GREENHOUSE GLASS FOR REDUCTION OF OVERHEATING DURING THE HOT SEASONS

Abstract

Greenhouses designed for hot climate geographical zones and hot periods of a year in both hot and cold climate geographical zones. The greenhouses are made with a specific coated glass allowing a very high hemispherical transmittance, a very high PAR transmittance and a tunable hortiscatter, when requested. The glazing contains a selectively high NIR reflectance and a high emissivity of glass, to allow the heat to leave the greenhouse to avoid a high temperature increase in the greenhouse. The glass can perform longer due to its durability.

Claims

1: A highly PAR transmitting glazing for a greenhouse comprising: (a) a glass and (b) an antireflective coating on at least one face of said glass, said antireflective coating comprising, a first oxide layer having a high refractive index, a second oxide layer having a low refractive index, a third oxide layer having a high refractive index, and a fourth oxide layer having a low refractive index; wherein the highly PAR transmitting glazing has an NIR reflectance of at least 18%.

2: The highly PAR transmitting glazing of claim 1, wherein the antireflective coating is deposited on a glass surface facing an inside or an outside side of the greenhouse.

3: The highly PAR transmitting glazing of claim 1, wherein the glass face coated with the antireflective coating is textured and is facing a inside of the greenhouse.

4: The highly PAR transmitting glazing of claim 3, wherein each side of the glass is coated with the antireflective coating.

5: The highly PAR transmitting glazing according to claim 1, wherein the first and the third oxide layers have a high refractive index of at least 1.9.

6: The highly PAR transmitting glazing according to claim 1, wherein the second and the fourth oxide layers have a low refractive index of at most 1.7.

7: The highly PAR transmitting glazing according to claim 1, wherein the first oxide layer has a thickness between 5 and 15 nm, the second oxide layer has a thickness between 30 and 50 nm, the third oxide layer has thickness between 100 and 130 nm, and the fourth oxide layer has a thickness between 80 and 110 nm.

8: The highly PAR transmitting glazing according to claim 1, wherein the fourth oxide layer is a two part layer comprising a first part and a second part, both the first part and the second part being oxide layers having a low refractive index.

9: The highly PAR transmitting glazing according to claim 1, wherein the antireflective coating is hydrophilic and has a contact angle below 32?.

10: The highly PAR transmitting glazing according to claim 1, wherein a PAR transmittance is at least 92%.

11: The highly PAR transmitting glazing according to claim 1, wherein a hemispherical transmittance is at least 83%.

12: The highly PAR transmitting glazing according to claim 1, wherein an emissivity is at least 80%.

13: The highly PAR transmitting glazing according to claim 1, wherein the highly PAR transmitting glazing has an NIR reflectance of at least 19%.

14: The highly PAR transmitting glazing according to claim 1, wherein the first and the third oxide layers have a high refractive index of at least 2.1.

15: The highly PAR transmitting glazing to claim 1, wherein the second and the fourth oxide layers have a low refractive index of at most 1.5.

16: The highly PAR transmitting glazing according to claim 1, wherein the antireflective coating is hydrophilic and has a contact angle below 30?.

17: The highly PAR transmitting glazing to claim 1, wherein a PAR transmittance is at least 94%.

18: The highly PAR transmitting glazing to claim 1, wherein a hemispherical transmittance is at least 89%.

19: The highly PAR transmitting glazing according to claim 1, wherein an emissivity is at least 83%.

20: The highly PAR transmitting glazing according to claim 1, wherein the highly PAR transmitting glazing has an NIR reflectance of at least 20%.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0031] This and other aspects of the present invention will now be described in more detail, with reference to the appended drawings and by showing various exemplifying embodiments of the invention.

[0032] FIG. 1 shows the structures corresponding to the three embodiments of the invention: FIG. 1a illustrates the first embodiment; FIG. 1b illustrates the second embodiment; FIG. 1c illustrates the third embodiment.

[0033] FIG. 2 is a graph of the light transmittance from 300 to 2500 nm of the coated glass of the invention (solid line) and a low iron float glass (dashed line).

