10 air distribution basics

ASHRAEASHRAE‐‐ChicagoChicago Air Distribution Selection BasicsAir Distribution Selection Basics

June 8, 2010June 8, 2010

© 2010. All rights reserved

ASHRAE ‐

Air Distribution Systems 2007 Applications Handbook, Ch. 56

ASHRAE ‐

Air Distribution Systems 2007 Applications Handbook, Ch. 56

Local Temp.

Ele

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n

Ele

vatio

n

Local Temp.CO2 Concentration

Ele

vatio

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Local Temp.CO2 Concentration

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Local Temp.CO2 Concentration CO2 Concentration

Partially Mixed Room Air Distribution Systems

Upper Zone

Lower Zone

Fully Mixed

Upper Zone

Lower Zone

Upper Zone

Lower Zone

height varies

Fully MixedPartially MixedFully Stratified

Displacement Under Floor Air Distribution G.R.D.


ASHRAE Standard 55‐2004 Occupant Comfort Goal

Dry Bulb = 73-77 °F.Relative Humidity = 25-60%.Local Velocities =

Heating < 30 fpm. Cooling < 50 fpm.

Clo. Rate 0.5 -

1.1Met. Rates 1.0 -

2.0

Floor level to 66”; < 5.4 °F (3 °C)Occupied Zone:

Floor to 6’0”; except:

(Clear, Near, Adjacent) Zone.


Occupied Zone for ComfortOccupied Zone for Comfort

6' FOccupied Zone

1'

Floor

Ceiling

Underfloor Plenum UFAD Outlet D.V.

Mixed Air Outlet


Fully Mixed Air DistributionFully Mixed Air Distribution

Air Patterns

Mapping Room Air Motion

Vertical Projection

ADPI

Perimeter Heating


Air Flow Patterns

High Sidewall –

No Ceiling

Horizontal Pattern

Deflected (less drop)

Spread (shorter throw)

High Sidewall with Ceiling

Longer throw with less drop

High Sidewall near Ceiling

Deflect up for longer throw/less drop


Supply Sidewall Grilles

Adjustable:

Horizontal (spread)

Vertical

(deflection)

Duct Mounting

Velocity & Pressure

Air Patterns


Return Sidewall GrillesReturn Sidewall Grilles

Return

Non Adjustable

Zero Degree Deflection

30-45 Deflection

Other


Air Flow Patterns

Radial Air Pattern

Shorter Throw

More Induction


Round Pattern DiffusersRound Pattern Diffusers


Air Flow Patterns

Cross Flow

Longer Throw

Increased Drop


Cross Pattern DiffusersCross Pattern Diffusers


Linear with Plenum or T‐Bar DiffusersLinear with Plenum or T‐Bar Diffusers

With Spreader W/O Spreader

LinearPlenum

WithSpread

WithoutSpread


Linear‐Plenum Slot DiffusersLinear‐Plenum Slot Diffusers


Air Flow Patterns

Radial Pattern

-

Exposed Duct


Air Flow PatternsAir Flow Patterns

Cross Pattern -

Exposed Duct


POORLY ADJUSTEDDIFFUSER

THERMOSTAT

POOR PATTERN EXAMPLE


PROPERLY ADJUSTEDDIFFUSER

THERMOSTAT

GOOD PATTERN EXAMPLE


Mapping Room Air MotionMapping Room Air Motion

5-step approach

Primary air

Total air

Convection currents

Room intake

Room air


Step 1: Identify the Primary AirStep 1: Identify the Primary Air

Primary Air

-

mixture of air supplied to the outlet and induced room air within an envelope of velocities > 150 FPM

Primary air

patterns are temperature independent1

Catalog Throw:

150 –

100 –

50

10 -

17 -

25

Inside

Wall

Exposed

Wall

Step 1Primary Air

Outlet


Step 2: Identify the Total AirStep 2: Identify the Total Air

Total Air -

mixture of primary air and room air which is under the influence of the outlet conditions

Air has a tendency to scrub surfaces

Temperature difference between total air and room air produces a buoyancy effect which cause the cool air to drop and the warm air to rise

Total air has no defined terminal velocity limit

Step 2Total Air


Step 3: Identify Natural Convection Currents

Step 3: Identify Natural Convection Currents

Natural Convection Currents -

Caused by

difference in temperature between room air and air in contact with a warm or cold surface

Affects room air motion and affects the comfort in the space

Step 3Natural

convection currents and stratification

zone


Step 4: Identify the Return IntakeStep 4: Identify the Return Intake

Return Intake -

return intake affects only the air motion within its immediate vicinity

Even natural convection currents will overcome the draw of the intake


Step 5: Identify the Room AirStep 5: Identify the Room Air

Room Air Diagram is complete when remaining room air drifts back towards the primary air and total air

Lowest air motion is in stratification zone

Most uniform air motion is between stratification zone and total air

Highest air motion is in and near the primary and total air


Mapping Throw


Mapping ThrowMapping Throw

Cooling


Estimating Downward ProjectionEstimating Downward Projection

Chart provides vertical throw of a free jet to 50 fpm for heating and cooling with the same diffuser.

