GB2552941A

GB2552941A - A low cost flat plate solar thermal hot water panel that can tolerate freezing or lack of water without damage, can be used as roofing sheets

Info

Publication number: GB2552941A
Application number: GB1613592.3A
Authority: GB
Inventors: Ian Williams Christopher
Original assignee: Individual
Current assignee: Individual
Priority date: 2016-08-08
Filing date: 2016-08-08
Publication date: 2018-02-21

Abstract

A flat panel solar water heater may be made from transparent plastic 4 matrix comprising multiple water channels. An outer layer of channels 12 may act as insulating means above an inner layer of channels 13. The inner layer may be located adjacent to a layer that absorbs solar energy (Fig 1, 2) and may also have a further layer made from a closed cell foam and/or rubber gel 6, these layers may also be insulated 7 against heat loss. The foam or gel may be a resilient layer that, in the event of the liquid in the panel freezing and consequently expanding, absorb any compressive forces thus generated. Similar layers may be placed in the header tubes of the panels (FIG 10, 10). The panels may be roof mounted and may be used as roofing sheets. The panels may also be free standing and may be joined together in an assembly. The aim of the device is to prevent warping or bursting of the panel in the event of ice forming within.

Description

(54) Title of the Invention: A low cost flat plate solar thermal hot water panel that can tolerate freezing or lack of water without damage, can be used as roofing sheets Abstract Title: Anti burst solar thermal flat panel with compressible layer (57) Aflat panel solar water heater may be made from transparent plastic 4 matrix comprising multiple water channels. An outer layer of channels 12 may act as insulating means above an inner layer of channels 13. The inner layer may be located adjacent to a layer that absorbs solar energy (Fig 1,2) and may also have a further layer made from a closed cell foam and/or rubber gel 6, these layers may also be insulated 7 against heat loss. The foam or gel may be a resilient layer that, in the event of the liquid in the panel freezing and consequently expanding, absorb any compressive forces thus generated. Similar layers may be placed in the header tubes of the panels (FIG 10, 10). The panels may be roof mounted and may be used as roofing sheets. The panels may also be free standing and may be joined together in an assembly. The aim of the device is to prevent warping or bursting of the panel in the event of ice forming within.

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Intellectual

Property

Office

Application No. GB1613592.3

RTM

Date :31 January 2017

The following terms are registered trade marks and should be read as such wherever they occur in this document:

COROTEX - See page 2 line 3 of description.

Intellectual Property Office is an operating name of the Patent Office www.gov.uk/ipo

TITLE

A low cost flat plate solar thermal hot water panel that can tolerate freezing or lack of water without damage, can be used as roofing sheets or be free standing, and can be mass produced.

BACKGROUND

There are many needs for hot water including for domestic use and for swimming pools among others. There are also many types of solar panel that have been developed around the world to produce hot water. They range from the simplest such as a black painted water tank left in the sun, to more complicated such as vacuum tubes filled with antifreeze. The basic problem faced by all systems is a trade off between efficiency and functionality, and cost. More costly systems may be more effective, but the pay back period for the initial investment may not be economic, or the capital may just not be available.

In addition to the cost of a solar panel, it faces the following technical problems:

-- It needs to effectively produce water hot enough, and in sufficient quantity for a domestic supply. In some countries this is fairly easy as there is a great deal of hot sunshine, but in more temperate climates it needs a measure of efficiency.

-- If the panel is accidentally run in the sun with no water inside it, it will reach very high temperatures. It must be able to cope with these without damage

-- It needs to be able to cope with temperatures that go below freezing without damage. If the panel contains water, this will freeze and expand by about 10%, potentially damaging the panel. Even in hot countries with plenty of sun, temperatures may fall below freezing at night or in winter. This problem has been solved in several ways, including building a water filled panel that is freeze tolerant that can be frozen without damage, by using an anti-freeze working fluid in the panel, or by draining down the water in the panel in cold weather.

Freeze tolerant solar thermal panels have been made in several ways, but many run the water through flexible pipes in the panel made of something like silicone rubber. When the water freezes they are not damaged due to their flexibility.

This adds complexity and cost to the panel and reduces efficiency.

Alternatively the panel can be filled with an ant-freeze working fluid, which is heated by the sun. This fluid is then circulated through a heat exchanger, which heats the hot water. This also adds complexity and cost to the panel, and reduces efficiency.

The panel can have the water running directly through it, which is ideal for low cost and higher efficiency, but it can be drained when the temperature falls below freezing, thus avoiding damage. This either involves draining every time it is necessary by hand, or by some kind or automatic temperature sensor and valves. Both methods carry the risk that if it is not done on one single occasion when it freezes, or some portion of the water remains in the panel for some reason, the panel will be damaged. The first method requires constant attention by someone, and the second again adds cost and complexity to the system.

