1) having a primary thermostat (30) which normally operates to maintain the heated water at a working temperature. The system also includes radiators (24) in heating circuits (17 to 22) for heating associated zones (4 to 9), and a calorifier (2) in another heating circuit (23) for heating water in a tank (3). The flow of water in each heating circuit is controlled by an associated valve (25) which (in the absence of an over- ride signal) can open only when an associated time clock (10 to 13) permits it and is then under the control of an associated thermostat (26, 27). When all the valves are closed the primary thermostat ceases to maintain the water in the heater at its working temperature, thereby enabling heat energy to be saved. The circulating pump (16) is also turned off. The temperature of the water in the heater may be maintained above ambient temperature to reduce delay in returning to normal operation. <IMAGE>

Description

SPECIFICATION Central heating systems This invention relates to central heating systems and has been developed largely in connection with central heating systems for use in licensed premises, although it is not restricted to systems for that particular purpose.

One known type of central heating system, for domestic use, comprises a water heater (often referred to as a "boiler" although it does not boil the water) operative in use to burn gas or oil so as to heat water, and a circulating pump, operative in use to circulate heated water from the water heater around a circuit or circuits containing radiators. That type of system usually includes a time clock operative to permit operation of the water heater and circulating pump only during certain predetermined periods, and a temperature-sensitive device (often referred to as a "thermostat") operative to stop the circulating pump, or to prevent its operation, when it senses an ambient temperature greater than a predetermined temperature.The system may also include a calorifier operative to heat water in a hot water tank which can then be drawn off for use, the water for the calorifier being supplied from the water heater by gravitational circulation. A commonly used kind of calorifier comprises a coiled tube through which hot water is passed, the coiled tube being housed inside the hot water tank. A second time clock (or separate electrical contacts on the first-mentioned time clock, for the radiator system) may enable the water heater to operate at times when the first-mentioned time clock prevents operation of the circulating pump, this arrangement enabling hot water to circulate through the calorifier without it circulating through the radiators.Finally, the system usually includes an internal thermostat operative to prevent operation of the water heater when the temperature of the water inside the water heater exceeds a predetermined value. This enables the water in the water heater to be maintained at a relatively high temperature, even when water is not being withdrawn from the water heater.

While such a system is often quite satisfactory for domestic use, it would normally require modification to make it suitable for use in larger premises and premises that are used for purposes other than wholly domestic purposes. In licenced premises, for example, there may well be areas or zones of the premises that need to be heated to different extents at different periods. Thus, there may be accommodation for the licensee needing to be heated in the same way as normal domestic premises, and public rooms, such as bars, restaurants, meeting rooms and games rooms, that need to be heated only at certain periods, those periods being different from those during which licensee's accommodation needs to be heated (it being understood that the periods, although different, may overlap one another). There may also be a call for relatively large quantities of hot water for use in washing-up.

A system capable of satisfying those needs clearly requires more complex controls than those of a simple domestic system, and also requires a relatively large water heater, that is a heater capable of heating relatively large quantities of water to a predetermined temperature per unit time.

An aim of the present invention is to provide a system for that purpose or for a similar purpose, but which is capable of being operated in such a manner as to avoid undue wastage of heat.

According to the present invention there is provided a central heating system comprising a water heater incorporating a primary thermostat which, when operative, serves to control the heater so that the temperature of the water in the heater remains within a range of working temperatures, a plurality of water circuits containing space-heating means through which water from the water heater can flow, the circuits including valves which can be opened and closed, to permit and prevent the flow of hot water therethrough, in response to control signals received from one or more time clocks and from one or more secondary thermostats which, when operative, serve to assist in stabilizing the ambient temperature, the arrangement being such that when said control signals, and signals from any other relevant devices, indicate that there is at that time no requirement for hot water from the water heater, the primary thermostat is rendered inoperative (in the absence of any overriding signal) so that the temperature of the water in the water heater can fall below said working range of temperatures.

When the system is in use, but all the valves are closed, the water heater normally ceases to heat the water, so that the loss of heat from the water heater itself is thereby reduced.

In addition to the water circuits containing space-heating means, there is preferably at least one additional circuit containing a calorifier disposed in a hot water tank. This additional circuit is preferably provided with a valve which can be opened and closed, to permit and prevent the flow of water therethrough, in response to control signals received from the time clock, or from a time clock, and from a secondary thermostat which, when operative, serves to assist in stabilizing the temperature of the hot water in the tank, these control signals constituting signals from another relevant device or from other relevant devices as referred to above.

