WO2016203260A1

WO2016203260A1 - Insulating elements and structures

Info

Publication number: WO2016203260A1
Application number: PCT/GB2016/051823
Authority: WO
Inventors: Leslie JAMES SQUIRES; Averil COX
Original assignee: Hunt Technology Limited
Priority date: 2015-06-18
Filing date: 2016-06-17
Publication date: 2016-12-22
Also published as: EP3310570A1; GB201510769D0; GB2539649A; GB2539649B

Abstract

A flexible, light-transmissive multi-layer thermal insulation element comprising: first and second air-impermeable outer layers; and an inner fibrous wadding layer sandwiched between the outer layers.

Description

INSULATING ELEMENTS AND STRUCTURES

TECHNICAL FIELD

This invention relates to light-transmissive thermal insulation. In particular, though not exclusively, this invention relates to light-transmissive thermal insulation elements and structures, and their use in thin shell structures, in particular tensile fabric structures.

BACKGROUND

Lightweight constructions, such as thin-shell structures, are an attractive architectural option due to the considerable savings in construction materials achievable versus heavier construction. Tensile fabric structures, for example, use high tensile materials such as textile laminates as external coverings and may be incorporated into roofing, canopies, or other constructions. Suitable tensile fabrics for such structures include polyvinyl chloride (PVC), polytetrafluoroethylene (PTFE) or silicone polymeric layers on textile substrates such as woven polyester or glass fabrics. Alternatively an outer tensile layer might be formed of heavy-gauge polymeric film such as ethylene tetrafluoroethylene (ETFE), which has the advantage of having good light transparency. ETFE films may be used as single layers, or be formed into air cushions as an outermost component of a tensile structure.

Tensile structures, sometimes also referred to as architectural membranes, offer a great deal of flexibility. They are often bespoke designs in which tensile fabric is designed to adopt particular shapes when supported and tensioned by structural anchors.

A known disadvantage of thin-shell structures, and in particular tensile fabric structures, is that they tend to lead to a higher operational energy requirement, largely because they offer less thermal insulation than heavier structures. In tensile fabric structures in particular, a trade-off exists between insulation and light levels. Thermal insulation can be added to tensile fabric structures but conventionally does not allow the ingress of sunlight. Furthermore, tensile fabric structures are often complex geometric shapes and may involve curves in three dimensions, making it difficult and expensive to introduce window panels. As a result, tensile fabric structures incorporating conventional insulation tend to be dependent upon artificial light sources. This leads to higher operational energy and may impact negatively on the feel of the environment within the structure. A thermal insulation is therefore required which provides a thermal insulation function whilst letting sufficient light into the building that the requirement for supplementary artificial light during daylight hours is either obviated or significantly reduced.

WO2008/118776A2 discloses an architectural membrane structure preferably including an aerogel material disposed between two outer layers. A plethora of potential options for forming the layers of the membrane structure is suggested, based on wide range of objectives. No specific examples of membranes are described but the presence of an aerogel appears to be considered essential.

According to one part of WO2008/1 18776A2, at least one and preferably both outer layers may be translucent. It is disclosed in WO2008/118776A2, that aerogels can be nearly transparent or translucent, scattering blue light. Furthermore, WO2008/1 18776A2 teaches that, if translucency is important, aerogel material can be combined with transparent or translucent non-aerogel material, for instance glass microbeads or microspheres.

Aerogels are synthetic, porous ultralight materials derived from a gel in which the liquid component of the gel has been replaced with a gas. They are costly to manufacture, which is a particular concern in the context of tensile structures, which are often considerable in size. Furthermore, aerogels are fragile and require careful handling and support.

Aerogels and aerogel-containing products such as aerogels trapped in polyester fibre webs or matrices, for example, may also have the disadvantage of shedding fine particulate silica when handled. This may especially be the case if an aerogel product is cut or otherwise has its integrity breached which is generally necessary when fitting insulation. While amorphous silica in fine powder form is not considered to be carcinogenic, the fine powder has a drying effect on the skin and can be an irritant to eyes and mucous membranes. Care must therefore be exercised when cutting, and either vacuum powder removal or personal protective equipment - gloves, eye and respiratory protection - provided.

The hydrophobicity of spilt silica aerogels is also a disadvantage since they cannot be wiped up with a damp cloth or otherwise controlled using water. Dry vacuuming equipment is the recommended first line of control when handling these materials.

It is an object of the invention to address one or more of the above problems, or at least one other problem associated with the prior art. SUMMARY OF THE INVENTION

From a first aspect, the invention provides a flexible, light-transmissive multi-layer thermal insulation element comprising: first and second air-impermeable outer layers; and an inner fibrous wadding layer sandwiched between the outer layers.

