Impact of form factor variability on building energy assessment: A computational and empirical analysis for early-stage design

While energy efficiency is increasingly recognised as an integral factor in building design, form-related considerations in Nigeria remain underexplored. This study explores the influence of compactness on building energy demand and carbon emissions using computational simulations tailored for early-stage residential design. Ten distinct building forms consisting of six one-storey, three two-storey and one three-storey building were modelled in SketchUp to collect building entity data and systematically transformed for compactness assessment while maintaining the same volume and floor area. A weather file for location-based energy requirements was generated using Meteonorm, while dynamic thermal modelling, energy performance and carbon emissions were evaluated using EnergyPlus. Python programming was utilised for advanced statistical evaluation, pattern recognition and data visualisation. Findings revealed that single-storey buildings have higher surface-to-volume (SV) ratios and are more energy efficient than more compact, multi-storey counterparts. Principal Component Analysis (PCA) confirmed that building volume accounts for more than 97% of form factor variability, establishing it as the most dominant driver of compactness, while regression analysis reinforced its statistical significance (P-value = 0.038). However, cluster analysis demonstrated that energy efficiency is not solely a function of form factor but is informed by complex interplays between building morphology parameters and façade exposure. Unexpectedly, despite improvements in SV ratios of the transformed buildings, energy demand intensified by up to 30.27%, challenging conventional assumptions that compactness universally enhances energy efficiency. These findings highlight the limitations of compactness as a standalone metric for evaluating energy performance in tropical climates, stressing the need for integrating passive design strategies, such as solar-responsive façades and optimised building orientation, into form optimisation. This study redefines performance assessments for early-stage design by advocating for a more context-sensitive approach to building form in tropical climates.