STATEMENT OF THE INVENTION

The present invention is a flat type solar thermal panel for hot water. The basis is a transparent flat plastic panel with longitudinal cells or channels running along it, the matrix, similar to polycarbonate roofing sheets or Corotex plastic sheets. The water to be heated runs along these channels. The channels incorporate a solar energy absorbent layer which absorbs the solar energy and heats the water, and a layer of closed cell foam or gel like material. The solar energy absorbent layer absorbs the solar energy and becomes very hot if there is no water present to cool it, but this does not damage or warp the panel matrix, which does not get so hot. The Layer of closed cell foam or gel like material squashes if the water freezes to ice and expands by about 10%, without damaging the panel. These two layers can be combined in one, which absorbs the solar energy, but is also flexible and gel like. The panel is structurally rigid, and is designed to fit together with other panels or roofing sheets, so it can be used as a roofing material, or be free standing as required.

ADVANTAGES’

-- The panels are simple, and easy and low cost to mass produce.

-- The efficiency is high as the water to be used is directly heated in the panel.

-- If the panel freezes it will not be damaged, so it can be forgotten about once fitted. It does not require anti-freeze or draining down in cold weather.

-- If the panel is left in the sun without any water inside, it will not be damaged or warp with the heat produced.

-- The panel is suitable for use in a pumped system, or more basic thermal syphon type system. In fact the panels contain an appreciable volume of water, so at their most basic, the hot water contained in the panels alone should be enough for low domestic use without the addition of a hot water tank, especially if more than one panel is used.

-- The panels are self-supporting and simple and cheap to fit and plumb in.

-- The panels can be free standing, or used as roofing panels, and joined together to make larger or smaller roofs, or used alongside other non-solar roofing panels to make a roof.

INTRODUCTON TO THE DRAWINGS

An example of the invention will now be described by referring to the following drawings:

Figure 1: A cross section of the panel showing a slice cut through the end of the panel matrix.

Figure 2: A cross section of the black flexible layer which absorbs the solar energy, showing an example of how the upper surface can be corrugated to increase heat transfer to the water and reduce heat loss due to radiation.

Figure 3: A Cross section of the panel showing the black solar energy absorbing layer and the closed cell foam or rubberoid material layer combined into one layer, and a layer of rear insulation.

Figure 4: The complete solar panel showing header tanks at top and bottom

Figure 5: A cross section of a header tank showing the internal closed cell foam or rubberoid material that protects it from damage if it freezes.

Figure 6: Sketch showing how the panels can be clipped together to form a larger panel or expanse of roofing material.

Figure 7: Cross section of a joining pipe, showing the internal closed cell foam or rubberoid material that protects it from damage if it freezes.

Figure 8: Cross section of a panel with an additional layer of channels or cells for the circulation of the water

Figure 9: Sketch illustrating the circulation of water in the panel shown in figure 8, viewing from the edge of the panel.

Figure 10: Sketch showing the way two panels can be joined or clipped together, and showing the arrangement of the top manifold and water circulation, viewed from the top of the panel, being direction A in Figure 9

THE DRAWINGS ARE LABELLED AS FOLLOWS

1. Water filled channel

2. Flexible solar energy absorbing layer

3. Closed cell foam or rubberoid or gel material layer

4. Transparent plastic matrix of the solar panel

5. The sun

6. A black flexible solar energy absorbent material which is made of closed cell foam, rubberoid, or gel material, being a combination of 2 and 3.

Insulation layer

8. Water inlet

9. Water outlet

10. Blanking plug

11. Water pipe outer wall

12. Outer water channel

13. Inner water channel

DESCRIPTION

The invention is a flat panel solar thermal hot water heater. It is rigid and can be used as a roofing panel, or incorporated into a roof, as well as being free standing.

The structure or matrix of the panel is made of transparent plastic materiel, labelled 4 in figure 1. This matrix has longitudinal channels running through it, similar to polycarbonate roofing sheets, or Coroplast sheets (polypropylene).

The transparent plastic material should be as clear as possible to allow sunlight to pass through it as much as possible. It should be able to withstand temperatures of about 150 degrees or more without melting, because if the panel is left in the sun with no water inside, high internal temperatures will be reached. It should also be inert to hot water, and long lasting. The upper surface will require washing and cleaning periodically, so it should be abrasion resistant.

The channels running up and down the matrix are divided into three layers. The outer layer is filled with water, labelled 1 in Figure 1. The second layer is a solar energy absorbing layer, the heating element, labelled 2 in Figure 1, and probably black or whichever colour heats up best. The third layer is a layer of closed cell foam or rubberoid or gel type material, the expansion layer, labelled 3 in Figure 1.

Sunlight from the sun 5 passes through the upper transparent layer ofthe panel matrix and through the water channels 1. The heating element 2, which is probably black, absorbs the solar energy from the sun and heats up. In turn this heats the water in channels 1. The heating element can have some form of roughening or corrugations on the upper surface which is in contact with the water. This will improve heat transfer to the water and reduce heat loss due to radiation. An example is shown in Figure 2. The heating element should be made of a material that is inert to hot water.

