Modelling the life cycle energy and greenhouse gas emissions of responsive shading systems for office buildings

© 2011 Dr. Myles E. BunningTechnological advances in office facade construction have resulted in better sealed buildings in which humidity and temperature can be tightly controlled within predefined ranges. However, one consequence of ‘tighter buildings’, is that the modes of heat transfer are restricted. In temperate and sub-tropical climates, tighter buildings can also be more likely to trap heat. Since the application of curtain walling techniques for highly glazed buildings, the transmission of heat through the building envelope has become one of the primary determinants of the heating, cooling and ventilation requirements of office buildings. Solar energy can be absorbed and reflected away from the interior using shading and daylighting devices and is an important measure to reduce the energy consumption of an office building. To distribute solar energy at the facade level with different shading devices, the energy expended on producing and using and disposing of components of the building can differ over different periods in the building’s life. This thesis examines two related strategies to mitigate against solar-radiation causing overheating whilst maintaining daylight levels and addressing the issue of glare over a building’s life cycle. In contrast to solar protection with static shading overhangs or louvres, the responsive shading system considered here allows for real-time adjustments to venetian blinds through a building automation system which tracks changes in weather and luminance. The facade permutations are tested against a base case for overall life cycle energy performance by tracking operational and embodied energy and the associated greenhouse gas emissions. The importance of embodied energy in such an application is prone to underestimation. An input-output-based hybrid analysis method was used to provide a more comprehensive overview of the embodied energy than other methods of analysis. Thermal peak load and light control simulations of the case-study building were undertaken to determine system component sizing for a hydronic system comprising a chilled beam cooling and baseboard heating loops. For this system, it was found that even though the largest amounts of life cycle energy and emissions were associated with a subtropical Australian climate when compared with a temperate southern Australian climate, the proportional reduction in life cycle energy and emissions achieved with an external automated shading device was greater for the temperate southern Australian climate. The importance of this study lies within tracing additional indirect energy impacts beyond the direct energy impact of shading, within the context of current facade and HVAC office refurbishment practice. By tracking the direct and indirect energy impacts throughout a building’s life cycle, the potential for greenhouse gas emission reductions can be assessed