FR2511131A1 - Collector for solar energy - employing double-skinned metal collector plate through which coolant circulates - Google Patents

Abstract

Collector for solar energy employs the green house effect to collect heat behind glass. A collector element comprising two metal plates about 20 mm apart sealed together at the edges rests on insulation so that its heat absorbing face is about 20 mm from the glass. Absorbed heat is removed from the element by means of coolant circulating between the plates of the collector element. Various means are employed to promote heat transfer to the coolant in the space between the collector plates, including perforated baffles and packed steel wool. Used for the collection of solar energy for domestic heating purposes.

Description

 The present invention relates to a planar solar collector, improved, for heating premises for residential, industrial and sports use.

 The solar collector with greenhouse effect is conventionally produced by an absorbing element housed inside a box the bottom of which is coated with an insulating mattress intended to avoid heat loss and the upper part of which comprises one or more glazings .

 According to the general principle of operation of such a sensor, the capture of solar radiation is carried out by the absorbing element which transforms it into heat and transmits it to a heat transfer fluid intended to transport this energy towards devices of use or storage. . This heat transfer fluid can be a gas for example air or a liquid such as water.

In an air heating device using such a sensor two types of absorbers have been developed responding to two different modes of use - direct heating of the renewal air, for this purpose
the Applicant has developed a porous absorber described
in patent EN 78 23854 in which the outside air is
heated on passage through the absorber - heating the recirculated air inside a room or
renewal air previously heated in a
preheating system such as: exchanger, economizer,
greenhouse or whatever.

 Depending on the mode of use adopted, the temperature of the air introduced into the sensor is equal to the outside temperature in the first case or higher than this in the second case.

 The object of the present invention relates more specifically to a heat exchanger absorber corresponding to the second mode of use.

 This mode of use is particularly well suited for air heating in winter.

 According to a conventional arrangement, such an exchanger absorber is constituted by a sub-assembly formed by the assembly of two metal plates providing between them a space for the circulation of the heat-transfer fluid and assembled at their periphery by a continuous, hermetic connection produced for example by crimping , soldering soldering with a thumbwheel or any other waterproof means.

 The external surface of the front or absorbent plate being generally covered with a selective coating such as a deposit of chromium black, the rear plate being provided with connection sleeves capable of cooperating with supply and outlet conduits for the fluid coolant.

 The sensors disclosed by the prior art, produced according to this model have at least one of the drawbacks below - low efficiency - significant pressure drop - poor mechanical strength - high manufacturing cost.

 Compared to the conventional design of the prior art, the present invention is distinguished in that it defines an optimized exchanger absorber which achieves a good compromise between heat transfer and pressure drop and which moreover lends itself to industrial manufacture. at a reduced cost.

 At the thermal level, such an exchanger is defined by a good conductance of the order of 50W / m2 x OC which makes it possible to effect a significant heat transfer of the order of 680 Watts, under a small temperature difference, between l 'exchanger and the heat transfer fluid which can be around 20 C.

This results in a steady state, a moderate temperature of the body of the exchanger absorber which has the effect of limiting the heat losses of the latter and thus increasing the thermal efficiency of the sensor.

 This characteristic is obtained by the use of a material of high thermal conductivity such as aluminum in the production of an exchanger whose internal structure is defined by a value of the ratio: surface of exchange, surface of capture at least greater than 3.

 To limit the pressure drop of the exchanger, the internal circuit thereof is characterized by a minimum of singularities offering a useful passage section which ensures the circulation of the flow of coolant fluid with a moderate speed which will be order of m / s.

Under these conditions, the estimated pressure drop of such an exchanger will be of the order of a dynamic, ie, in the case of a speed of 1 m / s, 0.6 Pa / approximately. In this case, the mechanical power to be used to overcome the pressure drop, expressed by the relation: P = Q-Xn p will be for an average flow of 40 m3 / h / m of the order of 0.01
Watt.

 Furthermore, this useful passage section is defined by a transverse dimension of the order of cm but generally less than this value, for example 4 to 5 mm to remain compatible with good conductance.

 In fact, the influence of the rear plate in the overall conductance of the exchanger absorber sub-assembly is inversely proportional to the value of the spacing between these plates. This influence is determined by the radiative coupling which is established between the two internal faces opposite said metal plates and which for this purpose have good emissivity in the infrared.

