The energy-saving benefits of urban trees

The research facility at Burnley campus continuously measures the energy-saving benefits of native evergreen eucalypts and European deciduous trees. In summer, the sun’s energy passing into the building is directly measured using heat flux sensors on the walls, ceiling and floor, measuring heat coming in during the day and heat lost overnight and during winter. Through direct measurements this research is able to quantify the combined cooling from canopy shade on the walls and the affects of transpiration.

The facility was built and instrumented by an interdisciplinary team from the Melbourne School of Land and Environment, Engineering and Architecture, and funded by the Nursery and Garden Industry Australia.

Dr Stephen Livesley from the School of Land and Environment said most people know the cooling benefits of tree shade. “What is interesting is that most of the cooling is coming from transpiration, where trees release moisture to cool themselves and the air around them,” he said.

“These energy-saving benefits are another reason to value trees and they should be seen as an asset, adding value to houses and communities. Trees are often an afterthought in the planning process, but if you can quantify in dollar terms the benefits they provide, you can communicate the long-term advantages. But to do that you need to have clear, scientifically backed data.”

To this end, the facility will measure the energy entering into and out of a single-dwelling building over a 12-month period. This will enable a fair comparison between evergreen trees and deciduous trees by accounting for the various factors involved in year-round energy savings.

“The shade from the evergreen trees cools the building in summer, which is good, but it can also make it colder in winter; while the deciduous trees allow the sun through during winter and often develop a dense canopy in summer which provides excellent shade,” Dr Livesley said. This study is also able to quantify the amount of water that these trees use in providing their shade and transpiration benefits.

The City of Melbourne’s Urban Forest Manager, Ian Shears, said trees are increasingly being viewed by local and state governments and the community from an environmental services perspective, rather than traditional amenity or heritage values.

“Research that quantifies the benefits of trees in energy conservation greatly enables mechanisms and strategies to be put in place to influence positive urban forest outcomes on both private and public land,” Mr Shears said.

“This form of research enables trees to be viewed as a benefit rather than a cost in budgetary and works considerations, planning controls and development planning.”

Similar studies in the US have estimated that the shade of large trees can save an average household between $100 and $250 per year, depending on the climate of the area.

The results of the research are intended to give ‘proof-of-concept’ and to provide direct measurement data that can be used to validate models used by engineers and architects to predict the energy balance of a building or a community.

See: www.landfood.unimelb.edu.au/green