The term "light-transmissive" is used herein to refer to the capability to transmit at least some light. The extent to which light is transmitted is referred to as "light transmittance". Light transmittance may be measured by one of the published standard test methods such as ASTM E424 "Standard test methods for solar energy transmittance and reflectance (terrestrial) of sheet materials" or BS EN 410:201 1 "Glass in building. Determination of luminous and solar characteristics of glazing" or DIN 67507 "Light transmittance, radiant transmittance and total energy transmittance of glazings" or ISO 9050:2003 "Glass in building - Determination of light transmittance, solar direct transmittance, total solar energy transmittance, ultraviolet transmittance and related glazing factors".

On account of its multiple layers, the flexible multi-layer thermal insulation element achieves a highly space-efficient insulation performance. The air-impermeable outer layers of the thermal insulation element restrict mass movement of air to form barriers to convection, whilst the inner fibrous wadding layer entraps air to act as a barrier to conduction whilst also counteracting internal convection. This highly efficient design of the thermal insulation allows it to be relatively thin and hence implemented as a light-transmissive element whilst maintaining a good level of thermal insulation performance.

It has been found that, in many applications, even a relatively low light transmittance has a disproportionately great benefit. In particular, thin-shell structures, such as tensile fabric structures, often have a significant light-transmissive area. It has been found that a relatively low light transmittance can be sufficient to provide adequate daylight levels in such structures. The flexible multi-layer thermal insulation element comprising air-impermeable outer layers and an inner fibrous wadding layer can allow for both adequate light transmittance and good thermal insulation. It can also be cut to a size and shape suitable for installation in geometrically complex applications. The first and second air-impermeable outer layers of the multi-layer thermal insulation element may be of any suitable type consistent with providing flexible, light-transmissive insulation. Conveniently, the first and second outer layers may be of identical structure. Alternatively, the first and second outer layers may differ from each other.

Of course the outer layers must be light-transmissive to provide for a light-transmissive multi- layer thermal insulation element. Suitably, the first and/or second outer layer(s) may have a light-transmittance of at least 10%, in particular at least 30%, or at least 50%, preferably at least 60% or at least 70% or even at least 80% or at least 90% when measured using the method in EN 410. The outer layers are "air-impermeable" in the sense that they restrict mass movement of air to form a barrier to convection. Suitably, such air impermeability may be achieved with a substantially non-porous outer layer, or an outer layer having a mean flow pore size of at most 0.3 μηι, suitably at most 0.2 μηι, as measured by mercury intrusion porometry. To resist the ingress of liquid water into the inner fibrous wadding layer, the first and/or second outer layer(s) may advantageously have a resistance to water penetration corresponding to a hydrostatic head of at least 30 cm (BS EN 2081 1 :92 at 60 cm/min, three repetitions, taking the endpoint as the first breakthrough). Advantageously, the hydrostatic head may be at least 100 cm, or even at least 200 cm, or at least 300 cm. Conveniently, the first and/or second outer layer may be liquid water impermeable, i.e. show no signs of water breakthrough at a hydrostatic head of 500 cm.

In principle, one or both of the first and second outer layers may be moisture vapour permeable with a view to mitigating build-up of condensation. However, moisture vapour permeability may be counter-productive, where the insulation is to be installed in structures that are themselves substantially moisture vapour impermeable. In such circumstances, a moisture vapour permeable insulation element could trap moisture, which could lead to condensation and mould. To resist the ingress of water vapour through the insulation element and into the inner fibrous wadding layer, the first and/or second outer layer(s) may advantageously have a moisture vapour transmission rate (MVTR), if any, of at most 100 g/m².day, or even at most 50 g/m².day or at most 5 g/m².day. In an embodiment, the first and/or second outer layer(s) are substantially moisture vapour impermeable, i.e. have a MVTR, if any, of at most 1 g/m².day. In this specification MVTR may be determined with a Lyssy Model L80-5000

Water Vapour Permeability Tester at 100%/15% RH, i.e. 85% RH difference and at 23 degrees C. Alternatively, a gravimetric method of measurement may be used such as EN ISO 12572 "Hygrothermal performance of building materials and products. Determination of water vapour transmission properties".

Conveniently, the first and/or second outer layer(s) may comprise or consist of a film or membrane. Suitably, the film or membrane may have a thickness in the range of from 1 μηι to 1 mm, in particular in the range of from 5 μηι to 500 μηι, such as in the range of from 10 μηι to 400 μηι, or in the range of from 20 to 200 μηι.

A single film or membrane advantageously aids light transmittance of the layer. However, the outer layers may alternatively be formed as composites of a plurality of films or membranes (e.g. two or three overlying films or membranes), for example to further enhance thermal insulation.

In an embodiment, the first and/or second outer layer(s) comprise a composite of films or membranes defining a plurality of air/gas cushions in the outer layer.

