• Energy Research
• 12. Responsible consumption close

An increased awareness of the impacts of synthetic refrigerants on the environment has prompted the refrigeration industry and researchers worldwide to seek better alternatives in terms of technical, economic and environmental performance. CO2 refrigerant, also known as R744, has re-emerged as a potential alternative to existing refrigerants with its zero ozone depletion potential (ODP) and impressively low global warming potential (GWP). A refrigeration system utilising this refrigerant, however, suffers performance degradation when it operates in warm or hot climatic regions due to its inevitable operation in the supercritical region. In addition, the CO2 refrigerant properties necessitate the need for components designed to withstand very high operating pressures. These challenges have not been let unnoticed; related industries and researchers are actively involved in research and development of various components and systems which in turn encourages increased applications of these systems. In this paper, a comprehensive review of CO2 refrigeration systems and the state of the art of the technology and its applications in various industries is presented. In particular, the paper reviews recent research and developments on various aspects of CO2 systems including cycle modifications, exergy analysis of the systems, system modelling, transcritical operation consideration and various existing and potential applications.

The life cycle energy of a residential building consists of the embodied energy involved in the building materials and construction, and the operational energy of the building. Previous studies into the life cycle energy of buildings have concluded that embodied energy is a relatively small factor and can generally be ignored. A review and analysis of previous life cycle energy analysis studies was conducted re-examining this conclusion. This reevaluation has identified that this is not the case when considering climatic factors, and that in milder regions embodied energy can represent up to 25% of the total life cycle energy. The time value of carbon is generally ignored in life cycle energy analysis studies, however in a national emissions reduction regime, when the energy consumption is reduced, can become an important factor. Applying Net Present Value principles the impact of embodied and operational energy was analysed in the context of a future emissions target. It was demonstrated that embodied energy can represent 35% of the future emissions target of a building in a mild climate. The research highlights that a more wholistic approach is needed to achieve low life cycle energy buildings in the future.