Dilution ventilation, or general ventilation, introduces fresh outdoor air throughout an occupied space to reduce contaminant concentrations through mixing rather than capturing pollutants at their source. This approach assumes contaminants distribute evenly and relies on ventilation rate to achieve acceptable air quality. It works effectively for spaces with low emission rates but performs poorly where concentrated pollution sources exist.
Operating Principles and Applications
Dilution ventilation supplies conditioned outdoor air uniformly via ceiling diffusers or displacement ventilation systems, allowing contaminants to distribute throughout the space and exhaust through return vents. Required ventilation rates depend on contaminant type and acceptable concentration limits. Offices, classrooms, and typical commercial spaces use dilution ventilation as their primary air quality strategy. The method requires higher total ventilation volumes compared to source control approaches, increasing energy costs.
Limitations and Effectiveness
Dilution ventilation cannot effectively control highly toxic or odorous emissions and performs poorly when pollution sources remain localized. Effectiveness decreases with poor air distribution patterns or dead zones where air stagnates. Modern practice combines dilution ventilation with source control and local exhaust systems for spaces with identified emission sources. ASHRAE standards recommend dilution ventilation complemented by source capture for laboratories, kitchens, and manufacturing areas to achieve both energy efficiency and adequate protection.