Where appropriate, the film or membrane may be microporous or microperforated, to enhance moisture vapour transmission. A microporous film or membrane is defined herein as a film or membrane comprising a tortuous network of sub-micrometre diameter pores, the tortuous network extending through the entire thickness of the film or membrane and over substantially the whole area of the film or membrane. A microperforated film or membrane is defined herein as any film in which perforations greater than 50 μηι, typically 100 μηι or greater, are provided and where such perforations extend directly from one planar surface of the film to the other through the thickness of the film. In general, if moisture vapour permeability is required, a microporous film or membrane would be preferred to a microperforated film or membrane since microporous films have negligible or no air permeability under ambient conditions thus minimising heat loss by mass air transport across the film or membrane boundary. Advantageously, to resist flow of air, liquid water, and water vapour, the film or membrane may be substantially non-porous. The film or membrane may conveniently be monolithic.

Suitably, the film or membrane may be polymeric. Examples of polymers which may be used to form light-transmissive films or membranes include homopolymers or copolymers or blends of different polymers including, but not limited to, polyethene (commonly called polyethylene), polypropylene, polybutylene, copolymers of polyethene (for example poly(ethene-propylene) or ethylene vinyl acetate (EVA) or ethylene alkyl acrylates, in particular ethylene methyl acrylate (EMA)), polyesters such as polyethylene terephthalate or poly butyl terephthalate, polyamides, fluoro-ethylene polymers (FEPs), polyimides or mixtures thereof. Films which are co-extrusions of chemically similar or dissimilar polymers may also be used.

For ease of manufacture of the thermal insulation element, the polymer may advantageously be thermoplastic. Advantageously, the first and second outer layers may be chemically compatible to allow them to be thermoplastically bonded to each other. Many polymers are susceptible to ultraviolet (UV) degradation, i.e. may discolour, crack or disintegrate on prolonged exposure to UV. Common synthetic polymers that can be attacked include polypropylene and polyethylene, where tertiary carbon bonds in chain structures are the centres of attack. UV rays interact with these bonds to form free radicals, which then react further with oxygen in the atmosphere, producing carbonyl groups in the main chain. The exposed surfaces of products may then discolour and crack. Polymers which possess UV-absorbing groups such as aromatic rings may also be sensitive to UV degradation.

To preserve physical properties such as tensile strength and light-transmittance under exposure to UV, the film or membrane may advantageously incorporate a UV stabiliser. Such stabilisers are well known in the art and act by absorbing the UV radiation preferentially, dissipating the energy as low-level heat. One group of suitable UV stabilisers are hindered amine light stabilisers (HALS). A UV-stabiliser may be blended with the polymer or copolymerised with the base polymer to provide the required UV stability. The lifetime of such polymers depends on many factors, including the extent of UV exposure, temperature, humidity and the thickness of the polymer film but can extend to several years under typical European exposure conditions.

UV stabilisers may be particularly useful in the context of homopolymers or copolymers comprising polyethene, polyesters or polyamides.

In an embodiment, the film or membrane comprises or consists of UV stabilised polyethene. Such a film or membrane can provide adequate UV resistance, as well as air impermeability, liquid water vapour impermeability and moisture vapour impermeability. Such a film is also thermoplastic and has a visible light transmittance of up to 83% by ASTM E424-71 at a film thickness of about 300 μηι. One example of a suitable commercially available product consisting of UV-stabilised polyethene is available under the brand Polydress® LP-Keder from the RKW Group. This is a film composite defining a plurality of air/gas cushions. Polyethene can offer desirable resistance to UV-exposure when a suitable UV-stabiliser (such as hindered amine light stabiliser (HALS)) is added to the polymer. The polyethene product referred to claims a UV stability equivalent to 5 years in central Europe at an average annual solar radiation of 4184 MJ/m² or 100 kLy/year.

Additionally or alternatively, the film or membrane may be inherently UV stable. Two polymer groups are known to provide materials with much higher UV-resistance than the polymers mentioned heretofore: fluoroethylene polymers (FEPs) and polyimides. These groups of polymers may be regarded as inherently UV-stable. Kaptan®, the brand name for a polyimide polymer produced by Du Pont, for example, has found application in high radiation applications such as nuclear power stations and the Hubble telescope in outer space. Polyimides, however, are not very optically clear and are known to darken on prolonged light exposure. Fluoroethylene polymers, in contrast, can have very high clarity and light transmission properties. In an embodiment, the film or membrane comprises or consists of ethylene tetrafluoroethylene. Such a film or membrane can provide high UV resistance, as well as air impermeability, liquid water vapour impermeability and moisture vapour impermeability. Such a film is also thermoplastic and has a light transmittance of up to 91 % by DIN EN 410.

