GB2071306A

GB2071306A - Apparatus for heating water and for keeping it in store in heated condition

Info

Publication number: GB2071306A
Application number: GB8101495A
Authority: GB
Original assignee: Stichting Bouwcentrum
Current assignee: Stichting Bouwcentrum
Priority date: 1980-01-22
Filing date: 1981-01-19
Publication date: 1981-09-16
Also published as: DE3101199A1; FR2476286A1; NL8000402A; BE887158A

Abstract

Apparatus for heating water and storing said heated water and comprises a housing (1) in which one or more cylindrical containers (3) for the water are disposed side by side, and a connection (6) for connecting a supply conduit (7) to a header conduit (5) for cold water and with a connection for connecting a discharge conduit (10) to a header conduit (9) for hot water, the housing consisting of a box in which the tubes lie on insulation, closed with a cover permeable to solar radiation. The diameter of the tubes is between 5 and 10 cm, and they are made of brass, aluminium, or synthetic plastic material. The cover, Fig 2 (not shown) comprises evacuated glass tubes mounted side by side between two panes of glass. To prevent overheating temperature sensors and a ventilation fan may be provided. <IMAGE>

Description

SPECIFICATION Apparatus for heating water and for keeping it in store in heated condition This invention relates to apparatus for heating water and, so long as no hot water is withdrawn, keeping the water in store in heated condition, comprising a housing in which one or more containers for the water to be heated and to be kept in store are disposed, which housing is provided with a connection for connecting a supply conduit for cold water and with a connection for connecting a discharge conduit for hot water.

Such an apparatus is generally known by the name of "boiler" or water heater. Prior apparatus of this type is generally provided with means for heating the water in the container or containers. In the prior apparatus, such means may consist of a supply of air heated for example by means of a gas burner, which air is passed around the containers, or may consist of electrical heating means. The water heated by means of the heating means is kept in store in the apparatus, and hot water is withdrawn from the apparatus only if needed. The conduit for supplying cold water to the boiler is commonly a conduit connected to the water mains, so that the pressure at which cold water is supplied to the apparatus is equal to the pressure at which water is supplied to the house or other space in which the boiler is arranged. Means may be provided for controlling the supply of water.

The discharge conduit is commonly connected to taps in the house or other space in which the boiler is arranged. Hot water is withdrawn from these taps only when needed by consumers.

It is an object of the present invention to provide an apparatus of the above type in which the manner of heating the water is different from the manner in which the water is heated in prior apparatus, and a particular object is to provide an apparatus in which the heat of solar radiation is used for directly heating the water in the apparatus.

The object contemplated is achieved, according to the invention, with an apparatus designed as a collector for collecting solar heat, for which purpose the containers for the water consist of a plurality of substantially cylindrical tubes arranged in side-by-side relationship in the housing, the housing proper consisting of a box in which the tubes lie, covered with a cover permeable to solar radiation.

In the apparatus according to the invention, the water is heated by direct irradiation of the cylindrical containers in which the water is kept in store. In a suitable embodiment of the apparatus according to the invention, the cylindrical tubes are connected at one end by means of a connector to a supply conduit for cold water, and at the opposite end coupled by means of a connector to a discharge conduit for heated water, the supply conduit and discharge conduit being contained in the housing and being connected to the above connections. The supply conduit for cold water is connected by means of the connection to the cold-water conduit in the housing or other building in which the apparatus is disposed, and the discharge conduit is connected by means of the connection to the conduits from which hot water is withdrawn by consumers.

The number of cylindrical tubes contained in the apparatus according to the invention depends on the amount of water which it is desired to keep in store, and is partly determined by the permissible diameter of the tubes. It will be clear that the diameter of the container tubes cannot be taken of just any large size, as in that case the capacity of the sun's rays for sufficiently heating water stored in such a tubular container will be insufficient. A suitable interior diameter for the container tubes is 7 to 8 cm. The minimum diameter should be approximately 5 cm, or the storage capacity per tube is insufficient, and the maximum diameter is approximately 10 cm. When the diameter is larger than 10 cm the amount of water per unit of cross-sectional area is too large for it to be heated to a suitable temperature level.

