GB2237863A

GB2237863A - A hot water supply system

Info

Publication number: GB2237863A
Application number: GB8921694A
Authority: GB
Inventors: Brian James Williams
Original assignee: GWENT HEALTH AUTHORITY
Current assignee: GWENT HEALTH AUTHORITY
Priority date: 1989-09-26
Filing date: 1989-09-26
Publication date: 1991-05-15
Also published as: GB8921694D0

Abstract

A hot water supply for hospitals and hotels generally indicated at 10 has first and second heat exchangers 11, 12 having respective heat exchange elements 13 and 14 and 15 and 16. The first heat exchanger 11 is supplied with cold water and this is fed, through a diverting valve 18, to heat exchange element 14. From there water passes to heat exchange 15 and then back to heat exchanger element 13 into a single pipe domestic hot water supply 21. The arrangement enables the incoming cold water to be heated in heat exchanger 12 to a temperature which is sufficiently high to destroy any legionella bacteria and that water can then be cooled by the incoming cold water in heat exchanger 11 to the temperature required in the single pipe supply 21. The water temperature is maintained in the supply 21 by electrical heater tape 28 wrapped around the pipe and/or by insulation. <IMAGE>

Description

A Hot Water Supply System This invention relates to hot water supply systems and in particular, but not exclusively, to systems for large buildings such as hospitals and hotels.

Whilst the publicity relating to legionella outbreaks has tended to concentrate on problems with air conditioning towers, it is now appreciated that a considerable problem can arise where large quantities of stored hot water are kept in calorifiers and the like.

It is now recognised that the legionella bacteria can be killed if heated to a high temperature but in most instances it is not possible simply to heat up the stored water, because of the risk of scalding and the very large heat losses which would occur.

From one aspect the invention consists in a hot water supply system comprising means for heating water to a temperature above 600C, means for cooling the heated water to below 600C, a single pipe water supply system for supplying the cooled water and means for maintaining the water in the single pipe water supply within a predetermined temperature range.

The use of the single pipe water supply to store hot water overcomes the need for any calorifiers, whilst the cooling of the first-heated water means that the problem of scalding can be removed. The system can also be operated on an immediate supply and demand basis, thus reducing considerably the amount of plant required in a hot water system both in terms of storage and return pipes.

The system is preferably arranged so that from time to time the cooling means can be switched off so that the whole system can be "sterilised" by the heated water.

From another aspect the invention consists in a hot water supply system, including a single pipe water supply, first and second heat exchangers having first and second and third and fourth heat exchanger elements respectively, means for connecting a cold water supply to the input of the first element, means for connecting the output of the first element to the input of the third element, means for connecting the fourth element into a hot water circuit, means for connecting the output of the third element to the input of the second element, means for connecting the output of the second element to the single pipe water supply and means for maintaining the temperature in the single pipe water supply within a predetermined range.

The supply may further include the hot water circuit in which the hot water circuit may heat the water in the third element to over 600C and preferably to between 70-75 C. Similarly the water in the second heat exchanger is preferably cooled to below 600C and is maintained in the range 40-600C. The supply may include bypass means for bypassing the first element so as to vary the rate of cooling the water in the second element and hence the temperature of the water supplied to the single pipe supply. The supply may also include further bypass means for bypassing the fourth element so as to vary the rate of heating of the water in the third element.

In any of the above cases the means for maintaining the temperature in the single pipe water supply may include an electrical heater tape wrapped around at least part of the pipe. Advantageously it is wrapped around all of the pipe so that "hot" water is available immediately at any tape at the end of the supply. Additionally or alternatively the pipe may be insulated.

Although the invention has been defined above it is to be understood that it includes any inventive combination of the features set out above or in the following description.

The invention may be performed in various ways and a specific embodiment will now be described, by way of example, with reference to the accompanying drawing which is a schematic diagram of a hot water supply system.

