Week 12 - Passivhaus Design Blog

 Passive Design

The Movement of the Sun

• The sun rises (morning) in the east and sets (evening) in the west.

• The sun is approximately due south at noon.

• The sun is higher in the sky in the summer then in the winter.

• Summer days are long; winter days are short.

Solar Heat Gain

• Solar gain, also known as solar heat gain, is the term used to describe the increase in temperature in a space or material that results from solar radiation.

• The amount of solar gain increases with the strength of the sun and the ability of the material to absorb the radiation.

• Dark-coloured, rough-textured objects absorb solar energy, holding the heat.

• Light-coloured, shiny objects do not absorb the heat as good as dark rough objects, but they reflect the light far better meaning your room will become a lot brighter.

Optimising Solar Gain in the Home

Homes designed to optimise solar gain have 3 features:

1. A façade that faces South.

2. Lots of glazing in the south-facing façade.

3. An interior layout that positions the main living spaces on the south of the building.

Exploring Latitude

• Geographical latitude, is the measure of the position of a point on the Earth’s surface above (north of) or below (south of) the Equator.

• Solar radiation is strongest when it falls on the earth’s surface at an angle of 90° to the surface.

• It is important to find your latitude to determine the angle of the sun at any given day of the year, for your specific location.

Benefits of Natural Light in the Home

• Boosts vitamin D. When exposed to sunlight, the skin absorbs vitamin D, a critical nutrient that prevents bone loss and reduces the risk of heart disease, weight gain, and various cancers.

• Wards off seasonal depression.

• Improves sleep.

• Reduces health risks of fluorescent lighting.

• Cost effective, reduces the need to artificially light a room during the day, meaning electricity bills will be lower as a result.

Standard Sky

• All Natural light comes from the sun.

• The light varies with the weather, in Ireland the overcast sky is the usual source of light.

• This variability creates the need to adapt the idea of a standard sky.

Natural light can be classified as:

• Daylight – diffuse light from the whole of the sky.

• Sunlight – direct “beam” of light from the sun.

Uniform Standard sky:

• Uniform standard sky is the term used to describe a notional hemisphere of overcast sky that has the same level of luminance in every direction when viewed from an unobstructed point on the ground.

• This sky is usually assigned a value of 5,000 lux.

• The notional sky is used when designing fenestration patterns to ensure adequate indoor light levels.

CIE Standard sky:

• The CIE sky is another notional sky that is used in building design.

• In the model on the left, the luminance of the sky steadily increases above the horizon.

• The luminance of the CIE sky is three times brighter than at the horizon.

• This is a more realistic model and works well in the Irish context.

Daylight Factor

• As the amount of light available from the sun/sky varies it is not possible to specify a particular amount of natural light when deciding on the window size and position for a room.

• Instead the amount of light to be supplied to a room is described as a proportion of the actual available light at all times.

• The proportion is called the daylight factor.

• Daylight factor is defined as: The ratio between the actual illuminance at a point inside a room and the illuminance possible from an unobstructed hemisphere of sky.

• In a cloudy climate, the average daylight factor can be used to estimate the appearance of a room during the day.

Less then 2%:

• Room looks gloomy under daylight alone.

• Full electric lighting often needed during daytime.

• Electric lighting dominates daytime appearance.

Between 2% and 5%:

• Windows give a predominantly daylit appearance but supplementary electric lighting needed.

5% or more:

• The room is strongly daylit.

• Daytime electric lighting rarely needed.

• A simple rule of thumb is that a window area equivalent to 4% of the floor area of a room will give a daylight factor of 2%

Daylight Factor Components

The level of Natural light indoors depends on several factors:

• The brightness of the sky.

• Reflections and obstructions outside.

• The size, shape and position of the windows.

• Reflections inside the room.

Completing The daylight Factor calculation for a bedroom in my house design