For a boiler for normal domestic use, a total surface area of the apparatus of 4-5 m2 appears to be suitable. Using container tubes approximately 2 m long, this means an overall width of side-by-side tubes of approximately 2-2.5 m. The apparatus according to the invention can be easily adapted to suit requirements by using standard container tubes.

The number of tubes is then selected in accordance with the consumer's requirements.

The tubes in the apparatus according to the invention may consist of any suitable material capable of absorbing heat from solar radiation and transmitting it to water contained in the tubes.

From the point of view of heat absorption, brass is most satisfactory, but this is a rather expensive material. In practice, aluminium has been found to be very satisfactory. It is also possible to use synthetic plastics material for the tubes, although such material has the drawback of being a poor heat conductor. Tubes made of synthetic plastics materials accordingly run the risk, when used in the apparatus according to the present invention, of being rapidly heated, and becoming hot, at the front, i.e., the side exposed to the sun's rays, whereas the back still remains cold, which could give rise to bending.

In the apparatus according to the invention, the container tubes are preferably connected at their ends to rather heavy supply and discharge conduits, so that there is virtually no difference in pressure between the various input openings of the various tubes, no more does such a pressure difference occur at the output openings.

In a suitable embodiment, the housing of the apparatus according to the invention is a box in which the tubes with supply conduits and discharge conduits are arranged, the tubes being preferably laid on a layer of insulating material provided on the bottom of the box. Such material is desirable to prevent undesirable dissipation of heat to the surroundings by the apparatus. In addition to the bottom, every sidewall and also the edge of the box will be covered with insulating material. The box with the container tubes therein is covered at the side directed to the sun's rays by a cover of material permeable to solar radiation.

Suitably the container is closed with a cover consisting of two glass panes. Preferably the space between the two glass panes is partially evacuated. This will considerably reduce loss of heat from conduction. It is also possible for the cover to consist of two glass panes with a layer of glass tubes interposed between them, which glass tubes are sealed at opposite ends, the cavity within the glass tubes being evacuated, and a heat-reflecting layer, permeable to solar radiation, being provided on the inner wall of the glass tubes. A cover constructed in this way is known per se.

In order to be able to operate, the apparatus according to the invention must be arranged so that the tubes are accessible to the sun's rays through the glass cover or through the radiationpermeable cover. Suitably, therefore, it will be possible for the apparatus to be built into the roof of the building in which the apparatus is used, approximately in the manner in which conventional solar collectors are built in. It is observed that there are solar collectors which at first sight bear some resemblance to the apparatus according to the present invention.

Such solar collectors comprise a housing or box accommodating tubes through which water is conducted, the tubes being heated, directly or indirectly, by means of the heat from the solar radiation. With such known collectors, however, the water is used as a fluid for transporting heat.

The water heated in the collectors is immediately discharged from them, and the heated water gives up its heat to a heat storage apparatus elsewhere.

In contrast therewith, in the apparatus according to the present invention, the water remains present. Only a small portion of the water may be tapped by the consumer from time to time at moments hot water is needed. The difference between prior collectors in which water is used as a transporting medium and the apparatus according to the present invention will immediately be clear when the diameter of the water tubes is regarded. In the apparatus according to the present invention, this diameter is rather large and, as stated before, is determined on the ground of considerations with regard to the amount of water which it is desired to keep in store in heated condition and the amount that can be heated. In the case of collectors, where water is used as a heat transporting medium, the diameter is relatively small.Another difference between the apparatus of the present invention and prior collectors in which water is used as a heat transporting fluid consists in that, in the apparatus according to the invention, no mechanical means are provided for transporting the water. It is therefore a passive system. In the case of collectors in which water is used as a heat transporting fluid, however, a pump is provided for circulating the heat transporting fluid from the collector to a storage system and back to the collector.

On very sunny days, when accordingly a great amount of heat is supplied, there may be the problem in the apparatus according to the invention of the water becoming too hot. In such cases a certain protection from overheating is needed. Preferably, therefore, the apparatus is provided with means for determining the temperature of the water in the tubes and with means for causing air to flow along and around the tubes, if necessary, in dependence on the temperature determined. It is thus possible to provide for air cooling, if the temperature rises above a pre-determined value. It may be sufficient to provide suitable apertures in the wall of the apparatus according to the invention, so that there is naturai circulation of air from the house through the apparatus to the outside, or back into the house. In this way, undesirable boiling effects can be prevented.

