Jon den Hartog, PE

Using Autodesk Building Design Suite
for Airflow Analysis in the Cloud
Jon den Hartog, P.E.
Product Manager
© 2012 Autodesk
Class Summary
As demand for high performance buildings increases, more sophisticated techniques
are needed to ensure a balance between energy efficiency and occupant comfort.
Innovative ventilation and energy management approaches require an understanding
of airflow patterns and the influence of heat gains or losses. Computational Fluid
Dynamics (CFD) enables detailed modeling of these physics yet has historically been
too difficult to leverage early in a project cycle during conceptual design and design
development. Over the past 10 years simulation technologies have evolved to
become faster, more user-friendly, and more accurate. Simulation CFD 360 is a
proven cloud-based tool for examining how air is delivered to and exhausted from a
space and the impact of thermal loads. This class will introduce you to CFD workflows
and show you how to leverage Simulation CFD 360 for rapid ventilation analysis.
© 2012 Autodesk
Learning Objectives
At the end of this class, you will be able to:
 Explain historical challenges in simulation and how they are being
addressed
 Map out a basic workflow for taking an Autodesk® Revit® model and
using it for CFD analysis
 Use the power of the cloud to simultaneously simulate multiple design
alternatives or conditions
 Access software and training resources for Simulation 360
© 2012 Autodesk
CFD: a quick primer
© 2012 Autodesk
What is CFD?
•
Computational Fluid Dynamics
•
Fluid flow (liquids and/or gases)
• Heat transfer (convection, conduction, and/or radiation)
• Mixing (contaminant and emissions tracking)
•
Virtual testing of a design or configuration
before building the real thing
•
Hardware advances + 3D modeling +
energy consciousness  broader usage
within AEC/MEP
© 2012 Autodesk
Application : Interior Ventilation
• Assess occupant comfort
• Examine stratification & stack effect
•
Nat’l ventilation feasibility
© 2012 Autodesk
Application : Healthcare and Labs
•
Determine optimal air changes / hour
•
Locate stagnant air regions
•
Ensure adequate “wash” over working areas
© 2012 Autodesk
Application : Data Centers
•
Identify / test Energy Conservation Measures
•
Simulate CRAC failure
CAD/BIM Model
Modified Layout
© 2012 Autodesk
Recent Developments in CFD : Historical Context
Difficult
Resource Intensive
Expensive
© 2012 Autodesk
Recent Developments : Instigators of Change
Not Specific to
Building Design
Specific to Building
Design
Motivators
Project Cost and Risk
Reduction
Energy Efficiency
Objectives
Critical and High
Performance Facilities
Enablers
Increased Computing
Power
Simulation Software
Maturity
Rich 3D Building Models
© 2012 Autodesk
Recent Developments : Cost Motivators
2
Effort/Effect
1
4
3
Time
1
Ability to impact performance
2
Cost of design changes
3
4
Traditional design process
Preferred design process
© 2012 Autodesk
Recent Developments : Efficiency Motivators
 Demand
for green building is
growing

55% of architects and 36% of
engineers report a high level of
involvement in green projects
 Gov
regs driving demand globally
© 2012 Autodesk
Recent Developments : Performance Motivators
 Healthcare
 Hospital Acquired Infections (99K deaths/yr in the US)
 More than 30% of surgical infections due to airborne pathogens
 Data Centers
 Total power consumption ~30GW
 Rapid growth particularly in China
© 2012 Autodesk
Recent Developments : Platform Enablers
CPU Power
Cost of RAM
PC
cloud
© 2012 Autodesk
Recent Developments : CFD Market Enablers
Market competition has made sim software…

