IBPSA-Australasia has submitted comments to the draft National Construction Code (NCC) 2022. While the update on energy efficiency provision in this cycle focuses on improving residential sectors, the industry is expecting increased stringency and streamlining of energy efficiency requirement for residential sector to be on par with the commercial sector. Unfortunately, the draft has not met such expectations. The following summarises some key points and recommendations submitted by IBPSA-Australasia to the NCC consultation hub.
The proposed J1V5 and sub-clauses (and J1P2 and J1P3) do not allow streamlining energy modelling to test compliance of mixed-use buildings which include the entire apartment building, retails, or offices or other classes. The requirement to report on the heating and cooling loads of each individual Class 2 SOU completely negates the advantages provided by the use of modern energy simulation software system and works against the more efficient shared service arrangement. IBPSA-Australasia recommends comparison of total greenhouse emissions from mixed-use buildings (class 2 common areas, SOUs and other classes) similar to NCC 2019 JV3 methodology.
Building fabric should be tested for its ability to provide occupants with a thermally comfortable space at a minimum energy/GHG emission criteria. A thermal comfort test is critical for every habitable space in Sole-Occupancy Units (SOU); without it, there is no backstop for minimum building fabric performance. IBPSA-Australasia recommends an appropriate thermal comfort test should be applied to every INDIVIDUAL space of interest in every sole-occupancy unit, for the complete apartment building. Individual space/zone thermal comfort tests are already being applied in JV3 (or the proposed J1V3), and this is simply an extension of this approach to apply this to Class 2 habitable zones. Industry has already developed significant experience in carrying out such analysis.
The Deemed to Satisfy (DtS) requirement for SOUs is stated to be based on achieving NatHERS 7 stars. Since NatHERS ‘star bands’ are the same for a Class 1 house and a Class 2 SOU apartment, the energy budget for class 2 was generated against the same thermal performance of single dwelling houses. This and other inappropriate setting (explained below) within NatHERS result in inequitable energy budget for multi-dwelling units (Class 2). IBPSA-Australasia recommends that all reference to stringency derived from NatHERS be deleted and the DtS requirement (Reference building model description for J1V5) be based on a set of newly devised, stringent, deemed-to-satisfy (DTS) performance requirements using SYSTEM Total R-values for elements forming the thermal envelope of the SOEs (Roof, Floor, Partitions, External walls and Shared walls), and the Wall-Glazing approach in J3D9 – with corrections to solar admittance.
As per the elemental provision for Class 2, the ‘Housing Provisions’ for Class 1 Buildings were based on NatHERS methodology that under-predicts annual heating energy consumption by assuming air tightness that is better than what the industry can deliver in practice. Air tightness assumptions in NatHERS must be set to the average level that the industry can achieve. However good or best practice air tightness must be backed-up with mandatory air leakage testing.
Full details on IBPSA-Australasia’s submission to the NCC 2022 Public Comment draft are below: