The present invention relates to a radiative cooling device .

More specifically, the present invention relates to a passive device suitable for producing dew, i.e. for producing water extracted from the atmosphere.

It is known that the atmosphere that surrounds us contains water in the form of humidity and that, whenever the relative humidity level is high enough, it is sufficient that an object being some degrees colder gets in contact therewith in order for such humidity to condensate on its surface .

This phenomenon also occurs in nature and is referred to with the name of "dew"; in this case, the cooling down that allows humidity to condensate is attributable to the radiation of the surfaces of the bodies in the direction of the sky, a radiation that takes place in the mid-infrared frequency range at the ambient temperature.

Whereas the atmosphere is to a large extent opaque to the infrared frequencies emitted by the Earth (which originates the so-called "greenhouse effect" which holds the temperature of the Earth's atmosphere at the ground level to a value considerably higher (by approx. 30 °C) with respect to that which would be there in the absence of an atmosphere or in the presence of an atmosphere that were totally transparent to the infrared rays) . However, this opacity, which limits the Earth energy loss, is not associated with the complete range of frequencies of the mid-infrared that are emitted: that portion of radiation emitted in the range of the infrared frequencies which features a wavelength ranging from about 8 to 13 micrometers is an exception, and the atmosphere lets it radiate directly toward the space: this frequency range defines a so-called "atmospheric transparency window".

So, the thermal energy emitted to the sky in the frequency range of the transparency window is not intercepted by the atmosphere but, under ideal air cleanliness and meteorological conditions, it is almost all lost in the space, which is very cold and, consequently, does not send any infrared waves back; a counterradiation-free radiation entails a loss of energy which, if not compensated for otherwise, entails cooling.

The opportunity of exploiting the atmosphere transparency window and taking advantage of radiation exchanges to dispose of heat and/or to produce cooling represents a technical solution that has presently been the subject of an extended scientific research in that it is completely ecologic and joins the photovoltaic technique and other "green" technologies in strategies aiming at possibly reducing the greenhouse effect. Such research aims, first of all, at identifying those emitters which are most suitable for exploiting the atmospheric transparency window at the best and under a variety of environmental conditions (the so-called "selective emitters") .

The identification of numerous alternatives of selective emitters and their integration into an even greater number of devices different from each other made it possible to maximize the operating efficiency of the exploitation of the atmospheric transparency window in various environmental contexts; however, such progresses almost exclusively concerned cooling of heat transportation bodies or liquids and cooling and air conditioning, whereas the water condensation technologies did not substantially take advantage therefrom.

As a matter of fact, atmospheric water condensation features a number of peculiar problems which, in the present status of the art, prevented an integration of the achievements pursued and obtained in the other main sectors of research on passive radiation into water collection operating devices. As a matter of fact, the devices that are the fruits of the mentioned progresses in the atmospheric transparence window exploitation technology can resort to the emission of radiative surfaces proposed in very numerous and different arrangements and compositions of materials and also, in order to reduce harmful heat exchanges with the hotter external environment to improve efficiency, such surfaces are usually insulated above by an insulating layer consisting of air (or another transparent gas in the wavelengths ranges from 8 to 13 microns); an air casing closed by a thin plastic film is usually created to contain such insulating gas; such containing film is in turn proposed in many alternatives in terms of composition, metallization etc. and in some cases it also performs incident radiation reflecting and/or filtering functions. In such applications, the "cold" generated by the emitting surface is transferred from the lower side of the emitter to the body to be cooled down or to the heat transport vehicle (a liquid or a gas), often with the aid of a thin layer of highly thermally conductive material put on or glued to the lower side of the radiative surface.

It is thus quite clear that, thus optimizing configurations feature major drawbacks which invalidate a recourse thereto or use thereto whenever the pursued function is condensing water from the atmosphere.

A first drawback is bound to the fact that, if one wishes to use the upper side of the radiating surface for condensation, it would be necessary to remove the layer of insulating gas and the film that contains it, which entails the following problems: 1) presence of major heat losses which would considerably reduce the efficiency of the device; 2) the water that would condensate on the surface would have emissivities different from those of the selected emitters, thus in fact almost zeroing the usefulness of their use; 3) in the absence of a wind having a speed greater than 0.5/0.6 m/s, no dew can be obtained because the water flow toward the surface would only take place by diffusion, which would render the process too slow .

