Transparent radiant cooling panels

Abstract

A device surrounded by ambient air that radiantly heats or radiantly cools subjects. The device includes a planar heat exchanger with at least one radiantly active face and which at least partially transmits visible radiation, a support frame, and one or more membranes that create sealed, planar, gas-filled cavities that isolate radiantly active faces of the planar heat exchanger from contact with the ambient air.

Description

Atty. Dkt. No. 01296-0082Transparent Radiant Cooling PanelsRELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Patent Application No. 63 / 680,328, filed August 7, 2024 and entitled FUNCTION OF RADIANT COOLING PANELS, the contents of which are incorporated herein by reference in their entirety.BACKGROUND

[0002] Extreme heat around the world is making it intolerable, if not dangerous, to be outdoors without some means of protection against the heat. Radiant cooling panels can be the low- power protection that allows people to work, play, socialize and, in general, safely be outdoors during very hot weather.

[0003] Radiant cooling of people and animals occurs when they are in the vicinity of cold surfaces that absorb significantly more thermal radiation emitted by their warm bodies than the cold surfaces emit back to them. As a means of providing comfort, radiant cooling has been popular in limited market niches since the 1970s. Although cooling people radiantly can be much more energy efficient than cooling them convectively (i.e., the circulation of cool air over them), radiant cooling has struggled with a practical problem — the cold surfaces that absorb the thermal radiation also condense water vapor from the surrounding air if their temperature is lower than the air’s dewpoint temperature.

[0004] In 1961, Morse and Kaletzky published a paper entitled “ANew Approach to Radiant Cooling for Human Comfort” (Morse and Kaletzky, “A New' Approach to Radiant Cooling for Human Comfort,” Paper No. 1535. Engineering Conference, Melbourne, Australia, 27th February to 3rd March, 1961) in which they recognized that cold surfaces could keep a person comfortable when the room air temperature is high, but that the need to prevent condensation on the cold surfaces limits the temperature of the cold surfaces to values above the dewpoint of the room air. Morse and Kaletzky explored the use of membranes in the form of 100-micron thick films of polyethylene that were highly transmissive to thermal IR radiation (i.e.. radiation emitted by a warm body typically with wavelengths between 4 and 25 microns) to create a buffer or cavity of sealed air between the cold surface and the humid room air. The buffer isolated the cold surface from the humid room air, thereby preventing condensation, but since the membrane was highly transmissive for thermal radiation it did not impede the exchange of radiation between the cold surface and a person in the room.Atty. Dkt. No. 01296-0082

[0005] U.S. Patent No. 10.371,398 discloses a radiant cooling panel similar to the one described by Morse and Kaletzky but with the innovations that the panel (1) used a “dehumidifying apparatus” to expel water vapor from the buffer between the IR-transmissive membrane and the cold surface, and (2) used a wicking non-woven fabric that covers at least a portion of the cold surface and extends outside of the buffer to expel condensate that might form on the cold surface out of the buffer.

[0006] In 2018, Teitelbaum, et al. (“Membrane-assisted radiant cooling for expanding thermal comfort zones globally without air conditioning”, PNAS, vol. 117, no. 35, September 1, 2020. www.pnas.org / cgi / doi / 10.1073 / pnas.2001678117), demonstrated that most occupants of an outdoor pavilion in hot, humid Singapore would be relatively comfortable when the air within the pavilion was close to outdoor conditions (i. e. , the air was 30°C and 66.5% relative humidify) but the walls and ceiling of the pavilion were cooled by 17°C chilled water. Using technology taught by Morse and Kaletzky. thin, IR-transmissive membranes, in the form of 50-micron low- density polyethylene fdms, were used to create buffers or cavities of sealed air that isolated the pavilion’s cold surfaces from the high dewpoint (22.5°C) air within the pavilion, thus preventing condensation on the cold surfaces without significantly impeding the exchange of radiation between the cold surfaces and the pavilion’s occupants. The cooled walls and ceiling of the Singapore pavilion were formed from planar heat exchangers referred to as capillarytube mats that together with exterior insulation blocked ambient light from entering the pavilion, thus creating a relatively dark, cave-like environment within the pavilion.

[0007] Although planar heat exchangers for radiant cooling panels other than capillary -tube mats are available, their cold surfaces also are opaque. Examples of the planar heat exchangers in commercially available radiant cooling panels are: (1) water-cooled heat exchangers “having top and bottom panels with channels formed there between for receiving a heat exchange fluid... wherein the heat exchanger is made of thermally transmissive material including polymers, stainless steel, aluminum, or copper” (as used here, “thermally transmissive material" refers to a material with a high thermal conductivity) as disclosed in U.S. Patent No. 8,944,162 and manufactured by Therma-HEXX of Portsmouth. NH, US. (2) linear aluminum extrusions with embedded copper cooling tubes manufactured by Armstrong World Industries, Lancaster, PA, US and (3) bent aluminum faceplates with bolted copper cooling tubes manufactured by Solray (Cornyn Ching & Co (Solray) Ltd,. UK) and sold as Trident panels.

[0008] The product brochures for Therma-HEXX describe radiant heating and cooling panels with top and bottom surfaces that are formed sheets of linear low-density polyethylene andAtty. Dkt. No. 01296-0082 high-density polyethylene (all panels shown in the Therma-HEXX brochures have black, opaque walls.) When joined together the top and bottom surfaces form a planar heat exchanger with channels for the flow of a heat transfer fluid. Heat exchangers made from polymer extrusions, as taught in U.S. Patent Nos. 5,638,900 and 6,079,481, can also provide the hot or cold surfaces of a radiant heating or cooling panel.

