Development and assessment of a low cost sensor for solar heat flux measurements in buildings

This paper presents a new type of low cost solar sensor, i.e. a black and white sensor (BWS). The BWS uses the difference in temperature of a white surface (solar energy highly reflected) and a black surface (solar energy highly absorbed) to estimate the solar heat flux through building openings. Results are obtained through a correlation based on a thermal model of the sensor. The correlation contains calibration factors determined from an initial on-site calibration. Results of estimated solar heat flux with two designs of the BWS over two different periods of time were compared with solar measurements of a high precision pyranometer. The two designs of BWS have shown mean weighted relative errors over the sampling periods under 4% for the daily integrated solar energy measured. Finally, a sensitivity analysis of the calibration period was conducted and it was observed that ideal calibration period should consider at least half a day of measurements, including solar peak time, and should be done during clear sky conditions.