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The Institute forWindows and Facades, Doors and Gates, Glass and Building Materials

© ift Rosenheim

ift-TECHNICAL INFORMATION WA-19engl/1February 2012

Solar protectionEnergy efficient building with solar shading systems, glare pro tection and daylight control

Contents

n Introduction -------------------------------------------------------------------------------------------------------------- 2n 1 Holistic planning of solar shading, glare control etc. ---------------------------------------------------------- 2n 2 Characteristic values and calculation methods ----------------------------------------------------------------- 4n 3 Solar shading systems ------------------------------------------------------------------------------------------------ 8n 4 Conclusion --------------------------------------------------------------------------------------------------------------- 21 Glossary and characteristic values -------------------------------------------------------------------------------- 21 Standards and regulations ------------------------------------------------------------------------------------------- 21 Guidelines and literature --------------------------------------------------------------------------------------------- 22

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© ift Rosenheim

ift-TECHNICAL INFORMATION WA-19engl/1Solar protection – Energy efficient building with solar shading systems, glare protection and daylight control

Content

Page

Introduction 2

Energy-efficientsolarshadingandglare control systems 2

1 Holistic planning of solar shading, glare control etc. 2

2 Characteristic values and calculation methods 4

2.1 Calculation methods as per DIN 4108-2 52.2 Calculation methods as per EN 13363-1 52.3 Calculation methods as per EN 13363-2 62.4 Calorimetric measurement techniques 73 Solar shading systems 83.1 Glazing systems 83.2 Printed glass 103.3 Building-integrated photovoltaics 113.4 Electrochromic glass 123.5 External blinds and shutters –

venetian blinds 123.6 Roller shutter boxes – thermal

insulation and tightness 143.7 Films without angular-selective properties 173.8 Angular-selektive systems 173.9 Daylight control and deflection and glare

protection – internal blinds and shutters 184 Conclusion 20 Glossary and characteristic values 21 Standards and regulations 21 Guidelines and literature 22

Solar protectionEnergy efficient building with solar shading systems, glare pro tection and daylight control

© ift Rosenheim Page 2 of 22

ift-TECHNICAL INFORMATION WA-19engl/1Solar protection – Energy efficient building with solar shading systems,

glare protection and daylight control

Introduction

Modern buildings need to be energy-efficient. They also need to satisfy a demand for greater comfort, convenience, safety, security and sustainability. How-ever, making a building more comfortable and conve-nient can also increase its energy consumption, so it is important to decide what features are really neces-sary and what are superfluous luxuries. Windows, facades, glass and solar shading systems have a substantial influence on living comfort and energy efficiency, and therefore play a key role in sustain-able, energy-efficient buildings. Automated control systems can optimise energy consumption, safety, security, comfort and convenience yet further – pro-vided, however, that these systems are planned and designed carefully with the active involvement of buil-ding users, and that professional support is offered in both the design and use stages of the building.

Energy-efficientsolarshadingandglare control systems

In many European countries there is an exclusive em-phasis on thermal insulation in winter, in other words keeping U-values as low as possible. But even in temperate zones such as in Germany, attention also needs to be given to thermal insulation in summer (solar shading): cooling loads need to be kept to a minimum or avoided altogether, as they can have a negative impact on a building‘s energy performance, particularly if the energy used for cooling comes from non-renewable sources. The requirements for ther-mal insulation, solar shading and daylight utilisation are complex and in some cases mutually opposed. During the heating season, for example, glass g-values need to be as high as possible to allow maxi-mum use to be made of the available solar gains. But in summer they need to be low to prevent overheating of the rooms in the building. A holistic approach is therefore called for when designing glass facades and solar shading systems. Things get really interesting when the time comes to design an air conditioning system (or decide whether or not one is needed at all) – because for their decision-making the building services planners will need accurate, reliable data for the complete facade/solar shading system.

1 Holistic planning of solar shading, glare control, etc.

The overall aim of solar shading devices is to reduce the amount of solar radiation entering a buil-ding in order to create a pleasant indoor climate at all times of year and day. However, all of the follow-ing objectives need to be considered:

• Reducing solar irradiation to ensure pleasant indoor temperatures,

• Ensuring sufficient daylight utilisation to keep artificial lighting to a minimum,

• Protecting against glare and avoiding direct ex-posure of people to solar radiation, particularly at computer workstations; night privacy,

• Ensuring vision from inside to outside,• Avoiding high temperatures on the internal

surfaces of glass.

When choosing a suitable solar shading system, it is important to know how it will be used and what the conditions will be at its place of installation. It is necessary to evaluate its energy performance and luminous and mechanical properties, including its fitness for use and durability. Today, systems pro-viding thermal insulation in summer in Germany must satisfy the requirements of the EnEV (Energy Saving Regulation), Articles 3 and 4. Adherence to these requirements is verified using the simplified procedure in DIN 4108-2, which involves determi-ning a maximum permissible solar gain value (Szul) for each room, based on design, climate zone and window orientation/inclination. An overall solar gain value for the solar shading systems chosen by the planner is then calculated on the basis of the glass g-value, the window surface area and the reduction or tolerance factor (Fc). The resul-ting figure must not exceed the maximum permis-sible solar gain value. It is important to note that DIN 4108-2 only sets out minimum requirements, which will not necessarily ensure that a system provides adequate thermal insulation in summer under all circumstances. Guidance Sheet ES.04, produced jointly by the ift Rosenheim and the fenestration association VFF, can provide assis-tance in this area.



