Outdoor thermal energy panels

Abstract

A thermal energy system includes an outdoor panel having a first surface exposed outwardly to an outdoor environment. The first surface is an emissive and reflective surface. The outdoor panel is in heat exchange relationship with an air passage adapted to be connected to a ventilation system of a building or process. A selective layer can be applied onto a second surface of the panel opposite to the first surface thereof. A system may be provided to pivot the panel from a first position in which the emissive surface faces the outdoor environment and a second position in which the selective surface faces the outdoor environment. The panel can be perforated and depression can be formed in the emissive surface to collect water between the perforations when the thermal panel is used in a cooling mode. The emissive and reflective side of the panel can be oriented to redirect solar radiations towards a solar collector to improve the performance thereof.

Description

OUTDOOR THERMAL ENERGY PANELSTECHNICAL FIELD

[0001] This disclosure generally relates to heating and cooling systems and more, particularly, to such systems including an outdoor panel with an emissive surface.BACKGROUND

[0002] Thermal energy systems including outdoor panels with radiating cooling coatings are known. While these known systems may be suitable for their intended purposes, there is always room in the art for improvement.SUMMARY

[0003] It should be understood that any or all of the features or embodiments described herein can be used or combined in any combination with each and every other feature or embodiment described herein unless expressly noted otherwise.

[0004] According to an aspect of the present disclosure, there is provided a thermal energy system comprising: an outdoor panel having a first surface adapted to be exposed outwardly to face an outdoor environment and a second surface opposite the first surface, the first surface having an emissive layer and a solar reflective layer; and an air passage for directing a flow of air in heat exchange relationship with the outdoor panel.

[0005] In any of the aspects or embodiments described above and herein, the first surface has water retention means provided on the first surface, the water retention means configured to promote water retention and / or minimize water evaporation on the emissive layer.

[0006] In accordance with one general aspect, there is provided a thermal energy system comprising an outdoor reversible panel having back-to-back emissive and selective surfaces adapted to be selectively exposed outwardly to respectively provide cooling and heating.

[0007] For example, the thermal energy system may be used to reduce or increase solar heat gains on a building’s envelope or structure. This can be done passively (without any mechanical means) or actively (with the use of a pump, a fan, etc.). The system will help cool the building / structure if the emissive surface is installed facing outward. The system will help heat the building / structure if the selective surface is installed facing outward. So by installing the thermalenergy panel with its emissive surface or its selective surface facing outward, it is possible to selectively use the thermal energy system as a cooling system or a heating system.

[0008] According to another aspect, the system may comprise a pivot arrangement to pivot the panel between a first position in which the emissive surface of the panel faces the outdoor environment and a second position in which it is the selective surface of the panel that faces the outdoor environment, thereby allowing for a permutation between a cooling mode and a heating mode.

[0009] In accordance with another general aspect, there is provided a thermal energy system comprising a substrate covered on opposite sides thereof with two optical coatings having different thermally beneficial properties:• On one side, there is a selective surface, and• On the opposite side, there is an emissive surface.

[0010] In use, one side is typically exposed outwardly towards the sky or the sun, while the other side is inwardly exposed.

[0011] In accordance with another aspect, the thermal energy system can be used to cool or warm a fluid in gaseous or liquid form. More specifically, the warm or cold substrate can be used to warm up or cool down a fluid disposed in heat exchange relationship with the substrate.

[0012] In accordance with a further aspect, the substrate of the thermal energy system can be provided in the form of a perforated outdoor panel for use as part of a transpired type air collector.

[0013] In accordance with a further general aspect, the substrate may be provided in the form of a corrugated panel to create water collecting pockets in the emissive surface, each water collecting pocket disposed in a trough between two adjacent crests in the emissive surface of the panel. In the case of a transpired type air collector, the perforations in the perforated outdoor panel are located at or near the crests.

[0014] In accordance with a still further general aspect, there is provided a thermal energy system comprising: one or more cooling panels having an emissive and reflective surface facing outward and an opposed selective surface facing inward; one or more solar collectors oriented tointercept both direct solar radiations from the sun and indirect solar radiations reflected from the emissive and reflective surface of the one or more cooling panels.

[0015] In accordance with a still further general aspect, there is provided a thermal energy system comprising: one or more cooling panels having an emissive surface and reflective surface facing outward and water retention means for retaining water on the emissive and reflective surface.

[0016] The water retention means can take the form of cavities or recess into the emissive and reflective surface or a treatment surface to cause adherence of the water onto the emissive and reflective surface. The system may further comprise water supply means to provide water onto the emissive and reflective surface. The water supply means may include a hose, nozzles or sprinklers configured and disposed to spray water onto the emissive and reflective surface. Furthermore, a selective surface may be provided on a back side of the cooling panel opposite to the outwardly facing emissive and reflective surface of the panel.

