dc.description.abstract
The work in hand investigates the quality and the quantity of the indoor daylight supply, emphasizing the human photo-physiological needs. Furthermore possible interdependencies between daylight-oriented design and thermal optimization goals are explored. This is done against the background of firstly the ongoing social development to spend already 90% of human lifetime indoors and of secondly the use of coated, multy-layer functional glazings, which cause significant change of the light passing through both in quality and quantity. Consequently, the following hypotheses are proposed and examined.<br />Hypothesis 1: There is a causal relationship between the evidence of epidemic occurrences of light deficiency disorders and extended periods of time spent indoors behind glazing in general, and thermally optimized glazing in particular.<br />Hypothesis 2: There is a conflict of goals involved between optimization of daylight supply and optimization of the daylight-induced thermal performance of a room in relation to the positioning of the room's transparent vertical surfaces.<br />Basic principles have been collected and edited in the following three fields: Firstly we calculate the spectral distribution of outdoor daylight supply for a specific location at certain reference times. Secondly the radiation transmission through a set of four characeristic, frequently used, functional glazings is investigated.<br />Thirdly the fundamentals of human photobiology are compiled from respected medical reference works and, in the selective perspective of the paper, complemented by results from selected medical studies. In particular, photobiological response curves, threshold values and effective doses are investigated.<br />Both hypotheses are dealt with by the means of potential studies. In case of hypothesis 1 the photobiological response potentials of the solar radiation right behind the functional glazing is calculated for defined reference conditions such as time, place and type of glazing.<br />Special attention was given to pre-vitamin D3 photosynthesis, erythema formation, melatonin suppression, and light sensitivity in photopic vision conditions. The resulting response potentials were compared with the borderline and threshold values, and effective doses compared with values from existing studies in medical literature.<br />In case of hypothesis 2 the three reference values of a) heating demand, b) cooling demand, and c) daylight supply are calculated for an archetypical defined apartment, while changing the facades' orientation by steps of 30 degrees. For this purpose a totally new reference value for he daylight supply, the Light Penetration Factor (LPF) was defined by the authors and fort he first time applied in this work. The results are illustrated by a graphic summarizing the orientation to the solar ecliptic relative to the potential profile. Both hypothesises can be clearly confirmed.<br />Hypothesis 1: Spectral transmission at the reference times displays characteristic, significantly heterogeneous courses. It is clearly shown that every investigated pane is virtually impermeable for the UV radiation spectrum that is necessary for the process of photosynthesis of pre-vitamin D3. Moreover the attained erythema dose falls drastically. Both the threat of erythema formation as well as the chances of skin adaptation are remote. In the visible light spectrum, however, the selected glazings are so transparent that the photophysiological-relevant threshold values are significantly exceeded for all presently known non-visual indirect effects of melatonin suppression. Nonetheless the reduced radiation intensity is often readily perceptible, leading to increased use of artificial lighting as daylight compensation. Hypothesis 2: The conflicting relationship between high thermal performance as concerns heating demand and cooling demand, on the one hand, and high daylight potential as concerns lighting, on the other hand, is presented concisely. The optimization approaches clearly show just how sensitively the dimension of room depth impacts all three potentials. Generally, one may conclude that north-south-lit apartments simultaneously display beneficial thermal characteristics and poor lighting. Apartments whose longer axis is moderately angled away from north-south display a very balanced thermal, or optical, performance. In contrast, apartments whose longer axis is angled east-west create situations with excellent lighting, yet with poor basic conditions for favorable thermal performance. Based on the confirmation of the two hypothesises, some basic recommendations for decision-making in daylight conscious architectural design are worked out: 1. Daylight falls in the building interior quantitatively and qualitatively compromised after passing high-tech functional glazings.<br />Thus it is our recommendation to increase daylight supply in general, and that of direct sunlight in particular. From this perspective, consideration of the spatial geometry of direct solar radiation when designing building volumes, shells and floor plans becomes absolutely essential. 2. Every building that is intended for extended use of indoor spaces by its inhabitants should be connected with the outdoor space in such a manner that regular, sufficient consumption of unfiltered daylight is assured. One should explicitly consider the functions of living, working, care-giving, supervising, instructing and similar activities. 3. Exploitation of thermal energy by passive solar utilization in buildings, as well as the most extensive availability of daylight possible requires proportionately large windows as collecting surfaces.<br />In order to avoid resulting superfluous thermal gains in the warm season, one must provide for uncompromising, effective, functionally independent, user-specific shading systems for the interior rooms coupled with ventilation options.<br />4. We strongly recommend ensuring natural night-time darkness in the interior, especially in sleeping areas, or in cases of artificial exterior light, taking appropriate planning measures to create such conditions.
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