Non-residential buildings have more complex thermal comfort and daylight utilisation require-ments than residential ones, so their building ser-vices need to be planned with greater precision. Verification according to DIN 4108-2 is therefore only suitable to a limited extent for non-residential buildings; it is advisable to use more precise, more engineering-based methods here. For this reason the new draft version of the German standard DIN 4108-2 also includes special requirements for non-residential construction.

Internal thermal and visual comfort are very sub-jective, varying widely from user to user. They also depend on a broad range of factors such as the solar radiation at a given time (due to position of sun, cloud cover), the external temperature, any natural shading (buildings, trees, etc.), transpa-rent areas of the building (design, size, compass direction and inclination), the g-values of glass and solar shading, air change and type of venti-lation, internal heat sources (people, computers, artificial lighting), building services (types of con-trol, air conditioning), room size, and the heat storage capacity of internal and external compo-nents. Thermal and visual comfort are described in terms of operative temperature (a combination of the air temperature and the thermal radiation emitted by the surfaces enclosing the room), and the availability of glare-free light. The influence of internal heat sources in particular should not be underestimated: just one additional PC worksta-tion can increase the thermal load in a room by up to 270 W. Different internal temperatures are acceptable for administrative buildings as com-pared to living spaces or workshops. A tempera-ture range of 25-27 °C is considered to represent an acceptable level of thermal comfort in administrative and residential buildings (ISO 7730, DIN 4108-2:2003-07).

The energy label for windows

EU Directive 2010/30/EU has extended the ob-ligation to display an energy label to all energy consumption-relevant products. Windows, facades and their associated solar shading devices now therefore also need to be assessed. This means

that all factors influencing the energy performance of a window now need to be summarised on a „con-sumer-friendly“ energy label. Energy gain, energy loss and daylight utilisation must all be taken into account according to their respective importance. Hence the products‘ energy performance not just in winter (heating season) but also in summer (cooling season) needs to be evaluated.




The label should take account of the following factors.

• Energy efficiency in winter and summer,• Any solar shading devices,• Daylight utilisation, comfort and health consi-

derations,• Fitness for use and safety in use.

There is widespread consensus on the require-ments forming the basis of the evaluation process: it should be based on simple, transparent, verifiable, scientifically determined input variables, should not present any barrier to trade or innovation, and should be uncomplicated and inexpensive. This will be particularly appropriate for the refurbishment of residential buildings, for which it is generally not worth carrying out a detailed analysis.

The evaluation procedure developed by the ift Rosenheim is based on ISO 18292 (Energy perfor-mance of fenestration systems for residential buil-dings – Calculation procedure). Here a reference building is used to determine heat losses and solar gains, and energy performance indices for the heating and cooling seasons are derived from these. The product is then rated according to energy efficiency classes. The average effective solar radiation and average temperature difference can be determined via simulation calculations. Climatic conditions differ so greatly between summer and winter that a single value is not sufficient here; ISO 18292 thus specifies two values for energy performance (EP), one for the heating and one for the cooling season:

EPH: energy performance of the heating seasonEPC: energy performance of the cooling season

The problem posed by the different climatic con-ditions across Germany and – more problematic still – across Europe is circumvented by defining an „average climate“, based on the same idea as the „average orientation“. This avoids the problem of needing to identify boundaries between climatic zones, and allows a simple product label to be produced based on just two categories: EPH and EPC. The label also includes a Daylight Potential value (as per ISO 18292). Recommendations for use can then be given to take account of real-life climatic and installation conditions, in order for the

most economical option to be selected. D/A (EPH/ EPC) might make sense for south-facing windows in Southern Italy, for example, whereas A/C would be more appropriate for northern Sweden. The Energy Label developed by the ift Rosenheim makes fast, consumer-friendly evaluation possible. The ift Rosenheim has also developed an online tool for ease of calculation (www.ift-service.de).

2 Characteristic values and calculation methods

Planners need reliable, precise characteristic va-lues for evaluating solar shading systems. One of the most important of these is the total energy trans-mittance – g or gtotal (value for glass in combination with solar shading). An initial assessment of a solar shading system can be obtained from the characte-ristic values for its transmittance, reflectance and absorptance. According to the law of conservation of energy these three factors must add up to 1:

τ + ρ + α = 1

In order to assess the behaviour of a solar shading system for various solar wavelength ranges, it makes sense to consider its spectral data, characterised by the indices e and v (e for energy, v for visual in the visible range 380-780 nm). The energy distribution across the various wave-lengths also needs to be considered: almost 50 % of energy transmitted is in the visible range, hence any solar shading system must inevitably reduce the amount of daylight entering the building.

Fig. 1 Energy distribution of solar radiation (AM=1.5)



2.1 Calculation method as per DIN 4108-2

Thermal insulation in summer must be evaluated and verified according to the EnEV, Articles 3 and 4. In the simplified method for determining the total energy transmittance (g) of glass and a solar shading device, gtotal is the product of the g-value of the glass and the reduction factor (Fc) for the solar shading. Here Fc is not constant for a given solar shading device, but depends on the glass used. Conservative values for Fc are given in DIN 4108 and DIN V 18599. For non-residential buildings and large glazed surfaces, gtotal needs to be considered and determined more precisely. More precise values can be obtained by perfor-ming calculations for the individual glass and solar shading components and for the complete system

(EN 13363, ISO 15099). This gives lower g-values which do not include the safety factors of the tabu-lated method.