[0017] Many further features and combinations thereof concerning the present improvements will appear to those skilled in the art following a reading of the instant disclosure.DESCRIPTION OF THE DRAWINGS

[0018] Fig. 1 is a schematic view of an example of a thermal energy panel having back-to- back emissive and selective surfaces, the panel illustrated in a heating mode with its selective surface exposed outward and its emissive surface exposed inward;

[0019] Fig. 2 is a schematic view of the thermal energy panel illustrated in a cooling mode with its emissive surface exposed outward and its selective surface exposed inward;

[0020] Fig. 3 is a schematic view of a thermal energy system installed on an exterior of a building envelope, the system including a plurality of thermal energy panels installed with their respective emissive surfaces exposed outward in a cooling mode configuration;

[0021] Fig. 4 is a schematic view of a thermal energy system installed on the exterior of a building envelope, the system including a plurality of thermal energy panels installed with their respective selective surfaces exposed outward in a heating mode configuration;

[0022] Figs. 5 and 6 are schematic views of a hollow thermal energy panel respectively installed in a cooling mode and a heating mode configuration;

[0023] Figs. 7 and 8 are schematic views of another example of a hollow thermal energy panel installed respectively in a cooling mode and a heating mode configuration;

[0024] Fig. 9 is a schematic view of a transpired solar collector with a front perforated thermal energy panel with emissive and selective surfaces;

[0025] Figs. 10a and 10b are schematic views of a glazed collector having perforated thermal energy panels with back-to-back emissive and selective surfaces, the panels rotatable between a cooling mode position in which the emissive surface of the panels faces the front glazing of the collector and a heating mode position in which the selective surface of the panels faces the front glazing of the collector;

[0026] Figs. 11a and 11 b are schematic views of a perforated thermal energy panel having depressions on the on the emissive side to collect water between adjacent perforations;

[0027] Fig. 12 is a schematic view of a perforated thermal energy panel with water collecting pockets or depressions, the panel installed along a slope (e.g., a sloping roof surface);

[0028] Figs. 13a and 13b are schematic views of the corrugated, perforated thermal energy panel shown in Fig. 11a but installed in a heating mode configuration in which the selective surface of the panel is outwardly exposed;

[0029] Fig. 14 is a schematic view of another thermal energy system including an arrangement of solar collectors and cooling panels having outwardly facing emissive / reflective surfaces for reflecting sun rays towards the solar collectors;

[0030] Figs. 15a to 15c illustrate various throughflow air schemes through a thermal energy panel;

[0031] Fig. 16 illustrates an embodiment of a thermal energy panel including an emissive and reflective surface bonded onto a twin-wall polymer sheet, the emissive and reflective surface having water beads retained thereon;

[0032] Fig. 17 is a longitudinal cross-section view of the thermal energy panel of Fig. 16 and illustrating the enhanced cooling effect of the wetted emissive and reflective surface on the air flowing through the twin-wall polymer sheet; and

[0033] Fig. 18 is a schematic cross-section view of another embodiment of a thermal energy panel including wind breaker ribs or projections extending from the emissive surface of the panel.DETAILED DESCRIPTION

[0034] The term “emissive surface” is defined herein as a surface that can emit long infra-red waves (8 to 13 microns) through the earth’s atmosphere and thereby cool itself below ambient at least during nighttime, using nocturnal sky radiation. To achieve this, a material with a thermal emissivity of at least 0.7 in a spectral range of 8 pm to 13 pm and, more preferably, with a thermal emissivity of 0.8 in the spectral range of 5 pm to 15 pm may be used. An emissive surface has very high emissivity, which promotes radiation to the environment. For instance, an emissive surface as described in US Patent No. 1 1 ,359,841 , the entire contents of which are incorporated herein by reference, may be used.

[0035] The term “selective surface” is defined herein by a surface that has very low emissivity in the infrared wave range from 5 pm to 15 pm, so that it heats up more than black paint when exposed to sunlight. To achieve this, a material or a compound assembly of superposed layers, with overall optical properties such that the combination has a thermal emissivity of a maximum 0.2 in the spectral range of 5 pm to 15 pm, or preferably a maximum thermal emissivity of 0.1 in the spectral range the 0.8 pm to 13 pm, may be used. A selective surface has very low emissivity, which blocks the radiation losses to the environment. For instance, a selective surface as described in US Patent Pub. 2012 / 0224256, the entire contents of which are incorporated herein by reference, may be used.

[0036] The term “emissive surface compound” is used herein to refer to a multi-layer compound having an emissive surface layer, a solar-reflective layer and a protective layer. Emissive surface compounds were successfully tested. The tested surface compounds included: 1) an emissive surface layer having an emissivity of at least 0.8 in spectral range of 5 pm to 15 pm; 2) a solar-reflective layer having an ultraviolet reflectivity of at least 0.5 in the spectral range of 275 nm to, an ultraviolet absorptivity of at least 0.75 in the spectral range of 275 nm to 375 nm; and 3) a protective layer permeable to UV radiation and configured to provide protection against long-term UV degradation caused by exposure to solar radiation.

[0037] Such emissive surface compounds can be used to achieve sub-ambient temperatures 24 hours per day, since most incoming solar energy radiation during daytime are reflected back to space during daytime. As a result, cooling can be achieved not only during nighttime, but alsoduring daytime, even at full sunshine at 1000 W / m2, since, for instance, a 98.5% reflective compound would reflect 1000 W / m2 x 98,5% 0 = 985 W / m2 of it is reflected to the sky, leaving only a heat gain of 15 W / m2 during full sunshine hours. The reflective layer has an ultraviolet reflectivity of at least 0.5 in the spectral range of 275 nm to 375 nm, an ultraviolet absorptivity of at least 0.75 in the spectral range of 275 nm to 375 nm, or a combination thereof.

