HOT LOOP WATER SUPPLY APPARATUS

Abstract: A hot loop water supply apparatus comprises a heating vessel (1), an electric heater (5) to heat the water in the heating vessel, a hot water outlet (6) from near the top of the vessel, a hot water return inlet (7) to return hot water to near the bottom of the heating vessel, a hot water loop (9) interconnecting the hot water outlet and the hot water return inlet and arranged to feed hot water to single lever mixer taps (8) provided around the loop and recirculate hot water from the hot water outlet to the hot water return inlet, a thermostat (11) in the heating vessel controlling the electric heater and set at a predetermined temperature to maintain the water in the heating vessel and the hot water loop at a pasteurisation temperature, which is preferably above the maximum viable temperature of legionella bacteria.

Description: This invention relates to hot loop water supply apparatus to provide hot water to hot water outlet taps. When hot water is required from conventional hot water systems, once the tap is opened, it will usually take some time for hot water to reach the tap since the water in the pipe between the tap and the hot water storage vessel has cooled during non use. The time delay can be substantial when the length of pipe is long. This is wasteful of hot water and the pipe run from the storage vessel to the tap can be breeding ground for water-borne bacteria such as legionella. Thus it would be advantageous if the water in the pipes could be maintained at a pasteurisation temperature where pasteurisation is defined in this specification as being the heating of water to a temperature sufficient to kill water-borne pathogens. DE-A-3334103.6 discloses a hot water circuit wherein hot water is circulated by gravity in a loop. The amount of water circulated is controlled by an economy valve which can interupt the flow. DE-A-3723089 discloses a hot water circuit wherein a tap is supplied with hot and cold water. When a hot water demand by the tap is detected hot water is drawn from the tank and dumped into the cold water pipe in order to avoid water wastage and provide hot water sooner to the tap. Neither of these circuits provide a system which provides a hot water loop close to the tap and maintains the water in the loop and the tank at a pasteurisation temperature. Further, neither of these circuits consider the problem of scalding by hot water delivered from the tap. The invention provides hot loop water supply apparatus including at least one hot water supply outlet tap and comprising a heating vessel; an electric heater to heat the water in said heating vessel; a pressurised cold water supply inlet to said heating vessel; a hot water outlet to draw water from near the top of said vessel; a hot water return inlet to return hot water to near the bottom of said heating vessel; a hot water loop interconnecting said hot water outlet and said hot water return inlet, said hot water loop being arranged to feed hot water to the or each hot water supply outlet tap such that hot water is available substantially immediately the tap is turned on, and to recirculate hot water from said hot water outlet to said hot water return inlet; a thermostat in said heating vessel controlling said electric heater and settable to predetermined temperature to maintain the water in said heating vessel and said hot water loop at a pasteurisation temperature which is sufficient to cause scalding; wherein the or each said hot water supply outlet tap comprises a single lever mixer tap provided with separate cold water supply and set to limit the maximum proportion of hot water flow to cold water flow so as to limit the maximum temperature of mixed water from the single lever mixer tap to a temperature below that which causes scalding. The water may be heated to between 45° and 85°C and preferably the water is heated to a temperature above the maximum viable temperature of legionella bacteria. In order to reduce the risk of a scalding injury due to the high temperature of the hot water, the or each said hot water supply outlet tap comprises a single lever mixer tap set to limit the maximum proportion of hot water flow to cold water flow so as to limit the maximum temperature of mixed water from the tap. This invention will now be illustrated by way of example with reference to the drawing. The heating vessel 1 is provided with a hot water outlet 6 near the top, and a hot water return inlet 7 near the bottom and these are connected together by a hot water loop 9. The heating vessel 1 is also provided with a drain cock 10 near the bottom to facilitate draining and flushing of the hot loop water supply system when necessary. Within the heating vessel 1 there is an electric heater 5, the element of which is sheathed in a dezincification resistant material such as Incalloy. Also within the heating vessel 1 is a thermostat 11 which is used to control the electric heater 5 and maintain the water within the heating vessel 1 at a constant preset temperature within the range 45° to 85°C: 85° being the maximum temperature for compliance with British Standard Number 3456. A pressurised cold water inlet 2 is connected to the top of the heating vessel 1, and provides a supply of cold water to replace the water drawn from the heating vessel 1 when hot water outlet taps 8 are opened. The pressurised supply also provides the pressure to the system necessary to facilitate the flow of hot water out of the taps 8, when they are opened. When in use water is heated within the heating vessel 1 by the electric heater 5 under the control of the thermostat 11. As the water is heated within the heating vessel 1, the hotter water will tend to rise and thus exit from the heating vessel 1 via the hot water outlet 6. This water will be replaced within the heating vessel 1 by cooler water through the hot water return inlet 7 which has travelled through the hot water loop 9. This is the process of thermal syphoning. As a result, the entire loop 9 is kept hot and the system is designed so that the water throughout the loop is maintained above that which is fatal to water-borne pathogens such as the legionella bacteria. The loop 9 provides water at this temperature right up to the outlet taps 8 so that hot water is available substantially immediately the taps 8 are turned on. In this way the wastage of hot water is minimised. It will be understood that the pipe of the loop 9 as well as the vessel 1 is well lagged. The vessel 1 is provided with a jacket 3 having insulating material 4. If any of the taps 8 are opened and hot water drawn from the system, then the pressurised cold water supply, will replenish the heating vessel 1 via the pressurised cold water inlet 2. The thermostat 11 within the heating vessel 1 will then cause the electric heater 5 to be switched on to keep the temperature of the water in the vessel 1 at the predetermined value. Since the cold water is input into the heating vessel 1 near the top and cool water is input near the bottom via the hot water return input, then there is little stratification within the heating vessel 1 since the flow of water into and out of the tank will tend to mix the water. Therefore, if the temperature 11 is set to control the electric heater 5 to maintain the water temperature at a temperature that is above the maximum viable temperature of water-borne pathogens such as the legionella bacteria, there should be no localised areas within the heating vessel 1 which provide favourable conditions for growth of the bacteria. Thus the risks of infection by water-borne pathogens such as the legionella bacteria within the water heater installation are greatly reduced. According to the invention the hot water outlet taps 8 are integrated into single lever mixer taps provided also with cold water supplies (not shown). These mixer taps can be provided for hand wash basins for example and the taps are set such that the maximum temperature of mixed water from the mixer taps is restricted to below that at which scalding occurs. The risk of scalding is otherwise high due to the high temperature of the hot water necessary to prevent the growth of legionella bacteria. In the diagram three hot water supply outlet taps 8 are shown. There may of course be any number of these taps according to the present invention. Also, although two connections 6 and 7 to the heater vessel 1 are shown in the diagram, any arrangement can be used that provides for hot water to flow out from near the top of the heating vessel and cooler water to be returned to near the bottom of the heating vessel 1. Further, the circulation of the water has been described hereinbefore as being facilitated by thermal syphoning. This provides a simple system with no moving parts, but the heating vessel 1 must be provided either lower than or at a level with the hot water loop 9. In another arrangement the heating vessel 1 can be provided at any elevation relative to the hot water loop 9 and a pump can be provided in the hot water loop 9 to provide the circulating force.

