GB2425347A - An on-demand water heater as a heat source in a central heating circuit - Google Patents

Abstract

A heating system includes a gas-fired on-demand water heater 10 having a hot water outlet 11 and a cold water inlet 12. A hot water heating circuit 15,18 includes at least one radiator 16 and a pump 19 to cause water to circulate round the circuit. The water heater outlet 11 feeds hot water into the heating circuit and cooled return water from the circuit is supplied to the cold water inlet 12 of the heater. An electrically operated valve 17 is provided in the circuit to control the flow of water therearound. A hot water top 14 may be connected to the hot water outlet 17. A controller may be arranged to cause a period of operation of the heating system, once triggered, by opening the valve 17 and causing the pump 19 to run.

Description

HEATING SYSTEM

This invention relates to a heating system and in particular - though not exclusively - to a heating system for a relatively small space such as a cabin configured to provide welfare facilities for example on a construction or building site or at other places where temporary washroom, toilet or other facilities have to be provided.

The term "welfare facilities" is used herein to refer to such facilities as need be provided for workers on construction or building sites, as well as in other circumstances. Thus, in addition to simple hand-washing facilities, there normally would also be provided one or more toilets and urinals, perhaps a shower unit and maybe also cooking facilities. Further, the facilities may include an office or other open space, or perhaps just an open plan area for use as required. For convenience, all such facilities are hereinafter referred to simply as "welfare facilities".

This invention may be used for space heating areas other than temporary welfare facilities on construction sites. Despite this, it will hereinafter be described exclusively with reference to the provision of such facilities, but the invention is not to be regarded as limited thereto.

It is known to provide temporary welfare facilities within a cabin expressly manufactured for the purpose. It is also known to provide such facilities within a conventional cargo container, fitting out that container internally with the required equipment and also providing doors, windows and so on in the walls of the container. In either case, some form of heating must be provided, in order that the facilities are useable other than just in the summer months.

Many temporary welfare facilities cannot be connected to a mains electricity supply and so the power required for those facilities must be provided by batteries for lighting, and by gas, stored in cylinders, for hot water. Space heating is more of a problem, but can be achieved by a gas wall heater.

However, gas wall heaters installed in welfare facilities tend to lose their efficiency particularly as the servicing of such heaters may be somewhat intermittent. An alternative might be to provide diesel or petrol generators to run electrical heating devices but these are expensive and on developments close to housing, but there may be restrictions on running a generator more or less continuously, in view of the noise pollution.

This invention aims at addressing the problem of providing space heating within temporary welfare facilities, by using a typical on-demand water heater as is conventionally employed in such facilities, for the provision of hot water for washing purposes.

According to this invention, there is provided a heating system comprising a hot-water heating circuit including at least one radiator, a pump to cause water to circulate around the circuit, a gas-fired on- demand water heater having a cold water inlet and a hot water outlet and connected to feed hot water from the outlet into the heating circuit and to accept into the cold water inlet of the heater cooled return water from the circuit, an electrically-operated valve provided in the circuit to control the flow of water therearound, and a controller arranged to control operation of the electrically-operated valve.

It will be appreciated that in this invention, a conventional gas-fired on- demand water heater is employed in conjunction with a hot water heating circuit including at least one radiator in order to provide space heating. On-demand water heaters are well known and are normally supplied with cold water from a mains water supply or from a tank, using gravity feed or a pump. The cold water supply is connected to a cold water inlet of the heater and the hot water outlet of the heater is connected to one or more outlet taps. Opening a tap reduces the pressure at the heater hot water outlet which drop in pressure is detected by the heater and causes the heater to commence operation, initiating an ignition cycle. The heater is arranged so that the flow rate through the heater allows the water temperature at the outlet to be raised sufficiently, in real time without the need to store hot water remote from the heater.

In the heating system of this invention, a hot water heating circuit including at least one radiator and a circulation pump is connected to the heater, in series with an electrically-operated valve whereby opening of the valve causes a pressure drop at the outlet of the heater, whereby operation of the heater is commenced. Thus, whenever space heating is required, all that is needed is opening of the electrically-operated valve to permit water circulation to occur and the on-demand heater will then start to operate, so heating the water being circulated through the heater.

For many applications, it may be sufficient to have only one radiator in the heating circuit, though depending upon the size of the radiators and the capacity of the on-demand heater, two or even more radiators may be connected in series or in parallel, in the heating circuit.

For optimum operation and detection of the pressure drop on opening the electrically-operated valve, that valve should be disposed in the heating circuit between the hot water outlet of the water heater and the radiator, if there is a plurality of series-connected radiators, before the first radiator. The pump preferably is arranged between the cold water inlet of the heater and the radiator, or if there is a plurality of radiators, after the last radiator.

