Passive solar systems structures are conceptually simple but sunspace designers and builders must pay close attention to details to ensure maximum performance and reliability of the structures.
Computer software is now available to help design and establish criteria for specific projects such as passive solar sunspaces. This software makes it relatively easy to avoid making uninformed, potentially expensive and disappointing decisions on a sunspace addition. Some sources for software are identified in the Source list at the end of this publication.
A sunspace facing south. Because solar south is ideal, but 30 degrees east or west of due south is acceptable. If your project is a retrofit parts, consider how the new addition will look at the southern side of the house. If the south side facing the street, the design must be well integrated in the home country to avoid a “tacked-on” look. And you have to protect your family’s privacy. If the south side of the house faces the backyard, privacy may be less of an issue.
When the sun is low in the sky in winter, any restriction of 10 feet (3 meters) high within 15 feet (4.6 meters), in the south windows is likely to block solar heat. If sunspace be shaded only in the early morning or late afternoon, there is no greater cause for concern. However, it is important that the room receives direct sunlight between 10:00 and 3:00 You shall not plant trees near the south windows, and seriously consider removing existing trees from the area. Contrary to previous opinion, even deciduous trees that lose their leaves in winter are able to block the sun. Indeed, a mature, well-deciduous tree will display more than 40% of winter sunlight passes through its branch structure.
If you have a choice, find sunspace the walls of the house serve as one or both end walls of sunspace (to reduce heat loss) and is adjacent to kitchens, dining rooms, children’s play rooms and family living areas occupied during the day and early evening.
In northern latitudes, the sun is much lower in the sky in the winter than in the summer. For this reason, vertical glazing receives much more solar gain in the coldest part of the year. Sloped glazing takes in the most solar radiation in the summer.
Warm air is blown through ductwork to other living areas. It can also move passively from sunspace into the house through doors, vents or open windows between sunspace and interior accommodations. Strategically placed openings in the common wall may distribute heated air from sunspace to the house with “thermosiphoning” circulation of air. In a thermosiphon, warm air rises in sunspace and passes into the adjacent compartment through an opening and cold air from the adjacent compartment is drawn into the sunspace to be heated.
The minimum opening shall be approximately 8 square feet (0.7 square meters) per 100 square feet (9.3 square meters) of glazing area. If the design calls for two openings, one high in sunspace and a low minimum area of each opening is approximately 2.5 square feet (0.2 square meters) per 100 square feet (9.3 square meters) of glass panes, with 8 vertical feet (2.4 meters ) of separation. Again, these are rules of thumb to be refined by computer modeling and confirmed by local experts. An uninsulated masonry wall between the house and sunspace will also transfer some heat to the living space by conduction.
Sunspaces incorporate thermal mass to absorb solar heat. Solar-heated air can then be used to heat the house, either passively through openings in the common wall or by blowing through ductwork into other parts of the house.
Although the sloped glazing collect more heat during the winter, many designers prefer vertical glazing or a combination of vertical and sloped glazing. Sloped glazing loses more heat at night and can lead to overheating in warmer weather. Vertical glazing for maximum gain in the winter when the angle of the sun is low and less heat gain as the sun rises from its summer Zenith. A well-designed overhang may be all that is needed to shade the windows in summer. Compared with sloped glazing, vertical glazing is cheaper, easier to install and insulation, and less prone to leaking, fogging, breaking, and other glazing failures. Vertical glazing is often more aesthetically compatible with the design of existing dwellings.
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