## 2 Literature Review and Background Studies
### Energy Simulation Programs in Buildings  
Building energy simulation software plays an integral role in the choice of the best energy efficiency measures for a given geographic location [PERSON] et al. (2018).  
Building energy simulation programs (BESP) are an important tool for analysing and predicting the thermal performance and energy consumption of buildings to meet the building energy efficiency design and green building energy ratings.  
An overview report by [PERSON] et al. [PERSON] et al. (2018) provided the features and contrasting capabilities of twenty major BESP, offering users key performance indicators such as energy use and demand, temperature, humidity and costs. Energy modelling has been used increasingly to strategize the specific design decisions that affect energy consumption of buildings.  
Among the widely used open-source freeware BESP are eQuest, Energy Plus and cloud computing under BIM Autodesk@Revit-GBS. These freeware have their roots in the DOE-2 model. eQuest is an easy-to-use building energy use analysis tool but its input data are not graphically user-friendly and its unit is still based on imperial. EnergyPlus is a modular, structured code based on the features and capabilities of Building Loads Analysis and System Thermodynamics (BLAST) and DOE-2. The simulation module, which has a variable time step, calculates heating and cooling loads and plant and electrical system response [PERSON] et al. (2018).  
Autodesk integrated its energy application tools (Revit, Vasari, GBS-DOE2) seamlessly in the BIM environment into one called Insight 360, where energy modelling is carried out in Revit and the energy simulation energy analysis under GBS--DOE-2 [PERSON] et al. (2018).  
[PERSON] et al. [37] reported on the effects of thermal mass on energy use and found that thermal comfort requires suitable energy simulation software with the following features:  
1. 3D-building geometry input to define surface areas and orientations to evaluate thermal mass behaviour.
2. The ability to calculate surface, radiant and air temperatures, humidity, wind and buoyancy air movement, thermal storage, inter-zone conduction, convection and radiation.
3. Hourly space heating and cooling load and energy balance calculations conducted with hourly weather data.  
Autodesk@GBS was chosen because of its ease in generating 3D building geometry inputs for its building elements and conceptual mass in Revit, which can be converted into 3D energy modelling for the energy simulation compared with other energy simulation programs.  
Autodesk@GBS offers easy interoperability with BIM tools and other software. It offers great interoperability with Autodesk Revit, ArchiCad, Ecotect, eQuest, and EnergyPlus [38]. Autodesk@GBS has the highest score as compared to Integrated Environmental Solutions Virtual Environment (IESVE) and Ecotect in terms of interoperability, usability and speed [39]. Autodesk@GBS is used to quantify the predicted energy savings against actual baseline energy loads of an envelope retrofit on a university dormitory. The validation study showed GBS prediction on electricity is 96%, at par with eQUEST (98%) and better than IESVE (72%) [40]. Autodesk@GBS has been used in scientific research since 2013 and validated with the actual energy use.