ASHRAE Journal - October 2021 - 59

COLUMN ENGINEER'S NOTEBOOK
FIGURE 3 The perfect load for an integrated economizer-equipped AHU in Portland, Ore., contrasted with an identical unit in Atlanta.
Constant Volume, Economizer, 24/7
Portland, Ore.: Tons vs. OAT
Atlanta: Tons vs. OAT
350
300
250
200
150
100
50
80,000 cfm, 25% OA
51°F LAT Setpoint
OA Dry Bulb-Based Economizer High Limit
Looking for Shapes in the Clouds
As a proud member of the Cloud Appreciation
Society,** I whimsically look for shapes in atmospheric
clouds. But that same fascination serves me well in my
" day job " because data cloud shapes can be revealing.
For example, in Figure 3, the steepness of the inclined
line of perfection and the data scatter that exists around
it is affected by the climate.
Note the difference in the pattern created by the much
more humid Atlanta environment relative to Portland,
Ore., even though the design dry-bulb temperatures are
within 2.6°F (1.4°C) of each other.
A dense cloud correlates with many hours at a given
tonnage and OAT (many " dots " plotted on top of each
other). A barely visible cloud correlates with very few
hours at those conditions.
Figure 4 illustrates how common operating variables
impact the cloud shape. By comparing Figure 4a with
the other charts, you can see how moisture (Figure 4b),
economizer high limit settings (Figure 4c), VAV operation
(Figure 4d) and schedules (Figure 4e) manifest themselves.
Figure 5 illustrates using this approach for a plant serving
a hypothetical 200-room full-service hotel with:
* Economizer-equipped VAV systems;
* Constant volume (CV) makeup air unit systems
(MAUs),
* Fan coil units serving the guest rooms; and
* Chilled water-cooled ice machines and walk-in coolers.
**There really is one: https://cloudappreciationsociety.org/
Key Takeaways
* The cloud created by the variables in Figure 5 follows
the lines of perfection.
* The variables introduce data scatter.
* The base load shifts the horizontal portion of the
perfect cloud upward.
* The transitions from horizontal to an incline are the
result of the OAT exceeding system LATs.
* The change in the slope at warmer temperatures
is the result of the economizer high limit. This is more
apparent in Figure 5b (the inset is the economizer system
cloud, isolated by fi ltering).
* For a given climate and high limit setting, the slope
of the economizer portion of the cloud when operating
on MOA is related to the MOA percentage, outdoor
design conditions and high limit settings.
* Variable fl ow and schedules create bands correlating
to those drivers.
The Clues
For a real facility, deviations from the perfect cloud are
indicators of opportunity.
* Data points in the green and yellow areas in Figure 2
indicate the potential to improve the use of OA cooling.
* A base load that deviates from known loads requiring
year-round cooling often correlates to unnecessary
preheat.
* A facility with alleged schedules and VAV systems
that does not show distinct bands in the cloud may have
O CTO B E R 2 0 2 1 ashrae.o rg ASHRAE JOURNAL
59
Portland, Ore.: 0.4% Design Condition = 91.2°F tdb /67.5°F twb
Atlanta: 0.4% Design Condition = 93.8°F tdb /74.3°F twb
Line of Perfection
10
20
30
40
50
60
Outdoor Temperature (°F)
70
80
90
100
Tons
https://www.cloudappreciationsociety.org/ http://ashrae.org

