Modelling an existing building in DesignBuilder/EnergyPlus: Custom versus default inputs

This paper describes an effort to build and partially validate an energy model of an existing educational building located in Cambridge, MA, USA. This work was carried out as part of a research seminar for graduate architecture/design students and included four related tasks: Modelling the building’s geometry and thermal properties in DesignBuilder/EnergyPlus, generating a site-specific weather file based on near-site measured data, assessing internal load schedules based on a detailed building survey, and collecting monthly metered data for heating lighting and cooling over a whole year. The purpose of the seminar was (a) to evaluate how effectively design students can use a state-of-the-art graphical user interface (GUI) such as DesignBuilder and (b) to quantify the value of using customized weather data and internal load schedules as opposed to default GUI inputs. The authors found that the students quickly learned how to navigate the DesignBuilder GUI but were frequently confused by the model data hierarchy/inheritance and frustrated that customized schedules cannot be assigned more  efficiently. The benefit of using customized weather data as opposed to a local TMY3 file turned out to be small whereas using customized as opposed to default internal load schedules reduced the relative error of predicted versus metered annual electricity use from 18% to 0.2%