2.2 Calculation method as per EN 13363-1

For simple solar shading/glass systems, DIN EN 13363-1 offers a simple, flexible method for deter-mining gtotal using integral data for the glass and the solar shading system; no spectral data are needed for the solar shading system. Generally the data provided by the manufacturer for the glass and the solar shading system can be used. This method does have its limitations, however, because it gives relatively high g-values, particularly for internal and mid-pane solar shading systems. In other words, it gives more conservative values for determining the cooling load of a building than the more complex and hence more precise methods in EN 13363-2. The calculation to EN 13363-1 requires the follow-ing input data:

g: Total energy transmittance of glass as per EN 410

Ug: Thermal transmittance of glass as per EN 410τeB: Transmittance of solar shading device in the

solar wavelength rangeρeB: Reflectance (internal/external side of solar

shading device in solar wavelength range

Fig. 2 Energy formulas for solar radiation τ + ρ + α = 1

Fig. 3 Determining the g-value for a combined solar shading/glazing system

Fig. 4 More precise determination of the Fc-value for internal solar shading devices dependent on the glazing




The simplified procedure in 13363-1 only takes account of normally incident radiation: it does not take account of the angle of incidence, in other words variations in the g-value according to the solar altitude. It does, however, allow the light transmittance to be determined.

2.3 Calculation method as per EN 13363-2

EN 13363-2 offers more detailed calculation methods for assessing solar shading devices com-bined with glazing systems. These are particularly suitable for complex systems, as they take into account not just the spectral properties of the glass, the solar shading devices, but also the openness factor of the fabric, ventilation, and the height of the apertures. With these characteristic values a plan-ner is in a position to perform reliable calculations relating to summer overheating and winter thermal comfort. Because of the complex relationships in-volved, this method requires numerical simulation. For solar shading devices it is also possible to use the calculation method in ISO 15099 which, un-like EN 13363, makes a distinction between direct and diffuse radiation. ISO 15099 thus gives more precise results, but requires additional separate input data for the diffuse radiation. This calcula-tion method also takes into account the type of light incidence and transmission (direct, diffuse or hemispherical), particularly in the case of angular-selective, adjustable and projecting systems. The Fig 5 Calculation of gtotal to DIN EN 13363-1

Table 1 Comparison of methods for calculating gtotal (EN 4108, EN 13363 Parts 1+2)



crucial characteristic values here are reflectance (ρ) and transmittance (τ); it is also possible to diffe-rentiate between different light conditions (direct/oriented, diffuse and hemispherical) and angles of incidence (incident, vertical, azimuth and pro-file angles). A product‘s luminous properties are generally measured using an Ulbricht sphere.

For angular-selective systems – for example venetian blinds – the established method is to measure the spectral transmittance and reflec-tance of an individual slat as per EN 14500/ DIN 5036 at various angles of incidence and sub-sequently adjust the spectral data, provided, how-ever, that the system is not selective across the wavelength range 280-2500 nm. Light grids and stretch moduli can be characterised as complete systems using a large Ulbricht sphere (integration sphere) or with sophisticated „ray tracing“ simula-tion software. Applications for precisely simulating the energy performance of buildings will improve and become more widely available with time, thus further facilitating the optimisation of energy con-

sumption, thermal comfort and daylight control and deflection. The upcoming generation of young engineers will use programs of this kind as a matter of course. Manufacturers of solar shading systems should therefore obtain the relevant characteristic data and make them available to planners.

2.4 Calorimetric measurement techniques

Complex solar shading systems cannot always be characterised by calculation. Where calculation is not possible, g-values can be obtained by calorimetric measurement. Here the component is irradiated with artificial sunlight and the energy transmitted through it is measured using a liquid calorimeter. The total energy transmittance, g, is derived from the ratio of the transmitted energy measured to the flux on the component to be eva-luated. This method is suitable for all transparent, translucent, light-guiding and scattering compon-ents. It can also be used to measure surface tem-peratures.

Fig. 6 Characteristic values for transmittance τ




Values can additionally be obtained for different solar elevation angles, in other words for specific times of year or day.

3 Solar shading systems

Fixed and adjustable solar shading and glare con-trol systems and different types of solar control glass have advanced in recent years and a wide variety of these products are now available: for example printed glass; electrochromic glass with variable transmittance; new kinds of products based on innovative materials; surface coatings; and even PV modules for actually generating energy. Not just their solar shading properties, but also their fitness for use needs to be considered. Modern external solar shading systems can withstand considerably higher wind speeds than their predecessors – up to force 7. Some products have even been tested up to force 9-10, and are thus storm-resistant. Solar control glazing has also advanced, and today‘s products now feature highly selective neu-tral coatings that combine high light transmittance with low g-values.

3.1 Glazing systems

Architecture today makes heavy use of glass, and for maximum transparency, slim load-bearing structures made from aluminium, wood or steel are available. Solar control glass has the fundamental advantage over other solar shading systems that it does not impair the view from the inside to the outside of the building. However, the coatings ap-plied to solar control glass do not offer glare control, so additional glare control is required, particularly around computer workstations. Solar control glass on its own is also often not capable of ensuring a pleasant indoor climate, meaning that additio-nal measures are frequently required in order to achieve this. A glass with a low g-value also tends to reduce the amount of daylight in a room, thus solar control glass needs to combine the highest possible light transmittance with a low g-value. The ratio of light transmittance (TL) to total energy trans-mittance (g) is known as the selectivity (S) of the solar control glass. Solar control glass also reduces the solar gain that is so desirable during the heating season. A balance therefore needs to be found between solar shading and solar gain in the plan-ning stage, and additional solar shading systems must be installed if necessary.

Fig. 7 Determining the g-value of complex components by calorimetric measurement

Fig. 8 Examples of architectural glazing at Potsdamer Platz, Berlin (Photo: Michael Rossa, ift Rosenheim)



Solar shading devices - types Advantages Points to note

External solar shading–fixed(fixed slats, shade sails, etc.)

