Energy efficiency for residential buildings: Nathers heating and cooling load limits Consultation ris

A.2Current practice and research

Having heating and cooling load limits is not a new concept. The New South Wales Government introduced heating and cooling caps under the Building Sustainability Index (BASIX) in 2004. The BASIX ‘thermal comfort’ element does not require dwellings to achieve a NatHERS star rating. Instead, BASIX requires compliance with individual heating and cooling caps unique to each climate zone.

At the international level, the benefits of heating and cooling limits is also well acknowledged. In California, design heating and cooling loads must be met for a building, with specific rules applying for how to calculate heating and cooling loads³.

In the European Union (EU), the ENTRANZE Project has involved wide-scale research on heating and cooling energy demand and loads for building types in EU countries. This project supports policy making on the transition to nearly zero energy buildings in the EU by 2020 for new buildings⁴.

A.3Policy context

In 2016, the ABCB was requested to investigate having separate load limits as part of the energy efficiency project under Measure 31 of the National Energy Productivity Plan (NEPP). Funding was provided for this work through the Council of Australian Governments (COAG) Energy Council. This work was endorsed by the ABCB Board and included in the ABCB work plan. Introducing heating and cooling load limits, in addition to the existing star rating, for the NCC’s NatHERS compliance pathway is one of the key elements of the proposed energy efficiency changes for residential buildings in NCC 2019.

Appendix BHow to determine heating and cooling load limits

The focus of the energy efficiency changes for residential buildings in NCC 2019 is to improve the interpretation and application of the current provisions without increasing stringency. Thus the proposed heating and cooling load limits are not intended to change the overall stringency of NCC (i.e. the total energy load is to remain unchanged). The load limits will capture the worst performing dwellings with minimal effort to fix issues at the design stage.

The ABCB engaged Tony Isaacs Consulting (TIC) and Energy Efficient Strategies (EES) to develop the heating and cooling load limits for the NatHERS compliance pathway.

B.1Scope of this work

The proposed load limits cover the NatHERS compliance pathway as it appears in NCC 2016 (ignoring jurisdictional variations).

In general, using the NatHERS compliance pathway, a Class 1 building must achieve a minimum 6 star rating. A minimum 5 star or 5.5 star rating is allowed in NCC climate zones 1 and 2 if the building has an outdoor living area and/or a ceiling fan⁵. For Class 2 sole-occupancy units, a minimum of a 5 star rating and a collective average of a 6 star rating across all sole-occupancy units must be achieved⁶.

When considering building type, floor type and NatHERS star rating, the following scenarios for heating and cooling load limits have been explored in this analysis.

Table Scenarios for heating and cooling load limits

Building type	Floor type	NatHERS star rating
Class 1	On ground (Concrete slab)	6 star
Class 1	On ground (Concrete slab)	5.5 star
Class 1	On ground (Concrete slab)	5 star
Class 1	Suspended (Timber)	6 star
Class 1	Suspended (Timber)	5.5 star
Class 1	Suspended (Timber)	5 star
Class 2	On ground (Concrete slab)	6 star
Class 2	On ground (Concrete slab)	5 star
Class 2	Suspended (Timber)	6 star
Class 2	Suspended (Timber)	5 star

B.2Methodology

The heating and cooling load limits have been developed based on building permit records from the NatHERS data portal, comprising over 170,000 dwelling records. However, only limited data was available for some regional areas with low construction activity. Thus, two methods were adopted for determining the heating and cooling load limits.

B.2.1Method 1

In those climate zones where sufficient data existed, the total energy load was split into heating and cooling fractions consistent with the available NatHERS assessments.

To retain a reasonable level of compliance within the current stringency, it was determined that 90 per cent of current dwelling designs should comply with the proposed new heating and cooling load limits without alteration. This is to say that 95 per cent of the sample data meets the new heating load limit, and the same for the cooling load limit. Outliers, in terms of each load limit, represent 5 per cent of the sample. To demonstrate this, each data point in Figure 1⁷ stands for a sample dwelling, with the green data points being compliant with the proposed heating and cooling load limits.

Figure 1 Sample output from the universal certificate sample analysis tool

B.2.2Method 2

Method 2 uses a correlation approach, with data from an additional database of NatHERS simulation results, to derive the average heating fraction⁸ for compliant dwellings. This method supplements the NatHERS portal data in climate zones where there is only limited data to derive the load limits. This was done using statistical analysis to correlate the average heating load as a proportion of 6 stars. The data set was originally used for calculating NatHERS star bands, which includes at least 30 compliant houses in every climate zone.

TIC’s report covers heating and cooling load limits for all 69 NatHERS climate zones. However, the load limits are not recommended for every climate zone. It is proposed to only apply the heating and cooling load limits to those climate zones where the heating fraction is between 5 and 95 per cent of the total energy load. On this basis, the load limits will not apply in the Northern Territory, Tasmania and parts of Western Australia and Queensland. Also, the load limits will not override the heating and cooling caps, which are adopted in New South Wales under BASIX.