GB2364766A

GB2364766A - Domestic hot water recirculation arrangement for a combination boiler system

Info

Publication number: GB2364766A
Application number: GB0113682A
Authority: GB
Inventors: Nicholas Julian Jan F Macphail
Original assignee: Individual
Current assignee: Individual
Priority date: 2000-06-06
Filing date: 2001-06-05
Publication date: 2002-02-06
Anticipated expiration: 2021-06-05
Also published as: GB0113682D0; GB2364766B; GB0013594D0

Abstract

A combination boiler 9 provides hot water to tap 8 via a heat exchanger 5. The arrangement includes a domestic hot water circulation loop 30 formed by conduit 36 extending from a point adjacent the tap 8, to a cold water supply pipe 2 to the heat exchanger 5. To prevent excessive water pressure in the loop, due to expansion of the water when heated, a pressure responsive device is included which may be a pressure relief valve 32 and/or an expansion vessel 34. The means to provide flow of water in the loop may be a pump 38 and the arrangement may also include a pressure reducing valve 31 and temperature and timer controls.

Description

<Desc/Clms Page number 1> DESCRIPTION OF INVENTION "IMPROVEMENTS IN OR RELATING TO A COMBINATION BOILER ARRANGEMENT" THE PRESENT INVENTION relates to a combination boiler arrangement, and more particularly relates to a combination boiler arrangement incorporating a heat exchanger, an input to the heat exchanger being connected, by a conduit, to a source of cold water, and an outlet of the heat exchanger being connected, by a conduit, to a tap. In this Specification the word "tap" is used broadly to mean any sort of tap including a tap on a sink, a tap on a basin or a tap on a bath, and a tap incorporated into a shower fixing. It is now becoming common to use so-called "combination" boilers, which incorporate a heat exchanger which caii receive cold water directly from the main water supply to produce domestic hot water. Such boilers have the advantage that they do not need a cold water or "header" storage tank, and also do not need a hot water tank or "cylinder" for the storage of hot water. Therefore, such combination boilers have found great demand in today's smaller, space-limited houses.

Where a relatively long pipe run extends from the combination boiler to a hot water tap, when the hot water tap is turned on, all of the cold water in the pipe must first be drawn off before hot water emerges from the tap. This can lead to an undesirable delay in the provision of hot water at the tap. This can cause considerable wastage of water, since the cold water is usually permitted to drain away. A similar problem exists, of course, in connection with a more conventional hot water system which utilises a hot water tank or cylinder. It has been proposed, in such a situation, to use a "secondary loop" in which water is circulated from the hot water cylinder to a remote hot tap and then back to the hot water cylinder. Because hot water is always circulating in this "loop", and the length of conduit extending from the loop to the tap is very short, hot water is available almost instantly at the tap. This eliminates time delay and also eliminates the amount of cold water that is drawn off and simply goes to waste. Secondary loops, of the type generally discussed above, have not previously been used with combination boilers because the small, but finite, increase in the volume of water in the loop caused by the water in the loop being intermittently heated, can cause substantial pressures within the loop and boiler heat exchanger. This can lead to catastrophic pressure failure. The present invention seeks to provide an improved combination boiler arrangement.

According to this invention there is provided a combination boiler arrangement adapted to supply hot water to a tap, the boiler arrangement

incorporating a heat exchanger, an input to the heat exchanger being connected, by a conduit, to a source of cold water, an outlet of the heat exchanger being connected, by a conduit, to the tap, the arrangement further including a conduit extending from a point adjacent the tap, in the conduit extending from the heat exchanger to the tap, to a point in the conduit connecting the source of water to the heat exchanger, means being provided to cause a flow of water around the loop thus created, means being provided, communicating with the loop, responsive to an increase of water pressure within the loop, to reduce the water pressure within the loop.

Preferably the means responsive to pressure comprise a pressure relief valve.

Conveniently the pressure relief valve is adapted to discharge expansion water to waste.

Preferably the means responsive to pressure comprise a expansion vessel.

Advantageously a pressure reducing valve is provided in the conduit connecting the heat exchanger to the source of cold water, the pressure valve being located at an upstream position.

Preferably the means to cause a flow of water within the loop comprises a pump.

Conveniently the pump is controlled by control means.

Preferably the control means comprises a thermostat responsive to the temperature of water in the conduit supplying water to the inlet to the heat exchanger. Conveniently the control means comprises a timer. In order that the invention may be more readily understood, and so that further features thereof may be appreciated, the invention will now be described, by way of example, with reference to the accompanying drawings in which: FIGURE 1 is a diagrammatic representation of a prior art combination boiler arrangement without a secondary loop, and FIGURE 2 is a corresponding diagrammatic view of a combination boiler arrangement in accordance with the invention. Referring initially to Figure 1 of the accompanying drawings, a source of cold water 1, such as a mains water supply, is connected to a conduit 2, which incorporates within it a flow responsive switch 3. The flow responsive switch 3 is adapted to close when a flow of water through the conduit 2 occurs. The conduit 2 extends to the inlet 4 of a water-to-water heat exchanger 5. The outlet 6 of the water-to-water heat exchanger 5 is connected, by means of a second conduit 7, to a tap 8. The tap may be associated with a sink, basin or bath, or may form part of a shower fitting, or may form a tap leading directly to an appliance such as a washing machine or dishwasher. The conduit 7 may have a substantial length.