Typically, cfm and jet velocity are known.

2009 Fundamentals Chapter 20

+10 -20 0

23 40 28

1000 cfm

1000 fpm


ADPI & ComfortADPI & Comfort

Air Diffusion Performance IndexStatistically related the space conditions of local

or transversed temperature and velocities to occupants’

thermal comfort

ADPI >= 80 is considered acceptableEffective draft temperature

= (tx

-tc

) –

0.07(Vx

-30)

% of points where -3<= <= +2 = ADPI

Velocity below 70 fpm


ADPIADPI

The grey area represents -3<= <= +2You can vary

temperature or velocity to maintain comfort15 fpm = 1 °F


Throw vs. Characteristic LengthThrow vs. Characteristic Length


ADPI Selection IllustrationADPI Selection Illustration

MaxMinADPI

T50/L

1.20.6

20x20 Room400 cfm = 1 cfm/sq ftCharacteristic Length = 10

80 ADPI Min

Therefore, look for T50 = 12 feet at 400 cfm (Max VAV)Check Turndown point at .6 T50/L (Min VAV)

Point A

Set constant volume systems at Point A.


Outlet T50

/L Range Calculated T50

& L Data

Sidewall Grilles1.3-2.0

LT50

1013-20

1520-30

2026-40

2533-50

3039-60

Ceiling DiffusersRound Pattern

0.6-1.2

L

T50

5

3-6

10

6-12

15

9-18

20

12-24

25

15-30Ceiling DiffusersCross Pattern

1.0-2.0

L

T50

5

5-10

10

10-20

15

15-30

20

20-40

25

25-50Slot Diffusers

0.5-3.3L

T50

53-18

105-33

159-50

2010-66

2515-83

Light Troffer

Diffusers

1.0-5.0

L

T50

4

4-20

6

6-30

8

8-40

10

10-50

12

12-60Sill & Floor Grilles

All Types 0.7-1.7L

T50

54-9

107-17

1511-26

2014-34

2518-13

Recommended ADPI Ranges for OutletsRecommended ADPI Ranges for Outlets


ASHRAE Standard 62.1 Table 6.2 Ventilation Air Ez

Factor

ASHRAE Standard 62.1 Table 6.2 Ventilation Air Ez

Factor

Ceiling supply of cool air 1.0Ceiling supply warm air < 15 °F Δt

1.0

150 fpm supply jet reaches 4.5’

AFFCeiling supply warm air >15 °F Δt 0.8Floor supply cooling ceiling return UFAD:

T 50 > 4.5’

AFF

1.0

T 50 < 4.5 AFF (RP-1373) 1.2Displacement Ventilation

1.2


Typical Perimeter SolutionTypical Perimeter Solution

50/50 throw pattern is the best compromise for both heating and cooling

Half of the air is always directed in the wrong direction

ASHRAE Std. 62.1-2007

T150

to 4’-5’

AFF

Max Δt = 15 °F


Auto Changeover Diffuser SolutionAuto Changeover Diffuser Solution

Sill

Win

dow

Diffuser

Air flow does not pause in intermittent pattern to cause sustained drafts pop action of air flow pattern.

Cooling

Heating


Auto Changeover DiffuserAuto Changeover Diffuser

Vertical Pattern For Heating

Horizontal Pattern For Cooling

30% Increase In Energy Efficiency

Room reaches set-point faster

Room Stratification for heating similar to cooling


Sills & Soffits on PerimeterSills & Soffits on Perimeter

Soffits cause air to turn up prematurely

Aim air under the soffit to hit the glass or cold wall

Sills deflect cold air into the room

Sill height sets the stratification layer height

Sill

Soffit


Air Distribution, Partition Effects


Partially Mixed Air DistributionPartially Mixed Air Distribution

UFAD –

Interior Zone

Perimeter with Series Fan Terminal

Perimeter with Plenum VAV Cooling

Perimeter with Passive Heating


Underfloor Air Distribution (UFAD)Underfloor Air Distribution (UFAD)

StratifiedZone


Round Access Floor DiffuserRound Access Floor Diffuser

High induction air flow pattern

Occupant adjustable damper

Actuated version available

Typical design point is 80-100 cfm

Throw between 4-5 ft.

