ARTICLE IN PRESS JID: ENBENV [m5GeSdc;October 31, 2020;18:27] Energy and Built Environment xxx (xxxx) xxx Contents lists available at ScienceDirect Energy and Built Environment journal homepage: http://www.keaipublishing.com/en/journals/energy-and-built-environment/ nZEB: bridging the gap between design forecast and actual performance data N. Aste, R.S. Adhikari, M. Buzzetti, C. Del Pero ∗ , H.E. Huerto-Cardenas, F. Leonforte, A. Miglioli Politecnico di Milano - Dept. of Architecture, Built Environment and Construction Engineering, Via Ponzio 31, 20133 Milano, Italy a r t i c l e i n f o Keywords: nZEB Energy performance gap Building energy dynamic simulation Post occupancy evaluation Model calibration GIGO a b s t r a c t The nZEB objectives have raised the standard of building performance and changed the way in which buildings are designed and used. Although energy dynamic simulation tools are potentially the most suitable way for accurately evaluating and forecasting the thermal performance, they need several data inputs and user’s knowledge that can affect the reliability of the results. It is precisely these two aspects that proved to be particularly critical, since the reliability of the ICT calculation tools has been widely proven in recent time. However, in order to foster credibility in sustainable architecture, bridging the gap between predicted and measured performance is pivotal to boost the building market towards energy efficiency and provide reliable data to inhabitant, investors and policy maker. The present research aims to identify and quantify the main factors that affect the energy performance gap through a detailed energy analysis carried out on a case study, which can be considered one of the first nearly zero energy residential complex built in Italy. Based on the analysis, the study identifies the main causes of the deviation between the calculated and measured data and demonstrates how it is possible to achieve very reliable models and, therefore, real buildings. Although the procedure traces a classic model calibration scheme, actually it consists of a verification of possible downstream errors mainly due to human factors, such as the provision of incorrect technical data or inappropriate operation. Some observations on the technical, management and regulatory gaps that may generate these errors are reported at the end of the study, together with practical suggestions that can provide effective solutions. 1. Introduction As well known, efficient buildings are an essential component of sustainability and energy transition strategies and represent a techno- economic and socio-economic challenge. The decarbonisation of build- ing stock is one of the most important goals of policies, considering the energy impact of buildings at the global scale [1]. During the coming years, building sector will be galvanized by mandatory codes and standards that aim to reach nearly zero energy buildings (nZEBs) 1 [2–5]. The European Performance of Buildings Di- rective (EPBD) requires all new buildings to be nearly zero energy build- ings by 2020, including existing buildings through major renovations [6]. Despite the recent global health emergency, caused by the spread of COVID-19 [7] and the related socio-economic issues are likely to slow down this process, the road ahead is already marked. ∗ Corresponding author E-mail address: claudio.delpero@polimi.it (C. Del Pero). 1 nZEB definition varies across different EU countries based on different indi- cators; one of the most common indicator is related to Primary Energy Require- ment [8] A recent study [8] shows that so far, the penetration of nZEB in new and renovated buildings varies a lot across EU countries. This study also demonstrates that nearly-zero energy standards are preferably applied to newly constructed buildings, i.e. on EU28 level 27% times more new buildings are constructed in nearly-zero energy buildings standard than renovated buildings. However, it is not still possible to properly com- pare the ambition level of national nZEB definitions due to different indicators, calculation methodologies, applied primary energy factors, system boundaries, etc. [9,10]. Although building dynamic simulation tools are commonly recog- nized as a suitable way for accurately assessing the performance of buildings and thus to develop the nZEB policies, in general, more or less large discrepancy between simulated and real features can still be observed both for new or existing buildings [11–15]. Moreover, the ac- tual gap observed in many cases seems too wide to be acceptable; in fact, measured energy use can be as much as 2.5 times the predicted energy use [12,13]. Consequently, the design phase methodologies can negatively im- pact the reliability of building expected performance, considering the https://doi.org/10.1016/j.enbenv.2020.10.001 Received 12 May 2020; Received in revised form 4 October 2020; Accepted 8 October 2020 Available online xxx 2666-1233/© 2020 Southwest Jiaotong University. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Please cite this article as: N. Aste, R.S. Adhikari, M. Buzzetti et al., nZEB: bridging the gap between design forecast and actual performance data, Energy and Built Environment, https://doi.org/10.1016/j.enbenv.2020.10.001