Prediction of Energy Use of a Swedish Secondary School Building : Building Energy Simulation, Validation, Occupancy Behaviour and Potential Energy-Efficiency Measures

Abstract: Residential and public buildings account for about 40% of the annual energy use in Europe. Many buildings are in urgent need of renovation, and reductions in energy demand in the built environment are of high importance in both Europe and Sweden. Building energy simulation (BES) tools are often used to predict building performance. However, it can be a challenge to create a reliable BES model that predicts the real building performance accurately. BES modelling is always associated with uncertainties, and modelling occupancy behaviour is a challenging task.This research presents a case study of a BES model of a school building from the 1960s in Gävle, Sweden, comprising an example of a validation strategy and a study of energy use and potential energy-efficiency measures (EEMs). The results show that collection of input data based on evidence, stepwise validation (for unoccupied and occupied cases), and the use of a backcasting method (which predicts varying occupancy behaviour and airing) is an appropriate strategy to create a reliable BES model of the studied school building. Several field measurements and data logging in the building management system were executed, in order to collect input data and for validation of the predicted results. Through the stepwise validation, the building’s technical and thermal performance was validated during an unoccupied period. The backcasting method demonstrates a strategy on how to predict the effect of the varying occupancy behaviour and airing activities in the school building, based on comparisons of BES model predictions and field measurement data. After applying the backcasting method to the model, it was validated during an occupied period. The annual predicted specific energy use was 73 kWh/m2 for heating of the studied building. The distribution of heat losses indicates that the best potential EEMs are changing to efficient windows, additional insulation of the external walls, improved envelope airtightness and new controls of the mechanical ventilation system.