TREES PROVIDE ENERGY SAVING BENEFITS TO ADJACENT BUILDINGS FOR A SMALL WATER COST Stephen Livesley 1 , L Aye 1 1 The University of Melbourne, Melbourne, Australia, 2 City of Melbourne Council, Melbourne, Australia INTRODUCTION Urban centres are a major source of greenhouse gas emissions and energy use. In Australia, Building energy use is responsible for 23% of greenhouse gas (GHG) emissions, more than half of which comes from the residential sector (CIE, 2007). In Australian residential homes, about two thirds of energy is used for heating and cooling (incl. water) (CIE, 2007). Residential (and commercial) space cooling is forecast to rapidly increase by up to 16% per annum (DEWHA, 2008), but will still only represent 4% of total residential energy consumption in 2020. However, the problem of space cooling on hot summer days is a key issue to sustained electricity provision at times of peak demand. The urban heat island and extreme summer heat waves both intensify the cooling load that residential, office and commercial buildings experience, and consequently that the occupiers may experience. Trees can reduce the cooling load through direct shade, and cool the external micro-climate through transpiration. Trees require rainfall or irrigation to provide these benefits, otherwise these benefits are limited and tree health suffers. There have been several key studies investigating the cooling energy savings achieved through tree shade (Simpson and McPherson, 1996; Akbari et al. 1997; Donovan and Butry, 2009; Pandit and Laband, 2009). These studies document the impact of tree shade on the cooling energy demand through small-scale empirical data collection, large-scale modelling and large-scale surveys. Akbari et al., (1997) measured seasonal cooling of two full-scale residential buildings provided energy savings of up to 30% (4 kWh per day) and estimated peak energy demand savings of 0.7 kW for each of the houses. Simpson and McPherson (1996) reported that shading on the west side of houses showed the highest reduction in cooling energy demand and that adding two shade trees on the west would reduced annual cooling costs for the house by between 10-50%. Pandit and Laband (2009) through a broad survey of 160 households in Auburn Alabama and economic analysis of behavioural energy use estimated that 50% shade could reduce power use by almost 20% in a “typical” residential house. Similarly, Donald and Butry (2009) used energy bills from 460 households in Sacramento, California alongside their levels of tree shade to estimate that tree shade was reducing electricity use by 5.2%. The simulations Akbari et al., (1997) performed subsequent to their field measures underestimated the energy savings by up to 50%. This indicates the complexity of modelling the impact of tree canopy processes and the problem of inherent assumptions and approximations. The thermal load reduction and energy saving benefits of trees is not due simply to the direct shade effect, in fact the transpirative cooling process can provide the greatest benefit in warm dry climates (Akbari et al. 2009). This highlights the important realtionship between tree shade and tree water availability to realise the maximum thermal and energy savings. Comparable studies on the impact of tree shade upon builing thermal loads and energy use have been undertaken in the southern states of North America. This climate typically produces hotter summers and colder winters than those expereinced in Melbourne, Victoria. It can be assumed that the energy savings from the presence of trees shading a building will be smaller. Similarly, many of these studies have investigate the energy saving benefits of deciduous trees as it is assumed they provide the greatest annual benefit, through deep summer shade whilst enabling some solar gain in winter months. However, in Australia evergreen native canopies are found throughout our urban landscape and comparative research is required to place their benefits in context. The aim of this study is to directly quantify the reduction in cooling loads upon external walls from the presence of deciduous exotic or evergreen native trees in a Melbourne climatic context. The water use of these trees will be quantified concurrently to gauge temperature reduction benefit in consideration of water uptake cost. Several hypotheses were contructed to be tested:  Deciduous tree shade will provide greatest reduction in summer thermal load and inward heat transfer.