GB2153499A

GB2153499A - Improvements in water heating systems

Info

Publication number: GB2153499A
Application number: GB08402170A
Authority: GB
Inventors: Arthur Godfrey Money
Original assignee: WORCESTER ENGINEERING Co
Current assignee: WORCESTER ENGINEERING Co
Priority date: 1984-01-27
Filing date: 1984-01-27
Publication date: 1985-08-21
Also published as: GB8402170D0

Abstract

A water heating system comprises a boiler 10 for providing a supply of heated primary water, a hot water circuit comprising an accumulator 13 with a heat exchanger 14 in which cold secondary water is heated by heat exchange with the primary water, flow and return conduits 16, 18 for connection to a space-heating circuit 17, a pump 11 for pumping the heated primary water around the circuits. A three-way, two-position valve 12 controls the flow of heated water from the boiler to the circuits in such manner that, in one position of the valve, heated water from the boiler flows only through the hot water circuit and not through the space-heating circuit and, in the other position of the valve, heated water from the boiler flows through the space-heating circuit and not through the accumulator. <IMAGE>

Description

SPECIFICATION Improvements in water heating systems The invention relates to water heating systems, particularly for domestic use, of the kind comprising a boiler for providing a supply of heated primary water, a hot water circuit comprising, in series, an accumulator and a heat exchanger in which cold secondary water is heated by heat exchange with the primary water, flow and return conduits for connection to a space-heating circuit including one or more space-heating radiators, valve means for controlling supply of heated primary water from the boiler to said hot water and space-heating circuits, and a pump for pumping the heated primary water around said circuits.

Hitherto, in water heating systems of this kind, it has been the practice for the valve means to be in the form of a two-way, two-position motorised valve controlling the supply of heated water to the space-heating circuit in such manner that, in one position of the valve, heated water from the boiler flows only through the hot water circuit, and, in the other position of the valve, heated water from the boiler flows through both the hot water circuit and the space-heating circuit. Usually, the motorised valve is under the joint control of a programmed timer, boiler and room thermostats and a priority sensor which ensures that priority is given to maintaining the water in the hot water circuit at a predetermined temperature.

A water heating system of the above kind is described in our Patent Specification No. 1,437,784.

According to the invention, in a water heating system of the kind referred to, said valve means comprise a three-way, two-position valve controlling the flow of heated water from the boiler to said circuits in such manner that, in one position of the valve, heated water from the boiler flows only through the hot water circuit and, in the other position of the valve, heated water from the boiler flows only through the space-heating circuit.

By being able to direct the primary water flow separately through either the hot water circuit or the space-heating circuit, there is reduced cold mixing of the heat stored in the accumulator in circumstances where the accumulator is at the required temperature and the three-way valve has opened to allow circulation of the primary water through the space-heating circuit. In the known arrangements utilising two-way valve, there is, in such circumstances, immediate cold mixing since a major portion of the returning low temperature water from the space-heating circuit circulates through the accumulator of the hot water circuit.

Also, there is no requirement for a balancing valve between the heat exchanger and boiler, should there be a high resistance space-heating circuit as is the case with designs using two-way valves.

The heat exchanger may also be disposed in the space-heating circuit as well as in the hot water circuit, so that flow occurs through the heat exchanger in both positions of the valve means.

In earlier known arrangements, such as that de scribed in our above-mentioned Specification No.

1,437,784, separate but linked means are provided for controlling the pump for pumping the heated primary water around the hot water and space heating circuits. Thus there is provided a hot water priority sensor which ensures that heated water flows in the hot water circuit when the temperature of water in the accumulator is below a predeter mined level, and a secondary flow sensor which ensures that there is a flow of heated water through the hot water circuit whenever there is a flow of cold secondary water to be heated through the heat exchanger. In such arrangements the pump either ran continuously or was controlled by a flow switch. According to another aspect of the present invention, the functions of the hot water priority sensor and secondary flow sensor are combined into one sensing means which may be referred to as a hot water priority/flow sensor.

The following is a more detailed description of various embodiments of the invention reference being made to the accompanying drawings in which: Figure 1 is a diagrammatic view of the arrangement of components in a water heating system according to the invention, Figure 2 shows diagrammatically the flow and control arrangement of a modified embodiment of the invention, and Figures 3 and 4 are circuit diagrams showing alternative interconnections between the control components of systems according to the invention.

Referring to Figure 1, heated primary water from a boiler 10 is circulated by a pump 11 through a three-way two-position motorised valve 12, an accumulator 13 and a heat exchanger 14.

The heat exchanger 14 includes a coil 15 through which cold mains water flows so that the mains water, which constitutes the afore-mentioned secondary water, is heated as it passes through the coil, the coil being in contact with the heated primary water.

A flow conduit 16, for supplying heated primary water to one or more space-heating radiators indicated diagrammatically at 17, extends from the motorised valve 12, and a return conduit 18 connects the radiators to the boiler 10.

In one position of the two-position valve 12 the flow of primary heated water from the boiler is delivered by the pump 11 through the hot water circuit comprising the accumulator 13 and heat exchanger 14, whereas in the other position of the valve the heated water is delivered through the space-heating circuit comprising the radiators 17.

A hot water priority/flow sensor 21 is located in the accumulator 13 and adjacent the heat exchanger coil 15 so as to be sensitive both to the temperature of water in the accumulator and also to the flow of cold secondary, mains water through the coil.