• Low g-value (< 0,2)• Functional even at high wind loads

and building heights• Fixed elements reasonably easy

to clean• Design element• Protects facade against hail

• Only adapts to limited extent to radiation conditions at different times of day/year

• Cannot be adapted to user requirements• Complex planning of interface with facade/glass

required• CE marking as per EN 13659

External solar shading – adjustable(venetian blinds, panel shutters, cur-tains, roller blinds, etc.)

• Low g-value (< 0,2)• Adjustable daylight utilisation• Adaptable to user requirements

• Limited functionality at high wind loads and building heights

• Cleaning the small elements is time-consuming• CE marking as per EN 13659

Internal solar shading(venetian blinds, vertical blinds, roller blinds, etc

• Functional even at high wind loads and building heights

• Adjustable daylight utilisation• Adaptable to user requirements• Easy installation and integration

into windows and facades

• Provides limited thermal insulation in summer• Cleaning the small elements is time-consuming• Influences interior design• Increased temperatures on indoor surfaces

possible• EN 13120 (no CE marking)

Solar control glass,fixedlight

• Low g-values possible (0,2 – 0,5)• Functional even at high wind loads

and building heights• Easy to clean• Easy to install: no interfaces

between glass and solar shading

• No protection against glare (additional glare control required)

• Coating changes colour of glass• Only replaceable as a complete glass unit• Cannot be adapted to user requirements or radia-

tion conditions at different times of day/year• Increased temperatures on indoor surfaces• CE marking as per EN 1279

Awnings and solar screens

• Adjustable• No impairment of vision from inside

to outside

• CE marking as per EN 13561• Limited functionality at high wind loads and

building heights

Solar shading in cavity of insulating glass unit (IGU), mid-pane devices)(roller blinds, venetian blinds, etc.)

• Low g-valu (< 0,2)• Functional even at high wind loads

and building heights• Adjustable daylight utilisation• Adaptable to user requirements• No cleaning of solar shading

required• Easy installation and integration

into windows and facades

• Only replaceable as a complete unit• Increased temperature load in cavity• High demands placed on product quality and

fitness for use• High cost factor• Additional planning for electrics and controls

required• Verification of fitness for use as per ift Guideline

VE-07/2

Table 2 Criteria for use/benefits of various solar shading systems




3.2 Printed glass

Printing on glass is another technique that allows glass to be used as both an architectural design ele-ment and a solar shading element. Here screen prints combined with a thermal insulation or solar control layer are applied to position 2 of an IGU. The screen print also provides glare control. The relationship between the g-value of the glass and the degree of coverage of the screen print can essentially be con-sidered to be linear. Besides the degree of coverage, the g-value is also dependent on the type of coating, the colour of the screen printing ink. It is important to determine the surface temperature on the internal side of the glass, which is the result of absorption and which considerably influences thermal comfort. Ca-lorimetric measurement techniques are an effective means of characterising printed glass systems.

Fig. 9 Transmittance of various glass types

Fig. 10 Relationship between g-value and degree of coverage (The graph clearly shows the linear relationship between the degree of coverage of the screen print and the g-value as per EN 410. The total energy trans-mittance at 31 % and 69 % coverage was obtained by geometrically weighting the values at 0 % and 100 % coverage. Additional calorimetric measurements performed on an IGU correlated well with the calculated values.)



3.3 Building-integrated photovoltaics (BIPV)

PV modules whose shading effect and light trans-mittance can be varied according to the area co-verage of the PV cells are an ideal way of com-bining solar shading with energy generation, particularly in glazing systems for atrium roofs,

where solar shading can be difficult to achieve. Thin-film PV modules are suitable here as they can be produced in a particularly wide range of formats and their light transmittance, design, colouring and transparency can be conveniently modified using laser technology. The g-values and light transmittance values of PV modules are

Fig. 11 Optimisation and characteristic values of solar control glazing with screen print




determined in a similar way to those of screen printed glass. Recent studies at the ift Rosenheim have shown that the g-value of PV modules under load – in other words while generating electricity – is significantly better than their g-value when not under load, and therefore PV modules offer more effective shading in practice than that suggested by their declared g-values which are determined by testing to standard specifications and unex-posed to load.

3.4 Electrochromic glass

Electrochromic glass is glass with a variable solar control effect: its total energy transmittance can be modified between 38 % and 9 % and its light transmittance between 50 % and 15 %. It is a type of laminated glass consisting of two panes of float glass, an ion-conductive polymer film, and a transparent, electrically-conductive (TCO) coa-ting on its inner and outer glass panes. The two layers of TCO are the electrodes used to switch the electrochromic glass. The outer glass pane is coated with an additional electrochromic film (tungsten trioxide). When a voltage is applied to the electrodes, so-called F-centres form in the electrochromic coating as a result of ionic migra-tion from the electrolyte embedded in the coating system, which switch the glass from transparent

to coloured. Electrochromic glass is available in small thicknesses of just 9 mm and can easily be used to produce insulating glass units

Electro-chromic glass

Light transmis-sion

Total solar energy transmit-tance

Ug-value according to DIN EN 673

bright 50 % 38 % 1,1 (W/m2.K)dark 15 % 12 % 1,1 (W/m2.K)

3.5 External blinds and shutters ─ venetian blinds

External blinds and shutters – for example exter-nal venetian blinds, roller shutters, wing shutters, venetian shutters, concertina shutters and sliding panel shutters – are all tried-and-tested ways of providing effective solar shading. However, they can often restrict the amount of daylight entering the building, making artificial lighting necessary. All of these systems are either angular-selective or adjustable systems that can be positioned and adjusted in various ways for different use stage scenarios, and are therefore very effective. They do not have a fixed g-value, however, because

