Cathedralized attics in energy efficient homes in hot, humid climates provide a hospitable, performance-enhancing environment for air handlers and ductwork. This is because a well-insulated, airtight building enclosure is constructed at the roof line and indoor temperature and humidity levels are not near outside levels. Although cathedralized attics with space conditioning systems located within them are not typically provided with dedicated supply and return air, it is not clear if more energy would be saved if the space, and the air distribution system in it, were directly conditioned, thereby turning the space into a conditioned mechanical room. Or, would the energy cost of directly conditioning the space negate the possible air distribution system performance benefits that result from the system being in a directly conditioned space?

Research is ongoing at a Building America house built in 2005 in Orlando, Florida that has a cathedralized attic. The attic contains dedicated supply and return air ductwork that can be activated remotely and is alternatively directly and indirectly conditioned for several weeks at a time. Temperature and humidity monitoring sensors within the attic space and the living space below provide comparative information on the conditions within both spaces.

Results of measurements taken during cooling conditions and the analysis of the energy performance of the air distribution system during directly conditioned and indirectly conditioned cases indicate that marginally more energy is used when the cathedralized attic is directly conditioned. When the attic was directly conditioned during cooling, over-cooling occurred periodically in one of the living spaces. Similar circumstances occurred when the attic was directly conditioned during heating.

Presented at Thermal Performance of Exterior Envelopes of Whole Buildings X - December 2007

Units: Dual