A critical review of the CSIRO Weather and Climate Data (Part 4)
The CSIRO developed a set of Representative Meteorological Year (RMY) weather and climate data sets as the baseline for the organisation’s work in creating so-called “predictive” weather files that can be used to investigate the impact of climate change on building energy consumption (further information on this important work is available at https://acds.csiro.au/future-climate-predictive-weather). The RMY data are presented in the EnergyPlus Weather (.epw) format, transcribed from the Australian Climate Data Bank (ACDB) which is the basis for climate information in the Nationwide House Energy Rating Scheme (NatHERS) software tools and provides data for 70 geographic climate zones across Australia.
These climate data sets have been made freely available by the CSIRO since August 2021, and have become the de facto standard for building energy modellers seeking to demonstrate compliance with the energy efficiency requirements of the National Construction Code (NCC) along with a variety of other applications. Thus the accuracy of the RMY data sets has significant implications for the energy efficiency of Australia’s future building stock, and Exemplary Energy have undertaken a timely review the CSIRO weather and climate data sets ahead of the 2022 publication of the NCC.
Our critique has already highlighted several major shortcomings with the data sets, and discussions of the first three issues can be accessed by clicking on the following links:
The differences between the .epw and ACDB formats mean that the transcription is non-trivial and is grossly flawed regardless of the method. For example, solar radiation data in the ACDB format is timestamped at the centre of the time period (each hourly data point representing 30-minutes either side of the timestamp), whereas in the .epw format it is timestamped at the end of the period. These data should always be integrated from the original high frequency observations.
On the other hand, the transcription of instantaneous1 elements such as dry bulb temperature, dew point and wind speed should be straightforward. However, the CSIRO method appears to introduce a 60-minute offset error in several weather elements including dry bulb, dew point, atmospheric pressure and wind.
The issues arising from these errors need to be considered by policymakers and modellers alike. In mid-November 2021, we advised our colleagues at CSIRO and the Australian Department of Industry Science, Energy and Resources (DISER, responsible for the NCC) of these findings but they have yet to even add a warning to the distribution website. We will continue to work with them to avoid further propagation of the errors and offer our support to improve the data going forward. We urge users and policymakers to be mindful of these issues as modelling inaccuracies arising now are embedded in building operations for many years to come.
In the interests of full disclosure, we note that Exemplary Energy offers high quality climate and weather data, including ersatz future climate data, that avoid the issues of the CSIRO datasets. These are available for modellers demonstrating NCC compliance through the JV3 pathway (simulating a compliant reference building as well as the actual building being proposed), along with non-regulatory applications in design and optimisation and resilience testing of buildings and energy systems.
1 Most observations (i.e. those other than solar radiation and precipitation) are actually averaged from a series of high frequency measurements taken over a period on the order of a few seconds, or in the case of wind observations a period of ten minutes. For our purposes, these are taken is representing the instantaneous conditions at the time of the timestamp.