Easier to Use

Faster to Run

More Affordable
© 2012 Autodesk
Recent Developments : CAD Market Enablers
Rich 3D models becoming the norm
© 2012 Autodesk
Historical Workflow
Dimensional Information
Mesher
Material Information
Pre-Processor
Build Simulation Mesh
(2-3d)
Setup
(<1d)
Solver
Post Processor
Solving
(1-2d)
Explore
Results
(<1d)
Results
Operating Parameters
-
Air velocities
Pressurization
Heat loads
Contaminant sources
© 2012 Autodesk
Current Workflow (desktop)
Design Insight
Material Information
- Velocity, temp, comfort, LMA, etc
Simulation CFD
Revit / CAD
Simplify Model
(<8 hr)
Setup
(<1 hr)
Solving
(<8 hr)
Explore
Results
(2 hr)
Operating Parameters
-
Air velocities
Pressurization
Heat loads
Contaminant sources
© 2012 Autodesk
Current Workflow (cloud)
Design Insight
- Velocity, temp, comfort, LMA, etc for all configs
- Comparison (which is best?)
- Sensitivity (what matters?)
Material Information
Revit / CAD
Simplify Model
(<8 hr)
Setup
(<1 hr)
Simulation CFD 360
Solving (<8 hr)
Solving (<8 hr)
Solving (<8 hr)
Solving (<8 hr)
Solving (<8 hr)
Solving (<8 hr)
Solving (<8 hr)
Solving (<8 hr)
Explore
Results
(2 hr)
Operating Parameters
-
Air velocities
Pressurization
Heat loads
Contaminant sources
© 2012 Autodesk
CFD: basic workflow and best practices
© 2012 Autodesk
Workflow and Best Practices:
Use BIM/CAD Model as the Sim CFD Model
© 2012 Autodesk
Simulation Geometry Concepts

Every detail shown in the 3D view is included in the sim model

Small geometric details require very many small mesh elements

Time & computing resources increase with number of elements

It is beneficial to eliminate geometric detail wherever possible
© 2012 Autodesk
Revit Geometry Clean Up Examples
© 2012 Autodesk
Revit Geometry Clean Up Examples
© 2012 Autodesk
Revit Geometry Clean Up Examples

Hiding electrical fixtures, furniture, railings, beams inside cladding

Closing off tiny gaps between walls, floors, and ceilings

Eliminating any small overlaps (ie. interferences or clashes) that result in small
edges and/or thin volumes

Editing a family to reduce the complexity or number of parts
(ex = removing trim & double panes from the Fixed Window family)

Use the section box to crop out wings, floors, or other parts of a building that
aren’t of interest
© 2012 Autodesk
Specific Items You’ll Probably Want to Simplify

Duct fittings (elbows and bends)
 Molding (embedded surfaces)
 Complex curtainwalls (embedded surfaces)
 Topography
 Plantings
 Railings
 Any 2D features or images
© 2012 Autodesk
Representing the Air
 An
air volume is needed for running any analysis involving airflow
 Options for internal flow models:

seal up a room or building in CAD (most common)
 or use the “Void Fill” tool in Sim CFD
 or create an air volume as a generic volume in CAD
CAD
Sim CFD
© 2012 Autodesk
CAD Connection to Sim CFD
© 2012 Autodesk
Use Views for Multiple Configurations
© 2012 Autodesk
Geometry Cleanup Options In Sim CFD

Upon bringing geom into Sim CFD, you
may see a geom tools window

Edge Merging

Small Object Removal
© 2012 Autodesk
Workflow and Best Practices:
Leverage Setup Automation
© 2012 Autodesk
Materials: Solid Materials

Supplied Material Library Contains Standard Construction Materials

Brick
 Gypsum Board
 Hardwood and Softwood
 Steel
 Glass
 Concrete

Custom Materials Optional


Composites
Wall construction types
© 2012 Autodesk
Materials: Fluid Materials

Use the “Air” Material in the default database

Use “Fixed” properties for forced flow models


HVAC (where minimal thermal stratification is expected)

Datacenters

Lab spaces

External flow and wind loading analyses
Use Air with “Variable” properties to acct for buoyancy


Natural ventilation, with combined interior and exterior flows
Interior spaces served by HVAC systems but have large temp
differences, displacement ventilation, or high ceilings (factories, atria, etc)
© 2012 Autodesk
Materials: Use Rules to Automate Assignments
© 2012 Autodesk
Materials: Use Rules to Automate Assignments
© 2012 Autodesk
Boundary Conditions: Flow Boundaries

