The invention concerns apparatus and method for collecting solar radiation and converting same to a form of energy suitable for space heating in buildings.
The use of passive solar energy to heat buildings is well known. In September 1881, E S Morse obtained U.S. Pat. No. 246,626 for “Warming and Ventilation Apartments by the Sun's Rays” and the general concept of warming air beneath a glazing, before directing the warmed air to the interior of the building to provide space heating, has been developed during the intervening years. So called “Trombe Walls” typically comprise a glazing which is arranged in spaced apart relation with a building wall to define a heated cavity. Air enters the cavity via one or more vents near its bottom and is warmed by solar radiation which causes it to rise and exit the cavity via a vent to the interior of the building.
WO 2010/086126 discloses another approach to building heating using solar energy. In this document the solar collector comprises a collector panel which defines an at least partially enclosed space. The collector panel, known as a transpired solar collector, comprises energy absorbing sides, air-inlet openings connecting the outside environment with the at least partly enclosed space and an air-outlet duct connected to the at least partly enclosed space. Solar energy is absorbed by the energy absorbing sides and this causes heating of air in the outside environment, in the immediate vicinity of the panel.
A negative pressure is applied to the air-outlet duct and this causes the warmed air to pass through the air-inlet openings, through the at least partially enclosed space and out of the air-outlet duct, from where it is directed to the point of use in space heating, or heat storage. WO 2010/086126 also describes systems for storing and managing the heat derived from the panels.
The effectiveness of the apparatus described in WO 2010/086126 is affected by wind which disturbs the warmed air in the vicinity of the panel, before it passes through the inlet openings.
Chinese Utility Model No. eN 201517854 U describes another system in which air, warmed by solar radiation, is used for space heating. Again, a panel is disclosed, with holes through which warmed air passes and is recovered for building heating. The apparatus also includes a glazing, arranged in parallel spaced relationship with the panel so that air between the glazing and the panel is warmed by solar radiation before being passing through the holes. A glazing comprising glass having a high iron content is recommended because such glass absorbs solar radiation more effectively, better to heat the air between the glazing and the panel.
The requirement for ever improving means for collecting solar energy remains. The present invention provides such means, whereby solar energy is collected with a high degree of efficiency and made available for uses such as internal space heating in buildings or heat storage and management e.g., according to the methods described in WO2010/086126.
According to the invention, apparatus for collecting solar energy comprises:
a cavity,
a glazing, arranged to allow solar radiation to pass therethrough and enter the cavity,
an inlet aperture, arranged to allow air to enter the cavity from an external environment and
an outlet aperture, arranged to allow air warmed by the solar radiation, to exit the cavity;
characterised in that the glazing comprises a coated glass.
The coating may comprises a low emissivity coating, a pyrolytically deposited fluorine doped tin oxide a titania coating or an antireflection coating.
In embodiments comprising a single glazing sheet, the coating is located on either the internal surface, or the external surface of the glass, relative to the cavity.
In one embodiment, the glazing comprises a major sheet and has integral glass sidewalls. Two glazings may be employed, each glazing comprising a major sheet and two integral glass sidewalls, and the glazings being arranged to define the cavity therebetween.
The apparatus may include an Insulated Glazing Unit (IGU), said IGU comprising at least two glass sheets. The IGU may comprise two glass sheets wherein the coating is located on surface #4 of the IGU. The coating on surface #4 of the IGU may comprise titania or pyrolytically deposited fluorine doped tin oxide.
Alternatively, the IGU may comprise two glass sheets wherein the coating is a low E coating located on surface #3 of the IGU. This coating may be the product of a sputter deposition process and may comprise silver or a compound of silver.
Alternatively, the coating may be located on surface #1 of the IGU and may comprise an antireflection coating, a titania coating or a pyrolytically deposited fluorine doped tin oxide.
The IGU may include a glass sheet comprising a tinted glass. Typically, the tinted glass would have a composition comprising at least 0.15 wt % iron.
The apparatus may include at least one sheet of glass comprises a low iron content glass, having an iron content of less than 0.02 wt %, preferably less than 0.015 wt % most preferably less than 0.01 wt %.