 The internal structure of the exchanger, thus defined, makes the establishment of a laminar flow regime compatible with the requirement of good conductance.

 These conditions are met in the most general embodiment, in accordance with the invention, which consists of means capable of maintaining a small and constant spacing between the metal plates of the exchanger absorber sub-assembly and which delimit inside the latter. ci passage circuits contributing to significantly increase the exchange surface.

 In one configuration, these passage circuits are constituted by flow channels which have constant passage sections in which the flow of the heat transfer fluid is in contact with the two metal plates.

 The distribution of the flow of the heat transfer fluid in the various channels being carried out in a substantially uniform manner from two collectors, such as gutters for example, located opposite one another at the ends of said plates and into which the outlet respectively supply pipe and the outlet pipe for the heat transfer fluid. These collectors are advantageously preformed aans the plate behind.

 According to an embodiment in accordance with this configuration, the spacing means consist of slightly crushed tubes interposed between two flat plates, the flow taking place simultaneously in the tubes and outside of them. The initial outside diameter of the tubes is appreciably greater than the spacing between the two plates which, in all cases, is of the order of a centimeter but preferably less than this value, for example 4 to 5 mm.

 In another configuration, these passage circuits are materialized by the networks of the structure of a steel wool pressed between the two plates of the exchanger absorber.

 To improve the collection efficiency, the absorbent surface has a large developed surface, the exchange surface being increased in the same proportion.

 To this end, according to a preferred embodiment of the invention, the metal plates of the exchanger absorber are constituted by corrugated sheets whose profiles of the corrugations are nested one inside the other, so that a corrugation of the front sheet or absorbent face is housed between two corrugations of the rear sheet and vice versa.

 In this configuration, the spacing means will preferably be arranged transversely to the profile of the corrugations. In a second variant, they are arranged longitudinally.

 To make the operation of a solar heating installation equipped with such collectors more profitable by a higher coefficient of use, this collector is also designed to produce hot water in summer.

 To this end, according to a variant of the invention, the absorbent plate of the exchanger absorber sub-assembly is equipped with a hydraulic circuit in which a heat-transfer liquid such as water circulates.

 This hydraulic circuit being materialized by a coil linked to the absorbent plate in a thermally conductive manner and which, in the case of a corrugated sheet, is advantageously inserted in the corrugations thereof.

 This coil is arranged on one of the faces of the absorbent plate but preferably on the rear face because in this configuration it collaborates in increasing the exchange surface for the aeraulic circuit.

 Furthermore, according to a preferred embodiment of this configuration, the air circulation takes place parallel to the elements of the coil, these delimiting, for this purpose, separate flow channels.

 This sensor is applicable to a mixed heating installation in which the hydraulic and aeraulic circuits are in service separately l the aeraulic circuit being used in winter.

 According to an original application of this invention, the exchanger absorber sub-assembly is removably arranged behind a canopy and thermally decoupled from the latter by spacers made of insulating material such as cork or reinforced resin. These spacers define a stationary air gap, between the absorber and the glass, confined by a peripheral sealing point such as an elastomer seal for example.

 The invention also includes certain details which make it possible to carry out thermal decoupling of the exchanger absorber from the frame of the case and from the glass.

 The description which follows, with reference to the appended drawings given by way of non-limiting examples details various embodiments of the invention and the art of implementing them.

 Figure 1 shows in section, the general structure of an exchanger absorber according to the invention, integrated inside a flat solar collector.

 FIG. 2 represents a partial section of a detailed view of the insulation of the exchanger absorber body with respect to the sensor housing.

 FIG. 3 represents a front view of the sensor of the same type.

 FIG. 4 represents a cross section along lines I - I or II - II of FIG. 3.

 FIG. 5 represents a preferred embodiment of the absorber-exchanger assembly integrated behind a canopy.

 FIG. 6 represents a plan view of the sensor according to FIG. 5.

 FIG. 7 represents a general solar heating installation comprising several collectors of the type according to FIG. 5, associated in series.

 Figures 8 and 9 show schematically another type of absorber according to a cross section and a longitudinal section respectively.

 Figure 10 shows schematically a mixed exchanger absorber according to a cross section.

 Figure 11 shows schematically the same type of absorber in a longitudinal section passing through the line I - I.

 Figure 12 shows schematically a variant of this type of absorber integrated in a solar collector presented in a cross section.

 FIG. 13 represents a longitudinal section of the absorber according to FIG. 12.

