GB2255161A - Heating system - Google Patents

Abstract

A heating system for domestic hot water comprises a thermostatically controlled boiler (2) provided with flow and return connections (R, F) for the passage therethrough of primary water, a thermal store (6) including a water-containing volume having an inlet connected to the flow connection (R) of the boiler (2) and an outlet connected to the return connection (F) of the boiler (2), and a heat exchanger (10, 12) housed within the thermal store (6) and through which passes secondary water to be heated by heat exchange from the primary water. The boiler thermostat (4) monitors the temperature of the water at or adjacent the return connection (F) of the boiler (2) such that activation of the boiler (2) is under the control of the thermal store thermostat or the temperature of the primary water returning to the boiler (2) from the thermal store (6). As shown the normal flow and return boiler connections are interchanged so that the thermostat (4) senses the return water flow. The thermal store has central heating and store thermostat 22 and 20, the latter being set to operate at the same temperature (82 DEG C) as the boiler thermostat. <IMAGE>

Description

HEATING SYSTEM The present invention relates to heating systems and more particularly to domestic hot water systems incorporating thermal stores.

Thermal stores are becoming increasingly popular in relatively small domestic dwellings where there is a requirement for a supply of instantaneous domestic hot water at mains pressure and s central heating function.

Heating systems incorporating thermal stores commonly comprise a boiler arranged to heat primary water which is supplied to the store from where it returns to the boiler either directly or, if the associated central heating is on, via the radiators.

The thermal store houses interconnected coiled tube heat exchangers, cold water from the mains being fed through the heat exchangers and to the taps whereby hot water at mains pressure can be provided on demand.

In order to achieve a satisfactory hot water draw-off performance, the temperature of the primary water in the thermal store must be maintained at more than 7O0C, and this requirement is causing some problems in existing arrangements.

More particularly, the maximum permissible setting for the boiler thermostat is 820C, this thermostat normally being located adjacent the boiler flow connection. Even with the boiler thermostat at its highest setting, the temperature of the primary water in the thermal store cannot be more than the boiler return temperature at any time during the boiler cycle.

The boiler flow and return temperatures will vary depending upon the temperature rise across the boiler, this rise being dependent upon, for example, the boiler output, the diameter of the interconnecting pipework, the distance between the thermal store and the boiler, the pump performance and the pipework resistance.

These factors are all variable and are out of the control of the thermal store manufacturer.

Generally, the boiler temperature rise varies between 0 0 and 20 C which means that, in a system running on boiler controls only, the thermal store temperature can vary between 620C and 760C at the highest.

Most thermal stores are fitted with associated thermostats to prevent the boiler cycling when the store is satisfied. However, if this thermostat has a higher switch off setting than the boiler, the boiler is unable to satisfy the heat demand at the thermal store, causing the boiler wastefully to heat and cool both itself and the store without the temperature of the primary water in the store being able to exceed the return temperature at the boiler.

The thermal store thermostat must therefore take control over the boiler thermostat at all times to prevent this unnecessary boiler cycling. As all thermostats have a manufacturing tolerance of +/- 3 0C, the thermal store manufactures must set their thermostats to switch off at between 560C and 700 to ensure trouble free operation.

Thus, with the thermal store thermostat set to switch off at 56 0C and 700, the temperature range of the primary water in the thermal store will vary between 560C and 70 C.

Clearly the upper and lower limits of this range could be increased by increasing the setting of the boiler thermostat to, for example, 88 0C. However, this would render the boiler unapproved and therefore is not a viable solution to the problem.

It would be desirable to be able to provide a heating system incorporating a thermal store capable of heating the primary water therein reliably to a temperature above that associated with existing arrangements but without contravening current regulations.

According to the present invention there is provided a heating system comprising a thermostatically controlled boiler provided with flow and return connections for the passage therethrough of primary water, and a thermal store including a water-containing volume therein provided with an inlet connected to the flow connection of the boiler and an outlet connected to the return connection of the boiler, said water-containing volume of the thermal store housing therein a heat exchanger for passage therethrough of secondary water to be heated by heat exchange from the primary water, characterised in that the boiler thermostat monitors the temperature of water at or adjacent the return connection of the boiler whereby activation of the boiler is controlled in accordance with the temperature of the primary water returning to the boiler from the thermal store.

It will thus be appreciated that the provision of a legally-acceptable boiler thermostat enables the temperature of the primary water returning from the thermal store to be up to 82 0C, whereby water in the thermal store can be maintained up to this value.

