ABSTRACT

Buildings with mechanical ventilation use fans to supply air to, and exhaust air from, the rooms. Mixed-mode ventilation combines mechanical ventilation with the use of natural driving forces. Mixed-mode systems are either low pressure fan assisted mechanical systems or two mode ventilation systems operating mechanical ventilation or natural ventilation depending on conditions. In commercial buildings the ventilation rates and requirements are usually higher than that in residential buildings. The idea of mechanical ventilation system is that the required ventilation rate can be maintained in all weather conditions without influence of occupants of the building. In mechanical exhaust ventilation systems air is exhausted from the rooms having higher pollutant generation and lower air quality. Mechanical supply and exhaust ventilation provides effective filtering of outdoor air. This has great importance in urban areas with high traffic or industrial combustion loads. Constant air volume systems may be easily combined with natural ventilation through openings resulting as mixed-mode ventilation system.