E Si l i d BIMEnergy Simulation and BIMBenjamin Welle, P. E . , C.E.M., LEED APBenjamin Welle, P. E . , C.E.M., LEED APPhD Student, CIFECEE DepartmentStanford UniversityyWhat is an Energy Model?An energy simulation model uses a computer to model the complex energy flows and processes in buildings.energy flows and processes in buildings.¾ Calculates cooling and heating loads by simulating the thermal performance of the building.¾Calculates energy use over the course of a year by simulating the performance of¾Calculates energy use over the course of a year by simulating the performance ofHVAC equipment in response to these loads.¾ Calculates annual utility costs using the energy use resultsWhat are the simulation results used for?What are the simulation results used for?¾ LEED energy performance calculations¾ Utility incentive calculations¾Energy code compliance calculations¾Energy code compliance calculations¾ Research¾ Policy development¾ Testing the building before it’s built¾Verifying performance after it’s built¾Verifying performance after it s builtHow do Energy Models work?¾ Energy simulation tools typically consist of a graphical user interface (GUI) and a thermal calculation engine. g¾ The thermal calculation engine predicts the annual energy use of the building, the energy costs, and in some cases, the thermal comfort for its occupants. ¾The simulation engine does this using a description of the building geometry and layout¾The simulation engine does this using a description of the building geometry and layout, constructions, operating schedules, internal loads, heating, ventilating, and air-conditioning (HVAC) systems, local weather data, and utility rates that are provided by the user . ¾ It performs an annual hourly simulation first calculating the building loads then calculating the system ihldrequirements to meet those loads.Building Thermal LoadsEnergy Simulation Inputsgy pOccupant LoadsLighting LoadsEquipment LoadsInfiltration LoadsThermal ZonesConstruction TypesWalls, Roofs, Floors, Windows, DoorsOccupant SchedulesLighting SchedulesEi ShdlEquipment SchedulesThermostat SchedulesHVAC SchedulesRemember: Garbage In=Garbage Out!Remember: Garbage In Garbage Out!DOE‐2 vs. EnergyPlusDOE-2 EnergyPlusSource: Birdsallet. al., 1990: “Overview of the DOE b ildi l i V i 2 1D”building energy analysis program, Version 2.1D”Source: EnergyPlus Documentation¾Integrated simulation¾Component based with modular structure¾10 minute time step¾ No feedback¾ Predefined system types¾ Hourly simulation¾New technologies (natural ventilation, underfloor air distribution (UFAD), displacement ventilation (DV))ySeveral GUIs….¾Riuska (DOE2 1)¾Riuska (DOE2.1)¾ VisualDOE (DOE2.1)¾eQUEST (DOE2 2)¾eQUEST (DOE2.2)¾ Green Building Studio (DOE2.2)¾DesignBuilder (EnergyPlus)¾DesignBuilder (EnergyPlus)¾ IES (Apache)¾Hevacomp (EnergyPlus)¾Hevacomp (EnergyPlus)¾ TAS (TAS Simulator)Using CAD Data for Energy SimulationDOE-2Green Building StudioDOE-2IESEnergyPlusAhApacheHevacompEnergyPlusTASTAS SimulatorSurvey of Sustainable Design Tool Capabilities and Interoperability Capabtesad teopeabtySpace Boundaries for Energy AnalysisThe greatest barrier to realizing BIM to thermal simulation during early design is consistent, repeatable, and automated rule‐based methodologies to transform the architectural view of a building to the thermal view (i e heat transfer surfaces) of the buildingbuilding to the thermal view (i.e. heat transfer surfaces) of the building.How do you define thermal space boundaries (2LSB and 3LSB) for different spatial configurations?Who should do it: BIM‐authoring vendors, middleware vendors, downstream analysis application vendors?Some development issues…• 1stlevel space boundary• 1stlevel = 2ndlevel space boundary• Same 1stlevel space boundary:• INTERIOR and EXTERIOR ?!?Copyright © Vladimir Bazjanac/LBNL 2007Bazjanac, 2008Typical Reality With Slabs• Walls below slab (slab as ceiling)•Wallsaboveslab (slab as floor)•Walls aboveslab (slab as floor)• How useful are 1stlevel space boundaries here?slabCopyright © Vladimir Bazjanac/LBNL 2007Bazjanac, 2008External Building Shading ElementsBazjanac, 2008External Building Shading Elements (cont’d)Bazjanac, 2008Zone-Based (Traditional) Modeling vs. BIM-Based Modelingvs. BIMBased Modeling¾Zone-based modeling does not respond as quickly to design iteration by the project(architect orengineeras does space-based modeling(assuming reasonable datatransfer).¾BIM-based modeling allows for more systematic and efficient results, assuming theiliifidff ifhdliliifsimulationinterface provides an effective means ofhandlinglarge quantities ofspaces¾ More space detail is not always better. Models must be created with downstreamli tiiidapplicationsinmind.¾Enhanced ability to layer/filter IFC/XML exports and customize HVAC zone exportwould greatly enhance conceptual design capabilities of existing software.Future Developments…¾2D or 3D heat transfer (instead of 1D)()¾Improved User Interfaces (smarter, simpler, user-friendlier)¾Improved data exchange with CAD platforms¾¾Automated comparison of predictions and measurements¾Integration with CFD and Daylighting