[0009] More recently, Abraham, et al. (Abraham, et al.. “Efficient Outdoor Thermal Comfort via Radiant Cooling and Infrared-Reflective Walls,” Nature Sustainability, https: / / doi.org / 10.1038 / s41893-025-01558-0, May 2025), studied ways to advance the work of Teitelbaum, et al., so that an outdoor shelter could be radiantly cooled while retaining natural lighting within the shelter and allowing people within the shelter to view outside and to be viewed from outside. As noted by Abraham, et al., “studies show that people prefer high visibility when in an outdoor structure, citing safety concerns in particular.” Abraham, et al., replaced several of the opaque water-cooled walls of the Teitelbaum pavilion with transparent membranes that reflect thermal IR radiation. Although not quite as effective as an actively cooled surface, the transparent, reflective surfaces direct some of the radiation emitted by an occupant of the shelter towards one of the shelter’s cold surfaces so that the occupant experiences cooling as he / she indirectly views the cold surfaces.

[0010] During the operation of a radiant cooling panel, there is a small flow of heat from the IR-transparent membrane towards the cold surface. The effect of this heat transfer — some of which is via radiation (since the membrane is not perfectly transparent and has an emissivity greater than zero) and some of which is via convection / conduction across the air gap — will reduce the temperature of the membrane. A practical lower limit on the temperature of the panel’s cold surface occurs when the membrane’s temperature falls below the dewpoint of the contacting air. Under these conditions, condensation forms on the membrane, and this condensation, which has a high emissivity' for thermal IR radiation, will be effectively cooled by the cold surface leading to an expanding layer of condensate.

[0011] Researchers have suggested ways to extend the operation of a membrane-based radiant cooling panel to lower cold-surface temperatures without condensation forming on the membrane. Morse and Kaletzky installed a resistance heater in the air gap between the IR- transparent membrane and the cold surface that warmed the membrane, preventing condensation. For a vertically oriented panel, Morse and Kaletzky minimized heat transfer from the resistance heater to the cold surface (which would penalize overall panel performance) by installing two additional IR-transparent membranes parallel to and between the cold surfaceAtty. Dkt. No. 01296-0082 and the outer membrane to create a flow loop with an upward leg and a downward leg. During operation of the panel, the buoyant warm air passing over the resistance heater, which was located near the bottom of the upward leg, first flowed upward in contact with and heating the outer membrane, and then, after cooling slightly, flowed back towards the heater in the loop’s downw ard leg. Since the innermost of the three membranes, which was one boundary of the downward leg, was spaced apart from the cold surface, heat transfer from the warm recirculating air to the cold surface was minimized.

[0012] U.S. Patent No. 10,371,398 shows up to three flat, spaced-apart, thin IR-transparent membranes on one or both sides of a radiant cooling panel’s cold surface. Each membrane is sealed along its perimeter to an “edge compound” to create one or more “gas-tight” cavities. As shown in U.S. Patent No. 10.371,398, the “edge compounds” maintain the membranes spaced apart, and they are external to the “gas tight” cavities. Condensation is prevented on the surfaces of the membranes in contact with the enclosed gas by means that include (1) sorption of the water vapor by a desiccant, (2) active pumping of the water vapor from within the cavity, and (3) filling the cavities with a dry, “protective gas”. The multiple membranes and “gas-tight” cavities shown in U.S. Patent No. 10,371,398 thermally insulate the outermost membrane from the cold surface, thus allowing the cold surface to operate at lower temperatures without condensation forming on the one membrane surface that contacts the surrounding ambient air.

[0013] In their review of cover-shield-assisted radiant cooling systems (Dharmasastha, et al., “A comprehensive review of cover-shield-assisted radiant cooling system,” Energy & Buildings 291 (2023) 113121), Dharmasastha, et al., recognized that membranes for a radiant cooling system may be fragile and “[t]he provision of thin wire mesh over the membrane can be a viable option to protect the membrane”.Atty. Dkt. No. 01296-0082SUMMARY OF INVENTION

[0014] The value provided by the invention described herein can best be appreciated in the context of past work to advance active radiant cooling. It should be noted that active radiant cooling is different from related efforts to advance Passive Daytime Radiant Cooling (PDRC), which uses materials that have very low emissivity7at wavelengths shorter than that for thermal radiation and high emissivities at wavelengths in the range of thermal radiation where the sky has a “window" that allows transmission to space.

[0015] Although the preceding background discussion focuses on radiant cooling, the innovations described herein can also be applied to a panel that provides radiant heating. Although condensation is not a problem for a panel that provides radiant heating, the increase in energy consumption to keep the radiating surface hot when it loses heat to the surrounding air can penalize operating efficiency. Similar to its function as part of a radiant cooling panel, one or more thin, IR-transmissive membranes can be applied to a radiant heating panel to create one or more buffers (i.e., cavities of sealed air) that insulate the hot surface from the surrounding air without significantly interfering with the exchange of IR radiation. Since the temperature of a radiating hot surface may be higher than the temperature of a radiating person or animal, the wavelength of the emitted wavelength will be shorter: the wavelengths at which radiant intensity7peaks for a surface with an emissivity7of one at 301 K, 373 K and 500 K are 9.6, 7.8 and 5.8 microns. In the context of a radiant heating panel, thermal radiation includes the shorter wavelength, infrared radiation emitted by surfaces with temperature as high as 500 K.

