Comparison of mechanical and natural ventilation using long-term evaluation model for indoor air quality, thermal environment, and energy consumption.

There are often tradeoffs among improving IAQ (Indoor Air Quality), maintaining thethermal comfort, and reducing energy consumption for HVAC (Heating, Ventilating, and Air-Conditioning) systems. A prediction model that can simultaneously treat these factors isrequired to realize good design of sustainable buildings. For this paper, a concept of OccupantContaminant Inhalation is used for long-term assessment of IAQ. A long-term evaluationindicator for other factors such as air temperature is also introduced (Occupancy-weightedAccumulated Deviation from thresholds). The paper also describes a long-term simulationmodel for evaluating IAQ, the thermal environment, and energy consumption. The model takesvertical temperature distribution within rooms and unsteady phenomena due to the thermalstorage capacity of buildings into account. Case studies are made using this model to comparethe performance of mechanical and natural ventilation in a normal office space in Tokyo. It isshown that natural ventilation is effective to reduce energy consumption for NAC systems andto improve IAQ while maintaining the thermal comfort when ventilation strategies areappropriate. The proposed design tool will help to create buildings with low energyconsumption without compromising comfort and occupant health.