Naturally, it is also possible to provide for mechanical ventilation, operated under the control of the means for determining the water temperature. In the case of cooling by means of currents of air, the air can be conducted between the tubes and the glass cover, but preferably the air is conducted behind the tubes for the cooling.

This prevents fouling of the glass cover on the inside.

In principle no pump is required for tapping hot water from the apparatus. The normal water pressure is mostly sufficient for operating the apparatus.

In winter, when there is little sunshine, whereas the temperature outside the house or other building in which the apparatus is arranged is very low, there is the danger that the water in the apparatus according to the invention is frozen.

Such a danger will presumably not occur if a cover is used consisting of a plurality of layers of glass between which a reduced pressure is maintained, or consisting of the above-described layer of hollow, evacuated, glass tubes. In apparatus in which the danger is realistic, there may be provided means for supplying heat to the apparatus. If the apparatus is provided with the above means for cooling in the case of overheating, such means can be similarly utilized for conducting air from the house along the tubes with water.

Some embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which Fig. 1 is a diagrammatic plan view of an embodiment of the apparatus according to the present invention; Fig. 2 illustrates a cross-sectional view of the apparatus of Fig. 1, taken on the line Il-Il; Fig. 3 is a diagrammatic cross-sectional view of a different embodiment of the apparatus according to the invention; and Fig. 4 illustrates a supporting element which can be used for supporting the cylindrical containers for water in the apparatus according to the invention.

In the drawings, corresponding parts are designated by the same reference numerals.

The embodiment of the apparatus according to the invention illustrated in Figs. 1 and 2 comprises a box 1. The box 1 may be made of any suitable material, e.g. of wood, and serves for containing and supporting the containers of the water to be heated and already heated. When the apparatus according to the invention is used in a houseor other building the box 1 will commonly be built into the roof, with the bottom side facing the building, and the top side being directed outwardly.

Provided on the bottom and along the sidewalls and the upper and lower edges of box 1 is a layer of heat-insulating material. Positioned on top of layer 2 on the bottom are a plurality of closelyspaced side-by-side tubes 3, in which the water to be heated is kept in store. As shown, the top surface of layer 2 on the bottom of container 1 may be adapted in form to tubes 3, so that, as it were, tubes 3 lie in a bed of insulating material.

The cylindrical tubes 3 are, for example, 2 m long and have an interior diameter of 7 to 8 cm. Tubes 3 preferably consist of a material which is a fairly good or good heat conductor, e.g. aluminium or brass. Nevertheless, tubes of synthetic plastics material could be used. Box 1 has such dimensions that, for example, 20 to 30 tubes can be disposed in it in side-by-side arrangement.

When the tubes have an interior diameter of 8 cm, this means a capacity of 200 to 300 litres. If a larger capacity is required, the number of tubes can of course be increased. Box 1 should then be enlarged as well, but it is also possible to use a second box.

Storage tubes 3 are provided at opposite ends with connectors or short pipes 4. All tubes 3 are connected through the short pipes 4 at one end to a supply conduit 5. The supply conduit 5 is passed through the wall of container 1 and provided at the end projecting from the wall of container with a flange 6 for connection to a water supply pipe 7, which, for example forms part of the water mains, and is also provided with a flange 8 for the purpose. Naturally, a different manner of coupling to the water mains may be provided. Supply conduit 5 preferably has a rather large interior diameter, so that there is virtually no difference in flow resistance between the input openings of the coupling pipes 4 of the various tubes 3.

At the other end, tubes 3 are connected through short pipes 4 to a discharge conduit 9.

Conduit 9 is also such that there are virtually no differences in pressure between the various outlet openings. Discharge conduit 9 is passed through the wall of container 1 and connected to a water discharge pipe 10. Pipe 10 is provided elsewhere in the house or other building in which the apparatus according to the invention is arranged with one or more tap points. If necessary, an afterheater may be included in pipe 10 to provide for the case that the water is insufficiently heated in the apparatus. Accordingly, every time water is taken from the water discharge pipe at a tap point, a portion of the water is removed from tubes 3.

Box 1 is closed at the top with a cover which in the embodiment illustrated in Fig. 2 consists of a pair of glass panes 11 and 12 accommodating between them a large number of glass tubes 13, which lie closely together. Tubes 1 3 are hollow tubes, sealed at their ends after being evacuated.