Claims: Hot loop water supply apparatus including at least one hot water supply outlet tap and comprising a heating vessel; an electric heater to heat the water in said heating vessel; a pressurised cold water supply inlet to said heating vessel; a hot water outlet to draw water from near the top of said vessel; a hot water return inlet to return hot water to near the bottom of said heating vessel; a hot water loop interconnecting said hot water outlet and said hot water return inlet, said hot water loop being arranged to feed hot water to the or each hot water supply outlet tap such that hot water is available substantially immediately the tap is turned on, and to recirculate hot water from said hot water outlet to said hot water return inlet; a thermostat in said heating vessel controlling said electric heater and settable to predetermined temperature to maintain the water in said heating vessel and said hot water loop at a pasteurisation temperature which is sufficient to cause scalding; wherein the or each said hot water supply outlet tap comprises a single lever mixer tap provided with separate cold water supply and set to limit the maximum proportion of hot water flow to cold water flow so as to limit the maximum temperature of mixed water from the single lever mixer tap to a temperature below that which causes scalding. Hot water supply apparatus as claimed in Claim 1 wherein said thermostat is settable to maintain the temperature of the water in said heating vessel and said hot water loop between 45° and 85°C. Hot water supply apparatus as claimed in Claim 1 wherein said thermostat is settable to maintain the temperature of the water in said heating vessel and said hot water loop above the maximum viable temperature of legionella bacteria. Hot loop water supply apparatus as claimed in any Claims 1 to 3 wherein said heating vessel is thermally insulated. Hot loop water supply apparatus as claimed in any preceding claim wherein said hot water loop is thermally insulated. Hot loop water supply apparatus as claimed in any preceding claim wherein the hot water is circulated through said hot water loop by thermal syphoning. Hot loop water supply apparatus as claimed in any of Claims 1 to 5 wherein the hot water is circulated through said hot water loop by means of a pump. Hot loop water supply apparatus as claimed in any preceding claim wherein said heating vessel is provided with a drain cock to facilitate draining and flushing of the water in said heating vessel.

Inventors: BRAHAM, GEORGE DERRICK, STEPHEN, FRANK REID
Applicants: ELECTRICITY ASSOCIATION SERVICES LIMITED
Application year: 1991
Main classification: F24D17
IPC codes: F24H1, C02F1, F24D17