One example of a suitable commercially available product consisting of ethylene tetrafluoroethylene is available under the brand NOVOFLON from Nowofol® Kunststoffprodukte GmbH & Co. KG. This is a film or membrane available in a range of thicknesses from, for example, 12 μηι to 400 μηι.

The first and/or second outer layer(s), in particular polymeric film or membranes forming such layers, may optionally be coated to reduce the emissivity of a surface of the film or membrane. Techniques for forming such low emissivity coatings are known in the art. Suitably the first and/or second layer may comprise a metal or metal oxide coating. The coating may, for example, be a stainless steel or silver coating, or a tin or zinc oxide coating. Advantageously, the coating may be at most a few nanometres thick. Lower emissivity surfaces have the beneficial effect of improving the thermal insulation value of any unventilated air layer adjacent to the low emissivity surface - the effect being calculable using the standards EN ISO 6946 and EN ISO 15099. Thus, advantageously, a low emissivity coating may face an unventilated air layer. Such an air layer may be defined between the outer layers of the insulation element or outside the outer layers of the insulation element (e.g. in an insulation structure comprising the insulation element).

A lower emissivity surface is bought at the expense of light transmittance, which is reduced, often significantly. For example, a commercially available 50 μηι polymeric film coated with a stainless steel coating for application to window glazing may be obtained with light transmittance in a range from 9% to 43% when measured on 4 mm plate glass. The use of multiple layers of such coated films in a light-transmissive insulation product may reduce the light transmittance of the total insulation product to unacceptable levels.

In an embodiment, to preserve a desirable level of light transmittance, the insulation element may advantageously comprise at most one low emissivity coating, in particular metal or metal oxide coating. However, a plurality of low emissivity coatings may also be used, provided light transmittance is not adversely affected. The or each low emissivity coating may advantageously be arranged to face an unventilated air layer in use.

The inner fibrous wadding layer sandwiched between the first and second outer layers may be provided to control the thickness of the insulation element and to limit internal convective heat transfer between the two outer transparent films.

Of course the wadding layer must be light-transmissive to provide for a light-transmissive multi-layer thermal insulation element. Suitably, the wadding layer may have a light- transmittance of at least at least 5%, in particular at least 7%, or at least 10%, preferably at least 12% or at least 15% or even at least 20% or at least 40% when measured using the method in EN 410.

Advantageously, the fibrous wadding layer may comprise or consist of a fibrous or filamentous air-open wadding. Such wadding has good thermal properties and tends to be cost-effective to manufacture (much more so than an aerogel). It has also been found that, surprisingly, such wadding can provide levels of light transmittance which are adequate for most applications, in particular for tensioned fabric structures.

Suitably, the fibres forming the wadding may range from 1 to 10 dtex, such as in the range of from 2 to 8 dtex, in particular in the range of from 3 to 7 dtex. It has been found that a wadding with dtex of at least 5 tends to have a good thickness recovery following compression. The inclusion of a proportion of finer fibres will increase the thermal resistance of the wadding although the resilience may be adversely affected. Conveniently, the wadding may be polymeric. Suitable polymers may be selected, for example, from those listed hereinabove for forming the first and/or second layers. In an embodiment the wadding comprises or consists of poly(ethylene terephthalate) (PET) fibre.

Bi-component fibres may be used for all or a proportion of the component fibres. Bi- component fibres consist of two polymers of differing melt temperatures such that the lower melt temperature polymer enables inter-fibre bonds to be formed on the application of heat. The disposition of the two differently melting polymers in a bi-component fibre may take many forms, but a core-sheath and a side-by-side arrangement are two common geometries. Examples of polymers used in bi-component polyester fibres are polyethylene terephthalate as the high melt point component (e.g. the core) and polyethene or copolyester as the low melt point component (e.g. the sheath). The inclusion of bi-component fibres can enable finer fibres to be used, hence improving the thermal resistance whilst maintaining or improving the resilience by providing a degree of inter-fibre bonding within the wadding structure.

The thickness and density of the wadding will depend on the desired insulation and light- transmittance, as well as the particular wadding material.

In some embodiments, to offer a good balance between insulation and light transmittance, the wadding layer has a total wadding thickness, according to EN823, in the range of from 5 mm to 100 mm, such as in the range of from 10 to 70 mm, in particular in the range of from 20 to 60 mm, and/or an average wadding density in the range of from 2 to 20 kg/m³, such as in the range of from 5 to 15 kg/m³, in particular in the range of from 7 to 14 kg/m³.

Advantageously, a wadding, in particular a polymeric wadding, may provide a significantly better weight to insulation performance ratio than an aerogel-based insulation product. The fibrous wadding layer may comprise or consist of a plurality of waddings. Optionally, the fibrous wadding layer may comprise a plurality of waddings interleaved with one or more inner separating layers of the insulation element.