[0038] The expression “exposed outwardly” is used herein to refer to a surface or a part that is exposed to an outdoor environment towards the sky or the sun.

[0039] The expression “exposed inwardly” is used herein to referto a surface or a part hidden from the sky or the sun by an opaque substrate, facing the back of a collector, an inner wall, an enclosed space or the ground to name a few.

[0040] The term “transpired collector (TC)” is used herein to refer to a solar collector configuration by which exterior / outdoor air flows through a perforated plate into a plenum and then into a ventilation system of a building or process.

[0041] The term “maximum heating power” generally correspond to the amount of incident solar radiation on any surface facing the sun at any time. On a typical clear sky, this value is around 1000 W / m2. During cloudy conditions, this can be around 200 W / m2. A one square meter solar air collector with 100% efficiency would theoretically produce 1000 W in sunny conditions or 200 W in cloudy conditions. In reality, all collector efficiencies are below 100%. Solar efficiency = solar heat captured by collector / total maximum solar radiation.

[0042] The maximum cooling power is the theoretical maximum quantity of energy emitted to outer space of a body whose surface is at ground level. The maximum cooling power is influenced by the body’s temperature (through Stefan Bolzmann equation), clearness of the sky, cloud cover, relative humidity of the air at ground level.

[0043] The parameter “radiative cooling efficiency” is defined herein as the following ratio:Radiative cooling efficiency = cooling energy captured I maximum cooling power.

[0044] Referring now to the drawings, it can be appreciated that Fig. 1 illustrates a system comprising a thermal energy panel 10 mounted to an outdoor structure S, such as a building roof, a building wall, an enclosure or a back side insulation of a solar collector to name a few. The thermal energy panel 10 is mounted at a distance from the structure S so as to form an air gap Gor air flow passage therebetween, the air gap G operatively connected to a ventilation system (not shown) of a building or process. The thermal energy panel 10 includes a thermally conductive substrate 12 having a first side 12a and a second side 12b opposite to the first side 12a.

[0045] According to some embodiments, the substrate 12 is made out of a highly conductive material, such as copper, aluminum or zinc. However, it is understood that other less conductive materials such as steel, stainless steel, or polymers could be used as well. In some applications, the substrate 12 could even include plastic, mineral, wooden and fibrous materials in combination with thermally conductive materials.

[0046] The substrate 12 may be provided in various forms, wall thickness or geometries. According to some embodiments, it can be provided in the form of a plate, a planar sheet or a corrugated sheet component (Figs. 1 and 2), but many different profiles of different shapes, dimensions, thicknesses or ribs, reveals, surface trims, etc. are contemplated. For example, as will be seen hereinafter, according to some embodiments, the substrate 12 may include or be provided in the form of an assembly of finned tubes (see Figs. 5 and 6). Still according to some embodiments, the substrate can include a twin-walled structure, such as commercially available twin-wall plastic sheets S as for instance illustrated in Fig. 16.

[0047] The thermal energy panel 10 has an emissive surface 14 on the first side 12a of the substrate 12, and a selective surface 16 on the second side 12b of the substrate 12. This provides for a panel with back-to-back emissive and selective surfaces 14, 16. As will be seen hereinafter, the provision of such back-to-back emissive and selective surfaces 14, 16 allows for the creation a highly-efficient cooling or heating system. Indeed, applicant has found that both surfaces 14,16 enhance the performance of the other when they find themselves on each side of a same substrate.

[0048] As shown in Figs. 1 and 2, the panel 10 can be installed with its selective surface 16 outwardly exposed (Fig. 1) or with its opposite emissive surface 14 outwardly exposed ( Fig. 2). The first orientation with the outwardly exposed selective surface 16 as shown in Fig. 1 corresponds to the heating mode, whereas the second orientation with the emissive surface 14 outwardly exposed as shown in Fig. 2 corresponds to the cooling mode. That is for heating, the selective surface 16 is outwardly exposed and the emissive surface 14 is inwardly exposed (Fig. 1). For cooling, it is the opposite, the selective surface 16 is inwardly exposed and the emissive surface 14 is outwardly exposed (Fig. 2).

[0049] When the selective surface 16 is outwardly exposed, the inwardly exposed emissive surface 14 helps to better radiate the solar heat within the collector, cavity, plenum or air gap G. And when the emissive surface 14 is outwardly exposed, the inwardly exposed selective surface 16 stops the emission of coolth within the collector, cavity, plenum or air gap G.

[0050] The emissive surface 14 and the selective surface 16 can both consist of a paint, a film, a layer, surface treatment, or any suitable finish applied to, coated, sputtered, deposited on the substrate 12 to alter its optical and thermal properties. The thermal resistance of the bond between the emissive surface 14 (in the form of a film, paint, layer, etc.) and the substrate 12 should be negligible. Likewise, the thermal resistance of the bond between the selective surface 16 (in the form of a film, paint, layer, etc.) and the substrate 12 should be negligible.

[0051] From the foregoing, it can be appreciated that the surfaces 14, 16 are applied to opposed sides of the substrate 12 so that a 180° rotation of the substrate 12 would cause the initially inward surface to be exposed outwardly and the initially outward exposed surface to be exposed inwardly. As will be seen herein after, the panel 10 can be operatively connected to a mechanical sub-system to selectively pivot the panel 10 between a heating mode position and a cooling mode position.

