Scorecard and NatHERS: comparing the two

There are a number of tools and programs available in Victoria to rate the energy efficiency of a home. One of the best-known is the Nationwide House Energy Rating Scheme, or NatHERS. Like Scorecard, NatHERS uses a star rating. Below are some of the similarities and difference between Scorecard and NatHERS.

How does the Scorecard work?

The Victorian Residential Efficiency Scorecard (the Scorecard) is a unique program that provides an energy star rating for your home. In the same way as a fridge or washing machine has a star rating, a Scorecard rating represents the energy cost of the fixed appliances in your home.

The Scorecard:

  • has been developed for existing homes, providing a rating and upgrade options
  • can be used for new homes
  • is not part of any regulatory program or the building code
  • is a voluntary program.

Scorecard ratings cannot be used to meet minimum energy performance requirements for new homes.

Under the Scorecard program, every home receives a Scorecard certificate. This provides further information on what makes up the home's rating and ways to improve the rating. Scorecard assessors are trained and provide advice on how the information can be used. This is a significant resource that can be used to reduce energy bills, improve the home's thermal comfort, guide renovations or suggest simple behaviour changes. Home owners, renters, community housing organisations, and landlords can use the information in many ways to improve home comfort, reduce energy bills or support other goals such as reducing greenhouse gas emissions.

The Scorecard star rating represents the energy cost of the home under average conditions. It covers the fixed appliances, the building shell and on site energy generation from solar panels. These are the elements that drive energy bills, have a relatively long life, and stay with the home whoever lives there.

The Scorecard certificate includes a hot weather rating showing how the house performs in heatwaves without air conditioning and how to improve this rating. This is an important feature to help householders improve summer performance when they have no air conditioner, or when the power fails.

The Scorecard program aims to make improving the energy performance of existing homes as straightforward as possible:

  • Trained assessors walk through the house and enter data; house plans are not required.
  • All the data collected must be visible or provable, avoiding subjective assessment.
  • Data is collected on a mobile device optimised to reduce the time taken for data entry.

How does NatHERS work?

NatHERS, the National House Energy Rating scheme, focuses on assessing the thermal performance of the building shell. This program accredits a number of building simulation tools – including AccuRate, FirstRate5 and BERS Pro. They are most commonly used for regulatory purposes under the Building Code of Australia, to demonstrate the building shell meets the minimum energy performance requirements. Getting a rating is part of the process of building a new home or undertaking a major renovation.

In most cases, NatHERS is used to rate the home during the design phase, with assessors entering house plan information into one of the rating tools.

  • The NatHERS assessment covers the building shell. An assessment requires full and accurate home plans.
  • The NatHERS assessment does not cover fixed appliances.
  • NatHERS tools assume that the home is heated and cooled most of the time, and seeks to ensure the home will perform well under more testing scenarios.
  • The NatHERS star rating indicates how much energy a householder would need to use to keep the building shell comfortable. The rating does not aim to represent energy costs or consider different fuel sources.

NatHERS ratings are undertaken to comply with regulatory requirements for building new homes or undertaking major renovations. Homes generally must meet a 6-star minimum standard.

NatHERS ratings are not generally used by homeowners to understand why energy bills are high and the options they have to reduce these costs. They can be used at the building design stage to help a designer maximise the thermal efficiency of the new home.

How do the tools compare?

Each tool has features that the other does not have, because they service different needs. For example the Scorecard includes hot water systems and provides upgrade options, or recommends solar PV. NatHERS tools don't do this. NatHERS provides a very flexible tool to design a new home to ensure the building shell (eg window locations and building materials) performs well.

Both tools treat the building shell similarly. The Scorecard is a simpler version of a NatHERS rating, and has been correlated against NatHERS to confirm the two tools are consistent. A home with a good NatHERS building shell rating should also rate well under the Scorecard building shell elements.

Scorecard

Technical details

The Scorecard star rating considers:

  • the building shell
  • heating appliances
  • cooling appliances
  • hot water appliances
  • lighting
  • pools and spas
  • solar PV systems.

