Surface-to-volume ratio: How building geometry impacts solar energy production and heat gain through envelopes

This paper explored the relationship between building geometry and renewable energy production of building-integrated photovoltaics (BIPV). Heat gain was incorporated as a conflicting constraint with respect to energy performance. The building façade was mathematically analyzed by taking into account heat transfer pertaining to site conditions along with different parameters that included shading, orientation, PV tilts (β) and surface-to-volume ratio (S/V) as a measure of building compactness. The study involved calculating the impact of each parameter on the convection, conduction and radiation components of the incoming solar energy. S/V was shown to be directly proportional to the amount of solar energy received by the façades and gained by the building in the form of heat. The positive correlation of heat gain with S/V was nearly linear with a slope of around 41.8 kWh/m²/m⁻¹ and a mean of approximately 3.4 times more. With the most suitable geometry in terms of net energy gain, S/V of 0.14 m⁻¹ yielded the highest difference between energy production and heat gain. In terms of β, the results demonstrated negative slope of energy production with respect to the tilt at about 2.12 times higher than that displayed by heat gain. Accounting for inter-building effects, a shading reduction equal to d percent can be estimated to an increase of 1.37d degrees in β at a building consumption of 60 kWh/m².