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Getting practical with push for zero-carbon homes

How close have we come to zero-carbon homes? Stephen Berry

Australia is moving towards more energy-efficient houses. But are we doing enough? We think Australia could be aiming for zero-carbon homes; the tricky bit will be working out how to get there for the lowest possible cost.

Australia’s building energy standards are still low: most developed nations push beyond the equivalent of eight stars (the Building Code of Australia (BCA) aims for six stars). Many countries are moving to net zero energy or net zero carbon. Building codes across Europe, the UK, US, and Asia are being modified to approach a net zero-carbon standard as early as 2016-2020.

Here in Australia, the Prime Minister’s Task Group on Energy Efficiency asked whether the future of our housing regulation should move in a similar direction. We are investigating whether net zero-carbon homes are technically feasible and economically rational in Australian climates.

Our research into the feasibility of net zero-carbon homes will form part of the work program for a new a Cooperative Research Centre for Low Carbon Living.

Wouldn’t it be nice if this wasn’t at the other end of the light switch. Flickr/marinal

What is a zero carbon home?

What do we mean by net zero-carbon homes? For the past few decades engineers and architects have been creating homes such as the Freiburg Solar House in Germany or larger residential developments such as BedZED in the UK that have a net lower impact on the environment.

Zero-energy homes, zero-carbon homes, zero-emission homes, carbon-neutral or positive homes, hybrid homes and autonomous homes are just a few of the terms used to describe the same basic concept. All are talking about super energy-efficient houses, designed to work in harmony with the local climate. They are full of energy-efficient appliances and equipment, and generate electricity on or near the building with renewable technologies.

How do we define a zero-carbon home? There are a few important issues that help us communicate what we mean. For example: should we measure performance in energy or carbon terms; should the calculation be on an annual basis or for the life of the building; and should the building be self-sufficient or connected to the local electricity grid?

Building standards can be prescriptive or performance-based. Prescriptive codes might say “install no less than R3 insulation in the ceiling”, while a performance based code might say “reach 6-star performance” - thus allowing the builder to innovate to achieve the right performance. Any definition used within a performance-based regulation such as the Building Code of Australia is limited by three key characteristics:

  • Targets must be quantified.
  • Performance must be verifiable using a simple test methodology.
  • Assessments must be certifiable, that is, readily and repeatedly calculable by a suitably qualified person.

This means that for our research we have used the definition:

A net zero-carbon home generates sufficient renewable energy on-site over the course of a year to supply all expected on-site energy services for the household.

This is a very practical definition because: the calculation is based on the energy which would be measured at the meter box; the renewable energy technologies can be verified by the building certifier at the building site; the measurement is annual; and the standard is based on expected energy needs for an average household in the region - which allows climatic differences to be included.

Critics of our definition may argue that a full life-cycle assessment (LCA) approach, which means calculating all the energy used to build, operate and deconstruct the home, would give us the best idea of a house’s environmental impact. But currently there are no nationally or internationally agreed libraries of LCA assessments, or rigorously tested LCA assessment tools, to allow the use of a full life-cycle approach in building regulation. So if we are talking about a definition that can be used for building regulation today, the definition is limited to the energy used to operate the house.

Twenty-three centuries before the first electric refrigerator, Persians engineered cold storage units that made ice available year-round even through scorching desert summers. Flickr/davehighbury

Lochiel Park Green Village

To test the concept of net zero-carbon building standards we have based our research on detailed energy monitoring of homes at the Lochiel Park Green Village in Adelaide. When completed, this suburb-scale development will accomodate 106 households in a variety of building types, sizes and ownership arrangements.

All the buildings follow stringent Urban Design Guidelines, a set of performance requirements designed to create near-zero carbon homes in a near-zero carbon development. The guidelines set minimum requirements such as:

  • 7.5 Stars
  • solar hot water, gas-boosted
  • 1.0 kW peak photovoltaic array for each 100m² of habitable floor area
  • high-rated energy and water appliances
  • low-energy lighting (CFLs & LEDs)
  • ceiling fans
  • rainwater harvesting
  • greywater harvesting.

We have been recording the energy and water consumption, and separately measuring the energy used for heating and cooling, lighting, water heating, refrigeration, kitchen, laundry, and the electricity generated by the photovoltaic panels.

For the first time in Australia, this level of monitoring for such a large number of homes will allow us to truly understand where and when energy is used by present-day households. Because there are many different technologies installed across the large sample of homes, and many different household types and sizes, the research will provide ground-breaking insights into the efficiency of various systems and the behaviour of contemporary households.

Our research will quantify the real impact of high-star-rating building design, high efficiency appliances and renewable energy systems on the demand profile of households during periods of peak summer demand. This insight will allow peak load savings to be incorporated into the economic tests that underpin Australia’s building standards, increasing the economic feasibility of higher standards.

Amazing what people can think of when there’s no switch to flick: by incorporating wind towers, Iranian architects from a millennium ago dropped interior temperatures several degrees. Flickr/nomenklatura

So how zero carbon is a zero carbon house?

While the monitoring exercise is only two years into a planned nine-year program, we are already seeing strong trends. For example, the energy used in homes in Lochiel Park is significantly less than the average South Australian home, and amounts to only a third of that used to operate equivalent new homes. This is a significant saving to Lochiel Park households.

The energy performance in periods of peak summer heatwaves is outstanding. Electricity demand in Lochiel Park homes is not only appreciably less but - due to the excellent level of thermal comfort - the demand peaks later in the day, helping to flatten the Adelaide-wide electricity load profile.

Due to the production of renewable electricity by the solar photovoltaic panels, many homes at Lochiel Park are operating at or near the performance expected by net zero-carbon homes. Detailed monitoring will help us to understand which elements of the guidelines could be improved to deliver, on average, a cost-effective net zero carbon standard for all new residential construction.

Further information about high performance housing is available in the book Creating Sustainable Communities in a Changing World from the Barbara Hardy Institute at the University of South Australia.

Professor Wasim Saman of the University of South Australia also contributed to this article.

Comments welcome below.

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