Air Ducts: Flow and Thermal Performance

An important part of HVAC design involves distributing air to meet the heating and cooling loads of a house, usually calculated for a specific design load day. Improving home performance involves increasing air sealing and insulation levels of the home, leading to loads that are lower and less need for air volume to condition the home. This session will discuss air distribution basics and the difficulty of delivering the design volumetric flow rate of air at the desired temperature. We will discuss the needs for insulating ducts, both from a thermal and an acoustic performance need. The relevant parameters that need to be delivered by the system, including proper air temperature at the supply, surface temperature above the dew point in cooling mode, and reduce heat gain and heat loss through the duct to install smaller equipment and to save money, will all be discussed. We will also discuss types of insulation, including buried ducts and reflective insulation, and the code requirements.