Daylighting Improvement

Transcription

1 EU framework programme Daylighting Improvement Guidelines Introduction Daylighting is the efficient use of skylight and sunlight through the design, materials and components, and, control strategies. Daylight design depends on the visual requirements as determined by from the building / space use. It also depends on the availability of daylight at the building site and is related to latitude, meteorological conditions and to the surrounding built space. Daylight design, building plan and elevation design all have reciprocal impacts to one another. Therefore, it is important that daylighting be considered as a basic design parameter from the very initial steps of the building design. In retrofitting schemes, improving daylighting may be more difficult and costly. For example it is not always straightforward or possible to enlarge the window aperture or bring daylight in the inner core of deep plan buildings. In such cases advanced daylighting systems as detailed in chapter 3, may be appropriate if increased capital cost can be handled. 1.1 Why use this technology Daylight is essential to human beings and therefore its use in buildings has an important effect on people s well being. Results of many studies associate users higher productivity and state of well being with the presence of daylight in the working space. In non-residential buildings where the users have limited control on the internal environmental conditions -visual and thermal- it is very important to ensure sound daylight conditions suitable to the space use. If properly designed, daylighting can contribute to large energy savings and reduction of CO2 emissions by replacing electric lighting. Also additional savings may be obtained, where applicable, from the reduction of space cooling demand as a consequence of electric lighting replacement. 1.2 Requirements in regulations In most member states current regulations foresee a minimum level of daylight opening size, usually given as a percentage of the treated floor area. In some countries, there are also requirements in the form of a) minimum daylight factor (DF) to be ensured for specific uses and, b) location of openings in order to ensure view and a minimum brightness level. Across EU the requirements vary following daylight availability. The Table below gives an overview for certain EU member states. Italy Norway Greece Minimum window area represents 12.5% of the room floor area. Some local rules require 10%; and some 20% (i.e. classroom of school building) A DF of 2% is required for living rooms, lounge, public rooms, day rooms (where you stay for a while during the day) A minimum window area equal to 10% of the treated floor area is required. Figure 1 The Burrell Art Gallery, Glasgow, UK More recent regulations in certain member states set requirements for the overall energy performance of the building, initiating thus a design process for a) optimal energy demand year round and b) greater energy efficiency. In this context daylighting may be considered as an energy design parameter that can be integrated within an overall energy performance target. This view is supported by the EU Directive EPBD, (2002/91/EU). Also the Directive dictates that large public buildings should obtain and display an energy efficiency certificate. Day-

2 1 lighting improvement as a means to reduce electric energy can contribute so that a building can obtain a better energy efficiency ranking. 2 Current practise 2.1 Daylight opening types Daylighting is commonly provided with windows located on the perimeter of the building envelope. Their size depends on the (i) space use that dictates the required range of illuminance level, (ii) the optical characteristics of glass, and (iii) the daylight availability as results form microclimatic conditions of the natural and man made environment. Rooflight openings admit the strong bright light and for this reason is an efficient lighting technique. Horizontal rooflight openings admit nearly three times the amount that a vertical opening of equal size does. They are frequently met in Northern climates where daylight availability is lower. Rooflight is preferred for many space uses such as museums and exhibition halls because of its high intensity and the flexibility in managing the distribution of light over the space. It is also an effective option to improve daylighting levels in deep plan buildings but is limited to the top floor. Clerestories and atria (Figure. 