Sunspace Heat Distribution and Control
When designing a sunspace, two important passive solar design considerations are how heat will be distributed and controlled.
Heat Distribution
Warm air can be blown through ductwork from the sunspace to other living areas. It can also move passively from the sunspace into the house through doors, vents, or open windows between the sunspace and the interior living space.
Strategically placed openings in the common wall can distribute the warmed air from the sunspace to the house by the "thermosiphoning" circulation of the air. In a thermosiphon, warm air rises in the sunspace and passes into the adjoining space through an opening. Cool air from the adjoining space is drawn into the sunspace to be heated.
The minimum opening should be about 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 the sunspace and one low—the minimum area for each opening is approximately 2.5 square feet (0.2 square meters) per 100 square feet (9.3 square meters) of glazing, with 8 vertical feet (2.4 meters) of separation. Again, these are rules-of-thumb that should be refined through computer modeling or confirmed with local experts. An uninsulated masonry wall between the house and the sunspace will also transfer some heat into the living space by conduction.
Climate Controls
Overheating can kill plants and make the sunspace unlivable. To control overheating, some designers place operable vents at the top of the sunspace where temperatures are highest and at the bottom where temperatures are lowest. For times when you are not home to open vents manually, thermostatically controlled motors can be installed to automatically open them.
If passive (i.e., nonmechanical) circulation is not possible or practical, fans with thermostatic controls can be used to circulate air to the rest of the house. Other types of climate controls include window coverings that can be operated with electric timers or sensors.
