Tap water boiler

Abstract: A tap water boiler (1) comprising a closed water tank (2) having a first connection (8) for supplying cold water, a second connection (9) for tapping hot water, as well as a closed tubing (3) placed in the water tank, through which tubing (3), in operation, hot water provided by a suitable hot water source circulates, wherein the tubing comprises a freely mounted double wound coil having an outer helically bent tube (32) and an inner helically bent tube (33), which double wound coil extends over a relatively small height compared to the height of the water tank.

Description: This invention relates to a tap water boiler comprising a closed water tank having a first connection for supplying cold water and a second connection for tapping hot water, as well as a closed tubing placed in the water tank, through which tubing, in operation, hot water provided by a suitable hot water source circulates, wherein said tubing comprises a double wound coil having an outer helically bent tube at some distance from the inner wall of said water tank and an inner helically bent tube. Tap water boilers are known in various embodiments and are normally applied in combination with a central heating tank. The central heating tank is connected with the tubing in the water tank and passes hot water through the tubing under control of a thermostat. Via the tubing, heat of the central heating water is transferred to the tap water in the water tank. It is to be noted that another hot water source, e.g. a solar collector, is also applicable. The tubing usually consists of a tube bent along a helical line, also referred to as a coil, located in the water tank and extending along the wall thereof. In the prior art tap water boilers, the coil extends over substantially the entire height of the water tank, the supply of hot water to the coil taking place near the bottom of the water tank, and the return to the hot water source taking place from the top of the water tank. The cold water supply is so arranged that the cold water is added to the stock of water in the lower area of the water tank. The hot water tapping point is provided at the top, i.e. the hot water comes from the upper area. It is a drawback of these prior art tap water boilers that the stock of water in the tank in the lower area often remains cold, e.g. in the order of 10-20 degrees C. In the upper area the water temperature may then be ± 60 degrees C. This means, however, that in proportion to the contents of the water tank such a boiler only contains a relatively small portion, e.g. in the order of 50-60% of the total contents, of hot water of the desired temperature. Moreover, in such a boiler a zone develops in which the temperature is ± 40 degrees C. In this zone the dreaded legionella bacteria may flourish, which is of courser undesirable. A tap water boiler of the type described above comprising a double wound coil which extends over substantially the entire height of the water tank has been disclosed in DE-A-1779233. Even though a double wound coil will provide an improved exchange of heat between the tubing and the water in the water tank, similar drawbacks as described above do exist in this known tap water boiler. European patent application 0 320 678 further discloses a tap water boiler having a coil placed in the space between two concentric bushes, which coil may be a double coil. In the area above the coil the outer bush narrows to an ascending pipe having a relatively small diameter, which is provided with lateral outlet openings provided in the ascending pipe wall. The inner bush is closed at the top or the bottom. The hot water tapping point is immediately above the top end of the ascending pipe. As a result of the use of the closed inner bush and the outer bush which fully encloses the coil and narrows to the top, the free circulation of the water in the hot water tank is very strongly limited. This effect is increased by the fact that the hot water tapping point is immediately above the top end of the narrowed part of the outer bush. Owing to this construction the degree of filling of the boiler is not optimal. The degree of filling of a boiler is connected with the amount of water (measured as a percentage of the total contents of the tank) that can be tapped before the temperature of the water tapped decreases significantly. Moreover, in the prior art construction there are formed zones of hardly moving water having a temperature in the order of 40 degrees C, which is an ideal condition for the development of the dreaded legionella bacteria. It is therefore an object of this invention to provide an improved tap water boiler in which the above drawbacks do not exist or occur to a lesser degree. In general, the object of the invention is to provide a high-efficiency tap water boiler having a more uniform temperature distribution in the water in the water tank. For this purpose, according to the invention, in a tap water boiler of the above type said double wound coil is mounted completely in the lower half of said water tank, in such a manner that the coil is in direkt contact with the body of water surrounded by the coil and with the water between the coil and the inner wall of said water tank and wherein the water tank is composed of two deep drawn shell portions which are connected by a weld about halfway up of the tank. The invention will be described in greater detail hereinafter with reference to the accompanying drawings in which Fig. 1 is a diagrammatic, cross-sectional representation of an example of a prior art tap water boiler; and Fig. 2 is a diagrammatic, partly cross-sectional view of an example of a tap water boiler according to the invention. Fig. 1 is a diagrammatic, cross-sectional representation of a conventional tap water boiler 1 having a closed water tank 2, in which a helically bent tube 3, often referred to as a coil, extends along the inner wall over a great portion of the height of the water tank. The coil 3 has a bottom end 4, which, in operation, is connected via a supply line 5 to a hot water source, such as a central heating furnace for supplying hot water of, e.g., 90°C to the coil. The coil further has a top end 6, from where the central heating water is returned via a return line 7 to the central heating furnace. The return water may have a temperature of, e.g., 70°C. The water tank further has a first connection 8 for supplying cold water from the mains and a second connection 9 for tapping hot water from the water tank. In the example shown, the connection 8 is provided at the top of the water tank, but is connected to a tube 10 extending in the water tank to near the bottom and having an outlet opening at the bottom of the water tank, so that the supply of cold water takes place at the bottom of the water tank. The hot water tapping point 9 is provided at the top of the water tank and also withdraws water from the upper area of the water tank; for the hot water rises in the tank. At each hot water tapping, cold water having a temperature of, e.g., 10-20°C is supplied at the bottom of the water tank. Thus, a cold zone continues to exist at the bottom of the water tank, so that the capacity of the water tank is only partly utilized. At the top of the water tank, the water is hottest, e.g. 60°C, so that between the cold zone and the upper hot zone there is a transitional area where a temperature in the order of 40°C obtains. This is a temperature at which the legionella bacteria flourish well, which is undesirable. Moreover, in the upper boiler half, a flow hardly occurs in the water, which is conducive to bacteria development and is unfavourable to a uniform temperature distribution in the water. Fig. 2 is a diagrammatic, partly cross-sectional view of an example of a boiler according to the invention. In the example shown, the tap water boiler 20 has a water tank 23 composed of an upper and a lower deep drawn shell portion 21, 22. The two shell portions are welded together about halfway up the tank, as indicated at 24. In the example shown, all connections are arranged at the bottom of the tank, but this is not strictly necessary. At 25, a connection for supplying cold water is shown. Inside the water tank, at the level of connection 25, there is provided a deflector means 26 which brings about a distribution of the inflowing cold water. In the example shown, the deflector means is plate-shaped. At 27, the hot water tapping point is shown. This tapping point consists of a connecting piece 28 which is connected to a tube 29 extending in the water tank to near the top of the water tank, so that the tapped water comes from the upper area of the tank. The main difference between the boiler of Fig. 1 and that of Fig. 2 is constituted by the tubing connected to the hot water source, such as a central heating furnace. A double wound coil arranged completely in the lower half of the water tank extends between a first connecting point 31 for supplying hot water, provided at the bottom of the water tank, and a connecting point 30 for a return line to the central heating furnace, which, in this example, is likewise provided at the bottom. The double wound coil has an outer portion 32 having a relatively large diameter and an inner portion 33 arranged inside the outer portion and having a smaller diameter. The double wound coil is located exactly in the area of the coldest zone, so that the heat transmission can take place at a maximum efficiency. Thus, a smaller total length of the coil is sufficient in principle. In the exemplary embodiment shown, the outer coil 32 is located at some distance from the inner wall of the water tank. This configuration may result in a flow within the water tank, which flow is directed upwards from the area inside the coil, fans out in the upper portion of the water tank, and then returns again along the inner wall of the water tank. Such a circulation flow results in a more uniform water distribution within the water tank. Thus, a real cold zone is avoided, as well as a zone with a temperature favourable to the formation of bacteria and hardly moving water. Experiments have shown that when using a double wound coil in only the lower half of the water tank, the effective volume of the water tank may increase to the order of 90% and more of the real tank volume. In the example shown, the central heating water first flows through the inner coil 33 from the bottom upwards and then through the outer coil 32 from the top downwards. This mode of connection is conducive to the formation of a flow in the tap water within the water tank, as described above. The connecting pints 25, 27, 30 and 31 may be passed through the tank wall at other places.

