System Effects

Presented by:

Joe Brooks, AMCA International, Inc.

AMCA International TechnicalSeminar 2009

System Effects, Slide 2

The Air Movement and Control Association International (AMCA), has met the standards and requirements of the Registered Continuing Education Providers Program. Credit earned on completion of this program will be reported to the RCEPP. A certificate of completion will be issued to each participant. As such, it does not include content that may be deemed or construed to be an approval or endorsement by NCEES or RCEPP.

System Effects, Slide 3

Learning ObjectivesLearning Objectives

Describe system resistance of componentsDescribe system resistance of components

Know how a fan interacts with the systemKnow how a fan interacts with the system

Define System Effect and System Effect Factor Define System Effect and System Effect Factor (SEF)(SEF)

Know how to avoid system effect factorsKnow how to avoid system effect factors

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Two Components of System Design

Calculate flow resistance losses for each component in the system

Select and position fan to avoid system effect loss If loss cannot be avoided, estimate loss and

select fan for higher pressure

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Ductwork Example

System Resistance

System Effect Controlled by Inlet and Outlet Conditions

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Causes of Non-Performing Systems

System resistance miscalculated.

Fan not properly selected.

Defective fan (or fan rating).

There is a system effect loss.

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Fan Manufacturer’s Responsibility

Provide accurate fan performance ratings.

Provide a fan built within tolerance so that it is capable of meeting its rating.

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What is System Effect?

A factor used to correct for system induced installation effects.

The difference in performance between a fan tested in the laboratory and one tested in a real installation.

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Inlet Connections

ASHRAE Guidelines

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Outlet Connections

ASHRAE Guidelines

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Outlet Connections

ASHRAE Guidelines

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What is Missing?

Only guidelines to avoid losses.

No way to quantify losses.

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AMCA Publication 201-02

The bible of system effects

Generated from ASHRAE funded research

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Credibility Gap

Are system effects just fudge factors that the fan manufacturers made up?

System effect video.

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Definition of System Effect

Fan ratings are established using AMCA 210 test codes that are close to ideal conditions.

Fans in actual systems are often less than ideal.

The difference in performance for the same fan tested in both conditions is the “System Effect”.

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Purpose of Discussion

Aimed primarily at the fan system designer

There are two goals:

Avoid poor fan system configurations

When optimum conditions cannot be met, use the “system effect” factors to estimate any losses during system design.

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Why System Effect is Important

May have to accept deficient performance, or... Speed up the fan (if possible) May require more energy to meet performance May exceed motor horsepower limit

Many cause excessive noise

Many cause excessive vibration

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Normal System Performance

Design volume

Fan curve

Calculated duct system curve

Des

ign

pre

ssu

re

1

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Deficient Performance With System Effect

Design volume

Original fan curve

Deficient volume

3

Calculated duct system with no allowance for system effect

4

System effect at actual flow volume

Des

ign

pre

ssu

re

1

Operating point is at point 3 Operating point is not

on fan curve!

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Correcting For System Effect

Design volume

Original fan curve

New fan curve

System effect loss at design volume

2

Deficient volume

3

Calculated duct system with no allowance for system effect

4

System effect at actual flow volume

Actual duct system with system effect

Des

ign

pre

ssu

re

1

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The fan will be selected for the higher pressure (no need to speed up).

The motor will be selected to include the anticipated loss.

With System Effects Added:

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What are the Causes of the Losses?

Inlet losses are caused by: Unequal loading of the fan blades (eccentric

flow). Improper fan blade attack angle. Turbulence which disrupts the flow.

Outlet losses are caused by: Loss of conversion of local high velocity into

pressure.

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Inlet induced losses tend to be higher than outlet losses.

Losses induced on the inlet can often exceed 20%.

Losses as high as 50% have been reported.

Inlet vs. Outlet Losses

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Straight uniform flow directed only in the axial direction--on the fan inlet

For Ducted fans - a straight length of outlet ductwork

Good Flow Conditions for a Fan:

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AMCA Publication 210-07

Defines standard methods of testing fans for rating purposes

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How are the Losses Quantified?

AMCA 201 publishes data for a variety of configurations

Most identify a “Loss Curve” which is based on the configuration and identified by a letter Most also need the air velocity as a parameter.

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System Effect Curves

4000 FPM

Curve T

Add 0.55 to Static Pressure

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Outlet System Effects

In addition to the flow velocity, may need to know: effective duct length blast area

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System Effect Curves for Outlet Ducts - Axial Fans

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Fan Outlet Velocity Profile - Centrifugal

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System Effect Curves for Outlet Ducts - Centrifugal Fans

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Outlet Duct Elbows - Centrifugal Fans

BAD

WORSE

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S. E. Curves for Outlet Elbows on Centrif.

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S. E. Curves for Outlet Elbows - Axial

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S. E. Curves for Inlet Elbows - Axial

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Percentage of Unobstructed Inlet Area

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Fans and Plenum – Two Losses

Distance L / (Inlet Dia.) gives one loss

Loss factors given for 0.3 to 0.75 clearance

Note: Spacing for two fans is important

Keep inlet centerline on centerline of unit

No loss factors given

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Elbows Change the Velocity Profile

Fan inlet here will create a system effect loss for any type of fan

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Right Angle Turns At Fan Inlet

Inlet with rectangularinlet Duct(POOR)

Inlet with 3-piece elbow

Inlet with specialdesigned inlet box

All methods will induce some system effect loss. Some methods are better than others

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System Effect - Round Inlet Ducts

R

Lengthof Duct

R

R

Lengthof Duct

Lengthof Duct

D D D

System Effect Curves

R/D NoDuct

2DDuct

5DDu ct

-- N P R-S

System Effect Curves

R/D NoDuct

2DDuct

5DDuct

0.5 O Q S

0.75 Q R-S T-U

1.0 R S-T U-V

2.0 R-S T U-V

3.0 S T-U V

System Effect Curves

R/D NoDuct

2DDuct

5DDuct

0.5 P-Q R-S T

0.75 Q-R S U

1.0 R S-T U-V

2.0 R-S T U-V

3.0 S-T U V-

2 piece miteredround section

3 piece mitered round section

4 or more piecemitered round section

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Forced Inlet Vortex (Inlet Spin or Swirl)

Pre-Rotating Inlet Swirl

Counter-Rotating Inlet Swirl

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Corrections for Inlet Spin

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Normalized Pressure-Volume Curve

Note that this is similar to a variable system effect.

A new curve is generated at each vane setting

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Pressure Drop Multipliers for Volume Control Dampers on a Fan Outlet

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Measured Inlet Sound Power

70

80

90

100

110

63 125 250 500 1000 2000 4000 8000

Fan Only 2 PC Elbow on Inlet 2 PC Elbow 3 De

Blade Pass - 135 Hz

Vaneaxial Fan System Effect

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System Effect Factors are Real

When designing your fan/system, do everything possible to avoid a “system effect” for efficient use of energy

When conditions leading to system effect cannot be avoided, add the calculated loss to the fan pressure requirement at the system design stage.

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Thumb Rules

Minimum of 2-1/2 Duct Diameters on Outlet,

Minimum 3 to 5 Duct Diameters on Inlet, and

Avoid Inlet Swirl

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Questions?Questions?

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