GB2326703A

GB2326703A - Hot Water Supply System

Info

Publication number: GB2326703A
Application number: GB9813773A
Authority: GB
Inventors: George Hanson-Graville
Original assignee: DEDICATED PRESSURE SYSTEMS LIM
Current assignee: DEDICATED PRESSURE SYSTEMS LIM
Priority date: 1997-06-26
Filing date: 1998-06-25
Publication date: 1998-12-30
Anticipated expiration: 2018-06-25
Also published as: GB9713530D0; GB2326703A8; GB2326703B; GB9813773D0

Description

Title: Hot water supply systems This invention relates to hot water supply systems and is primarily, but not essentially, concemed with domestic pressurised hot water supply systems that is systems which are at mains supply pressure Systems are known commonly called "heat banks" wherein a heat energy store is provided formed by a mass of water contained in an insulated tank and heated by a boiler. This water is not pressurised and the tank is fully vented to atmosphere for safety reasons and simplicity.

The water may be heated directly from the boiler or indirectly by use of a coil. One advantage of such systems is that the water forming the energy store never changes and thus build-up of scale in the tank and frost protection can be avoided by addition of chemicals if required. The water can be heated to, typically, 900 C thus providing a large amount of stored heat energy. The hot water for consumption is not stored and is supplied direct from the pressure mains and is thus potable. This water is heated by feeding through a heat exchanger and the flow is sensed following the opening of an outlet which operates a pump to draw water from the top of the tank, where the water is hottest, and to feed the hot water through the heat exchanger and return to the bottom of the tank The mains water is thus rapidly heated by the flow through the heat exchanger but is separated therefrom. The temperature of the mains water is controlled by means of a thermostatic mixer valve which combines hot water from the heat exchanger outlet with cold supply water.

A problem encountered in known systems relates to the heating of the heat bank water by means of a boiler and to the pumped flow feed and return through the heat exchanger. This invention seeks to provide an improvement to the known systems allowing flow temperatures to stabilise and to prevent hunting of the boiler control valves. This invention further provides a means of allowing the boiler to more directly heat the water passing through the heat exchanger.

Broadly, and in accordance with this invention, there is provided a system for the supply of primary pressurised hot water, the said primary supply being passed through a heat exchanger wherein heat is transferred from a secondary supply of hot water without intermixing of the water forming the two supplies, the secondary supply being in a closed circuit, preferably vented to atmosphere and contained within an insulated tank and heated by a heat source, a pump means circulating secondary water from the top of the tank through the heat exchanger to a return in the bottom of the tank and the pump being operable on commencement of primary water flow, characterised by the tank being partitioned into an upper heating chamber and a lower main chamber by a baffle with a through flow port connecting the chambers, a hot water feed inlet from a boiler connected with the heating chamber and a draw-off return to the boiler being connected through a three port valve means with the lower part of the main chamber on the one hand and the heating chamber on the other hand, a temperature sensor associated with the tank effecting control of the said valve to modulate the return flow draw off between the heating and main chamber.

With such an arrangement the main chamber is temperature controlled by means of a thermostat to set the temperature of the main body of water in the heat bank whilst the smaller volume heating chamber preferentially controls recirculation through the boiler to achieve a rapid rise in water temperature. This being controlled through the three port valve operated by a sensor in the heating chamber. The three port valve thus modulates between the two return feed ports to allow variable temperature setting and preventing hunting of the boiler temperature control thus allowing flow temperatures to stabilise. The heating chamber provides a means for more direct heat transfer to the heat exchanger from the boiler output without mixing with the main body of water. The return flow to the boiler can thus be maintained at a more constant temperature thus providing for the boiler to raise the water temperature to the optimum in one pass To enable a better understanding of this invention to be obtained practical embodiments are now described by way of examples only and in conjunction with the accompanying drawings. In the drawings: Fig. 1 shows a general partly schematic sectional view of a tank arrangement for the exchange of heat from a secondary boiler heated source to a primary mains supply Figs 2 to 9 show views as in Fig 1 for various different operational phases, Fig 10 shows a view of part of a modified tank construction Fig 11 shows a system using a feed and expansion tank to maintain the secondary supply tank water Figs 12 (a) to (f) show a number of arrangements for the heat exchanger coupling the primary and secondary supplies, Fig 13 shows a modified arrangement for the circulation to the heat exchanger, Fig 14 shows a different arrangement of thermostatic control, and Fig 15 shows an alternate position for the heating chamber 2.