The assessor enters details of each based on what they can see in the home, and on any available documentation (such as star ratings, model numbers etc of appliances). Data is entered per zone; a zone is usually a room. Heaters and coolers are assumed to heat and cool the zones they are in, and any other zones which cannot be closed off from the appliance (for example, by a door).

Energy use is calculated using climatic data for the home's location. Energy costs for each fuel are based on average tariffs.

Behaviour assumptions

Heating and cooling thermostats and usage patterns are based on an average profile. Hot water use is based on occupancy, which is derived from the floor area of the home.

Outputs

The Scorecard's overall star rating, shown at the top of the certificate is a rating from 1 to 10 stars. This represents the energy cost of running the home.

A 10-star home is modelled to export energy; that is, the energy generated from the PV system exceeds the energy cost of the fixed appliances of the home.

The Scorecard certificate breaks down the star rating by the elements that contribute to it (heating, cooling etc), so it is clear what is driving the overall rating.

The hot weather rating gives the home a score out of five for its performance in hot weather, in the absence of any mechanical cooling. Options to improve this rating are provided on the certificate.

The Scorecard certificate also provides ratings for each of the fixed appliances and the building shell, as well as suggested improvements. It also lists features that benefit the energy performance but are not included in the rating, as their impact is too difficult to calculate. This includes home features such as battery storage and shading plants.

NatHERS

Technical details

The NatHERS tools assess the thermal shell of a home and do not consider appliances or onsite power generation such as PV systems.

Assessors enter very detailed information on all aspects of the building shell. For instance, wall insulation is entered to an accuracy of R0.1. Wall constructions are defined by describing the material and thickness of each layer, including air spaces. The position of each window relative to the wall is entered as well as its size, orientation and other aspects.

Behaviour assumptions

NatHERS tools split a home into zones, and each zone has a particular use, such as living room or bedroom. The zone type sets assumptions for each zone for thermostat settings, internal heat gains and hours of use.

NatHERS is used as the standard to construct new homes that will often have a long life span. Over its life, the home will need to perform well under intensive use conditions, so NatHERS uses an intensive user behaviour model to ensure the home can perform well in these situations. Living areas are heated and cooled during the day and evening, bedrooms are assumed to be heated and cooled in the evening and overnight. NatHERS calculates the heating and cooling energy required to keep the home comfortable, but does not consider the fuel type or efficiency of any heaters or coolers. Occupant behaviour is standardised, windows are assumed to be opened and closed when appropriate and blinds lowered and raised.

Outputs

NatHERS gives the home a star rating for its thermal performance. This shows how much energy is required per unit of floor area to keep the home comfortable. The energy, in megajoules, is the amount that needs to be added by heating or removed by cooling.

How do the star ratings compare?

The NatHERS' overall star rating represents the thermal shell performance of a home.

The Scorecard's overall star rating represents the energy cost of a home. Scorecard also provides a building shell rating of 1-5 that is similar to the NatHERS star rating.

In Melbourne, a NatHERS 6-star house, of average size (220 m2) with market average appliances (5-star instantaneous gas hot water, 4-star gas ducted heating, ducted evaporative cooling) is likely to be a Scorecard 6-star house.

Summary

 

NatHERS

Scorecard

How many stars?

Out of 10 stars

Out of 10 stars

Housing type

Predominantly new build or renovation (at design stage)

All houses, new or existing

Measure

MJ/m2

Normalised to floor area

Energy costs for fixed appliances

Data source

Information taken from detailed plans

Information must be discoverable on walk through

Includes

No appliances

Fixed appliances (heaters, coolers, hot water systems,  lights) and PV systems and pools.

Customer interaction

Often the customer is the building designer or architect, sometimes householder interaction can occur

Assessors provide tailored advice for each customer, answers any questions that they have about their house

Uses

Usually used to meet minimum standards, occasionally for above standards. Can be used for National Construction Code Compliance.

Improvement options are generated by the tool and included in the certificate. Easy to run upgrade scenarios. Cannot be used for National Construction Code Compliance.