2.1, 2.2) are the other alternative used to daylight the inner core of large buildings. Figure 2.1 Clerestories at Tate Gallery, St Ives [1] 2.2 Interaction of shading with daylighting For the above mentioned opening types, solar protection must be foreseen, where necessary, in order to avoid glare generation and potential overheating during the warm periods. The latter is of utmost importance in warmer climates whilst in the northern ones it may be necessary for use-dominated buildings where internal gains are significant and give rise to cooling loads. Shading devices obstruct the direct sunlight but permit the diffuse light to enter the space. They are more efficient if placed externally because they obstruct the direct solar radiation before it enters the space and partially transform to heat. Shading should be considered as a design parameter and be integrated in the daylighting design brief. Care must be taken in order to: use materials that will not generate glare, avoid any reduction of daylight levels that would increase the use of artificial lighting, integrate morphologically the shading devices on the façades. When necessary, shading devices may be used to enhance daylight levels by reflecting the light into deeper parts of the room. Daylighting improvement options currently used are given in the following Light Shelves Light shelves are horizontal protrusions installed internally and/or externally. They divide the window in two parts, namely, upper and lower. The upper surface of the light shelf reflects the incident light through the upper window glazing to the ceiling and eventually to inner room spaces. The shelf acts as a shading device for the lower part, obstructing the high angle solar radiation. The reflector is made of a highly reflective surface (i.e. semispecular, polished surface, etc). With the exception of the anidolic system (see ch ) light shelves usually decrease the overall incoming daylighting. However, they are recommended when there is a need for smoothing out daylight distribution and reducing glare. External light shelves have a large impact on the building façades that needs to be addressed in case of retrofitting schemes. The integration design should tackle thermal bridging and issues related to aesthetics, morphology and architectural style. Various configurations of light shelves have been used since longtime. The innovative aspect lies with reflecting materials and surface optical treatment. New systems have improved reflecting properties minimising the loss from absorption or uncontrolled diffusion. Figure 2.2 Chelmsford, U.K. [2] The atrium at the Anglia Polytechnic University, 2.3 Glazing materials An important component of daylighting systems is glazing which has a significant impact on visual conditions. The following type of glazings are most commonly used. - Clear glazing has very good transmissivity allowing in average 75% - 85% (for double and single glazing respectively) of the incoming light to enter the space. Clear glazing is good for view purposes and does not interfere with colour rendering.

3 2 - Tinted and reflective glazings that are heavily used in the last ten to fifteen years have low transmissivity reducing the available daylight to low levels. They are used however, for architectural as well as solar protection purposes. - Translucent glazing either deflects or scatters the incoming solar radiation. These glazing are suitable for daylighting openings when the view out is not necessary or the requirement is met by other non-translucent openings. When the incoming radiation is scattered it is more uniformly transmitted in the space; and this is very beneficial for many daylighting applications. Translucent glazing also needs solar protection in summer to avoid any overheating. In the recent years the glazing industry has come up with a series of products that allow a greater flexibility in the design and sizing of glazing. These new products have considerably greater thermal resistances and s improved optical properties. Such glazings are the low-e type that can be used either to trap the infrared radiation and keep it inside or inhibit its entrance to the internal space. This operation is determined by the location of the lowemissivity film between the glass panes. The following chapter gives a more detailed account on the glazing improvements. 2.4 Problems and limitations identified in current practice - In the recent years there is a tendency to increase the percentage of glazed area in new buildings, including those of the residential sector. However, in most cases this is done at the expense of extra energy required to cover the resulting excess load in heating and/or cooling. Thus it is important to design daylighting systems as part of the overall energy design of the building aiming at an optimal year round performance with reduced heating, cooling and lighting demands. - In most contemporary non-residential buildings, it is common that daylighting alone does not suffice to provide comfortable visual conditions. One frequently sees new non-residential buildings with large