Referring to the drawings, wherein the same references indicate the same or similar parts throughout, the heat bank system includes a thermally insulated storage cylinder or tank which provides pressurised domestic hot water. Fig 1 is a section and shows the general layout. In Fig 1 the reference numerals indicate the following parts: 1. Main Store Chamber 2. Heating Chamber 3. Return Chamber 4. Separator Plate 5. Diffuser Plate 6. Thermostatic Three port Valve 7. Hot Inlet Port 8. Cold Inlet Port 9. Mixed Output Port 10. Sensor Head 11. Sensor Capillary Tube 12. Plate Heat Exchanger 13. Domestic Cold Inlet Port 14. Domestic Hot Outlet Port 15. Primary Hot Inlet Port 16. Primary Outlet Port 17. Store Circulating Pump 18. Automatic Air Vent 19. Air Outlet Pipe 20. Draw Pipe between Heating & Main Chamber 21. Flow from Boiler 22. Return from Heat Exchanger to Return Chamber 23. Domestic Cold Water Feed 24. Domestic Hot Water Supply 25. Flow from Heating Chamber to Store Pump 26. Flow from Store Pump to Heat Exchanger 27. Drain Off Cock 28. Insulation 29. Cylinder Thermostat 30. Flow from Heating Chamber to Three Port Valve 31. Flow from Return Chamber to Three Port Valve 32. Flow Switch 33. Return to Boiler The characteristic features of the construction shown are the hot water heat bank formed by chambers 1 and 2 heated by a boiler (not shown) feeding hot water into chamber 2 through pipe 21 and taking return flow of cooler water by pipe 33 fed selectively by pipes 30 and 31 through three port valve 6. The valve 6 is controlled by sensor 1. The hot water is drawn from chamber 2 through pipe 25 by pump 17 and passed through heat exchanger 12 via port 15 and returned to the main chamber 1 through port 16. The cold pressurised mains water enters through pipe 23 and through the heat exchanger via port 13 and out through port 14 to the hot water feed 24. The heat exchanger allows high supply pressures to be used without pressure in the chambers 1 and 2 which are vented to atmosphere through valve 18 which may be an automatic air vent to allow air to be completely removed from the chamber 2. A feature of this invention is the means by which the flow of stored water to the boiler is controlled by the three port valve 6. This is possible by use of the heating chamber 2 to overcome hunting in the operation of the three port valve 6 allowing temperatures to stabilise.

More specifically the apparatus shown in Fig 1 is divided into three chambers.

The mains store chamber 1 contains the main body of primary water which is heated to a set temperature to store heat energy. The upper heating chamber 2 contains a small volume of primary water which is recirculated through the boiler to achieve a set water temperature for storage. The heating chamber 2 is separated from the main chamber 1 by a plate 4 with a connecting pipe 20 to allow water to flow from one chamber to the other. The main store is fitted with a diffuser plate 5 in the base, creating the return chamber 3. The diffuser plate 5 prevents turbulence within the return chamber 3 from affecting water in the main chamber 1.

Water is pumped between the boiler and the invention by means of a remote boiler pump. The boiler and remote boiler pump operate on a signal provided by the cylinder thermostat 29. Whenever the cylinder thermostat 29 detects that the water in the main chamber 1 is below a set limit, Ts, it sends a signal to switch on the boiler and boiler pump.

The invention makes use of a three port valve 6 controlled by a remote sensor 10 to control the flow temperature of primary water going to the boiler to be heated. The three port valve 6 has two inlet ports, the upper 7 connected to the heating chamber 2 and the lower 8 to the return chamber 3. The outlet port 9 of the three port valve 6 runs to the boiler for heating. The three port valve allows variable setting of the control temperature, and modulates between the two input ports.

In the first heating stage shown in Figure 2, from cold, with all primary water at temperature Tc, the cylinder thermostat 29 will switch on the boiler and boiler pump, providing there is hot water demanded by the system controller/programmer.

If the primary system uses the boiler for another use, such as central heating, then the call for hot water demand should divert all boiler output to the hot water system of this invention. On a typical installation this may be done with the use of zone valves.

In Figure 3, the three port valve sensor 6 detects the temperature of the primary water in the heating chamber 2. If the sensor detects that the water in the heating chamber 2 is below a set flow temperature THO then the three port valve 6 modulates so that.outlet 9 will draw water from the upper port 7, thereby drawing water from the heating chamber 2 to go to the boiler.

The flow to the boiler 33 will be heated by the boiler and be returned to the heating chamber 2 via boiler flow connection 21.

The water in the heating chamber 2 will be recirculated through the boiler until the temperature of the water in the heating chamber approaches the set flow temperature THC.

