Functional Sun Space Can Be Energy Efficient
Q. I am thinking about adding a sun space to my house. How do I make sure it’s energy efficient?
A. A sun space can be a nice addition 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, it can be aesthetically pleasing and useful, while reducing your heating costs. Sun space design is a combination of art and science. 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.
Among the elements of an energy-efficient sun space is unobstructed solar access during the late fall and winter months. No trees or buildings should block the direct sunlight from 9 a.m. to 3 p.m. Place the addition on the south side of your house with the long axis oriented east/west.
Use double insulated clear glass. Low-E glass or argon gas-filled glass is OK. Place glass in the vertical position (not tilted). Vertical glass will provide adequate light for most plant applications. Face glass to the south. South-facing glass will 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 take time to grow. (Don’t use evergreens for this purpose; you’ll still need unobstructed solar access during the late fall and winter.)
Insulate the walls on the north, east and west sides, as well as the roof.
Summer overheating and heat loss in the winter are comfort and energy losers. Avoid orienting the glass westward or eastward, putting glass in the roof, tilting the glass, selecting glass with a tinted or mirrored finish, or using interior blinds or curtains to provide shading (they are expensive and will not adequately resolve overheating).
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 or rise above the outdoor air temperature during the summer. Operable windows can provide natural ventilation in warmer weather. An electric exhaust fan can be installed 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. For more information, call the Energy Hotline at (800) 962-9731 (or 324-7980) for the following free factsheets: Designing and Building a Solar Greenhouse or Sun Space, and Passive Solar Design for Northwest Homes.
Mark Williams assisted with the writing of this column.
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