Microcontroller-based integrated data logging system for solar air heater performance assessment

Efficiency curves for assessing solar air heater (SAH) performance are determined by measuring different parameters under certain operating conditions recommended by different test standards such as American Society of Heating, Refrigerating and Air-Conditioning Engineers. In this work, development and testing of a low cost integrated datalogging system for tracing efficiency curves are presented. Pyranometer (CMP11) and temperatures sensors (DS18B20) are integrated with microcontroller (AT89S52) for continuous data recording at desired time interval. Switching devices are integrated to automatically control operations of electric heater for maintaining inlet air stream temperature as per testing requirements. Using the system, efficiency curves of a 1.46 m2 SAH installed in Tezpur University, India, are determined at two mass flow rates of air. Results are comparable with published literatures revealing negative slope (energy loss component, FRUL) and positive intercept (energy absorption component, FR(τα)n) of efficiency curves. SAH shows better performance at lower mass flow rate of air (0.0235 kg/m2-s), with FRUL as 13.5 W/m2-K compared to operation at 0.0430 kg/m2-s mass flow rate of air where slope increases by around 23% with same intercept. Higher slopes of the SAH demonstrate its highest sensitivity to prevailing wind compared to three previously published designs. Present study shows that the integrated system can replace individual traditional measuring instruments for respective parameters like solar irradiance and temperatures as well as additional control equipment required to maintain desired test conditions. Further development of the system can lead to a modular and portable efficiency curve tracer for SAH performance assessment.