[0052] As shown in Figs. 3 and 4, thermal energy panels 10 such as the one described above with respect to Figs. 1 and 2 can be used in a fixed and passive environment, with no passing fluid or moving parts. An example of a passive use of the thermal energy panels 10 is as a roof or wall cladding on a building B. In this configuration, the thermal panels 10 will help cool the building B if the emissive surface 14 is installed outward. Conversely, the panels 10 will help heat the building B if the selective surface 16 is installed facing outward.

[0053] The panels 10 can be used on cladding or roofing materials to either protect from the sun or collect the sun’s heat. In some embodiments, there is no forced circulation of fluids being heated or cooled. Only the substrate 12 can cool or heat itself depending on which surface of the emissive and selective surfaces 14, 16 is exposed outward.

[0054] Now referring to Figs. 5-8, it can be appreciated that a hollow substrate 12’ with back- to-back emissive and selective surfaces 14, 16 can be used to cool or warm a fluid F in gaseous or liquid form. More specifically, the warm or cold substrate 12’ can be used to warm up or cool down a flow of fluid F disposed in heat exchange relationship with the substrate 12’. As shown in Figs. 5 and 6, the substrate 12’ can be provided in the form of a finned tube including a centralhollow cylindrical body 12c’ an a pair of opposed fins or wings 12d’ extending laterally from opposed lateral sides of the hollow cylindrical body 12c’. A first side of the finned tube is coated with an emissive surface 14 and a second side of the fined tube opposite the first side is coated with a selective surface 16.

[0055] According to another embodiment shown in Figs. 7 and 8, the substrate 12’ can take the form of a pair of superposed corrugated panels 12e’ and 12f joined to one another along adjacent troughs so as to define a plurality of side-by-side channels therebetween. The channels may be used to contain or direct a working fluid F. A selective surface 16 is applied on the outwardly facing surface of the first panel 12e’ and an emissive surface 14 is applied on the outwardly facing surface of the second panel 12f , thereby providing a hollow substrate with back- to-back emissive and selective surfaces. Fig. 7 illustrates a cooling mode in which the emissive surface 14 is outwardly exposed and the selective surface 16 is inwardly exposed. Fig. 8 illustrates a heating mode in which the selective surface 16 is outwardly exposed and the emissive surface 14 is inwardly exposed.

[0056] Fluids, such as air or water, can be heated or cooled through the hollow substrate 12’ depending on which of the emissive and selective side is outwardly exposed to the outdoor environment. The fluid F is preferably gaseous (e.g., air). However, in some applications, the fluid can be a liquid (e.g., water) or of a viscous form (oils, paraffins, creams, etc.).

[0057] The geometry of the fins, plates and / or tubes shown in Figs. 5 to 8 can be used as possible heat exchanger designs aimed at transferring the substrate’s thermal energy into a passing fluid.

[0058] Fig. 9 illustrates an unglazed transpired type air collector 20 mounted outside a building or process space for heating or cooling a stream of outdoor air. In such a transpired type air collector, the thermal panel 10 can be used to cool or heat a stream of outdoor air, depending on the outwardly exposed surface of the panel 10. As shown in Fig. 9, the thermal energy panel 10 can be provided in the form of a perforated panel and placed in the front or outwardly exposed face of a closed environment (such as a box or the plenum of a collector) maintained under negative pressure by an air mover AM so that is becomes:• a solar air heater when the selective surface 16 is outwardly exposed,• an emissive air cooler when the emissive surface 14 is outwardly exposed.

[0059] The perforations 52 of the perforated panel 10 can be scattered or orderly aligned over a portion or the total surface of the panel 10 and forms part of the air passage that is in heat exchange relationship with the panel 10. Also, the density of the perforations 52 and their sizes can vary overthe surface of the panel as needed. As shown in Figs. 15a and 15b, the perforations 52 can extend at various angles relative to the emissive surface 14 and the selective surface 16. For instance, as shown in Fig. 15a, the perforations 52 can be normal to the emissive surface 14 and the selective surface 16. That is the perforations 52 can extend at right angles through the thickness of the panel 10. Referring to Fig. 15b, it can be seen that the perforations 52 can also be angled relative to the emissive surface 14 and the selective surface 16 of the panel 10. For instance, according to the illustrated example, the perforations 52 are shown at 25 degrees and at 70 degrees to the emissive surface 14 of the panel 10. It is understood that perforations 52 with different angular orientations can be provided on the same panel 10.

[0060] The primary role of the perforations 52 shown in Figs. 15a and 15b, is to allow the incoming throughflow air stream to retrieve the coolth generated by the emissive surface 14 or the heat generated by the selective surface 16 depending on which of the emissive and the selective surface is exposed outwardly. By properly selecting the angular orientation of the perforations 52, the transfer of thermal energy from the panel to the airflow can be optimized.

[0061] Turning to Fig. 15c, it can be appreciated that instead of flowing the air thicknesswise through the panel 10, the air to be heated or cooled down can be circulated in a direction parallel to the emissive surface 14 and the selective surface 16. As shown in Fig. 16, this can be achieved by applying an emissive and selective film and a selective film on opposed faces of a twin-walled structure, such as commercially available twin-wall plastic sheets S having opposed top and bottom surfaces S1 , S2 connected with internal supports S3 to create parallel and side-by-side channels S4 between the top and bottom surfaces S1 , S2 of the twin-wall plastic sheets, the channels collectively forming a fluid passage in heat exchange relationship with the panel. In this embodiment, the air or the other fluid to be cooled or heated is circulated between the emissive surface 14 and the selective surface 16 in a direction parallel thereto.