A hot water supply system generally indicated at 10 has first and second heat exchangers 11,12 having respective heat exchange elements 13 and 14 and 15 and 16.

The first heat exchanger 11 is supplied with cold water from a cold water source 17 and this is fed through a diverting valve 18 to heat exchange element 13. From there it passes via a pipe 19 to heat exchange element 15 of the second heat exchanger 12 and then back, by pipe 20 to the first heat exchanger 11 where it passes through the exchange element 14 into a single pipe domestic hot water supply 21, which feeds a number of taps and the like 21.

The other heat exchange element 16 of the second heat exchanger 12 is fed with hot water from a boiler (not shown) via a hot water circuit generally indicated at 23. The hot water passing through the element 16 heats the hot water in the element 15 to a temperature of 70-750C thus killing the legionella bacteria which existed in the water from the source 17. This treated water is then cooled, by the inflowing cold water in element 13, as it passes through the element 14 to the domestic hot water supply 21.

This operation also has the effect of preheating the incoming cold water before it is fed into the second heat exchanger 12.

The temperature of the water entering the domestic hot water supply 21 is detected by temperature detector 24 which controls the diverting valve 18 to enable it to bypass the first heat exchanger when, and to the extent required, so that the rate of cooling in the first heat exchanger can be lowered to increase the temperature of the water leaving the second element 14.

A similar diverting valve 25 is provided in the hot water circuit 23 so that the heating effect of element 16 can be varied in accordance with a control signal produced by temperature detector 26 located adjacent the output of element 15.

The domestic hot water supply 21 is in the form of a single pipe 27 which is surrounded by insulating tape 28 which includes an electrical heating element which can be switched on and off under the control of temperature detectors (not shown) to maintain the water in the tap to that required by the user.

It will thus be seen that there is no need for any large scale water storage and that all water passing through the domestic hot water supply 20 will have first been sterilised. To prevent the unlikely build up of any legionella bacteria in the system downstream of the element 15 the diverting valve 18 can be set for full bypass flow so that the whole system can be flushed out with water at a temperature over 700C hence killing any colonies of bacteria which may have built up.

The invention also includes the method of operating a supply in the manner set out above.

Claims

l. A hot water supply system, comprising means for heating water to a temperature above 600C, means for cooling the heated water to below 60 C, a single pipe water supply system and means for maintaining the water in the single pipe water supply within a predetermined temperature range.
2. A hot water supply system, including a single pipe water supply, first and second heat exchangers having first and second and third and fourth heat exchanger elements respectively, means for connecting a cold water supply to the input of the first element, means for connecting the output of the first element to the input of the third element, means for connecting the fourth element into a hot water circuit, means for connecting the output of the third element to the input of the second element, means for connecting the output of the second element to the single pipe water supply and means for maintaining the temperature in the single pipe water supply within a predetermined range.
3. A supply as claimed in Claim 2, further including a hot water circuit and wherein the hot water circuit heats the water in the third element to over 600C.
4. A supply as claimed in Claim 3, wherein the water in the third element is heated to between 0 70-75 C.
5. A supply as claimed in any one of Claims 2 to 4, wherein the water in the second heat exchanger is cooled to below 600C.
6. A supply as claimed in any one of Claims 2 to 5, wherein the water in the single pipe water supply is maintained in the range 400C to 600C.
7. A supply as claimed in any one of Claims 2 to 6, further including by-pass means for by-passing the first element so as to vary the rate of cooling of water in the second element and hence of the temperature of the water supplied to the single pipe supply.
8. A supply as claimed in any one of Claims 2 to 7, further including further by-pass means for bypassing the fourth element so as to vary the rate of heating of the water in the third element.
9. A supply as claimed in any one of the preceding claims, wherein the means for mounting the temperature in the single pipe water supply includes an electrical heater tape wrapped around at least part of the pipe.
10. A supply as claimed in any one of the preceding claims wherein the pipe is insulated.
11. A hot water supply substantially as hereinbefore described with reference to the accompanying drawings.