Patent Application
20110197878
The invention relates to a device for absorbing electromagnetic radiation, in particular solar radiation, according to the preamble of patent claim 1.
DE 32 24 688 A1 discloses a solar collector of the type in question which is formed by welded-together sheets of plastic. The sheets of plastic are divided by weld seams into chambers. These chambers can be flowed through by a heat transfer medium in the form of water. For this purpose, the chambers are connected in a communicating manner to a common inlet and a common outlet.
This known device has been successfully used for forming solar collectors on flat roofs and is particularly distinguished by its low-cost construction. However, use of such a solar collector on sloping roofs is precluded, since in this case the heat transfer medium separates into layers. In the region of the lower chambers especially, this causes pressures that can no longer be withstood by this sheet type of structure. Consequently, this known solar collector has only a moderate application range. Furthermore, there is the fundamental problem that this known solar collector is usually operated in a closed cycle, allowing unfavorable pressure conditions to occur during operation even in the case of collectors that are lying flat.
DE 42 37 228 C2 discloses an absorber for solar collectors that is distinguished by particularly high energy efficiency. For this purpose, the actual absorber is surrounded on the underside and around the periphery by a heat insulating material. On the upper side, facing the sun, there is a vacuum insulation, which is closed off by a window. In this way, good heat insulation is obtained around the absorber, so that this absorber can generate high temperatures in the heat transfer medium even when the ambient air is cold, such as for example in winter. However, it is not possible for this known solar collector to be formed from sheets in accordance with the aforementioned document, since a vacuum insulation cannot be obtained with sheets because of the lack of dimensional stability.
DE 27 20 755 A1 discloses a further solar collector, which has a radiation-absorbent liquid as a heat transfer medium. This measure is intended in particular to prevent problems of overheating during the operation of the solar collector.
DE 88 10 095 U1 discloses an autonomous solar device for providing hot water. The device comprises a thin-walled sheet collector which is connected to a service water line. Since the collector cannot withstand the pressure in the service water line, a pressure reducer is provided between the service water line and the collector. However, this pressure reducer serves exclusively for lowering the pressure in the water line, and consequently cannot limit differences in pressure within the collector system.
The invention is based on the object of providing a device of the type mentioned at the beginning that can be used universally while being of a low-cost construction.
This object is achieved according to the invention by the features of patent claim 1.
The device according to claim 1 serves for absorbing electromagnetic radiation, in particular solar rays. The main intended use of this device is in the area of solar collectors for the conversion of sunlight into heat. To make the device inexpensive, it has at least one flexible sheet pocket, which is divided into chambers. This sheet pocket is in this case flowed through by a heat transfer medium. The construction in the form of sheets offers the advantage that the device can be transported very easily. In particular, this device can be rolled or folded up. Sheets can be produced at very low cost, since they use only little material. The sheets preferably consist of a polymer material, not only pure polymers but also mixed polymers being suitable for use. Polyvinyl chloride, polyethylene and polyurethane have been found to be particularly successful. To form the sheet pockets, one sheet may be folded over. It is alternatively possible for two sheets to be welded together. Dividing the sheet pocket into chambers allows heat transfer medium to flow uniformly through the sheet pocket and increased stability of the sheet pocket to be achieved. This is important for making optimum use of the sunlight. The division may be obtained by weld seams and/or by spaced-apart weld spots. A silicone oil, which remains well below its boiling point under operating conditions, is preferably used as the heat transfer medium. In this way, increases in pressure caused by boiling effects in the heat transfer medium are reliably avoided. For supplying and discharging the heat transfer medium, the sheet pocket has at least one inlet and at least one outlet. These communicate with the chambers of the sheet pocket.
If the sheet pockets described are laid on a sloping roof, there is the fundamental problem that different pressures are obtained within the sheet pocket. In particular, owing to gravity, a much greater pressure is obtained in the region of the lower end of the roof than in the region of the ridge, which leads to considerable pressure loading and stressing of the sheet pocket in the lower region. In principle, this situation could be counteracted by forming the sheet pocket with correspondingly thick walls. However, this measure is contrary to the stated object. Furthermore, in this way the sheet pocket becomes flexurally more rigid, which makes it considerably more difficult to handle.