Also, if one wishes to use the lower side of the radiating surface instead of the upper side for condensation, further drawbacks would come out, consisting of the difficulty of finding a way to bring the humid environmental air in contact with such lower side in the form of a continuous flow, finding a way to make sure that the favorable conditions are there in order for condensation to take place (as a matter of fact, diffusion, if taken alone, is a too slow process to effectively support condensation) , and finally the problem would arise of how to curb heat losses and how to collect the produced water.

Because of such impediments and difficulties, in the present status of the art production of water by radiative condensation of the atmospheric humidity is obtained, in a little efficient manner, by way of devices that pursue formation of dew on the upper surface of (more or less selective) emitters being in direct contact with the environmental air.

This takes place with different disadvantages such as, for instance, the fact that heat losses are very high, which drastically reduces the allowed thermal differentials with the environment and consequently a very high relative humidity (about 85%) is necessary, which usually can only be obtained during the night time or at dawn, as well as the fact that the presence of wind increases heat losses, but, on the other hand, a wind at a speed greater than 0.5/0.6 m/s is necessary for a device to be effective because, at wind speeds lower than such value, the transport of water to the cold surface would almost exclusively take place via a diffusion process, which is too low and insufficient to produce the dew settling phenomenon, and disadvantageous is the fact that the use of selective emitters is almost zeroed by water condensing on the emitting surface.

Therefore, dew production is poor and discontinuous and, considering the poor thermal differentials allowed and the sensitivity of a direct exposure to the sun, it will be limited, over one year, to few hours during the night and in the early morning, for some periods of the year only. A further drawback affecting the dew devices according to the present status of the art consists in that a high percentage of the dew formed remains deposited in the morning on the emitting film in the form of droplets which cannot flow toward the even though tilted, surface of the film and needs to be possibly collected from its surface by way of a manual removal, in order to prevent it from evaporating during the mid-hours of the day; this is little acceptable, also considering the fact that the "dew" thus obtained might be dirty because of the presence of dusts and/or defecations by birds and insects.

An object of the present invention is to obviate the above- mentioned drawbacks.

More specifically, an object of the present invention is to provide a radiative cooling device suitable for providing an air flow onto the cold and condensing surface of an emitter.

A further object of the present invention is to provide a device for making the dew condensate not on a surface of the emitter facing the sky, but rather inside an air casing having a calibrated thickness and built on a lower side of the surface of the emitter itself.

A further object of the present invention is to provide a dew condensation device capable of fully exploiting the properties of the most selective emitters and, in particular, the metamaterial-based last-generation ones. A further object of the present invention is to provide a device that allows to generate a continuous and self- regulated flow of air taken from the environment inside an air casing.

A further object of the present invention is to provide a device suitable for supplying a greater quantity of absolutely clean water (dew) extracted from the atmosphere, the surface being equal, as compared to the prior art systems, and, also, in ways that are less dependent on the meteorological conditions, sun radiation, and need for particularly high relative humidity values.

Another object of the invention is to provide an environmentally safe device as one that does not consume nor produce condensate water.

A further object of the present invention is to provide a cooling device suitable for obtaining such a differential density between the processed air and the environmental air as to be able to produce an air flow in the device.

A further object of the present invention is to put at users' disposal a radiative cooling device suitable for providing high reliability and lifetime and also such as to be realized in an easy and cost-effective manner.

These objects and others are achieved by the invention that presents the characteristics according to claim 1.

According to the invention, a radiative passive cooling device is provided for producing dew, which comprises a multilayer structure which comprises an upper film, a first air casing containing a layer of air or another gas which is interposed between said upper film and a radiating film, a second air casing interposed between the radiating film (16) and a lower wall, a third intermediate air casing between said lower wall and a further lower wall, the first air casing making-up a buffer for insulating the radiating film from conductive heat exchanges with the environmental air, the second air casing making-up a duct for creating a humid air flow, and the third air casing making-up an insulating means for insulating a lower side of the second air casing.

Advantageous embodiments of the invention are apparent from the dependent claims.

