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Influence of retrofitting on daylighting
Some building physics projects can have a direct impact on daylighting. Optimized lighting has very many positive features that should be considered when modernizing a building. For instance, light directly impacts building users’ mental capacity and visual perception [Ba 1999]. Light also regulates physical processes, such as the release of hormones, and provides the natural pacemaker for the human circadian rhythm [Rüger 2006]. Inadequate light intensity for a sustained period may also trigger symptoms of depression. In addition to psychological and physiological effects, optimized daylighting also has energy benefits. For example, reducing artificial light periods by improving daylight autonomy saves electricity.
Non-residential buildings can get a lot of their lighting from daylight. Figure 1 compares the hours during which an office is used (8 am to 6 pm) with daylight hours. When a building has good daylighting, daylight can cover approximately 85 % of the period during which lighting is needed (maintained illuminance E = 500 lux), thereby shortening the time when artificial lighting is in use [Boer 2006]. This is why optimal daylighting is desirable. Most existing buildings have defined daylight openings that can be altered only minimally. Retrofits can also have a negative impact on daylight supply, primarily in the following areas:
- Additional reveal shading by external insulation
- Light transmission losses caused by retrofitting glazing (such as upgrading from double-pane to multi-pane glazing)
- Existing obstructions whose architecture cannot be influenced (atria, etc.)
An automated assessment loop was developed to examine these light issues, combining the Matlab math software with light simulation program Radiance. A parametrized model helps replicate widely varying geometry and material characteristics, and examines their impact on daylighting [We1 2012]. Beyond systematically analyzing daylighting, the goal is to develop a simplified lighting planning tool for PHPP that determines the amount of supplemental artificial light as accurately as possible. The results of this parameter study, which was based on retrofits, are detailed below. Part of this work was presented at the 48th working group on the use of Passive House technologies when modernising non-residential buildings [We2 2012]. Excerpts from this publication are also quoted.
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Good daylighting can help to keep artificial lighting usage very low. But retrofits to upgrade heat insulation can make buildings less self-sufficient in terms of daylighting. Any such losses can be avoided or offset by taking the necessary measures. For instance, external insulation adds reveal shading and thus reduces daylighting. But this can be lowered by cutting back the window reveal or designing the reveal to have a high reflection factor. Choosing different glass and coatings can achieve a variety of glazing properties. For instance, multi-pane glazing can have high transmission if developers select non-reflecting glazing and Low-E coatings with high visual transmission. In the event of significant obstructions (such as atria), designing structures to have a high reflection factor can also enhance daylighting.
The K-Light project is supported by the Austrian Ministry of Transport, Innovation, and Technology (BMVIT), the Ministry of Economy, Family and Youth (BMWFJ) and the Austrian states of Vorarlberg, Tirol, and Burgenland as part of the Competence Center for Excellent Technology (COMET). The COMET program is administered by the Austrian Research Promotion Agency (FFG).
[Ba 1999] Bartenbach,Ch., Beleuchtung für Bildschirmarbeitsplätze, 5th Symp. Innovative Lichttechnik im Gebäude, OTTI Technologie Kolleg, Regensburg 1999
[Boer 2006] Boer JD, Aydinli S, Cornelius W, et al. Ein umfassendes Instrumentarium zur Ermittlung des Energiebedarfs für Beleuchtungszwecke. 2006:1-27.
[Calumen] Calumen II, Saint Gobain; http://saint-gobain-glass.com/
[Rüger 2006] Rüger M, Gordijn MCM, Beersma DGM, de Vries B, Daan S. Time-of-day-dependent effects of bright light exposure on human psychophysiology: comparison of daytime and nighttime exposure. American journal of physiology. Regulatory, integrative and comparative physiology. 2006
[We1 2012] Werner, M., Pfluger, R., Feist, W., & Geisler-Moroder, D. (2012). TAGESLICHT-PARAMETERSTUDIE MIT HILFE EINER MATLAB-RADIANCE- KOPPELUNG. BauSim 2012. Berlin: BauSIM 2012.
[We2 2012] Werner, M., Feist, W., & Pfluger, R. (2012). Möglichkeiten optimierter Tageslichtnutzung und Kunstlichtsysteme bei der Modernisierung von Nichtwohngebäuden. AK 48 „Einsatz von Passivhaustechnologien bei der Modernisierung von Nichtwohngebäuden“. Darmstadt.
[Win 2010] Lawrence Berkeley National Laboratory. THERM 6.3 / WINDOW 6.3 NFRC Simulation Manual. 2010; (October). http://windows.lbl.gov/software/window/window.html.