HVAC Systems: Humid Climates

In humid climates, two of the functions of the heating, ventilation, and air conditioning (HVAC) system are essential—providing proper dehumidification and positive building pressurization—to prevent moisture problems. Although concepts for dehumidification are being discussed and taught to HVAC designers, the HVAC designer must always consider the impact of part-load conditions on the relative humidity levels in the building. The concepts for providing positive building pressurization are less well understood by the HVAC design community. Pressurization must be looked at in each pressure zone at the exterior of the building as well as from a whole-building perspective to ensure the success of the building.Following a few simple rules when designing HVAC systems for humid climates can help prevent the catastrophic failures seen in such buildings as Florida&s;s Martin and Polk county courthouses in the early 1990s. These buildings suffered rampant mold growth, complaining occupants, and escalating remediation costs because the HVAC system designers did not understand what is required to produce a successful building in a humid climate. Ultimately, the designers and contractors of these buildings were held liable for millions of dollars in remediation costs, which exceeded the original construction costs of the buildings.