Annual Energy and Heat Flows in Vented and Sealed Attics--Parametric Study: Climate Zone 2A ✓ Most Recent

Placing ducts in conditioned or semiconditioned space can be one of the most energy-saving as well as potentially cost-effectivemeasures for high-performance buildings. The moisture management in a building with a sealed attic is very different whencompared to conventional vented attics, with respect to the mold and mildew exposure of the occupants as well as maintainingthe structural integrity of the home (Salonvaara et al. 2013). It is also important to fully quantify the thermal benefits of differentadvanced attic systems and then to analyze the applicable moisture strategies for high performance. This paper provides asummary of an exhaustive analysis comparing the energy performance of three attic systems: unvented attic, vented attic, andthe hybrid attic. The computer tool AtticSim (ASTM 2004) was used to simulate vented, sealed, and semiconditioned attics to evaluatethe energy and economic trade-off between sealing the attic as compared to sealing and better insulating an HVAC duct systemcontained in the attic (vented). The duct diameter, R-value of duct and roof insulation, leakage rate of ducts and attics, roof slopeand orientation, attic size, and climate were simulated parametrically to judge the potential for making ducts in attics operateas if they were operating in the conditioned space. More than 250,000 simulations were performed in 33 locations spanningClimate Zones 1 to 6. This paper is focused on the performance of attics in International Energy Conservation Code (IECC)Climate Zone 2A. Unvented attics outperformed the other configurations when simulated with current duct-air sealing technologiesand duct insulation as per the ICC (2015). At the same time, it is also demonstrated that when a better designed, insulated,and air-tight ducts were considered, vented attics can perform as well as the sealed, semiconditioned attic.