In heating stage 2, shown in Figure 4, as the water in the heating chamber 2 approaches the set flow temperature Tc then the three port valve 6 will start to modulate, and draw some water from the lower port 8 and hence from the return chamber 3, where the water temperature is lower.

The return to the boiler 33 is maintained at a temperature TR, below the set flow temperature THO by an amount equal to the temperature that the boiler raises the water temperature in one pass. In this way, the temperature of the heated water returning from the boiler 21 is maintained by the three port valve 6 at the set flow temperature THC.

As the three port valve 6 draws water from the return chamber 3.

an equal volume of water, at set flow temperature THC. will pass from the heating chamber 2 into the main chamber 1 via the draw pipe 20. The main chamber 1 is thereby heated from the top down, to the set flow temperature THO.

in Figure 5, if the cylinder thermostat 29 is set to the set flow temperature THC. the cylinder thermostat 29 will turn off the boiler and boiler pump and heating will finish.

In heating stage 3 shown in Figure 6 provided the cylinder thermostat 29 is set to a temperature greater than the set flow temperature Tc, heating will continue.

Once the main chamber 1 is heated to the set flow temperature THC. the temperature of the water in the return chamber 3 will rise to a point where it is greater than the minimum return temperature TR. As a result, the three port valve 6 will not be able to keep the return to the boiler 33 at a temperature TR. The temperature of the return to the boiler 33 will increase, and as a result, the temperature of the flow from the boiler 21 will also increase.

At this stage, the three port valve 6 will be drawing completely from the return chamber. The temperature in the heating chamber 2 will increase above the set flow temperature THC, and as water is drawn from return chamber 3, the heating chamber water 2 will pass into the main chamber 1.

In Figure 7, the main chamber will be heated above the set flow temperature THO, until the cylinder thermostat 29 is satisfied and turns off the boiler and boiler pump.

For domestic hot water as shown in Figure 8 the base of the tank unit of this invention is fitted with a plate heat exchanger 12. This is used to transfer heat from the water system of this invention to a separate domestic supply of water, to provide domestic hot water. The plate heat exchanger 12 contains two sets of waterways, separated by numerous plates through which heat transfer can take place.

The incoming cold domestic supply 23 is fitted with a flow switch 32 which detects when there is a flow of domestic water to a hot water outlet. When a domestic hot outlet is opened, cold domestic water will flow through the flow switch 32 and into the plate heat exchanger 12 via connection 13. The flow switch turns on the circulating pump 17.

Primary water from within the unit of this invention is drawn from the heating chamber 2 and pumped by the circulating pump 17 into the plate heat exchanger 12 via connection 15.

As primary water passes through the plate heat exchanger 12, heat is transferred through the heat exchanger plates to the domestic water flowing through the other side of the heat exchanger, thereby heating the domestic water and cooling the primary water.

The primary water, now cooled, returns from the heat exchanger 12, via connection 16, and the connecting pipe 22, into the return chamber 3.

As primary water is drawn from the heating chamber 2, water will flow from the main chamber 1 into the heating chamber 2 through the draw pipe 20, and similarly, primary water returning from the heat exchanger 12 into the return chamber 3 will pass through the diffuser plate 5 into the main chamber 1. The diffuser plate 5 prevents turbulence caused by the returning primary water from affecting the water in the mains chamber 1 and thereby helps keep the water in the main chamber 1 well stratified.

The domestic water, now heated, exits the heat exchanger via connection 14, to supply the domestic hot outlets.

When all hot outlets are closed the flow of domestic hot water will stop and the flow switch 32 swill turn off the circulating pump 17.

In Figure 9. as domestic hot water is drawn off and the primary water returning from heat exchanger 12 to the return chamber 3 passes up through the diffuser plate 5, the cylinder thermostat 29 will detect the cooler returning primary water and will turn on the boiler and boiler pump to recover (re-heat) the primary water in the unit as described in heating stage 2.

The flow of water 21 from the boiler at set flow temperature THO is hot enough for use by the plate heat exchanger 12. In this way the boiler contributes additional heat for domestic use.

Modifications to the construction are shown in Fig 10 and described in the following.

The boiler flow pipe 21 may be brought into the top of the heating chamber 2 as shown in Figure 10. This may remove the need for the automatic air vent 18 fitted onto the unit of this invention as air can be removed via the boiler flow pipe 21. Some method of removing air from the boiler flow pipe must be used in this case. Alternatively an air vent may be provided on the top of the chamber 2.

The drain-off cock 27 may be alternately located on the connecting pipe 22 from the heat exchanger 13 to the return chamber 3, or on the connecting pipe 26 from the circulating pump 17 to the heat exchanger 12. The flow switch 32 may be fitted onto the domestic hot outlet 24 instead of the cold inlet 23.