The inner separating layer(s) may suitably have one or more properties and/or a structure as described above in respect of the outer layers. Conveniently, the inner layer(s) may consist of a light-transmissive polymeric film or membrane. An inner separating layer has the benefit of reducing internal convection across the total thickness of the fibrous wadding layer. To hold the multi-layer thermal insulation element together, at least the first and second outer layers, and optionally the inner wadding layer and/or any inner separating layers, may be bonded together at, or close to, oppositely facing side edges of the insulation element.

The first and second outer layers, and optionally any inner separating layers, may suitably comprise portions which overhang or extend peripherally beyond the inner fibrous wadding layer. Advantageously, said portions may be bonded together at, or close to, oppositely facing side edges of the insulation element.

Where the layers are compatible, they may suitably be bonded by thermal bonding. In an embodiment, the layers are bonded by ultrasonic welding. Additionally or alternatively, the layers may be bonded with an adhesive. The bonding may be intermittent or continuous. Advantageously, the layers may be bonded without there being any perforations or punctures in the inner and outer layers and insulation element as a whole since such perforations or punctures would allow air transport through the component film or membrane layers leading to a reduction in thermal insulation efficiency.

It may also be advantageous to provide additional bonding between the component layers i.e. between a film layer and a fibrous wadding layer or between two overlying fibrous wadding layers to improve the dimensional stability and handling of the insulation during preparation and installation. Such bonding may comprise an adhesive layer, for example a sprayed adhesive layer which effectively will comprise localised droplets or small particles of adhesive. The adhesive may be any suitable adhesive for the purpose such as a water- based adhesive or a hot melt adhesive or a silicone-based adhesive. Such adhesive bonding may be over substantially the whole of the planar area between the component layers to be bonded or preferably may be over parts of the planar area, for example in lines or in dots.

The total thickness of the thermal insulation element will depend on the desired insulation and light-transmittance, as well as the particular materials used.

In some embodiments, to offer a good balance between insulation and light transmittance, the thermal insulation element has a total thickness, according to EN823, in the range of from 5 mm to 100 mm, such as in the range of from 10 to 70 mm, in particular in the range of from 20 to 60 mm. The multi-layer thermal insulation element may advantageously have a thermal resistance (R, m².K/W, BS EN 12667: 2001) of at least 0.2, in particular at least 0.3 or even at least 0.8. In some embodiments, the thermal resistance is in the range of from 0.5 to 1 , in particular in the range of from 0.6 to 0.95.

The multi-layer thermal insulation element may advantageously have a light transmittance of at least at least 5 %, in particular at least 7 %, or at least 10 %, preferably at least 12 % or at least 14 % or even at least 20 % or at least 40 % when measured using the method in EN 410.

In some embodiments, the light transmittance is in the range of from 5 to 30%, in particular in the range of from 10 to 25 %, such as in the range of from 14 to 22% measured using the method in EN 410. In a published document entitled "Lighting at Work", publication reference HSG38, the U.K. Health & Safety Executive relates poor lighting conditions in the workplace to various detrimental effects including eyestrain, migraine, headaches, irritability and poor concentration. HSG38 states that different light levels will be appropriate for different environments. A corridor, for example, may require only 50 lux whilst at least 300 lux is recommended for a process control room. 500 lux is a good level of lighting for the general work environment and lighting levels are commonly within the range 300 - 500 lux. HSG38 also refers to the disadvantage of directional light causing glare from reflective surfaces, especially off display screens (computer screens for example). Lighting which is non- directional avoids these problems.

The light transmittance of the insulation element may be low, for example as low as 14%, yet still provide adequate levels of light as defined by HSG38. The relevant factors here are not just the light transmittance of the material but the structure of the building and the total area of light-transmissive materials. In tensile fabric structures, light-transmissive thermal insulation may be installed over substantially the whole of the roof area and indeed, due to the geometry of the roof, the light-transmissive area may exceed the ground area, i.e. the footprint, of the structure or building. Thus, the light levels required for comfortable working in a work environment may be met in such circumstances with materials with relatively low light-transmittance with the additional benefit of being regarded as non-directional in the sense used in HSG38. In an embodiment, the thermal insulation element comprises an optical brightening agent. Optical brightening agents absorb light in the violet to ultra-violet range of the spectrum (typically approximately 340 nm to 370 nm) and re-emit the absorbed energy in the form of blue light (420 nm to 470 nm). They are usually added to mask the appearance of yellowing in textiles to give a more white appearance. However, there is evidence that additional blue light in ambient light has beneficial effects for those living or working in such conditions. An example is a paper by Viola, James, Schlangen and Dijk in the Scandinavian Journal of Work and Environmental Health, 2008 August, 3494) pp 297-306. The paper concludes "Exposure to blue-enriched white light during daytime workhours improves subjective alertness, performance and evening fatigue". Similar conclusions are reached in a summary paper, referencing other academic papers on the subject, in Environmental Health Perspectives 2009, Jan 117(1): A20-A27 by Chepesiuk.