[0062] It is understood that the throughflow air angle values affect the resulting air pressure drop as the air flows through / across the panel 10. For the same hole cross-section and same spacing, an angled (Fig. 15b) or a parallel (Fig. 15c) airflow path will exhibit a higher pressure drop than a shorter perpendicular airflow path (Fig. 15a) through the thickness of the panel. This increased pressure drop must be taken into account when selecting and sizing the propermechanical means (e.g., fans or pumps) to draw the fluid (e.g., air) through / across the thermal plate 10.

[0063] As shown in Fig. 18, according to some embodiments, wind breaker projections 17a, 17b, 17c, 17d can extend from the emissive and reflective surface 14 of the thermal energy panel 10 to afford protection against the effects of lateral winds on the outwardly facing surface of the panel. The inventor has found that sideways winds on the outwardly exposed panel surface affect the coolth output of the system, by breaking the cool film on the panel’s surface. That is the cool energy swept away by the passing wind that is not drawn through the panel 10 may cause the performance to drop on windy days or locations. The effective air velocity on the panel surface can be advantageously reduced through the inception of wind breaker projections 17a, 17b, 17c, 17d, such as ribs, on top of the emissive and reflective surface 14 of the panel 10.

[0064] It is understood that the distance between the wind breaker projections 17a, 17b, 17c, 17d, their height, their shape, their color may vary, depending on outside conditions. As shown in Fig. 18, various combinations of shape and configuration of wind breaker projections 17a, 17b, 17c, 17d can be used over the emissive and selective surface 14 of the panel 10. According to some embodiments, all the wind breaker projections 17a, 17b, 17c, 17d can be identical. Also it is understood that the wind breaker projections 17a, 17b, 17c, 17d can be positioned anywhere on the panel or around its edges to reduce the effective velocity of lateral wind. The wind breaker projections 17a, 17b, 17c, 17d can also be configured to locally retain humidity and condensation on the emissive and reflective surface 14. As will be described hereinafter, the retention of a water content on the emissive and reflective surface 14 of a thermal energy panel 10 may advantageously be used to further enhance the adiabatic cooling when the panel is used in a cooling mode with its emissive and reflective surface exposed outwardly.

[0065] The wind breaker projections 17a, 17b, 17c, 17d can be positioned, horizontally, vertically or diagonally on the panel to fit the specific conditions of the site. For instance, horizontal and vertical ribs can cross each other or be placed on top of each other, creating a grid on the emissive and reflective surface 14 of the panel 10. It is also understood that while the wind breaker projections 17a, 17b, 17c, 17d are shown in connection with a thermal panel having 90 degrees perforations 52, the wind breaker projections 17a, 17b, 17c, 17d could be used in combination with any other embodiments of the thermal energy panels herein disclosed.

[0066] As shown in Figs. 10a and 10b, a manual or motorized system 30 can be designed to rotate the thermal panels 10 so that the user can switch between heating and cooling modes. That is, the thermal panels 10 can be pivoted to selectively outwardly expose the emissive surface 14 or the selective surface 16, thereby allowing one installation to be use to either heat or cool a passing fluid, such as water or air. The repositioning of the panels 10 can be done on an hourly basis, on a daily basis between night and day, or annually between winter and summer, or whenever suits the need of the user.

[0067] As shown in Fig. 10a, the motorized version of the system 30 can include one or more motor(s) 30a operatively connected to the thermal panels 10. Each individual panel 10 may be mounted to a rotating shaft 30b for rotation therewith. One motor can be provided per shaft or as illustrated in Fig. 10a a linkage or transmission system 30c may drivingly connect the shafts 30b to the one or more motors 30a for allowing the rotational driving force of the motors 30a to be transferred to all the of the shafts 30b at once, thereby causing unison rotation of the panels 10 between the heating and cooling positions thereof.

[0068] It is understood that such a motorized panel system may be integrated to all embodiments disclosed in the present disclosure and is not limited to the specific embodiment illustrated in Figs. 10a and 10b. Figs. 10a and 10b only illustrate one of such embodiments in which perforated thermal energy panels 10 are integrated to a glazed air collector 40 of the type comprising a front glazing 40a and insulated back and side panels 40b defining an air plenum 40c in which the thermal energy panels 10 are pivotally mounted for selectively heating or cooling a flow of incoming air admitted through an air inlet 40e before discharging the heated or cooled air via an air outlet 40d for further processing or use. An air mover 40f, such as a fan, can be used to draw air from the plenum 40c via the outlet 40d. As shown in Fig. 10b, the system may be configured as a double pass system in which the air is forced to flow from the back side of the panels 10 to the front side thereof and then to the front side to the back side again prior to being discharged through the outlet 40d, as for instance disclosed in WO 2023 / 205878 filed on March 28, 2023, the entire contends of which is herein incorporated by reference. In this way, the air flows twice through the panels inside the glazed air collector 40. Depending on which one of the emissive surface 14 and the selective surface 16 of the panels 10 is facing the front glazing 40a, the air drawn through the perforated thermal energy panels 10 is heated or cooled. Such a glazed air collector can thus be used to selectively cool or heat an air stream.