There are preferably two or more time clocks each with at least one switch or there is a single time clock with more than one switch, each switch being associated with a different valve or group of valves. With this arrangement different valves can be rendered inoperative, so that they cannot open, during different off periods, as determined by the setting of the clock or the associated clock.

Where one switch is associated with a plurality of valves, those valves may be sub-divided into two or more groups, each associated with a different secondary thermostat.

The space-heating means in each of the circuits that contains space-heating means comprises a radiator or radiators.

The system may include intermediate-temperature means such that in use when the primary thermostat is inoperative the water in the water heater is maintained at or near an intermediate temperature, which is above ambient temperature but is below said range of working temperatures. The intermediate-temperature means may comprise a tertiary thermostat. Alternatively the intermediate-temperature means is operative to keep heating means for heating the water in the water heater operative but at a lower heat output than that at which it operates when the primary thermostat is operative.

The system may include control apparatus operative to modify the operation of the time clock or time clocks or the control signals therefrom so as to compensate at least partially for changes in the outside temperature, whereby in use when the outside temperature falls an increased period of time is set for enabling the ambient temperature to reach the value determined by the secondary thermostat or thermostats. The term outside temperature is used herein to denote the temperature of the neighbourhood surrounding that space heated by the space-heating means or a relevant part of the space-heating means.

The system may include frost-damage-prevention means operative in use, when the outside temperature falls to a predetermined cool value, firstly to open at least some of said valves, if those valves are not already open, and to cause water to be circulated through the water circuits associated with those valves, and secondly to cause the water in the water heater to be heated if the temperature thereof falls below or has fallen below a predetermined value. Alternatively the system may include frost-damage-prevention means operative in use, when the ambient temperature falls to a predetermined cool value, to open at least some of said valves and to bring the water heater into operation (if it is not already in operation) whereby the ambient temperature is prevented from falling to a value substantially lower than said cool value.

An embodiment of the present invention will now be described in more detail, by way of example only, and with reference to the accompanying drawings which is a schematic plan of a central heating system embodying the present invention and the preferred features thereof outlined above.

The central heating system illustrated is installed in licenced premises including a flat for the accommodation of the licensee, three bars that are open to the public during licensing hours only and a restaurant that is open to the public only during periods that are different from but overlap with the licensing hours.

Each of these three main areas, that is the flat, the bars and the restaurant, contains radiators through which hot water can be circulated to heat those areas. There is a single water heater 1, which may be gas-fired or oil-fired, to supply hot water for the radiators and for a calorifier 2 disposed in a hotwater cylinder 3. The water heater may be a relatively large one, and may for example be rated at 250 K Btu./hr. Hot water drawn from the cylinder can be used for domestic purposes in the flat and for washing-up glasses from the bars and dishes and cutlery etc. from the restaurant. Some of the main areas referred to above are subdivided into separate heating zones. For example the flat may be divided into two zones 4 and 5, one, 4, comprising the rooms used mainly during the day and the other, 5, comprising the bedrooms.Each of the three bars may comprise a separate zone 6, 7 and 8, but the restaurant may constitute a single zone 9.

The system incorporates four time clocks 10, 11, 12 and 1 3. Each of the three main areas referred to above has a different one of the clocks 10, 11 and 1 2 associated with it, while the fourth time clock 1 3 is associated with the calorifier. Each of the clocks can be set to close an associated electric switch for an appropriate period or periods during each day. Thus the clock 10 associated with the flat may close its switch during those periods when room-heating would normally be required, that is for a period around breakfasttime and a period in the late afternoon and evening.The clocks 11 and 1 2 associated with the bars and restaurant respectively may be set to close their switches during those periods when those rooms are likely to be occupied by the public and for a short while before those periods. The clock 1 3 associated with the calorifier may be set to close its switch for much of each day, as hot water will probably be required at frequent intervals from early in the morning until late at night.

The water heater 1 has a hot water outlet pipe 1 4 and an inlet pipe 1 5 for cooled water returning from the remainder of the system.

An electrically-powered circulating pump 1 6 is disposed in the water inlet pipe 1 5. Seven water circuits, 1 7 to 23, lead from the hot water outlet pipe 14 back to the inlet pipe 1 5.

The circuits are arranged in parallel. One circuit, 23, contains the calorifier, while each of the others contains radiators 24. Each of the circuits 1 7 to 22 extends through an associated one of the zones referred to above, and in use the radiators in the circuit heat the associated zone.

