The empirical validation of house energy rating (HER) software for lightweight housing in cool temperate climates

Against a background of a recognised need to reduce Australia‘s energy consumption and hence greenhouse gas emissions, the Building Code of Australia (BCA), in 2003, introduced its first thermal performance requirements for residential buildings. It mandated a minimum performance rating of 4 Stars for new housing, when assessed by an approved rating method. While the introduction of a 4 Star requirement had a minor impact on construction practices, that of 5 Stars (from 2006) and 6 Stars (from 2010) imposed considerable changes, especially in the use of timber platform floors. The adoption of the prescribed energy efficiency measures in the BCA raised concerns from industry and manufacturing groups, as to the accuracy of AccuRate software used to model the building envelope. This software was developed by the CSIRO and as a result of the thermal performance requirements, had evolved from a design tool to a regulatory tool. Both industry and government recognised the need to validate empirically the National House Energy Rating Scheme (NatHERS) benchmark software 'AccuRate'.

The University of Tasmania, in collaboration with Forest and Wood Products Australia, the Australian Government, the CSIRO and industry, constructed three test buildings for the purpose of validating empirically the AccuRate software, in particular for cool temperate climates. The test buildings followed standard residential construction practices and represented the three most common forms of construction: unenclosed-perimeter platform-floored, enclosed-perimeter platform-floored and concrete slab-on-ground floor. An array of environmental measuring equipment was installed to measure actual thermal performance in each of the test cells. A detailed house energy rating simulation was completed and a comparison of the measured and simulated data was undertaken.

This research presents the findings of the graphical and statistical analyses of variations between the measured and simulated data from the three test cells. The findings demonstrate that while the AccuRate software modelled energy flows well, discrepancies were measured between the simulated and measured temperatures of the test cells. In particular the analyses identified relationships between the discrepancies in all zones and outside air temperature, wind speed, global solar radiation and diffuse solar radiation, and possibly the ground model. Consequently, these require further investigation and resolution for the ongoing improvement and calibration of the AccuRate software.