GB2304877A

GB2304877A - Water supply with heat recovery

Info

Publication number: GB2304877A
Application number: GB9618584A
Authority: GB
Inventors: Peter Selley
Original assignee: Individual
Current assignee: Individual
Priority date: 1995-09-09
Filing date: 1996-09-05
Publication date: 1997-03-26
Anticipated expiration: 2016-09-05
Also published as: GB2304877B; GB9618584D0; GB9518453D0

Abstract

Incoming water passes through the primary circuit of a heat exchanger 2 into a storage vessel 4 having means for heating the water therein. Hot water is drawn off from the vessel as required and passes to waste after use, and the path to waste incorporates a pump arrangement 8 for diverting waste water to a thermally insulated reservoir 9. Water passes from the reservoir 9 through a secondary circuit 10 of the heat exchanger, such that heat energy in the water passing to waste can be transferred to the incoming water. A pumped recirculation path 3, 12 exists between the storage vessel 4 and the primary circuit of the heat exchanger 2.

Description

WATER SUPPLIES TECHNICAL FIELD OF THE INVENTION This invention relates to water supply installations, particularly hot water supplies.

BACKGROUND Considerable heat input is often required in order to raise the temperature of an incoming water supply to a level which is suitable for baths, showers, washing machines and the like. As well as being costly to the user, there is a penalty to the environment in terms of the resources which must go into production of the required energy.

It has been proposed in EP 492 031-A to supply water to a wash basin via a heat exchanger and an instantaneous heater. A flow sensor in the supply line operates a pump to transfer the used water through a secondary circuit of the heat exchanger, thereby pre-heating the incoming supply. In practice, such an arrangement would have to be duplicated at each point of use, which would be very costly. In addition, it is difficult to pump at a rate which ensures, on the one hand, that the waste water is removed from source at an adequate rate and, on the other hand, that the flow rate is optimised for maximum heat recovery.

An aim of the present invention may be viewed as being to devise a form of water supply installations which is patentably different from known installations.

SUMMARY OF THE INVENTION The present invention proposes a water supply installation in which incoming water passes into a storage vessel having means for heating the water therein, and hot water is drawn off from the vessel as required and passes to waste after use, and the system incorporates a reservoir arranged to receive and hold the waste water before passing through a heat exchanger which is arranged such that heat energy in the water passing to waste can be transferred to the incoming water.

BRIEF DESCRIPTION OF THE DRAWINGS The following description and the accompanying drawings referred to therein are included by way of non-limiting example in order to illustrate how the invention may be put into practice. In the drawings: Figure 1 is a block diagram of a water supply installation in accordance with the invention.

DETAILED DESCRIPTION OF THE DRAWINGS The illustrated water supply system is typical of a small domestic residence or small commercial premises, although the same principle could be used with larger installations.

Cold water from a mains supply, a storage tank or a well for example, passes through an inlet pipe 1 into the bottom of a heat exchange vessel 2. Water leaves the top of the vessel via a pipe 3 to enter the lower part of a thermally insulated hot water storage vessel 4, which contains thermostatically controlled heating means (not shown), e.g. an electrical immersion heater or a tubular coil through which hot water is circulated from a boiler or the like.

Hot water is drawn off from the top of the vessel 4, as required, to pass via a pipe 5 to one or more points of use. Such points of use may typically comprise sinks, baths, showers, washing machines and the like.

As is conventional, waste water from each point of use is conducted away to a suitable drain via pipes 6 and 7. At this point the waste water will often contain considerable residual heat, making it significantly warmer than the temperature of the incoming water supplied through the pipe 1. A pump 8 is now inserted in the path to drain via pipes 6 and 7, to allow a proportion of the waste water to be diverted to a holding tank 9. The pump could be arranged to draw water from the pipes 6, 7 via a simple Tee joint, or via an electro-mechanical diverter valve which diverts all of the waste flow to the pump. The tank 9 has a jacket 1 2 or other means of thermal insulation, and is typically located at a high level relative to the installation, e.g. in a roofspace.The pump 8 is controlled by a temperature sensor (not shown) arranged to monitor the temperature of the water passing through the waste pipes 6 and 7 so that the pump only operates when the temperature is above a predetermined level. Thus, when the waste water is cold the pump does not operate so that the water travels directly to the drain via pipes 6 and 7, as normal.

