Australian Climate Data Bank (ACDB), Typical Meteorological Year (TMY2, TMY3), and EnergyPlus Weather (EPW) files are different formats for data sets containing hourly values of meteorological elements and solar radiation for a single year period. These files can be utilised for building performance simulations (like energy and peak load analyses or, where the files include precipitation data, water ingress and condensation prediction) and solar and other renewable energy system output simulations.
The ACDB data set, originally developed by CSIRO in collaboration with the BOM and in consultation with ACADS-BSG which became the distributor, consists of an hourly record of 60 character columns containing the information described in the following schedule, produced in that specific format required for Nationwide House Energy Rating Scheme (NatHERS) software. Because the last five of the columns are spare (blank), it has been concurred by CSIRO that we will use them for precipitation data (mostly rainfall) even though there is no current plan for NatHERS to make use of that potential.
The EPW data set was developed for use with simulation programs such as EnergyPlus and ESP-r and has since then been adopted as a quasi-standard format by many other building and solar system simulation tools. The format is a text-based comma separated value (CSV), and can be transposed from data available in other weather format data-sets such as TMY2 with the addition of <minute data> and <infrared sky> fields. Additionally, EPWs are capable of recording data down to 1-minute intervals while the other three formats cannot store data more frequent than hourly.
Thanks to the simple text CSV format, the EPW files facilitate visual inspection and analysis with simple spreadsheet software such as Microsoft Excel (whereas the ACDB data needs to be parsed into Excel with the user indicating the breaks between adjacent values). Additionally, EPW files are easy to open, visualise and edit with a simple text editor tool. This is also thanks to the particular method of gathering and displaying any data source and uncertainty flag, which is carried out from the original weather file (e.g., TMY2). In fact, while those items of QA information are kept in the EPW, they are clumped together in a single space which immediately follows the day and time stamp, rather than occupying the different spaces within the file, requiring extra field separators and confusing these non-numerical data to the generally more important meteorological and solar radiation elements.
On the other hand, TMY data sets contain time-series meteorological measurements and modelled or measured solar radiation values, with occasional inferred and/or interpolated data when satellite or terrestrial observations are missing from the data source. These 12-monthly time-series data sets are widely used for building simulations and renewable energy systems modeling. Except for changes in the weighting criteria of solar radiation and other meteorological elements used in selecting climate files of typical months or years, TMY2 and TMY3 are created in a similar fashion to the first TMY data set produced by Sandia National Laboratories in 1978 for 248 locations in the United States, using long-term weather and solar data from the 1952–1975 SOLMET/ERSATZ database (Hall et al. 1978).
While TMY2 format uses columnar or positional formats, which enhance data storage optimisation to the detriment of visual inspection ease but have no capacity to include precipitation data, TMY3 files adopt a CSV format, which has the advantages discussed for the EPW files. Despite the different format, TMY2 and TMY3 contain similar data. While present weather, snow-depth and days since last snowfall are present in the TMY2 (but rarely used in the Australian context), they have been removed from the TMY3. Additionally, in TMY3 files surface albedo and liquid precipitation have been added, which were not present in the older TMY2. Lastly, some of the TMY2 measurement units have been updated to SI or equivalent in the TMY3, as summarised below:
- Precipitable Water: TMY2 [mm], TMY3 [cm]
- Horizontal Visibility: TMY2 [Tenths of kilometers], TMY3 [m]
- Wind Speed: TMY2 [Tenths of m/s], TMY3 [m/s]
- Dew Point: TMY2 [Tenths of Deg C], [Deg C]
- Dry Bulb Temperature: TMY2 [Tenths of Deg C], TMY3 [Deg C]
Based on the information provided, it appears that EPW has become the de facto standard for data sets containing hourly values of meteorological elements and solar radiation in Australia. This is likely due in part to the fact that CSIRO has chosen to use EPW for their datasets, making it a convenient and widely-supported choice for building performance and renewable energy system simulations. Additionally, the Australian Building Codes Board has even elected to reference EPW in the National Construction Code (NCC) 2022, further solidifying its position as the standard format for building energy modeling.
To conclude, although TMY3 may have some advantages over EPW, the widespread adoption of EPW by building energy modellers seeking to demonstrate compliance with energy efficiency regulations makes it the more practical choice in many cases, and for this reason we have chosen to distribute our Exemplary Energy data in the EPW format. We also continue to directly generate data in the ACDB format, which as we have seen cannot be reliably transcribed from or to EPW due to the different timestamp conventions for solar data.
We can also produce data in any format on a custom basis should the need arise.
Reference
Hall, I., Prairie, R., Anderson, H. & Boes, E. (1978). Generation of Typical Meteorological Years for 26 SOLMET Stations. SAND78-1601. Albuquerque, NM: Sandia National Laboratories.