GB2335029A

GB2335029A - A combined expansion and thermal storage vessel

Info

Publication number: GB2335029A
Application number: GB9804792A
Authority: GB
Inventors: Gerald Uttley
Original assignee: BAXI HEATING Ltd
Current assignee: BAXI HEATING Ltd
Priority date: 1998-03-07
Filing date: 1998-03-07
Publication date: 1999-09-08
Anticipated expiration: 2018-03-07
Also published as: GB9804792D0; GB2335029B

Abstract

A combined expansion and thermal store container 3 for a pressurised heating system has a displaceable wall displacement which accommodates expansion of a heating medium in a heating circuit to which the container is connected. The container 3 has an inlet and an outlet to enable the connection of the container in series with a heating circuit and the container has an internal volume sufficient to enable the container to serve as a thermal store. The displaceable wall may be formed by a resilient diaphragm 15 which divides the interior of the container 3 into two compartments 12, 13 one of the compartments 12 being filled with heating medium and the other being filled with air. A perforated support wall 16 may be located adjacent the diaphragm 15 in the water-filled compartment 12 to maintain a minimum volume for that compartment.

Description

. j 2335029 1 HOT WATER EXPANSION VESSEL The present invention relates to

an expansion vessel for a pressurised heating system and to a heating system incorporating an expansion vessel.

Conventional heating systems generally rely upon the circulation of a heating medium such as hot water to provide space heating and to heat water which is to be distributed for further use. Generally space heating is provided by purnpin,11, hot water through one or more heat output vessels in the form of for example radiators. Water can be heated and stored for subsequerit distribution by passing hot water through for example a heat exchanger located iii a water cylinder from which water to be dispensed is drawn, but in more modem systems water is heated by. passing hot water through a heat exchanger througli whicii the dispensed,. atel. is drawil. lil sucli a system therefore there is a primary, licat exchanger in which a fuel is burnt to heat the heating medium and a secondary,. lieat exchanger which is heated by; the heating medium and through which water to be dispensed is drawn.

Generally modern hot water circulation heating systems incorporating primary and secondary heat exchangers are sealed and pressurised to a pressure of for example one and a half atmospheres. This improves the overall efficiency, of the systern and in particular reduces the probability of cavitation.

Sealed systems require the provision of an expansion chamber to accommodate expansion and contraction of the heating medium as the system is heated and cooled. In conventional sealed systems the expansion chainber is situated directly up-stream of a pump which is used to circulate water around the system. This means that the expansion vessel is located close to the primary. heat exchanger and is connected via a single connector to a pipe extending between the primary heat exchanger and the pump. In such an arrangement the expansion vessel is connected to what is in effect a neutral point of the system.

In conventional pressurised systems in which water to be dispensed is drawn through a secondary heat exchanger, the speed of response of tile system in terms of the time taken for the temperature of water being dispensed to reach a predetermined c) 1 1 level can be relatively slow. In order to improve the response of such systems, it is known to incorporate a thermal store in the form of a container for storing a predetermined volume of heated heating medium, such a thermal store generally being referred to as a buffer. When a demand for the dispensing of hot water is sensed, heating medium from the primary heat exchanger is pumped through the buffer into the secondary heat exchanger. The presence in the buffer of preheated heating medium substantially improves the rate of response.

It is necessary to connect a thermal storage buffer close to the secondary heat exchanger if a rapid response is to be achieved. As a result thermal storage buffers have heretofore always been in the form of separate containers having ail inlet and an outlet which are independent of the expansion vessel. The result is a system in which a total of three connections must be provided to connect both the expansion vessel and the thermal storage buffer. A relatively large volume of valuable space is occupied by the separate expansion vessel and thermal storage buffer. and the overall cost of the two separate components is relatively high.

It is an object of the present invention to obviate or mitigate the problems outlined above.

According to the present invention. there is provided an expansion vessel for a pressurised heating system, comprising a container having a displaceable wall C_ C_ displacement of which accommodates expansion of a heating medium in a heating circuit to which in use the container is connected, wherein the container has an inlet and an outlet to enable the connection of the container in series with a heating circuit, and the container has an internal volume sufficient to enable the container to serve as a thermal store.

The invention also provides a heating system comprising a primary heat exchanger, a secondary heat exchan(Yer through which water to be dispensed i-nay be drawn, a thermal store, at least one heat output vessel, an expansion vessel. and a pump interconnected by a heating medium distribution circuit. the circuit being arranged such that heating medium heated in the primary heat exchanger may be circulated by the pump to the heat output vessel and the secondary heat exchanger, the c 1 expansion vessel being arranged to accommodate expansion of the heating nledium, the thermal store being arranged to store heated heating medium, and means being provided to circulate heating rnediurn to the secondary heat exchanger through the thermal store when water to be dispensed is drawn through the secondary, heat exchanger, wherein the expansion vessel and thermal store are defined by, a single container having a wall whicii is displaceable to accommodate expansion of tile heating medium and an inlet and an outlet connected to the distribution circuit such that the container may be connected in series with the secondary lieat exchanger.

