As you work to manage energy costs by paying attention to the systems in your facility, keep in mind that a number of factors beyond your control will affect the amount of energy you use. Your task is to maintain desired interior conditions, but the exterior factors—climate, topography, and building orientation—are beyond your control.
Climatic conditions will influence a building designer’s choice of building orientation, configuration, and envelope, as well as a building’s energy requirements for heating, cooling, ventilation, and, to a lesser degree, illumination.
Daily or seasonal temperature variations, as well as peak temperatures, will affect the size and selection of mechanical and electrical equipment. Daytime variations are often a result of the topography of a specific building site. For example, a building located at the base of a mountain is likely to have a large range of temperature variations due to different temperature air masses moving up and down the mountainside.
Large variations also occur in desert regions and other areas that have a high percentage of clear skies and sunshine. During the day, the ground heats up from the large quantity of sunlight. At night, this heat is lost because there are few clouds to trap the heat close to the ground.
While such large variations may require the installation of larger electrical and mechanical equipment than would otherwise be necessary, these variations may also provide an opportunity to employ a heating and cooling storage system, such as an active or passive solar heating system, that can reduce energy consumption.
Quantity of Sunlight
The amount of sunshine a building receives is another climatic factor that will affect a building’s energy consumption. In fact, the annual heating energy consumption of two buildings in different geographic areas experiencing similar temperatures but dissimilar amounts of sunshine can vary by more than 30 percent.
Monthly solar loads must be accurately calculated to determine the quantity of sunlight striking a building during different times of the year. Some solar controls include internal or external shading of glazed areas; outdoor cooling ponds; and solar panels for heating or cooling air, heating hot water in residences, or generating power by using photovoltaic cells. These controls can be used so that a building maximizes the sunlight’s heating capabilities during the winter and minimizes them during the summer.
The color of outside surfaces should also be considered. Use dark colors for absorption on north walls or roofs in cold climates and light colors for reflection on roofs in warm climates.
Wind Velocity and Direction
Wind velocity and direction will affect the strategic orientation, configuration, and envelope of a building as well as its energy consumption. Wind disturbs the film of still air that surrounds and insulates a building, thereby increasing heating and cooling loads. Furthermore, wind can evaporate moisture on wet building surfaces, causing the surface to cool to below the ambient air temperature.
In the northern hemisphere, the north and west sides of a building are exposed to the highest winds. Buildings should have their most vulnerable areas, such as entrances and glazed areas, located away from prevailing winds in order to minimize air leakage around doors, windows, and other openings.
If an entrance is constructed to the north or the west, it should be properly shielded from the wind. If not, a combination of high winds and low temperatures during winter months could cause high infiltration, resulting in high energy consumption.
While high winds often result in increased energy consumption, in some locations they might actually reduce consumption if the wind’s natural cooling properties are harnessed and used throughout a building.
In areas where snowfall is heavy and consistent during winter months, snow cover on the roofs of low-rise buildings can act as a natural insulator for buildings constructed to retain it. In addition, the reflection of ground snow on adjacent low buildings may enhance the illumination level of a building and increase the efficiency of solar collectors, reducing the need for artificial lighting.
The topography of a building’s site, which includes natural and man-made features, can affect its energy consumption by diminishing or increasing the effects of the climatic influences previously discussed. The trees surrounding a building, for example, can diminish the intensity of sunlight or decrease the velocity of wind. If located close enough to the building, trees can also modify outdoor humidity in the immediate building area.
Building Orientation and Configuration
The direction a building is facing and its configuration determine how climatic and topographic factors affect building energy consumption. Orientation affects the power required for lighting systems by influencing the amount of ambient sunlight that may be used for indoor illumination. Configuration affects heat gains or losses. A building with a round configuration, for instance, has less surface area than other building shapes and therefore experiences less heat gain or loss than other configurations with equal floor space. A building with a square configuration has less surface area than a rectangular one and likewise experiences less heat gain or loss.
Understanding the external factors that affect interior building conditions will help you as you work to develop an effective energy management program, taking into consideration the demand on building systems and the building envelop.
This article is excerpted from the BOMI International course Energy Management and Controls, part of the SMA® and SMT® designation programs. Sign up for this or other BOMI International classes today and begin to work toward your professional designation. More information regarding this course and BOMI International’s education programs is available by calling 1-800-235-2664. Visit BOMI International’s website, www.bomi.org.