Fig. 12 PV modules offer solar shading and generate electricity (Source: ertex solartechnik GmbH, Amstetten)

Fig. 13 Basic structure of electrochromic glass (Source: Econtrol)

Table 3 Typical characteristic values of electrochromic glass



this depends on the angle of the elements and the solar angle of incidence. To obtain the characteristic values required for precise planning, it is therefore necessary to measure or calculate the g-value for a variety of typical application scenarios, because the best possible g-value alone does not allow sufficiently accurate building planning. Simulating all possible element angles, on the other hand, is too time-consuming and therefore rarely done in practice. The following factors also influence the temperature in the cavity and on the internal sur-face, and hence also the g-value (heat flow, or qi):

• Installation situation (vertical or roof glazing) and orientation of facade,

• Incident radiation and solar angle of incidence,• Type and position of coating,• Absorptance of installation details and colour

of slats,• Type of ventilation,• Thermal surface resistance inwards and out-

wards,• Internal and external temperatures.

In addition to luminous and thermal require-ments, which are generally defined by the archi-tect or planner, assemblers also need to consider numerous other factors when selecting and instal-ling solar shading devices. These requirements are set out in the product standard DIN EN 13659: 2004-11 (Shutters – performance requirements

including safety). According to the product stan-dard, CE marking is mandatory and must be taken into account during the design/planning, installa-tion and use of external blinds and shutters. The standard identifies wind resistance as a manda-ted characteristic which can be determined by te-sting according to EN 1932. A number of “resis-tance to wind load” classes apply, each denoting a different level of performance. Calculation of wind pressure and assignment of the relevant wind resistance classes are based on Annex B of EN 13659. Information on classification and calls for tenders, and practical examples, can be found in the ift Guideline AB-01/1 (Recommendations for the use of external blinds and shutters).

The other characteristics listed in DIN EN 13659 are not mandated, i.e. values can be determined and declared for these characteristics if desired. They are not governed by building supervisory regula-tions and refer to: resistance to snow load, ope-rating forces, misuse operations, edge loading of wing shutters, burglar resistance of locking devices, mechanical durability, safety in use or durability (colour fastness, degradation of aspect, resistance to breakage, resistance to corrosion and dimen- sional stability).

Fig. 14 Typical slat positions used for more precise determi-nation of g-values

Fig. 15 Relationship between glass g-value/Fc-value and solar angle of incidence




Venetian blinds with improved geometries and reflective materials can provide effective solar shading/glare protection and good daylight avail-ability as part of an internal or external solar shading system. Angular-selective solar shading systems can adapt particularly well to altered light conditions, with different luminous properties of the slats enabling them to be used in a wide range of applications. Calculation, planning and con-trol are particularly important for these systems, because even small variations in slat angle can affect their functionality.

3.6 Roller shutter boxes – thermal insulation and tightness

Roller shutters have proven their worth as tried and tested building components to ensure thermal in-sulation in summer above all when installed in the external building envelope of residential buildings and in administrative buildings of simple design. Conventional roller shutter boxes used in new

buildings with high-performance thermal insulation features, or integrated into the energy efficiency upgrade of buildings may become the weak point of thermal insulation. This is caused by transmission heat losses (U-value), air leakages (a-value) and thermal bridges which may be the result of poor workmanship in installation and which runs counter the objective to improve energy performance. Design and installation of roller shutters and roller shutter boxes must take account of any special features in order to pre-vent unpleasant draught, condensation and mould formation and to comply with the requirements of the German „Energieeinsparverordnung“ (EnEV) Energy Saving Code) for minimum thermal insula-tion (Article 7) and air tightness (Article 6). Details and tables referring to the mandatory verification of air tightness as per EnEV are given in the research report „Erarbeitung von Konstruktionsempfeh-lungen für die Luftdichtheit von Rollladenkästen“ (Design recommendation for the air tightness of roller shutter boxes) as well as the ift Guideline AB-02/1, „Luftdichtheit von Rollladenkästen – An-forderung und Prüfung“ (Air tightness of roller shut-ter boxes – Requirements and testing).

The basic principle still holds true, i.e. ensure air tightness of the construction around its internal perimeter with the objective of preventing the pas-sage of air through the connecting joint from inside to outside. As regards water vapour diffusion, the design of the overall system must be based on the principle „inside more tightly sealed than outside“. For the building component „roller shutter“, the weak points of possible leakage that cannot be absolutely excluded are the roller shutter box, the joints between window/external wall and the belt winding space. Therefore, for roller shutter boxes, the following is recommended:

1. If roller shutter boxes are not provided with any special design features to ensure air tightness, the increased air passage is mainly caused by transverse joints (lateral joints of the inspection lid).

2. If built-on lintel boxes are installed it is the design of the transverse profile connecting to the lateral parts of the roller shutter box which has a decisive influence on air tightness.

Fig. 16 Wind load test of an external venetian blind (accor-ding to prEN 1932:2011)



3. As a rule, a tight clip connection to attach the lid of the roller shutter box provides sufficient tightness.

4. Butt joints and using a rebated design to con-nect the inspection lid do not provide sufficient tightness so that efficient sealing systems must be integrated.

5. The connecting joint between roller shutter box and window should, for instance, be sealed with a sealing tape.

6. Roller shutter curtains have a very minor effect on air tightness.

For verification of conformity with the requirements for air tightness, the research project identified specific design criteria to demonstrate conformity without testing, but based on tables and design/detailing recommendations.

