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:

1. Reliance on weather data ending in 2015 for the characterisation of a warming climate ;

2. A 30-minute error in solar data in the .epw format; and

3. A lack of coincident precipitation data despite the .epw format expressly inviting it.

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.

Notes:
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.

A critical review of the CSIRO Weather and Climate Data (Part 3 of 3) 

The CSIRO weather and climate data sets discussed in our previous post are widely employed by building energy modellers, including applications to demonstrate compliance with the energy efficiency requirements of the National Construction Code (NCC). Exemplary Energy’s timely critique of the CSIRO weather and climate data sets ahead of the 2022 publication of the NCC, and highlighted three major shortcomings:

1. Reliance on weather data ending in 2015 for the characterisation of a warming climate;

2. A 30-minute error in solar data in the .epw format; and

3. A lack of coincident precipitation data despite the .epw format expressly inviting it.

Discussions of the first two issues can be accessed here and here. In this final article of our three-part series, we investigate the opportunity for incorporation of coincident precipitation.

Precipitation data is important for a wide variety of applications. The AIRAH DA07, Criteria for Moisture Control Design Analysis in Buildings, provides specifications for predicting, mitigating, or reducing moisture damage to buildings, and requires detailed consideration of precipitation. In 2019, minimum condensation requirements were incorporated into the NCC, designed to minimise impacts related to moisture on the health of the occupants in the building. Further measures for moisture management are being proposed for the NCC 2022.

One challenge is that, until recently, many sources of precipitation data are reported at inadequate temporal resolutions. For instance, the Bureau of Meteorology’s (BOM) observations network typically only reported daily totals prior to the early 2000’s.

Exemplary Energy has developed algorithms to estimate hourly precipitation from the daily historical figures reported by the BOM for over 200 Australian locations, including the 69 locations built into NatHERS. This work was recently peer reviewed and was presented by Exemplary Energy in the Asia Pacific Solar Research Conference (APSRC) in December 2021.

The issues outlined herein need to be considered by policymakers and modellers alike. We have advised our colleagues at CSIRO of these findings and 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 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 compliance through the JV3 pathway, along with non-regulatory applications in design and optimisation and resilience testing of buildings and energy systems.

A critical review of the CSIRO Weather and Climate Data (Part 2 of 3)

The CSIRO weather and climate data sets discussed in our previous post are widely employed by building energy modellers, including applications to demonstrate compliance with the energy efficiency requirements of the National Construction Code (NCC). Exemplary Energy’s timely critique of the CSIRO weather and climate data sets ahead of the 2022 publication of the NCC, and highlighted three major shortcomings:

1. Reliance on weather data ending in 2015 for the characterisation of a warming climate;

2. A 30-minute error in solar data in the .epw format; and

3. A lack of coincident precipitation data despite the .epw format expressly inviting it.

Discussion of the first issue was previously covered on this blog. This article will review the 30-minute error in the solar data. In this second article of a three-part series, we investigate the 30-minute time offset in the CSIRO solar data.

The issue is likely caused by transcription error. One of the key differences between the .epw and NatHERS formats relates to the timestamp applied to solar irradiation data: the .epw format requires that the solar irradiation data represents the period prior to the timestamp, whereas the ACDB format specifies that the solar irradiation represents the hour centred on the timestamp. Failure to adjust to this time convention most notably affects the time of peak loading, and has major impacts on evaluations which incorporate on-site renewable energy generation.

Hourly plots comparing the diffuse radiation of the CSIRO .epw data with the Exemplary Energy .epw and ACDB datasets for Canberra for Days 13 to 24 in January. Note the half-hour time offset and the difference in radiation

A comparison between CSIRO’s datasets and those produced by Exemplary Energy further illuminates the differences. As an example, a detailed analysis of the Canberra climate – where the two datasets theoretically share the same source for January’s data – reveals a difference of 2.3 kWh/m² in global horizontal radiation for the month, 7.3 kWh/m² direct normal radiation, and 9.1 kWh/m² in diffuse radiation. These differences highlight the shortcomings of transcription between formats – even when applied correctly, interpolation between datapoints to account for timestamp differences will always introduce errors¹.

