Wind Engineeringfor HVAC Engineers

John J CarterVice PresidentJohn.Carter@cppwind.comwww.cppwind.com

CPP Inc. CPP Pty Ltd2400 Midpoint Drive 500 Princes HighwayFort Collins, Colorado St. Peters, NSWUSA

Who is CPP?

• Founded in 1981 in Fort Collins from Colorado State University College of Engineering

– research dating back to early 1950s

• CPP Pty Ltd formed in 2008

Graeme Wood, Ph.D Matt Glanville, Ph.D

What is wind engineering?

…the study of the interactions of wind and structures

…the mitigation of any negative effects of those interactions

To Provide

• Better efficiency

• Better reliability

• Better comfort

• Better safety

• Better value

What is wind engineering?

Sub-disciplinesMechanical Engineering

– Dispersion• Pollutant• Thermal

– Internal airflow– natural ventilation

Structural Engineering– Cladding loads– Structural loads

Architectural– Pedestrian wind environment

What is wind engineering?Tools of the trade

Experience

Computational models (simple to complex)

Atmospheric boundary layer wind tunnels

2226 )(

2

1exp

)(

2

1exp

2

1exp

2

10

z

rs

z

rs

yzy

hhzhhzyy

UQ

C

Dispersion for HVACThe Problem

Exhaust Fume Re-entry(research, healthcare, commercial, residential)

Typical Air Quality Sources of Concern

Cooling Tower

Diesel Generator

Animal Room Odor

Kitchen Grease Hood Odor

Helicopter

Traffic

Idling Diesel Vehicle

Fume Cupboard

Radioisotope

Biosafety CabinetIsolation Room

Boiler

The ProcessIdentify Exhaust Sources of Concern

Develop Design Criteria

Concentration Predictions(Numerical Modeling; Physical Modeling; Full Scale Testing)

Design

Acceptable?

Modify Design

or Criteria,

Hazard

Assessment

Yes

GOOD DESIGNNo

Include Wind Statistics

For Risk Assessment or Energy Optimization

Criteria

no such thing as “zero” re-entrainment

Gather information to develop allowable re-entrainment criteria

Frame as normalized concentration (C/m)health/odor

Exposure Limit Chealth

Odor Threshold Codor

Emission rate m

Concentration Predictions

• Mathematical

• Wind Tunnel

• ComputationalFluid DynamicsCFD

CFD Modeling

• Expensive and time consuming if done properly

• Needs same domain as wind tunnel

• Multiple simulations– Wind Directions: minimum of 16

(ideally +/- 5 degrees around critical)

– Wind Speeds: 3 to 7 at critical wind direction

– Large Eddy Simulations (LES) to capture turbulence/separated flow around buildings

• No established consistently conservative method

• Useful in some circumstances

Mathematical Modeling

• Simple Gaussian models for simple environments(ASHRAE/AERMOD/AUSPLUME)

– Isolated building or tallest building

– Homogeneous surroundings

Plume Rise

x

y

z

σz

hs+hr

3/13

,

3

, brmrr hhh

mf

hj

mmr h

U

xFh ,

3/1

22, ,3

min

bf

h

b

br hxU

Fh ,

3/1

2

32, ,2

3min

s

aseb

T

TTdgVFBuoyancy

4

)(:

2

4:

22 d

VT

TFMomentum e

s

am

e

hj

V

U 2.14.0

6.0

Gaussian Dispersion Equation

C = Pollutant concentration (ug/m3)

Q = Pollutant emission rate (g/s)

hr = plume rise (m)

y /z = horizontal/vertical dispersion

coefficients

U = wind speed (m/s)

z = receptor height (m)

2226 )(

2

1exp

)(

2

1exp

2

1exp

2

10

z

rs

z

rs

yzy

hhzhhzyy

UQ

C

x

y

z

σz

hs+hr

Plume Rise Example

INPUTSHb = 40 mHs = 90 mVe = 5 m/sTs = 430KTa = 279Kd = 2.1 mNeutral stability

Building Wake Cavities

Wind

Upwind Recirculation Cavity

Rooftop Recirculation Cavity

Downwind Recirculation Cavity (wake)

Wind Tunnel Modeling

Conservative method established (EPA Guideline)

• Most Accurate (EPA “analog computer with infinite resolution”)

– includes complex surroundings

– includes rooftop/local massing and architectural features (e.g. screens)

– multiple wind directions and wind speeds

• Allows for probabilistic risk assessment by incorporating local wind data

• Allows for optimization of exhaust energy consumption

Complex model for complex environment

Wind from right in both videos

Thermal PlumeHospital Chiller Application

With Wall WithOUT Wall

Other things we have learned

Prevailing Wind?

“Gang” StacksAll stacks must operate

Most effective at increasing plume rise of small stack near large stack

Entrained Air Exhaust - Concept

Bldg Exhaust

Wind Band

Flow & Velocity

Entrained Flow

Bypass

Fan Flow

Nozzle Velocity

Entrained Air Exhaust - Reality

0.00

10.00

20.00

30.00

40.00

50.00

60.00

0.00 20.00 40.00 60.00 80.00 100.00 120.00 140.00 160.00 180.00 200.00

Downwind Distance (ft)

Plu

me

Cen

terl

ine

Hei

gh

t (f

t)

Induced Air Specs

34850 cfm Wind Band

3622 fpm

Fan Specs

20500 cfm Exit

5125 fpm

Typical Fan Specs

20500 cfm Exit

3000 fpm

Briggs Complete

Final Rise Equation

(9.7 m3/s)

(26 m/s) (18 m/s)(9.7 m3/s)(16 m3/s)

(15 m/s)

(9.7 m3/s)

Entrained Air ExhaustExtra Dilution?

2

1

2

1exp

2 zzyse

h

U

V

C

CD

If the flow, V, increases by 2 the

Ce decreases by 2.

Hence, no change in C if plume

rise is constant.

Architectural ScreensNo Screen

Screen Effect

Questions?

CPP, Inc. CPP Pty Ltd

2400 Midpoint Drive, Suite 190 500 Princes Highway, Suite 2

Fort Collins, CO 80525 St. Peters, NSW

+1 970 221 3371 +61 (0)2 9551 2000

www.cppwind.com @CPPWindExperts