Building Orientation and Energy Efficiency, Part 1
Mechanical systems consume a lot of energy in buildings-approximately 35% of a building's total energy use. While HVAC equipment is becoming more efficient, the main strategies that can reduce building energy consumption start at building planning and siting.
There are four major categories for climatic regions: hot-arid, cold, temperate, and hot-humid. Each of these regions offers a unique set of climate conditions when designing a building. Regarding the design of mechanical systems, these regions determine if the building needs more heating, more cooling, more or less humidification, or a balanced system. Not understanding this and designing a building without considering its integration with the climate could potentially create an environment that is inefficient and more taxing on the environment and resources.
Designing an efficient building begins with the building site. One of the first steps that the designer should consider is the climatic region of the project, as it can affect the building form depending on the particular region.
In cold regions, the concern for building design is the loss of heat as well as infiltration through the building envelope. Building form should be compact to minimize the surface area and should be oriented to allow for the maximum exposure to solar radiation.
Temperate regions favor a building that is elongated in the east-west axis allowing for maximum solar exposure in the cooler season while employing shading devices to keep out the hot summer sun. This introduces the natural heat of the sun during the times of the year when it is needed and keeping it out when it is not needed-designed using the solar angles of the sun determined by the solar path. The building orientation for this region minimizes exposure on the east and west facades, which are harder to control with shading, and gains are far greater in summer months.
Hot-arid regions suffer from exposure to hot air and harsh sun. In these climates, the building should be well-shaded (not only through shading devices but vegetation, if possible). Inner courtyards are an effective design feature that may employ water features to promote evaporative cooling as the wind travels over them creating cooler air that enters adjacent building spaces. As an aside, what I find particularly interesting about this methodology is that it can be found back in ancient times. Windcatchers were prominent in desert regions, and this passive strategy is still relevant today.
Lastly, there are hot and humid regions. For these regions, like temperate regions, buildings are elongated in the east-west axis reducing the east and west facade exposure. Shading devices are used to reduce solar heat gain. Additionally, the incorporation of inner courtyards promotes the movement of air through spaces providing cooling through evaporation and making the hot air more comfortable with air movement. A schematic of this orientation is given in the above figure.
While there are other passive strategies that can also reduce the need for mechanical systems, these focus on integrating the building with the climate for determining site strategies. Part 2 on this topic covers the location of a building vertically regarding climatic regions.
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