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.

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The author believes CO₂ to be a promising future refrigerant due to the threat to the HFCs of restriction or elimination posed by legislation planned in many countries. This thesis addresses the feasibility of using reciprocating compressors in a transcritical CO₂ heat pump working in cooling and/or heating modes through the use of computer modeling. A detailed simulation model of a reciprocating compressor is combined with semi-detailed gas cooler, evaporator and internal heat exchanger models to produce complete cycle model of systems having one and two stages of compression. Measured data from the open literature for CO₂ compressors and single-stage heat pumps was used to validate the models. Piston ring-cylinder leakage and valve dynamics are included in the compressor model. The influence of ring-cylinder clearance on heat pump performance is investigated as is the influence of heat pump running conditions on valve dynamics. Prior to this study, there were no models known to the author for CO₂ heat pumps which incorporate a detailed simulation of the compression process. Furthermore, there were no models for CO₂ heat pumps incorporating multi-stage compression. This study provides insight into the manner in which a CO₂ heat pump might perform in both cooling and heating modes for running conditions representing summer and winter. The models are believed to be of value to other research workers, plant designers and plant operators. As a result of this study, useful techniques have been provided for the design and manufacture of environmentally safe and energy efficient heat pump systems; it is hoped that they will make a positive contribution to the reduction of effects harmful to the environment and its inhabitants in the future.

International environmental concern led to the control and phase out of traditional chlorofluorocarbon refrigerants (CFCs) under the terms of the Montreal protocol. CFCs used in domestic applications were initially replaced with hydrofluorocarbons (HFCs) such as R134a which has a zero ozone depletion potential (ODP). The use of HFCs has also come under scrutiny as they have high global warming potential (GWP) and inferior thermodynamic and lubricating properties and have been replaced by hydrocarbon (HC) refrigerants such as R600a in much of the domestic European and Asian markets. Despite this, there has been little research into the long-term environmental consequences of their application. Domestic refrigeration compressors were analysed to ascertain the tribological contact conditions for both R600a and R134a systems. A novel pressurised micro-friction test machine was developed to simulate the tribological conditions of the critical components using aluminium on steel samples. Refrigerant charges of R600a with mineral oil (MO) and poly-ol-ester (POE) lubricant and R 134a with POE were tested for their tribological performance within the test rig. Experimental tribological information is presented from the physical test procedures to establish wear mechanisms and friction coefficients within the critical components. The tribological performance is used to predict deterioration in energy consumption and system durability. Results indicate that for higher contact stresses R600a MO charges provide a lower wear regime than R600a and R134a POE charges. At lower contact stresses the R600a and R134a POE charges provide a very low wear, very low friction regime. Despite contact conditions lead to a faster deterioration in durability, hence increase in energy consumption compared to the R600a system.