WATER HEATING SYSTEM

Field of the Invention

The invention relates to water heating systems.

The invention is applicable in theory to fluid heating systems generally and the term "water" in this specification is to be interpreted accordingly. In practical embodiments, however, the invention is especially readily applicable to hot water heating systems and will be described, by way of example only, with reference to one such system.

The State of The Art

Water heating systems in which water from a relatively low pressure closed-loop heated water circuit flows through a heat exchanger to heat either or both of a relatively high pressure mains cold water inflow, and a heated water consumer such as a radiator or a shower, are known.

Such systems will be referred to in this specification as (a) system(s) of the kind in question.

In such a system, the water flowing round the closed-loop heated water circuit is usually pumped and the heat is provided by a boiler, the output of whose heating coil is fed to a

water storage tank. The mains cold water circuit, by contrast, enters at the relatively high mains-fed pressure. Solenoid valves sense when hot water is needed by the mains circuit and divert the flow from the storage tank appropriately through a heat exchanger - through which the mains cold water circuit also passes to be indirectly heated. In the summer months, when demands from radiators for example, may be non-existent, the valves divert the heated water from the boiler- and -pump driven low pressure closed-loop circuit wholly through the heat exchanger when demand is sensed from the mains. In the winter, the boiler via its storage tank must supply both the radiator circuit and the mains hot water demands.

A known drawback of these systems of the kind in question is the need to maintain a relatively and wastefully large volume of water in the storage tank for large parts of the time. In the summer months, again, for example the need for hot mains-fed water at the taps which fill bath or basin may be the only demand on the system; and that demand may arise only in the early morning (when the inhabitants wash before going out) and again in the relatively late evening (when the washing-up needs to be done after dinner). Yet the storage tank has to be heated, for both of these, throughout its whole volume to a high temperature. If the tank is a large one, as is often the case in houses with large families, the surplus will be wasted.

The problem to be overcome is therefore how to mitigate this inefficiency in systems of the kind in question whilst ensuring the continuity of relatively readily available hot water throughout the normal waking day to heated water consumers (such as radiators and showers) and mains hot water users (such as baths and basins).

Relevant Prior Proposal

Patent specification number GB2353506 (Dedicated Pressure Systems Limited) discloses a system of the kind in question in which a flow sensing switch, provided in the mains pressure water circuit of a heat exchanger, detects a demand from the mains supply for hot water and operates to divert heated water from the relatively low pressure circuit to the heat exchanger to provide the demanded supply. When demand ceases, the flow from the low pressure circuit into the heat exchanger is automatically stopped.

This goes some way into obviating the need for a large volume of water in a storage tank to be kept continually hot to supply intermittent needs of baths or basins in the building serviced by the system. But it still lacks thermal efficiency in absolute terms. In the current age in which we live, demands to maximise thermal efficiency are becoming intense. The system of patent specification GB2353506 goes only part of the way to satisfying these demands.

Summary of the Invention

A water heating system according to the invention differs from that shown in patent specification GB2353506 in that water from the relatively low pressure closed-loop heated water circuit always flows through the heat exchanger; and/or always flows first through the heat exchanger before supplying any of the heated water consumers such as radiators, showers etc.

In another, independent, broad aspect the invention comprises the incorporation into a system of the kind in question of one or more flow restrictors in the high pressure mains entry to the heat exchanger circuit at or adjacent the point where the infeed flow enters the heat exchanger matrix.

These independent aspects of the invention may be combined but are clearly so linked as to form part of the same inventive concept, namely, the provision of means to increase the thermal efficiency of a system of the kind in question by positive structural modification.

Where one or more flow restrictors is incorporated then the or each such restrictor may be inserted into the flow line in the form of a collar with essentially no function other than to restrict the flow through the bore of the collar by a single predetermined amount dictated by the collar bore size. Such an insert is therefore distinguished from, for example, known flow line valves which have an essential function of diverting flow and/or incrementally increasing or decreasing it and whose flow restricting effect is incidental to that primary function.

Preferably in any system embodying the invention, there is provided a plurality of heat exchangers, one or some at least of which are plate heat exchangers, operating in parallel.

In the instance just outlined, preferably both or all the heat exchangers are plate heat exchangers.

Each of these last-mentioned possibilities, whether used alone or together, again goes to increasing the thermal efficiency of the system.

The invention includes within its scope a water heating system substantially as herein described with reference to and/or as illustrated in any appropriate combination of the accompanying text and all but Figure 1 of the accompanying drawings.

