Variations in results of building energy simulation tools, and their impact on BREEAM and LEED ratings: A case study

• Performance prediction variation exists in Building Performance Simulation tools.
• Comparative analysis of BREEAM and LEED ratings with a focus on energy credits.
• BREEAM and LEED resulted in different energy performance credit scores.
• Using different BPS tools minimally affects energy credit scores.
• BREEAM and LEED awarded a case study considerably different rating levels.

The increased awareness of building energy consumption and sustainability has resulted in the development of various means of predicting performance and rating sustainability. The Building Research Establishment Environmental Assessment Method (BREEAM) and Leadership in Energy and Environmental Design (LEED) are the most commonly used Performance Rating Systems.To predict energy consumption and award relevant energy performance credits, these systems use computer-based Building Performance Simulation tools (BPS). Predictive inconsistencies between BPS tools have been acknowledged in various studies. The probability of achieving different ratings by using different BPS tools or rating systems raises questions concerning the ability to rate ‘sustainability’ in a consistent manner. To investigate this, a case-study based inter-model comparative analysis was implemented to examine the extent of the variation in the results produced by three of the most widely used BPS tools (Tas, EnergyPlus and IES), and assess their influence and impact on overall BREEAM and LEED scores.Results showed that different simulation tools resulted in different energy consumption figures, but had only a minor effect on BREEAM or LEED energy performance credit scores. Nonetheless, due to the differences between BREEAM and LEED assessment procedures, the case study building was awarded a considerably different rating level in each.