The arrangement shown in Figure 2 differs from that shown in figure 1 in that the heat exchanger 14 is disposed in the space-heating circuit as well as in the hot water circuit so that primary heated water passes through the heat exchanger at all times. Figure 2 also indicates a boiler thermostat 19, a room thermostat 20 as well as the combined hot water priority/flow sensor 21.

In the arrangement of Figure 2, the hot water priority/flow sensor 21 fulfils the following two essential factors: a) At those times when both space-heating and hot water requirements are selected by the programmer, both initially and at those times where there is loss or withdrawal of heat from the accumulator 13, the sensor 21 operates to divert the total flow of primary water from the boiler to the hot water circuit until the predetermined accumulator temperature is reached, at which time the sensor will become "satisfied" and will allow the motorised valve 12 to be energised to the position where it directs the flow of heated primary water only through the space-heating circuit.

b) When the sensor 21 is "dissatisfied", i.e. the accumulator temperature is less than the predetermined temperature, the sensor energises the pump 11, should it not already be operating.

In the arrangement shown, if the programmer is "off", i.e. neither hot water nor space heating is selected, the sensor 21 will not energise the pump even though the accumulator temperature may be below that required. However, the arrangement could be modified so that the sensor 21 energises the pump even though the programmer is in the "off" condition.

Thus, the priority/flow sensor 21 is arranged within the control system so that pump operation occurs for: 1) circulation of heated primary water in the hot water circuit to raise the temperature in the accumulator to the predetermined value (hot water priority temperature).

2) circulation of heated primary water through the space-heating circuit when called for by the room thermostat 20 which, when satisfied, deenergises the motorised valve 12 which returns to the position in which heated primary water flows only through the hot water circuit. At this point, with no call for heat from the boiler thermostat 19, room thermostat 20 or priority/flow sensor 21, the pump will be de-energised.

3) circulation of the heated primary water through the hot water circuit, and hence delivery of heated water from the accumulator 13 to the heat exchanger 14, whenever any cold mains water flows through the coil 15 of the heat exchanger.

In both of the arrangements shown in Figures 1 and 2 the flow from the boiler and through the hot water circuit passes first through the heat exchanger 14 and then through the accumulator 13. This results in the initial slug of drawn domestic water being at a higher temperature than would be the case where the hottest primary water from the boiler is passed firstly through the accumulator.

However, in an alternative arrangement the primary flow from the boiler could pass first through the accumulator and then through the exchanger, so that the first slug of drawn water is at a lower temperature.

As previously mentioned, in the alternative arrangement of Figure 2, when the motorised valve 12 is in the position in which flow takes place through the space-heating circuit only, water returning through the boiler from the space-heating circuit passes through the heat exchanger 14. This results in any hot water drawn initially being at no higher temperature than the returning central heating water, subject to the returned ceiltr.al heating water being at a temperature higher than the hot water priority/flow sensing temperature. This feature is not, of course, given by the arrangement of Figure 1 in which the heat exchanger 14 is not disposed in the space-heating circuit.

In the arrangements shown, the pump 11 and motorised valve 12 are located on the outlet side of the boiler. However, it will be appreciated that either or both of them could be positioned on the return pipe work to the boiler.

There may be provided, in the described arrangements, a central thermostat to provide overall temperture control of the hot water supplied by the system, thus making it unnecessary to have independent thermostats at outlets for mixed hot and cold water.

Claims

1. A water heating system comprising a boiler for providing a supply of heated primary water, a hot water circuit comprising, in series, an accumulator and a heat exchanger in which cold secondary water is heated by heat exchange with the primary water, flow and return conduits for connection to a space-heating circuit, a pump for pumping the heated primary water around said circuits, and a three-way, two-position valve controlling the flow of heated water from the boiler to said circuits in such manner that, in one position of the valve, heated water from the boiler flows only through the hot water circuit and not through the space-heating circuit and, in the other position of the valve, heated water from the boiler flows through the space-heating circuit and not through the accumulator.

2. A water heating system according to Claim 1, wherein, in said other position of the valve, heated water from the boiler flows only through the space-heating circuit and not through either the accumulator or the heat exchanger of the hot water circuit.

3. A water heating system according to Claim 1, wherein, in said other position of the valve, heated water from the boiler flows through the heat exchanger as well as through the space-heating circuit.

4. A water heating system according to any of Claims 1 to 3, wherein the pump is located in a conduit through which heated primary water is delivered from the boiler to said valve.

5. A water heating system according to any of Claims 1 to 4, including a water priority sensor located and adapted to sense the water temperture in the accumulator, which sensor effects operation of said valve to said one position, or maintains it in said position, when the temperature in the accu mulator is below a predetermined value, so that heated water from the boiler then flows only through the hot water circuit.

6. A water heating system according to Claim 5, wherein the water priority sensor is also located and adapted to sense the flow of cold secondary water through the heat exchanger and, when such flow occurs, effects operation of said valve to said one position, or maintains it in said position, so that heated water from the boiler then flows only through the hot water circuit.

7. A water heating system according to Claim 5 or Claim 6 wherein said sensor is adapted to energise the pump, should it not already be energised, when effecting operation of said valve to said one position.

8. A water heating system according to any of Claims 1 to 7, wherein, in the hot water circuit, the flow of heated water from the boiler passes through the heat exchanger before passing through the accumulator.

9. A water heating system substantially as hereinbefore described with reference to Figure 1 of the accompanying drawings.

10. A water heating system substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings.