Mechanical Air Distribution Interactions with the House System in Hot and Humid Climates

A large and growing body of research has proven that there are important and often dangerous interactions taking place in homes across America. The key element in all of these findings is a new understanding of the pressure differences and the resulting air flows that are occurring in our homes. These powerful driving forces or pressures are caused by the fans in HVAC systems and venting appliances. Other contributory factors are today's tight building envelopes. door closure and badly leaking forced air duct systems. We now know that on average 25%-40% of the air handler fan flow is either coming from, or being lost to, areas outside of the thermal envelope by residential duct systems. My experience in testing and repairing over 1,000 homes in Austin, Texas has confirmed these findings. It has also been shown in tracer gas testing that in most homes the air change rate of the home will double or triple when the HVAC system is in operation thus introducing large amounts of moisture and heat into the house. Another surprising fact is the fact that interior closing doors can cause combustion appliances to experience backdrafting of their combustion by products into the home. This paper will present a review of the basic principles of Mechanical Air Distribution And Interacting Relationship