Study on calculation method and influencing factors of equivalent heat transfer coefficient of building integrated photovoltaic facade

The thermal generation effect of photovoltaic cells in building integrated photovoltaic facades (BIPV facades) alters internal heat transfer paths, making precise calculation of the heat transfer coefficient crucial for evaluating the thermal performance. This study developed a mathematical model for heat transfer in heterogeneous facades, incorporating BIPV modules, air channels, and multi-layer walls. An equivalent heat transfer coefficient calculation method based on “extraction unit, integral layering, block partition, and combined superposition” was proposed, and the influence of structural parameters on the coefficient was analyzed. Results revealed that the coefficient negatively correlates with the thickness of BIPV module cover/backplate glass and insulation layer, with insulation thickness significantly affecting the coefficient (an 61.34 % reduction when thickness increases from 10 mm to 120 mm). The coefficient positively correlates with thermal conductivities of embedded parts, concrete and insulation, with insulation conductivity having the greatest impact. When insulation conductivity increases from 0.024 W/(m·K) to 0.12 W/(m·K), the coefficient increases by 96.97 %. Additionally, the coefficient has a nonlinear relationship with air layer thickness, reaching its lowest value (0.4683 W/(m2·K)) at 300 mm air layer thickness, yielding optimal thermal performance. Research provides a simplified and effective thermal performance evaluation method for BIPV facade in preliminary design phase.