 The exchanger absorber sub-assembly 1 according to the invention, shown in FIG. 1, consists of two metal plates 2 and 3 delimiting between them a space for the circulation of the heat-transfer fluid and assembled at their periphery by a continuous connection 5, hermetic, produced for example by crimping, soldering, seam welding or any other waterproof means.

 The exchanger absorber sub-assembly 1 is integrated in a box or case preferably made up of a frame 6 made of aluminum profile for example, the bottom of which is coated with an insulating mattress 7 applied to the rear plate 3 of the sub-assembly exchanger absorber 1 and the upper part of which has one or more glazing units Se Thermal decoupling of the changer absorber subassembly 1 of the frame 6 is supplemented by shells 9 or supports made of carbonite material such as reinforced resin, glass fiber, cork in discrete numbers distributed at the periphery associated with a continuous seal 10 made of plastic, rubber or similar material which isolates the air space 20 between the front or absorbent plate 2 and the glazing 8 immediately opposite.

The dimensions of this sensor correspond to standard building values, for example 1 x 2 m; the transverse dimensions of the housing 6 are defined by the thickness of the various elements which are housed therein and a distribution of which is given below for information only o
- absorber window space: 20 mm absorber o 1 0 10 mm
- insulation: 50 mm
The metal plates 2 and 3 of the sound absorber and exchanger sub-assembly; maintained at a small and constant distance from each other by spacers or spacers which delimit inside thereof passage circuits, inside which the distribution of the flow of the heat-transfer fluid is carried out so substantially uniform and which contribute to significantly increase the heat transfer fluid exchange surface and at the same time stiffen the structure of the subassembly 1.

 The rear plate 3 is provided with connection sleeves il and 12 shown in two "orthogonal" arrangements 11 and 11a, 12 and 12a capable of cooperating with supply and outlet conduits not shown in the heat transfer fluid.

 These connection sleeves 11 and 12 communicate respectively with two collectors 21 and 22 or gutters.

 The distribution of the heat transfer fluid flow being carried out in a substantially uniform manner, inside the exchanger absorber, from the inlet manifold.

 To this end, the inlet manifold in this case 22 constitutes a chamber of notable volume in which the kinetic energy acquired by the heat transfer fluid in the supply duct is canceled.

 The air circulation in this type of sensor symbolized by arrows in bold line is ensured by a conventional system of controlled mechanical ventilation.

 These collectors 21 and 22 are either preformed in the rear plate 3 by stamping, for example, or constituted by independent added elements which are then hermetically assembled to the plates 2 and 3 of the absorber sub-assembly 1. For this purpose the rear plate 3 is shorter than the front plate 2 and the collectors 21 and 22 formed by stamping are welded in a leaktight manner thereon.

 According to a variant, the flow rate of the heat-transfer fluid is distributed uniformly in the interior aeraulic circuit delimited by the plates 2 and 3, by a distribution grid, shown diagrammatically in FIG. 4, arranged transversely to the upstream and downstream sections of said circuit.

 Another means conventionally used for uniform distribution of the flow consists in adapting the inlet sections of the supply duct and the passage of the exchanger 1.

 According to the embodiment shown in Figures 8 and 9 the spacer means are constituted by tubes 13 slightly crushed interposed between the two plates 2 and 3; the flow of the heat transfer fluid taking place simultaneously in the tubes 13 and inside them. These tubes 13 with an internal diameter less than one cm and of the order of 4 mm are distributed substantially in steps of 10 mm, so that they contribute to increasing the exchange surface offered to the heat transfer fluid in a proportion of 3 to 4. The connection between the tubes 13 and the plates 2 and 3 being carried out in a thermally conductive manner, for example by spot welding or with a thumbwheel.

 According to another embodiment, the passage circuits for the flow of the heat-transfer fluid are materialized by the networks of a porous structure represented at 14 in FIG. 1 such as a steel wool pressed between the two plates 2 and 3 of the subset 1. These are kept at a constant spacing from each other by isolated studs integral with the plates 2 and 3 at a number of points distributed over their surface so that they provide good rigidity to the subset 1.