The apparatus may include a transpired solar collector arranged to divide the cavity into first and second regions, the first region being bounded by the glazing wherein the collector comprises a sheet of material having a plurality of holes, the holes providing communication between the two regions, and wherein the inlet aperture is arranged to allow air to enter the first region and the outlet aperture is arranged to allow air to leave the second region.
Where the apparatus includes a titania coating on the innermost glass surface relative to the cavity, means may be included for directing a flow of water on to said surface.
According to a second aspect of the invention, apparatus for collecting solar energy comprises:
a cavity,
a glazing, arranged to allow solar radiation to pass therethrough and enter the cavity,
an inlet aperture, arranged to allow air to enter the cavity from an external environment and
an outlet aperture, arranged to allow air warmed by the solar radiation, to exit the cavity;
characterised in that the glazing comprises a low iron glass.
Preferably, the glass comprises less than 0.02 wt % iron, more preferably less than 0.015 wt % iron and even more preferably, less than 0.01 wt % iron.
The invention will now be further described using non-limiting examples, with reference to the attached figures in which:
Referring to
During operation, cold air enters the cavity via a lower aperture 4, is warmed by solar radiation passing through the glazing and then exits cavity via an upper aperture 5. After exiting the cavity, the warmed air may be directed to the interior of a building to provide space heating or the heat may be extracted for storage or other use by means well known to persons skilled in the art.
Warming of the air in the cavity 1 is aided by the so-called greenhouse effect, whereby solar radiation passes through the glazing and is absorbed by the interior of the cavity to cause heating. The glazing is less transmissive to infrared radiation associated with this heating and hence inhibits heat loss. A low iron glass such as Pilkington Optiwhite™ may be used for the glazing as this further reduces the amount of solar energy absorbed by the glass and facilitates transmission of energy to the cavity. Preferably, the low iron glass comprises <0.02 wt % iron, more preferably <0.015 wt % and most preferably <0.010 wt %.
In various embodiments of the invention, a coating 6 is applied to the inner surface of the glazing.
In one embodiment, the coating 6 comprises a low emissivity (low E) coating (designated 6a in subsequent drawings) which reduces the transmission of infrared radiation. Thus loss of heat through the glazing, from within the cavity, is reduced.
The low E coating is preferably chosen to optimise the trade-off between solar gain and heat trapping by balancing transmission of solar radiation into the cavity against heat loss by infrared radiation from the cavity. In this connection, an optimum sheet resistance of between 15 and 30 ohm per square has been established. Pilkington K Glass™ is a low E glazing material suitable for use in this embodiment of the invention. K Glass™ comprises a fluorine doped tin oxide coating on a colour suppressing silicon oxycarbide coating.
In another embodiment the coating 6 may comprise a functional coating (designated 6b in subsequent drawings) such as titanium dioxide (titania). Titania coatings are known to offer an antimicrobial effect via a photocatalytic effect, whereby highly reactive free radicals are generated from oxygen and moisture under the influence of ultraviolet radiation in (for example) sunlight. Inclusion of such a coating on the inner surface of the glazing causes decomposition of organic contaminants and killing of microorganisms to provide a purified air supply for the building.
Use of such a coating along with means for irrigating the inner surface of the glazing provides for easy cleaning of the inner glazing surface. Such irrigation means (not shown) typically comprises a water outlet such as a nozzle, array of nozzles or a pipe with one or more holes, connected to a water supply and arranged to direct a flow of water on to the coated surface.
The self-cleaning action is enhanced where a hydrophilic coating is used which causes water droplets to spread on the surface and run off easily.
Pilkington Activ™ is a titania-based self-cleaning glazing which serves in this embodiment.
In general, in all of the embodiments described herein, where a titania-based self-cleaning coating is used on a interior surface of the glass, relative to the cavity, such embodiments may optionally include means for irrigating said inner surface.
Referring to
Alternatively, the functional coating 6b could comprise a self-cleaning coating such as found on Pilkington Activ™ so that the exterior glass surface remains relatively free from contaminants that would otherwise inhibit transmission of solar radiation and adversely affect the visible appearance of the installation. Pilkington Activ™ also offers anticondensation properties in this orientation as its hydrophilic properties cause water droplets which gather on the outer surface to spread and readily run off.