The joint between roller shutter box and window is not an inherent feature of the roller shutter box and is therefore ignored when it comes to the air permeability of roller shutter boxes. The joint is governed by the requirements of DIN 4108-2 which specifies air permeability (a-value) to be less than 0.1 m3/(h m daPa2/3). This requirement can be met by the designs described below:

• using a one-part (milled groove) or a glued connection detail for wood elements,

• using a compression sealing tape between frame member and transverse profile/built-on box (internal orientation),

• sealing the internal clip-connection with sealant,• using rebated design, with self-adhesive seal-

ing tape for the internal face or• using other comparable sealing systems.

No. Type Joint between roller shutter box and frame memberLinear air volume

flowQ10 at 10 Pa in m3/(h m)

Requirement for air tight-nessfulfilled

1 AK Rebated and screw-fastened, without metal clip profile, without seal 0,52 No

5 ASK With transverse profile clipped-on and screw-fastened, length = BRAM**, notched at area of lateral parts, without seal 0,07 Yes

8 ASKRebated with system-specific transverse profile and screw-fastened, length = clearance between roller shutter guide, without seal

0,92 No

17 AKInstalled with system-specific transverse profile and screw-fastened, length = clearance between head plates, box hooked in, without seal

0,93 No

18 ASKInstalled with system-specific two-part transverse profile and screw-fastened, length = clearance between head plates, sealed with sealing tape

0,04 Yes

SK – lintel box, ASK – built-on lintel box, AK – built-on box

Table 4 Linear air volume flows of linear joint between window and roller shutter box (Extracts from table 6 of research report)




Thermal bridges are local, point-shaped, linear or surface-related thermal weak points of the building envelope. They occur, e.g., when joining different building components or combining building mate-rials with different thermal conductivities and are characterised by higher heat flows (Φ) and lower internal surface temperatures (ϴsi). But there is not only an increase in thermal losses, there is also the risk of condensation causing mould formation, a problem that should be given utmost attention. This is also the reason why concrete requirements

for minimum thermal insulation, prevention of condensation and mould formation have been specified in DIN 4108-2 and the “EnEV”. Supple-ment 2 of DIN 4108 contains proposals for design details that do not need to be additionally verified. If there are deviations from the specified installation situations, conformity with the requirements must be demonstrated on the basis of thermal bridgecatalogues or by calculating the temperature factor with fRsi,min ≥ 0.7.

Fig. 17 Different layouts of inspection lids (internal/external) – the layout of the insulating zone/thermal barrier changes the thermal quality of the roller shutter box (13 °C isotherms, more examples in the installation guide)



3.7 Films without angular-selective properties

Films with or without a coating are often used for external vertical awnings and internal roller blinds. When the incident light comes from vertically above, the solar disc becomes visible, however, and the high luminance values can result in glare effects. These systems are therefore generally characterised for the complete closed system at a solar incident angle of 0°. If figures are needed for intermediate positions of the solar shading device in combination with the glass, the gtotal-value for each position can be determined by weighting the g-value of the glass and the gtotal-value for the gla-zing and the solar shading according to the area covered by the shading device.

Whereas film roller blinds permit vision from the inside to the outside, fabrics are non-transparent. Special fabric structures are however available to provide visual contact with the outside. In these cases the internal surface of the fabric should be a dark, non-reflective colour – ideally black. According to EN 14501, vision from the inside to the outside in opaque systems is characterised on the basis of the „normal“ (τv, n-n) and „normal/diffuse“ light transmittance (τv, n-diff). The openness coefficient, C0, is the ratio of the area of the open-ings in the fabric to the total area of the fabric, and is closely connected to light transmittance (τv, n-n), from which it can be approximately determined for practical purposes. Here the planner will always need to find a compromise position between visual contact with the outside and glare from the sun, because visual contact with the outside inevitably means that luminance from low-lying sun will not be sufficiently reduced by the fabric, and the user will suffer from glare. A dense fabric, on the other hand, reduces the risk of glare but blocks visual contact with the outside.

3.8 Angular-selective systems

Examples of fixed angular-selective systems include prismatic films, prismatic acrylic glass panels, metal laths and systems featuring specially- shaped stainless steel laths. These systems are generally also used for daylight control. They func-

tion by blocking or preferentially transmitting solar radiation coming from a specific incident angle. Fixed angular-selective systems are often adapted to the geometry of the facade and building to which they are fitted. The total energy transmittance of these systems should be determined at least for the solar altitude angles 0° (low-lying sun), 30° and 60° (high sun).

Fig. 18 Examples of non angular-selective systems

Fig. 19 Functionality of angular-selective slats (RETROFlex slat, source: Köster Lichtplanung)




Adjustable systems – which should ideally be used with a control system – can be adapted to the position of the sun at different times of year and day and thus allow selective blocking of the sun and direct glare. Standard concave slats have improved in recent years: examples include the Genius, Retro, Retrolux and Retrosolar slats, whose geometry permits both an improved solar shading and glare protection effect, and good vision – dependent, however, on the angularity of the slats. The slats can also be perforated to improve vision from the inside to the outside. The RETROFlex slat from Köster Lichtplanung has highly reflective microstructured aluminium mir-rors on its concave upper side, whose focus is be-yond the edge of the facade. The benefits of these systems include their angular-selective solar shading effect or light transmittance, which allows them to block the sun at both high and low solar altitude angles; they allow partial vision to the out-side despite their solar shading slats; and they offer flexibility in use, either indoors, or in the cavity of an insulating glass unit, i.e. mid-pane, or in a double-skin facade.