The constructional and functional characteristics of the radiative cooling device according to the present invention can be better understood from the following detailed description, wherein reference is made to the attached drawing tables which illustrate preferred, non-limitative embodiments thereof, and wherein:

figure 1 schematically shows a cross sectional view of the radiative cooling device according to the present invention;

figure 2 schematically shows a first exemplary embodiment of the cooling device wherein said device is shown leant to a natural ridge;

figure 3 schematically shows a second exemplary embodiment of the device according to the invention wherein said device is shaped like a "canopy" or an awning open on one side;

figure 4 schematically shows a third exemplary embodiment, the device according to the invention being of a transportable type coiled and unrollable for use (in particular, a configuration is shown wherein the device is secured to a tree or a pole;

figures 5 and 5A schematically show the device according to the invention in a fourth exemplary embodiment in the form of an inflatable floating craft (figure 5 shows a cross- sectional view and figure 5A shows a top view) ;

figure 6 schematically shows a fifth exemplary embodiment of the device according to the invention, the device being used in street furniture structures of a bus shelter type; figure 6A shows in details an internal section of the street furniture structure equipped with a device according to the exemplary embodiment of figure 6; figure 6B schematically shows a detailed view of a component part of the street furniture structure equipped with a device according to the exemplary embodiment depicted in figure 6 ;

tables 1 and 2 show the numeric data relevant to a use of the device according to the invention, relevant to the use of a small-size device and a big-size device respectively. In principle, all exemplary embodiments of the radiative cooling device according to the present invention, which will be described below with reference to the technical- functional characteristics and which, as said above, define preferred, non-limitative embodiments, feature and retain a number of peculiar characteristics which are valid for all of them, and specifically: a) the presence of an air casing featuring a calibrated thickness and adjacent to the lower side of the emitter, b) a progressive cooling taking place along the air path in said air casing, c) the presence of a difference in level between the air inlet and outlet in the device, which creates a condition fostering the formation of a column of air that is colder and features a lower content of condensate water, hence more dense than the environmental air, d) the generation of an air flow resulting from the difference in pressure produced by the column of air being colder and having a lower content of condensate water, e) the device always being arranged slightly inclined in the initial length, inclination being even more pronounced in the subsequent sections of the length .

More specifically, the device according to the invention supplements an emitter film with further components on both sides, the outer one exposed to the sky and the inner one facing the ground. In this specific case, the upper face of the cold radiating surface is thermally isolated thus creating a sealed airspace, as usually done in radiative heat disposal devices and an air casing featuring a calibrated thickness beneath such lower face of the cold radiating surface is provided to make environmental air flow onto the lower face of the radiating surface which is used as a condensing surface; this is made possible thanks to the addition of a layer of a properly insulating material to the radiative and conductive heat exchanges with the external environment. Also, in the device according to the invention a motive force has been created suitable for allowing air to flow through the calibrated air casing, thanks to the differential pressure that is generated by the greater density of the cooled air inside the air casing with respect to the environmental air; such differential pressure is obtained by providing a difference of level of a proper amount in the path of the cooled air through the device.

Also, the surface of the film of the selective emitter, possibly apart from the initial length, has always been arranged at least a little inclined with respect to the ground and to the sky, so as to allow for the water produced by condensation to go out and be easily recovered. The device performs a cooling of the air taken from the environment which, thanks to condensation, results in a reduced content of water in the cooled air; the temperature being equal, a lower content of water (humidity) results in a greater density, and a decreased temperature entails, in turn, a further and more noticeable increase of density. A column of air cooled by means of this device and having a reduced content of water will consequently exert a greater pressure as compared to environmental air, and it is this differential pressure that is exploited to produce the sought air flow.

The amount of such differential pressure and its respective produced air flow, as well as the amount of condensable water, will be a function of the environmental air data (including temperature, relative humidity, density, more or less favorable meteorological conditions, etc.) and of the design parameters/data (including refrigerating power of the radiating surface under ideal conditions, air casing thickness, air casing length, cold air column height, insulating capacity, etc.) .

