Passive Solar Design Information
By Colin Szasz


Passive solar buildings are designed to take full advantage of the energy provided by the sun to reduce energy consumption and carbon dioxide emissions, and to conserve non-renewable fossil fuels.  A passive solar building uses no moving or mechanical parts for heating or cooling; it relies entirely on the natural air flow created by the heating of the air by the sun's energy, and by the heat storage capacities of large masses.  This is in contrast to active solar buildings which rely on pumps and fans to control and distribute the sun's energy.

How Passive Solar Buildings Work

The principle behind passive solar heating is very simple: use the sun to heat a large mass which will slowly realease the heat energy it has stored once the surrounding air begins to cool.  The larger the mass, the more heat stored.  The challenge in desiging a passive solar building is to evenly distribute the stored heat and to control it so that that building is neither too hot (during the day) or too cold (at night).  There are three basic design types to consider in passive solar construction: Direct Gain, Trombe Wall, and Isolated Gain.  In all designs, there are some common features that must be incorporated.  The building should be aligned on an east-west axis, and the majority of its windows should face south.  South facing windows must be provided with some sort of sun shade for the summer when heating is not required; usually extending the eves is sufficient as this allows the lower winter sun to enter, but blocks the higher summer sun.  Spaces requiring the most heating and lighting should be on the south face of the building, while spaces requiring less heat and light can be kept on the north face.

Direct Gain

In a direct gain passive solar building, the living space serves as the heat-storage mass.  Floors and walls are heated by the sun during the day, and then slowly release the stored heat at night.  Windows face south to catch the sun, and should be double glazed to prevent excessive heat loss at night.  Storage masses should be isolated from the outside and properly insulated to prevent heat loss via conduction to colder masses like the ground.

Trombe Wall

Trombe wall systems, also known as indirect gain systems, use the same principle as direct gain systems, but instead of directly heating the occupied space, heat from the sun is collected by the storage mass which it then transfers to the space.  The storage mass is located directly behind a large, glazed, south-facing wall.  During the day, openings in the Trombe wall allow heated air from the cavity to flow into the room and cool air from the room to flow into the cavity where it is heated.  At night, the vents are closed, and the heat stored in the mass radiates into the room.  Often, a curtain is pulled across between the storage wall and the glazing to prevent loss of heat to the outside.  The storage wall is generally stone or concrete, but can also be large containers of water (water storage wall).

Isolated Gain

Indirect gain passive solar systems are the most common type of passive solar heating that is applied to an existing building.  The system consists of a solarium or greenhouse attached to the outside of the building.  The sun heats the air inside the solarium during the day and the air circulates through vents in the wall between the solarium and living area.  The sun also heats the heat storage wall, which radiates heat into both the living area and the solarium after the sun goes down.  This system is less effective than the previous two systems as heat is lost to the solarium, but it is the easiest modification to make to an exisiting building to improve its heating efficiency.  The solarium works as an extra living space all year round and is perfect as a greenhouse for growing plants outside of the regular growing season.

Page 2: Examples, Links and more...

Passive Solar Demonstrator

SolarPlex: The Passive Solar Building

U2 Winter