Environmental Assessment of Air-conditioning Systems in Offices. Some Aspects Related to Design

Licentiate thesis, 2003

The primary function of an air-conditioning system, i.e. to fulfil given requirements on indoor climate in a specific building, can generally be achieved by several system designs. The systems may have varying environmental performance. Today, the final selection of the most appropriate air-conditioning system is, however, seldom based on relevant information about the environmental performance due to lack of incentives and methods. The aim of this thesis is to describe how the environmental performance of air-conditioning systems for comfort cooling in office buildings can be assessed and evaluated at the design stage. The more traditional design aspects of air-conditioning systems related to thermal climate, energy efficiency, flexibility, etc. are outlined and how they affect the environmental performance are discussed. Moreover, environmental assessment methods are discussed and the use of an LCA based weighting method is exemplified in four case studies. In addition, the impacts of energy use and component materials, as well as the influence of technical and environmental assumptions, are discussed in general. It is shown, in the work of the thesis, that LCA based weighting methods can be used for environmental assessment of air-conditioning systems. The required effort to use these methods is further reasonable in relation to design practice. Therefore, the LCA based weighting methods are appropriate for the early stage of design process and may lead to a wider usage of the environmental assessment. The interpreters of the results and decision-makers have, however, to be aware of the limitations and trade offs of these methods in order to draw appropriate conclusions. It is also shown that the major contributor to the environmental impact of air-conditioning systems in general is the operating energy use, especially the use of electricity for the operation of fans. Accordingly, the environmental performance is strongly affected by assumptions about the electricity mix used. To facilitate the use of environmental assessment the selection of an appropriate method should be implemented in the environmental management system of the design company. Moreover, to create and implement a database in the environmental management system would lead to timesaving and improve the environmental assessment in the design company.