[0069] Transpired systems such as shown in Figs. 9, 10a and 10b have been tested at night to study nighttime cooling, but heretofore little has been documented. The emissive phenomenon and the behavior of air cooling in a transpired setting are not yet well understood by physicians. However, Applicant own in-house testing has shown the following:• Extra cooling performance can be gained with a selective surface on the back side of a collector panel, and• Extra cooling performance can be gained when water evaporation occurs on the outwardly exposed emissive surface of the thermal panel.

[0070] Regarding evaporation management, Applicant has noted that as the thermal energy panel 10 cools, the dew point of the surrounding air is sometimes reached and moisture condenses out on the panel surface. Condensation accumulates on the surface of the collector begins to add heat to the air stream, or fluid.

[0071] As the panel 10 heats up, for example when solar radiation hits the surface, the formed condensation can again vaporize, thereby drawing heat away from (e.g., cooling) the passing air (or fluid) stream.

[0072] Figs. 11 a and 11 b illustrate an embodiment of a perforated thermal energy panel 10, which is configured to take advantage of water accumulation for later evaporation in a transpired cooling mode. The air passing in close contact with the water before it is drawn through the perforations cools in adiabatic mode, so that the temperature of the air is cooled by two phenomena at once: Adiabatic of the air above the substrate + Emissive cooling of substrate. This is facilitated by the fact that water is transparent to long-wave radiation.

[0073] As shown in Fig. 11 a, depressions also herein referred to as water collection pockets 50 can be formed on the emissive side of the substrate 12 to provide additional cooling capability. The water collection pockets 50 are interspersed between the perforations 52 extending thicknesswise through the panel 10. According to the illustrated embodiment, the panel 10 is corrugated so as to define a trough between two successive crests. The perforations 52 are defined at the crests (i.e., at the top of the wave) and the water collection pockets 50 are formed by the troughs. With the perforations 52 located at a higher elevation than the water collection pockets 50, only moist air can flow through the perforations 52, and not the collected water.

[0074] As shown in Fig. 12, if aligned on a sloped roof or angle, the transpired collector can still be designed to withhold water as a strategy to take advantage of evaporative cooling. In this case, the perforations 52 can be defined in the upper side wall of the trough adjacent to the top of the wave above the surface level of the immediately adjacent water collection pocket 50.

[0075] It is understood that the panel 10 does not need to be corrugated to promote water retention on the emissive surface 14. Indeed various other water retention means may be provided on the emissive surface to obtain a wet emissive surface. For example, ribs or various surface treatments (e.g., embossment) could be applied to the panel in order to create the water collection pockets 50 or simply promote water retention on the emissive surface 14. For example, according to some embodiments, the emissive surface 14 can have a rough surface finish or other treatments to promote water retention and minimize water evaporation to the ambient. In some of the embodiments, the mechanical bonding properties of the emissive surface 14 or its surface finish may be sufficient to retain water on the emissive surface 14 by itself (no need for water collection pockets). Accordingly, the emissive surface 14 could be flat or substantially flat as for instance depicted in Figs. 16 and 17. According to this embodiment, the emissive surface 14 is bonded onto a planar face of a twin-wall polymer sheet S. The emissive surface 14 is, thus, selected or treated to provide a mechanical bond to retain beads of water W onto the emissive surface 14. The water Won the emissive surface 14 can be provided by different means including: rainfall, nighttime condensation, mechanical means (nozzles, hoses, sprinkler, etc.) and any combinations thereof.

[0076] Applicant has found that the presence of water W on the emissive surface 14 contributes to increase the cooling effect of the emissive surface 14 as the throughflow air passes through the air channels of a twin-wall polymer sheet or other type of air-through flow substrates. Surface water beads typically evaporate to the surrounding air. Natural convection with the surrounding air happens especially when the surrounding ambient air temperature is higher than the surface temperature. The pace of evaporation increases along with the surface temperature. The higher the surface temperature, the higher the rate of evaporation to the ambient. This is unwanted, as the desired effect is to cool the passing throughflow air instead of the ambient air.

[0077] As shown in Fig. 17, the combination of an emissive surface and water beads on the surface increases the cooling effect on the throughflow air. The cooling effect can be further improved by adding a reflective layerto the emissive surface to have a wet emissive and reflective surface on top of the air channels. The higher the convection coefficient in the throughflow airwithin the air channels S4, the higher the cooling effect of the throughflow air. If the twin-wall polymer sheet was painted with typical white color instead of an emissive / reflective surface, more surface water would evaporate to ambient, resulting in less cooling in the throughflow air. It is understood that the wetted emissive and reflective surface could be applied to other substrate than the twin-wall polymer sheet. The combination of an emissive and reflective surface and water beads on the surface has a synergic effect which enhances the cooling effectiveness of the thermal panel. In some cooling applications, the selective surface on the back side of the thermal panel can be omitted.

[0078] Having an emissive and reflective surface, therefore, reduces the amount of water needed to achieve throughflow adiabatic air cooling.

[0079] As shown in Fig. 17, the flat thermal panel shown in Fig. 16, thanks to its water surface retention properties, can also be installed at an angle from the horizontal as, for instance, on a sloped roof of a building.