[0016] According to an exemplary embodiment of the present invention, a device is provided that radiantly heats or radiantly cools people, animals or plants, collectively referred to as subjects, the device being surrounded by ambient air and comprising: a planar heat exchanger with a front face and a back face, at least one of the faces being radiantly active in that the face exchanges thermal radiation with the subjects, and the planar heat exchanger having at least a 0. 1 transmissivity7for visible radiation incident on at least one of the front face or the back face, a heat transfer fluid that enters the planar heat exchanger through an at least one inlet fitting and leaves through an at least one outlet fitting, the heat transfer fluid either supplying thermal energy to or removing thermal energy from the planar heat exchanger, a mounting base to which the planar heat exchanger is directly or indirectly attached, the mounting base having one or more openings through which may pass both visible radiation and thermal radiation that are incident on the planar heat exchanger, one or more membranes, one or more of whichAtty. Dkt. No. 01296-0082 contact the surrounding ambient air, that are directly or indirectly attached to the mounting base and spaced apart from each radiantly active face to create one or more sealed, planar gas-filled cavities, each cavity with a width of at least 5 mm, that isolate each radiantly active face from contact with the surrounding ambient air, the one or more membranes being made of a polymer film no more than 160 microns thick that transmits both visible and thermal radiation, wherein the one or more membranes that contact the surrounding ambient air are outer membranes having external sides that contact the surrounding ambient air.

[0017] In an exemplary embodiment, the mounting base is a frame with a continuous perimeter that encloses one or more central openings.

[0018] In an exemplary embodiment, the planar heat exchanger has at least a 0.85 wavelength- averaged transmissivity for visible radiation incident on at least one of the front face or the back face.

[0019] In an exemplary embodiment, the one or more membranes have at least a 0.1 wavelength-averaged transmissivity for visible radiation and a 0.5 wavelength-averaged transmissivity for thermal radiation, where thermal radiation has a wavelength between 5 and 25 microns.

[0020] In an exemplary embodiment, the one or more membranes have at least a 0.85 wavelength-averaged transmissivity for visible radiation and thermal radiation.

[0021] In an exemplary embodiment, the planar heat exchanger has a radiantly inactive face and the device further comprises a window that is at least partially transparent or partially translucent to visible radiation, the window being mounted and sealed either directly or indirectly to the mounting base so that it is spaced apart from the planar heat exchanger's radiantly inactive face to create a sealed, planar, gas-filled cavity with a width of at least 5 mm in front of the radiantly inactive face that isolates the radiantly inactive face from contact with the surrounding ambient air.

[0022] In an exemplary embodiment, an outward face of the window that contacts the surrounding ambient air reflects radiation that is not part of the visible spectrum.

[0023] In an exemplary embodiment, the outward face of the window comprises a coating or film.

[0024] In an exemplary embodiment, the coating or film reflects up to 78% of the thermal radiation energy and 99% of the ultraviolet radiation energy incident on the window.

[0025] In an exemplary' embodiment, an outward face of the window that contacts the surrounding ambient air reflects radiation that is part of the visible spectrumAtty. Dkt. No. 01296-0082

[0026] In an exemplary embodiment, the outward face of the window comprises a coating or film

[0027] In an exemplary embodiment, the coating or film reflects at least 25 percent of the visible radiation energy7incident on the window7.

[0028] In an exemplary embodiment, the planar heat exchanger is a heat exchanger formed from a polymer, twin-wall, multi-channel extrusion.

[0029] In an exemplary embodiment, the polymer for the twin-wall, multi-channel extrusion is polypropylene, polycarbonate, polyethylene, polyethylene terephthalate, polysulfone, polyphenylsulfone or combinations thereof.

[0030] In an exemplary embodiment, the device further comprises one or more screens that are either directly or indirectly attached to the mounting base, each screen located proximate to an external side of a respective one of the one or more outer membranes.

[0031] In an exemplary embodiment, the one or more screens are adjacent to or in contact with at least one of the outer membranes.

[0032] In an exemplary7embodiment, one or more screens are spaced apart from at least one of the outer membranes.

[0033] In an exemplary embodiment, the one or more screens comprise at least one of the following: an open-cell yvoven sheet, yvith metal, fiberglass, ceramic or polymer yvarp and yveft strands, a perforated metal or polymer plate, sheet or film, an open-cell mesh yvith twisted yvire strands, or a thin plate or sheet w ith an expanded metal structure.

[0034] In an exemplary embodiment, each of the one or more screens has an open area of at least 50%.

[0035] In an exemplary7embodiment, each of the one or more screens has an open area of at least 80%.

[0036] In an exemplary embodiment, each of the one or more screens has an open area of at least 90%.Aty. Dkt. No. 01296-0082BRIEF DESCRIPTION OF THE DRAWINGS

[0037] FIG. 1 is a conceptual drawing in cross-section of a conventional panel that provides either radiant heating or radiant cooling and has two spaced-apart membranes that are highly transmissive for thermal IR radiation positioned so as to create buffers (i.e., planar cavities of sealed gas) that isolate the panel’s hot planar heat exchanger (in heating mode) or cold planar heat exchanger (in cooling mode) from direct contact with surrounding air.

