ASHRAE Journal - April 2022 - 56

COLUMN ENGINEER'S NOTEBOOK
FIGURE 10 Rooftop unit data plotted against the perfect economizer lines.
90
85
80
75
70
65
60
55
50
45
40
35
30
-40
Ideal Integrated Economizer Operation
Mixed Air Temperature Setpoint = 52°F
Target Minimum Outdoor Air Percentage = 11%
Preheat Coil Discharge Setpoint = 51°F
Cooling Coil Discharge Setpoint = 53°F
Assumed Return Air Temperature = 73°F
Outdoor Air Dry-Bulb Limit Setpoint = 66°F
Design % Outdoor
Air (11%)
Estimated Actual %
Outdoor Air (25%)
Preheat, Min. OA
Economizer Cooling
Integrated Economizer
Mechanical Cooling, Min. OA
Preheat LAT vs OAT/Preheat Active
Mixed Air vs OAT
Coolant LAT vs OAT/Cooling Active
Reheat LAT vs OAT/Reheat Active
-30
-20
-10
10
20
30
40
50
60
Outdoor Temperature (°F)
* For this system, given the climate, the point when
preheat would be active is off the chart. Yet preheat was
active, along with chilled water cooling and reheat, so a
definite opportunity for improvement.
I'll take you further down the analysis path in a future
column.
Conclusion
Hopefully, in addition to illustrating technique, this
column and the " Modeling Perfection " column help you
see how one thing can lead to another. Deviations from
perfection in the chilled water plant data cloud led the
team to explore their AHUs. Applying the perfect economizer
concept there revealed where the root cause of
the problems lay, allowing them to focus their O&M and
capital projects to maximize the benefits.
Acknowledgments
I want to thank my fellow column writers and editor
for their thoughtful and insightful review comments,
which helped me fine-tune the final draft of the
column.
And I wanted to thank CERL and Dewberry for the
latitude they granted me when I worked with them on
a recent project, which gave me time to further develop
some of the concepts I discuss here.
70
80
90
100
110
Reheat Active
Cooling Active
Preheat Active
Not Active
120 130 Not Active
100% Outdoor Air
0% Outdoor Air
56
ASHRAE JOURNAL ashrae.o rg
A P R I L 2022
Mixed Air, Preheat, Cooling and
Reheat Coil Leaving Temperature (°F)
Preheat, Cooling and Reheat Active
(Reheat may or may not be active at the conditions indicated
by the red dotted line depending on process requirements)

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ASHRAE Journal - April 2022

Table of Contents for the Digital Edition of ASHRAE Journal - April 2022

Contents
ASHRAE Journal - April 2022 - Intro
ASHRAE Journal - April 2022 - Cover1
ASHRAE Journal - April 2022 - Cover2
ASHRAE Journal - April 2022 - 1
ASHRAE Journal - April 2022 - Contents
ASHRAE Journal - April 2022 - 3
ASHRAE Journal - April 2022 - 4
ASHRAE Journal - April 2022 - 5
ASHRAE Journal - April 2022 - 6
ASHRAE Journal - April 2022 - 7
ASHRAE Journal - April 2022 - 8
ASHRAE Journal - April 2022 - 9
ASHRAE Journal - April 2022 - 10
ASHRAE Journal - April 2022 - 11
ASHRAE Journal - April 2022 - 12
ASHRAE Journal - April 2022 - 13
ASHRAE Journal - April 2022 - 14
ASHRAE Journal - April 2022 - 15
ASHRAE Journal - April 2022 - 16
ASHRAE Journal - April 2022 - 17
ASHRAE Journal - April 2022 - 18
ASHRAE Journal - April 2022 - 19
ASHRAE Journal - April 2022 - 20
ASHRAE Journal - April 2022 - 21
ASHRAE Journal - April 2022 - 22
ASHRAE Journal - April 2022 - 23
ASHRAE Journal - April 2022 - 24
ASHRAE Journal - April 2022 - 25
ASHRAE Journal - April 2022 - 26
ASHRAE Journal - April 2022 - 27
ASHRAE Journal - April 2022 - 28
ASHRAE Journal - April 2022 - 29
ASHRAE Journal - April 2022 - 30
ASHRAE Journal - April 2022 - 31
ASHRAE Journal - April 2022 - 32
ASHRAE Journal - April 2022 - 33
ASHRAE Journal - April 2022 - 34
ASHRAE Journal - April 2022 - 35
ASHRAE Journal - April 2022 - 36
ASHRAE Journal - April 2022 - 37
ASHRAE Journal - April 2022 - 38
ASHRAE Journal - April 2022 - 39
ASHRAE Journal - April 2022 - 40
ASHRAE Journal - April 2022 - 41
ASHRAE Journal - April 2022 - 42
ASHRAE Journal - April 2022 - 43
ASHRAE Journal - April 2022 - 44
ASHRAE Journal - April 2022 - 45
ASHRAE Journal - April 2022 - 46
ASHRAE Journal - April 2022 - 47
ASHRAE Journal - April 2022 - 48
ASHRAE Journal - April 2022 - 49
ASHRAE Journal - April 2022 - 50
ASHRAE Journal - April 2022 - 51
ASHRAE Journal - April 2022 - 52
ASHRAE Journal - April 2022 - 53
ASHRAE Journal - April 2022 - 54
ASHRAE Journal - April 2022 - 55
ASHRAE Journal - April 2022 - 56
ASHRAE Journal - April 2022 - 57
ASHRAE Journal - April 2022 - 58
ASHRAE Journal - April 2022 - 59
ASHRAE Journal - April 2022 - 60
ASHRAE Journal - April 2022 - 61
ASHRAE Journal - April 2022 - 62
ASHRAE Journal - April 2022 - 63
ASHRAE Journal - April 2022 - 64
ASHRAE Journal - April 2022 - 65
ASHRAE Journal - April 2022 - 66
ASHRAE Journal - April 2022 - 67
ASHRAE Journal - April 2022 - 68
ASHRAE Journal - April 2022 - 69
ASHRAE Journal - April 2022 - 70
ASHRAE Journal - April 2022 - 71
ASHRAE Journal - April 2022 - 72
ASHRAE Journal - April 2022 - Cover3
ASHRAE Journal - April 2022 - Cover4
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