E Si l i d BIMEnergy Simulation and BIM

Benjamin Welle, P.E., C.E.M., LEED APBenjamin Welle, P.E., C.E.M., LEED APPhD Student, CIFECEE Department

Stanford Universityy

What 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.

Calculates cooling and heating loads by simulating the thermal performance of the building.Calculates energy use over the course of a year by simulating the performance ofCalculates energy use over the course of a year by simulating the performance ofHVAC equipment in response to these loads.Calculates annual utility costs using the energy use results

What are the simulation results used for?What are the simulation results used for?

LEED energy performance calculationsUtility incentive calculationsEnergy code compliance calculationsEnergy code compliance calculationsResearchPolicy developmentTesting the building before it’s builtVerifying performance after it’s builtVerifying performance after it s built

How do Energy Models work?

Energy simulation tools typically consist of a graphical user interface (GUI) and a thermal calculation engine. g

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.

The simulation engine does this using a description of the building geometry and layoutThe 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 .

It performs an annual hourly simulation first calculating the building loads then calculating the system i h l drequirements to meet those loads.

Building Thermal Loads

Energy Simulation Inputsgy p

Occupant LoadsLighting LoadsEquipment LoadsInfiltration Loads

Thermal ZonesConstruction TypesWalls, Roofs, Floors, Windows, Doors

Occupant SchedulesLighting SchedulesE i S h d lEquipment SchedulesThermostat SchedulesHVAC Schedules

Remember: Garbage In=Garbage Out!Remember: Garbage In Garbage Out!

DOE‐2 vs. EnergyPlusDOE-2 EnergyPlus

Source: Birdsallet. al., 1990: “Overview of the DOE b ildi l i V i 2 1D”building energy analysis program, Version 2.1D”

Source: EnergyPlus Documentation

Integrated simulationComponent based with modular structure10 minute time step

No feedbackPredefined system typesHourly simulation

New technologies (natural ventilation, underfloor air distribution (UFAD), displacement ventilation (DV))

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Several GUIs….

Riuska (DOE2 1)Riuska (DOE2.1)

VisualDOE (DOE2.1)

eQUEST (DOE2 2)eQUEST (DOE2.2)

Green Building Studio (DOE2.2)

DesignBuilder (EnergyPlus)DesignBuilder (EnergyPlus)

IES (Apache)

Hevacomp (EnergyPlus)Hevacomp (EnergyPlus)

TAS (TAS Simulator)

Using CAD Data for Energy Simulation

DOE-2

Green Building Studio

DOE-2

IES

EnergyPlus

A hApache

HevacompEnergyPlus

TASTAS Simulator

Survey of Sustainable Design Tool Capabilities and Interoperability Capab t es a d te ope ab ty

Space Boundaries for Energy Analysis

The 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…

• 1st level space boundary

• 1st level = 2nd level space boundary• Same 1st level space boundary:• INTERIOR and EXTERIOR ?!

?

Copyright © Vladimir Bazjanac/LBNL 2007

Bazjanac, 2008

Typical Reality With Slabs

• Walls below slab (slab as ceiling)• Walls above slab (slab as floor)• Walls above slab (slab as floor)• How useful are 1st level space boundaries here?

slab

Copyright © Vladimir Bazjanac/LBNL 2007

Bazjanac, 2008

External Building Shading Elements

Bazjanac, 2008

External Building Shading Elements (cont’d)

Bazjanac, 2008

Zone-Based (Traditional) Modeling vs. BIM-Based Modelingvs. BIM Based Modeling

Zone-based modeling does not respond as quickly to design iteration by the project(architect or engineer as does space-based modeling (assuming reasonable data

transfer).

BIM-based modeling allows for more systematic and efficient results, assuming thei l i i f id ff i f h dli l i i fsimulation interface provides an effective means of handling large quantities of

spaces

More space detail is not always better. Models must be created with downstreamli ti i i dapplications in mind.

Enhanced ability to layer/filter IFC/XML exports and customize HVAC zone exportwould greatly enhance conceptual design capabilities of existing software.

Future Developments…

2D or 3D heat transfer (instead of 1D)( )

Improved User Interfaces (smarter, simpler, user-friendlier)

Improved data exchange with CAD platforms

Automated comparison of predictions and measurements

Integration with CFD and Daylighting Programsg y g g g