Thermal Performance of Building Envelope Details for Buildings in (ASHRAE RP-1365)
The reduced thermal resistance due to thermal bridging through steel and concrete framing can have a significant impact on the whole building energy performance. Uncertainty about the thermal performance of the building envelope can lead to inefficient design of HVAC systems, building operation inefficiencies, inadequate condensation resistance at intersections of components and compromised occupant comfort. ASHRAE 1365-RP‘s objective was to provide thermal performance data of 40 common building envelope details for mid- and high-rise construction. The goal of the project was to develop procedures and a catalogue that will allow designers quick and straightforward access to information but with sufficient complexity and accuracy to reduce uncertainty in the thermal performance of building envelope components.
Modeling for this project was done using a three-dimensional finite element analysis heat transfer software package by Siemens PLM Software; FEMAP and Nx, with Maya‘s TMG thermal solver. The ability of the software and techniques used to predict conductive thermal performance of building envelope details containing high conductivity (non-insulating) thermal bridges was demonstrated by calibrating and benchmarking against measured public-domain thermal performance data and deterministic analytical solutions. Validation exercises in ISO standards were modeled to demonstrate that the TMG solver will yield high precision results for well-defined problems. Numerous guarded hot-box test measurements, 29 in total, were compared to simulated results. Good agreement between simulated and measured thermal performance for both steady-state and transient conditions was found. Sensitivity analysis showed the importance of assuming appropriate values for contact resistance particularly between steel flanges and sheathings when modeling steel framed assemblies.
The catalogue of 40 building envelope design details was developed based on a set of generic and common interface details suitable for mid- and high-rise construction. The objectives of the catalogue are to: be relevant to ASHRAE/IES Standard 90.1, be relevant to existing and future building stock, represent both high thermal performance envelopes and standard building practice, and to represent typical interior finishing and cladding systems and attachment methods. Selection of details gave high priority to details that have significant thermal bridges, particularly the ones that need three-dimensional analysis, and with a focus on details excluding those already addressed in ASHRAE publications.
Date Published: July 6, 2011