Energy performance, thermal comfort improvement and control strategies of building air-conditioning systems

Energy cost is one of the major expenditures throughout the lifecycle of a building. Due to the rising cost of energy, efficient operations of air-conditioning systems in buildings have become more and more important. The main objective of this study is to analyse the energy performance and thermal comfort improvement of air-conditioning systems in buildings in a subtropical climate, and to evaluate low energy cooling control strategies for energy conservation and retrofit of the existing facilities. The thesis is divided into four major sections. The first section presents details of the energy audit of the existing building systems. The second section discusses the development of the building energy simulation models for the existing system. The third section deals with different cooling control technologies for achieving better indoor thermal comfort and energy savings. The fourth section details the life cycle cost analysis for each of the control strategies to achieve better thermal comfort and energy saving, and to support decisions for retrofitting the existing building systems.Standard specifications based on the Australian/New Zealand Energy Audit Standard are followed in this study. DesignBuilder, an energy simulation tool, is used to predict energy performance and thermal comfort in existing buildings. Different measures of passive cooling that are compatible with existing buildings in a subtropical climate are studied with an aim to reduce the energy consumption and peak demand associated with the cooling. The energy performance, the indoor environment and green house gas emissions by office buildings in Queensland, Australia are studied under three passive cooling technologies namely chilled ceiling, pre -cooling of building thermal mass and economiser usages with life cycle cost analysis. The existing operating conditions and thermal comfort requirements of the occupants are considered to determine the most suitable retrofit strategies.The study suggests that the increased consumption to contest high temperatures and relative humidity can be minimised by improved control strategies and optimised use of the energy. The whole building energy simulation was performed based on the characteristics of the existing building systems. Good agreement between simulated and measured data was found. By comparing the retrofitting option, this study has found that, as passive cooling alternatives, chilled ceiling and pre -cooling have the higher potential for energy conservation and better indoor environment depending on the activities in buildings. Therefore, applications of chilled ceiling and pre -cooling of building thermal mass in subtropical regions like Rockhampton are essential. The study also reveals that passive measures can be successfully applied to buildings located in warmer climates, where high-energy use by air conditioning systems is required. In terms of greenhouse gas emissions, chilled ceiling is the best of the passive cooling technologies compared to current practice, and it produces less emission per year. Economiser system and pre -cooling of the building thermal mass would also generate less CO2 to the environment compared to current practice. It is found that chilled ceiling has the lowest life cycle cost and highest net energy savings of the strategies considered, and is the most cost effective passive cooling option for subtropical climate buildings.