Modeling for Underfloor Air in EnergyPlus

If you don't already know about technical briefs from California's Public Interest Energy Research Program (PIER), you should (PIER's web presence has been absorbed into a larger site on research and development). The folks at PIER research various topics related to energy efficiency, and come out with some great briefs that are published through ESource.

The most recent of these launches a useful plug-in for the U.S. Department of Energy's EnergyPlus modeling software. The plug-in allows a designer to model the performance of an underfloor air distribution system. Until now, these systems have not been accurately represented in energy models because of lack of data and the way the modeling software accounts for air flow.

PIER is touting three features of the new plug-in, which is based on several years of research and data collection.

•Improved representation of room air stratification--This allows the modeling software to divide a room into two temperature zones, a lower, occupied zone and an upper, unoccupied zone. The software analyzes where the separation between these zones will end up based on assumptions about the air distribution system and also takes heat sources such as computers and other equipment into account.

•Detailed plenum modeling--Based on data collected by PIER about various plenum configurations and materials, the plug-in can account for heat flow through the plenum from the slab and floor panels.

•Additional HVAC models--The plug-in allows a designer to model the use of two HVAC elements commonly used with underfloor air distribution systems: a variable-speed fan coil unit and a return-air bypass arrangement.