Passive Solar Design

Passive Solar Design, Heating, Cooling

Heat and light from the sun is free and renewable. Ironically, the majority of buildings today are not designed to harness this free energy. Instead buildings are often constructed to block sunlight in favour of insulated, opaque partition walls.

Passive solar design refers to the use of the sun’s energy for the heating and cooling of living spaces. In this approach, the building itself or some element of it takes advantage of natural energy characteristics in materials and air created by exposure to the sun. Passive systems are simple, have few moving parts, and require minimal maintenance and require no mechanical systems.

Operable windows, thermal mass, and thermal chimneys are common elements found in passive design. Operable windows are simply windows that can be opened. Thermal mass refers to materials such as masonry and water that can store heat energy for extended time. Thermal mass will prevent rapid temperature fluctuations. Thermal chimneys create or reinforce the effect hot air rising to induce air movement for cooling purposes. Wing walls are vertical exterior wall partitions placed perpendicular to adjoining windows to enhance ventilation through windows.

Key Word(s)
passive solar, thermal mass, orientation, latitude, building form

Details
Passive design is practiced throughout the world and has been shown to produce buildings with low energy costs, reduced maintenance, and superior comfort. Most of the literature pertaining to passive solar technology addresses heating concerns. This information is useful and relevant in our area; however, cooling issues, which are equally important in Austin, are less well documented. Key aspects of passive design include appropriate solar orientation, the use of thermal mass, and appropriate ventilation and window placement.

Consideration of high humidity is a key issue in Austin. For example, a basic passive cooling strategy is to permit cooler night air to ventilate a house and cool down the thermal mass (this can be brick, stone, or concrete walls or floors, or large water containers) inside the house. The thermal mass will absorb heat during the day; however, excessive humidity will reduce the cooling effect from the cooler thermal mass. Interior design elements of a home in our region also play a strong role in the effectiveness of passive cooling. For example, carpets, drapes, and fabric-covered furniture will absorb moisture from humid air, forcing the air conditioner to work harder to remove humidity.

As a design approach, passive solar design can take many forms. It can be integrated to greater or lesser degrees in a building. Key considerations regarding passive design are determined by the characteristics of the building site. The most effective designs are based on specific understanding of a building site’s wind patterns, terrain, vegetation, solar exposure and other factors often requiring professional architectural services. However, a basic understanding of these issues can have a significant effect on the energy performance of a building.

Solar energy in the form of heat and light is freely available in nearly all locations. In regions where heating is required, design for efficient use of passive solar energy. A building must first be oriented properly (See Sustainable Siting) to take maximum advantage of the solar energy. In locales that require air conditioning, the designer should attempt to minimize solar heat infiltration while allowing for maximum daylighting.

Every opportunity should be made to harness “free” solar energy in the form of heat and light. The design team must also pay particular attention to reducing excessive solar heating especially in temperate and hot climates.

Checklist

  • Every opportunity should be made to harness “free” solar energy in the form of heat and light. The design team must also pay particular attention to reducing excessive solar heating especially in temperate and hot climates.

Passive Solar Heating

  • Analyse building thermal-load patterns. Seek strategies that deliver daylight and solar heat when the building requires it.
  • Integrate passive solar heating with daylight design. They are complimentary strategies.
  • Design the building’s floor plan to optimize passive solar heating. Windows should face within 15 degrees of true south to take advantage of solar heating.
  • Identify appropriate locations for exposure to beam sunlight. Shorter occupancy spaces (i.e. atrium, lobby, hallways) can tolerate direct solar gains. Offices where people work for extended periods of time must include measures to disperse direct sunlight and heat (i.e. clerestory windows, light shelves, window tinting).
  • Avoid glare from low sun angles. Be aware of early morning and late afternoon solar exposure that penetrates deeper into interior spaces. Orient work stations north-south so that partition walls block low angled light.
  • Locate thermal mass so that it will be illuminated by low winter sun angles. In cold climates, take advantage of low solar angles when space heating is required in winter. The thermal mass will remain in the shade during summer.

Checklist

  • Analyse building thermal-load patterns. Seek strategies that deliver daylight and solar heat when the building requires it.
    Integrate passive solar heating with daylight design. They are complimentary strategies.
  • Design the building’s floor plan to optimize passive solar heating. Windows should face within 15 degrees of true south to take advantage of solar heating.
  • Identify appropriate locations for exposure to beam sunlight. Shorter occupancy spaces (i.e. atrium, lobby, hallways) can tolerate direct solar gains. Offices where people work for extended periods of time must include measures to disperse direct sunlight and heat (i.e. clerestory windows, light shelves, window tinting).
  • Avoid glare from low sun angles. Be aware of early morning and late afternoon solar exposure that penetrates deeper into interior spaces. Orient work stations north-south so that partition walls block low angled light.
  • Locate thermal mass so that it will be illuminated by low winter sun angles. In cold climates, take advantage of low solar angles when space heating is required in winter. The thermal mass will remain in the shade during summer.

Passive Solar Cooling

In temperate and hot climates, solar heat infiltrating the building has typically been the most costly thing to mitigate (i.e. air conditioning). However, effective passive solar cooling design can eliminate much of this conventional operating cost with proper building design. Passive solar cooling can reduce or even eliminate the need for air conditioning in homes. At its simplest, passive cooling includes overhangs for south-facing windows, few windows on the west, shade trees, thermal mass and cross ventilation. Some of the same strategies that help to heat a home in the winter also cool it in the summer. Consider preventing excess solar heat from entering the building envelope. A variety of design strategies are listed below.
Design buildings for cooling load avoidance. Utilize appropriate window glazing and shading devices to avoid the need for mechanical cooling.

Choose one or more shading strategies including: fixed shading devices as part of building design (porches, overhangs, extrusions), trees or other vegetation that provide seasonal shading, awnings that can be extended or removed, operable shades or blinds. In general, limit east and west glazings to avoid low solar angle exposure.

Consider other cooling strategies including: taking advantage of natural ventilation, radiative cooling in regions that have significant differences in day and night temperatures, ground coupled cooling, and dehumidification in humid climates.

Checklist

  • Design buildings for cooling load avoidance. Utilize appropriate window glazing and shading devices to avoid the need for mechanical cooling.
    Choose one or more shading strategies including: fixed shading devices as part of building design (porches, overhangs, extrusions), trees or other vegetation that provide seasonal shading, awnings that can be extended or removed, operable shades or blinds. In general, limit east and west glazings to avoid low solar angle exposure.
  • Consider other cooling strategies including: taking advantage of natural ventilation, radiative cooling in regions that have significant differences in day and night temperatures, ground coupled cooling, and dehumidification in humid climates.