Capture the Sun; Your House Will Thank You

QUESTION: I am thinking about adding a sun space to my house. How do I make sure it’s energy efficient?

ANSWER: A sun space adds personality to a home. It can be a room or an attached greenhouse designed to capture sunlight. A sun space can have one or more functions--actual living space, a collection point for auxiliary heat or a place for plants.

Designed properly, a sun space can be aesthetically pleasing and useful; it can also reduce heating costs. A passive solar sun space requires no mechanical heating or cooling equipment (hence the term passive) to maintain proper conditions. A few guidelines will ensure it is energy efficient and usable throughout the year.

Things to do

* Choose an area that provides unobstructed solar access during the late fall and winter. Trees or buildings should not block direct sunlight between 9 a.m. and 3 p.m.

* Place the addition on the south side of your house, with the long axis oriented east to west.

* Use double insulated clear glass, low-E glass or argon gas-filled glass.

* Place glass in the vertical position (not tilted). Vertical glass will provide adequate light for most varieties of plants.

* Face glass to the south to allow more sun in than heat out during the heating season. Orient the glass due south or within about 25 degrees of true (not magnetic) south. If you can’t orient south, orient the glass more east than west.

* Use thermal mass to save excess heat for the night time. A concrete floor and a partial masonry wall work adequately in the northwest climate.

* Install eaves or overhangs to shade the glass from the high summer sun. Properly located deciduous trees can work, but they take time to grow. (Don’t use evergreen trees for this purpose. You need trees that drop their leaves, producing unobstructed solar access during the late fall and winter.)

* Insulate the walls on the north, east and west sides, and insulate the roof.

Situations to avoid

Summer overheating and heat loss in the winter drain away comfort and energy. Avoid orienting the glass westward or eastward or tilting the glass. Don’t select glass with a tinted or mirrored finish.

Also, you’ll probably want to stay away from interior blinds or curtains to provide shading. They are expensive and they won’t adequately resolve overheating.

Ventilation

A sun space addition can be open to your home or isolated with walls, doors or windows. Closing off the sun space gives you more control over air circulation. A properly designed sun space normally doesn’t trap heat, and the temperature doesn’t rise above the outdoor air temperature during the summer. Install operable windows to provide natural ventilation in warmer weather. Install an electric exhaust fan to provide occasional forced ventilation.

A well-designed sun space will maximize solar gain in the cool seasons, have a little mass to store any excess energy at night and be comfortable all year round.

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Written by Mark Williams from the Education and Information Network of the Washington State Energy Office.