Performance Evaluation of Dual Purposes Solar Heating System Using Heat Pipe Evacuated Tube Solar Collector

Abstract

The aim of this work is to develop dual purposes solar heating system using heat pipe evacuated tube solar collector. The heat transfer fluid between the thermal loads and the solar collector loop was heating oil. The study provided two thermal loads; solar water heating system and solar baking/cooking system that had experimentally investigated under various weather conditions. The experimental pilot unit was installed in Solar Energy Department, National Research Centre, Giza, Egypt. Several test runs were performed to measure all assigned parameters that affect the system performance. The system is designed to provide high thermal energy through hot oil surrounding the inner vessel of the baker while the raw food can be baked/cooked and the outlet thermal energy can be used for heating water via immersed coil in the hot water storage tank; then the relatively cooled oil is returned to the solar collector via hot oil circulating pump. The water tank heat exchanger is designed with the following design parameters; specific heat of oil and water were 1.67 kJ/kg o C and 4.186 kJ/kg o C respectively; density of oil and water were 850 kg/m 3 and 1000 kg/m 3 respectively; mass flow rate of oil and water were 12 liters/min and 6 liters/min respectively. It is clear that the system in addition to provide thermal energy for baking/cooking unit, it can provide thermal energy for water heating purposes. The tested system can be positively contributed in baking and cooking purposes and providing hot water as well. It is found that, for the same flow rates of hot oil and water, as the hot oil temperature difference increased, the outlet hot water increased. The system is capable to produce hot water temperature up to 85 o C if the hot oil temperature difference was 100 o C while it can produce hot water temperature about 60 o C if the hot oil temperature difference was 60 o C during the day which is suitable for residential purposes and industrial process as well. Based on the resultant data, it is found that the system solar fraction was estimated as 54%. The auxiliary heating system can be electric source in case of using in urban areas and can be renewable energy source like biogas or hydrogen fuels in rural and isolated areas.

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