An Exploration of Building Energy Model (BEM) Calibration in New Zealand

This study explored the use of Building Energy Modelling (BEM) and BEM calibration techniques for existing buildings as currently employed in New Zealand Industry.  Research on the use of BEM for existing building energy efficiency retrofits has increased dramatically over the past few decades. However, this use of BEM has been criticised for inaccurate and unbelievable results. These are often the result of not closely matching the building being modelled due to uncertainties around model inputs and modeller assumptions. As a result, researchers have responded by developing techniques to ‘calibrate’ models by comparing the simulated building with the actual building energy use thus providing quality assurance.  However, many of these techniques are difficult, esoteric, convoluted or impractical for industry professionals. This research explored if a simple calibration technique developed at Victoria University of Wellington by Dr. Shaan Cory would meet the needs of industry practitioners. The technique was turned into a usable tool and student trialled to prepare it for industry assessment. Four BEM experts were then interviewed in a series of individual interviews and workshops trialling the use of the technique.  The research concluded that the use of BEM is limited in New Zealand due to a perceived Industry value gap – building owners are not aware of the benefits of modelling whole-building retrofits. This leads to reduced uptake of calibration techniques from industry resulting in a credibility gap, where the modeller themselves may not be confident of their own BEMs. This is due, in part, to a lack of industry quality assurance guidelines, usable calibration tools, and certainty around model inputs. The adoption of the streamlined Cory method would be of significant benefit to practitioners. However, it was identified that it did not solve all issues relating to uncertainty estimation.