[0080] Now referring to Figs. 13a and 13b, when a "transpired + water retaining” design panel such as the one exemplified in Fig. 11 a is laid upside down, then the selective surface 16 is outwardly exposed. The perforations 52 are then located on the bottom of the troughs, and the substrate 12 bulges outward to the open space, giving it more contact surface to the sun. This further enhances the performance of the solar heating mode.

[0081] Turning to Fig. 14, there is shown a further embodiment of a thermal energy system that is, for instance, suitable for installation on a building roof (R) or directly on the ground, such as in the desert. The system generally comprises one or more inclined thermal panels 10a, 10b, 10c, 10d... (four in the illustrated example) that may have back-to-back emissive and selective surfaces 14, 16 and one or more solar collectors 60a, 60b, 60c, 60d... (four in the illustrated example) interspersed between the thermal panels 10a, 10b, 10c, 10d... The solar collectors 60a, 60b, 60c, 60d... are oriented to face the sun so as to be directly exposed to the sun rays. The thermal panels 10a, 10b, 10c, 10d... are installed with their respective emissive surfaces 14 outwardly exposed (face up) and their respective selective surfaces 16 inwardly exposed (face down) so as to act as cooling panels as explained hereinabove. In addition of being configured to be emissive, the outwardly facing emissive surfaces 14 of the cooling panels are configured to be reflective. For instance, such emissive / reflective surfaces can be obtained by applying an emissive surface compound on a side of a substrate (e.g., a heat conducting plate perforated ornot). The reflective properties of such an emissive surface compound, which as mentioned hereinabove, can comprise an emissive surface layer, a solar-reflective layer and a protective layer, allow to protect the compound from absorbing heat within the cooling panels. Moreover, by appropriately orienting the thermal energy panels 10a, 10b, 10c, 10d... relative to the solar collectors 60a, 60b, 60c, 60d... , the solar radiations reflected by the emissive / reflective surfaces 14 of the thermal panels 10a, 10b, 10c, 10d... can be redirected towards and absorbed by the solar collectors 60a, 60b, 60c, 60d...For instance, the emissive / reflective surface 14 of each of the panels 10a, 10b, 10c, 10d can be oriented to at least partly face an associated one of the solar collectors 60a, 60b, 60c, 60d. In some embodiments, each solar collector extends at generally right angles from a bottom end of the associated cooling panel upwardly to the upper end of the next cooling panel and so on to form a sawtooth wave arrangement of cooling panels and solar collectors. However, it is understood that the sawtooth wave or “zigzag” arrangement of interspersed inclined cooling panels and solar collectors shown in Fig. 14 is only an example of how the reflected sunlight of the cooling panels can be efficiently redirected to the solar collectors. Other suitable configurations and arrangements are contemplated as well.

[0082] The solar collectors 60a, 60b, 60c, 60d... can, thus, be fed by both 1) direct sunlight and 2) reflected sunlight redirected from the cooling panels 10a, 10b, 10c, 10d... to the solarabsorbing surfaces of the collectors as schematically depicted by the flow arrows in Fig. 14. In other words, the reflective property of the outwardly facing emissive surfaces 14 of the cooling panels 10a, 10b, 10c, 10d... can be used to both thermally protect the panels and redirect solar radiations to the solar collectors 60a, 60b, 60c, 60d. On cloudless conditions and depending on the season and / or time of day, the reflected sunlight allows the solar collectors 60a, 60b, 60c, 60d to receive extra solar radiation, which can then be converted into more electricity, hot water or warm air depending on the type of solar connector used.

[0083] It is understood that the sun ray reflection caused by the cooling panels can be directed towards solar collectors of any type (photovoltaic, solar water heater, solar air heater, hybrid photovoltaic-thermal panels, etc.) to improve their performance. Also, the solar collectors of a same system can be of a single type or include different types, classes or categories of solar collectors. All permutations are contemplated.

[0084] While reflective surfaces are mostly associated with white surfaces, it is understood that they can come in a variety of colors, materials and compositions. Accordingly, the reflective component of the emissive surface compound of the cooling panels can take various forms.

[0085] It can be appreciated from the foregoing, that at least some of the embodiments allows to increase the thermal output as compared to the use of a “single surface” thermal energy panel (i.e., a thermal panel having only one of a selective surface and an emissive surface). Providing both type of surfaces on opposed sides of a same substrate has many advantages. Indeed, both surfaces on each side of the substrate add to each other, in that the thermal output of the active surface, exposed to the outside environment, is helped by the opposite surface located on the opposite side of the substrate.• In heating mode: the selective surface heats up the substrate, then the substrate’s heat is radiated through the inner emissive surface, promoting heat transfer to the passing air inside the collector plenum or cavity. In this way, maximal radiative gains are achieved on the inside of the collector or cavity.• In cooling mode, the emissive surface on the outside radiates out to space, while the inside surface radiates out to the inside of the collector or plenum (cavity). Little or no radiation occurs on the inside of the panel, covered with the selective (non-emissive) surface. In that way, minimal radiative losses happen on the inside of the collector or cavity.

[0086] As can be appreciated from the foregoing disclosure, it is also possible to make use of adiabatic cooling on top of emissive cooling, when available. Water or condensation can accumulate on the substrate panel when the emissive surface is outwardly exposed. This further increases cooling of the passing air stream.