[0038] FIG. 2 is a conceptual drawing in cross-section of a panel according to an exemplary embodiment of the present invention similar to the one shown in FIG. 1 but adapted to allow visible light to pass through the panel.

[0039] FIG. 3 is a conceptual drawing in cross-section of a panel according to an exemplary embodiment of the present invention similar to the one shown in FIG. 1 that has a protective screen in front of the outmost membrane.

[0040] FIG. 4 is a drawing of a twin-wall, multi-channel, plastic plate.

[0041] FIG. 5 is a drawing of a twin-wall, multi-channel, plastic plate according to an exemplary embodiment of the present invention adapted for the internal flow of a heat transfer fluid.

[0042] FIG. 6 is an isometric, partial assembly drawing and cross section enlargement of an exemplary embodiment of the invention with a wood support frame, a planar heat exchanger and a transparent window, both fabricated from a twin-wall polycarbonate extrusion, and two polyethylene membranes.DETAILED DESCRIPTION

[0043] Embodiments of the invention will next be described in the context of a radiant cooling panel that has a rectangular, planar, cold heat exchanger with at least one of its tw o faces being radiantly active in that it can exchange infrared radiation with its surroundings. This exemplary7panel has two membranes spaced apart from each radiantly active face that create sealed planar buffers, also referred to as cavities, to isolate the cold heat exchanger from contact with the surrounding ambient air, thus insulating the cold heat exchanger from convective and conductive heat and mass exchange with the surrounding ambient air. Engineers, architects, designers and others familiar with HVAC applied to the built environment will appreciate that a panel with a hot planar heat exchanger that provides radiant heating will also benefit from the innovative features described herein for radiant cooling panels. They will also appreciate that a device for radiant heating or radiant cooling may have geometries other than rectangular, flat panels, including but not limited to devices that are non-rectangular, arcuate and tubular.Atty. Dkt. No. 01296-0082Many aspects of the invention can also be applied to devices that may have only a single membrane or more than two membranes spaced apart from each radiantly active face. Furthermore, although the invention will be described in the context of cooling people and / or animals, many aspects of the invention can also be applied to radiant heating and cooling panels for greenhouses where it is important to efficiently heat or cool the plants without shading the plants from the visible portion of the solar spectrum.

[0044] The conventional radiant cooling panel 100a shown in FIG. 1 has a rectangular, planar heat exchanger 110 that is cold and is secured within a rectangular, planar insulating base 140 that provides structure for the panel. As its name suggests, the planar insulating base has insulation to inhibit heat exchange between the planar heat exchanger 110 and its surroundings on all sides except for its rightward facing surface. This rightward facing side of the planar heat exchanger 110 in FIG. 1 will be referred to as its front face; similarly, the right ward facing side of the radiant cooling panel 100a will be referred to as panel’s front face. In FIG. 1, the front face of the planar heat exchanger 110 is the face that is radiantly active in that it can exchange infrared radiation with people and animals, collectively referred to as subjects, that might be on the front side of the radiant panel. Two rectangular membranes 120o and 120i, spaced apart from the planar heat exchanger 110 and from each other by at least 5 mm, preferably by at least 10 mm, are attached around their perimeters to the planar insulating base 140 by sealing elements 130 so as to create an inner buffer 122i and an outer buffer 122o, both buffers being sealed planar cavities of gas (e.g., air) that together greatly limit heat and mass exchange between the planar heat exchanger 110 and the ambient air that surrounds the panel by isolating the planar heat exchanger from direct contact with the surrounding ambient air. Both membranes have a high transmissivity for thermal radiation, which in the context herein is a wavelength-averaged transmissivity greater than 75% for infrared radiation with wavelengths between 5 and 25 microns and preferably greater than 85% for the specified range of wavelengths. The planar heat exchanger 110 has a high absorptivity for thermal radiation and so absorbs the thermal radiation that might land on its front face after passing through the membranes.

[0045] All masses with a finite temperature and one or more surfaces that have a finite emissivity emit electromagnetic radiation. The intensity7of the energy flux [W / m2] for this radiation varies with w avelength. A curve of intensity7versus wavelength for a mass with an emissivity of one has a shape referred to as the Planck Blackbody Curve. The PlanckAtty. Dkt. No. 01296-0082Blackbody Curve has a peak at a specific wavelength, the wavelength for the peak increasing and the intensity of the peak decreasing as the temperature of the mass decreases.

[0046] The intensity-vs-wavelength curve for radiation emitted by an unclothed, warm person, animal or inanimate object with a surface temperature of 28°C will peak at a wavelength of 9.6 microns. Approximately 85% of the radiated energy from the person will have wavelengths between 5 and 25 microns. Radiation with wavelengths that encompass at least 85% of the energy radiated by an emissive surface that might be as cold as 0°C or as hot as 500°C will be referred to as thermal infrared radiation.

[0047] The ability of a mass to emit and absorb radiation of a given wavelength, i.e., its wavelength-dependent emissivity and absorptivity, must be equal. Thus, a planar heat exchanger that has a high absorptivity for thermal radiation — which is required for a radiant cooling panel — will also have a high emissivity for thermal radiation — which is required for a radiant heating panel.

