Design, construction and performance testing of a solar powered refrigerator and heat-pump for urban streets vendors

Abstract

Solar powered refrigeration systems have been a prominent topic in recent years. Designing a system that relies on entirely solar energy will help in achieving some goals of developing countries, to have a clean source of energy and to reduce reliance on fossil fuels and national electricity grids. The main objective of this study is to design and conduct testing analysis of a refrigerator and heating-pump unit driven by solar energy; it is intended to introduce a hybrid system which can satisfy both cooling as well as heat collection. However, this research aimed at analysing an optimum solar powered cooling (refrigeration) and heating system that work as one unit by creating a solar cooler and solar warmer that is powered by the same compressor. Given that, the warming (heating-pump) system is dependent entirely on the performance of the condenser while the cooling system is made widely from available domestic refrigerator components based on the vapour compression principle, which components are to be matched to each other and to the solar PV system. The idea of using the heat (rejected to the atmosphere) from the condenser to warm up foods is a unique approach of research. Experimental and analytical methodologies are applied to give technical details on how this hybrid system will fit with the existing facility, to provide reasons why the model will be in small scale for street vendors, and to promote small enterprises in rural communities. This paper illustrates the design procedures and calculations necessary to properly size main components such as the battery, PV panel, charge controller and compressor as well as determine the heat load of the entire system. The model was designed and built in the mechanical engineering workshop of Cape Peninsula University of Technology, and the prototype was installed and tested under atmospheric conditions for performance evaluation at the Bellville campus. The design methodology applied was supplemented by both MATLAB programming and ANSYS simulation for validation; readings for wind speed, ambient temperature and solar radiation were taken from the Campbell scientific weather station and analysed. The testing was undertaken at no loads and then fully loaded compartments to evaluate the performance of the system. Experimental results showed that both systems work well at peak hours and also when there is more sunray. Irregularities occurred when the doors were left open for an extended period which caused loss of energy. Although the average COP of the entire system was 3.3, the data revealed that there is still room for improvement, especially if the prototype is to be marketed.