From the tank 9 the warm waste water is allowed to flow under gravity through a secondary circuit 10 included in the heat exchanger 2 before passing to waste. It will be noted that, for optimum efficiency, the flow through the primary and secondary circuits of the heat exchanger are arranged for counter-flow, the primary flow being from bottom to top and the secondary flow being from top to bottom. The secondary circuit may typically comprise a coiled pipe mounted in the vessel 2. The rate of flow through the secondary circuit 10 can be controlled by an adjustable restrictor valve (tap) 11 included on the output side of the circuit 10. In the heat exchanger 2, the warm water yields up a proportion of its heat to the cooler incoming water in the primary circuit, thereby raising the temperature of the water entering the storage vessel 4.Less heat input will therefore be required in the storage vessel 4 in order to raise the temperature of the incoming water to the required level.

In systems of relatively high water capacity recirculation is provided between the storage vessel 4 and the primary of the heat exchanger 2, in the form of a return pipe 12 (indicated in dashed outline only). The pipe 1 2 connects the bottom regions of the two vessels 4 and 2, and a recirculation pump 1 3 may be included in the pipe 3 to assist in the recirculation process. The pump can be thermostatically controlled so that it only runs when the temperature of the water flowing through the secondary circuit 10 of the heat exchanger exceeds that of the incoming water supply in pipe 1. With such recirculation more efficient heat recovery is possible.

The heat exchanger 2 could be incorporated into the storage vessel 4 by mounting the secondary coil 10 in the bottom of the vessel. It will also be appreciated that safety measures are required to prevent the holding tank 9 from overflowing. This could conveniently take the form of a level sensor which acts to shut off the pump 8 when the tank is full.

In a typical installation the time required to re-heat water in the cylinder 4 from cold is reduced by between 20 and 30%. The system has the advantage that water can be removed from the point/s of use at a rapid rate whilst, at the same time, the rate of flow through the secondary circuit of the heat exchanger can be optimised for maximum heat recovery. The efficiency of the system is further improved by the fact that the heat recovered from the waste water is retained in the tank 9 and the storage vessel 4 even if it is not required immediately.

Claims

1. A water supply installation in which incoming water passes into a storage vessel having means for heating the water therein, and hot water is drawn off from the vessel as required and passes to waste after use, and the system incorporates a reservoir arranged to receive and hold the waste water before passing through a heat exchanger which is arranged such that heat energy in the water passing to waste can be transferred to the incoming water.

2. An installation according to Claim 1, in which said waste water is supplied to the reservoir via pump means.

3. An installation according to Claim 2, in which said pump means is thermostatically controlled to supply the reservoir only when the temperature of the waste water exceeds a predetermined level.

4. An installation according to any preceding claim, in which said reservoir is thermally insulated.

5. An installation according to any preceding claim, in which means is provided for adjusting the rate of flow of waste water through the heat exchanger.

6. An installation according to any preceding claim, in which a recirculation path is provided between the storage vessel and the heat exchanger.

7. An installation according to Claim 6, in which said recirculation path includes means for pumped recirculation.

8. A water supply installation in which incoming water passes through the primary circuit of a heat exchanger into a storage vessel having means for heating the water therein, and hot water is drawn off from the vessel as required and passes to waste after use, and the path to waste incorporates means for diverting waste water to a reservoir arranged to receive and hold the waste water before passing through a secondary circuit of the heat exchanger arranged for counter-flow relative to the direction of flow through the primary circuit, such that heat energy in the water passing to waste is transferred to the incoming water, and in which a pumped recirculation path exists between the storage vessel and the primary circuit of the heat exchanger.

9. A water supply installation substantially as described with reference to the drawings.