Whole of Home Assessment
The focus of previous versions of NCC Vol 2 (for the residential dwellings) was to improve the building’s thermal performance through insulation and improved glazing. This approach was passive due to its focus being on the performance of the building envelope and not the building services. In the new NCC 2022 Vol 2.0, a Whole of Home (WoH) approach has been introduced to take into account:
- The efficiency of energy-using services on the building’s energy use; and
- On-site electricity generation and use via Solar PV system
This article outlines the information you need to know about the new Whole of Home approach.
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What is Whole of Home assessment?
The objective of Part H6 Energy Efficiency provisions of the New NCC 2022 is for Class 1 and Class 2 buildings to:
Reduce annual and peak thermal energy demand
To reduce annual and peak energy demand, a building must have a good-performing envelope. This means that the building must be insulated to an adequate degree and to have improved windows. A good-performing envelope reduces energy bills and improves the thermal comfort of the occupants.Reduce greenhouse gas emissions
Greenhouse emissions are the product of electricity and gas usage of building services. Efficient services produce lower levels of emissions. Also, renewables including solar PV systems can help offset the building’s net emissions.Reduce time-of-use impact on energy networks
Buildings with high ceilings and especially, with high raked ceilings cost more to build. Though the added value of a high ceiling could compensate for he high construction costs later, high costs buildings are not as easy to sell as the buildings with moderate costs in the market.
The new Whole of Home assessment approach ensures that all the above is considered in new-built homes in Australia. The holistic approach of the new NCC 2022 not only considers the performance of the building envelope but also considers the efficiency of building services and the impact of renewables on electricity use reduction.
What are Whole of Home requirements?
Energy consultants undertake Whole of Home (WoH) assessment to achieve compliance with Part H6P2. This part of NCC Vol 2 includes the Performance Requirements for the energy use of domestic services. These domestic services include the equipment used for:
- Space heating and cooling
- Mechanical ventilation
- Artificial lighting
- Pool and spa pump and heaters
- Heated water supply
- On-site renewable energy systems
And excludes:
- Cooking appliances and portable appliances
The new WoH assessment ensures that these domestic services are efficient or help to reduce the peak energy demand and greenhouse gas emissions, as well as reducing their impact on the energy network. WoH requirements are outlined in:
- NCC Vol 2 Part 13.6.2 for new residential dwellings (Class 1 buildings)
- NCC Vol 1 Part J3D14 for new apartments (Class 2 buildings)
Note: The WoH requirements for apartments are slightly easier to achieve compared to those for houses.
WoH requirements are flexible and no set of rigid rules can be applied to all projects. The metric used here is “Net Equivalent Energy Usage”. This means that you can choose how to achieve a Net Equivalent Energy Usage target; as an example, for a house in Melbourne with a floor area of 150m2 and no pool/spa, you can achieve compliance with Part 13.6.2 (Whole of Home) by following either of the options below and many more:
Option A
5.5 Stars non-ducted heat pumps*
Heat pump water heater
No photovoltaics
Option B
3.5 Stars non-ducted heat pumps*
Solar-assisted gas water heater
No photovoltaics
Option C
3.5 Stars non-ducted heat pumps*
Instantaneous gas water heater
1.2 kW photovoltaic system
How do you undertake Whole of Home assessments?
There are two options available for houses and apartments to satisfy the requirements of Whole of Home. These options are both Deemed to Satisfy (DtS) pathways and include:
Elemental provisions
This option is a prescriptive approach and mandates the use of specific formulas to calculate Net Equivalent Energy Usage. The compliance is achieved when the proposed building’s Net Equivalent Energy Usage is less than or equal to a calculated Energy Use Budget. Other details on compliance are accessible via NCC:
- For houses: DTS Provisions of Volume Two, H6D2(1)(b) and H6D2(2)(b), and
- For apartments: DTS Provisions of Volume One, J2D2(2)(b) and J2D2(3)(a)(i), (b) and (c).
Instead of going through with the above calculation details, you can simply use the ABCB Whole of Home Calculator to conduct the best solution available for you.
NatHERS energy rating
This method requires an accredited assessor to utilise a NatHERS tool for the development of an optimized solution. This approach takes the energy demand of the proposed building into account and fits better with the whereabouts of the building that is the subject of the assessment. Also, it is worth noting that using the NatHERS pathway, it is more probable to have a low-cost solution. For more information, refer to the NatHERS website.
To better understand the whole process, the following Figure helps:
NatHERS Whole of home
After the determination of the thermal performance of the proposed building using NatHERS-accredited tools (e.g. FirstRate5), the model file must be uploaded to be prepared for obtaining a certification. At this stage, the model could also be imported through the Whole of Home platform to determine the performance of building services. The thermal performance of the house and services are combined and the energy usage of the Whole of Home is calculated. If the energy usage is less than or equal to the energy use budget, then the proposed building is eligible for certification.