glazed façades that are artificially lit even under sunny conditions (Figure 2.3). Large glazed façades may result in different types of discomfort such as glare or, in the case of tinted glazing, in lower illuminance levels. The latter results in the use of artificial lighting even in room areas located close to glazing. - Sidelight can provide sufficient light roughly at depths 2 times the head height of the opening measured from the floor. Deep plan spaces cannot be satisfactorily daylit. Some innovative daylighting systems, discussed in the following chapter, may improve lighting levels by redirecting the incoming radiation. Also light pipes and ducts may guide the daylight from areas with large availability (external surfaces, roof etc.) to internal deep spaces. Figure 2.3 East facing building - Sunny day around noon time, in late spring. Electric lighting is on, even in areas next to glazing. 3 Innovative solutions A great deal of research in the last decades has focused on components and materials that can simultaneously improve the use of daylight and be easily integrated on building facades. The systems presented below are results of this research. They are classified in three categories: (i) redirecting systems, (ii) light guiding (transporting) systems, (iii) new glazing materials. 3.1 Redirecting Systems: alter by reflection or refraction the path of diffuse light or sunlight to deeper spaces of the room. There are many types and variations of such systems; Anidolic Light Shelf It consists of two curved reflectors made of materials of non-image optics that enable high reflection with very low loss in light intensity. The receiver aperture is covered with a glass pane horizontally positioned. It admits light coming from high altitude angles that is delivered in the room within an angle interval of ± 30º. The anidolic light shelf can admit both daylight and sunlight. At times when sunlight is not desirable the receiver can be shaded. Figure 3.1 Anodolic Light Shelf [2]

4 3 Unlike the other light shelf configurations the anidolic one has quite elevated light intensities both in front and back of the room. Compared to double glazing the overall intensity maybe slightly reduced but it ensures better uniformity ratio. Regarding retrofitting schemes the accommodation of the collector on existing façades could be difficult depending on the protrusion width that varies with the geometry of the system and room depth. The system shown in Figure 3.1 has a protrusion of 80cm whilst the inner part of the shelf extends to about 130 cm Prismatic panels They are semi-transparent devices with a flat surface towards the exterior and a sawtooth-like room facing side. They are made of acrylic polymer and have a thickness of 12 mm. They are usually sandwiched between glass panes to avoid dirt and ensure long lifetime. The panels may be used (i) as shading devices reflecting the incident sunlight and/or (ii) to redirect daylight to the inner upper part of the room. Figure 3.2 Configurations of prismatic panels [3] The location of the panel on the external or internal side of the opening depends on the design strategy to be adopted. If for example the panel is used as shading device, it is recommended that be positioned on the outside. The panel s efficiency, as shading device, depends on the angle of solar incidence that varies with season, daytime and opening tilt. Thus, requirements such as latitude, and opening position (orientation and tilt), should be taken into account when selecting panels, to ensure good performance. To increase shading performance the panels can be mounted on a sun-tracking axis to obstruct sunrays coming from the whole range of solar altitudes. Similar to prismatic panel is the prismatic film that is produced by a special etching process. It is placed on the internal side of a double glazed opening. Compared with clear double glazing the panels reduce luminus flux. From measurements performed in controlled environments [3] it is demonstrated the panel performs better under clear sky conditions. Under overcast sky it reduces illuminance by 20% to 35%. In the case of prismatic film the latter ratio becomes 10% to 30%. Figure 3.3 Museum of Natural Science in Bonn The roof is made of prismatic panels allowing skylight but excluding direct sunlight. Regarding building retrofitting the panels can be easily integrated on existing façades. However, the following should be taken into account: -Being semi-transparent the panel does not provide a clear view out (Figure. 