[0034] FIG. 3 is a graph of the light reflectance from 300 to 2500 nm of the invention (solid line) and a low iron float glass (dashed line).

[0035] FIG. 4 is a graph of the light transmittance from 700 to 5000 nm of the coated glass of the invention (solid line) and a low iron float glass (dashed line).

[0036] FIG. 5 is a graph of the light reflectance from 700 to 5000 nm of the invention (solid line) and a low iron float glass (dashed line).

DESCRIPTION

[0037] The features of our invention are the consequence of a combination of glass quality, glass surface treatment or not and deposition of an antireflective coating on one or both sides of a glass substrate. Each of those characteristics will now be described with more details.

Definitions

[0038] PAR meaning is photosynthetically active radiation and comprises wavelength between 400 to 700 nm, based on NEN 2675+C1:2018. This is the main part of natural light responsible for photosynthetic activities of plants. [0039] Near infrared radiations (NIR) is defined as the light wavelength comprised between 700 and 2000 nm, based on NEN 2675+C1:2018. [0040] Within the context of horticulture, Hortiscatter is the integral value of geometrical distribution of light intensity by bi-directional transmittance (or reflectance) distribution function BTDF under a given angle of incidence of incoming light beam (3D data), defined by Wageningen University and Research (WUR) in the standard NEN 2675+C1:2018. [0041] Hemispherical light transmittance (T.sub.hem) and haze are measured following the standard NEN 2675+C1:2018. The hemispherical light transmittance is the weighted value of the measure of light transmittance at different angles from the point of light incidence defined for a particular range of wavelength, as for example: [0042] PAR T.sub.hem is the weighted value of light transmission for different light incident angles over a wavelength range comprised between 400 and 700 nm, based on NEN 2675+C1:2018. [0043] NIR transmission is the perpendicular transmission from 700 to 2000 nm, based on NEN 2675+C1:2018. [0044] The normal emissivity is a ratio, in a direction normal to the surface, of the emissive power of the surface of the glass to the emissive power of a black body. The normal emissivity is measured in accordance with the norm EN 12898-2001F. [0045] The refractive index n is calculated from the light spectrum wavelength at 550 nm. [0046] The roughness is characterized through the Sa, Sz and Rsm values (expressed in micrometers). The roughness parameters were measured by confocal microscopy. The surface parameters (Sa and Sz) according to ISO 25178 standard, and the profile parameter (Rsm) by isolating a 2D profile which then gives access to the parameters defined in the ISO 4287 standard. Alternatively, one can use a 3D profilometer for the surface parameters (according to the ISO 25178 standard) and a 2D profilometer for the profile parameters (according to the ISO 4287 standard). The texture/roughness is a consequence of the existence of surface irregularities/patterns. These irregularities consist of bumps called peaks and cavities called valleys. On a section perpendicular to the etched surface, the peaks and valleys are distributed on either side of a center line (algebraic average) also called mean line. In a profile and for a measurement along a fixed length (called evaluation length). [0047] Sa (arithmetic mean height) expresses, as an absolute value, the difference in height of each point compared to the arithmetical mean of the surface, the Sa parameter is characterized by a standard deviation of 0.1 ?m; [0048] Sz (maximum height) is defined as the sum of the largest peak height value and the largest pit depth value within the defined area, the Sz parameter is characterized by a standard deviation of 0.6 ?m; [0049] Rsm (spacing value, sometimes also called Sm) is the average distance between two successive passages of the profile through the mean line; and this gives the average distance between the peaks and therefore the average value of the widths of the patterns, the Rsm parameter is characterized by a standard deviation of 1.0 ?m. [0050] The water contact angle is the angle made between the tangent to a water drop and the surface of the support. The measure is made following the standard method ASTM C 813-75 (1989) [0051] Durability of the coating is assessed following the norm EN 1096.

