Methods for assessing environmental, safety and performance of alternative refrigerants
This thesis addresses the general subject of implementation of refrigerants that are alternatives for ozone depleting substances. In particular it covers three topics, which are environmental assessment, system performance and safety aspects related to flammability. The first Part examines the current means of assessing the global wanning impact of systems, and proposes an improved approach. The second Part presents a new balancing technique for designing systems that use refrigerants with a temperature glide, as an advancement over the conventional technique for pure refrigerants. The third Part derives a quantitative risk assessment model to be employed for evaluating the safety of hazard of flammable refrigerants. The concept of'Total Equivalent Warming Impact'' is introduced in Part 1, which is currently used by manufacturers, installers and end-users of refrigerating systems to evaluate the contribution to climate change resulting from energy consumption and refrigerant leakage. It was found that existing methods rely on many assumptions, so a thorough approach was proposed to assess the relevance of the assumptions and providing ways of avoiding them. An alternative measure for interpretation of consequences of greenhouse gas emissions is also included. Part 2 investigated the existing approach for rating and balancing sy stem components, which were found to be incompatible when applied to zeotropic refrigerants. Differences in the performance of components using pure and zeotropic refrigerants were identified, and so a new method for component rating and an advanced system balancing technique were developed based on the properties specific to zeotropes. Within Part 3, a framework for calculating ignition frequencies and consequences of a release of hydrocarbon refrigerant is presented. A major element of these calculations is the evaluation of certain quantities of the flammable mixture, and the model developed for this purpose w as based on the results from a series of gas dispersion experiments.