3.4). If view is a requirement then only the upper part of the existing openings may be equipped with prismatic panels allowing the lower parts to ensure visual contact. -When the panel is used to redirect daylight towards the ceiling care should be taken (i) to avoid obstructions in the light s path and (ii) enhance ceiling s reflectivity. Several different commercial products are available on the market. They are designed to cutt-off specific range of sun angles. Figure 3.4 Interior view of a prismatic panel [3] Also alternative prism designs are available such as (a) the prism with one aluminised inner sawtooth surface for improved reflection (b) triangular prism Laser Cut Panels (LCP) They are thin acrylic panels divided in rectangular sections by laser cutting. The edges along the cuts are transformed into a series of reflectors. The sunlight after penetration in the panel is deflected travelling towards the edge where is either reflected back or exits the panel. High angle sunlight exits the panel with an upward direc-

5 4 Figure 3.5 Path of the sunlight within the LCP Figure 3.6 Left: use of LCP as shading louvers Right: use of LCP as sunlight redirecting system tion towards the ceiling. Light coming upwards is deflected downwards. Finally light incident perpendicular is transmitted with negligible alteration. The LCP is quite transparent thus allowing a view out (Figure. 3.7). It has a good level of light transmissivity. It is usually placed between two glazing to avoid dirt and dust. Under this arrangement it can transmit approximately 50% - 65% of the incoming sunlight Holographic optical elements Using laser light a series of microscopic strips is imprinted on a transparent film in such a way that forms a diffraction grating. The film is sandwiched between two glass panes to avoid dirt. Depending on the grating the system may deflect the skylight coming from the upper sky vault and can be either placed vertically on the non-view opening or as a shading device tilted at an angle (around 45 o ). Alternatively the grating can be made to reflect a certain range of incident solar beam and simultaneously be transparent to light coming from all other directions. This is a directionally selective shading device. It can be placed in front of large glazed façades or used to shade roof openings. To enhance shading performance and broaden up the range of angle dependent reflection of sunlight, the device can be mounted on one-axis sun tracking structure Louvers There are many louver designs suitable for either external, internal or in between the glazings installation. They may serve for both or either purpose of daylight and shading. Currently, daylight louver design focuses mainly on the reflection side coatings. Optically treated materials and bi- or tri-facet louver are among the new products. In the following, two types of narrow louvers are described. Figure. 3.8 shows the fish eye louvers. They have their upper part coated with a highly reflective material to redirect both the incident solar beam and skylight. They are 12 mm wide and are placed horizontally between the two panes of a double glazed opening. They can reflect approximately 60% (not including thereduction due to glazing) of daylight and sunlight coming from angles greater than 45 o [3]. Figure 3.7 LCP is quite transparent [3] Although LCP is well transparent, it is recommended, to place it on the upper part of openings, above view level. This is because of the downward direction of the emerging light which takes place when light incidents on the panel from below horizon (i.e. reflected from ground level). The LCP can efficiently diffuse sunlight coming from angles greater than 30 o and eliminate glare. Its cost is lower compared to other light redirecting options. It is easily integrated on existing facades with a low impact (Figure 3.8). Furthermore, LCPs can be used in conjuction with light shafts in order to direct more effectively the light to lower levels. In overall it is an attractive option for building retrofitting schemes. Figure 3.8 Fish Eye Louvers [3] Triangular type louvers Figure 3.9, (OKASOLAR system), are also integrated within a double glazed opening. They are designed to exclude sunlight coming from high angles but they let pass medium (as diffused) and low angle solar beams.

6 5 Anidolic ceiling may result in more than 30% electricity savings compared to double glazing especially under overcast conditions. Simultaneously the daylight factors are increased in the back and the response of the users is very positive Anidolic zenithal opening A similar concept is the anidolic zenithal opening (Figure 3.11). It is located on the roof and positioned to collect daylight from a large part of the hemisphere. It is recommended for atria, and upper floor areas. Its performance is very satisfactory since it can produce the same illuminance levels as a double glazed skylight but with half of the opening surface area. Moreover, it produces more uniform illuminance levels and completely eliminates glare. Figure 3.9 Triangular louvers Okasolar - Okalux [5] The louvers are fixed. However, their tilt and facets can be designed to suit latitude requirements. 