[0052] The glass used for the invention is a clear glass or preferably an extra clear glass. The clear glass has a composition characterized by an iron content expressed in weight percent of Fe.sub.2O.sub.3 which is at most 0.1%. This value drops to at most 0.015% for the extra clear glass. The glass substrate of the invention has a thickness that is greater than 1 mm, preferably greater than 1.5 mm and more preferably greater than 2 mm. The thickness of the glass substrate is at most 20 mm, preferably at most 15 mm and more preferably at most 10 mm. Advantageously the thickness of the glass substrate is comprised between 3 and 6 mm. A 4 mm glass substrate with the extra clear composition has a light transmittance of about 91.7%.

DESCRIPTION OF EMBODIMENTS/EXAMPLES

[0053] The following examples have been made in accordance with the invention.

Example 1

[0054] A PVD stack has been deposited on one side of a 4 mm thick extra clear glass surface. The PVD stack has the following structure:

Glass/TZO (10 nm)/SiO.sub.x (40 nm XX)/TZO (117 nm)/SiO.sub.x (74 nm)/SiZrO.sub.x (23 nm)

Where TZO is a mixed oxide comprising titanium oxide and zirconium oxide with a weight composition of TiO.sub.2/ZrO.sub.2 of about 65/35. SiO.sub.x means a layer based on silicon oxide that may contain other elements and x is equal or smaller than 2. In the present example the SiO.sub.x layer is a mixture of 95 weight percent of silicon oxide and 5% of aluminium oxide. The two last oxide layers (SiO.sub.x and SiZrO.sub.x) are together the fourth low refractive index layer of the invention.

[0055] Example 2 is the same as example 1 except that prior to the deposition of the antireflective stack, the glass surface is submitted to a treatment as follow: the sheet of extra clear glass has been washed with deionized water and then dried. An acid etching solution, composed by volume of 50% NH.sub.4HF.sub.2, 25% water, 6% concentrated H.sub.2SO.sub.4, 6% of a 50% by weight aqueous HF solution, 10% K.sub.2SO.sub.4 and 3% (NH.sub.4).sub.2SO.sub.4, at 20-25? C., was allowed to contact the glass surface for 1.5 minutes. After removal of the acid solution, the glass surface is rinsed with water and washed. The textured glass sheet is then transferred to the coating line for deposition of the antireflective stack on the etched glass surface. A second antireflective stack is deposited on the other surface of the glass. The second antireflective stack is the same as the first.

[0056] The roughness of the glass surface of example 2 has been assessed after the etching procedure and before the antireflective stacks deposition. The parameters are given in the table 2 here below.

TABLE-US-00002 TABLE 2 Sa (?m) Sz (?m) Rsm (?m) Example 2 0.5 5 80

[0057] Example 3 is the same as the example 2 but the acid etching solution was allowed to contact the glass surface for 3 minutes and as a consequence, the roughness is modified. The roughness parameters are given in the table 3 here below.

TABLE-US-00003 TABLE 3 Sa (?m) Sz (?m) Rsm (?m) Example 3 1.4 8 70

[0058] For all examples, the performance has been evaluated in terms of hemispherical transmittance (T.sub.hem), PAR transmittance (T.sub.PAR), NIR transmittance (T.sub.NIR), NIR reflectance (R.sub.NIR), emissivity and hortiscatter. The results of the examples of this invention are summarized below in the table 4 and values are given as percentage. The water contact angle has also been measured and is given at the end of the table 4.

TABLE-US-00004 TABLE 4 Example 1 Example 2 Example 3 T.sub.hem (%) 91.2 88.2 83.4 T.sub.PAR (%) 98 97.6 97.3 T.sub.NIR (%) 79.1 79.1 79.1 R.sub.NIR (%) 20.9 20.9 20.9 Emissivity (%) 87 87 87 Hortiscatter (%) 0 10 60 Water contact angle (?) 28.8 28.5 25.6

[0059] It appears that all examples of the table 4 are capable to satisfy our requirements. Namely, both hemispherical and PAR transmittance remains high while 20% of the near infrared radiation is kept outside. The high emittance allows the heat to escape the greenhouse and the hortiscatter may be adapted according to the needs of grower.