Conveniently the thermal store incorporates a thermostat, both the boiler thermostat and the thermal store thermostat being arranged to switch on at 68 0C and to switch off at the maximum permissible level of 820C. Such an arrangement achieves a temperature of the primary water in the thermal store of, typically, 78 0C without the possibility of the boiler thermostat switching off before the desired temperature is reached.

In one embodiment of the invention, the heating system incorporates a boiler of conventional construction with the thermostat located at or adjacent the flow connection, the flow and return connections to the boiler being reversed.

In an alternative embodiment of the invention, the thermostat is located at or adjacent the conventional return connection of the boiler.

By way of example only, an embodiment of the invention will now be described in greater detail with reference to the accompanying drawings of which Figs. 1 and 2 show a heating system according to the invention in two different modes.

Referring to the drawings, the system incorporates a conventional, thermostatically-controlled boiler 2, but in which the flow and return connections F and R have been reversed, the boiler including a thermostat 4 located adjacent the F connection and monitoring the temperature of the primary water returning to the boiler 2.

The primary water flows from the boiler 2 to a thermal store indicated generally at 6 and including a restricted compartment 8 therein from which the primary water can flow over coiled tube heat exchangers 10,12 and back to the boiler 2.

Pumps 14 and 15 and non-return valves 16 and 17 are provided for directing heated primary water from the compartment 8 either to the boiler 2 as shown in Fig. 1 or through radiators 18 prior to return to the boiler 2 as shown in Fig. 2.

The system further incorporates a thermal store thermostat 20 and a central heating thermostat 22. The thermostats 4 and 20 are both arranged to switch on at 68 0C (although this value can be varied to suit particular requirements) and to switch off at 82 0C thereby allowing the thermal store to achieve a temperature of around 76 0C and more without any possibility of the boiler thermostat 4 switching off first as occurs in conventional systems, while the central heating thermostat 22 is also arranged to switch off at 82 C.

The system of Fig. 1 is shown with the programmer P set to demand domestic hot water with the central heating on.

Primary hot water flows from the R connection of the boiler 2 to the thermal store 6, through the compartment 8, over the heat exchangers 10,12 and back to the F connection of the boiler via the non-return valve 17 which is open, thus heating mains cold water contained within the heat exchangers 10,12, said cold water being supplied from a mains source 24 and being available at a domestic hot water tap 26. The non-return valve 16 is closed and the pump 14 is switched off while the pump 15 is on.

Even though the central heating associated with the system is calling, the arrangement is such that heating of the thermal store 6 takes priority over central heating.

Clearly this arrangement can be altered to suit particular requirements with the central heating taking priority if desired.

On turning on the tap 26, hot water at mains pressure is drawn off via heat exchangers 10 and 12, and heated primary water continues to flow through the thermal store 6 to recover the temperature within the thermal store which continues to take priority over the central heating.

Fig. 2 shows the system of Fig. 1 with the thermal store satisfied and with the central heating calling, in which case the heated primary water from the boiler flows to the compartment 8 within the thermal store 6 and thence to the radiators 18 and back to the boiler 2. The pump 14 is now on, the non-return valve 14 is open, the pump 15 is off and the non-return valve 16 is closed.

Thus the described system enables heating of primary water to a temperature above that associated with existing arrangements without contravening current regulations.

Claims (5)

1. A heating system comprising a thermostatically controlled boiler provided with flow and return connections for the passage therethrough of primary water, and a thermal store including a water-containing volume therein provided with an inlet connected to the flow connection of the boiler and an outlet connected to the return connection of the boiler, said water-containing volume of the thermal store housing therein a heat exchanger for passage therethrough of secondary water to be heated by heat exchange from the primary water, characterised in that the boiler thermostat monitors the temperature of water at or adjacent the return connection of the boiler whereby activation of the boiler is controlled in accordance with the temperature of the primary water returning to the boiler from the thermal store.

2. A heating system as claimed in claim 1 in which the thermal store incorporates a thermostat, both the boiler thermostat and the thermal store thermostat being arranged to switch on at 680C and to switch off at 82 C.

3. A heating system as claimed in claims 1 or claim 2 and incorporating a conventional boiler having flow and return connections, the boiler thermostat being located at or adjacent the flow connection, and the flow and return connections being reversed.

4. A heating system as claimed in claim 1 or claim 2 and incorporating a conventional boiler having flow and return connections, the boiler thermostat being located at or adjacent the return connection of the boiler.

5. A heating system substantially as described with reference to and as illustrated by the accompanying drawings.