5.2 Passive solar design for buildings and landscapes

Passive solar design harnesses the sun's energy to heat and cool buildings naturally. This approach maximizes energy efficiency by strategically positioning structures, using thermal mass, and incorporating smart glazing techniques. It's a key component of sustainable architecture and landscape design.

In this section, we'll look at how passive solar principles can be applied to both buildings and outdoor spaces. We'll cover solar collection, thermal regulation, and site-specific factors that influence design choices. Understanding these concepts is crucial for creating energy-efficient, comfortable environments.

Solar Collection and Storage

Solar Orientation and Glazing

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• Solar orientation refers to the positioning of a building or landscape to maximize solar gain and minimize heat loss
  • Optimal orientation varies by latitude, but generally involves facing the longest side of the building towards the equator (south in the northern hemisphere, north in the southern hemisphere)
  • Glazing, such as windows and skylights, should be strategically placed on the equator-facing side to allow for maximum solar gain during colder months
• Glazing materials and technologies can enhance solar collection and regulate heat transfer
  • Double or triple-paned windows with low-emissivity (low-E) coatings and inert gas fills improve insulation and reduce heat loss
  • Selective surfaces on glazing can absorb and transmit solar radiation while minimizing heat loss through re-radiation

Thermal Mass and Trombe Walls

• Thermal mass refers to materials that absorb, store, and slowly release heat energy, helping to regulate indoor temperatures
  • Common thermal mass materials include concrete, brick, stone, and water
  • Thermal mass is most effective when placed in direct sunlight, such as on the floor or walls of a sun-facing room
• A Trombe wall is a passive solar design feature that combines thermal mass and glazing to collect and distribute heat
  • Consists of a thick, south-facing masonry wall (thermal mass) with a glass or plastic exterior (glazing) and an air gap in between
  • Sunlight passes through the glazing, heating the masonry wall, which then slowly releases the heat into the interior space
  • Vents at the top and bottom of the Trombe wall can be opened to allow for convective heat transfer and air circulation

Sunspaces and Greenhouses

• A sunspace, also known as a solar room or solarium, is an enclosed space attached to a building that is designed to collect and store solar energy
  • Typically features large areas of glazing, thermal mass flooring, and operable vents or fans for heat distribution
  • Can serve as a living space, greenhouse, or buffer zone between the outdoors and the main building
• Greenhouses and conservatories can be integrated into passive solar design to provide additional growing space and heat collection
  • Attached greenhouses can be designed to share heat with the main building through vents, fans, or thermal storage systems
  • Freestanding greenhouses can be oriented and glazed to maximize solar gain and minimize heat loss, using thermal mass and insulation to regulate temperatures

Thermal Regulation

Insulation and Earth Sheltering

• Insulation reduces heat transfer between the interior and exterior of a building, helping to maintain comfortable temperatures and reduce energy consumption
  • Common insulation materials include fiberglass, cellulose, foam, and natural fibers like wool or straw
  • Proper insulation in walls, roofs, and foundations is crucial for effective passive solar design
• Earth sheltering involves using the stable temperatures of the soil to regulate indoor temperatures
  • Buildings can be partially or fully buried in the ground, or built into a hillside (bermed) to take advantage of the earth's insulating properties
  • Earth-sheltered homes require careful design considerations for waterproofing, drainage, and ventilation

Shading and Natural Ventilation

• Shading devices help to prevent overheating during warm months by blocking or reflecting direct sunlight
  • Overhangs, awnings, and deciduous trees can provide seasonal shading, allowing solar gain in winter while blocking sun in summer
  • Adjustable shading devices, such as louvers or shade sails, can be used to regulate solar gain throughout the day or year
• Natural ventilation uses air pressure differences and wind to cool and freshen indoor spaces without mechanical systems
  • Cross ventilation is achieved by placing openings (windows, doors, vents) on opposite sides of a room or building to encourage air flow
  • Stack ventilation relies on the natural buoyancy of warm air to draw cool air in from lower openings and exhaust warm air through higher openings (clerestory windows, cupolas)

Site-Specific Considerations

Microclimates and Local Factors

• Microclimates are local atmospheric conditions that can differ significantly from the surrounding area due to factors such as topography, vegetation, and urban development
  • Understanding and designing for microclimates can help optimize passive solar performance and occupant comfort
  • For example, a south-facing slope may have a warmer microclimate than a north-facing slope, allowing for greater solar gain and extended growing seasons
• Other site-specific considerations for passive solar design include:
  • Prevailing wind directions and speeds, which can influence natural ventilation and heat loss
  • Surrounding vegetation and landscaping, which can provide shading, wind protection, and evaporative cooling
  • Adjacent buildings and structures, which can cast shadows or reflect sunlight
  • Local climate data, such as temperature ranges, solar radiation levels, and degree days, which inform design decisions and energy modeling