Can passive solar heating effectively warm underground spaces?

Underground Space Thermal Mass

When designing an underground space for passive solar heating, it’s essential to consider the thermal mass of the structure. Thermal mass refers to the ability of a material to absorb and release heat. In underground spaces, thermal mass can be achieved through the use of materials like concrete, brick, or stone. These materials can be used to line the walls and floors of the space, absorbing heat from the sun during the day and releasing it at night. For example, a 4-inch thick concrete wall can store up to 2,400 Btu of heat per square foot, which can provide warmth for several hours after sunset.

Insulation and Air Tightness

Proper insulation and air tightness are crucial for maintaining a comfortable temperature in an underground space. Insulation can be achieved through the use of materials like foam board, fiberglass, or spray foam. In underground spaces, it’s essential to insulate the walls, floors, and ceilings to prevent heat loss. A well-insulated space with a low air leakage rate can retain up to 90% of its heat, reducing the need for supplemental heating. For example, a 1-inch thick layer of foam board insulation can reduce heat loss by up to 50%.

Trombe Walls and Shading

A Trombe wall is a type of passive solar heating system that involves building a south-facing wall with a high thermal mass material, like concrete or brick. The wall is designed to absorb heat from the sun during the day, which is then stored in the thermal mass and released at night. To maximize the effectiveness of a Trombe wall, it’s essential to ensure that it receives direct sunlight during the winter months. However, excessive sunlight during the summer months can cause overheating, so it’s essential to provide shading for the wall during this time. For example, a 20-foot wide Trombe wall can absorb up to 20,000 Btu of heat per hour during peak sunlight hours.