Modeling to predict positive pressurization required to control mold growth from infiltration in buildings in a hot and humid climate

Commercial buildings in humid regions of the United State are generally designed to operate at a positive pressure to limit mold growth, material deterioration and other condensation related problems from infiltration in hot and humid climates. This paper combines existing models of infiltration and mold growth to predict the influence of pressurization level on the risk of mold growth. Walls are treated differently depending on their height and the direction they face. Local weather data are utilized to generate the outside pressure field. Temperature measurements performed on an actual building are applied to a multi-layer envelope temperature prediction model, used to simulate the performance of three different envelope constructions. Annual change in mold index is calculated for three humid locations for one construction type and for two other construction types in one location. The simulated results indicate that for a 22 °C indoor temperature set-point, 3 m high walls facing all directions in an unpressurized building in College Station, TX, will experience an annual increase in mold index. However, 1.5 Pa positive pressurization results in a negative annual change in mold index for all walls that should theoretically eliminate the long-term risk of an increasing mold index on all walls. The model also indicates that only 1 Pa pressurization is required to produce negative annual change in mold index if the same building is moved to Fort Worth, TX and no pressurization is required in Atlanta, GA with a 22 °C indoor temperature set-point.