ASHRAE Journal - June 2011 - 38
System Effect
To Believe It Is to See It
I
By Sutton G. Page, Member ASHRAE
dentifying system effect and determining its underlying cause has been a personal challenge for me for many years. With the
exception of inlet swirl, system effect has been difficult, if not impossible, to explain. In fact, many designers do not believe system effect exists, while others are focused only on fan curve and static pressure losses in the system. Both groups are wrong.
This article explains the real cause of system effect based on extensive experience and field testing on hundreds of fan systems that failed to perform as expected. Typically, an operator theorized a problem might be system effect, but looking at the fan curve and the static pressures, rpm, etc., decided it must be something else. And, as it turns out, that’s exactly the case. The presence of system effect is merely a symptom that an underlying problem exists. Chasing the symptom with the fan curve and static pressure measurements is not the right path and will not reveal the underlying problem.
38 ASHRAE Journal
The problem is velocity losses due to poor fan connections, improper fan selection, and poor downstream or upstream duct design. The actual underlying problem is turbulent flow, and I have termed it: velocity/counter velocity or simply V/CV. This article will help you visualize what cannot be seen or measured, and will provide a good representation of what is really occurring in fan/ duct systems. ASHRAE1 and AMCA International2 address system effect and its consequences when system effect is present.
ashrae.org
System Effect
In previous articles,3,4 I discuss how the presence of system effect can be determined. The articles illustrate how traditional fan measurements can be used to identify the presence of system effect; however, system effect cannot be measured due to the presence of turbulent flow. Too many people in the industry believe system effect is the result of pressure losses within the system. Deficient fan performance in the presence of system effect has nothing to do with static pressure losses. Often, traditional fan measurements may result in false-positive values that further confuse the issue. Poorly designed duct systems usually have several immediate hard turns (90 degrees) located at the fan inlet or, more often, the fan discharge. These types of connections are velocity killers with velocity losses far beyond the losses that static pressure measurements would indicate. The static pressure measurements will indicate little or no presAbout the Author
Sutton G. Page is CEO of Austin Air Balancing Corporation in Austin, Texas.
June 2011
ASHRAE Journal - June 2011
Table of Contents for the Digital Edition of ASHRAE Journal - June 2011
Contents
Commentary
Industry News
Meetings and Shows
Letters
Feature Articles
Saving Energy in Lab Exhaust Systems
System Effect: To Believe It Is to See It
What’s New in ASHRAE’s Standard on Comfort
On the Path to Net Zero: How Do We Get There From Here?
Technology Award Case Studies:
Walls to Heat, Cool
Building Sciences
Solar NZEB Project
HVAC Mythbuster
Emerging Technologies
IAQ Applications
Washington Report
Products
People
Classified Advertising
Advertisers Index
ASHRAE Journal - June 2011 - Intro
ASHRAE Journal - June 2011 - Cover1
ASHRAE Journal - June 2011 - Cover2
ASHRAE Journal - June 2011 - 1
ASHRAE Journal - June 2011 - 2
ASHRAE Journal - June 2011 - Contents
ASHRAE Journal - June 2011 - Commentary