[0048] If the radiant cooling panel 100a shown in FIG. 1 is to effectively exchange radiation 160 with a warm person 150 who is in the vicinity of the front face of the cold planar heat exchanger 110, the membranes 120o and 120i that are between the person and cold planar heat exchanger preferably have a high transmittance for thermal radiation. As reported by Ke, et al. (Ke Du, et al., “Condensation-free radiant cooling with double-skin infrared-transparent membranes,” Building and Environment, 193 (2021) 107660), a single membrane that is a film of linear low-density polyethylene (LLDPE) with a thickness of 20 microns will have a transmissivity of 87% for the thermal radiation with wavelengths between 2.5 micron and 25 micron emitted by a black body with an emissivity' of one (i.e., 87% of the energy radiated by the black body in the specified range of wavelengths will pass through the membrane and 13% will be either absorbed or reflected). Other thin membranes, such as films of polypropylene, have high transmissivity7for thermal radiation. Since transmissivity is inversely proportional to membrane thickness, it is advantageous to use very thin membranes (i.e., in the range of 10 microns to 120 microns) subject to practical limitations on membrane availability, membrane handling during fabrication and membrane robustness and durability. And. although it is preferred that the inner membrane 120i and the outer membrane 120o of a radiant cooling panel both have a w avelength-averaged transmissivity7for thermal radiation that exceeds 0.85, design requirements for the radiant cooling panel might be better met w ith membranes as thick as 160 microns with wavelength-averaged transmissivities as low as 0.5.Atty. Dkt. No. 01296-0082

[0049] A person 150 experiences cooling from the radiant cooling panel 100a in FIG. 1 because the panel’s cold planar heat exchanger 110 absorbs more thermal radiation emitted by the person than it emits back towards the person. If the planar heat exchanger is to maintain a low temperature under these conditions, it must have a means to remove the energy it gains from the net exchange of thermal radiation. In FIG. 1, the necessary means of energy removal from the planar heat exchanger 110 is provided by aheat transfer fluid 114 that enters the planar heat exchanger 110 through an inlet fitting 116i and exits the planar heat exchanger through an outlet fitting 116o. The heat transfer fluid can be, but is not limited to, a single-phase medium, such as water or a water / glycol mixture, or a two-phase medium, such as a refrigerant that evaporates from a liquid phase to a gas phase within the planar heat exchanger.

[0050] As discussed in the Background section of this specification, radiantly cooled outdoor shelters, pavilions, gazebos, pergolas and similar structures that allow the exchange of visible light between the outdoors and the structure’s interior (i.e. structures with natural lighting of the interior space, good visibility of the outdoors from within the interior space, and good visibility of the interior space from outdoors) are preferred by users of those structures. Since radiant panels now commercially available are all opaque to visible radiation, a radiantly cooled outdoor structure using available technology' must have conventional windows, openings or transparent exterior surfaces that reflect thermal radiation if they are to have adequate natural lighting and / or visibility to the outdoors.

[0051] In the exemplary7embodiment of the invention shown in FIG. 2, the radiant cooling panel 100b cools people, animals or plants, collectively referred to as the subjects, that are located on one side of the panel. The radiant cooling panel 100b allow s at least the partial transmission of visible radiation 165 that originates on either side of the panel. The exemplary radiant cooling panel in FIG. 2 has a cold planar heat exchanger HOT that transmits visible radiation (i.e., radiation with wavelengths between 0.38 micron and 0.70 micron that can be detected by the human eye) and absorbs thermal radiation 160. The planar heat exchanger HOT may be highly transmissive with a wavelength-averaged transmissivity greater than 0.85 for visible radiation, it may be weakly transmissive with a wavelength-averaged transmissivity less than 0.85 but greater than 0.10. The planar heat exchanger may transmit the visible radiation with minimal scattering (i.e., specular transmission) or with some or significant scattering (i.e., translucent transmission or diffuse scattering). The planar heat exchanger may be tinted so that the transmissivity of visible radiation varies with the radiation’s wavelength. The membranes 120i and 120o in FIG. 2 that are located in front of the planar heat exchanger’sAtty. Dkt. No. 01296-0082 radiantly active face, in addition to having a wavelength-averaged transmissivity for thermal radiation no lower than 0.5, preferably no lower than 0.85, at least partially transmit visible radiation, their wavelength-averaged transmissivity for visible radiation being greater than 0.1, preferably greater than 0.85 for application requiring interior illumination with natural light. The planar insulating base 140 for the generic radiant cooling panel in FIG. 1 is replaced in FIG. 2 by a support frame 140f, which may include insulation, to which is mounted the planar heat exchanger HOT and an optional window 170 that is at least partially transmissive for visible outdoor radiation 165. In some embodiments the window’s outward facing side that contacts the ambient surrounding air has a coating or film — commonly referred to as a low-e coating — that reflects outdoor radiation 165 that is not visible (i.e., radiation with a wavelength less than 0.38 micron or greater than 0.70 micron). The coating or film may be similar to 3MtmWindow Films that reflect up to 78% of thermal radiation and 99% of ultraviolet radiation. In some embodiments the window’s outward facing side that contacts the ambient surrounding air has a coating or film that reflects outdoor radiation that is visible. The coating or film may be similar to those sold on-line by Uline that reflect between 25% and 95% of the visible radiation incident on them. In some embodiments the window’s transmissivity for visible radiation is a function of the radiation’s wavelength (i.e., the window is tinted). In some embodiments, the window 170 is omitted since the heat exchange between the planar heat exchanger HOT and ambient air on the side of the panel opposite the people, animals or plants is an acceptable penalty on panel’s performance.