Low NC


Interior ApplicationsInterior Applications

Use Conventional Components…

Round (Swirl) Diffusers

Rectangular Diffusers

In Conventional Applications

One per worker or area measure


Series Fan Terminal for PerimeterSeries Fan Terminal for Perimeter

Used in perimeter and conference rooms

Any room with varying loads

10 ½”, and 14”

tall units for 12”

and 16”

raised floors300 cfm to 1200 cfmStandard series fan

powered terminalPrimary supply

air damper

Supply pulls from the floor

Option for two dampers


Typical Perimeter InstallationTypical Perimeter Installation

Low horsepower fan powered terminal unit ducted to rectangular floor diffuser plenums


Plenums Plenums

Plenum sizes vary

8”

x 16”

10”

x 10”

12”

x 12”

Cores are available in multi-piece

2-way or 4 way blow


ECM MotorECM Motor

Electronically Commutated Motor


Brushless, DC motorConverts AC to DC for motorUltra high efficiency motor

Efficiencies of up to 70% across the entire operating range

Energy savingsControl of fan speed through DDC controller

ECM MotorECM Motor


Energy SavingsEnergy Savings

350 watts savings = .350 kW

250 days/year x 12 hours/day = 3000 operating hours/year

.350 kW x 3000 hours = 1050 kWh

1050 kWh x $.10 per kWh = $105 per unit per year energy savings!

Does not include demand charges


PWM PWM

The ECM motor is controlled by a PWM (Pulse Width Modulated) signalVoltage pulses over a specific time periodVoltage is proportional to cfmLow voltage deviceManual PWM is adjusted like a SCR, with a

screwdriverRemote PWM is controlled by a 0-10V signal from

the DDC controller


Additional ECM BenefitsAdditional ECM Benefits

Soft start

Motors are set to start up slowly

No brushes

No noise associated with brushes

Titus has found no significant overall sound reduction with the ECM motor

No wearing of brushes

ECM motor life is ~90,000 hours (30 years of typical series fan box life)Cooler operation


Linear Perimeter SystemLinear Perimeter System

(Variable Air Volume)

(Water Heat)

(SCR Electric Heat)

(Return)


Perimeter Linear Diffuser SolutionPerimeter Linear Diffuser Solution


Transverse Apertures


Perimeter Smoke Demo VideoPerimeter Smoke Demo Video


Interior Zone VAV CoolingInterior Zone VAV Cooling

Waiting AreaConference


Underfloor System ChristmanUnderfloor System Christman

Linear Heat3900 Btu/h 4’

Length


Fin tube applicationFin tube application


Fully Stratified Air SystemsFully Stratified Air Systems

Energy & Comfort Optimization (ECO)

Basic system concepts

Displacement diffusers


DV‐

Basic ConceptsDV‐

Basic Concepts

Higher supply air temperature

Air change effectiveness factor of 1.2 Clear

Zone

Supply Air TL = 65°F


Displacement Ventilation ApplicationsDisplacement Ventilation Applications

Good application

Room height > 9.5 ft

Open Plan Offices, Classrooms, & Meeting Rooms

Casinos, Restaurants, Theaters, & Auditoriums


Displacement Ventilation ApplicationsDisplacement Ventilation Applications

Poor application

Room height < 8 ft

Surplus heat is the main problem –

not air quality

In combination with chilled beams


System EquipmentSystem Equipment

Higher equipment efficiency

Uses warmer supply air

65°F compared to 55°F

Energy consumption is often reduced by raising discharge temperature


System EquipmentSystem Equipment

Lower horsepower fans

0.04 in. pressure is required for proper diffuser performance

Results in lower horsepower fans required


HVAC System BenefitsHVAC System Benefits

Heat sources outside the stratification layer are not considered in airflow calculations

Lighting load is designed as “equipment load”, but not as “space load”

Effects cooling load capacity, but not air distribution capacity


Perimeter HeatingPerimeter Heating

Perimeter heating cannot be accomplished with the displacement ventilation system

Separate system is required:


Return AirReturn Air

Located at ceiling

Allows heat from ceiling light to be returned before it is able to mix with occupied zone


Return AirReturn Air

If 55oF supply air is used for humidity reasons, return air can be mixed with plenum air to achieve 65oF air

If 65oF supply air is used, return air can be brought back to the air handling unit to be filtered and dehumidified


Temperature GradientTemperature Gradient

ASHRAE Standard 55:

Occupied Zone

< 5.4°F

Risk of draft increases if ∆t > 36°F between

supply and exhaust air

(Displacement ventilation, REHVA)



Ceiling Height 9’-14’

50% Rule is applied

62°F –

72°F –

82°F

10°F - 10°F




33% Rule for > 14’ room heights

64°F –

72°F –

86°F

8°F - 14°F


33% 67%


Adjacent zoneAdjacent zone

Discharge Velocity < 80 fpm

Area where air velocity exceeds 50 fpm

Occupants should not be stationed within the adjacent zone


Comfort with Adjustable Air PatternsComfort with Adjustable Air Patterns

Standard adjacent zone from factory

Modified adjacent zone after adjusting pattern controllers to change pattern


Comfort Air Distribution

The ASHRAE 2009 Fundamentals handbook, Chapter 20, 2007 Applications handbook Chapter 56, and 2008 Systems & Equipment handbook provides guidance on diffuser selection.Select throw at Max. & Min. to meet ADPI

guidelines.It cost less for install a good design than to

replace a bad design.Employees cost 70 times the cost of Energy.

Questions?Questions?

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