3.2 Light Guiding Systems Anidolic ceiling This is a similar system to the anidolic shelf (see above). The light is guided by reflection to the exit where another parabolic reflector directs it at the horizontal glazed outlet (Figure 3.10). The guide is made of highly reflective aluminium tube that can be placed in a false ceiling. The two parabolic concentrators at the inlet are covered by glass and so is the outlet of the system. This is to keep the system clean and avoid any light intensity reduction. Figure 3.10 Anidolic Ceiling [3] The system collects diffuse light from nearly half the hemisphere. It is suitable for overcast skies and especially for areas, as in densely built urban conglomerations, with quite reduced daylight availability due to obstacles. Figure 3.11 Anidolic Zenithal Opening Sunpipes Sunpipes are used as daylight option for areas without direct access to outdoors. Although they are common in North America and Australia in Europe are not widely used. They are tubes, either straight or bend, with an internal lining made of highly reflective materials such as anodised aluminium or silver coated plastic films. The dome shaped receiver is covered with clear acrylic that reflects the UV radiation. The outlet is covered with a diffuser to ensure more even distribution and avoid glare. They collect both skylight and sunlight that is delivered as diffused light within the space. Its efficiency depends on the aperture ratio (length- over- tube cross section area), and the reflectance of the tube s internal surface. It should be noted that as the length of the pipe increases the efficiency decreases due to multiple reflections. An increase in length would be counteracted by an increase in cross section but the latter maybe confined by space and construction requirements. The advantage of sunpipes over skylights is that they can serve more floors than just the upper one and are flexible. They deliver less heat into the space, an important issue in hot climates. 3.3 New Glazing Materials A great advancement has been achieved in glazing technology over the last years. Very efficient glazing materials have been produced with very high thermal resistence. Some new glazings (i.e. photochromic, electrochromic) have dynamic solar transmittances varying form

7 6 high to very low values. However, along with sunlight they obstruct daylight as well and so they are not suitable for spaces requiring with light levels. In the following three glazing types are reported having properties that contribute to daylight improvement Transparent Insulation Materials (TIM): Aerogel Silica aerogel is a microporous material with entrapped air in very tiny holes. Aerogel granules are sandwiched between two glass panes. When sunlight falls on the aerogel is scattered entering the room as diffused light. The aerogel-glazing system transmits about 50% of the incident light. If sandwiched in polycarbonate panels its transmittance increases to 60%. Figure 3.13 Sun directing glass [3] A horizontal spread of the incoming beam may be also achieved with the addition of a holographic film in between the front glazings or with a special treatment of the external side of the inner glazing. Sun-directing glass works better with direct sun especially when the solar beam comes from higher angles. Its effect under overcast sky or clear conditions without direct sun is negligible. With direct sun the glass system can provide high levels of illumination about 500 Lux at 5-m depth. 4 Advantages/disadvantages Figure 3.12 Skylight covered with aerogel sandwiched between two polycarbonate panels [6] Honeycomb or capillary structure Honeycomb or capillary structures made of plastics or glass are sandwiched between glass or plastic panes. They reduce heat losses by suppression of convection and infrared radiation. They have a high solar transmittance depending on the thickness and structure of the capillaries. Transmittance values vary between 35% to a little over 60% for direct solar radiation depending on the thickness and structure of the capillaries. The diffuse radiation is transmitted at a ratio varying from nearly 20% to 45% roughly. No clear view through is possible. However, through redirecting solar radiation a good illumination of the room behind can be achieved Sun-directing glass Acrylic concave elements placed between two glass panes reflect upwards both sunlight and skylight towards the ceiling. The size and cutt-off angle of the cancave elements need to be designed according to latitude. Elements available on the market are designed for higher latitudes (high solar altitude up to 65 o ). To suite areas with higher solar altitude the elements may