The displaceable wall rna-v be formed by a resilient diaphragm which divides the interior of the tank into two compartments, one of the compartments defining the container and the other beinu, air-filled. A perforated support wall illay be located adjacent the diaphragm in the salel one compartment to maintain a rninimurn volume for the container.

The circulation means may comprise valves arranged to distribute licating t tn medium from the primary, heat exclianger to the heat output vessel through a first distribution subcircuit or to the secondary heat exchanger in series with the thermal store through a second distribution subcIrcult. The container may, be connected to the first subcircuit by a secondary heat exchanger bypass which is open only when the primary heat exchanger is arran-ed to distribute heatin- medium from the primary heat exchanger to the heat oMput vessel via the first distribution subcircuit. The heatiner system may be arranged sticii that the outlet of the heat output vessel is connected to an inlet of the primary lieat exchanger, an inlet of tile pump is connected to an outlet of the primary heat exchanger, a first valve is connected to an outlet of the pump and arranged to be switched either to a first condition to distribute heating medium to an inlet of the heal output vessel or to a second condition to distribute heating medium to the inlet of the container, a second valve is connected to the outlet of the container and arranged to be switched either to a first condition to connect the container outlet to an inlet to the primary heat exchanger via the bypass or to a second condition to connect the container outlet to an inlet of the secondary heat exchanger, 4 and means are provided for controlling the valves such that the first and second valves both assume either the first condition or the second condition at the sarne tirnes.

An embodiment of the present Invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a schematic illustration of portions of a heating system in accordance with the present invention in a first operational configuration; Figure 2 is an illustration of the system of Figure 1 in a second operational configuration; Figure 3 is a sectional view through a combined buffer and expansion tank incorporated in the system illustrated in Figures 1 and 2; and Figure 4 is a section on the line of 4-4 of Figure 3 and indicates by lines 3-3 the sectional view represented in Figure 3.

Referring to Figures 1 and 2. the illustrated systeni comprises a primary heat exchanger 1, for example a (,as-i'-ired boiler, a circulation puillp 2, a container 3) defining a combined buffer and expansion tank, and a secondary heat exchanger 4. Heat output vessels (not shown) such as waterfilled radiators are connected between a central heating flow pipe 5 and a central heating return pipe 6. Hot water distribution taps (not shown) arc connected to a domestic hot water outlet 7, and a cold water supply main (not shown) is connected to a cold water inlet pipe 8.

A first three-way valve 9 is connected between the purnp 2. the container 3 and the central heating flow pipe 5. The valve 9 is switchable between a first condition as shown in Figure 1 in which the output of the pump 2 is distributed to the central heating flow pipe 5 and a second condition as shown in Figure 2 in which the output of the pump is distributed to the container 3. A second three-way valve 10 is connected between the container '), the secondary heat exchanger 4. and a secondary heat exchanger bypass pipe 11. The valve 10 is switchable between a first condition in which the container 3 is connected to the central heating return pipe 6 as shown in Figure 1 and a second condition in which the secondary heat exchanger is connected in series with the container ').

The container 3 defines a first compartment 12 in which heated water is stored and a second compartment 13) which is air-filled. An air vent 14 prevents the formation of an airlock within the compartment 12.

In Figures 1 and 2, portions of the pipe network interconnecting the various described components which are filled with hot water are shown shaded. Thus it will be seen that when the system is switched to the space heating configuration of Figure 1, heated water flows through the radiators connected between the pipes 5 and 6. Heated water also passes from the central heating return pipe 6 via the bypass pipe 11 to the compartment 12. Thus water within the compartment 12 is heated and therefore even when the system is switched to the condition shown in Figure 1 the compartment 12 is filled with hot water. When the system is switched to the condition shown in Figure 2, the bypass pipe 11 is closed and the output of the purrip 2 passes via the compartment 12 and the secondary,, heat exchanger 4 to the central heating return pipe W C1 6. As a result, as soon as the circuit is switched from the condition shown ill Figure 1 to the condition shown in Flaure 2, hot water in the compartment 12 is immediately pumped through the secondary heat exchanger. Thus by sensing when water is drawl] from the domestic hot water outlet 7 and switching the valves 9 and 10 to the condition shown in Figure 2, the secondary,' heat exchaniger 4 is filled with hot water without any significant delay. The temperature of water from the outlet 7 therefore increases rapidly.

