Development and analysis of a practical absorption air conditioning system employing waste heat recovered from vehicle exhaust

The air conditioning and transportation sectors comprise the largest shares of energy consumption in Hong Kong, offering a key perspective on tackling the citys 2050 carbon neutrality goal. Traditional air conditioning systems in vehicles operate on a compression refrigeration cycle, expending a large amount of shaft power to compress the refrigerant in a gaseous state. In this project, an absorption refrigeration system that operates on waste thermal energy from vehicle exhaust was developed and analysed. The refrigerant is absorbed in water and pressurised using a solution pump, saving on shaft power compared to traditional air conditioning systems that compress the refrigerant in vapour form: in contrast to the process of gas compression, no work is done when the pressure of a liquid is increased because it is incompressible. A mathematical model was developed to simulate the systems working process under different conditions. Parameters such as the desired indoor temperature, the temperature of vehicle exhaust, and low- and high-ammonia concentration solution concentrations were manipulated to find the optimal combination that yielded the highest coefficient of performance. An experimental facility was then designed and constructed to verify the efficacy of the absorption air conditioning system. Findings from the theoretical and experimental investigations show that the system produces cooling at reasonable efficiency, bearing feasibility to be installed in vehicles to reduce energy consumption and minimise carbon emissions.