ASHRAE Journal - October 2021 - 62

COLUMN ENGINEER'S NOTEBOOK
FIGURE 5 The Perfect Chilled Water Load, 220-room hotel, Atlanta. The cloud in (a) is the sum of the clouds in (b). Figure 5b illustrates the individual clouds generated by
the different load types.
A.
120
110
100
90
80
70
60
50
40
30
20
10
-10
0 10 20 30 40 50 60 70 80 90 100 110 120
Outdoor Temperature (°F)
rect economizer high limit setpoints.
An Example of Perfection vs. Reality
The facility behind our example shown in Figure 6 is a
full-service, 620-room hotel in Atlanta. It has a mix of
The Perfect Chilled Water Load
200-Room Hotel, Atlanta
Design Cooling
Condition - 100%
OA System
B.
Economizer High Limit
Design Heating
Condition
Design Cooling Coil LAT
Design Cooling
Condition -
Economizer System,
25% MOA
120
110
100
90
80
70
60
50
40
30
20
10
-10
0 10 20 30 40 50 60 70 80 90 100 110 120
Outdoor Temperature (°F)
constant volume 100% OA systems and VAV reheat economizer
systems. It has approximately 70 tons (246 kW) of
24/7 cooling load without access to outdoor air, and aircooled
ice machines and walk-in coolers.
Scheduling and Variable Flow Opportunities
The area inside the green outline in Figure 6b has
no bands in it. This suggest that VAV systems are not
varying flow and/or that schedules are not implemented.
Moving into the project, we encountered both
opportunities.
Ventilation and Economizer High Limits
" Eye-balling " a line through the dense part of the
cloud (red line, Figure 6c, Figure 6d, Figure 6e) reveals a
flatter slope than the perfect line in Figure 6c (compare
the yellow line with the red line). When the perfect lines
are adjusted to reflect 0% MOA in Figure 6d (compare the
slope of the orange line in Figure 6c and Figure 6d), there
is much less of a difference in slope (Figure 6d). Thus,
underventilation is a possibility.
However, the slope mismatch can also be an indication
of an inappropriate economizer high limit setting.
Since we are dealing with a cloud rather than a line, the
inflection point where the cloud shape becomes more
horizontal is over a range of temperatures: 68°F to 72°F
(20°C to 22°C)-the green and purple lines in Figure 6e.
The perfect lines in Figure 6a to Figure 6d were set
assuming an OA dry-bulb economizer high limit of
65.7°F (18.7°C), which is appropriate given the Atlanta
location and the indoor design target (Figure 2 and
62
ASHRAE JOURNAL ashrae.o rg O CTO B E R 2 0 2 1
The Perfect Chilled Water Load
200-Room Hotel, Atlanta
Base Load and Guest Room Fan Coil Units
Makeup Air Systems
Scheduled VAV Reheat Economizer Systems
Load, Tons (%)
Load, Tons (%)
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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
ASHRAE Journal - October 2021 - 87
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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