Suitably, the optical brightening agent may be added to the wadding or one or more of the other layers of the thermal insulation element. The amount of the optical brightening agent in the wadding may be in the range of from 10 to 50,000 ppm, in particular from 20 to 30,000 ppm, particularly preferably from 50 to 25,000 ppm, based on the weight of the relevant layer. The optical brightening agent may suitably be incorporated into a polymeric material constituting the layer.

Suitable optical brightening agents may be bisbenzoxazoles, phenylcoumarins and bisstearylbiphenyls. Triazine phenylcoumarin, for example, is obtainable as the product Tinopal ® from BASF. Unlike traditional windows, the translucent insulation of this invention may be used over the major part or all of the roof area of a building. The addition of optical brightening agents to the insulation will thus increase the blue spectral component of the incident light within the building and have the beneficial effects described in the above papers. For particularly high levels of insulation, a plurality of layers of thermal insulation elements may be installed. Advantageously, an air gap may be left between layers of thermal insulation elements. Advantageously, the air gap may be in the range of from 1 mm to 20 mm, in particular in the range of from 2 mm to 13 mm, such as in the range of from 5 to 13 mm. Air gaps or cavities (air layers), especially non-ventilated air cavities, themselves act as insulation layers. The thermal resistance of air cavities may be calculated and a method of calculation is given in EN ISO 15099 - "Thermal performance of windows, doors and shading devices - Detailed calculations". Although written in relation to the thermal performance of the components described in the title, the calculation method given in the standard is applicable to air cavities in any structure. The method given in EN ISO 15099 is, however, mathematically complex and an alternative method of calculating the thermal resistance of air gaps is given in EN ISO 6946 - "Building components and building elements - Thermal resistance and thermal transmittance - Calculation method" which describes a mathematically simplified method of calculation. It is this latter, simplified method which is widely used in the U.K. since it is the method prescribed for use according to U.K. building regulations and detailed in the document "BR 443 Conventions for U-value calculations". Calculations according to EN ISO 6946 demonstrate an increasing thermal resistance for air cavities up to a limiting air layer thickness. For example, for insulation installed at an angle of <60° to the horizontal, the thermal resistance increases up to a limit of 13mm. No additional advantage in thermal resistance is seen for air layer thicknesses beyond this according to this method of calculation. However, this is an artefact of the simplified calculation method given in EN ISO 6946. Calculations according to EN ISO 15099 are more complex but, whilst agreeing closely with the thermal resistance values of EN ISO 6946 for air cavity thicknesses up to and including 13 mm in the example cited (i.e. insulation installed at <60° to the horizontal) it more realistically gives higher thermal resistance values for air layer thicknesses greater than 13 mm. To facilitate the installation of multiple layers of thermal insulation elements, the invention provides, from a second aspect, an insulation structure comprising first and second thermal insulation elements according to the first aspect of the invention, the insulation elements being linked at, or close to, oppositely facing side edges of the insulation elements. As aforesaid, the first and second outer layers, and optionally any inner separating layers, of the insulating elements may suitably comprise portions which overhang or extend peripherally beyond the inner fibrous wadding layer. Conveniently, the insulating elements may be linked by bonding together such overhanging portions. Advantageously, the insulating elements may be linked with sufficient drape, e.g. in overhanging portions, to allow an air gap to be formed between the insulation elements in use. In an embodiment, the insulating elements are linked with sufficient drape such that, when the first insulation elements is held generally horizontally at its oppositely facing side edges, the second insulation element is suspended below the first insulation element, with an air gap being defined between the first and second insulation elements. Advantageously, the air gap may define an air layer having a thickness in the range of from 1 mm to 20 mm, in particular in the range of from 2 mm to 13 mm, such as in the range of from 5 to 13 mm. Suitably, the insulation structure may comprise a low emissivity coating arranged to face the air gap. The low emissivity coating may form part of one of the insulating elements and may, for example, be as described hereinabove.

To preserve a desirable level of light transmittance, the insulation structure may advantageously comprise at most one low emissivity coating. However, a plurality of low emissivity coatings may also be used, provided light transmittance is not adversely affected. The insulation elements or structures of the invention may advantageously be substantially free from aerogel.

From a third aspect, the invention provides the use of an insulation element or insulation structure according to any aspect or embodiment of the invention for insulating a thin-shell structure, in particular a tensile fabric structure. One or more of said insulation elements or insulation structures may be used to cover at least 20%, at least 50%, at least 80% or at least 90%, or even substantially the entirety of a light-transmissive area of the thin-shell structure.