The on-demand water heater used in the heating system of this invention may still be employed to provide hot water to one or more taps, despite also providing space heating. For this purpose, there may be a cold water supply, such as a storage tank, connected to the cold water inlet of the heater. If the cold water is drawn from a tank, it is preferred that the cold water supply is connected to the heating circuit between the radiator (or the last radiator if there is a plurality of radiators) and the pump such that the pump will pump both water circulating round the heating circuit and water from the tank. If the cold water is drawn from a mains supply at an elevated pressure, it is preferred that the supply is connected to the cold water inlet of the heater, downstream of the pump.

In the heating system of this invention, the pump may be arranged to be continuously running, either whenever hot water may be required from a tap, or whenever the heating system is ready for use, whether or not hot water is being drawn or the heating system is in operation.

The controller may include a first timer to operate the electrically operated valve, which timer is arranged to set the duration of operation of the heating system, once triggered. The controller may further include a thermostat to detect the ambient temperature of the space being heated, the first timer commencing a period of operation of the heating system when the temperature detected by the thermostat falls below a pre-set value. Such a thermostat may be mounted remotely of the other components of the controller, and be connected thereto by a suitable electrical cable.

Preferably, the controller includes a second timer which is arranged to inhibit the first timer from commencing a further period of operation for a second pre-set period following the commencement of a first period of operation. This may be achieved by providing a relay controlled by the second timer and arranged to disconnect the thermostat from the first timer, for the further pre-set period timed by the second timer. This will ensure the heating system does not run continuously, or is not unnecessarily triggered by the thermostat.

By way of example only, one specific embodiment of heating system intended for use with a cabin providing welfare facilities on a building or construction site will now be described in detail, reference being made to the accompanying drawings, in which:- Figure 1 diagrammatically illustrates the components of the heating system; and Figure 2 is a diagram of the control circuit.

Referring initially to Figure 1, there is shown a gas-fired on-demand water heater 10 having a hot water outlet 11 and a cold water inlet 12, as is normally provided in a welfare facilities cabin for supplying hot water for hand washing. The heater has an internal gas burner connected to a source of bottled gas (not shown) and a flue arrangement (also not shown) for discharging flue gases to atmosphere. Within the heater, there is also a gas supply and ignition unit for controlling the supply of gas to the burner, and initiating an ignition sequence on detecting a drop in pressure at the hot water outlet 11. The unit also monitors safe operation of the heater.

Connected to the hot water outlet 11 is a pipe 13 leading to a hot water tap 14 in a conventional way. A further pipe 15 is connected to the pipe 13 and leads to a space heating radiator 16, a solenoid valve 17 being provided in further pipe 15. A return pipe 18 from the radiator 16 connects back to the cold water inlet 12 of the water heater 10, an electric pump 19 being provided in that pipe. In normal operation, the pump 19 is continuously running.

A cold water storage tank 21, vented to atmosphere, is provided at a suitable place in the welfare facilities, where it is protected from frost. A pipe 22 from that tank is connected to return pipe 18, upstream of the pump 19 so that cold water will be drawn from the tank 21 as required, by the pump 19, for supply to the water heater 10.

When there is a demand for hot water, the tap 14 is opened and this leads to a drop in pressure at the hot water outlet 11 of the heater. This is detected by the gas supply and ignition unit within the heater, so causing the commencement of the ignition cycle and the burning of gas to heat water passing though the heater. Water is drawn from the tank 21 by the pump 19 and is supplied to the tap 14 after being heated. When the tap is turned off, the pressure at the outlet 11 rises once more and so operation of the heater is stopped.

In the event that space heating is required, the solenoid valve 17 is opened by energising the coil of the solenoid, so permitting the pump 19 to cause circulation through the radiator 16, the return water from the radiator being supplied to the cold water inlet 12 of the heater. Opening the valve 17 also causes a pressure drop at the hot water outlet 11 which is detected by the gas supply and ignition unit, to cause operation of the heater whereby the water circulating through the radiator 16 and the heater 10 will be heated. Closing the solenoid valve 17 allows the pressure to rise at the hot water outlet 11, so shutting down operation of the heater until either the solenoid valve is operated once more or a hot water tap 14 is opened.