 According to a preferred embodiment of the invention shown in Figure 5 the metal plates 2 and 3 are formed by corrugated sheets whose profiles of the corrugations are nested one inside the other. These will preferably be carried out by aluminum sheets with a thickness of 5/10 mm. In this configuration and according to, for example, a feature of the invention, the flow takes place advantageously in a direction substantially normal to the undulations. To this end, the spacing means arranged transversely to the corrugations consist of continuous elements which are advantageously rigid, such as round or stamped metal wires, spot welded or with a seam on the two plates 2 and 3. These continuous elements distributed regularly over the entire dimension of the subassembly 1 delimit channels of constant passage section in which the flow of the heat transfer fluid is distributed in a substantially uniform manner by any of the means described above.

 These elements, such as metallic wires, also contribute to increasing the transverse rigidity of the subassembly 1.

 In this configuration, according to another variant, the flow takes place in a direction substantially parallel to the corrugations, in this case the spacing means are arranged parallel to the corrugations.

 In Figures 5 and 6 is shown a particular mode of application in which the sub-assembly 1 is removably arranged behind a canopy 8. This type of sensor will be referred to as the suction cup sensor. The sub-assembly 1 rests on isolation cells 15 made of insulating material, such as resin, cork, etc., fixed at a certain number of points on the structure or frame 16 of the canopy 8.

The seal 17 is in the form of a continuous strip of flexible material such as rubber, one of the edges 17d of which is advantageously compressed between the peripheral edge of the absorbent face of the subassembly 1 and the insulating shims 15 , the other edge 17b being applied to the window 8.

 FIG. 7 represents a general solar heating installation constituted by suction-cup collectors of the type described by FIGS. 5 and 6, applied behind a canopy 8 and arranged in the case shown in series. It would not go beyond the scope of the present invention if the supply of each sensor was independent or carried out in parallel.

 FIGS. 10 to 13 show an embodiment of a sub-absorber-exchanger sub-assembly of a sensor for mixed use, that is to say producing domestic hot water in summer and hot air in winter for example. To this end, the absorbent plate 2 of the subassembly 1 is equipped with a hydraulic circuit 18 in which a heat transfer liquid, such as water, circulates. This is materialized by a coil 19 fixed in a thermally conductive manner, for example by welding on one of the two faces of the plate 2.

 According to a variant not shown, the coil 19 is housed in the undulations of the absorbent face 2a of the plate 2. According to another arrangement shown in FIG. 10, the coil 19 is welded to the rear face 2b of the absorbent plate 2, crosspieces or not shown spacers arranged transversely to the hydraulic circuit 18 determine passage channels for the air flow. So that the hydraulic circuit 18 participates in the exchange surface of the aeraulic circuit even when it is out of service.

 According to another alternative embodiment of the mixed sensor, the labeller-exchanger consists of a single absorbent plate 2 on the rear face 2b of which is thermally conductive a hydraulic circuit 18 materialized by a coil 19 in direct contact with the insulating mat 7.

 According to this arrangement, the coil 19 itself delimits, between two neighboring elements, air passage channels whose direction of flow parallel to said elements is represented by the dotted arrows. For this purpose the elbows 19a of the coil 19 overflow into the collectors 21 and 22 allowing free passage thus to the circulation of air whose flow is regularly distributed over the entire transverse dimension of the sensor.

 In the case shown, the coil 19 is an open circuit: the inlet and the outlet being located in opposition and more precisely diagonally, the supply and the outlet of the air being located in the same places. It would not go beyond the scope of the invention if the coil 19 were a closed circuit: the inlet and the outlet thereof then being located at the same level.

 According to this variant, the collectors 21 and 22 will advantageously be preformed in the insulating mat 7; the air inlets and outlets are produced in the body of the insulating blanket 7, the seal being produced by cable glands which also allow connection to external air supply and outlet conduits.

 Another configuration of this variant, not shown is that in which the hydraulic circuit is inserted between two flat plates, the connection of the hydraulic circuit with each plate being carried out in a thermally conductive manner. The transverse dimension of the rear plate 3 is then smaller than that of the hydraulic circuit so that the air circulation can be established parallel to the elements of the coil and between them.

