GB2238104A

GB2238104A - Hot water heater with expansion space

Info

Publication number: GB2238104A
Application number: GB8925727A
Authority: GB
Inventors: Arne Vold-Johansen
Original assignee: Individual
Current assignee: Individual
Priority date: 1989-11-14
Filing date: 1989-11-14
Publication date: 1991-05-22
Also published as: GB8925727D0

Abstract

A hot water heater comprising a storage vessel (1) for heating water by means of a heating element, a supply pipe (3) with reduction valve and preferably a check valve, for supply of cold water, and a delivery pipe (2) for hot water. The delivery pipe (2) is arranged with its lower end at a level which always ensures a minimum water level in the storage vessel above the lower end of the delivery pipe such that the pressure in the air volume (4) above the water level, even at the lowest water level, does not fall below the pressure of the supply water even when the water in the storage vessel has the same temperature as the supply water. The air volume (4) functions as an expansion vessel during heating of the water avoiding the need for one separate from the storage vessel (1). <IMAGE>

Description

Hot Water Heaters The present invention relates to a method and apparatus for the accommodation of water expansion in hot water heaters.

A hot water heater is known which comprises a storage vessel having water heating means, such as an electrical heating element, a supply pipe with a reduction valve and, preferably, a check valve for the supply of cold water and a delivery pipe for hot water.

To avoid, in such a heater, return of water into the cold water supply pipe when the water expands during heating and at the same time to avoid expanded water escaping through the safety valve which is usually provided, it has been traditional to incorporate an expansion vessel in the supply pipe for the heater. Such a solution, however, involves increased heat loss when hot water passes into the expansion vessel which is connected with the cold water.

To avoid these disadvantages according to one aspect of the present invention, the delivery pipe is arranged with its lower end in the storage vessel at a level securing always a minimum water level in the storage vessel above the lower end of the delivery pipe such that the pressure in the air volume above the water level, even at the lowest water level, does not fall below the pressure of the supply water even when the water in the storage vessel has the same temperature as the supply water.According to a second aspect of the present invention, a method of accommodating water expansion in a water heater comprises maintaining an air volume in an upper portion of the heater storage vessel which volume by increased pressure accommodates the water expansion due to heating, and cold water is supplied when hot water is delivered in a quantity such that the air pressure decreases to the supply water pressure, and maintaining the water level in the storage vessel above a minimum level above the lower part of the delivery pipe to maintain the air volume pressure permanently at or above the pressure of the supply water.

The invention may be carried into practice in various ways but one water heater and its method of operation in accordance with the present invention will now be described by way of example with reference to the accompanying diagrammatic drawings, in which: Fig. 1 shows the heater as initially filled with cold water before the delivery pipe is closed; Fig. 2 shows the situation produced by continued filling with cold water after the delivery pipe has been closed; Fig. 3 shows the result of expansion of the water due to heating; and Fig. 4 shows the water level after hot water has been drawn out.

The hot water heater shown in the drawings comprises a water storage vessel 1, a delivery pipe 2 comprising a cock (not shown) and a supply pipe 3 comprising a reduction valve (not shown) and, preferably a check valve (also not shown). The storage vessel furthermore comprises an electrical heating element.

The function of an expansion vessel is provided by an air volume 4 in the upper portion of the storage vessel. The air volume is calculated according to the standard gas equation based on the expansion of the water volume in the storage vessel by heating and adjusted to the calculation of strength for the heater vessel in such a way that the pressure in the magazine will not increase more than the difference between the pressure of the water in the supply pipe which normally is 3 bar, which is set by the reduction valve, and a pressure slightly below the calculated pressure for the heater, thereby to ensure that the safety valve is not opened.

The pressure in the air volume 4 depends on the water volume in the storage vessel, the instant temperature of the water as well as the temperature and the volume of the air. When the pressure in the air volume decreases below the pressure of the supply pipe, water automatically will be supplied until the air has the same pressure as the supply water.

Fig. 1 shows filling of the vessel with cold water from the supply pipe 3 when the delivery pipe 2 is open. When the water has reached a calculated level at which for example the lower end of the delivery pipe 2 is arranged, the delivery pipe is closed by a corresponding valve and water will continue to flow into the storage vessel until the pressure in the storage vessel is the same as the water in the supply pipe, such as 3 bar. The air volume 4 now is reduced to 1/4 of the volume shown in Fig. 1. When the water is heated it will expand approximately 2.75% and the situation shown in Fig. 3 will be reached, with a pressure of approximately 8 bar and an air volume compressed to approximately 1/8 of the volume in Fig.

1. After the expansion of the water the air will be heated from the hot water and the pressure will increase further. If water now is delivered through the delivery pipe 2, the situation shown in Fig. 4 will be reached. The pressure in the storage vessel still is higher than in the supply pipe.

So far no cold water has been supplied, but when further hot water is delivered through the delivery pipe 2, the pressure in the storage vessel will decrease to the pressure of the supply pipe and cold water thereafter will flow into the storage vessel and constantly maintain an internal water level above the lower end of the delivery pipe 2. The supplied cold water will cool the water in the storage vessel. The water level in the storage vessel will now be higher due to the supplied water, thereafter will be lowered due to cooling of the total water volume and then again increased due to the heating of the water. The pressure in the storage vessel will follow such variations.

The air volume replaces an expansion tank by receiving variations of the water level due to expansion of water by heating and at the same time ensures maintenance of a minimum water level in the storage vessel as cold water automatically is supplied if and when the lower pressure limit corresponding to the pressure of the cold water is reached.

Claims

Claims:

1. A method of accommodating water expansion in a hot water heater which comprises maintaining an air volume in an upper portion of the heater storage vessel, which volume by increased pressure accommodates the water expansion due to heating, and cold water is supplied when hot water is delivered in a quantity such that the air pressure decreases to the supply water pressure, and maintaining the water level in the storage vessel above a minimum level above the lower part of the delivery pipe to maintain the air volume pressure permanently at or above the pressure of the supply water.

2. A method as claimed in claim 1 in which the necessary air volume at atmospheric pressure on initial filling of the storage vessel is calculated based on the water volume in the storage vessel, its expected temperature, the expected pressure and temperature of the supply water.

3. A method as claimed in claim 2, the hot water heater including a safety valve, in which method the opening pressure for the safety valve in relation to the calculated pressure is the basis for the strength calculation of the heater.

4. A method as claimed in claim 1 or claim 2 or claim 3, the hot water heater including a safety valve, in which the air volume is so selected that the opening pressure of the safety valve will not be exceeded when the water and the air in the magazine are heated to a maximum temperature.

5. A method of operating a hot water heater substantially as described herein with reference to the accompanying drawings.

6. A hot water heater comprising a storage vessel having water heating means, a supply pipe with a reduction valve for the supply of cold water and a delivery pipe for hot water, the delivery pipe being arranged with its lower end in the storage vessel at a level securing always a minimum water level in the storage vessel above the lower end of the delivery pipe such that the pressure in the air volume above the water level, even at the lowest water level, does not fall below the pressure of the supply water even when the water in the storage vessel has the same temperature as the supply water.

7. A hot water heater as claimed in claim 6 in which the supply pipe includes a check valve.

8. A hot water heater as claimed in claim 6 or claim 7 in which the heating means comprises a heating element.

9. A hot water heater constructed and arranged to operate substantially as described herein with reference to the accompanying drawings.