EP0747642A1

EP0747642A1 - Hot-water storage heater

Info

Publication number: EP0747642A1
Application number: EP96201587A
Authority: EP
Inventors: Johannes Albertus Hendrikus Willemsen
Original assignee: METAAL VRIES BV
Current assignee: Heatex BV
Priority date: 1995-06-06
Filing date: 1996-06-06
Publication date: 1996-12-11
Anticipated expiration: 2016-06-06
Also published as: DE69614926D1; EP0747642B1; NL1000503C2; DE69614926T2

Abstract

A hot-water storage heater comprises a reservoir (1), a heating element (2) in the reservoir (1), a supply channel (5) opening into the reservoir (1) adjacent a first end (6) of the reservoir (1), and a delivery channel (9) having an inlet (10) adjacent a second end (11) of the reservoir (1) located opposite the first end (6) and having at least one further inlet (12) adjacent the first end (6) of the reservoir (1). The inlet (10) and the further inlet (12) interconnect adjacent the first end of the reservoir (1). As a result, cold water in the cool area of the reservoir is admixed to the hot water, so that when water is being drawn off after no water has been drawn off for a longer time, there is no initial delivery of a plug of very hot water and calcium precipitation in the delivery channel as a consequence of water heating up therein is prevented.

Description

The invention relates to a hot-water storage heater for heating and storing a buffer stock of hot water.
In order to increase the amount of water to be delivered within a short period of time when using a hot-water storage heater of a given capacity, it is known to heat the water in the hot-water storage heater to a temperature above the intended draw-off temperature and to automatically admix cold water each time after the draining of water from the hot-water storage heater, so that the water delivered at the draw-off point has yet the intended, slightly lower maximum temperature. If, in the case of an intended maximum hot-water temperature of 60°, the water in the hot-water storage heater is for instance heated to 80°, then cold water is automatically admixed when water is being drawn off, so as to reach the intended temperature of 60°. Higher hot-water temperatures are not desirable for domestic use, because then the risk of scalds increases substantially.
For automatically admixing cold water during drawing off, a mixing device is used which is accommodated in the delivery pipe downstream of the hot-water storage heater. Also connecting to the mixing device is a cold-water supply pipe. However, a drawback of this mixing device is that the costs thereof and of additional piping for connecting the mixing device are considerable. Further, the mixing device and the required additional piping take up space.
GB-A-1 142 404 discloses a hot-water storage heater according to the preamble of claim 1. In operation condition, the first end forms the bottom end of the reservoir and the second end forms the top end of the reservoir. When water is being drawn off from the reservoir, cold water flows in via the supply channel. As a result, the temperature of the water in the area of the mouth of the supply channel drops. When water is being drawn off, relatively cold water is added, via the further inlet adjacent the bottom end of the reservoir, to the hot water supplied from the top end of the reservoir, so that the temperature of the drawn-off water is reduced to the intended draw-off temperature. Because hot water of the set temperature from the top and cold water from the bottom are mixed, water of a constant temperature can be delivered for a relatively long time. Fixing a further inlet entails few costs and no propivions are required for mixing (unduly) hot water and cold water outside the reservoir.
A drawback of this known boiler is that if water is drawn off after no water has been drawn off for a longer period, the drawn-off water first has a temperature which is too high for too long a period. Inspite of the initially cooling effect of the pipes through which the water generally flows before it reaches the user - these pipes have cooled down after no hot water has passed for a longer period - this causes a considerable risk of the user suffering scalds, especially when suddenly, after an initial flow of water from the tap which is colder than desired, very hot water flows from the tap. If the user, by operating a mixing tap, has admixed cold water from the beginning, another problem presents itself in that the temperature of the water flowing from the tap, after being set, drops and should be readjusted. Especially when the user is having a shower and is in contact with the outflowing water over a large surface, the danger of scalds and the inconvenience of the above-mentioned drop of temperature are of particular importance.
Another drawback of such known hot-water storage heaters is that the delivery temperature of the water increases gradually when they are installed and in operation for a longer time.
Further, such hot-water storage heaters entail the problem that the water delivery decreases when they are installed and in operation for a longer time.
The object of the invention is to provide a hot-water storage heater wherein, in use, less hot water is delivered when water is being drawn off after no water has been drawn off for a longer time, wherein the delivery temperature increases less when the hot-water storage heater is installed and in operation for a longer time and wherein the water delivery at a given pressure decreases less over the life of the hot-water storage heater.
In accordance with the present invention, this object is realized by designing a hot-water storage heater of the above-described type in accordance with the characterizing part of claim 1.
The fact that the inlet for hot water from the top area of the heater and the further inlet for cold water from the bottom area of the heater interconnect adjacent the first, lower end of the reservoir, i.e. in the cool area of the reservoir, avoids the effect that cold water to be admixed warms up in the delivery channel through heat exchange with the water in the portion of the reservoir through which the portion of the delivery channel with the water to be admixed extends. As a result, if water is drawn off after no water has been drawn off for a longer time, there is no initial admixture of a considerable plug of hot water instead of cold water to the unduly hot water from the top area of the reservoir, but cold or at least cool water from the bottom area of the reservoir is admixed immediately. Moreover, after no water has been drawn off for a longer time, the hot water in the delivery channel located in the central area and the bottom area of the reservoir has cooled down slightly. When water is then drawn off, this relatively cool water is first mixed with the slightly warmed-up water in the bottom area of the reservoir.
Because of these effects, the increase of the delivery temperature during drawing off after no water has been drawn off for a longer time does not occur or at least to a considerably limited extent, and the volume of water having an increased delivery temperature, if present, is considerably smaller.
The fact that the cold water in the cool area of the reservoir is admixed to the hot water further prevents the effect that through heat transfer from the hot water, the water in the delivery channel to the admixed is heated so that calcium precipitation or at least substantial calcium precipitation occurs in the delivery channel. In particular in the part of the delivery channel through which the water to be admixed should pass, this calcium precipitation causes an increase of the flow resistance, so that in the end, less and less cold water can be admixed. Also in the area where the inlets of the delivery channel for cold and hot water interconnect, calcium precipitation resulting from water heating up in the delivery channel is prevented, so that the problem of a decrease of the water delivery after the heater has been installed for a longer time is prevented.
Particular elaborations of the invention are described in the dependent claims.
Hereinafter, the invention will be specified on the basis of some exemplary embodiments with reference to the accompanying drawings, wherein:

Fig. 1 is a cutaway side elevation, shortened in vertical direction, of a hot-water storage heater according to the most preferred embodiment of the invention,
Fig. 2 is a larger side elevation, in section, of a central bottom portion of the hot-water storage heater according to Fig. 1, and
Fig. 3 is a view according to Fig. 2 of a hot-water storage heater according to a second embodiment of the invention.

In the drawings, corresponding parts of different embodiments are designated by mutually identical reference numerals.
At first, the invention will be specified with reference to the example shown in Figs. 1 and 2. After that, the types shown in Fig. 3 will be discussed.
The hot-water storage heater according to the example shown in Figs. 1 and 2 comprises a closed reservoir or vessel 1 for storing water. Accommodated in the reservoir 1 is a heating element 2 for heating the water in the reservoir 1. The heating element 2 of the hot-water storage heater shown is designed as a spirally extending pipe which can be connected to a heating boiler (for instance a boiler with which water of a central heating system is heated as well). The pipe extends between two nozzles 3, 4 sealingly mounted in the wall of the reservoir. Adjacent the bottom 6 of the reservoir 1, a supply channel 5 opens into the reservoir 1. The supply channel 5 is intended for supplying water to the reservoir 1 as indicated by the arrow 7. For delivering water, as indicated by an arrow 8, the reservoir 1 comprises a delivery channel 9 having an inlet opening 10 adjacent the bottom side 11 of the reservoir 1, which bottom side 11 is located opposite the bottom 6. The delivery channel 9 further has a further inlet opening 12 adjacent the bottom 6 of the reservoir 1. In Fig. 1, this further inlet opening is shown schematically by a dot and dash line. Further accommodated in the reservoir 1 is a sensor 20 of a thermostat which senses the temperature of the water above the heating element 2. The sensor 20 is coupled to a control valve (not shown) controlling the supply of hot water to the heating element 2. In this manner, the maximum temperature of the water above the heating element 2 can be controlled in an accurate manner.
When water is being drawn off from the reservoir 1 via the delivery channel 9, cold water flows into the reservoir adjacent the bottom 6, via the supply channel 5. A part of the drawn-off water is formed by hot water of approximately the set temperature, which water has flown into the delivery channel 9 from a position adjacent the top side 11 of the reservoir 1, via the upper inlet 10. Another part of the drawn-off water is formed by water which has flown into the delivery channel 9 from a position adjacent the bottom 6 of the reservoir 1, via the lower inlet 12. Generally, water adjacent the bottom 6 of the reservoir 1 is cooler than the water adjacent the top side 11 of the reservoir 1. Moreover, the water adjacent the bottom 6 of the reservoir 1 is mixed with inflowing cold water as soon as water is being drawn off from the reservoir. Owing to the low temperature of the part of the drawn-off water that is drawn off from a position adjacent the bottom 6 of the reservoir 1, the draw-off temperature of the water from the hot-water storage heater is lower than the set temperature of the hot-water storage heater. In use, the hot-water storage heater can deliver hot water for a long time, because during drawing off, only a part of the water consists of hot water supplied from the top of the hot-water storage heater. The rest of the drawn-off hot water is colder water, which has remained in the hot-water storage heater only briefly.
Only little mixing takes place between the hot water in a top portion of the hot-water storage heater and the cold water at the bottom of the hot-water storage heater. Consequently, the hot-water storage heater can deliver water of a fairly constant temperature for a long time.
When no water has been drawn off from the hot-water storage heater for a long time, water at the bottom of the reservoir will be relatively warm, so that during drawing off, the water temperature will initially be relatively high. However, to a limited extent, this effect does form a favorable compensation for the cooling action which, during drawing off, is initially caused by the pipes, still cold, downstream of the hot-water storage heater. As cool water from the bottom area of the reservoir is admixed directly, unlike hot-water storage heaters where admixing takes place in the top area of the revervoir, the delivery temperature is in any case always considerably lower than the water temperature in the top area of the reservoir 1.
