Full thermal-hydraulic and solar modeling to study low-cost solar collectors based on a single long LDPE hose

Abstract

A comprehensive analysis of low-cost solar collectors based on a single long plastic LDPE hose resting on a roof and working by thermosiphon is performed. This lay-out involves two challenging issues, high hydraulic resistances and low tilt angles, which shall be solved. We have developed a full thermal-hydraulic and thermal-solar modeling to optimize the collector's parameters to achieve a good performance under thermosiphon conditions. This modeling leads to strong coupling effects between the variables, showing that thermal-hydraulic mechanisms are as important as thermal-solar phenomena. We have investigated several cases comprising variation in the collector's parameters: hose diameter and length, tank height and volume, number and quality of glazing layers, roof tilt angle and climatic conditions. It is found that, all year round, this collector can provide 150l of sanitary hot water at minimum 45°C in tropical and temperate climates by using a 100-meter 1.5″-diameter LDPE hose, for roofs tilted 20° or more. In addition, for horizontal roofs, the desired goal could be achieved with a 2″-diameter hose instead. On the other hand, the model also shows that using longer hoses and many wrapping layers lead to worse performances, meanwhile to raise the tank causes slight improvements. The proposed modeling, comprising three coupled phenomena, makes possible to design a simple and robust collector that can be locally manufactured using materials available in hardware store. Due to cost and maintenance feasibility, we find that this option could be useful for developing countries with temperate and tropical climates.