Claims: A tap water boiler (20) comprising a closed water tank (23) having a first connection (25) for supplying cold water, a second connection (28) for tapping hot water, as well as a closed tubing (32,33) placed in said water tank (23), through which tubing, in operation, hot water provided by a suitable hot water source circulates, wherein said tubing comprises a double wound coil having an outer helically bent tube (32) at some distance from the inner wall of said water tank and an inner helically bent tube (33), said double wound coil being mounted completely in the lower half (22) of said water tank (23), in such a manner that the coil is in direct contact with the body of water surrounded by the coil and with the water between the coil and the inner wall of said water tank (23), and wherein the water tank is composed of two deep drawn shell portions (21, 22) which are connected by a weld (24) about halfway up of the tank (23). A tap water boiler according to the preceding claim, characterized in that said tubing (32,33) is so connected that, in operation, the water supplied by said hot water source first flows from the bottom upwards through the inner helically bent tube (33) and then from the top downwards through the outer helically bent tube (32). A tap water boiler according any of the preceding claims, characterized in that the connections for said tubing (32,33) and for supplying cold water and tapping hot water are located in the bottom of said lower shell portion (22). A tap water boiler according any of the preceding claims, characterized in that said connection (28) for tapping hot water is located in the lower portion (22) of said water tank (23) and is provided with a tube (29) extending in said water tank (23) to near the top wall thereof.

Inventors: WILLEMSEN JOHANUS ALBERTUS H, WILLEMSEN, JOHANUS ALBERTUS HENDRIKUS
Applicants: VRIES METAAL BV, METAAL VRIES B.V.
Application year: 1993
Main classification: F24D3
IPC codes: F24D3