To solve this problem, at least one pressure reducer is provided on the inlet side between at least two of the chambers or sheet pockets and reduces the pressure of the heat transfer medium in the chamber. This measure appears to be contrary to the stated object, since the pressure reducers do in fact represent a considerable cost factor. For example, a roof height of 3 m and a maximum pressure of the heat transfer medium of 2 kPa would require an arrangement of at least 14 pressure reducers, which makes a significant difference to the cost of the overall installation of the solar collector. However, it must be taken into consideration in this respect that only one pressure reducer is required for each section over the height of the solar collector, since no gravity-induced pressure differences can build up in a chamber extending horizontally over the entire length of the roof.
Furthermore, the pressure reducers can be of a very simple construction, since the aim is essentially for the heat transfer medium to be transported pressurelessly through the device.
In order to prevent pressures from building up between the chambers as a result of the communicating connection on the outlet side, it is advantageous according to claim 2 if at least one fluid diode or at least one pressure reducer is provided on the outlet side between at least two chambers or sheet pockets. A fluid diode has a low flow resistance in the preferential direction but a great flow resistance in the opposite direction. This prevents the outlet of a higher-lying chamber being able to force the heat transfer medium out on the outlet side into the chamber lying thereunder. In order to prevent corresponding pressures from being able to build up when the heat transfer medium is stationary, it is enough in this case to provide a sufficiently large storage tank, so that the heat transfer medium can always flow away unhindered. Consequently, the heat transfer medium is only stationary when the chambers are virtually empty.
This measure at the same time prevents the device from overheating when the heat transfer medium is stationary. Alternatively, a pressure reducer may also be provided on the outlet side and reliably exclude the possibility of excessive pressures occurring. These pressure reducers also work when the heat transfer medium is stationary.
Claim 3 provides a simple way of creating the pressure reducer, in the form of a section of pipe with foam or fibrous material inserted in it. This material provides the corresponding flow resistance, so that no pressures can build up. The foam or the fibrous material is preferably dimensioned in such a way that it has a capillary effect.
Alternatively or in addition, the pressure reducer may be formed by a drip chamber. This drip chamber interrupts the communicating connection between the individual chambers, so that no pressures can build up from one chamber to the next.
Alternatively or in addition, the pressure reducer may, according to claim 5, also be formed by a section of pipe with rungs running transversely in relation to the direction of flow. These rungs produce a cascade, which likewise has a pressure-reducing effect.
According to claim 6, it is advantageous if the pressure reducer is formed by at least one meander, which likewise has a pressure-reducing effect by increasing the length of the line.
To achieve a high final temperature of the heat transfer medium, it is important to keep heat losses as low as possible. The main heat loss of a solar collector is formed by the conduction of heat into the ambient air. This heat conduction becomes all the greater the cooler the ambient air is. However, it is particularly when the ambient air is cold that the greatest heating power is required. It is therefore expedient to keep down this loss mechanism. According to claim 7, it is proposed for this purpose to cover at least the underside of the sheet with at least one heat insulator. The underside of the sheet has no radiation coupling-in function and can therefore be thermally insulated in any way desired. However, the underside of the sheet has a large surface area in relation to the end faces, and therefore contributes considerably to the heat loss. For this reason, insulation of the underside of the sheet is particularly effective. Apart from that, it is expedient also to insulate additionally the end faces of the sheet pocket.
To obtain a further increase in the final temperature of the heat transfer medium, according to claim 8 it is advantageous if the sheet pockets are covered with a heat insulation, at least on the upper side. The insulation of the upper side is particularly expedient because this side is exposed directly to the ambient air. In addition, winds can also blow along the upper side of the sheet pocket and these winds can lead to an increased loss of heat. In order on the other hand not to impair the radiation absorption too much, however, it is important in the case of insulation on the upper side to form it from a transparent heat insulator.
Heat insulating materials that are often used are sensitive to wet and lose a considerable part of their insulating effect in the wet state. For this reason, according to claim 9 it is favorable if the heat insulator is surrounded by a protective film. This protective film essentially has the task of keeping wet, especially rain, away from the heat insulation.
To obtain a further improvement in the insulating effect, according to claim 10 it is favorable if the protective film is gas-filled. This has the effect that the protective film lifts off slightly from the heat insulation, so that the protective film acts like a greenhouse. In addition, good protection from hail is obtained in this way.
As a simple way of creating the chambers and the inlet and outlet, according to claim 11 it is advantageous to structure the sheet pocket by means of weld seams. In particular, these weld seams can be produced on a running web of sheet, which makes production particularly inexpensive.