[0087] And when a corrugated perforated panel with back-to-back emissive and selective surfaces of a the transpired collector is flipped into a heating position, thus when the selective surface is exposed to sunlight, the passing air has longer, better exposure to the hot selective surface, thereby increasing solar heating efficiency.

[0088] As explained hereinabove with the possibility of rotating the panels between the heating and cooling mode positions, the system can easily provide either cooling or heating with the same bifacial plate depending on which side is exposed to ambient.

[0089] While various inventive aspects, concepts and features of the disclosures may be described and illustrated herein as embodied in combination in the exemplary embodiments, these various aspects, concepts, and features may be used in many alternative embodiments either individually or in various combinations and sub-combinations thereof. Unless expresslyexcluded herein all such combinations and sub-combinations are intended to be within the scope of the present application. Still further, while various alternative embodiments as to the various aspects, concepts, and features of the disclosures--such as alternative materials, structures, configurations, methods, devices, and components, and so on--may be described herein, such descriptions are not intended to be a complete or exhaustive list of available alternative embodiments, whether presently known or later developed. Those skilled in the art may readily adopt one or more of the inventive aspects, concepts, or features into additional embodiments and uses within the scope of the present application even if such embodiments are not expressly disclosed herein. For example, in the exemplary embodiments described above within the Detailed Description portion of the present specification, elements may be described as individual units and shown as independent of one another to facilitate the description. In alternative embodiments, such elements may be configured as combined elements.

Claims

WHAT IS CLAIMED IS:1 . A thermal energy system comprising: an outdoor panel having a first surface adapted to be exposed outwardly to face an outdoor environment and a second surface opposite the first surface, the first surface having an emissive layer and a solar reflective layer; and an air passage for directing a flow of air in heat exchange relationship with the outdoor panel.

2. The thermal energy system of claim 1 , wherein the first surface has water retention means provided on the first surface, the water retention means configured to promote water retention and / or minimize water evaporation on the emissive layer.

3. The thermal energy system of claim 2, wherein the water retention means include a surface treatment applied to the first surface of the outdoor panel.

4. The thermal energy system of claim 2 or 3, wherein the water retention means comprise water collection pockets formed on the first surface.

5. The thermal energy system of any one of claims 2 to 4, further comprising mechanical means to supply water onto the first surface of the outdoor panel.

6. The thermal energy system of claim 4, wherein the air passage includes a plurality of perforations extending through the outdoor panel, the plurality of perforations being interspersed between the water collection pockets.

7. The thermal energy system of any one of claims 1 to 6, wherein the second surface of the outdoor panel is a selective surface.

8. The thermal energy system of claim 7, wherein the outdoor panel is a reversible panel permutable between a first and a second position in which the first surface and the second surface of the panel are respectively exposed outwardly to the outdoor environment.

9. The thermal energy system of claim 8, wherein in the outdoor panel is pivotally mounted to a support structure, and wherein an actuator is provided for pivoting the outdoor panel between the first and second positions.

10. The thermal energy system of any one of claims 1 to 7, further comprising a solar collector oriented to be directly exposed to sun rays, and wherein the first surface of the outdoor panel with its emissive and solar reflective layers is positioned so that solar radiations reflected by the first surface of the outdoor panel are redirected towards the solar collector.11 . The thermal energy system of any one of claims 1 to 10, wherein the air passage extends through the outdoor panel in a plane parallel to the first and second surfaces of the outdoor panel.

12. The thermal energy system of claim 11 , wherein the outdoor panel comprises a twin-walled substrate having opposed faces connected via side-by-side internal supports creating parallel air channels between the opposed face, the air channels forming at least part to the air passage.

13. The thermal energy system of claim 12, wherein the twin-walled substrate is a twinwall plastic sheet, and wherein the emissive layer and the solar reflective layer are integrated to a film bonded to one face of the twin-wall plastic sheet.

14. The thermal energy system of any one of claims 1 to 13, wherein the emissive layer has a thermal emissivity of at least 0.8 in the infrared wave range of 5 pm to 15 pm.

15. The thermal energy system of claim 6, wherein the outdoor panel is corrugated so as to define a series of side-by-side troughs and crests, wherein the water collection pockets are formed by the troughs in the substrate, and wherein the perforations are at the crests.

16. The thermal energy system of any one of claims 1 to 15, further comprising wind breaker projections extending from the first surface of the outdoor panel, the ribs configured to act as wind breakers to reduce wind speed at the first surface of the outdoor panel.

17. A thermal energy system comprising:one or more cooling panels having an emissive and reflective surface facing outward; and one or more solar collectors oriented to intercept both direct solar radiations from the sun and indirect solar radiations reflected from the emissive and reflective surface of the one or more cooling panels.

18. The thermal energy system of claim 17, wherein the one or more cooling panels and the one or more solar collectors are disposed in alternance to form a sawtooth wave pattern over a building roof or a ground surface.

19. The thermal energy system of claim 18, wherein the one or more cooling panels have means for retaining water on the emissive and reflective surface.

20. The thermal energy system of any one of claims 17 to 19, wherein each of the one or more cooling panels has a selective surface opposite the emissive and reflective surface thereof.

21. The thermal energy system of any one of claims 17 to 20, wherein water supply means are provided for supplying water onto the emissive and reflective surface of each of the one or more cooling panels.

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