22 October 2014

Design to Maximise the Sun

Designing around the sun is a very important element of the design. The sun will keep the home warm and comfortable in a cost-effective and environmentally friendly way. Think of the sun as a massive free heater that can reduce or eliminate paid for heating. Of course a tiny house has the added advantage of being mobile so it can be adjusted to suit season and location. The following are factors to consider when designing a mobile tiny house or any hsoue around the sun.

  • Elongate the home along the east-west axis, to maximise north-facing area. The optimal ratio for north to east should be at least 1:1.5. This is generally the default for a mobile house anyway, we have a ratio 1:2.5. Refer to Tiny House Design 2.0 for current design.
  • Put living areas and frequently used rooms on the north-facing side - of the house to make the most of the heat and light from the sun. Kitchen and living space will receive sun most of the day.
  • Sun-collecting windows face north - they should be within 20 degrees plus or minus of due north to capture a least 6 hours of sun on a sunny winters day. I have modelled the house at 20 degrees from due north but of course this can be adjusted.
  • South-facing windows receive minimal sun and should be relatively small to avoid heat loss but allow for light and ventilation. We have two narrow long windows in the living space which will create a sense of space and let light in. 
  • Properly designed overhangs will limit summer sun, but allow plenty of sun in during winter. Overhangs are good for northerly windows. I have been thinking hard about incorporating an overhang to the north but weight and space compromise this. Instead we are thinking a simple wind/shade sail that can be adjusted for the seasons might work for us.
  • Reduced sized windows west face - to reduce late afternoon overheating and glare. One smaller window on this face should balance view, sun, and thermals efficiency. 
  • Overhangs don't work well on east and west sides as the sun is too low - deciduous trees and movable shades or louvers are better options here. 
  • Ventilation is important for preventing overheating, and is most easily achieved with windows that can be opened, particularly in rooms prone to overheating. You should be able to open a minimum of 30% of your windows. Having windows at opposite ends of the house means we can cross flow ventilation.

Sun Study

I have done a sun study for our tiny house design. I set the location to Napier, New Zealand. This is important as the sun projects at different angles around the globe. The house in ordinated 20 degrees from due north as shown by the compass in the images below. I have taken snapshots of sunrise, midday and sunset to compare the difference on sun angles and orientation. Southward Equinox is the shortest day and the Southern Solstice is the longest. These times do not account for daylight savings and are approximate.

Southward Equinox 6am

Bathroom and kitchen will pick up early morning sun and start heating the house.

Southern Solstice 5am

As we all know the sun rises early and also rises more towards south. 

Southward Equinox 12pm

Sun sits lower in the sky, flooding into windows to warm house on cold clear days.

Southward Equinox 12pm
The sun is very steep and warm at this time of the year - great for solar panels (another blog post). 

Southward Equinox 6pm
Sun sets pretty square to west face.

Southward Equinox 8pm
In the summer the sun will set behind the house on the west and south faces. This time of year it will be important to reduce the late afternoon sun to reduce over heating the glare. 

Its interesting to see how the sun changers over a year. Sun modelling has been fantastic to simulate and consider the design before building takes place. 

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