ASHRAE Journal - April 2020 - 73

COLUMN ENGINEERS NOTEBOOK

CHWS-T (°F)

CHWR-T (°F)

Coil Flow Rate (gpm)

Total Coil Capacity (MBH)

Coil ∆T (°F)

Leaving Air Temperature (°F)

Figures 9 and 10 for coil
FIGURE 9 Chilled water supply temperature vs. leaving air temperature.
simulation software outCoil LAT
Coil ∆T
puts demonstrating the
70.0
30
impact on performance
60.0
from increasing the tem25
50.0
perature of chilled water
supplied to the coil.
20
40.0
For the coil performance
30.0
15
referenced in this article,
20.0
the basis of design coil was
10
selected with the following
10.0
parameters to match the
5
0
case study coil discussed
38
43
48
53
58
60
below:
CHW Supply Temperature (°F)
* 6 rows, 9 fins per in.
(3.5 fins per centimeter);
FIGURE 10 Chilled water supply temperature vs. total coil capacity.
* 40°F (4.4°C) entering
Total Coil Capacity
Coil Flow Rate
chilled water temperature;
1,000
2,500
* 83.0°F (28.3°C) enter900
ing air temperature;
2,000
800
* 51.1°F (10.6°C) leaving
700
1,500
air temperature;
600
500
* 56.7°F (13.7°C) leaving
1,000
400
chilled water tempera300
500
ture; and
200
* 9.0 ft (26.5 kPa) head
0
100
water pressure drop.
38
43
48
53
58
60
In practice, the chilled
CHW Supply Temperature (°F)
water pumps may be
selected for a margin of
FIGURE 11 LAT vs. CHW return temperature.
additional head capacity
90.0
and pump power when
95
80.0
compared to design load.
70.0
85
But as pump power has
60.0
75
an approximate cube
50.0
65
40.0
relationship with flow,
58 59 60
55 56 57
54
30.0
53
52
55
51
the pump will rapidly
48 49 50
45 46 47
20.0
44
43
42
45
exceed its design operat10.0
ing point as chilled water
35
0.0
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
supply temperature
LAT (°F)
is increased. To better
40°F
EWT
(CHWR-T
Axis)
Warmer EWT Supplied (CHWR-T Axis)
approximate anticipated
40°F EWT (CHWS-T Axis)
Warmer EWT Supplied (CHWS-T Axis)
performance in the field,
chilled water flow is
maximum waterside pressure drop of ~23 ft (68.7 kPa)
increased as the chilled
water supply temperature is increased to attempt to
was reached across the coil.
maintain the leaving air temperature setpoint until a
As the temperature of chilled water supply is
APRI L 2020

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ASHRAE Journal - April 2020

Table of Contents for the Digital Edition of ASHRAE Journal - April 2020

Contents
ASHRAE Journal - April 2020 - Intro
ASHRAE Journal - April 2020 - Cover1
ASHRAE Journal - April 2020 - Cover2
ASHRAE Journal - April 2020 - 1
ASHRAE Journal - April 2020 - Contents
ASHRAE Journal - April 2020 - 3
ASHRAE Journal - April 2020 - 4
ASHRAE Journal - April 2020 - 5
ASHRAE Journal - April 2020 - 6
ASHRAE Journal - April 2020 - 7
ASHRAE Journal - April 2020 - 8
ASHRAE Journal - April 2020 - 9
ASHRAE Journal - April 2020 - 10
ASHRAE Journal - April 2020 - 11
ASHRAE Journal - April 2020 - 12
ASHRAE Journal - April 2020 - 13
ASHRAE Journal - April 2020 - 14
ASHRAE Journal - April 2020 - 15
ASHRAE Journal - April 2020 - 16
ASHRAE Journal - April 2020 - 17
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ASHRAE Journal - April 2020 - 19
ASHRAE Journal - April 2020 - 20
ASHRAE Journal - April 2020 - 21
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ASHRAE Journal - April 2020 - 36
ASHRAE Journal - April 2020 - 37
ASHRAE Journal - April 2020 - 38
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ASHRAE Journal - April 2020 - 49
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ASHRAE Journal - April 2020 - 52
ASHRAE Journal - April 2020 - 53
ASHRAE Journal - April 2020 - 54
ASHRAE Journal - April 2020 - 55
ASHRAE Journal - April 2020 - 56
ASHRAE Journal - April 2020 - 57
ASHRAE Journal - April 2020 - 58
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ASHRAE Journal - April 2020 - Cover3
ASHRAE Journal - April 2020 - Cover4
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