A combination boiler 9 is provided associated with a primary loop to circulate water from the boiler through the water-to-water heat exchanger 5. The primary loop comprises a first flow conduit 10 extending from the boiler 9, through a pump 11 to a three-way control valve 12 which is controlled by a actuator 13. The loop continues with a further conduit 14 extending from one outlet of the three-way valve 12 to a thermal store 15. The thermal store may comprise a thermally insulated tank adapted to contain a quantity of hot water. A conduit 16 extends from the thermal store to an inlet 17 of the water-to-water heat exchanger, and an outlet 18 of the water-to-water heat exchanger 5 is connected, by means of a return flow conduit 19 forming part of the primary loop back to the boiler 9. The boiler 9 is associated with an expansion system 20 in order to prevent undue pressures arising in the boiler. In the illustrated embodiment, the three-way control valve 12 has a conduit 21 connected to one of the outlet ports, that conduit being connected to a radiator system incorporating radiators such as the radiator 22. The radiator system has a return flow conduit 23 which combines with the flow conduit 19 of the primary loop, so that water flowing through the radiator system is returned to the combination boiler 9. The arrangement shown in Figure 1 is of a conventional design. If a thermostatic control indicates that heat is required in the house in which the combination boiler arrangement is mounted, the actuator 13 will open the appropriate outlet of the three-way valve 12, and will activate the pump 11, so that water flows through the combination boiler and through the radiator system. When the tap 8 is opened, water will begin to flow from the main water supply 1, through the conduit 2 and through the heat exchanger 5, before flowing through the conduit 7 to the tap 8. This flow is sensed by the flow responsive switch which activates the pump 11 and the boiler 9, and also

adjusts the three-way control valve so water flows through the primary loop, thus flowing through the conduit 14 and the thermal store 15 to enter the water- to-water heat exchanger 5 through the inlet 17, the water subsequently leaving the heat exchanger 5 through the outlet 18, and flowing through the return flow conduit 19 back to the boiler. If the conduit 7 is of substantial length, there may be an undesirable delay before hot water emerges through the tap 8, and the cold water that emerges from the tap 8 may simply be permitted to drain to waste, which is undesirable in parts of the country where water is in short supply. Turning now to Figure 2 which illustrates an embodiment of the invention, it is to be appreciated that many components of the described embodiment of the invention are the same as the components of the prior art aiTangement described above. These components will not be re-described, but are identified with the same reference numerals as used in Figure 1. In the embodiment shown in Figure 2, in addition to the primary loop present in the prior art arrangement of Figure 1, a secondary loop 30 is provided which, as will be described, extends from a point adjacent the tap 8 back to the cold water supply pipe 2. This enables hot water to be circulated, under the control of the pipe thermostat 35, through the loop so that hot water is always available immediately adjacent the tap 8.

Referring now to Figure 2, the conduit 2 that extends from the main water supply 1 is provided with a pressure reducing valve 31, which is located at a position upstream of the heat exchanger which is typically set to 3 bar,

thus ensuring that the water from the mains flowing through the pressure reducing valve enters the described secondary loop at a pressure of no more than 3 bar. The pressure reducing valve 31 is connected to a pressure relief valve 32 which is adapted to discharge water to waste through a waste conduit 33, when the pressure of water experienced within the valve exceeds a predetermined threshold which may be 5 bar. In the described embodiment, additionally an expansion vessel 34 is provided which is connected to an output extending from the pressure relieve valve 32 to the secondary loop. The expansion vessel may typically accommodate about 25 cc of expansion in the domestic application. The expansion vessel is typically set by being pre- -. pressurised to about 0.5 bar above the set pressure of the pressure reducing valve 31. The conduit 2 continues, past a pipe thermostat 35 adapted to sense the temperature of water within the conduit 2, to the closed sensor 3 and thus through the input 4 of the water-to-water heat exchanger 5, and through the output 6 of that heat exchanger to the conduit 7 leading to the tap 8. Immediately adjacent the tap 8 there is a connection between the conduit 7 and a further conduit 36 that forms the secondary loop 30. The conduit 36 includes a non-return valve 37 to prevent flow of water in an inappropriate direction, and a pump 38, the conduit 36 rejoining the conduit 2 at a junction 39 located between the pressure relief valve 32 and the expansion vessel 34, and the pipe thermostat 35. It is to be appreciated that, as regards the central heating system incorporating the radiator 22, the described arrangement will operate in the same way as the arrangement of Figure 1.

