Assessing the impact of modelling approach, modeller and inter-model variability on building performance simulation results

Different modelling software are developed for building performance simulation. However, modelling uncertainty and variability can impact the reliability of modelling results and contribute to the performance gap. To bridge the gap and improve prediction accuracy at the design stage, the CIBSE TM54 protocol was introduced to promote accurate performance modelling. This study investigated its application in practice by UK practitioners through a modelling task and questionnaire based on a simplified school building. Participants were asked to simulate energy use in IES VE or DesignBuilder using either the template HVAC or detailed component-level HVAC modelling approach outlined by CIBSE TM54. The study revealed significant variations in annual total energy consumption predicted by 20 participants, ranging from 24.2 kWh/m 2 to 186.3 kWh/m 2 . Participants using the detailed HVAC modelling self-reported that the average time taken was 1.5 times longer than participants using template HVAC modelling, however this increased modelling effort did not improve the consistency of the results. It was found that even explicit building information was interpreted differently by different modellers. This points to a gap between modellers and design or engineering teams, and highlights the need for better communication, improved modelling-relevant information from suppliers, and more effective software and data frameworks. Practical Application This study demonstrates the performance of different modelling approaches and software in practice, and identifies modelling challenges faced by practitioners under the current modelling framework. The findings provide evidence-based insights to support improvements in the provision of modelling information, modelling processes, and validation steps, with the aim of improving the reliability of simulation results.