Using Natural Ventilation | |
Natural air movement is created by two key forces: thermal effect and wind. Thermal effect It's the inherent property of warm air to rise. A well-designed system takes advantage of that movement in two ways: First, since warm air rises, an effective system will include exhaust vents at or near the ridge. That placement allows the hottest air to be removed from the attic most efficiently. Second, the thermal effect creates a natural circulation of air, because as warm air rises, cooler air falls. A well-designed system assists this momentum by placing intake vents at the lowest point in the attic, typically in soffit. The cooler air entering these vents (cooler as compared to the attic air) speeds this circulation of air. Wind By itself, however, thermal effect cannot create the high volume of air movement needed for effective ventilation. That's why the influence of wind is the key element in the design of a non-powered ventilation system. Wind, after all, is a natural flow of air. So when designing a ventilation system, you want to make the wind work to your advantage. To use the power of wind, you have to understand how wind force affects ventilation. It isn't the velocity of the wind by itself that causes air to move through an attic. Instead, it's the wind's speed as it moves against and over a home's exterior surfaces. A wind-driven flow of air creates areas of positive and negative air pressure. Positive pressure forces air into the attic, while negative pressure draws air out. Source: Air Vent Inc. A Certainteed Company Reprinted with permission, HouseNet, Inc. |