The diffuser plate 5 may be replaced by a diffuser tube, fitted onto the return from the heat exchanger 22. This will remove the return chamber 3 and the draw pipe 31 will instead draw from the bottom of the main chamber 1.

A backup electric immersion heater may be provided. Safety devices such as pressure relief valves and over temperature relief valves or overheating thermostats may be included.

In the embodiment described using an 80 litre copper cylinder as the tank hot water flow rates up to 30 litres per minute were obtained. In addition over 170 litres of water at 450 C could be drawn off with the first 120 litres at an average of 500 C at an average flow rate of 25 litres per minute. Within three minutes a further 15 litres at 450 C was drawn.

After 23 minutes recovery 160 litres at 450 C was drawn off.

The embodiment shown in Fig 11 illustrates an arrangement using a feed and expansion tank to maintain the water level in the system and to permit air to escape. As shown the tank 110 connects by pipe 111 to the base of the main system 1.2.3 and the top of the system has a vent pipe 112. The tank 110 will have a water level maintained by a customary arrangement such as a float valve whereby the system is kept charged with water.

Fig 12 (a) to (f) illustrate various configurations for the positioning of the heat exchanger unit 12 from the basic position disclosed in the forgoing shown in Fig 12 (a) to positions shown respectively in Figs 12 (b) to (f) being at the side at the top within the tank at the bottom within the tank at the side and within the tank at the top.

A modification is shown in Fig 13 and here the draw-off 25 for the pump 17 is taken from below the separator plate 4 rather than from above. The connection 20 between chambers 1 and 2 may comprise a pipe, as shown in Fig 1 or may simply be an aperture through the plate 4.

The boiler feed and return flows 30, 31 may be internal (Fig 1) or external as shown in Figs 11 to 13. The flow switch 32 may be in the inlet 23 or outlet 24 of the heat exchanger 12. Instead of a diffuser plate 5 a tube may be provided at the base of chamber 1 into which pipe 22 feeds.

The arrangement described uses the three port valve 6 to combine the flows through pipes 30 and 31 but this can be replaced by a valve 140 in pipe 30 under control of a thermostat and a second valve 141 in pipe 31 under control of a thermostat as shown in Fig 14. The sensors for these valve controls my be in the chamber 2, the flow from boiler 21 and return from the boiler 33.

The chamber 2 may be separate from the main system as illustrated in Fig 15.

Various safety devices may be included as required such as overtemperature sensors, pressure relief devices as well as back-up electric immersion heaters.

Claims

1. A system for the supply of primary pressurised hot water, the said primary supply being passed through a heat exchanger wherein heat is transferred from a secondary supply of hot water without intermixing of the water forming the two supplies, the secondary supply being in a closed circuit and contained within an insulated tank and heated by a heat source, a pump means circulating secondary water from the top of the tank through the heat exchanger to a retum in the bottom of the tank and the pump being operable on commencement of primary water flow.

characterised by the tank being partitioned into an upper heating chamber and a lower main chamber by a baffle with a through flow port connecting the chambers, a hot water feed inlet from a boiler connected with the heating chamber and a draw-off return to the boiler being connected through a three port valve means with the lower part of the main chamber on the one hand and the heating chamber on the other hand, a temperature sensor associated with the tank effecting control of the said valve to modulate the return flow draw-off between the heating and main chamber.

2. A system in accordance with Claim 1, wherein the temperature sensor is located in the heating chamber.

3. A system in accordance with Claim 1 or 2, wherein the, or a further, temperature sensor is located in the main chamber.

4. A system in accordance with any preceding Claim, wherein the heat exchanger is integral with the tank structure but located externally of the water chambers preferably within an insulated compartment.

5. A system in accordance with any preceding Claim, wherein the baffle comprises a transverse plate with a substantially central aperture forming the through flow port, the aperture preferably being connected to a pipe projecting into the heating chamber.

6. A system in accordance with any preceding Claim, wherein the boiler hot water feed is disposed within the heating chamber opposite to the feed to the secondary water pump means.

7. A system in accordance with any preceding Claim, wherein the return from the secondary water pump means feeds the bottom of the main chamber and is positioned beneath a transverse baffle.

8. A system for the supply of pressurised hot water constructed and arranged to function substantially as described herein and with reference to Figures 1 to 9 of the drawings and as modified by Figures 10 to 15.

9. A water tank and heat exchanger unit for use in the system of any preceding Claim, substantially as herein described and illustrated with reference to the drawings.