Abstract:In an effort to reduce the environmental impact of the energy sector that is mostly based on fossil fuels, researchers are looking for a clean alternative of our existing energy sources. Hydrogen Energy and Fuel Cells, and in particular Polymer Electrolyte Membrane Fuel Cells (PEMFCs) have emerged as a leading candidate for transportation as well as stationary and portable applications. Due to the irreversibility of the electrochemical reactions and ohmic heating in the fuel cell components, the PEMFC produces a significant amount of heat and this heat has to be removed in order to avoid cell or stack overheating. In this paper, a review of the key heat transfer mechanisms and the various cooling strategies that are available for heat removal from PEMFCs are presented. Due to the interrelated nature and difficulty of conducting in-situ thermal measurements on the operating PEMFCs, computational modelling provides a fast and efficient way of designing PEMFC cooling systems and understanding the heat transfer mechanisms. Therefore PEMFC thermal modelling is also highlighted together with present challenges and potential areas for further research and development works.

A 35kW pilot solar powered absorption cooling system was designed and constructed at Moot Hospital in Pretoria to investigate the technical and economic performance of the technology. Technically, the system produced an estimated 43.938MWh of cooling energy per year and reached a maximum power of 31kW and operated with an average COP of 0.63, which compares favourably with the 0.7 given by the manufacturer. This system has since been decommissioned. Unfortunately, due to a lack of standard design and operation information, the system was overdesigned. As a result, the economic performance of this technology could not be accurately determined.

The demand for air conditioning is increasing due to changing architectural trends and increased standards of living and indoor comfort conditions. Coupled to this, refrigerants used in conventional refrigeration systems have detrimental effects on the environment. As a result, there is an urgent need to implement environmentally cleaner ways of satisfying this air-conditioning demand. Absorption cooling systems have shown great potential to do so. In this study, system performance data for an autonomous solar heating and cooling system installed at the Vodafone Site System Innovation Centre, at the Vodacom Campus in Midrand was collected and analysed. The system comprises a 116 m2 vacuum tube collector array, a 6.5 m3 hot water storage tank, a 35 kW LiBr-Water absorption chiller, 1 m3 of cold water storage, a dry cooler for the chiller, and two underground thermal stores to pre-cool the supply air to the building and the dry cooler respectively. System performance data was collected from the beginning of December 2011 to the end of January 2012 and used to estimate the system long term performance. The chiller has an average coefficient of performance (COP) of 0.51 whilst the solar COP has an average value of 0.24. The total installation cost is R2 822 436.89, with an annuity of R225 949.75 and a cost per kWh of R28.88.