A sunspace is a glazed room that is part of or attached to a building but which can be completely closed off from the main occupied areas. They are also commonly called conservatories. Sun enters through equator-facing windows and warms the room. This warm sunspace air is then circulated to the building's interior for heating. Techniques can be employed to store the heat and prevent daytime overheating. One method is to include thermal mass to absorb excess heat during the day and release it at night.

Figure 1 - A typical attached sunspace system with a large glazed room and controlled ventilation into an adjacent room. Modified section through the Simpson-Lee House, by Glenn Murcutt.
The actual residence does not contain an attached sunspace.
Drawn by craines.

Attached sunspaces work in a similar manner to Trombe walls, only the space between the glass and the absorbing surface is so large it is habitable. Basically, very large areas of glazing allow sunlight to directly heat the surfaces within the sunspace. As these surfaces heat up, they impart some of their energy to the air. As this heated air rises, cooler air from the internal space is drawn in through low level vents. This, in turn, draws warm air out of the top of the sunspace through high level vents into the internal space. This convection current continues throughout the day, gently warming the air within the internal space.

Both the warmed air and the direct solar radiation act to heat up the thermal storage wall between the internal space and the sunspace. After sundown, the vents that allow air movement are closed to prevent a reverse cooling convection current from occurring. As the internal space begins to cool, the heat slowly passing through the thick mass wall begins to reach the inside surface, radiating its heat energy for several hours thereafter.

Important Factors

The important considerations in the design of attached sunspaces and conservatories are as follows:

• In very cold climates, double glazing should be considered in order to reduce conductive losses through the glass to the outside.
• The darker the internal surfaces of the sunspace, the more effective the ability of the thermal mass to store heat during the day.
• Care should be taken when populating an attached sunspace with vegetation and pot-plants as their foliage can significantly obscure and shade the main floor and wall, reducing the effectiveness of the system to absorb and conduct heat though at night.

Variations

Once again, similar to a Trombe wall, it is possible to use a water-wall in place of a thick masonry wall. In this case, heat is conducted and convected from outside to inside via the water wall, not by direct air exchange. Due to convection currents within the water itself, heat is transferred through much quicker than a masonry wall which relies solely on conduction.

Summary

Sunspaces are very popular passive design elements because they expand the living areas of a building. Night-time heat loss is not as critical in the sunspace as with direct gain systems since it can be closed off from the rest of the building. However, night insulation or double-glazing is recommended if the sunspace serves as living space after sundown.

Related Links

Sunspace Basics

http://www.eren.doe.gov/erec/factsheets/sunspace.html