A study on variation laws of infiltration rate with mechanical ventilation rate in a room

Mechanical ventilation system is commonly used or recommended to supply the outdoor fresh air for both centralized and non-centralized air-conditioning buildings. ASHRAE requires a positive pressure (i.e., zero infiltration rate) for mechanically ventilated rooms. In fact, positive pressure is difficult to be maintained under poor building airtightness or low mechanical ventilation rates. When the positive pressure is not achieved, the existence of air infiltration brings two problems-the outdoor air pollutants infiltrating indoors and the excessive fresh air cooling/heating load. In order to solve the above problems, air purifiers can be used to remove the indoor pollutants, and the mechanical ventilation rate should be reduced to prevent the excessive ventilation. Therefore, in order to determine the Clean Air Delivery Rate (CADR) for the air purifier and to calculate the amount of mechanical ventilation that should be reduced, the influence of mechanical ventilation on the room infiltration rates must be figured out. This study investigates the variation laws of the infiltration rate with the mechanical ventilation rate, and then theoretically deduces the relational expressions between the two rates for stack effect and wind dominant ventilation models. The theoretical derivations were validated by tests in actual rooms. From a practical perspective, this study can be used to improve the indoor environment and ventilation rates for mechanically ventilated rooms, demonstrated by the case study.