CSIRO: Green housing cheaper to build and run

24 February 2014 — Energy efficient homes cost less to run and build, a CSIRO study into the effectiveness of increased energy efficiency standards for houses has found, challenging the fierce counter moves to greener housing from the building and housing lobbies.

According to the report the savings can be up to a substantial $7500 on construction costs alone.

But there’s a catch. The report also found a large proportion of houses were not meeting the NatHERS environmental rating indicated for the premises.

The report, The Evaluation of the 5-Star Energy Efficiency Standard for Residential Buildings, looked at the effectiveness of the 5-star NatHERS energy efficiency standard for houses introduced in 2006, compared with the previous 3.5-4 star standard.

A source told The Fifth Estate it was recently released on the Department of Industry’s website without fanfare or publicity. Under the previous Labor government, the now-abolished Department of Climate Change and Energy Efficiency had engaged the CSIRO in 2012 to work out whether the 5-star standard increase was having the intended effect of reducing heating and cooling costs, and reducing greenhouse gas emissions, as well as looking at the costs and benefits involved in meeting the increased standard.

The main findings of the report were:

Lower cost buildings

Higher-rated houses cost at least $5000 less in Adelaide and Melbourne for those elements of the building related to energy efficiency than lower-rated houses, and up to $7500 less in Brisbane. The report said that increases in insulation and a shift to more rectangular house design (leading to a larger floor area per unit of wall and glazing) were the most influential aspects leading to lower costs observed in the shift to higher-rated houses.

“In the [regulation impact statement], the costs of meeting the 5-star standard were expected to be more than for lower-rated houses,” the report stated. “However, our results show that based on the sampled house designs, it has actually been less expensive to meet the 5-star standard than the previous standard.”

“The average cost for those elements of a building that are related to achieving the star rating were $7500 less in Brisbane, $5500 less in Adelaide and $5000 less in Melbourne.

Although the cost of insulating a property increased, this was more than offset by savings made on walls and windows.

To estimate the costs incurred in achieving the various star-rating standards, the analysis focused on elements directly related to the star rating:

• window area
• window orientation
• glazing material
• floor, wall and roof materials
• wall area
• insulation

Lower energy costs in winter, and warmer houses

The 5-star standard significantly reduced the energy needed to maintain house temperatures in winter. As well as saving energy, high-rated houses also maintained a temperature that was 1°C higher than lower-rated homes during winter.

If higher-rated houses maintained the same temperature as the low-rated houses, there would be a 20 per cent reduction in electricity used for heating in Brisbane, a 30 per cent reduction in Adelaide, and a 56 per cent reduction in gas use in Melbourne.

Higher cooling costs

Surprisingly, the average cooling energy use in summer was greater in higher-rated houses in Brisbane and Melbourne.

“It is not clear whether this was due to the 5-star standard, the make-up of the house occupancy of higher-rated houses with more children and higher rates of full-time occupancy, or other behavioural factors,” the report stated. “These include the extent of window opening and closing during summer, and the scale of heat loads from other home appliances and equipment.”

It also noted “particularly hot 2012–13 summer months” and airconditioning running at full capacity as a potential confounding factor.

“If this was the case, then the measured energy consumption is merely an indicator of the installed capacity of the airconditioners, rather than a measure that can be used to assess the effect of star rating.”

Running costs

The net impact of heating and cooling costs resulted in higher-rated homes being cheaper to run in Adelaide and Melbourne. The reduction in running cost in Melbourne was significant, on average $194 a year cheaper than a low-rated house.

However, homes were found to be more expensive to run in Brisbane, due to increased cooling costs.

When considering whole-of-house energy consumption, cost reductions were observed in Adelaide and Melbourne for higher-rated houses, with a three per cent reduction in costs in Adelaide and a 13 per cent reduction in Melbourne. Brisbane houses showed no difference.

Overall, there was a reduction of 195 gigawatt hours of energy, saving $11.6 million.

Reduced greenhouse gas emissions

Greenhouse gas emissions were reduced in all cities for higher-rated homes, though summer emissions increased. Overall, however, there was a seven per cent reduction in GHG emissions across the board, a saving of 25,000 tonnes of carbon dioxide-equivalent.

Houses not meeting their reported star rating

The report found that many houses, when re-rated, were not meeting their initial NatHERS ratings.

A significant proportion of houses were below their original rating, even allowing for a half-star tolerance, the report stated.

“Adelaide was the best performing, yet still had 43 per cent of houses rating below their original rating; in Brisbane and Melbourne, around 50 per cent of the houses were re-rated below their original rating.”

The report said that caution was needed in interpreting the results, as the NatHERS software used to re-rate properties was a newer version than would have been used to calculate the original rating, and that assessment protocols used by the assessors would have also changed over time.

In general, average NatHERS star ratings have increased over the past nine years, however.

Need for further investigation

The report only focused on a sample size of 414 detached (including 20 semi-detached) houses built in the last 10 years in Brisbane, Adelaide and Melbourne, so the authors expressed concern about generalising the results to other house types, and noted that the small sample size made it difficult to draw firm conclusions.

The authors said more research was needed into why there was an increase in cooling energy use in higher-rated buildings, and that the data could be used to explore a range of industry issues, including:

• quantifying the impact of thermal loads, such as cooking appliances, entertainment and home office electronics, standby loads and human metabolism, which may favour heating efficacy in winter over cooling efficacy in summer
• identifying the variety of human behaviour (such as opening windows) and thermal comfort factors (for example, thermostat settings) affecting energy consumption, and informing the Australian public about improving thermal comfort and saving energy in their houses
• using this information to better understand which house design solutions are most appropriate for summer cooling-dominated climates
• identifying the relationship between the peak cooling demand predicted by the Chenath engine and airconditioner sizing, and informing the residential airconditioning industry of opportunities for improving energy efficiency and reducing costs

Read the full report.