The Australian Building Codes Board (ABCB) hosted a webinar and discussion on 24th May, 2024 on NCC 2025: Proposed changes and Section J discussion. This session provided an overview of proposed changes to the next edition of the NCC. The NCC sets the minimum required level for the safety, health, amenity, accessibility and sustainability of buildings. Between 1 May and 1 July, the ABCB is seeking public comments on the proposed changes. These include an increase in the stringency of Section J, which deals with energy efficiency. As part of the update, there are changes proposed to J1V1, J1V3 and Specification 34.
The session covered:
- Changes to the J1V3 energy modelling pathway.
- Updates to existing building envelope solar admittance requirements.
- New requirements related to mandatory onsite solar photovoltaic systems (PV) and electric vehicle (EV) charging.
- Updates to existing fan efficiency and HVAC chiller requirements, including requirements for variable speed control.
- New provisions which facilitate the future electrification of buildings with mixed fuel use.
However, the J1V3 proposal is based on CSIRO Projected Weather Files (actually climate files) for building energy modelling, all of which have multiple time off set errors making the simulation results poentially misleading and counterproductive. ABCB used this data mandatory for the NCC 2025 changes however, we addressed this issue two times (CSIRO timing offset error in several weather elements (2022-04-21) and Solar data timing error skews simulation results (2022-01-17)), We have re-checked future climate scenario RCP 8.5 on 2050, but the timing offset errors remain despite the CSIRO knowing about their errors for over two years.
The data files available from CSIRO have two versions: Australian Climate Data Bank (ACDB) format for NatHERS and Energy Plus Weather (EPW) format for non-residential simulations. The solar and cloud cover datai 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), while EPW format is timestamped at the end of the period. However, CSIRO’s EPW format data is transposed from the ACDB format without considering this time convention difference. Also, the ACDB format’s timestamp for the other weather elements is from 00:00 – 23:00 while EPW format is from 1:00 – 24:00. Transposing the data line-for-line created a 1-hour offset errors in those other weather elements.
We set an example to describe why simply tranposing the solar data is wrong. Let’s say the Global Horizontal Irradiation (GHI) value is 33Wh/m2 at 6:00 (i.e. from 5:30 to 6:30), 103Wh/m2 at 7:00, and 97Wh/m2 at 8:00 in ACDB format. Then in CSIRO’s EPW format, GHI is recorded as 33Wh/m2 at 7:00 (i.e. from 6:00 til 7:00), 103Wh/m2 at 8:00, and 97Wh/m2 at 9:00. When we plot the GHI data according to each format’s half-hour timeline and we can find both format’s GHI values on time are not identical. From ACDB format, between 5:30 and 6:30 GHI value is 33Wh/m2, while between 6:00 and 7:00’s GHI value is 33Wh/m2 in EPW format. This 30 minute time discrepancy happened to not only GHI, it happens to all other solar and cloud cover variables. The other weather variables are out by a whole hour.
To make more reliable data for simulation, this time offset error needs to be improved. We will comment on this issue to ABCB so that they can correct this long standing and long known mistake.
Our overriding concern is that all of the simulations done to validate the proposed changes to the NCC are unreliable because these multiple erroneous files were used for that very sensitive purpose.
i And in the case of Exemplary files, the precipitation data as well.
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