Each circuit has a separate electrically-operable valve 25, which controls the flow of hot water through the circuit and can be moved between an open position and a closed position. At a suitable location in each zone there is a secondary thermostat 26 comprising an electric switch which opens only when the ambient temperature in the zone exceeds a predetermined, set value. That value can be altered, as desired, by manual operation of a setting knob (not shown) which carries a pointer co-operating with a scale of temperatures.

The hot water cylinder 3 also contains an electric thermostat 27 switch which opens when the water temperature exceeds a predetermined value and closes again when the water temperature falls somewhat below that value. This again constitutes a secondary thermostat. The valve 25 for each circuit is controlled both by the switch of the associated thermostat 26, 27 and the associated one of the time clocks 10 to 13, the arrangement being such that the valve opens only on occasions when the switch of the associated thermostat is closed and also the switch of the associated time clock is closed. In all other states of those two switches the valve is closed.

The water heater 1 is fired by a burner 28 which can be lit and extinguished automatically by a burner control 29. The heater contains a primary thermostat 30 which, when operative, serves to maintain the water in the heater within a range of working temperatures. The thermostat 30, however, is rendered operative only when there is a requirement for hot water. This requirement is signalled to the thermostat by the same signals that open the valves 25. Therefore, if no valve is open the thermostat is inoperative; if any one or more of the valves is open the thermostat 30 becomes operative. Furthermore, the arrangement is such that when all the valves 25 are closed, the circulating pump 1 6 is also switched off, the re-opening of any one or more of the valves causing the pump to start operation again.The consequence of this arrangement is that when there is no requirement for hot water the temperature of the water in the water heater 1 is not maintained within the range of working temperatures but can fall below that range. Experiments have shown that this can lead to a significant saving in fuel.

If the water in the heater 1 is relatively cold, and one or more of the valves 25 is then opened, the burner control 29 causes the burner 28 to be lit and the water to be heated. It is believed that the slight delay that necessarily occurs before hot water can pass through the water circuit or circuits concerned is likely to be acceptable. If desired, this may be partially avoided by appropriate adjustment of the time clocks 10 to 1 3 and/or the secondary thermostats 26 and 27. Alternatively, or in addition, the water heater may be so arranged that when the primary thermostat 30 is inoperative, the water in the water heater 1 is maintained at or near an intermediate temperature, which is above ambient temperature but is below the range of working temperatures at which it is maintained when the primary thermostat 30 is operative.The water can be maintained at an intermediate temperature either by means of a tertiary thermostat (not shown) in the water heater 1 or by keeping the burner or part of the burner alight but with a relatively low heat output. By employing a tertiary thermostat or maintaining combustion with a low heat output, the temperature of the water starting to circulate when any of the valves 25 re-opens is initially higher than the ambient temperature, and the temperature of the water will therefore return to within the operating range more quickly than would otherwise be the case.

Other controls of known kinds may also be included in the system. For example there may be control apparatus (not shown) which is associated with one or more of the time clocks 10 to 1 3 and in effect adjusts the time at which the clock switch or each clock switch is closed in accordance with the temperature outside the building in which the system is installed. The apparatus may include a thermosensitive device mounted in a suitable position outside the building or in a part of the building of which the temperature varies with the ambient temperature outside the building.

The arrangement is such that when the ambient temperature outside the building is relatively low, at least one of the clock switches is closed, to enable the associated valve or valves to be opened, at a time somewhat earlier than would be the case if the ambient temperature outside the building were higher.

With this arrangement, it is possible for the ambient temperature in any of the zones 4 to 9 to be brought up to substantially the desired temperature at the same hour or hours each day, substantially independently of the ambient temperature outside the building. Alternatively, or in addition, use may be made of similar apparatus operative to modify the time or times at which at least one of the clock switches opens, in a manner dependent on the ambient temperature outside the building, the arrangement being such that the associated valves close and the radiators 24 in any of the zones 4 to 9 can cease to receive hot water at a time or times such that the ambient temperature within the associated zone or zones remains above a predetermined acceptable value until the same hour each day, substantially independently of the ambient temperature outside the building.

Another form of control apparatus that may be included in the system is intended to prevent frost damage. It, too, includes a thermosensitive device outside the building.

When it detects a temperature of as low as about 1 "C it gives rise to an overriding signal which causes all the valves 25 to open, except the valve in the circuit containing the calorifier 2, and the circulating pump 1 6 to operate. This redistributes heat within the system. The overriding signal also causes the burner control 29 to light the burner 28 and heat the water as soon as the temperature of the water returning through the inlet pipe 1 5 falls to 1 0'C. The burner remains alight until the temperature of the returning water reaches 15"C.

