Computational Modelling of Incident Solar Radiation and Application for Thermal Loads Calculation in Buildings

Solar radiation is a significant factor in the heat gains of buildings, directly affecting indoor comfort and increasing the demand for air conditioning systems, and consequently, energy consumption. The present work aims at computationally modelling incident solar radiation, allowing its integration into the calculation of thermal loads in buildings. The adopted methodology considers three main components: the sun position, the radiation intensity and the characteristics of the surfaces exposed to this radiation. The sun position is determined based on latitude, longitude, date, and local time. Radiation intensity is estimated according to the sun position on a given day and time of analysis. The radiation model was developed and implemented in Python and validated by comparing its results with those of a commercial reference program. The results showed differences of less than 0.1% in the maximum annual analysis and a maximum deviation of 4.9% during hours of increased irradiance variation. The annual analysis, considering a building located in Lisbon, revealed that the maximum irradiance on North-facing surface occurred in June (219 W/m²), while the maximum for the East and West surfaces was verified in April (812 W/m²). The maximum irradiance on the South-facing surface was observed in January (913 W/m²). The hourly analysis on the day of maximum thermal load showed that the highest irradiance was verified on the East-facing surface (747.8 W/m² at 8 a.m.), followed by West-facing surface (744.7 W/m² at 4 p.m.) and the South-facing surface (734.5 W/m² at 12 p.m.), with the lowest irradiance observed on the North-facing surface (117.9 W/m²). The model was evaluated for various locations, demonstrating that latitude variation influence both the maximum irradiance and the duration of solar exposure, with these factors depending on the specific period of the year. The variation in longitude resulted in a time shift in the irradiance profile throughout the day.