A number of datasets can characterise the ‘typical’ climate for a location: Reference Meteorological Years (RMY) are intended to provide an indication of 50th percentile weather-sensitive performance for small (RMY-B with a 33% weighting for solar) or deep plan (RMY-C with a 17% weighting for solar) non-residential buildings, or for solar sensitive infrastructure (RMY-A with a 50% weighting for solar) such as housing and PV generation; while eXtreme Meteorological Years (XMY) reflect to Nth percentile of performance for solar PV, HVAC1 and moisture1.
However, our concept of ‘typical’ climate is changing. The years spanning from 2015 to 2022 have marked the eight warmest years on record, and it is expected that this trend of increased warming will persist due to rising anthropogenic greenhouse gas emissions and consequential ice-cap retreats. These developments have significant implications for the relevance and quality of climate data employed for building and energy system simulations.
Within the context of a warming climate, the reference period for these data become a critical consideration. Fundamentally, the conventional reference period—1990-2015, as used by the Commonwealth Scientific and Industrial Research Organisation (CSIRO) for their problematic data—no longer accurately represents the current climate at a given location.
For example, the climate in Canberra has changed to be warmer, more humid and windier but with reduced solar irradiation.
One serious consequence of this is that the climate data commonly used by modellers for demonstrating construction code compliance, sizing HVAC systems and optimising building and energy system designs is likely not an adequate representation of the climate that the building will experience during its operating life.
A shorter reference period accounts for recent climatic change, but comes at the risk of tracking short-term “blips” rather than providing an indication of long-term climate normals. Advice from the Bureau of Meteorology2 suggests that a balance between the stable reference baseline and provision of an implicit predictor of the most likely near-future conditions may be found with a reference period of 10-15 years.
Clear Trends: Simulation Results for Sydney over 33 Years
We evaluated the results of applying 33 years of Sydney’s weather data to simulations of the three archetype buildings used in our Exemplary Weather and Energy Index (EWEI), finding that annual cooling, heating and total energy demand (see figure, L-R respectively) show a clear trend of rising cooling and decreasing heating. This result held for each building archetype and when averaged across all three building types.
The net result is about a 2 per cent per decade increase in total energy demand. This is despite the results of cooling seen since 2018 (an 8.8 per cent reduction in cooling energy was seen over the period 2018-2022) and should be a serious concern to energy planners and facility managers in light of the warmer years that the climate models tell us are coming our way.
We have proposed shorter, more recent reference periods to better characterise evolving climate dynamics. One of our papers to this year’s Asia-Pacific Solar Research Conference will present the results of implementing RMY datasets with a 15-year reference period spanning 2008-2022 (taking account of BoM advice2), and comparing this to a 33-year reference period from 1990-2022 as well as the outdated CSIRO reference period of 1990-2015. Further, we intend to revise this work in future years to better understand the sensitivities between energy and climate as it unfolds.
For the sake of standardisation we suggest that users seeking to demonstrate compliance with the National Construction Code continue to use our Industry Standard Meteorological Year (ISMY) data, which is a corrected version of the data based on the 1990-2015 reference period that is published by CSIRO, without the gross errors contained in CSIRO’s data (see here, here and here for a summary of just some of the problems we have encountered).
However, modellers seeking to provide deeper insights will be interested to know that all of the RMY datasets described above are available now from our sales portal alongside a range of data products covering the eight Australian capital cities and all eight of the NCC climate zones.
- NB Exemplary’s XMY’s for HVAC and precipitation are under development and not yet commercially available ↩︎
- Trewin, B, 2007, ‘The Role of Climatological Normals in a Changing Climate’, World Meteorological Organisation. Available at: https://library.wmo.int/records/item/52499-the-role-of-climatological-normals-in-a-changing-climate. Accessed 5 September 2023. ↩︎