The energy efficiency of buildings and the use of energy from renewable sources in the building sector constitute important measures needed to reduce the European Union’s energy dependence and greenhouse gas emissions. Since changes in the building sector are slow, good examples and analysis of real performance are needed to motivate investors, constructors, and designers to evoke changes and warn against possible failures. In this paper data on the monitored and simulated performance of energy use, indoor climate, and building service systems of two non-residential buildings (a refurbishment case and a new building) are presented. In both cases very high energy efficiency goals were set initially (passive house standard), but neither building meets the desired levels. Both buildings do have a high-quality envelope, but their performance is unsatisfactory because of too simplified control of building service systems, too optimistic and inadequate assumptions in energy calculations and initial data, overheating of rooms during winter and summer seasons, and failure to achieve a low air leakage rate of the building envelope. The main reasons for these shortcomings are lack of conscious project leadership and inadequate final component selection. The lessons learnt from these cases should be taken into account when moving forward with nearly zero-energy buildings in the future.
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