[0052] When it is part of the radiant cooling panel 100b, the window 170 is mounted on the support frame 140f and spaced apart from the planar heat exchanger HOT to create a sealed planar buffer 122e of gas (e.g., a cavity filled with air) that shields the planar heat exchanger HOT from contact with the ambient air that surrounds the panel, thereby inhibiting convective and conductive heat and mass exchange between the planar heat exchanger and the surrounding ambient air. The sealed buffer 122e may have a width of 5 mm, preferable a width of at least 10 mm. The creation of a sealed buffer 122e may be facilitated by using sealing elements 130.

[0053] The membranes 120i and 120o are bonded, fastened or otherwise mounted on the support frame around their perimeters and spaced apart from the radiantly active, front face of the planar heat exchanger to create two sealed planar buffers 122i and 122o that shield the planar heat exchanger HOT from contact with the ambient air that surrounds the panel, thereby inhibiting convective and conductive heat and mass exchange between the planar heat exchanger and the surrounding ambient air. Each sealed buffer 122i and 122o may have a widthAtty. Dkt. No. 01296-0082 of 5 mm, preferable a width of at least 10 mm. The creation of sealed buffers 122i and 122o may be facilitated by using sealing elements 130 to bond, fasten or otherwise attach the perimeters of the membranes to the support frame.

[0054] Alternative approaches to mounting the membranes to the support frame 140f to create sealed buffers include, but are not limited to the following: a. The perimeters of each of the two membranes are pressed against, but not attached to the support frame; discrete sealing elements 130 are not required. b. Each of the two membranes is affixed to a planar frame with an enclosing perimeter (similar to a common framed window screen, but with the membrane replacing the screen) and each frame is clamped, attached, pressed or otherw ise sealed against the support frame. In the context herein, a frame with an enclosing perimeter is one whose outermost segments, (i.e., the frame’s perimeter) are contiguous, similar to a window frame or screen frame. c. Each of the two membranes is affixed to opposite sides of a planar frame, the perimeter of the frame having sufficient thickness to keep the membranes spaced apart by a specified amount; the frame is clamped, attached, pressed or otherwise sealed against the support frame.

[0055] The planar heat exchanger HOT has inlet and outlet fittings 180 through which a heat transfer fluid 182 enters and leaves the planar heat exchanger, thereby maintaining the planar heat exchanger 110T at a low temperature as it absorbs thermal radiation 160.

[0056] In some applications, people, animals or plants to be radiantly cooled are on both sides of the radiant cooling panel 100b. In an exemplar}' embodiment for these applications, both faces of the planar heat exchanger are radiantly active and the window 170 in FIG. 2 is replaced by one or more membranes that are spaced apart from the planar heat exchanger and are mounted on the support frame to create one or more sealed planar buffers. The one or more membranes that replace the window' 170 have geometrical, physical and radiative properties similar to or identical to the membranes 120i and 120o shown in FIG. 2.

[0057] The support frame 140f shown in FIG. 2 serves as a mounting base to which the other elements of the radiant cooling panel 100b are directly or indirectly attached. As shown in FIGS. 2 and 6, the support frame has a continuous perimeter that encloses a central opening. However, the support frame is not an essential element of a radiant cooling panel that applies the innovations of (a) a planar heat exchanger that exchanges thermal radiation and that at least partially transmits visible radiation, and (b) one or more membranes transparent to thermalAtty. Dkt. No. 01296-0082 radiation that are spaced apart from the planar heat exchanger so that they create one or more sealed, planar, gas-filled cavities that isolate the planar heat exchanger from contact with the air that surrounds the radiant cooling panel. Thus, in an exemplary embodiment of the invention, the wall of a building functions as the mounting base to which the other elements of the radiant cooling panel are directly or indirectly attached, the wall having an opening that allows visible light and thermal radiation to be incident on the planar heat exchanger.

[0058] The membranes now available for radiant cooling panels are thin so that they are highly transmissive for thermal infrared radiation. Depending on the end use for a radiant cooling panel, its thin outer membrane 120o may be vulnerable to incidental or intentional damage. In the exemplary embodiment of the invention shown in FIG. 3, a screen 210 that is more robust and resistant to damage than the membrane is installed on the panel’s front face to cover and protect the membrane. In some embodiments the screen 210 is mounted adjacent to or in contact with the outer membrane 120o, and in other embodiments it is mounted spaced apart from the outer membrane. The screen 210 may be secured in position with brackets 220 that overlap or attach to the screen and are fastened to the panel’s insulating base 140.

[0059] The screen 210 that protects the outer membrane 120o of a radiant cooling panel can have different geometries including, but not limited to: (1) an open-cell woven sheet, similar to a common window screen, with metal, fiberglass, ceramic or polymer warp and weft strands, (2) a perforated metal or polymer plate, sheet or film, (3) an open-cell mesh with twisted wire strands similar to fencing referred to as ‘'chicken wire”, or (4) a thin plate or sheet with a structure commonly referred to as expanded metal, where the term “expanded metal” refers to sheet metal which has been cut and stretched to form a regular pattern (often diamond-shaped) of mesh-like material. Since the screen 210 will interfere with the exchange of thermal radiation, it should have a large open-area fraction, preferably greater than 0.8. (A screen’s open-area fraction is the ratio of the sum of area of its openings to its total area.) McNichols Co. of New Brunswick, New7Jersey, US, manufactures suitable woven metal wire screens, perforated metal screens and expanded metal screens with open-area fractions of 0.92, 0.79 and 0.80, respectively. Although screens with large open-area fractions are preferred if radiation exchange is to be maximized, screens with smaller open-area fractions, such as a screen with a 0.50 open-area fraction, may better protect the membrane.

