Natural ventilation

Abstract

Proper utilization of natural ventilation can provide large ventilation rate without the consumption of energy. This chapter introduces the prediction, measurement, form, and design of natural ventilation along with an example. The prediction model includes single-zone model, multi-zone model, and CFD model, among which CFD model is the most frequently used tool to analyze airflow distribution inside or around buildings. Porous screens fixed on openings to prevent insects and particulates could increase the airflow resistance through openings, resulting in great reduction in ventilation rate. Tracer gas methods are considered as the most commonly utilized method to measure ventilation rate, especially the tracer gas concentration decay method. As natural ventilation is driven by wind or buoyancy, the commonly used natural ventilated building form includes wind- driven ventilation form, buoyancy-driven ventilation form, and the combination of those two. In addition, measures which can be used to enhance natural ventilation performance such as atrium ventilation, ventilation cap, and solar chimney are also involved. A general procedure of natural ventilation design includes architectural plan, system layout, component selection, vent sizing, control strategy development, and detailed design drawing. The opening size is calculated based on factors such as certain geometry, climate, and building's configuration. The methods of opening size calculation consist of direct methods and indirect methods. Direct methods are derived from simple buildings where the ventilation rate is a simple function of the governing parameters. Indirect methods try different opening size combinations and identify the best one based on network models. Besides, an existing architecture example and its natural ventilation performance are also introduced.