With a specific reference to figure 1, the radiative cooling device according to the invention, identified by the reference numeral 10 as a whole and schematically shown in a cross-sectional view, comprises an upper film 12 for containing a layer of air or another gas that is contained in a first air casing 14, an air casing the function of which is to insulate the upper surface of the radiating film 16 from conductive heat exchanges with the environmental air, so as to define a kind of "buffer" for this purpose, while conversely allowing for radiative exchanges with the sky; this allows to prevent power/efficiency losses as well as to prevent condensation from taking place just on this upper surface of the radiating film 16, which would alter its peculiar emissive characteristics. It is worth noting that the film 12 shall be as much thin as possible in order to minimize absorptions and reflections of the radiations output from the device; naturally such thinness shall also take account of the peculiar situations of use. As a matter of fact, a greater difficulty in a possible need for its replacement in the case of wear and tear and/or the bigger dimensions of the device might suggest to give up a part of the efficiency in favor of a greater sturdiness of the film. The material making-up the film 12 shall be transparent in the frequency range of the atmospheric window corresponding to wavelengths in the range from about 8 to 13 micrometers: the very popular polyethylene is one of the most efficient materials for this function.

The film 12 is secured to the radiating film 16 at the edges so as to guarantee an air tightness of the upper air casing and prevent humidity from entering and condensing on the radiating film 16.

At least one spacer 15 is present, and its function is to keep the film 12 spaced away at a distance HI from the radiating film 16; this distance HI, which is predetermined, cooperates with the thermal conductivity of the gas (lambda value) to determine the insulating capabilities of the device as far as its upper side is concerned .

In a closed system, as this first air casing 14 is, having the colder surface below and the hotter above, there are practically no convection phenomena, and heat loss is exclusively given by conduction through the layer of air (or another gas) and, consequently, this heat loss is determined by the lambda value of the gas contained in the air casing divided by the thickness of the same; the lambda value for air is around 0.025 (w/m - ⁰ ^ ¹ ) and consequently it is a very favorable value for lowering heat loss.

The greater the thickness of the air casing is, the smaller efficiency losses are and consequently it is advisable to evaluate the best trade-off between lower values for the height HI of the spacers 15 and, consequently, lower overall dimensions of the device, and a greater height thereof and, consequently, greater overall dimensions, but greater efficiency, on a case by case basis.

The at least one spacer 15 is obtained from a bubble in the film 12 which is obtained, for instance, according to a technology similar to that of the films used as shock- absorbers in the packing technology and commonly referred to as "pluriball"; however, such spacer 15 might even consist of spacers secured in the radiating film 16 or, alternatively, these spacers might consist of elastic elements so as to allow to compact and wind the device according to the invention for transportation and/or recovering purposes (in this case, the air tightness of the air casing 14 will not be completely sealed) .

The radiating film 16 possibly comprises several layers, and the upper part which makes up the true emitter possibly consists of a simple painting or a layer or film of metamaterials (for instance, in a preferred solution, a hybrid metamaterial like that disclosed by Yao Zhay et al . in Scalable-manufacture randomized glass-polymer Hybrid metamaterial for daytime radiative cooling (Scienze 10.1126/'science . aail'899 (2017))) or of a radiative surface whatsoever selected from known radiative surfaces operating in the infrared range, a support film, if any (provided this solution is not intrinsically performed by the radiating film itself) and finally a layer of a highly conductive material (for instance, a film or metal laminate strips suitable for fostering the windability of the radiating film) might be present.

In the case that all of the three above-described component parts of the radiating film are present, they will be kept in a strict contact to each other, possibly by using adhesives, and they shall be thin to facilitate an efficient transmission of heat (cold in this specific case); for this purpose, the radiating film 16 usually does not need to feature a big mechanical strength, not even in the case of bigger-size devices, because mechanical strength is preferably completely committed to a lower wall 17 and/ or 27.

A second air casing 20 is defined between a lower layer of the radiating film 16 and a lower wall 17 with the function of making-up a duct as necessary for creating the air flow to cool down.