The heating element should be flexible, and flexibly located inside the matrix of the panel. If the panel is left out in the sun with no water inside, this element will heat up to a high temperature, say 150 degrees centigrade or more. The material it is made of should withstand this temperature without melting or degrading.

The transparent matrix will not absorb so much solar energy, so it will heat up much slower and not reach such a high temperature. It will be in contact with the heating element, so should similarly be able to withstand temperatures in excess of 150 degrees C without melting or degrading.

The heating element will expand as it heats up. If it is made of flexible material, or in moveable segments (like a tape worm), it is able to move and will not warp and distort as it expands. Coupled with the flexible way it is located inside the matrix, this will ensure that the panel can heat up to high temperatures if left in the sun with no water inside, and the panel matrix itself will not distort or warp, or be damaged by the high temperature.

The third layer (3 in Figure 1) is a layer of closed cell foam, or rubberoid or gel material, the expansion layer. This layer gives the panel some internal expansion space if the water in the panel freezes. When freezing, the water will expand about 10%. This layer should be capable of compressing 10% of the volume of the water filled channels, so that if the panel freezes, the expansion of the water is taken up by compression of this layer, without damaging the panel matrix. When the ice melts, the expansion layer expands back to the original volume and shape. The pressure needed to compress the expansion layer should be less than that which will burst or damage the panel matrix, but more than the normal water pressure in the panel, so that it will expand back to the original shape when the ice melts.

It is possible that the two layers 2 and 3 could be made in one layer that accomplishes both purposes, ie a black heat absorbent flexible rubberoid/gel/closed cell foam material. This can become very hot without degrading, distorting, or damaging the plastic matrix of the panel 4. It can also compress to absorb the expansion of water of about 10% when it freezes. Figure 3 shows this variation, and 6 is the dual purpose layer.

The efficiency of the panel can be increased by a layer of insulation on the back, 7 in Figure 3. If this insulation is rigid, and bonded to the panel, it can also add further structural rigidity to the whole design. The finished panel is extremely robust, and can be used as a roofing material or panel.

The complete panel has a header tank top and bottom, as sketched in Figure 4. Water enters at pipe inlet 8, heats up as it rises through the panel, and exits through exit pipe 9.

The header tanks and pipes are lined internally with the flexible material (3 in Figure ), to allow the water to freeze without damaging them. This is shown in figure 5.

The panels can be constructed to clip together to form a larger roof if required, the inlets and outlet are arranged opposite in male and female fittings, as in Figure 6, and the two superfluous couplings blanked off with plugs 10.

The edges of the panels should be made to clip together and form a seal with each other, and with other mating roofing panels, so they can be made into a roof. Alternatively they can be designed to fit together with joining roof bars which seal, similarly to polycarbonate roof sheets.

The panels are suitable for systems where the water circulates naturally by solar syphon, or more active pumped systems.

Connection pipes and other attachments such as a hot water tank are also lined with the flexible material (3 in Figure 1), to protect from damage when frozen. Figure 7 shows a connecting pipe in cross section, where 11 is the water pipe wall, following prior art GB1613218.5.

The efficiency of the panels can be improved with the addition of a second layer for the circulation of the water. In Figures 1 and 2 the water circulates in channels

1. There will be a certain amount of heat loss due to conduction through the front face of the panel. By dividing the water channels 1 into an outer layer 12 and and inner layer 13, as in Figure 8, the outer layer will effectively insulate the inner and reduce heat loss. This is shown in Figures 8, 9, and 10.

The cold water entering the panel first passes down the outer layer 12, and is preheated by the inner layer of hotter water 13 to some extent. It then progresses into the inner layer next to the black solar energy absorbing material 6, for final heating. The water circulation is shown in Figure 9.

This means the outer face of the panel which is in contact with the air is at a lower temperature than it would be if there was only a single layer of heated water, thus reducing heat loss by conduction to the outer air, and raising the efficiency of the panel.

To achieve this a manifold needs to be incorporated into one of the header tanks as in Figure 9. The expansion material 3 for freeze protection is also incorporated into these header tanks but is not shown in figure 9 for clarity of the sketch.

Figure 10 shows the manifold viewed from the top of the panel, from direction A in Figure 9. This shows how the panels can be joined together as before to form a roof.

Claims

1. A solar hot water heating panel where the water circulates along channels in a transparent matrix and is heated directly by contact with a solar energy absorbing layer.

2. A solar hot water heating panel according to claim 1 where a compressible internal layer allows the water in the panel to freeze without damaging the panel.

3. A solar hot water heating panel according to claiml where the solar energy absorbing layer also acts as a compressible layer which allows the water in the panel to freeze without damaging the panel.

4. A solar hot water heating panel according to claim 1 where the panels can be used as roofing sheets

5. A solar hot water heating panel according to claim 1 where the panels can be free standing

6. A solar hot water heating panel according to claim 1 where the water circulates in two layers, the outer layer acting as heat insulation for the inner layer

Intellectual

Property

Office

Application No: GB1613592.3