be placed with a tilt, however, glare problems may result. Sun-directing glass has greater transmittance with the direct sunlight than with skylight. Daylighting improvement is directly benefcial to (i) increasing building energy efficiency whilst reducing operational costs and (ii) improving human well being, productivity and users satisfaction. These advantages may be counteracted if daylighting openings are not properly sized. Oversized windows may result in overheating thus increasing cooling energy. Additionaly, not carefully selected photometric characteristics of the room surfaces together with poor window design (i.e. size, positioning glazing materials, shading) may result in unwanted glare causing visual discomfort. As a means to counteract this effect is the increased use of electric lighting. Disadvantages associated with the previously presented innovative systems are (a) higher capital costs and, (b) in refurbishment schemes, the integration of systems on the building shell needs special care i.e. aesthetics, structural adequacy, accessibility for maintenance, overall thermal and visual performance. 5 Costs 5.1 Investment costs As previously mentioned most innovative systems require higher capital costs. The following Table gives an overview of a sample of these systems. Table 5.1 Capital Cost System /m² Prismatic panels Prismatic films Laser cut panels Sun directing glass 200

8 7 5.2 Energy saving potential The performance of the systems is reported here as a function of illumination improvement [3]. Table 5.2 Performance Increase in Performance (%) Prismatic Increases by 30% the illumination at panels the rear wall and 14% as average Prismatic It increases illumination by 10% to films 20% (middle and back) under clear sky but reduces it by 30% at low sun angles. Laser cut panels Sun directing glass A minimum of 10% - 30% depending on panel configuration and sky conditions Very high performance under clear sky, compared with a grey venetian blind, but reduced under overcast sky. Figure 7.1 iii) iv) Borgen school Daylight in the inner core create highly reflective surfaces to guide light in the inner core, equip the apertures with suitable louver shades to either obstruct the sunlight or redirect it towards the roof according to the aperture orientation, 5.3 Additional costs Carefull integration design and construction is required for protruding systems (i.e. triangular systems or the anidolic zenithal openings) to avoid thermal bridges that might occur between the mounting structure and the building envelope. This special care often results in additional costs. 6 Maintenance and service In order to maintain good daylighting efficiency the systems must be kept clean. This is very important for both specular and diffusively reflective surfaces. Easy access of the devices is an important issue for maintenance and should be tackled at the design phase. Especially in the refurbishment design the accessibility issue is a determining parameter. Greater care is required for moving devices as mechanical parts have shorter lifespans. 7 Best practise example 7.1 Borgen Coomunity Centre The old school of Borgen Community Centre, Asker, Norway (59 50 northern latitude), is a BRITA in PuBs refurbishment project tackling daylighting improvement. The school having a 27m by 27m plan was initially built as an open plan but was partitioned to smaller areas over the years. Daylight conditions were poor, especially in the inner core of the building. The refurbishment design tackled the improvement of daylight conditions and visual comfort. This was accomplished with the following design options: i) increase window areas on the perimeter, ii) replace the roof with a new one and create skylight openings to introduce light in the inner core of the building, Figure 7.2 Skylights with horizontal louvers on the south side and vertical on the west side. v) introduce daylight sensors to control the use of electric light The daylight refurbishment options result in average energy savings of 23 kwh/m2 a or kwh /a. 8 Calculation tools A series of design tools are available and may be used to support sizing and positioning, evaluate visual comfort and calculate the resulting energy efficiency. The tools are commonly classified in three categories: (i) Physical models and sky Simulators, (ii) Computer models, (iii) Simplified tools. (i) Modelling is an old method and designers are well acquainted with it. The size of the mock up, ranging usually from 1:500 to 1:10, depends on the investigation objectives; for example the smaller sizes of mock ups are suitable to investigate the impact to and from the neighbouring buildings whilst the larger ones allow to investigate daylight penetration, detailed views and taking photos or making videos on the internal space.