It is considered in principle to make the side of the sheet pockets that is facing the radiation source transparent and to color the side facing away black. This achieves the effect that the electromagnetic radiation penetrates through the facing sheet and is absorbed by the sheet facing away. The heat produced in this way in the sheet is then transferred to the heat transfer medium. According to claim 12, however, it is more favorable to form the heat transfer medium itself as radiation-absorbent. This also brings into consideration, along with the configuration described above of the sheet pockets, an alternative in which, for example, both sides of the sheet pocket are transparently formed. The use of a radiation-absorbent heat transfer medium means that the heat is generated directly in the heat transfer medium, so that heat conduction between the absorber surface and the heat transfer medium is no longer required. In this case, the absorption of the device can also be controlled.
If, for example, a circulating pump for the heat transfer medium fails, there is in principle the risk of the heat transfer medium overheating, which could lead to the sheet becoming damaged. If it is provided that the heat transfer medium can in this case flow out of the sheet pocket unhindered, the system regulates itself to the extent that, in the event of failure of the circulating pump, the absorptivity of the device is also reduced. In this case, the device protects itself from overheating.
In order to shorten the response time of the overheating protection, according to claim 13 it is favorable to use a heat transfer medium with temperature-dependent radiation absorption. In this case, as the temperature increases, the absorption of the heat transfer medium decreases, possibly abruptly. In the case of imminent overheating of the heat transfer medium, for example if the circulating pump is at a standstill, the radiation absorption is reduced in this way, since the heat transfer medium becomes increasingly more transparent. This, however, also reduces the energy input into the heat transfer medium, which prevents overheating.
According to claim 14, it is favorable to make the sheet pocket or the protective film UV-resistant or gnaw-proof. Conventional UV stabilizers are used for this. It is additionally considered to incorporate odorous substances in the polymer, which deter animals that could bite into the sheet. Examples of such animals are martens and raccoons.
To improve the energy yield, according to claim 15 it is advantageous if the sheet pocket or the protective film has at least one photovoltaic cell of semiconducting material. This allows part of the sunlight to be converted directly into electrical energy, while the portion of the solar energy that cannot be used for this is converted into heat. This portion then serves for heating up the heat transfer medium, to allow it in this way to be put to further use. In this way, a favorable synergistic effect is obtained, since the heat transfer medium cools the photovoltaic cells, and consequently also increases their efficiency.
According to claim 16, it is advantageous if at least one valve influencing the through-flow of the heat transfer medium or at least one circulating pump is provided in the supply line or discharge line. It is thereby possible in a simple way to set or control the through-flow rate of the heat transfer medium, in order to obtain an adaptation to ambient conditions. In particular, it is considered to increase the through-flow rate of the heat transfer medium when there is strong solar irradiation, in order in this way to obtain more heat. When there is reduced solar irradiation, on the other hand, the through-flow rate of the heat transfer medium is reduced, in order to ensure a sufficiently high temperature level. This valve or this circulating pump is preferably in operative connection with at least one sensor, so that closed-loop control can be achieved in this way. In the simplest case, the temperature of the heat transfer medium in the outlet line is controlled to a value that still makes it possible for the heat to be used for the planned purpose. Alternatively, however, more complex closed-loop controls are also conceivable, for example controls which optimize the energy conversion of the overall system. It is also considered to use the at least one sensor to sense when the collector is covered with snow, in order to reverse the heat flow of the heat transfer medium. In this way, when the collector is covered with snow, the heat transfer medium can introduce heat into the collector, in order to melt the snow that is on the collector, so that it can subsequently slide off.
Finally, according to claim 17 it is favorable if the device is adhesively fixed on a base. This has the advantage of ruling out movement of the device in relation to the base that could lead to abrasion caused by scraping effects, and consequently to destruction of the device. Furthermore, in this case the device can always be mounted in the same way irrespective of the actual form of the roof. In particular, it is not necessary for fastening means to be adapted to the actual form of the roof.
The subject matter of the invention is explained by way of example on the basis of the drawing, without restricting the scope of protection.
Further advantages and features of the present invention are presented in the following detailed description on the basis of the associated figures, in which a number of exemplary embodiments of the present invention are contained. However, it should be understood that the drawing serves only for the purpose of representing the invention and does not restrict the scope of protection of the invention.
In the drawing:
The supply line 5 is in this case in connection with a pressure side of a circulating pump 7, which pumps a heat transfer medium from a storage tank 8 into the supply line 5. The discharge line 6, on the other hand, is in connection with a heat exchanger 9, which extracts from the heat transfer medium the heat absorbed, in order to make it usable in the house 1. From the heat exchanger 9, the heat transfer medium returns to the storage tank 8.