The delivery channel 9 extends through a pipe 13 which extends from the bottom side 6 to a position adjacent the top side 11 of the reservoir 1. The further inlet opening 12 is obtained in a very simple manner by providing a passage in the wall of the pipe 13, as appears most clearly from Fig. 2. In principle, this passage can have any suitable shape, but it is preferably designed as a bore in the tube 13. The surface of the bore determines the ratio between the amounts of water passing through the upper inlet 10 and the further lower inlet 12 during drawing off, and, accordingly, the temperature of the drawn-off water.
In front of the mouth of the supply channel 5, a distributing surface 19 is mounted, directed approximately transversely to the supply channel 5. By this distributing surface, water flowing in via the supply channel 5 during drawing off is distributed, which prevents the inflowing, cold water from directly reaching the higher parts of the reservoir 1. As the inflowing water is thus held in the area of the bottom, the water temperature adjacent the bottom 6 is kept relatively constant, so that an even temperature of the drawn-off water is obtained.
To ensure that via the upper inlet opening 10 hot water is delivered as long as possible, and via the lower inlet opening 12 water is delivered which is warmed up as little as possible, the upper inlet opening 10 should preferably be located at a highest possible position and the lower inlet opening 12 should preferably be located at a lowest possible position. A guideline which can be adopted is that these openings 10, 12, in installed condition and calculated from the lowest point of the bottom 6, should be located at a position higher than 90-95% and lower than 5-10% respectively of the height of the reservoir 1.
Fig. 3 shows a portion of an embodiment of the hot-water storage heater according to the invention, wherein the passage 12 is designed as a pasage 12 in a fitting 14 sealingly connecting to the tube 13. This fitting also projects through the bottom 6 of the reservoir 1 and is sealed relative to the bottom 6.
The embodiment according to Fig. 3 is provided with several passages to obtain a better mixing of the water in the delivery channel 9.
If several further inlet openings 12 are provided, it is also advantageous to provide them at different distances from the bottom 6 of the reservoir 1. As a result, water is in each case admixed stepwise at different heights in the delivery channel 9, so that any fluctuations of the water temperature at a particular height have a lesser impact on the temperature of the drawn-off water.
It will be understood by anyone skilled in the art that within the framework of the invention, many variants of the embodiments described are possible. For instance, as heating element, a electric heating element (for instance a heating spiral) to which electric lines connect, can be used.

Claims

A hot-water storage heater comprising a reservoir (1), a heating element (2) in the reservoir (1), a supply channel (5) opening into the reservoir (1) adjacent a first end (6) of the reservoir (1), and a delivery channel (9) having an inlet (10) adjacent a second end (11) of the reservoir (1) located opposite said first end (6) and having at least one further inlet (12) adjacent said first end (6) of the reservoir (1), characterized in that said inlet (10) and said further inlet (12) interconnect adjacent said first end of the reservoir (1).
A hot-water storage heater according to claim 1, wherein the delivery channel (9) extends through a pipe extending from said first end (6) to a position adjacent said second end (11), and at least one of said inlet openings (10, 12) is designed as a passage in the wall of said pipe (13).
A hot-water storage heater according to claim 2, wherein said pipe comprises a tube (13) and said passage is designed as a bore (12) in said tube (13).
A hot-water storage heater according to claim 2, wherein said pipe comprises a tube (13) and a fitting (14) connecting to said tube (13), said fitting (14) projecting through a wall of the reservoir (1) and being sealed relative to said wall, and wherein said passage (12) is provided in said fitting (14).
A hot-water storage heater according to claim 1, comprising a number of said further inlet openings (12), said further inlet openings (12) being located at different distances from said first end (6) of the reservoir (1).