Experimental Study of Hybrid Flat-Plate Solar Collector/Nocturnal Radiator for Water Heating and Cooling in Owerri, Nigeria

Abstract

The quest for new, alternative energy sources and technologies have risen due to myriads of crises associated with fossil fuel dominated energy mix in Nigeria, in terms of supply and its adverse effect on the environment. Experimental study of hybrid flat-plate solar collector/nocturnal radiator for water heating and cooling in Owerri, Nigeria, is presented. The experimental rig consists of a single flat surface (absorber plate) made of a mild steel plate, film-coated with an acrylic resin which made the surface spectrally selective. Underneath, were arrays of copper tube risers. A sample test on acrylic resin’s coating, on a metallic substrate showed that it has high clear spectral absorptivity (low emissivity) in the solar radiation band (0.2-0.3µm) as well as low absorptivity (high emissivity) in the atmospheric window band (3-8µm). A water reservoir 2m above was connected to the system inlet header to supply water. Experimental data were harvested for days/nights through a read-out basic language programmed data logger. The experimentation were conducted under the metrological condition of Federal Polytechnic Nekede Owerri (5.49oN, 7.02oE), South-East Nigeria. The results obtained under solar heating phase showed a peak water temperature of 60⁰C at a plate temperature of about 80⁰C and a heat collection efficiency of 31%. The peak insolation was about 900W/m2 and the ambient temperature was between 27⁰C and 32⁰C throughout the diurnal phase. Also, under the nocturnal radiation phase, a cooling power of 41w/m2 was achieved during cooling on clear night and about 20w/m2 on a cloudy night. Water temperature in the range of 19⁰C to 20⁰C was recorded at temperature depression of about 5⁰C. The night sky temperature of the location was obtained in the range 10⁰C to 16⁰C for the period under study. The result shows that the system can provide substantial energy savings when incorporated into building structure, to providing hot and cold water for domestic/process use, space heating and cooling applications.