Building Orientation and Energy Efficiency, Part 2
Part 1 of Building Orientation and Energy Efficiency examined the role of building siting and passive strategies according to the major climatic regions. As a recap, those four major climatic regions are: cold, temperate, hot-arid and hot-humid.
We covered the orientation in plan regarding sun exposure and internal heat gains for the benefit (or detriment) of the building. In addition to location in plan on the site, the vertical orientation of a building-especially on a hill-is also as important.
Air moves with temperature and terrain. Different terrains channel the wind in varying paths. These-along with the climate regions-create microclimates, which are essentially the climates of the immediate site based on a very local set of conditions. Besides the terrain channeling or dispersing/moving wind in unique ways, we must also recognize how temperature affects air movement.
Hot air rises because it is less dense than cold air. During the day, air moves over land and through valleys and rises as the sun warms it. Because of this, air moves uphill in valleys throughout the day. As that air cools during the evening and night, the direction reverses as the land cools. This is due to the loss of heat in the air resulting in the air flowing down the valley walls and settling in the valley floor, only to start the process again once when the sun comes up.
The temperature changes in the air and land can create different effects throughout the day and in different seasons. For example, in a cold climatic region, buildings placed on the tops of hills (especially within narrow valleys) should be avoided, especially without a windbreak. This is because of the cold winds to which the building would be exposed in those locations. Assuming conventional construction (not air-tight or similar), cold air can infiltrate a building and introduce cold air into a warm interior, making it inefficient to heat the building on the interior (cold climates need higher internal heat gains as they are heat dominated). Additionally, buildings should not be located at the bottom of a hill, where cold air can pool in valleys, etc. for the same reasons.
Buildings in hot-humid climates are often lifted off the ground to promote air movement around and through them for natural ventilation and to keep them away from the humid ground covered in vegetation.
Buildings in hot-arid climates benefit from being located at the bottom of a hill/valley because of the pooling of cooler air and the potential of shadows from the valley walls that may block harsh sun.
Often, when siting buildings for construction, the solar path takes the dominant priority. However, siting in regard to the environment, is complex. Sun and shading are two factors. Wind movement and terrain profile are equally as important in considering the factors that can affect a building's performance.
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