Applying these data to a one-month simulation of a 3-storey office building in Canberra, the Exemplary data resulted in increased cooling by 4.4% and increased peak cooling load by 3.3%, along with a 30-minute timing offset in the peak cooling load.

The opportunity for including precipitation data will be discussed in a future article.

The issues outlined herein need to be considered by policymakers and modellers alike. We have advised our colleagues at CSIRO of these findings and 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 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 compliance through the JV3 pathway, along with non-regulatory applications in design and optimisation and resilience testing of buildings and energy systems.

¹ Exemplary Energy’s weather and climate data products are always produced from meteorological observations at the highest-available temporal resolution. In the case of solar data, our datasets are directly based on Himawari satellite observations recorded at ten-minute intervals. 

A critical review of the CSIRO Weather and Climate Data (Part 1 of 3) 

Since August 2021, the CSIRO has distributed three important weather and climate datasets for use by building energy modellers:  

• Typical Meteorological Year (TMY) – a collation of selected meteorological measurements, listing data at 8,760 hourly intervals to describe a ‘typical’ year of weather for a specific location. This data is published in the EnergyPlus (.epw) format and is available at https://acds.csiro.au/future-climate-typical-meteorological-year.

• Reference Meteorological Years (RMY) – conceptually representing the same information as TMY but presented in an amended version of the fixed record format of the Australian Climate Data Bank (ACDB). This data is the basis for climate information in the Nationwide House Energy Rating Scheme (NatHERS) software tools and is distributed with the CSIRO’s AccuRate software and its competitors. 

• Predictive weather files – CSIRO’s predictive weather files are based on a typical meteorological year of historical weather data drawn from 1990 to 2015 and can be used to investigate the impact of climate change on building energy consumption. These are available in .epw and NatHERS-compatible formats at https://acds.csiro.au/future-climate-predictive-weather.

As the basis for NatHERS, the CSIRO’s RMY dataset is arguably the most commonly-applied pathway to demonstrate compliance with the residential energy efficiency requirements of the National Construction Code (NCC). With its transcription to the .epw format, closely related data is commonly used for simulations of commercial buildings that are used to demonstrate compliance with section JV3 of the NCC, as well as simulations for other purposes.

Exemplary Energy’s review of the CSIRO weather and climate datasets is timely as the 2022 version of the NCC is currently being finalised. Its publication is scheduled in early 2022 and the Code will come into effect mid that year.

Our detailed review of the CSIRO climate and weather data sets has revealed three major shortcomings:

1. Reliance on weather data ending in 2015 for the characterisation of a warming climate;

2. A 30-minute error in solar data in the .epw format; and

3. A lack of coincident precipitation data despite the .epw format expressly inviting it.

The first issue is well-known: The CSIRO climate and weather files are derived from historical data to December 2015. It is imperative for the NCC to accurately reflect real weather conditions. In a changing climate, this can only be achieved using regular updates that incorporate recent observations.

While it is challenging to justify changes to the NatHERS data – any change which creates an average impact of more than 0.2 stars in NatHERS ratings requires a burdensome Regulatory Impact Statement and/or a recalibration of the star-band thresholds – there is no reason for the accuracy of commercial building modelling to be held back on this basis.

Exemplary Energy offers representative data that incorporates the most recent years up to 2020 and soon plans an update that will incorporate all observations to the end of 2021.

The second and third issues will be discussed in forthcoming articles.

The issues outlined herein need to be considered by policymakers and modellers alike. We have advised our colleagues at CSIRO of these findings and 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 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 compliance through the JV3 pathway, along with non-regulatory applications in design and optimisation and resilience testing of buildings and energy systems.