Figures 3) and 4 illustrate the structure of the container 3. It will be seen that the compartment 12 is separated from the compartment 1 ') by, a flexible diaphragm 15. The compartment 12 is divided into two sections by a perforated wall 16 such that all of the space within the container to the right of the diaphragm 15, in Figure 3 is filled with water. An inlet pipe 17 will in Lise be connected to the valve 9 of Figure 1 and an outlet pipe 18 will in use be connected to the val,,,,e 10 of Figure 1. The compartment 13) is sealed and filled with air at a pressure of approximately one and a half atmospheres. The position adopted by the diaphragm 15 will depend upon its flexibility and the differential pressure between the compartments 12 and 13)- In normal use the diaphragm 15 will be substantially planar. The perforated wall 16 6 ensures that if the pressure within the compartment 12 falls substantially the diaphragm 15 is supported by the wall 16. A temperature sensor 19 may be provided to monitor the temperature of water within the compartment 12. An output of the sensor 19 may be used to control the primary heat exchanger so as to ensure that at all times the system is operational the compartment 12 is filled with water to an appropriate minimum temperature. The air vent 14 of F1gire 1 may be fitted to all opening 20 indicated in broken lines in Figure 4.

In Thus the described embodiment of the present invention comprises a single container defining an expansion vessel and a hot water biiffeistorage compartment. Such an arrangement enables cost savings to be achieved both ill teri-ns of system components, the complexity of connections to the heating system distribution circuit, and the space requirements of the overall system.

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Claims

An expansion vessel for a pressurised heating system, comprising a container having a displaceable wall displacement of which accommodates expansion of a heating medium in a heating circuit to which in use the container is connected, wherein the container has an inlet and all outlet to enable the connection of the container in series with a heatin,_., circuit, and the container has all internal volume sufficient to enable the container to serve as a thermal store.
2. An expansion vessel according to claim 1, wherein the displaceable wall is formed by a resilient diaphragm,k.lilcli divides the interior of a tank into two compartments, one of the compartments defining the container and the other being air-filled.
1 An expansion vessel according to claim 2, wherein a perforated support wall is 1 located adjacent the diaphragm in the said one compartment to maintain a minimum volume for the container.
4. A heating system comprising a primary, heat exchanger. a secondary heat W C> 1 exchanger through which water to be dispensed may be drawn, a therinal store, at least one heat output vessel, an expansion vessel, and a pump interconnected by a heating medium distribution CirCUlt, the circuit being arranged slich that heating medium heated in the primary heat exchanger may be circulated by. the pump to the heat output vessel and the secondany heat exchanger, the expansion vessel being arranged to accommodate expansion of the heating medium, the thermal store being arranged to store heated heating inedluni, and means beIng provided to circulate heating medium to the secondary heat exchanger through the thermal store when water to be dispensed is drawn through the secondary heat exchanger, wherein the expansion vessel and thermal store are defined by, a single container lia,,,,lna a wall which is displaceable to accommodate expansion of the heating medium and an inlet 8 and an outlet connected to the distribution circuit such that the container may be connected in series with the secondary heat exchanger.
5. A heating system according to claim 4, wherein the circulation means comprises valves arranged to distribute heating medium from the primary heat t C1 exchanger to the heat output vessel through a first distribution subcIrcult or to the secondary heat exchanger in series with the thermal store through a second distribution subcircuit.
6. A heating systems according to claim 5, wherein the container is connected to 1 the first subclIcuit by a secondary, heat exchanger bypass which is open only, when the primary heat exchanger is arranged to distribute heating rnediurn fi-oni the primary CI -- -- - heat exchanger to the heat output vessel via the first distribution subcli-cult.
7. A heating systems according to claim 5, wherein an outlet of the heat output vessel is connected to an inlet of the primary heat exchanger. an inlet of the pump is connected to an outlet of the primary heat exchanger, a first valve is connected to an outlet of the pump and arranged to be switched either to a first condition to distribute heating medium to an inlet of the heat output vessel or to a second condition to distribute heating medium to the inlet of the container, a second valve is connected to the outlet of the container and arranged to be switched either to a first condition to connect the container outlet to an inlet to the primary heat exchanger via the bypass or to a second condition to connect the container outlet to an inlet of the secondary, heat exchanger, and means are provided for controlling the valves such that the first and second valves both assume either the first condition or the second condition at the same times.
8. An expansion vessel substantially as hereinbefore described \vith reference to the accompanying drawings.

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9. A heating system substantially as hereinbefore described with reference to the accompanying drawings.