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- Climate & Site Analysis
- Building Energy Fundamentals
- Building Envelope
- Passive Design Strategies
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Humans first created shelters to provide thermal comfort and protection from natural elements, and this still remains a primary objective of buildings. The building envelope is the physical separator between the interior and exterior of a building.
Components of the envelope are typically: walls, floors, roofs, fenestrations and doors. Fenestrations are any opening in the structure: windows, skylights, clerestories, etc. When designing the building envelope, knowing some fundamentals of building materials and heat transfer will help you make the right trade-off decisions.
Envelopes for Climate Types
Arid Climate Envelope
The City Palace in Jaipur, India. Photo: Jeremy Faludi |
Arid climates are very dry, and usually hot, but they often have large swings of temperature from day to night. Thus thermal mass on the outside of the building is the most crucial design strategy to even out such temperature swings. For consistently hot locations, it also helps to have high ceilings, shaded breezeways, light colors, and daylighting via reflected light (not direct sun), such as in this audience hall in the Jaipur city palace. Courtyards with natural ventilation and pools or fountains can provide evaporative cooling as well. |
Tropical Climate Envelope
A traditional home in Papua New Guinea. Photo: Jeremy Faludi |
Tropical climates are hot and humid. Therefore, keeping the heat of the sun off is the top priority, as well as maximizing ventilation—essentially a reflective insulated roof with walls that pass breeze but not rain is ideal. This traditional Papua New Guinean home’s thick light-colored thatch roof keeps out the sun’s heat, while open eaves and porous bamboo slats for walls and floor maximize natural ventilation. The materials are all low-mass to avoid condensation and mold growth, which can happen with high-mass materials in humid climates. (Note: Jalousie windows are found in the tropics, but are not as common elsewhere, because they are so porous to breezes.) |
Cold Climate Envelope
A vernacular-design cabin in Finland. |
Cold climates have many more heating degree says than cooling degree days. Thus maximizing insulation is the key to keeping warm, as well as using windows for solar gain on thermal mass inside the building envelope (not outside as in arid climates). Part of having effective insulation in cold climates is an air-tight envelope, avoiding infiltration. This Finnish cabin has very few and very small windows except on the south side, to maximize solar gain while minimizing losses elsewhere. Before modern insulation, thick solid log walls such as these provided better insulation than board walls could. |
Mixed Cold / Hot Climate Envelope
The Aldo Leopold Center in Baraboo, Wisconsin. Photo: Jeremy Faludi |
Many “temperate” inland climates actually have two extremes--cold in winter, hot and humid in summer. Flexibility is the key to designing for these climates. The Aldo Leopold Center in Wisconsin, first building to be LEED certified as carbon-neutral, uses deep overhangs to allow low winter sun in through the windows to heat up a high-mass concrete slab inside, while blocking high summer sun. It also uses a light roof and darker walls to repel summer sun but absorb winter sun. Extra insulation retains heat in winter, but operable windows passively cool it in summer. |
Envelope Energy Flows
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WallsUnderstanding and optimizing the heat transfer through the walls is important in high performance building design. Using thermal mass and insulation to your advantage with passive design strategies can help reduce the amount of energy that active systems need to use. |
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WindowsHeat flow through windows and skylights requires special attention for several reasons. Despite dramatic improvements, these transparent/translucent envelope components still usually have the lowest R (highest U) of all components of an envelope.
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Aperture Placement & AreaAperture placement and area are important because strategic use of windows and skylights can help you achieve thermal and visual comfort passively, saving both energy and money. |
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Shading & Redirecting SunlightShading is an important set of strategies for visual comfort and thermal comfort. As such, successful shading is measured by the overall success of visual and thermal comfort. |
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Infiltration & Moisture ControlWater also moves through building envelope assemblies—in both liquid and vapor states. The focus here is upon water vapor movement. Water vapor will often need to be handled by a climate control system through the use of energy (termed latent heat). |
Links and References
- Information from tables in ANSI/ASHRAE/IESNA Standard 90.1-2007
- This document of climate data was made for designers to inform energy-conscious design decisions. Climate Zones are summarized, and suggestions are given for passive design strategies appropriate to each climate.
- This interactive page allows you to view building examples tied to passive design strategies for locations within the US.
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