Anticondensation properties are also achieved using pyrolytically deposited fluorine doped tin oxide based coatings such as found in Pilkington K Glass™ or Energy Advantage™. These so-called ‘hard coatings’, which are deposited during the float glass manufacturing process, are highly stable and fused to the glass surface. This makes them suitable for applications where they are exposed to the external environment.
Referring to
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In
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In
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Apparatus according to the invention may also include a transpired solar collector comprising a perforated sheet, arranged to absorb energy from solar radiation and cause warming of the air in the vicinity of its surface.
Referring to
A negative pressure is applied to region 1b of the cavity, via outlet aperture 5, by means not shown (for example an extractor fan) and this causes warmed air to pass through the perforations (holes) in collector 11 from region 1a to region 1b. The warmed air is then directed as described previously for the functions of space heating or heat storage.
Inclusion of the glazing 2 enhances the effectiveness of the apparatus by the greenhouse effect as previously described. As before, a low iron glass such as Pilkington Optiwhite™ is preferred as this increases the effectiveness of the glazing in this regard. In addition, the glazing prevents dispersal of the warmed air by wind so that it is able to pass through the transpired solar collector panel 11 undisturbed.
The single glazed system illustrated in
The transpired solar collector may also be used in conjunction with an IGU. As before, the IGU offers a number of options in terms of surfaces to which various coatings might be applied.
In the embodiment illustrated by
In
In
Referring to
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Utilisation of a glazing having integral glass sidewalls allows for more solar energy to enter the cavity. Such a glazing may be provided as Pilkington Profilit™ linear channel glass.
Referring to
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Glazing systems employing Pilkington Profilit™ in this manner are commercially available.
As in other embodiments, various surfaces of the glazings may be coated. For example, inner surface of major sheet 3a may include a low e coating. Also, use of a low iron glass will facilitate greater transmission of solar radiation to the cavity. Pilkington Profilit™ is commercially available in a low e glass (Pilkington Optiwhite™).
Referring to
During testing, a plurality of assemblies as illustrated in
N.B. In
The air flow was maintained at a linear velocity of about 1 m/s which, for the apparatus used, equates to a volumetric flow of about 3.3×10−3 m3/s.
A comparison of the air temperature, as measured by thermocouple 15, with the ambient (inlet) air temperature provides a measure of the effectiveness of the glazed cavity for warming air.
Table 1 shows the coating stacks associated with each of the coatings used (all thicknesses in nm). The coated stacks were tested on a simple glazed cavity (
However, a much greater benefit is obtained by use of a coated glazing.
The Pilkington K Glass™ on Optiwhite™ produced the most significant increase in air temperature. Without wishing to be bound by theory, it is believed that these coatings showing best performance offer the optimum compromise between the need to allow solar radiation to pass therethrough and enter the cavity, and the need to retain the heat in the cavity once it has been captured. (N.B. TEC 15 R refers to the TEC 15 product being used in ‘reverse orientation’ i.e. the coated surface was on the outside of the cavity).
Referring to
The horizontal axis in
The coating used on both the single and double glazed cavities was an anticondensation coating produced by Pilkington Group Limited, whose composition is also indicated in table 1.
Table 2 below summarises a further set of experiments performed using various embodiments of the invention.
Table 2 further illustrates the effect of the invention in providing heated air for space heat heating and heat storage.
Numbers 5 and 7 of each series illustrate the improvement that can be achieved by a combination of a coated glazing and a transpired solar collector panel, as compared with a coated glazing only. In both series, the coated glazed Transpired Solar Collector (number 7) achieved greater temperature increases and efficiencies that the corresponding glazing without transpired solar collector panel (number 7).
In this regard it should be noted that the K Glass S OW #3 DGU and the 22 ohm OW #4 DGU have been shown to be similar in performance, so the differences between numbers 5 and 7 are attributed to the presence or absence of the transpired solar collector panel. (OW 22 ohm is an anticondensation coating on Pilkington Optiwhite™).
Number | Date | Country | Kind |
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1407814.1 | May 2014 | GB | national |
Filing Document | Filing Date | Country | Kind |
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PCT/GB2015/051314 | 5/5/2015 | WO | 00 |