3.9 Daylightcontrolanddeflectionandglareprotection ─ internal blinds and shutters

Ensuring freedom from glare and sufficient daylight availability is not simple, but necessary, because light quality is the second most important factor after the various thermal aspects. Light quality is assessed in terms of its ability to facilitate good visual perception, and its biological effects. The op-timal illuminance level for performing visual tasks is between 2000 lx and 4000 lx; minimum values (500 lx) for nominal illuminance and additional requirements can be found in the relevant stan-dards (EN 12464, DIN 5034, DIN 5035). The fol-lowing factors are important in good light planning:

• Absolute amount of daylight (quantity),• Gradation/distribution of daylight in room (day-

light factor),• Solar shading (g-value as an indicator of the

effectiveness of solar shading,• Visual perception conditions; direct glare;

glare by reflection),• Visual contact with the outside (transparency,• Turn-off times for artificial light.

Fig. 20 g-value of angular-selective systems as a function of slat angle



The luminance at a window can often reach more than 4000 cd/m², impairing work at monitors even despite there being a solar shading system in place. In these cases glare can often only be prevented by an additional glare control or angular-selective shading device that blocks direct solar radiation but still allows sufficient indirect, glare-free light to enter the room. If the sun shines directly onto a window or facade, light transmission can result in building users experiencing visual discomfort even when the solar shading or glare protection device is closed: the solar disc can become visible and sunlight spots can appear on floors and furniture. Excessive luminance values can also result in strong contrasts between the solar shading device and its surroundings. Glare protection as per DIN EN 14500 should therefore control the luminance level of openings, reduce the luminance contrasts between different zones within the field of vision, and prevent reflections on visual displays. The ideal solution – particularly at visual display workstations – is hence a combination of solar shading and glare protection. The requirements described above relate to the performance of visual tasks. However, they do not take account of the recent discovery of a third type of photoreceptor cell in the retina that controls the biological impact of light on the human body. These receptor cells control a person‘s daily and annual biological clock (sleep and waking

phases) and affect brain activity, well-being and health, but only respond at illuminances of more than 1000 lx at the eye. This discovery demands a complete reassessment of the understanding of light quality and thus the design and planning of glazed areas and solar shading elements. The two mutually opposing factors of light intensity and glare protection now need to be reconciled even more efficiently, and a good way of achieving this is by using angular-selective solar shading elements. On the one hand these block direct solar radiation, but on the other hand they allow sunlight into the room above the direct field of vision and distribute it diffusely, evenly and without any glare. This can be achieved with light control and deflection ele-ments that exploit physical laws such as refraction (prisms) or reflection (specular reflectors).

Glare protection is in any case closely related to solar shading. Information on numerous aspects of thermal and visual comfort can be found in EN 14500 and EN 14501. The task of a glare protection device is to protect building users against exces-sive luminance values from solar radiation, with the specific requirements strongly dependent on the task that is to be carried out. Visual display worksta-tions, for example, are subject to luminance limits. Information on planning in this area can be found in EN ISO 9241 and EN 12464-1.

Fig. 21 Glare despite solar shading?




4 Conclusion

Energy-efficient, cost-effective, sustainable solar shading and glare protection can only be achieved through integrated design and planning. Relevant measures include daylight control and deflection systems, which distribute the available light opti-mally throughout a room and so enhance visual comfort while reducing electricity costs. Yet more energy can be saved if automated systems are used and the control systems for these are incor-porated during the design and planning stage and further optimised during the use stage. Thermal comfort can be achieved even for large glazed areas provided that this is taken into account during design and planning. A „not only but also“ rather than an „either or“ approach is therefore needed when it comes to designing and planning facades, building services and lighting.

Fig. 22 Glare despite internal solar shading



Glossary and characteristic values

Total solar energy transmittance gtotal

gtotal = g x Fc

gtotal Total solar energy transmittance of glazing incl. solar shading

g Total solar energy transmittance of glazing as per EN 410

FC Reduction factor solar shading as per DIN 4108 (only to be con-sidered in connection with glazing)

Solar gain value

t ( )G

j jtotaljW

A

gAS

∑ ⋅=

,,

Max. allowed solar gain value

Smax = S0 + ∑∆Sx

Aw Window surface in m² (opening dimensions of bare brickwork)

gtotal Total solar energy transmittance of glazing incl. solar shading. Calculation of gtotal as per E DIN EN 13363-1

AG Net floor space of room or room area in m²

S0 Basis of solar gain value for buildings, S0 = 0,12

∆Sx Additional value as per table 3, DIN 4108-2

Equivalent U-valueUeq = Ug – S x g

g Total solar energy transmittance

S Amount of radiation coefficient

Ug U-value of glazing

Selectivity value SS = TL/g

S SelectivityTL Light transmittanceg Total solar energy

transmittance

Standards and regulations:

[1] EN 410: Glass in building – Determination of lumi-nous and solar characteristics of glazing; Berlin, Beuth Verlag GmbH

[2] DIN EN 673: Glass in building – Determination of thermal transmittance (U-value) – Calculation method; Berlin, Beuth Verlag GmbH

[3] EN 1932: External blinds and shutters – Resistance to wind loads – Method of testing and performance criteria; Berlin, Beuth Verlag GmbH

[4] prEN1932: External blinds and shutters – Resis-tance to wind loads – Method of testing and perfor-mance criteria; Berlin, Beuth Verlag GmbH

[5] DIN 4108-2: Thermal protection and energy eco-nomy in buildings - Part 2: Minimum requirements to thermal insulation; Berlin, Beuth Verlag GmbH

