Do our green buildings perform as expected?

Project examines gaps between expected and actual performance

Buildings are complex entities that rely on both technical systems and human behaviour to create appropriate environments with optimal use of resources. There are often significant gaps between predicted [or expected] performance and measured performance in areas such as energy use, carbon emissions, water use, indoor environmental quality and comfort.

By Dr Mark Gorgolewski

Discrepancies arise for many reasons such as modelling inaccuracies, envelope and systems integration problems, construction grades, and can help designers integrate lessons from existing buildings into future projects. Quality issues, occupancy changes, commissioning, operational issues, and motivation of occupants can lead to additional costs for building owners, reduced occupant productivity and buildings that fail to live up to their potential. To better understand how buildings are performing and can be improved it is important for the industry to develop a system of effective feedback between practice and policy, where lessons learned from actual buildings can inform the next generation of buildings.

A project initiated by iiSBE Canada investigated the “performance gap” of nine Canadian green buildings. The aim was to better understand real performance issues by documenting the differences between predicted and measured performance for energy, water and indoor environment, and comparing this with benchmarks for “typical” performance of similar buildings. Such an investigation can help building owners improve their buildings by better understanding how to optimise performance and prioritise up.
An important aspect of the project was to combine quantitative data such as metered energy use and spot measurements of environmental conditions [such as temperatures, lighting, and acoustics] with qualitative data from occupant-generated feedback about satisfaction levels for various aspects of the building [collected through questionnaires].

Analyzing occupant satisfaction helps to highlight shortcomings in the indoor environmental conditions of the project, which can affect occupant productivity, well-being, health, and business competitiveness.
The nine building performance evaluations have identified key areas where a better understanding of building design and operational issues is needed.

Figure 1 shows a summary of modelled, measured and benchmark values for energy use intensity for the nine buildings. This shows how the gap between measured and predicted performance varies significantly.
All but one building uses less energy than the reference benchmarks and five are more than 50% below their reference benchmark.  Most use more energy than the design stage predictions, and three buildings do not meet their predicted performance by a significant margin.

One of the key findings of the project was that each building has its own individual “story” that provides an important context for effective management and improvement of the building in its ongoing life, and needs to be understood.

Dr Mark Gorgolewski is in the Department of Architectural Science, Ryerson University, Toronto, and an iiSBE Canada member,