ASHRAE Journal - April 2020 - 28

TECHNICAL FEATURE

Scenario Two - Fan "On"

FIGURE 4 Indoor temperature data (°F) collected from November 2 to November 10 at 5 ft, 15 ft and 35 ft (1.5 m,
4.6 m and 10.7 m) above finished floor (AFF) and plotted with outdoor air temperature for comparison.

100
Indoor Air Temperature (°F)

one of the lowest recorded during the
week. The relevance of the temperature
differential being the highest on a low
temperature day is apparent by the gas
heaters in the space operating more
frequently, consuming more natural
gas.

35 ft AFF

15 ft AFF

5 ft AFF

Outside Air

90
80
70
60
50

Indoor Air Temperature (°F)

40
The second set of data, Figure 5, dis30
plays measured indoor air tempera12a 12p 12a 12p 12a 12p 12a 12p 12a 12p 12a 12p 12a 12p 12a 12p 12a
tures over the week of November 9 to
Nov. 2 | Nov. 3 | Nov. 4 | Nov. 5 | Nov. 6 | Nov. 7 | Nov. 8 | Nov. 9 |Nov. 10
November 16 in addition to the outdoor
air temperature with the fan operating slowly in
TABLE 1 Stratification results while fan was "off" showing daily average temperatures (°F) from
5 ft, 15 ft and 35 ft (1.5 m, 4.6 m and 10.7 m) away from floor with outside air conditions (OA)
the downward direction. Table 2 shows average
for comparison. Temperature differentials (DT ) from 35 ft (10.7 m) and 15 ft (4.6 m), and 35 ft
daily temperatures while the fan was on as well
(10.7 m) and 5 ft (1.5 m) are displayed.
as temperature gradients between 5 ft (1.5 m)
FAN OFF
35 FT
15 FT
5 FT
OA
DT (°F)
to 35 ft (10.7 m) and 15 ft (4.6 m) to 35 ft (10.7 m)
DAILY AVERAGES TEMP. (°F) TEMP. (°F) TEMP. (°F) TEMP. (°F) 35 FT - 5 FT 35 FT - 15 FT
above the floor.
Nov. 2
69.5
66.9
64.2
57.7
5.2
2.6
In contrast to when the fan was off, the indoor
Nov. 3
68.2
66.9
63.3
50.1
4.9
1.4
temperatures across all heights were signifiNov. 4
69.2
67.4
62.5
47.4
6.8
1.8
cantly more uniform, as shown in Figure 5. The
Nov. 5
70.8
69.0
64.1
48.8
6.6
1.8
maximum daily average recorded temperaNov. 6
72.6
70.8
64.0
47.6
8.5
1.7
ture gradient during the study occurred on
Nov. 7
71.9
70.6
66.8
58.9
5.2
1.3
November 16 at 1.3°F (0.7°F) between 5 ft (1.5 m)
Nov.
8
72.7
71.2
67.8
60.3
4.9
1.5
to 35 ft (10.7 m). The average outdoor air temNov. 9
70.7
68.9
65.1
51.2
5.7
1.8
perature was one of the lowest during the week
Overall Average
70.7
69.0
64.7
52.8
6.0
1.7
at 53°F (11.7°C), meaning on cold days when gas
Maximum
Value
72.7
71.2
67.8
60.3
8.5
2.6
heaters were operating frequently, stratification
was greatly reduced when compared
FIGURE 5 Indoor temperature data (°F) collected from November 9 to November 16 at 5 ft, 15 ft and 35 ft
to the "fan off" measurements in the
(1.5 m, 4.6 m and 10.7 m) AFF and plotted with outdoor air temperature for comparison.
facility. Additionally, the lower air
100
35 ft AFF
15 ft AFF
5 ft AFF
Outside Air
temperatures high in the space reduce
90
the difference between the indoor and
80
outdoor air temperatures. Overall tem70
perature gradients for both 5 ft (1.5 m)
to 35 ft (10.7 m) and 15 ft (4.6 m) to 35 ft
60
(10.7 m) remained within 1.3°F (0.7°F)
50
despite the average outdoor air tem40
peratures being colder than when the
30
fan was off.
12a 12p 12a 12p 12a 12p 12a 12p 12a 12p 12a 12p 12a 12p 12a 12p 12a
Nov. 9 |

Nov. 10 | Nov. 11 | Nov. 12 | Nov. 13 | Nov. 14 | Nov. 15 | Nov. 16 |Nov. 17

Time to Destratify and Restratify
Figure 6 compares the duration required for the indoor
air temperatures to reach a near uniform profile across
all space heights. The chart is labeled to indicate the
time when the fan was turned on, the amount of time
28

ASHRAE JOURNAL

ashrae.org

APRI L 2020

mixing occurred and the point at which the temperature gradient was minimized.
The indoor temperature variation in Figure 6 displayed
air stratification before the fan was turned on, the


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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
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ASHRAE Journal - April 2020 - 14
ASHRAE Journal - April 2020 - 15
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ASHRAE Journal - April 2020 - 17
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ASHRAE Journal - April 2020 - 28
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ASHRAE Journal - April 2020 - Cover4
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