Figure 2 is a circuit diagram of a controller for the solenoid valve 17. The controller includes a first timer 24, a second timer 25 and a relay 26, these components being provided within a control box 27. Remotely of that control box 27 there is provided an adjustable room thermostat 28 connected to the relay 26 by a suitable cable. Power is supplied to the control circuit by cable 29, for example from an accumulator, the negative supply also being connected to the thermostat 28. The accumulator may be charged off-site, or a low capacity generator may be provided to re-charge lighting accumulators provided in the welfare facility.

The first timer 24 is connected to the solenoid valve 17, such that when the first timer has been triggered to start a timing interval, the solenoid of the valve 17 is energised, to open the valve. The period of timing of the first timer 24 may be pre-set to any suitable interval (such as five minutes), to define the duration of operation of the heating system.

The first timer 24 is triggered by a negative pulse at its input 31, derived from the thermostat 28. Thus, closing of the thermostat will trigger the first timer to commence a timed period of heating, so long as the relay 26 is closed.

Operation of the relay 26 is controlled by the second timer 25, also triggered by a negative pulse on its input 32 from the thermostat. The output of the second timer is supplied to the relay 26 such that the relay then opens, so inhibiting further triggering of the first timer 24 until the expiry of the period timed by the second timer 25. The period timed by the second timer 25 may typically be one hour, though it is adjustable to suit the circumstances.

Operation of the controller is monitored by a green LED 33 connected between the output of the first timer and the negative return, and a red LED 34 connected between the output of the second timer and the negative return.

Thus, when heating is occurring, both LEDs 33,34 will be illuminated but when a further period of heating is being inhibited by the second timer 25, only the red LED will be illuminated. The arrangement is such that continuous operation of the heating system is prevented so long as the period timed by the first timer 24 is less than the period timed by the second timer 25. Repeated triggering of the first timer 24 by the thermostat 28 is inhibited by the action of the second timer and relay 26.

The embodiment of heating system described above may be implemented at a relatively low cost since it uses an on-demand water heater which often is already provided in a welfare facility, for supplying hot water. The system is arranged so that consumption of gas and electricity is minimised, while providing a sufficient level of space heating for the facility.

Claims (15)

1. A heating system comprising a hot-water heating circuit including at least one radiator, a pump to cause water to circulate around the circuit, a gas-fired on-demand water heater having a cold water inlet and a hot water outlet and connected to feed hot water from the outlet into the heating circuit and to accept into the cold water inlet of the heater cooled return water from the circuit, an electrically-operated valve provided in the circuit to control the flow of water therearound, and a controller arranged to control operation of the electrically- operated valve.

2. A heating system as claimed in claim 1, wherein the on-demand water heater is automatically ignited on detecting a drop in water pressure at the hot water outlet, occurring on opening of the electrically-operated valve.

3. A heating system as claimed in claim 2, wherein the electricallyoperated valve is disposed in the heating circuit between the hot water outlet and the radiator or the first radiator if there is a plurality of radiators.

4. A heating system as claimed in any of the preceding claims, wherein the pump is arranged between the cold water inlet of the heater and the radiator or the last radiator if there is a plurality of radiators.

5. A heating system as claimed in any of the preceding claims, wherein there is provided a cold water storage tank arranged to supply cold water to the cold water inlet of the on-demand water heater.

6. A heating system as claimed in claim 4 and claim 5, wherein cold water storage tank is connected to the circuit between the pump and the radiator or the last radiator if there is a plurality of radiators. - 10-

7. A heating system as claimed claim 6, wherein there is provided at least one hot water tap, connected to the hot water outlet of the on- demand water heater.

8. A heating system as claimed in claim 7, wherein the pump is arranged to be continuously running whenever hot water may be required from the tap.

9. A heating system as claimed in any of the preceding claims, wherein the pump is arranged to be continuously running whenever the heating system is required for use.

10. A heating system as claimed in any of the preceding claims, wherein the controller includes a first timer to operate the electricallyoperated valve, which timer is arranged to set the duration of operation of the heating system, once triggered.

11. A heating system as claimed in claim 10, wherein the controller includes a thermostat to detect the ambient temperature and to trigger the first timer whereby a period of operation of the heating system is commenced when the temperature detected by the thermostat falls below a preset value.

12. A heating system as claimed in claim 11, wherein the controller includes a second timer which is arranged to inhibit the first timer from commencing a further period of operation for a further pre-set period after the commencement of a first period of operation.

13. A heating system as claimed in claim 12, wherein the controller includes a relay controlled by the second timer and arranged to disconnect the thermostat from the first timer for the further pre-set period timed by the second timer. -11 -

14. A heating system as claimed in any of the preceding claims, wherein the electrically-operated valve comprises a normally-closed solenoid valve which is opened on energisation of the solenoid.

15. A heating system as claimed in claim 1 and substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.