The earliest refrigerants used were R40, R764, R717, R290 and R600a but these had drawbacks of flammability, toxicity, unpleasant smell as well as a challenge of leakage through the shaft seals of compressors. In 1931, these were replaced by CFCs and HCFCs due to safety and reliabilty concerns. However in 1986, CFCs and HCFCs were confirmed to have an ozone depleting effect and their use discouraged under the Montreal Protocol. Manufacturers responded to this call by introducing HFCs with no ozone depleting effect. Today, there is immense pressure to shift to natural refrigerants after the discovery that emission of these substances to the atmosphere contributes to atleast 20% of the greenhouse gas emissions. The use of synthetic refrigerants has led to the breakdown of strastospheric ozone molecules and emission of greenhouse gases to the atmoshere causing global warming and global climate change. Today, there is increasing pressure from legislators, business partners and consumers to seek for new methods to achieve cooling that does not depend on global warming working fluids.  Therefore, companies are tasked to rethink established solutions  and implement environmentally friendly yet economically sensible technologies to seize their individual eco-advantage.  For that matter, the use of refrigerants free of ozone depleting and global warming characteristics in Heating, Ventilating, Air Conditioning and Refrigeration continues to take a central role in measures to reduce greenhouse gas emissions. This study aimed at investigating the application of environmentally friendly solutions in refrigeration applications of Uganda with major emphasis on natural refrigerants. This was accomplished by ascertaining the current status of refrigeration in the country as well as computer simulation modelling of the available systems and comparison of the results with those of recommended systems. A field study was carried out to assess the current status of refrigeration in the country i.e refrigerants used and the type of systems currently in use. It was found that synthetic refrigerants predominate and the systems currently installed are single stage, vapor compression. Operating parameters of these systems were then measured and models of these systems developed using EES software and their efficiencies determined. Furthermore, models were developed and proposed  for each sector using an appropriate natural refrigerant and efficiencies determined. Comparisons were then made with installed systems and it was found that natural refrigerants offer a promising solution in the refrigeration applications of Uganda and should be adopted for energy, safety and environmental issues. However, for this transition to be realized, there is need to create awareness in industry as well as the government taking the lead in the development of a phase out plan with support from industry and research institutions.

A key challenge of current multi-user web applications is to provide users with interesting events and information in real-time. This research reviews the most common real-time web techniques to identify drawbacks while exploring solutions to improve simplicity, efficiency, and compatibility within a client-server environment. Two solutions are proposed for enhancing the efficiency of real-time web techniques by reducing client-server communication. First, a model of browser monitoring control observes the browser activity and decides if to postpone client-server communication in the case of inactive tabs. This model was implemented and tested with results demonstrating that a significant number of client-server connections can be avoided in the browser background. These results suggest the solution can be optimised for any real-time technique as it benefits from being a developer side technique that works consistently on all browsers. Second, ‘Adaptive Polling’ is a pull-based real-time web technique to overcome bandwidth issues of the reverse AJAX method of ‘Polling’ by controlling the frequency of requesting updates from the server based on the last server response. This approach is implemented and tested with results showing how a significant number of redundant connections can be avoided while the server does not return updates. This solution is a good alternative to other real-time web techniques as it features low latency, the simplicity of implementation, and compatibility with all browsers and servers.

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