The pipe thermostat 35 will sense the temperature of water within the part of the conduit 2 that extends past the pipe thermostat 35. If the temperature of water drops below a predetermined level, for example 45 C, then the pipe thermostat 35 will actuate the secondary loop pump 38. Water will then flow from the pump 38 to the junction 39, past the pipe thermostat 35 and through the flow sensor 3. The flow sensor will thus actuate the boiler .9. The water will flow through the heat exchanger 5 along the conduit 7 to a point almost adjacent the tap 8 where the water will flow through the conduit 36, and through the non-return valve 37 back to the pump 38. Water will flow until the pipe thermostat 35 senses an appropriate temperature within the water circulating in the secondary loop. It is thus to be understood that the water within the secondary loop will always be at a temperature of at least approximately 45 C. The temperature of 45 is appropriate for most domestic situations, but another temperature may be selected as appropriate in any specific situation. If the tap 8 is opened, water will flow immediately from the tap 8, with that water being drawn from the conduit 7 which forms part of the secondary loop. That water will, of course, be hot. As the tap 8 is opened, water is also introduced into the described arrangement from the main water supply through the conduit 2. Water will thus flow past the flow sensor 3 which will actuate the boiler. As the boiler is actuated, warm water from the thermal store 15 immediately flows through one side of the water-to-water heat exchanger 5 and thus, by the time the hot water present in the part of the secondary loop extending back to the junction 39 has flowed into the heat exchanger 5, the heat exchanger 5 is fully operational and is then able to heat the cold water from the main supply which then flows through the heat exchanger 5. Consequently, a

virtually endless stream of hot water at an appropriate temperature may be drawn off through the tap 8. Should the pressure within the secondary loop rise undesirably during a period in which the tap is closed, and the pipe thermostat is sensing water at a temperature of less than 45 C, then that expansion is accommodated either within the expansion vessel 34, or by actuation of the pressure relief valve 32, with a small quantity of water being discharged to waste. The safety valve will, it is envisaged, only discharge a very small amount of water, even if an expansion vessel were not used. Consequently, it is envisaged that it may be practicable to have an alternative embodiment of the invention without an expansion vessel, although it would initially be appropriate to obtain the authority of the necessary Water Authority since, inevitably, a small amount of water will be discharged to waste. . Alternatively, the pressure relief valve may be omitted, and simply an expansion vessel may be used. In some circumstances a pressure reducing valve will not be necessary or appropriate. Whilst a pipe thermostat, such as thermostat 35 is preferred, an intermittent timer system may alternatively be utilised to ensure that hot water is frequently provided to the secondary loop 30. Although the invention has been described with reference to a combination boiler having a thermal store, it is to be understood that the invention may equally be used with combination boilers which do not have such a thermal store.

Whilst the invention has been described with reference to an embodiment in which a single secondary loop is provided with a single hot tap, it is to be appreciated that a secondary loop, such as the secondary loop 36,

may accommodate a plurality of hot taps, and indeed it is to be noted that a plurality of secondary loops may be provided in appropriate circumstances.

In the present Specification "comprises" means "includes or consists of and "comprising" means "including or consisting of'.

The features disclosed in the foregoing description, or the following Claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims

CLAIMS: 1. A combination boiler arrangement adapted to supply hot water to a tap, the boiler arrangement incorporating a heat exchanger, an input to the heat exchanger being connected, by a conduit, to a source of cold water, an outlet of the heat exchanger being connected, by a conduit, to the tap, the arrangement further including a conduit extending from a point adjacent the tap, in the conduit extending from the heat exchanger to the tap, to a point in the conduit connecting the source of water to the heat exchanger, means being provided to cause a flow of water around the loop thus created, means being provided, communicating with the loop, responsive to an increase of water pressure within the loop, to reduce the water pressure within the loop.
2. An arrangement according to Claim 1 wherein the means responsive to pressure comprise a pressure relief valve.
3. An arrangement according to Claim 1 or 2 wherein the pressure relief valve is adapted to discharge expansion water to waste.
4. An arrangement according to any of the preceding Claims wherein the means responsive to pressure comprise a expansion vessel.
5. An arrangement according to any one of the preceding Claims wherein a pressure reducing valve is provided in the conduit connecting the heat exchanger to the source of cold water, the pressure reducing valve being located at an upstream position.

<Desc/Clms Page number 12>
6. A arrangement according to any one of the preceding Claims wherein the means to cause a flow of water within the loop comprises a pump.
7. An arrangement according to Claim 6 wherein the pump is controlled by control means.
8. An arrangement according to Claim 7 wherein the control means comprise a thermostat responsive to the temperature of water in the conduit supplying water to the inlet to the heat exchanger.
9. An arrangement according to Claim 8 wherein the control means comprises a timer.
10. An arrangement substantially as herein described with reference to and as shown in Figure 2 of the accompanying drawings.
11. Any novel feature or combination of features disclosed herein.