ASHRAE Journal - October 2021

Table of Contents for the Digital Edition of ASHRAE Journal - October 2021

Contents
ASHRAE Journal - October 2021 - Intro
ASHRAE Journal - October 2021 - Cover1
ASHRAE Journal - October 2021 - Cover2
ASHRAE Journal - October 2021 - 1
ASHRAE Journal - October 2021 - Contents
ASHRAE Journal - October 2021 - 3
ASHRAE Journal - October 2021 - 4
ASHRAE Journal - October 2021 - 5
ASHRAE Journal - October 2021 - 6
ASHRAE Journal - October 2021 - 7
ASHRAE Journal - October 2021 - 8
ASHRAE Journal - October 2021 - 9
ASHRAE Journal - October 2021 - 10
ASHRAE Journal - October 2021 - 11
ASHRAE Journal - October 2021 - 12
ASHRAE Journal - October 2021 - 13
ASHRAE Journal - October 2021 - 14
ASHRAE Journal - October 2021 - 15
ASHRAE Journal - October 2021 - 16
ASHRAE Journal - October 2021 - 17
ASHRAE Journal - October 2021 - 18
ASHRAE Journal - October 2021 - 19
ASHRAE Journal - October 2021 - 20
ASHRAE Journal - October 2021 - 21
ASHRAE Journal - October 2021 - 22
ASHRAE Journal - October 2021 - 23
ASHRAE Journal - October 2021 - 24
ASHRAE Journal - October 2021 - 25
ASHRAE Journal - October 2021 - 26
ASHRAE Journal - October 2021 - 27
ASHRAE Journal - October 2021 - 28
ASHRAE Journal - October 2021 - 29
ASHRAE Journal - October 2021 - 30
ASHRAE Journal - October 2021 - 31
ASHRAE Journal - October 2021 - 32
ASHRAE Journal - October 2021 - 33
ASHRAE Journal - October 2021 - 34
ASHRAE Journal - October 2021 - 35
ASHRAE Journal - October 2021 - 36
ASHRAE Journal - October 2021 - 37
ASHRAE Journal - October 2021 - 38
ASHRAE Journal - October 2021 - 39
ASHRAE Journal - October 2021 - 40
ASHRAE Journal - October 2021 - 41
ASHRAE Journal - October 2021 - 42
ASHRAE Journal - October 2021 - 43
ASHRAE Journal - October 2021 - 44
ASHRAE Journal - October 2021 - 45
ASHRAE Journal - October 2021 - 46
ASHRAE Journal - October 2021 - 47
ASHRAE Journal - October 2021 - 48
ASHRAE Journal - October 2021 - 49
ASHRAE Journal - October 2021 - 50
ASHRAE Journal - October 2021 - 51
ASHRAE Journal - October 2021 - 52
ASHRAE Journal - October 2021 - 53
ASHRAE Journal - October 2021 - 54
ASHRAE Journal - October 2021 - 55
ASHRAE Journal - October 2021 - 56
ASHRAE Journal - October 2021 - 57
ASHRAE Journal - October 2021 - 58
ASHRAE Journal - October 2021 - 59
ASHRAE Journal - October 2021 - 60
ASHRAE Journal - October 2021 - 61
ASHRAE Journal - October 2021 - 62
ASHRAE Journal - October 2021 - 63
ASHRAE Journal - October 2021 - 64
ASHRAE Journal - October 2021 - 65
ASHRAE Journal - October 2021 - 66
ASHRAE Journal - October 2021 - 67
ASHRAE Journal - October 2021 - 68
ASHRAE Journal - October 2021 - 69
ASHRAE Journal - October 2021 - 70
ASHRAE Journal - October 2021 - 71
ASHRAE Journal - October 2021 - 72
ASHRAE Journal - October 2021 - HR1
ASHRAE Journal - October 2021 - HR2
ASHRAE Journal - October 2021 - HR3
ASHRAE Journal - October 2021 - HR4
ASHRAE Journal - October 2021 - HR5
ASHRAE Journal - October 2021 - HR6
ASHRAE Journal - October 2021 - HR7
ASHRAE Journal - October 2021 - HR8
ASHRAE Journal - October 2021 - HR9
ASHRAE Journal - October 2021 - HR10
ASHRAE Journal - October 2021 - HR11
ASHRAE Journal - October 2021 - HR12
ASHRAE Journal - October 2021 - HR13
ASHRAE Journal - October 2021 - HR14
ASHRAE Journal - October 2021 - HR15
ASHRAE Journal - October 2021 - HR16
ASHRAE Journal - October 2021 - HR17
ASHRAE Journal - October 2021 - HR18
ASHRAE Journal - October 2021 - HR19
ASHRAE Journal - October 2021 - HR20
ASHRAE Journal - October 2021 - HR21
ASHRAE Journal - October 2021 - HR22
ASHRAE Journal - October 2021 - HR23
ASHRAE Journal - October 2021 - HR24
ASHRAE Journal - October 2021 - 73
ASHRAE Journal - October 2021 - 74
ASHRAE Journal - October 2021 - 75
ASHRAE Journal - October 2021 - 76
ASHRAE Journal - October 2021 - 77
ASHRAE Journal - October 2021 - 78
ASHRAE Journal - October 2021 - 79
ASHRAE Journal - October 2021 - 80
ASHRAE Journal - October 2021 - 81
ASHRAE Journal - October 2021 - 82
ASHRAE Journal - October 2021 - 83
ASHRAE Journal - October 2021 - 84
ASHRAE Journal - October 2021 - 85
ASHRAE Journal - October 2021 - 86
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ASHRAE Journal - October 2021 - 88
ASHRAE Journal - October 2021 - 89
ASHRAE Journal - October 2021 - 90
ASHRAE Journal - October 2021 - 91
ASHRAE Journal - October 2021 - 92
ASHRAE Journal - October 2021 - 93
ASHRAE Journal - October 2021 - 94
ASHRAE Journal - October 2021 - 95
ASHRAE Journal - October 2021 - 96
ASHRAE Journal - October 2021 - Cover3
ASHRAE Journal - October 2021 - Cover4
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