TABLE 1 - Stratification results while fan was “off” showing daily average temperatures (°F) from 5 ft, 15 ft, 35 ft (1.5 m, 4.6 m, 10.7 m) away from floor with outside air conditions (0A) for comparison. Temperature differentials (Δ T ) from 35 ft (10.7 m) and 15 ft (4.6 m), and 35 ft (10.7 m) and 5 ft (1.5 m) are displayed. FAN OFF 35 FT 15 FT 5 FT 0A ΔT(°F) DAILY AVERAGES TEMP. (°F) TEMP. (°F) TEMP. (°F) TEMP. (°F) 35-5 FT 35-15 FT
TABLE 2 - Stratification results while fan was operational showing daily average temperatures 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 for comparison. Temperature differentials from 35 ft (10.7 m) and 15 ft (4.6 m), and 35 ft (10.7 m) and 5 ft (1.5 m) are shown. FAN ON 35 FT 15 FT 5 FT 0A ΔT(°F) DAILY AVERAGES TEMP. (°F) TEMP. (°F) TEMP. (°F) TEMP. (°F) 35-5 FT 35-15 FT
Nov. 2
Nov. 10
69.5
66.9
64.2
57.7
5.2 2.6
67.8
67.4
67.2
59.1
0.6 0.4
Nov. 3
Nov. 11
68.2
66.9
63.3
50.1
4.9
1.4
66.4
66.2
66.0
54.7
0.4
0.2
Nov. 4
Nov. 12
69.2
67.4
62.5
47.4
6.8
1.8
65.9
65.7
65.1
50.0 0.8 0.2
Nov. 5
Nov. 13
70.8
69.0
64.1
48.8
6.6
1.8
66.6
66.5
65.5
50.9
1.1
0.1
Nov. 6
Nov. 14
72.6
70.8
64.0
47.6 8.5
1.7
66.8
66.9
66.5
52.8
0.3
-0.1
Nov. 7
Nov. 15
71.9
70.6
66.8
58.9 5.2
1.3
67.7
67.8
67.4
55.3
0.3
-0.1
Nov. 8
Nov. 16
72.7
71.2
67.8
60.3
4.9
1.5
67.7
67.4
66.4
52.6
1.3
0.3
Nov. 9
70.7
68.9
65.1
51.2
5.7
1.8
Overall Average
67.0
66.8
66.3
53.6
0.7
0.2
Overall Average
70.7
69.0
64.7
52.8
6.0
1.7
Maxiumum Value
67.8
67.8
67.4
59.1
1.3
0.4
Maxiumum Value
72.7
71.2
67.8
60.3
8.5 2.6
The figures below compare the time required for the indoor air temperature to reach a near uniform profile across space heights and the time it took for the air to restratify after the fan was turned off. When the fan was turned on, it took only 10 minutes of mixing for the temperature difference to fall within 1 degree F. When the fan was turned off, the air began to restratify in the facility to a temperature difference of 3 degrees F between the 5 foot and 35 foot temperature loggers. The amount of time observed for the air to restratify was 10 minutes. The rapid return to stratified air indicates fans need to be operated continuously during the cold weather season.
The addition of the HVLS fan reduced stratification and achieved near uniform temperature conditions within 10 minutes of operation. Once the fan turned off, stratification of the air started to reappear in as little as 15 minutes. This indicates that continuous or nearly continuous operation of the fan may be required to minimize heat loss through the envelope. The HVLS fan also reduced the normalized gas use by 29%, which consequently translated to significantly lower winter energy usage. Using HVLS fans in hangars is an energy-efficient method of creating a more uniform thermal environment due to the fan’s low power requirements and high potential for utility savings in the cold weather season. CONCLUSIONS: Gas heater use was also monitored during the same weeks. The HVLS fan created indoor air temperature uniformity in the facility, reduced heat loss from the building, and reduced heating system operating hours, consuming less natural gas. When the fan was operational, a 29% decrease in the gas usage was experienced. For Frankfort, Ky., gas savings during the heating season would be approximately $4,150 and the energy cost for operating the fan would be $50. The simple payback for the project would be approximately 2 years. While heating fuel savings and energy cost of operating fans will vary by building and locale, any building with tall heated spaces in a climate with heating demand should stand to benefit from the utilization of HVLS fans for destratification.
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