Transient Air Mixing in High Sidewall Diffusers

Compact duct systems are one of the secrets to building a net zero energy home. In typically built homes, ductwork is installed in exterior walls, the insulation is displaced and energy from the conditioned air is lost to the outside. In compact duct systems, all of the ducts are kept inside the conditioned building envelope (i.e., not in the attic), minimizing the amount of sheet metal used and eliminating ducts in exterior walls. Compact duct systems are 25% less expensive than traditional designs and are much more energy efficient. High sidewall diffusers are the most promising means of delivering air to a compact duct system because they are not blocked by furniture and they provide good mixing of the conditioned air in the space. However, high sidewall diffusers have only been researched in the cooling mode. The use of these diffusers in the heating mode is not well understood, including their effect on smoke detection systems by adequate movement of smoked-filled air. Finding out if these diffusers provide adequate air mixing in the heating mode is essential for compact duct systems to be acceptable to homeowners. We are studying the thermal mixing of warm air using computational fluid dynamics and laboratory and field experiments. This research also involves examining the design and placement of air supply registers and return grilles, which are important features of compact duct systems.