From a fourth aspect, the invention provides a thin-shell structure, in particular a tensile structure comprising a tensile fabric supported by a rigid structural anchor, the thin-shell or tensile structure comprising an insulation element or insulation structure according to any aspect or embodiment of the invention. The thin-shell or tensile structure may optionally have a light-transmissive area, which may optionally be larger than the footprint of the tensile structure. One or more insulation elements or structures according to any aspect or embodiment of the invention may suitably cover at least 20%, at least 50%, at least 80% or at least 90%, or even substantially the entirety of the light-transmissive area.

Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of the words, for example "comprising" and "comprises", mean "including but not limited to", and do not exclude other moieties, additives, components, integers or steps. Moreover the singular encompasses the plural unless the context otherwise requires: in particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise. Advantageous, preferred or optional features of each aspect of the invention may be as described in connection with any of the other aspects. Other features of the invention will become apparent from the following examples. Generally speaking the invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims and drawings). Thus features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. Moreover unless stated otherwise, any feature disclosed herein may be replaced by an alternative feature serving the same or a similar purpose.

Where upper and lower limits are quoted for a property then a range of values defined by a combination of any of the upper limits with any of the lower limits may also be implied.

In this specification, references to properties are- unless stated otherwise - to properties measured under ambient conditions, ie at atmospheric pressure and at a temperature of about 20°C.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Embodiments of the present invention will now be further described with reference to the drawings in which:

Figure 1 is a schematic sectional view of a flexible multi-layer thermal insulation element in accordance with a first embodiment of the invention; Figure 2 is a schematic sectional view of a flexible multi-layer thermal insulation element in accordance with a second embodiment of the invention; and

Figure 3 is a schematic sectional view of an insulation structure in accordance with a third embodiment of the invention.

DETAILED DESCRIPTION

With reference to Figure 1 , in a first embodiment of the invention, a flexible, light- transmissive multi-layer thermal insulation element 2 in accordance with a first embodiment of the invention comprises first and second outer layers 4, 6; and an inner fibrous wadding layer 8 sandwiched between the outer layers 4, 6. The outer layers 4, 6 each consist of an air, water and moisture vapour impermeable, non- porous, monolithic ETFE film with a thickness of 25 microns.

The inner fibrous wadding layer 8 comprises first and second overlying batts 10 of PET wadding. Each batt 10 has a basis weight of 190 g/m² and a thickness of 20 mm. The PET filaments 12 making up the batts 10 have a dtex of about 6.7.

The light transmittance of the layers 4, 6, 8 making up the insulation element was

determined using an in-house method. A fluorescent light grid was set up as a diffuse light source at a distance of 1.5 m from a light meter. Luminous emittance values (in lux) were measured at the light meter with and without the relevant layer interposed directly adjacent the light meter.

The light transmittance of the outer layers 4, 6 together was found to be 97%, i.e. the measured luminous emittance was 97% of that measured in the absence of the layers.

The light transmittance of each batt 10 of PET wadding was found to be 40%, i.e. the measured luminous emittance was 40% of that measured in the absence of the batt. The transmittance of two overlying batts 10, i.e. the fibrous wadding layer 8, was measured to be 17%.

To hold the multi-layer thermal insulation element 2 together, the first and second outer layers 4, 6 are bonded together close to oppositely facing side edges 14 of the insulation element. In particular, the first and second outer layers 4, 6 comprise portions 16 which overhang or extend peripherally beyond the inner fibrous wadding layer 8. These portions 16 of the outer layers are bonded together to encapsulate the inner fibrous wadding layer 8.

Additionally, the layers may be held together by adhesive 17. The adhesive was not included in the element for the purpose of the light transmittance testing.

The air-impermeable outer layers 4, 6 of the thermal insulation element 2 restrict mass movement of air to form barriers to convection, whilst the inner fibrous wadding layer 8 entraps air to act as a barrier to conduction whilst also counteracting internal convection. This highly efficient design of the thermal insulation element 2 allows it to be relatively thin and hence implemented as a light-transmissive element whilst maintaining a good level of thermal insulation performance. The light transmittance of the thermal insulation element 2 as a whole was determined to be 17% according to the in-house method set out above.

The thermal resistance (R) of a variant of the thermal insulation element 2 (identical save that the batts had a thickness of 13 mm each for a total inner layer thickness of 36 mm) was determined to be 0.9.