An alternative form of control apparatus that may be included in the system with a view to preventing frost damage comprises a plurality of frost thermostats, there being one such thermostat for each zone in the system.

Each frost thermostat comprises a temperature-sensitive device positioned in the zone but preferably in or near the coolest part of the zone, such as on a north-facing wall near a window or door. Each device is set to generate a control signal, as by opening or closing an electric switch, for example, when the temperature it senses falls to a predetermined cool value such as 5"C. The control signal is operative to open the valve associated with that zone (assuming of course that the value was previously closed). The opening of any valve, as before, initiates the normal operation of the water heater if the heater is not already in operation. Thereafter the frostthermostat or each frost-thermostat operates to maintain the ambient temperature in its associated zone substantially equal to said cool value.

Almost the entire system described above can be assembled from existing devices.

While it would doubtless be possible to provide a micro-processor-based control, it is believed preferable at present to use more robust electro-mechanical devices of existing, well-tried kinds.

It is to be understood that the central heating system illustrated may be modified in many ways while remaining within the scope of the present invention. Thus, the number of time clocks may be increased or reduced. For example there may be only three time clocks, one for the calorifier circuit, a second for one group of central heating circuits and a third for another group of central heating circuits.

Claims

1. A central heating system comprising a water heater incorporating a primary thermostat which, when operative, serves to control the heater so that the temperature of the water in the heater remains within a range of working temperatures, a plurality of water circuits containing space-heating means through which water from the water heater can flow, the circuits including valves which can be opened and closed, to permit and prevent the flow of hot water therethrough, in response to control signals received from one or more time clocks and from one or more secondary thermostats which, when operative, serve to assist in stabilizing the ambient temperature, the arrangement being such that when said control signals, and signals from any other relevant devices, indicate that there is at that time no requirement for hot water from the water heater, the primary thermostat is rendered inoperative (in the absence of any overriding signal) so that the temperature of the water in the water heater can fall below said working range of temperatures.

2. A central heating system according to claim 1 in which there is at least one additional circuit containing a calorifier disposed in a hot water tank.

3. A central heating system according to claim 2 in which said additional circuit is provided with a valve which can be opened and closed, to permit and prevent the flow of water therethrough, in response to control signals received from the time clock, or from a time clock, and from a secondary thermostat which, when operative, serves to assist in stabilizing the temperature of the hot water in the tank, these control signals constituting signals from another relevant device or from other relevant devices.

4. A central heating system according to any one of the preceding claims in which there are two or more time clocks each with at least one switch or there is a single time clock with more than one switch, each switch being associated with a different valve or group of valves.

5. A central heating system according to any one of the preceding claims in which there are may be sub-divided into two or more groups, each associated with a different secondary thermostat.

6. A central heating system according to any one of the preceding claims in which the space-heating means in each circuit that contains space-heating means comprise a radiator or radiators.

7. A central heating system according to any one of the preceding claims in which there is intermediate-temperature means such that in use when the primary thermostat is inoperative the water in the water heater is maintained at or near an intermediate temperature, which is above ambient temperature but is below said range of working temperatures.

8. A central heating system according to claim 7 in which the intermediate-temperature means comprises a tertiary thermostat.

9. A central heating system according to claim 7 in which the intermediate-temperature means is operative to keep heating means for heating the water in the water heater operative but at a lower heat output than that at which it operates when the primary thermostat is operative.

10. A central heating system according to any one of the preceding claims in which there is control apparatus operative to modify the operation of the time clock or time clocks or the contol signals therefrom so as to compensate at least partially for changes in the outside temperature, whereby in use when the outside temperature falls an increased period of time is set for enabling the ambient temperature to reach the value determined by the secondary thermostat or thermostats.

11. A central heating system according to any one of the preceding claims in which there is frost-damage-prevention means operative in use, when the outside temperature falls to a predetermined cool value, firstly to open at least some of said valves, if those valves are not already open, and to cause water to be circulated through the water circuits associated with those valves, and secondly to cause the water in the water heater to be heated if the temperature thereof falls below or has fallen below a predetermined value.

1 2. A central heating system according to any one of claims 1 to 10 in which there is frost-damage-prevention means operative in use, when the ambient temperature falls to a predetermined cool value, to open at least some of said valves and to bring the water heater into operation (if it is not already in operation) whereby the ambient temperature is prevented from falling to a value substantially lower than said cool value.

1 3. A central heating system substantially as hereinbefore described with reference to the accompanying drawing.