Preferably, a spectral-selective coating is provided on the inner wall of each tube. The cover thus constructed is maintained on box 1 with suitable fasteners 14 or otherwise.

In operation, tubes 3 are filled with water. As soon as the sun's rays fall through the cover onto the tubes, the tubes and the water contained in them are heated. Subsequently hot water can be tapped at any desired moment. No pump is required for transporting the water, the normal water pressure of the mains provides for transport as soon as a tap connected to the discharge pipe is opened. Transport only occurs at moments when hot water is withdrawn.

On days when much solar radiation is collected by the apparatus, the temperature of the tubes 3 and the water in them may reach high values. In order to prevent the temperature from becoming excessive, box 1 may be provided at suitable places with openings in its wall, to provide for natural circulation of air from the space beneath the roof in which the apparatus is built in, through box 1, whereby the tubes are cooled. It is also possible to provide for controlled mechanical ventilation. A possible embodiment of this is shown in Fig. 3.

In the embodiment shown in Fig. 3, tubes 3 are supported on a plurality of suitable supports 1 5.

Supports 15, made for example of wood or metal, with a selected suitable thickness in the order of a few centimeters, are arranged at a plurality of places, e.g., three to four, beneath tubes 3 at uniform distances from each other, to keep the tubes spaced from the upper surface of insulating material 2. At the underside of one or more of tubes 3, suitable temperature sensors are provided. The temperature signal provided by the sensors is transmitted through a line 1 6 to a controlling and switching device, shown for simplicity as a block 17. As soon as a temperature of a pre-determined level, recorded in the controlling and switching device, is reached, this device switches on a mechanical fan, which is likewise contemplated to be arranged in block 1 7.

The fan blows air through a passage 1 8 through the wall of box 1 along the underside of tubes 3, which air is subsequently discharged through passage 1 9. The air flowing along tubes 3 provides for the desired cooling. As soon as the temperature sensors indicate that the temperature has sufficiently decreased, the fan is stopped. The circulation of cooling air takes place in the manner indicated preferably through the space between tubes 3 and insulating material 2, and not through the space between tubes 3 and the cover. This in order to prevent, as much as possible, the deposition of dirt and the like on the cover.

Fig. 4 shows a different embodiment of a support for supporting tubes 3. Support 20 consists of a metal strip formed so that tubes 3 are supported by it in closely-spaced interrelationship. The advantage of support 20 relative to support 1 5 shown in Fig. 3 is that it virtually does not interfere with the flow of air along the underside of tubes 3. When support 20 as shown in Fig. 4 is used, it should be mounted in box 1 in such a manner that no heat is dissipated through the fastening to the wall of the box and further to the outside.

Claims

1. Apparatus for heating water and, so long as no hot water is withdrawn, keeping the water in store in heated condition, comprising a housing in which one or more containers for the water to be heated and to be kept in store are disposed, which housing is provided with a connection for connecting a supply conduit for cold water and with a connection for connecting a discharge conduit for hot water, characterized in that the apparatus is designed as a collector for collecting solar heat, for which purpose the containers for the water consist of a plurality of substantially cylindrical tubes arranged in side-by-side relationship in the housing, the housing proper consisting of a box in which the tubes lie, covered with a cover permeable to solar radiation.

2. Apparatus according to claim 1, characterized in that the cylindrical tubes are connected at one end by means of a connector to a supply conduit for cold water, and at the opposite end coupled by means of a connector to a discharge conduit for heated water, the supply conduit and discharge conduit being contained in the housing and being connected to the connections.

3. Apparatus as claimed either in claim 1 and 2, characterized in that the tubes have a diameter of 5--10 cm.

4. Apparatus as claimed in any of claims 1-3, characterized in that the tubes consist of brass or aluminium.

5. Apparatus as claimed in any one of claims 1-4, characterized by means for determining the temperature of the water within the tubes and by means for causing air to flow along and around the tubes, if necessary, in dependence upon the temperature determined.

6. Apparatus for heating water and, so long as no water is withdrawn, keeping the water in store in heated condition. substantially as hereinbefore described with reference to and as shown in Figures 12, and 4 or Figures 1, 3 and 4 of the accompanying drawings.