Common approach for interior flow

Assign volume flow rate on each inlet (diffuser or supply air source)
 Assign pressure = 0 on all outlets (returns, exhaust, or openings)

Alternatively, if all inlet and outlet flowrates are known, assign volume flowrate
everywhere but 1 outlet. Assign a 0 pressure to this one outlet.
CFM
CFM
CFM
CFM
P=0
 All flow boundary conditions need to be on exterior walls, ie. on the outermost walls of the
model (or on a suppressed part)
 Assign either a flowrate OR a pressure – not both!
© 2012 Autodesk
Boundary Conditions: Flow Boundaries

Common Approach for External Flow / Wind Loading

Assign Velocity on upwind face of outer air volume
 Assign Pressure on downwind face of air volume
 Assign Slip/Symmetry on top and sidewalls of air volume
Slip/Symmetry on top and sides (leave ground unassigned)
Wind velocity
Pressure = 0
© 2012 Autodesk
Boundary Conditions: Thermal Boundaries

Possible Known Thermal Conditions

Air inlet temperatures
 Heat generation/removal
 Temperature dependent heat exchange (film coefficients, radiation)
 Specified heat exchange (solar loads, heating systems)

Common Approach for Assigning Thermal Boundaries
1) Assign Temperature (Static) on all inlets
2) Assign Heat Generation or Total Heat Generation
3) Assign any other known thermal conditions on the outside. Common ones are:

Film Coefficient

Heat Flux / Total Heat Flux
© 2012 Autodesk
Boundary Conditions: Adding Additional Designs
© 2012 Autodesk
Workflow and Best Practices:
Run Many Conditions and Alternatives
Local CFD Solve
• 1 simulation at a time
• 1.8M elements / 39 sec per iteration
HP 8540w Workstation
• IntelCorei7 820QM @ 1.73GHz
• 4 cores, 24 GB RAM
• 10 MB/s connection
Cloud Based CFD Solve
• Many simulations at a time
• 1.8M elements / 16 sec per iteration
© 2012 Autodesk
Clone to Run Many Configurations and Alternatives
© 2012 Autodesk
Solving in the Cloud
© 2012 Autodesk
Workflow and Best Practices:
Results Processing and Comparisons
© 2012 Autodesk
Results Processing

Flow and temperature results

Create iso surfaces to quickly visualize flow
patterns and thermal stratification
 Use cut planes for…
 Reviewing flow direction vectors
 2D plots (ex = temp at top of occupied zone)
 Bulk flow calculations
 Traces
 Use wall calculator for forces, average
temperatures, pressures, or heat flow (use
only on solids)

Optional result quantities


Local Mean Age (LMA)
Thermal Comfort (PMV, PPD, etc)
© 2012 Autodesk
Results Processing
© 2012 Autodesk
Results Processing
© 2012 Autodesk
CFD: how to get started today
© 2012 Autodesk
Step 1: Get comfortable in CAD/BIM
(Revit, Inventor, Fusion or other CAD)
Step 2: Grab Simulation 360
www.autodesk.com/infinite-simulation
© 2012 Autodesk
Step 3: Run the first step tutorial
(Look for desktop shortcut to “AEC Ventilation” model)
Step 4: Familiarize yourself with the Wikihelp
Step 5: Try something on your own
(start small…then go big once you get the hang of it)
© 2012 Autodesk
Sim 360 Trial: www.autodesk.com/infinite-simulation
Autodesk, AutoCAD* [*if/when mentioned in the pertinent material, followed by an alphabetical list of all other trademarks mentioned in the material] are registered trademarks or trademarks of Autodesk, Inc., and/or its subsidiaries and/or affiliates in the USA and/or other countries. All other brand names, product names, or trademarks belong to their respective holders. Autodesk reserves the right to alter product and
services offerings, and specifications and pricing at any time without notice, and is not responsible for typographical or graphical errors that may appear in this document. © 2012 Autodesk, Inc. All rights reserved.
© 2012 Autodesk