Installed in the discharge line 6 is a valve 31, which influences the through-flow of the heat transfer medium through the discharge line 6. This valve 31 is in operative connection with a controller 34, which is influenced by sensors 32, 33. The sensor 32 is in this case a pure temperature sensor, which senses the temperature of the heat transfer medium in the discharge line 6. The sensor 33, on the other hand, is a snow sensor, which may, for example, be formed as a light-sensitive sensor and determines whether the sheet pockets 4 are covered with snow. In addition, the controller 34 influences the circulating pump 7 in the sense of reversing the direction of rotation.
In the simplest case, the controller 34 may effect a temperature control of the heat transfer medium in the discharge line 6. In this case, the flow of the heat transfer medium is controlled in such a way that a constant temperature of the heat transfer medium is obtained at the location of the temperature sensor 32. Furthermore, the controller 34 is influenced by the snow sensor 33, which in the simplest case effects the reversal of the direction of rotation of the circulating pump 7. If snow is covering the sheet pockets 4, in this case the heat transfer medium is reversed in its direction of flow, so that it does not give off heat in the heat exchanger 9 but is heated up in it. This heat is then introduced into the sheet pockets 4, in order to melt the snow lying on them, and thereby restore the function of the device 3. The snow sensor 33 is preferably constructed in such a way that, apart from sensing the thickness of the snow, it also senses snowfall, in order to prevent the sheet pockets 4 from being thawed out the whole time when there is continuous snowfall. This provides increased energy efficiency of the device 3.
The sheet pocket 4 is provided at the periphery with peripheral weld seams 12, which close the sheet pocket 4 on all sides apart from openings 13 for the supply line 5 and the discharge line 6. In order to be easily able to cascade the sheet pockets 4, the sheet pocket 4 has two openings 13 for the supply line 5 and two openings 13 for the discharge line 6.
The sheet pocket 4 also has separating weld seams 14, which separate the sheet pocket 4 into individual chambers 15. These chambers 15 are distributed two-dimensionally over virtually the entire sheet pocket 4 and are charged via the supply line 5 with a heat transfer medium (not represented), which can flow away via the discharge line 6. Consequently, the heat transfer medium, guided by the separating weld seams 14, can essentially only flow through the chambers 15 in the direction of flow 16.
Pressure reducers (not represented) may be fitted in the supply line 5 and discharge line 6 from chamber 15 to chamber 15. In addition, it is also conceivable to provide a pressure reducer respectively between only a certain number of chambers 15. It is also considered to arrange a pressure reducer respectively between at least two sheet pockets 4 in the region of the supply line 5 and the discharge line 6. In the region of the discharge line 6, a simple fluid diode may be used instead of a pressure reducer.
To reduce the losses from heat conduction with the surrounding air, the sheet pocket 4 is surrounded on all sides by a heat insulator 17. This heat insulator 17 is transparent, at least on the upper side, in order to keep reflection of the incident electromagnetic radiation as small as possible. On the underside of the sheet pocket 4, any desired heat insulator 17 may be used.
In order to prevent the heat insulator 17 from becoming soaked through, and consequently being restricted in its insulating capability, the entire arrangement is encased in a protective film 18, which in turn is peripherally sealed off by weld seams 19. Distributed in these weld seams 19 are eyelets 20, which allow simple fastening of the sheet pocket 4 to the roof 2 of the house 1 by lashing. Alternatively or in addition, the sheet pocket 4 may also be adhesively attached to the roof 2. On at least one longitudinal side, the sheet pocket 4 is drawn out until it overlaps with the weld seam 19 and is provided with flush eyelets 20. In this way, the sheet pocket 4 is kept in position within the protective film 18. The drawn-out periphery is preferably located at the higher longitudinal edge.
Arranged in the supply line 5 is a valve 24, which sits on a membrane 25. The membrane 25 is loaded from the outside with air pressure of the ambient air and in this way forms a pressure sensor. On the left side, the membrane 25 is acted upon by the heat transfer medium, so that the valve 24 closes whenever the pressure of the heat transfer medium in a membrane chamber 26 exceeds a specific value. In this way, a defined fluid pressure is obtained in the membrane chamber 26. The membrane chamber 26 is in connection via an opening 27 with the supply line 5 of the following pressure reducer 21.
Finally,
Since some exemplary embodiments of the present invention are not shown or described, it should be understood that many changes and modifications to these described exemplary embodiments are possible, without departing from the essential concept and protective scope of the invention that is established by the claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2008 050 618.4 | Oct 2008 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2009/007226 | 10/8/2009 | WO | 00 | 4/8/2011 |
