Non-mechanical HIU using flow sensor to open primary valve, June 2000
1. A water heating system having a heat source with a heated water feed to a consuming means and a return flow back to the heat source, characterised by a heat exchange unit having an inlet for mains pressure water feed to, and through, a heat exchange matrix and thence to an outlet for hot water supply at mains pressure, the heat exchange matrix being fed, for indirect heating of the mains water, through a heating water feed connected with the heated water feed and a heating water return connected with the heat source return flow, a flow sensing switch being provided in the mains pressure water circuit of the heat exchanger and connected so as to open a valve means in the heat source heating water circuit to the heat exchanger when flow is sensed in the mains pressure supply and to close said valve on the flow being interrupted.
2. A water heating system in accordance with claim 1, wherein the heat source comprises a boiler with a heated water feed to a central heating system or to hot water tank.
3. A water heating system in accordance with claim 1 or 2, incorporated into an existing hot water supply system having a low pressure circuit, for example one fed from a water storage tank, or one feeding a central heating system, and arranged to supply a direct mains hot water supply for a shower or the like on demand.
4. A water heating system in accordance with any preceding claim, wherein the valve means comprises a solenoid valve in the boiler return feed to the heat exchanger operating without interruption to the existing boiler circuit.
5. A water heating system in accordance with claim 4; wherein the valve is a three port solenoid valve which may selectively switch the boiler hot water feed to the heat exchanger or to the existing boiler hot water circuit thus temporarily cutting out the heating system to allow the boiler to supply the hot water circuit exclusively.
6. A water heating system as described herein and exemplified with a reference to the drawings.