Following the new NCC 2022, building services are also required to be taken into account. To obtain NatHERS certification, information about the following building services is required:
- Space heating and cooling equipment
- Hot water supply systems
- Pool/spa pumps
- Cooking
- Lighting and plug-in appliances
- On-site energy generation and storage
Whole of Home rating
After the basic information and efficiency data for the services are entered, a Whole of Home rating could be produced, scaling from 0 to 100; While rating of 100 means that the building produces the same amount of energy it consumes. The rating could go beyond 100 if the building generates more energy than it consumes. The new houses and townhouses require a Whole of Home rating of 60 and new apartment units require a rating of 50 before being certified.
The output of this Whole of Home assessment is a summary report that includes several valuable metrics:
- Energy Use: the net energy use of all end-uses of appliances that also includes the offset due to the electricity generation of solar PV systems and the storage of batteries. This metric is reported in Megajoules (MJ) and includes all energy sources (e.g. gas and electricity).
- Greenhouse Gas Emissions: the net greenhouse gas emitted due to the use of building services, including photovoltaics. This metric is reported in Tonnes.
- Energy Cost: depending on the state and territory in which the proposed building is located, energy tariffs are multiplied by energy use to produce the energy cost of individual services. This also includes the supply charges.
- Energy Value: this is the cost of all appliance end-uses and offsets by photovoltaics and battery that also includes the cost of carbon; which is the cost of dealing with the impact of greenhouse emissions produced by the building services.
- Target Energy Value: Target energy value is the calculated energy value for a 7-star reference dwelling with the same floor area as the proposed building under assessment.
- Whole of Home rating: this is the final generated score, calculated from the Target and Net Energy Value. For residential dwellings and townhouses, a minimum rating of 60 and for apartment units, a minimum rating of 50 is required.
FAQ
The Whole of Home is the new approach introduced in NCC 2022 for residential buildings that aim to reduce energy use and societal costs of energy use.
Energy value is the cost of all appliance end-uses (i.e. electricity and gas consumption) and offsets by photovoltaics and batteries. The cost of carbon is also included in the calculation of energy value, which is the cost of dealing with the impact of greenhouse emissions produced by building services.
For a building to achieve compliance with Whole of Home provisions, the energy value of building services must not exceed a target energy value. This target energy value is equal to 70% of the energy value of a house of a similar size, having a:
- 3-star ducted heat pump, rated under the 2019 GEMS for space heating and cooling; and
- 5-star instantaneous gas water heater, rated under the 2017 GEMS; and
- 4 W/m2 Lighting power density serving all internal spaces.
Cost of carbon is a cost that is associated with offsetting the negative impact of greenhouse gas emissions that are produced by the building’s appliances. Cost of carbon is included in the new Whole of Home standard.
Whole of Home rating scales from 0 to 100 and beyond. A rating of 100 suggests that the proposed building consumes the same amount of energy as it produces. Ratings beyond 100 mean the proposed building produces energy more than it consumes.
A Whole of Home rating of 50 means that the proposed building has the same performance as a similar-sized reference building.
There are no strict requirements for a water heating appliance. However, the more efficient the water heating system, the lesser the energy value of the building. The energy value of a building is calculated considering all appliances, including water heating appliances.
There are no strict requirements for space heating and cooling appliances. However, the more efficient the air conditioning system, the lesser the energy value of the building. The energy value of a building is calculated considering all appliances, including space heating and cooling appliances.
Before dealing with Whole of Home assessment, it is best if all required details for heating and cooling, water heaters and solar PV systems are specified on the design drawings. But if this is not the case, the latest NatHERS Technical Note sets the information for default appliances to use. The minimum information you need is the type and energy source of water heating and cooking appliances.
Yes. Class 2 apartment buildings require a Whole of Home rating of 50.
No. NSW government has a different scheme for residential building performance and energy use that is BASIX.
Apart from buildings located in NSW, all other residential dwellings and apartments are considered to adopt the new Whole of Home standard introduced by NCC 2022. See here for state and territory adoption dates.
Unlike commercial buildings which are subjected to NCC 2022 Vol 1.0, residential dwellings and apartments cannot use photovoltaics to compensate for their poor-performing building fabrics. However, installing photovoltaics helps residential buildings achieve the score required to achieve compliance with the new Whole of Home standard.
There are two methods of compliance for Whole of Home assessment: Elemental Provisions and NatHERS energy rating. Among these methods, NatHERS energy rating methods prove to be more accurate, connected with the energy demand of the house, more detailed and more inclusive (for example, it includes battery storage).
As no official rating scheme is available for heat pump water heaters or solar gas or electric water heaters, these types of water heaters can be eligible to generate Small-scale Technology Certificates (STCs) under Australia’s Renewable Energy Target. The number of STCs is required as an input in NatHERS Whole of Home assessment and the number of STCs for many products is available on Clean Energy Regulator’s website. Note that the STCs calculator shall not be used for NatHERS Whole of Home assessment as its results are not calculated based on a 10-year use.
Greenhouse and Energy Minimum Standards (GEMS) were last updated in 2019. Unlike the older standards, the new standard is location-dependent and the rating system depends on the climate zone the building is located in and separates the ratings for hot, cold or mixed climate zones.
The energy use budget or target energy value is calculated based on the total floor area of the apartment or house and its location. Details on how to calculate this are outlined in NCC 2022 Part 13.6.2.