ASHRAE Journal - April 2020 - 27

TECHNICAL FEATURE

the eaves and is located in Frankfort, Ky. A 20 ft (6 m)
diameter HVLS fan was installed in the center of the
facility with a blade height of approximately 27 ft (8 m)
from the floor. The primary goal of this study is to measure and evaluate the energy and cost impacts associated
with using an HVLS fan for air destratification during
the cold weather season.

Temperature Loggers
Air temperatures were monitored using temperature
and humidity loggers, shown in Figure 1. Three loggers
were placed along the back wall of the facility at 5 ft,
15 ft and 35 ft (5 m, 4.6 m and 10.7 m) above the floor.
An additional logger was placed in a sheltered location
outside the facility to collect outdoor air temperature.
Loggers were set to collect a data point once every 5
minutes.

FIGURE 1 (ABOVE) Temperature and humidity

loggers used to record air temperature in
the facility. Figure 2 (RIGHT ) Workers on a
lift near the forced air gas heaters inside the
hangar.

FIGURE 3 Workers installing an HVLS fan in the center of the hangar. Forced air
gas heaters are located in all four corners of the facility.

Gas Heaters
Forced air natural gas unit heaters are used to heat
the facility. A single heater unit was located at each of
the four corners of the hangar near the ceiling. All unit
heaters are rated at 250,000 Btu/h (73 kW). A dedicated
digital meter was installed on the natural gas supply
line to monitor gas consumption for the duration of
the study. The space temperature setpoint was 65°F
(18°C). The forced air gas heaters used in the hangar
are shown in Figure 2.

Fan Operation
The HVLS fan was operated on an alternating weekly
schedule. The alternating fan operation allowed data
collection to be consistent and to allow stratification when the fan was off. Data collection began on
November 2.
In the week when the fan was operational, the speed
was maintained at 25% of the maximum operating
speed to provide continuous air mixing. At 25% speed,
the fan drew approximately 100 W of power. When the
fan was turned on, it remained operational for 24 total
hours spanning a 16-day period. With a utility cost of
$0.0969/kWh, the electricity cost equates to $1.65 per
week. The fan operated in the downward direction only,
generating a column of warmer air moving directly
downward to the occupant and thermostat level. The fan
speed was selected so the air movement produced by the
fan did not interfere with worker operations or produce

a noticeable breeze (approximately 30 fpm (0.15 m/s)
per ANSI/ASHRAE Standard 55-2017) at the occupant
level. Figure 3 displays the fan location in the center of
the facility.

Results & Discussion
Scenario One - Fan "Off"
Figure 4 shows the comparison between indoor air temperatures at various heights, along with outdoor temperature, for the week of November 2 with the fan off.
Temperature varies significantly with space height. The
maximum recorded indoor temperature was 81°F (27°C)
at 35 ft (10.7 m) on November 6, with an average outdoor
air temperature of 52°F (11°C) recorded on site.
According to Table 1, over the recorded week the fan was
off, the highest temperatures were consistently recorded
at the 35 ft (10.7 m) level, while the lowest temperatures
remained at the 5 ft (1.5 m) level. The maximum daily
average temperature gradient of 8.5°F (4.7°C) between
the 35 ft (10.7 m) and 5 ft (1.5 m) level occurred on
November 6, while the outdoor air temperature was

ASHRAE Journal - April 2020

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