Claims (20)

RVEND I CATI ONS  1. Solar collector using the greenhouse effect in which the exchanger absorber is constituted by a subset, thermally isolated from the transparent surface, formed by two metal plates, the external surface of the front or absorbent plate of which is covered with a selective coating, such as a deposit of chromium black, providing between them a space for the circulation of the heat-transfer fluid, the two opposite internal faces of which advantageously have good emissivity in the infrared and assembled at their periphery by a connection continuous, hermetic produced for example by crimping, soldering with a seam weld or any other sealed means; the rear plate being provided with connection sleeves capable of cooperating with supply and outlet conduits for said fluid, characterized in that the above-mentioned metal plates are kept at a small and constant distance from one another by means which delimit passage circuits for the flow of the heat-transfer fluid inside which the flow is regularly distributed and which simultaneously contribute to significantly increasing the exchange surface between it and the absorbent plate.  2. solar collector according to claim 1 characterized in that these spacing means are constituted by slightly crushed tubes interposed between two flat plates the flow taking place simultaneously inside and outside of said tubes; the tube-plate contact being made by a thermoconductive connection of the solder type with a thumbwheel for example.  3. Solar collector according to claim 2 characterized in that the internal diameter of the tubes is substantially equal to the spacing between the two plates which is less than a centimeter.  4. Solar collector according to claim 3 characterized in that the distribution pitch of the tubes is of the order of twice the value of the outside diameter of said tubes, so that the increase in the exchange surface is of l '' from 3 to 4.  5. Solar collector according to claim 1 characterized in that these means consist of a material with a porous structure, having a high porosity, such as steel wool.  6. solar collector according to claim 1 characterized in that the metal plates consist of corrugated sheets whose profiles of the corrugations are nested one inside the other so that an undulation of the front tiller or absorbent face is accommodated between two corrugations of the rear plate and vice versa.  7. Solar collector according to claim 6 characterized in that the developed surface of these sheets is equivalent to an increase of about 50% of the planar surface corresponding to the same size.  8. Solar collector according to one of claims 6 or 7 characterized in that the spacing between the two corrugated sheets is less than a centimeter.  9. Solar collector according to claimt, characterized in that the spacing is achieved by continuous elements arranged transversely to the undulations delimiting separate channels regularly distributed and having constant passage sections.  10. Solar collector according to claim 9 characterized in that these elements are constituted by stamped rigid metallic wires linked in a thermally conductive manner, such as by seam welding, with the two corrugated sheets.  11. Solar collector according to claim 9 characterized in that these elements are made of deformable material such as rubber or elastomer seals.  12. Solar collector according to claim 8 characterized in that this spacing is achieved by continuous elements arranged parallel to the undulations delimiting separate channels regularly distributed and having constant passage sections.  13. Solar collector according to any one of claims 1 to 12 characterized in that the distribution of the flow of the heat transfer fluid in the different channels, delimited by the spacer elements, is carried out in a substantially uniform manner from two collectors such as gutters, for example, located opposite one another at the ends of said plates and into which respectively open the feed duct and the outlet pipe for the heat transfer fluid.  14. Solar collector according to claim 13 characterized in that these collectors are preformed in the rear plate.  15. Solar collector according to any one of the preceding claims, characterized in that the exchanger absorber subassembly is removably arranged behind a canopy and thermally decoupled from the latter by spacers made of insulating material such as cork or reinforced resin which hold an air space, immobile between the absorber and the glass, confined by a peripheral seal such as an elastomer seal for example.  16. Application of the solar collector according to any one of the preceding claims, to a space heating installation in which the heat transfer fluid is the air recycled from said spaces by a conventional controlled ventilation system.  17. Solar collector according to any one of claims i and 6 to 16, characterized in that the absorbent plate of the exchanger absorber sub-assembly is equipped with a hydraulic circuit, thermally conductive attached thereto, and in which a liquid circulates coolant such as water, the hydraulic circuit contributing to the increase in the exchange surface of the aeraulic circuit, even when it is out of service; the hydraulic circuit being used preferentially in summer and the aeraulic circuit being used in winter.  18. Solar collector according to claim 17, characterized in that the hydraulic circuit consists of a coil integrated on the internal face of the absorbent plate, the air flow taking place between two consecutive elements of the coil and parallel to those -this.  19. Solar collector according to claim 18, characterized in that the coil, fixed by a thermally conductive connection on the two plates of the exchanger absorber sub-assembly, slightly protrudes on each side of the rear plate so that the circulation of air can be established parallel to and between the elements of the coil.  20. Solar collector according to claim 18, characterized in that the coil of the hydraulic circuit is applied directly to an insulating mat in the body of which the air collectors are formed, in the form of a gutter, for example, into which the conduits open out. air inlet and outlet; these conduits are sealed using cable glands which also allow connection to air supply and outlet conduits.