[0060] An exemplary7embodiment for the planar heat exchanger HOT in FIG. 2 that transmits visible radiation is configured as a double-pane glass window that is adapted for the flow of a heat transfer fluid 182 between the two glass panes that are the inner face Il li and outer faceAtty. Dkt. No. 01296-0082 l llo of the planar heat exchanger. In another exemplary' embodiment, the planar heat exchanger HOT in FIG. 2 is configured as a water-cooled heat exchanger similar to one manufactured by Therma-HEXX under U.S. Patent No. 8,944,162 (the contents of which are incorporated herein by reference in their entirety) ‘'having top and bottom panels with channels formed there between for receiving a heat exchange fluid'’ and the panels are made from a polymer that transmits visible radiation.

[0061] In another exemplary embodiment, the planar heat exchanger HOT in FIG. 2 is a water- cooled heat exchanger made from the twin-wall, multi-channel, plastic-plate extrusion shown in FIG. 4 (which also appears as FIG. 3 in U.S. Patent No. 6,079,481, the contents of which are incorporated herein by reference in their entirety) and the polymer for the extrusion transmits visible radiation. Translucent, twin-wall, polypropylene extrusions adaptable to this exemplary embodiment of the invention are manufactured and sold under the tradename Coroplast™ and IntePro™ by the Inteplast Group of Livingston, NJ, US, and transparent, twin-wall polycarbonate extrusions adaptable to this exemplary embodiment of the invention are manufactured and sold by (1) Plaskolite of Columbus, Ohio, US, under the tradename Polygal™ in thickness of 4, 6, 8, and 10 mm; and (2) ePlast of Monona, WI, US, under the tradename Poly carb™ in thickness of 6, 8 and 10 mm. Although not a common, commercially available product, twin-wall, multi-channel, plastic-plate extrusions can be made from other polymers that transmit visible radiation. In particular, extrusions made from polyethylene, polyethylene terephthalate, polysulfone and poly sulfone-related polymers (e.g.. polyphenylsulfone) can be formed into heat exchangers, some polysufone-related polymers having working temperatures as high as 300°F. High working-temperature polymers could be used in a high-temperature radiant heating panel.

[0062] FIG. 5 shows an exemplary embodiment of a w ater-cooled heat exchanger 400 made from twin-wall, multi-channel, plastic-plate extrusion. To function as part of a fluid-cooled heat exchanger, the tw o edges 425 of the extrusion w ith channel openings are sealed by means that include, but not limited to, thermal welding, crimping, plugging with a gap-fdling adhesive, and bonding a cap over the openings. Cutouts 450 that intersect two or more of the extrusion’s internal channels are cut, punched, routed or otherwise made in each end of the plate. Cover plates 460 that overlap the cutouts 450 are bonded to the extrusion 410 so that the cutouts are sealed. At least one of the cover plates at each end of the plate has a fluid fitting 470 that provides a route for a heat transfer fluid 440 to enter one cutout (shown as the left cutout in FIG. 5), flow through all channels 415 that are in fluid communication with the cutout.Atty. Dkt. No. 01296-0082 enter the second cutout (shown as the right cutout in FIG. 5) and leave the heat exchanger though a fluid fitting in one or more of the cover plates that seal the second cutout. (The cover plates and fluid fitting for the second cutout in FIG. 5 have been omitted to more clearly show the cutout.)

[0063] Now that embodiments of the present invention have been shown and described in detail, various modifications and improvements thereon will become readily apparent to those skilled in the art. Accordingly, the spirit and scope of the present invention is to be construed broadly and not limited by the foregoing specification.EXAMPLE

[0064] FIGS. 6A and 6B shows an example of a radiant cooling panel that was constructed in accordance with the present invention and which included a cedar frame, a polycarbonate water-cooled, platelike heat exchanger, a polycarbonate window and two polyethylene membranes. The isometric rendering in FIG. 6A is a partial assembly of the panel that includes the cedar frame 140f, the polycarbonate ater-cooled, platelike heat exchanger HOT and the lower inlet fitting 180 that supplies cold water to the plate 110T and the upper outlet fitting 180 that collects the cold water after it has flowed through the plate. Sections of the frame have been deleted to more clearly show the water-cooled platelike heat exchanger HOT and its inlet and outlet fittings 180.

[0065] As shown in the isometric rendering in FIG. 6 A, the cedar frame I40f is a rectangular structure with overall dimensions of 2.13 m by 1 .00 m. Each of the frame’s four sides has the profile shown in the enlarged cross-sectional view shown in FIG. 6B. The overall dimensions of this profile are 150 mm by 50 mm. The four sides of the frame enclose a rectangular opening that is 2.03 m by 0.90 m.

