December 12th, 2017
Adding outdoor air in hot, humid climates causes moisture problems, right? The answer is sometimes. It all depends on the condition of the house before outdoor air is added. In fact, most houses in hot, humid climates are over-ventilated due to duct leakage and induced air change from internal air pressure effects. Outdoor air is added to a building via a controlled ventilation system. What isn’t controlled is the air change created by wind effects, stack effects and pressure effects caused by the operation of the HVAC system. In most houses, these uncontrolled effects typically are larger than the desired controlled ventilation.Adding outdoor air only makes a bad situation worse. The desired controlled ventilation is quantified here as: 7.5 cfm/person + 0.01 cfm/ft2 of conditioned floor area. Occupancy is defined as the number of bedrooms + 1