Environmental and health related criteria for buildings - ANEC

IBO - Environmental and Health related Criteria for Buildings
9. DAYLIGHTING
9.1. Introduction
Daylight has great influence on the endogenous 24-hour rhythm of the human body, it affects
the hormonal system and many metabolic processes and is therefore responsible for
physical as well as mental well-being. Bright rooms and direct sunlight are among the most
important parameters for consumers to lease a dwelling, apart from optimal layout and
acceptable costs 55 . Besides the positive psychosomatic effect of daylight, energy savings
can be achieved by reduction of artificial lighting and additional passive solar gains.
Daylight availability in buildings is influenced by various factors:
- the location (geographical coordinates)
- specific regional climate (foggy or cloudy days per year, temperature inversions in
winter, valley,..) and solar radiation (altitude)
- cardinal orientation of the building or dwelling units
- visual connection between building and surroundings
- shading through neighbouring buildings, trees, mountains, etc.
- shading caused by building edges and overhangs (balconies, loggias, roof, etc.)
- size, form and depth of rooms
- size, orientation and location of windows
- height of the window lintel
- light transmittance of glazings
- light loss factors (such as dirt, depth of reveals, etc.)
- reflectance of interior surfaces (ceiling, floor, walls, furniture, etc.)
- reflectance of exterior surfaces (e.g. loggias, exterior walls of neighbouring buildings,
surroundings: snow, etc.)
- use of daylighting systems (such as light tubes, light-directing prisms etc.)
The daylight factor allows to evaluate the visual quality of a room or building independently
from the sunlight availability of a location. The daylight factor is defined as the ratio of interior
illuminance to the exterior illuminance from overcast sky. A daylight factor of 1.5 % means
that 1.5 % of the available exterior illuminance is reaching a defined point inside the building.
The daylight factor DF is expressed (as a percentage) as follows: DF = (E i / E e ) x 100
E i …interior illuminance (lx)
E e…. exterior illuminance (lx)
It is a geometry-related figure (independent from orientation of the building or direct sunlight)
and determinable for all points of a room as a fixed parameter. Daylight factors can be
averaged over a defined horizontal (or vertical) reference plane (e.g. 0.85 m height over
floor). Daylight sections through these reference planes show the distribution of interior
illuminance levels over the whole room depth (or height).
55 Ornetzeder, M.; Rohracher, H., Nutzererfahrungen als Basis für nachhaltige Wohnkonzepte (Projektbericht im
Rahmen der Programmlinie Haus der Zukunft, im Auftrag des Bundesministeriums für Verkehr, Innovation und
Technologie, Wien, 2001), only available in German
Final Report 92 31 03 2011