Once such system will now be described with reference to those drawings and, whilst it is by way of example only, it is at this current undisclosed stage the best way known to the Applicant of putting the invention into practice.

Brief Description of the Drawings

Figure 1 shows the general form of a known system of the kind in question.

Figure 2, again in diagrammatic form, shows a system embodying the invention.

Figure 3 shows the valving arrangements around a heat exchanger in such a system.

Figures 4 and 5 show parallel-operating plate heat exchanger arrangements in the system.

Figures 6 and 7 illustrate different forms of flow restrictors used in the system.

Description of the Preferred Embodiment

In the generally known water heating system illustrated diagrammatically in Figure 1, a gas-fed or oil-fed boiler 11 heats the tubular coil 12 incorporated within it and a pump 13 sends the water from within the coil 12 around a relatively low pressure closed-loop system to feed one or more heat consumers in the form of radiators 14 and, alternatively

or additionally, as dictated by a three-way diverter valve 15, a heat exchanger 16 before the heated water is returned to the boiler 11.

When the sole or primary demand on this closed loop is heated from the central heating system incorporating the radiators 14, the valve 15 prohibits any supply to the heat exchanger 16. By contrast, when the relatively high pressure mains cold water infeed 17 demands a supply of hot water to the bath taps or basin taps in the building serviced by the system, the valve 15 cuts off supply to the radiators 14 and shunts the hot water from the boiler through the heat exchanger 16 before returning it to the boiler, and the mains water supply 17 is heated indirectly via the heat exchanger.

When the heated water consuming radiators 14 and the mains supply 17 simultaneously demand a supply of heated water, the valve 15 will divert heated water from the boiler to the one and to the other, selectively, as dictated by the action of temperature sensors in a known manner.

Because of the need to keep a relatively large volume of heated water readily available, a water storage tank 18 is incorporated into the low pressure closed-loop heated water circuit. As shown, the tank 18 is a conventional tank of the kind familiar from domestic practice. Equally conventionally, it will incorporate one or more electric thermostat- governed heaters to augment the heated water supply from the boiler 1 1 itself. The well known currently branded "Economy 7" tanks show just how large these water storage tanks 18 can be in practice.

In the system of Figure 2, by contrast, the heated water outflow from the boiler goes first through the heat exchanger, through which the high pressure mains cold water circuit also flows, before supplying any of the heated water consumers such as the radiators 14. Again an automatically activated temperature-sensing-driven diverter valve is used but which ever way the valve operates, it cannot shunt the heated water flow past the heat exchanger. The flow must at all times go first through the heat exchanger before proceeding, either via a direct return to the boiler, or to the radiators or showers served by the system.

In the figure 2 system there is therefore no need for a large water storage tank of the kind shown as tank 18 in Figure 1.

Plate heat exchangers are known for systems of the kind in question and the Figure 2 system, whilst illustrating diagrammatically only one such heat exchanger, in fact uses several of them plumbed to operate in parallel. Figure 3 shows the valving arrangements and its text makes the Figure self-explanatory. Figures 4 and 5 show how a bank of several plate heat exchangers is arranged and, whilst each of these plate heat exchangers has a designed flow rate of water to be heated at a given heating input temperature, by reducing the flow rate through the heat exchanger, a greater temperature rise is achieved.

A plate heat exchanger designed to pass, for example, 15 litres per minute at an input temperature of 80 ^° C will give a 35 ^° C temperature rise. Reducing the flow rate to, say, 6 litres per minute will achieve a temperature rise of 50 ^° C. With an ordinary unrestricted designed flow rate through the heat exchanger, an 80 ^° C heated water input will suffer a 20 ^° C drop across the heat exchanger as it exits. By reducing the flow rate as above the temperature drop will reduce and the infeed temperature to the heat exchanger can be reduced to, say, 70 ^° C.

Figures 6 and 7 show various forms that the flow restrictors might take. Again the text in these figures makes the construction self-explanatory. Each of them is designed to be fitted immediately adjacent the point of entry of the water flow to the heat exchanger. All of them have only one essential function, namely, to restrict the infeed flow rate and no other primary function. Each is designed to be retro-fitted to the existing pipework of a conventional system which is to be modified to operate in accordance with the invention, although ideally a system embodying the invention would have its plate heat exchanger fittings made specifically to suit the ready adoption of one or more of these flow restrictors.