ASHRAE Journal - June 2011 - 5
ASHRAE Journal - June 2011 - Industry News
ASHRAE Journal - June 2011 - 7
ASHRAE Journal - June 2011 - 8
ASHRAE Journal - June 2011 - 9
ASHRAE Journal - June 2011 - 10
ASHRAE Journal - June 2011 - 11
ASHRAE Journal - June 2011 - 12
ASHRAE Journal - June 2011 - 13
ASHRAE Journal - June 2011 - Meetings and Shows
ASHRAE Journal - June 2011 - 15
ASHRAE Journal - June 2011 - Letters
ASHRAE Journal - June 2011 - 16a
ASHRAE Journal - June 2011 - 16b
ASHRAE Journal - June 2011 - 17
ASHRAE Journal - June 2011 - 18
ASHRAE Journal - June 2011 - 19
ASHRAE Journal - June 2011 - 20
ASHRAE Journal - June 2011 - 21
ASHRAE Journal - June 2011 - 22
ASHRAE Journal - June 2011 - 23
ASHRAE Journal - June 2011 - 24
ASHRAE Journal - June 2011 - 25
ASHRAE Journal - June 2011 - Saving Energy in Lab Exhaust Systems
ASHRAE Journal - June 2011 - 27
ASHRAE Journal - June 2011 - 28
ASHRAE Journal - June 2011 - 29
ASHRAE Journal - June 2011 - 30
ASHRAE Journal - June 2011 - 31
ASHRAE Journal - June 2011 - 32
ASHRAE Journal - June 2011 - 33
ASHRAE Journal - June 2011 - 34
ASHRAE Journal - June 2011 - 35
ASHRAE Journal - June 2011 - 36
ASHRAE Journal - June 2011 - 37
ASHRAE Journal - June 2011 - System Effect: To Believe It Is to See It
ASHRAE Journal - June 2011 - 39
ASHRAE Journal - June 2011 - 40
ASHRAE Journal - June 2011 - 41
ASHRAE Journal - June 2011 - What’s New in ASHRAE’s Standard on Comfort
ASHRAE Journal - June 2011 - 43
ASHRAE Journal - June 2011 - 44
ASHRAE Journal - June 2011 - 45
ASHRAE Journal - June 2011 - 46
ASHRAE Journal - June 2011 - 47
ASHRAE Journal - June 2011 - 48
ASHRAE Journal - June 2011 - 49
ASHRAE Journal - June 2011 - On the Path to Net Zero: How Do We Get There From Here?
ASHRAE Journal - June 2011 - 51
ASHRAE Journal - June 2011 - 52
ASHRAE Journal - June 2011 - 53
ASHRAE Journal - June 2011 - 54
ASHRAE Journal - June 2011 - 55
ASHRAE Journal - June 2011 - 56
ASHRAE Journal - June 2011 - 57
ASHRAE Journal - June 2011 - 58
ASHRAE Journal - June 2011 - 59
ASHRAE Journal - June 2011 - 60
ASHRAE Journal - June 2011 - 61
ASHRAE Journal - June 2011 - Walls to Heat, Cool
ASHRAE Journal - June 2011 - 63
ASHRAE Journal - June 2011 - 64
ASHRAE Journal - June 2011 - 65
ASHRAE Journal - June 2011 - 66
ASHRAE Journal - June 2011 - 67
ASHRAE Journal - June 2011 - Building Sciences
ASHRAE Journal - June 2011 - 69
ASHRAE Journal - June 2011 - 70
ASHRAE Journal - June 2011 - 71
ASHRAE Journal - June 2011 - Solar NZEB Project
ASHRAE Journal - June 2011 - 73
ASHRAE Journal - June 2011 - 74
ASHRAE Journal - June 2011 - 75
ASHRAE Journal - June 2011 - 76
ASHRAE Journal - June 2011 - 77
ASHRAE Journal - June 2011 - HVAC Mythbuster
ASHRAE Journal - June 2011 - 79
ASHRAE Journal - June 2011 - 80
ASHRAE Journal - June 2011 - 81
ASHRAE Journal - June 2011 - Emerging Technologies
ASHRAE Journal - June 2011 - 83
ASHRAE Journal - June 2011 - 84
ASHRAE Journal - June 2011 - 85
ASHRAE Journal - June 2011 - IAQ Applications
ASHRAE Journal - June 2011 - 87
ASHRAE Journal - June 2011 - 88
ASHRAE Journal - June 2011 - 89
ASHRAE Journal - June 2011 - Washington Report
ASHRAE Journal - June 2011 - Products
ASHRAE Journal - June 2011 - 92
ASHRAE Journal - June 2011 - People
ASHRAE Journal - June 2011 - Classified Advertising
ASHRAE Journal - June 2011 - 95
ASHRAE Journal - June 2011 - Advertisers Index
ASHRAE Journal - June 2011 - Cover3
ASHRAE Journal - June 2011 - Cover4
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