Such second air casing 20 comprises: an upper part/surface consisting of a lower surface 18 in contact with the radiating film 16 (preferably made from a highly conductive material); in contact with such lower surface 18, the air routed via the air casing 20 will first cool down and then, after passing the dew point temperature, it will produce condensation of humidity and consequently formation of dew (water); at least one further spacer 22 which determines the thickness H2 of the second air casing 20, said at least one spacer possibly being defined either by spikes insulated from each other or by profiles longitudinally arranged with respect to the device, interruptions being possibly present to make it possible to fold and/or wind the device itself and meet the transportation and/or recovering requirements (should the spacers 22 be longitudinal, the distance LI therebetween also becomes important because, together with the thickness H2 and the speed of the air in the air casing, it contributes to determine the Reynolds number, hence to determine the nature of the air flow in the air casing) .

As a matter of fact, in the presence of a purely laminar flow, the possibility for the air contained in the innermost mass of the flow of reaching the condensing surface is exclusively limited to diffusion, and such water molecule transport phenomenon is too slow to be effective in this specific situation; in order to obviate the latter situation, which especially takes place in the case of smaller-size devices, it might be appropriate to use a water repellent condensing surface so as to make sure that water condensation takes place on the lower radiating surface 16 in the form of droplets, because they are capable of perturbating the air flow or, alternatively, to introduce longitudinal helical profiles 24 or the like or other suitable small obstacles to the laminar flow inside the second air casing 20.

As a matter of fact, an even small perturbation is sufficient to trigger a stirring in the flow, thanks to the fact that the air streams that are most closely in contact with the emitter, by cooling down first, acquire a density greater than that present in the body of the main air flow; such cold and more dense air streams are positioned in the device in a position above that of the main flow, which creates a possibly instable situation, and consequently running into an even small protuberance, such as a water droplet being formed, might be sufficient to trigger stirring .

In correspondence with the lower front facing an opposite side with respect to the radiating film 16, the second air casing 20 is closed by a lower surface or wall 25 which, having not to be transparent to radiations as the film 12 is, nor having to allow transmission of cold as the radiating film 16, preferably (but not necessarily) can have a thickness greater than those of the mentioned film 12 and radiating film 16 and it can also feature a greater mechanical strength.

The surfaces of the lower wall 25 and of a lower wall 27, together with a third air casing 26 comprised between said walls, are suitable for contributing to the insulating functions as much as possible; for this reason, such surfaces might be metallized in order to reduce radiation heat exchanges, whereas the air casing 26 might be filled with an insulating material such as, for instance, polyurethane foam.

The third air casing 26, unlike the air casing 20 arranged above (in accordance with figure 1), has its colder side above and for this reason a convection heat transmission might take place internally thereto in addition to the conductive one; for this reason, and in order to provide a best insulation in a net space as small as possible, it will be appropriate to adopt known measures such as filling such third air casing 26 with a foam (for instance a polyurethane foam) performing the function of slowing down and/or preventing convective flows, possibly metallizing the inner and outer surfaces of the walls or surfaces 25 and 29 or, alternatively, using "sandwiches" containing several layers of metallized films and/or vacuum panels for filling said third air casing.

In the case of bigger-size and several-meters-long devices or devices that are to be laid between anchoring points, the inside of the third air casing 26 might be the preferred seat where to accommodate/arrange cables and/or nets 28, if any.

The device according to the invention also always needs an even minimal slope (5-10°) all along the air path (with a possible exception for the initial length) in order to allow condensate water to flow out, and also needs that a column or a difference in level of more dense (i.e. more cold and less rich in water) air with respect to the environmental air be formed; considering that cooling down is only partial in the initial length, the most favorable arrangement for an optimum operation of the device is consequently that wherein the necessary difference in level is determined in a part of the path wherein air already underwent a consistent cooling down and increase in density.

Here below follow some exemplary applications of the radiative cooling device according to the invention.

Figure 2 shows a first embodiment or configuration of use of the device according to the invention, the device being leant on a natural ridge (whose upwards and downwards zones are indicated by the letters A and B respectively) ; this applies, account being taken of fact that, as discussed before, the device can be implemented in the form of a continuous flexible multilayer film, according to the so- called roll-to-roll manufacturing technology. In this case, the condensate water is collected in correspondence with an end portion 33 of the device 10 arranged downwards B of the ridge .