[6] DIN V 4108-6: Thermal protection and energy eco-nomy in buildings – Part 6: Calculation of annual heat and energy use; Berlin, Beuth Verlag GmbH

[7] DIN 5034: Daylight in interiors; Berlin, Beuth Verlag GmbH

[8] DIN 5035: Artificial lighting; Berlin, Beuth Verlag GmbH

[9] DIN 5036: Radiometric and photometric properties of materials; Berlin, Beuth Verlag GmbH

[10] ISO 7730: Ergonomics of the thermal environ-ment – Analytical determination and interpretation of thermal comfort using calculation of the PMV and PPD indices and local thermal comfort criteria; Berlin, Beuth Verlag GmbH

[11] EN ISO 9241: Ergonomic requirements for office work with visual display terminals VDTs); Berlin, Beuth Verlag GmbH

[12] EN 12464-1: Light and lighting – Lighting of work places – Part 1: Indoor work places; Berlin, Beuth Verlag GmbH

[13] EN 13120: Internal blinds – Performance require-ments including safety; Berlin, Beuth Verlag GmbH

[14] EN 13241-1: Industrial, commercial and garage doors and gates – Product standard – Part 1: Products without fire resistance or smoke control characteristics; Berlin, Beuth Verlag GmbH




[15] EN 13363-1: Solar protection devices combined with glazing – Calculation of solar and light trans-mittance – Part 1: Simplified method; Berlin, Beuth Verlag GmbH

[16] EN 13363-2: Solar protection devices combined with glazing – Calculation of total solar energy trans-mittance and light transmittance – Part 2: Detailed calculation method; Berlin, Beuth Verlag GmbH

[17] EN 13561: External blinds – Performance require-ments including safety; Berlin, Beuth Verlag GmbH

[18] EN 13659: Shutters – Performance requirements including safety; Berlin, Beuth Verlag GmbH

[19] prEN 13659: Shutters and external venetian blinds – Performance requirements including safety; Berlin, Beuth Verlag GmbH

[20] DIN ISO 14025: Environmental labels and declara-tions – Type III environmental declarations – Prin-ciples and procedures; Berlin, Beuth Verlag GmbH

[21] DIN EN 14351-1: Windows and doors – Product standard, performance characteristics – Part 1: Windows and external pedestrian doorsets without resistance to fire and/or smoke leakage charac-teristics; Berlin, Beuth Verlag GmbH

[22] EN 14500: Blinds and shutters – Thermal and visual comfort – Test and calculation methods; Berlin, Beuth Verlag GmbH

[23] EN 14501:Blinds and shutters – Thermal and visual comfort – Performance characteristics and classifi-cation; Berlin, Beuth Verlag GmbH

[24] ISO 15099: Thermal performance of windows, doors and shading devices – Detailed calculations; Berlin, Beuth Verlag GmbH

[25] prEN 15804: Sustainability of construction works – Environmental product declarations – Product cate-gory rules; Berlin, Beuth Verlag GmbH

[26] ISO 18292: Energy performance of fenestration systems for residential buildings – Calculation pro-cedure; Berlin, Beuth Verlag GmbH

[27] DIN V 18599: Energy efficiency of buildings – Calculation of the net, final and primary energy demand for heating, cooling, ventilation, domestic hot water and lighting; Berlin, Beuth Verlag GmbH

[28] DIN 18650-1: Powered pedestrian doors – Part 1: Product requirements and test methods; Berlin, Beuth Verlag GmbH

[29] DIN 18650-2: Powered pedestrian doors – Part 2: Safety at powered pedestrian doors; Berlin, Beuth Verlag GmbH

[30] EnEV: Energy Conservation Directive

[31] Machinery Directive 2006/42/EG

[32] VDI 2078: Cooling load calculation of air-condi-tioned rooms (VDI cooling load regulations); Berlin, Beuth Verlag GmbH

[33] VDI 2078 Blatt 1: Cooling load calculation of air-conditioned buildings with room-conditioning from cooled walls and ceilings; Berlin, Beuth Verlag GmbH

Guidelines and literature:

[1] ift-Guideline AB-01/1: Application Guideline for external Shutters Guideline for the selection of suitable classes of wind resistance according to EN 13659.

[2] ift-Guideline AB-02/1: Airtightness of roller shutter boxes

[3] ift-Guideline VE-07/2: Insulating glazing units with movable solar shading devices integrated in the in-terpane separation; Procedure to test the fitness for use of insulating glazing units (IGU) with integrated movable devices

[4] VFF Sheet ES.04: Thermal insulation in summer

Imprint

Editor:ift Rosenheim GmbHTheodor-Gietl-Str. 7-983026 Rosenheim, Germany

Phone: +49 (80 31) 261-0Fax: +49 (80 31) 261-290E-Mail: [email protected]

Publication:ift-technical information WA-19engl/1Solar Protection – Energy efficient building with solar shading systems, glare protection and daylight control

Notes:This documentation is primarily based on the work and findings by ift Rosenheim GmbH and the partners in-volved. The publication and all its parts are protected by copyright. Any utilisation outside the confined limits of the copyright provisions is not permitted without the consent of the publishers and is punishable. In particu-lar, this applies to any form of duplication, translation, storage on microfilm and the processing in electronic systems.

ISBN 978-3-86791-348-5 – ift RosenheimISBN 978-3-8167-9189-8 – Fraunhofer IRB Verlag

© ift Rosenheim, 2012

ift RosenheimTheodor-Gietl-Straße 7-9

D-83026 Rosenheim

Phone: +49 (0) 80 31 / 261-0Fax: +49 (0) 80 31 / 261-290E-Mail: [email protected]

www.ift-rosenheim.de

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