[0066] The radiant cooling panel in FIGS. 6A and 6B is the exemplary embodiment previously described in FIG. 2 reduced to practice, and elements common to the two figures have the same numerical labels. The transparent planar heat exchanger HOT in FIGS. 6A and 6B was configured similar to the water-cooled heat exchanger 400 in FIG. 5, being made from a 4-mm, twin-wall, multi-channel, polycarbonate extrusion. The window 170 in FIGS. 6A and 6B was made from the same 4-mm polycarbonate extrusion as the planar heat exchanger HOT. The inner membrane 120i and outer membrane 120o were both 20-micron films of clear, linear, low-density polyethylene. The membranes were attached to the frame 140f by sealing elements 130 that are EPDM cord-like splines with a 0. 140” diameter circular cross section that captured the membranes when they w ere pressed into grooves in the frame.Aty. Dkt. No. 01296-0082

[0067] While in the foregoing specification a detailed description of specific embodiments of the invention were set forth, it will be understood that many of the details herein given may be varied considerably by those skilled in the art without departing from the spirit and scope of the invention.

Claims

Atty. Dkt. No. 01296-0082Claims1. A device that radiantly heats or radiantly cools people, animals or plants, collectively referred to as subjects, the device being surrounded by ambient air and comprising: a. a planar heat exchanger wi th a front face and a back face, at least one of the faces being radiantly active in that the face exchanges thermal radiation with the subjects, and the planar heat exchanger having at least a 0. 1 wavelength- averaged transmissivity for visible radiation incident on at least one of the front face or the back face, b. a heat transfer fluid that enters the planar heat exchanger through an at least one inlet fitting and leaves through an at least one outlet fitting, the heat transfer fluid either supplying thermal energy to or removing thermal energy from the planar heat exchanger, c. a mounting base to which the planar heat exchanger is directly or indirectly- attached, the mounting base having one or more openings through which may pass both visible radiation and thermal radiation that are incident on the planar heat exchanger, d. one or more membranes, one or more of which contact the surrounding ambient air, that are directly or indirectly attached to the mounting base and spaced apart from each radiantly active face to create one or more sealed, planar gas-filled cavities, each cavity with a width of at least 5 mm, that isolate each radiantly active face from contact with the surrounding ambient air, the one or more membranes being made of a polymer film no more than 160 microns thick that transmits both visible and thermal radiation, wherein the one or more membranes that contact the surrounding ambient air are outer membranes having external sides that contact the surrounding ambient air.

2. The device of claim 1, wherein the mounting base is a frame with a continuous perimeter that encloses one or more central openings.

3. The device of claim 1, wherein the planar heat exchanger has at least a 0.85 wavelength-averaged transmissivity for visible radiation incident on at least one of the front face or the back face.Atty. Dkt. No. 01296-00824. The device of claim 1 wherein the one or more membranes have at least a 0.1 wavelength-averaged transmissivity for visible radiation and a 0.5 wavelength-averaged transmissivity for thermal radiation, where thermal radiation has a wavelength between 5 and 25 microns.

5. The device of claim 1 wherein the one or more membranes have at least a 0.85 wavelength-averaged transmissivity for visible radiation and thermal radiation.

6. The device of claim 18, wherein the planar heat exchanger has a radiantly inactive face and the device further comprises a window that is at least partially transparent or partially translucent to visible radiation, the window being mounted and sealed either directly or indirectly to the mounting base so that it is spaced apart from the planar heat exchanger’s radiantly inactive face to create a sealed, planar, gas-filled cavity with a width of at least 5 mm in front of the radiantly inactive face that isolates the radiantly inactive face from contact with the surrounding ambient air.

7. The device of claim 6, wherein an outward face of the window that contacts the surrounding ambient air reflects radiation that is not part of the visible spectrum.

8. The device of claim 7, wherein the outward face of the window comprises a coating or film.

9. The device of claim 8, wherein the coating or film reflects up to 78% of the thermal radiation energy and 99% of the ultraviolet radiation energy incident on the window.

10. The device of claim 6, wherein an outward face of the window that contacts the surrounding ambient air reflects radiation that is part of the visible spectrum11. The device of claim 10, wherein the outward face of the window comprises a coating or film12. The device of claim 11, wherein the coating or film reflects at least 25 percent of the visible radiation energy incident on the window.Atty. Dkt. No. 01296-008213. The device of claim 18, wherein the planar heat exchanger is a heat exchanger formed from a polymer, twin-wall, multi-channel extrusion.

14. The device of claim 13, wherein the polymer for the twin-wall, multi-channel extrusion is polypropylene, polycarbonate, polyethylene, polyethylene terephthalate, polysulfone, polyphenylsulfone or combinations thereof.

15. The device of claim 1 , further comprising one or more screens that are either directly or indirectly attached to the mounting base, each screen located proximate to an external side of a respective one of the one or more outer membranes.

16. The device of claim 15, wherein the one or more screens are adjacent to or in contact with at least one of the outer membranes.

17. The device of claim 15, wherein one or more screens are spaced apart from at least one of the outer membranes.

18. The device of claim 15, wherein the one or more screens comprise at least one of the following: a. an open-cell woven sheet, with metal, fiberglass, ceramic or polymer warp and weft strands, b. a perforated metal or polymer plate, sheet or film, c. an open-cell mesh with twisted wire strands, or d. a thin plate or sheet with an expanded metal structure.

19. The device of claim 15, wherein each of the one or more screens has an open area of at least 50%.

20. The device of claim 15, wherein each of the one or more screens has an open area of at least 80%.

21. The device of claim 15, wherein each of the one or more screens has an open area of at least 90%.

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