Figure 3 illustrates a second exemplary application, which is arranged and develops in a first length 10A featuring a first lower inclination and in a second length 10B (the prosecution of said first length) featuring a different inclination, greater than that of the first length; the device 10 is secured to the ground and is supported by a support 30 also secured to the ground, so as to define a wedge-like structure making-up an inclined coverage of the ground, which allows, for instance, a cultivation underneath, said covering configuration featuring a second length 10B more inclined than the first length 10A (in accordance with the previous discussion) to make it possible to convey the condensate water in correspondence with a collection point 31 located close to an end of the second length 10B.

Figure 4 illustrates a third exemplary application of the device 10 according to the invention, whereby the device 10 is wound on a coil or roll 35 transportable by a user and unrollable with a free end portion 36 (opposite to the portion secured to the coil or roll) which, for instance, might be installed against a tree, a pole, a wall, or another support 37, the film defining the device 10 being arranged according to an inclined plane in the direction of said support 37, so as to allow to collect condensate water in correspondence with an end portion 35 of the device opposite to the free portion 36 secured to the support 37. Figures 5 and 5A illustrate a fifth exemplary application of the radiative cooling device according to the invention, wherein the device 10 is applied to a buoy or inflatable floating craft 40 usable as a rescue kit for boats in trouble .

The film making-up the device 10 is arranged with a growing inclination from a base 40' of the floating craft 40, said film of the device 10 being such that the thickness of the air casing is variable and grows uniformly starting from the securing portion with respect to the base 40' of the floating craft 40. Figure 6 and the magnified details in figures 6A and 6B illustrate a fifth exemplary application of the radiative cooling device according to the invention.

In this case, the device 10 according to the invention is arranged so as to lean on an upper front of an inclined surface which develops with a growing inclination away from a vertical support 52 (defining a "cold column") of a structure 49; in this fixed configuration, the insulating air casings 14 and 26 making-up the devices 10 can have a substantial space at their disposal, as far as the thicknesses HI and H3 determining their insulating capacities are concerned, without any problem of space occupation; this allows to substantially reduce heat losses, also to the advantage of a greater efficiency in terms of volume of water produced per unit surface per hour. Just as an example, doubling or tripling the thicknesses HI (15mm) and H3 (20mm) in the basic device shown in Table 2 results in reducing heat losses by 47% and 64% respectively and in increasing the production of water per hour by 18% and 23% respectively; also, the substantial part of the cold column is accommodated in a separate and vertical structure, consisting of the vertical support 52, provided with insulating walls.

Figure 6A shows a magnified detail of the inside of the vertical support 52 which defines a cold column.

The inner space 54 of said cold column is preferably, but not exclusively, filled with chips or fibers so as to foster a complete deposition of the fraction of water possibly contained in the oversaturated air coming from the air casings 20A and 20B (in the embodiment according to figure 6, two of such air casings are provided) which makeup the cooling device according to the invention. The water coming from the air casing (20A or 20B) or from the air casings and that condensate on the filling of the inner space 52 is sent to collection tanks, via a surface 56 which makes-up the bottom of a chamber making-up the cold column 58.

With reference to figure 6B, a detail of figure 6A is schematically shown and, more specifically, a component part 60 of the device is schematically shown, the function of which deals with air discharge.

Said component part 60 comprises a cap 62 arranged in correspondence with an upper end portion of the component part 60 (facing the direction of the upper end of the support 52 which the surface 50 develops from) , the function of which is to prevent the condensate water coming from the air casing 20 (A or B) (or from the two air casings in the case of the preferred embodiment depicted in figure 6) from coming out from an air outlet duct 64 arranged below said cap 62.

The air outlet duct 64 can have the length of its longitudinal development adjusted by way of a movable part 66 externally put in said outlet duct 64.

The air output from the duct 64 is at a temperature lower than the dew point temperature of the external air and, consequently, a secondary condensation might be obtained, for instance, by interposing a basket of pebbles 68 arranged below the movable part 66 of the outlet duct 64 or letting new environmental air be sucked in the movable part 66.

The secondary condensate will be collected separately in a container 58, as shown in the case of the detail according to figure 6A. The possibility of adjusting the length of the output duct by way of the movable part 66 corresponds to the possibility of adjusting the height of the cold air column, hence the motive force of the air flow in the air casing 10.

