An Empirical Validation of the ‘AccuRate’ Software Envelope Model in an Australian Cool-temperate Climate
Authors: Dewsbury, Mark; Fay, Roger
In 2003, the Building Code of Australia introduced its first thermal performance requirements for residential buildings. It mandated a minimum performance rating of 4 Stars when assessed by approved rating methods. This requirement has been progressively increased to 5 Stars in 2006 and 6 Stars in 2010. While the introduction of a 4 Stars requirement had only a minor impact on construction practices, the move from 4 to 5 and then 5 to 6 Stars has forced considerable change, especially in the use of timber platform floors in cool-temperate climates. The adoption of the prescribed energy efficiency measures in the National Construction Code (previously known as the Building Code of Australia) raised concerns from industry and manufacturing groups, as to the accuracy of the simulation method when compared to the actual thermal performance of residential buildings. Both industry and government recognised the need to validate the National House Energy Rating’s (NatHERS) benchmark software ‘AccuRate’. The software ‘AccuRate’ has been developed over time by the CSIRO and has evolved from a design tool to a regulatory tool.
As a result, the School of Architecture & Design and its research arm, the Centre for Sustainable Architecture with Wood, was asked to validate the ‘AccuRate’ HER software. The University of Tasmania, in collaboration with Forest and Wood Products Australia, the Australian Government, the CSIRO and industry, undertook the construction of three test buildings for the purpose of empirically validating the ‘AccuRate’ software in a cool temperate climate. The three test buildings followed standard residential construction practises and included an unenclosed-perimeter platform-floored building, an enclosed-perimeter platform-floored building and a concrete slab-on-ground floored building.
The process of design, construction, environmental measurement, detailed simulation and methods of statistical analysis are discussed briefly. Graphical analysis is used to illustrate the variations that occurred between the measured and simulated zone temperatures for each test building. The statistical analysis of the measured and simulated data indicated the need for further investigation of the ground, subfloor, roof space, wind speed, infiltration, solar radiation and thermal mass algorithms. If the differences observed in this research were applied to full scale houses there may be a significant impact on the House Energy Star rating. The research identified the need for the continuous improvement and calibration of the AccuRate software.