LEARNING LOG

As of my Studio Course requires I am doing a learning log of my research for my projects. I am currently designing a luxury apartment for a made up client with many parrots(!) The building being used is placed in Dublin, and to make the best use of the daylight I did some research on it. 

"Achieve a minimum of daylight factor of 2 percent"

Light levels in a building space are typically measured in footcandles or lux. Light from electric lights is fairly constant so exact levels of lighting can be obtained through the selection and layout of light fixtures. When it comes to daylighting the light source is the sky vault which is outside the building so it becomes necessary to install glazed openings (windows and skylights) to admit adequate daylight to meet space needs. Designing for exact levels of light from daylight is difficult since the light source is constantly changing depending on time of day and weather conditions. Instead of calculating exact levels of light (footcandles or lux) in a given space from daylight a daylight factor was created to measure relative light levels. The daylight factor is best defined as:

DF = Iin/Iout x 100%
Where:
DF = daylight factor
Iin = illumiance due to daylight on the indoor working plane
Iout = illumiance outdoors on a unobstructed horizontal plane

There are three possible ways that daylight can reach the indoor working plane. They are:

Visable light directly from the sky vault (define)

Light reflected from exterior surfaces.

Light entering the space and reflecting from interior surfaces.

All three of these components need to be accounted for to determine the daylight factor.

A daylight factor of 2 is a typical level one would want to achieve for an office space. It assumes that 2% of the total light that is outside the building ends up on the working plane or desktop. Assuming an average outdoor illumiance of 2500 footcandles and a daylight factor of 2% the indoor illumiance on your desktop would be 50 footcandles (2% x 2500 footcandles = 50 footcandles). Other typical daylight factors for various spaces are:

Discussion Groups – 14
Residential Living Room – 1
Residential Kitchen – 2
Office - detail work – 4
Office - drafting – 6
Office - corridors – 0.5
Sports facilities – 2

Traditional “daylighting” excludes direct beam-sunlight which typically introduces unwanted heat, glare and extreme contrast which may lead to increased energy use and uncomfortable conditions.

The sun is constantly changing positions (altitude and azimuth) during the day and throughout the seasons.

The MOU guidance recognizes that excluding "all" direct sunlight penetration may not be possible or desirable. If the building design incorporates both passive solar heating and daylighting excluding the direct beam would not be desirable since this is the main source of heat.

Excluding direct beam sunlight starts with good building orientation, placing the long axis of the building facing due north and south. Windows facing north will receive the greatest amount of daylight and can dispense with overhangs and fins for most latitudes (recognizing that some direct beam penetration will be possible during summer sunrise and sunset - see Figure 1).

The second best daylighting is from south facing windows which can be protected from direct beam sunlight using fixed overhangs. The least desirable daylighting is from east and west facing windows because of the difficulty of eliminating direct beam sunlight during mornings (East side) and afternoons (West side). The only way to completely omit direct beam sunlight during this time is movable shading devices such as blinds and roller shades which will also block the daylighting. Figure 2 provides solar angles for various latitudes which can be used to size fixed south facing overhangs.

Keep in mind that these solar angles allow for both daylighting and passive solar heating so it will be necessary to divide the window wall into two areas, an upper glass area for continuous daylighting protected by a overhang that prevents both summer and winter direct beampenetration, and a lower area which provides both daylighting and view with light colored blinds or roller shades to control winter direct beam penetration. A more optimum design would make use of light shelves to bounce light further back into the space (see Figure 3).