Tables 1 and 2 show numerical simulations with data relevant to two devices, a small-size one and a big-size one respectively, having the following characteristics: a selective emitter of the type described by Yao Zhay (see reference above) featuring an emissivity of 120 w/m2 at 7.5 °C, an insulating thickness greater than 15mm (air lambda 0.028 W/ °K/m) , an insulating thickness lower than 20 mm (insulating lambda 0.032 w/ °K/m) ; condensing air casing thickness 22.5mm, film length 4m, and cold column 2 mt high for the small-size device and respectively 45 mm and 12 mt and 4 mt for the big-size device.

The basic environmental conditions are the following for both: ambient temperature 30 °C, relative humidity 70%, atmospheric permeability ideal.

In addition to the data relevant to the two basic performances, the tables provide, for explanatory/illustrative purposes only, sets of data relevant to performances of the devices wherein one only parameter is varied at a time; this allows to monitor and measure the effect of every parameter on effectiveness and to derive a guidance for designing purposes.

Specifically, the two tables describing numerical simulations provide the following information:

- in the first and second sets of data (identified by numbers 1 and 2 in the first column on the left) of every table, temperature and relative humidity only vary, respectively, and it can be noted that, in concomitance with an increase in said values, there is a substantial increase in the condensate water collection (efficiency) and in the percentage of radiated energy that is used for condensing humidity (energy conversion efficiency);

- in the third set of data (identified by number 3) the thickness of the air casing varies and it is noted that, as the thickness of the air casing increases, the condensation temperature and the cubic meters of treated air increase, the difference in temperature between the condensing surface and the environmental temperature and the differential pressure of the cold air column decrease; the behavior of the condensate water collection and of the percentage of radiated energy used for condensing humidity is characterized by a very wide and flat maximum;

- in the fourth set (identified by number 4) only the length of the air casing varies, and it is noted that, in this case too, the water collection features a very flat maximum; more specifically, it can be inferred from a joint analysis of the data of the two tables 1 and 2 that a greater length of the air casing, if offset by a greater thickness of the same and of the height of the cold air column, results in similar outputs;

- in the fifth set of data (identified by number 5) it is the radiative power that varies, and this can take place because of adverse atmospheric conditions (cloudiness/very high humidity), because of the presence of obstacles, such as trees or buildings which limit the visibility of the sky to the device or because of solar radiation; such power losses are absolutely the factors that might determine the biggest deviations in the efficiencies of the devices;

- in the sixth set of data (identified by number 6), it is the height of the cold air column that varies and it is inferred that, as the height of the column increases, the final temperature at which condensation takes place increases, as well as the cubic meters of processed air, and, in this case too, the water collection curve features a very flat maximum.

As inferrable from what described and detailed above, apparent are the advantages achievable by using a device according to the invention.

Advantageously a radiative cooling device according to the present invention allows to provide a flow of air onto the cold condensing surface of an emitter.

A further advantage is in that the device according to the invention allows to perform a dew condensation not on a surface of the emitter facing the sky, but rather inside an air casing featuring a calibrated thickness and being built on a lower side of the surface of the emitter itself and, also, it allows to generate a continuous, self-regulated flow of air taken from the environment, internally to said air casing.

A further advantage of the device according to the invention consists in that it allows to produce a continuous, self-regulated flow of air taken from the environment inside the air casing 20 and, also, the air taken from the external environment goes through the device all along its length and progressively cools down and condensates part of the humidity in its path internally to the air casing, thanks to the contact with the lower cold wall 17 of the radiating film 16.

Further advantageous is the fact that the device according to the invention allows to provide a greater quantity of cleaner water (dew) extracted from the atmosphere as compared to the prior art systems, the surface being equal, and also by using processes that are less dependent on meteorological conditions, solar radiation, and need for the presence of high relative humidity values.

Further advantageous is the fact that the device according to the invention is environmentally safe in that it does not consume energy nor does it produce pollution. A further advantage consists in that the device according to the invention is suitable for creating a differential pressure between the air cooled by it and the external environmental air capable of producing an air flow internally thereto. Even though the invention has been described above with a special reference to one embodiment thereof, provided for explanatory non-limitative purposes only, numerous modifications and variants will be apparent to a person skilled in the art in the light of the above description. Therefore, the present invention is to be construed to embrace any modifications and variants that fall within the scope of the following claims.