Referring now to Figure 2, in which like reference numerals are used for like parts, in a second embodiment of the invention, a flexible, light-transmissive multi-layer thermal insulation element 20 has the same structure as the element 2 of the first embodiment described with reference to Figure 1 , save that the element 20 additionally comprises an inner separating layer 22. The inner separating layer separates the first and second batts of wadding, thereby providing an additional barrier to convection within the insulation element. Referring now to Figure 3, in a third embodiment of the invention, a thermal insulation structure 30 comprises first and second thermal insulation elements 2a, 2b of the type shown in Figure 1. The insulation elements 2a, 2b are linked at, or close to, oppositely facing side edges 14 of the insulation elements by bonding together the overhanging portions 16 of the outer layers 4, 6 at the oppositely facing side edges 14 of the insulation elements 2.

The insulating elements 2a, 2b are linked with sufficient drape in the overhanging portions 16, to allow an air gap 32 of 13 mm to be formed when the first insulation element 2a is held generally horizontally at its oppositely facing side edges 14. Specifically, the second insulation element 2b is suspended below the first insulation element 2a, with the air gap 32 being defined between the first and second insulation elements 2a, 2b.

Claims

The element of claim 1 , wherein the first and second outer layers comprise a substantially non-porous film or membrane.

The element of claim 1 or claim 2, wherein the first and second outer layers comprise a polymeric film or membrane

The element of any preceding claim, wherein the first and second outer layers comprise a UV stabilised film or membrane or an inherently UV stable film or membrane.

The element of any preceding claim, wherein the first and second outer layers comprise flouroethylene polymer film or membrane.

The element of claim 5, wherein the fluoroethylene polymer comprises ethylene tetrafluoroethylene.

The element of any preceding claim, wherein the inner fibrous wadding layer has a light-transmittance of at least at least 15%.

The element of any preceding claim, wherein the inner fibrous wadding layer comprises a polymeric material.

The element of claim 8, wherein the wadding comprises poly(ethylene terephthalate) (PET) fibre.

The element of any preceding claim, wherein the inner fibrous wadding layer has a thickness in the range of from 20 to 60 mm.

1 1. The element of any preceding claim, wherein the fibrous wadding layer comprises a plurality of waddings interleaved with one or more inner separating layers of the insulation element.

12. The element of claim 1 1 , wherein the or each inner separating layer comprises a light- transmissive polymeric film or membrane

13. The element of any preceding claim, wherein at least the first and second outer layers, and optionally the inner wadding layer and/or any inner separating layers, are bonded together at, or close to, oppositely facing side edges of the insulation element.

14. The element of any preceding claim wherein the first and second outer layers, and optionally any inner separating layers, comprise portions which overhang or extend peripherally beyond the inner fibrous wadding layer.

15. The element of claim 14, wherein said overhanging portions are bonded together at, or close to, oppositely facing side edges of the insulation element.

16. The element of any preceding claim having a thermal resistance of at least 0.8 m²K/W.

17. The element of any preceding claim having a light transmittance of at least 14 %.

18. The element of any preceding claim comprising an optical brightening agent that

absorbs light in the violet to ultra-violet range of the spectrum (340 nm to 370 nm) and re-emits the absorbed energy in the form of blue light (420 nm to 470 nm).

19. An insulation structure comprising first and second thermal insulation elements

according any preceding claim, the insulation elements being linked at, or close to, oppositely facing side edges of the insulation elements.

20. The structure of claim 19 wherein the first and second outer layers, and optionally any inner separating layers, of the insulating elements comprise portions which overhang or extend peripherally beyond the inner fibrous wadding layer and wherein the insulating elements are linked by bonding together the overhanging portions.

21. The structure of claim 19 or claim 20, wherein the insulating elements are be linked with sufficient drape to allow an air gap to be formed between the insulation elements in use.

22. The structure of claim 21 , wherein the insulating elements are linked with sufficient drape such that, when the first insulation element is held generally horizontally at its oppositely facing side edges, the second insulation element is suspended below the first insulation element, with an air gap being defined between the first and second insulation elements.

23. The structure of claim 21 or claim 22 wherein the air gap defines an air layer having a thickness in the range of from 2 mm to 13 mm.

24. Use of an insulation element or insulation structure according to any preceding claim for insulating a thin-shell structure.

25. Use according to claim 24, wherein one or more of said insulation elements or

insulation structures covers at least 50% of a light-transmissive area of the thin-shell structure.

26. Use according to claim 24, wherein the light-transmissive area is larger than a footprint of the thin-shell structure.

27. A tensile structure comprising a tensile fabric supported by a rigid structural anchor, the tensile structure comprising an insulation element or insulation structure according to any one of claims 1 to 23.

28. The tensile structure of claim 27, wherein the tensile structure has a light-transmissive area that is larger than the footprint of the tensile structure.

29. The tensile structure of claim 28, comprising one or more insulation elements or

structures according to any one of claims 1 to 23 covering at least 50% of the light- transmissive area.