9 8 (ii) Computer models - tools, which can handle advanced daylighting systems and provide a vast variety of output (images, visual comfort calculations, etc.); A large variety of computer tools are currently available ranging from simplified models to very detailed simulations. Below is tabulated a sample of daylighting computer design tools. They have been selected on the ground that are most known in the E.U. member states and represent the state of the art of their category. SUPERLITE Accurately predicts the illuminance of a surface in complex building spaces resulting from both or either daylight and electrical light. Daylight conditions can be simulated for nearly any type of sky conditions and sun position. Results of illuminance and daylight factor, in tabular or graphical form, are provided at any plane and surface specified by the user. It runs on DOS and requires minimum hardware capacity. A disadvantage is the noninteractive input consisting of geometric and numerical data. LESO - DIAL Calculates daylight factor values on the work plane. According to lighting requirements, the software estimates the time during which artificial lighting can be switched off (Swiss climate). Diagnosis and advice on how to optimise the daylighting performance are provided. Based on fuzzy logic rules, the diagnosis facility of the software indicates possible weak points of the design. It is easy to use and intended for early stages of preliminary design phase. Input is performed by drawings, linguistic or numerical description of photometric and geometric data. RADIANCE A ray-back calculation model that can ensure accurate calculation of luminance, b) model both electric and daylight, c) supports various reflectance models and complicated geometry of building space, can use any unmodified input from CAD systems. It provides both numerical results and photo-realistic rendering. It can analyse CIE overcast sky and clear sky with and without sun. Also user defined skies are accepted. Results are very accurate but it requires a fairly long training period [2]. raytrace/radiance/daylight.html GENELUX A ray tracing method from the light source to the receiver s eye calculates both illuminances and daylight factors for the CIE overcast sky, sunlight and indoor artificial light. Results are provided on the user-defined working plane. However, some inaccuracies may arise from the fact that interreflections are calculated only between surfaces that are above the user defined plane. s/proceedings_body/bok4/rl4mitan.pdf PASSPORT LIGHT Using similar method as the Radiance software Passport Light calculates light levels and daylight factors for a large number of surfaces of rectangular shape. It can analyse CIE overcast and clear sky, uniform sky and user-defined sky luminances. It requires short computing time but this advantage is counterweighted by a rather difficult and time-consuming data input. / ADELINE Advanced Daylighting and Electric Lighting Integrated New Environment It is a software package enabling integrated energy calculations. Daylighting calculations can be performed with either SUPERLITE or RADIANCE. The resulting electric energy needed for lighting (for periods when daylighting is not available or sufficient), is calculated and used as input to an energy simulation tool such as SUNCODE, DOE2, TRNSYS, TSBI5. ADELINE combines graphical input using CAD or SCRIBE MODELLER files as well as numerical input. Graphical output includes a 2-D or 3-D representation of the space with iso-lux or iso-daylight factor contours or renderings when Radiance is used. (Erhorn and Dirksmöller) [3], (iii) Simplified tools Simplified tools can range from rules of thumb, to mathematical equations, nomograms, Tables or equipment. They are all suitable for the preliminary design. A thorough survey has been carried by IEA SHC Task 21 and by [4]. 9 References 9.1 Compilation This guideline was prepared as a part of the project BRITA in PuBs Bringing retrofit innovation to application in public buildings, EU 6th Framework programme Ecobuilding (TREN/04/FP6EN/S /503135). The author is Eva Athanassakos, from the EUDITI Energy & Environmental Design, Greece. Special thanks are due to Karin Buvik and Kari Tunshelle from Sintef NO, and Gilbert Snook from City college Plymouth UK, for their valuable feedback. The professional editing was closed in March Literature [1] Daylight Design in Architecture- Making the Most od a Natural Resource David Loe, K.P. Mansfield, Energy Efficiency Best Practice Programme, DTI Department of Enterprise, U.K., [2] Daylight Design of Buildings, Nick Baker, Koen Steemers, - James & James Science Publishers Ltd, with the support of European Commission, Science Research Development, [3] Daylight in buildings, IEA SHC TASK 21, ECBCS ANNEX 29, July 2000 [4] N V Baker, A Fanchiotti and K Steemers (eds), Daylighting in Architecture: A European Reference Book, London CEC DGII/ James & James, [5] Okasolar, [6]

10 9 10 Disclaimer The sole responsibility for the content of this publication lies with the authors. It does not represent the opinion of the Community. The authors and the European Commission are not responsible for any use that may be made of the information contained therein.