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De-Stratification Fans |
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rev. 2008-12-07
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De-Stratification Fans |
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rev. 2008-12-07
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Existing Conditions
The building has a large room where the height is greater than five meters, and the ceiling is immediately below the roof. Roof insulation is minimal, and air ex-filtration is high.
Retrofit Conditions
A ceiling mounted fan system should be mounted to reduce stratification in the room. The heat collecting in the ceiling will be re-distributed to the floor level.
Further Benefits
The fans are variable speed, and can change speed based on the difference in temperatures at the two heights. This will reduce fan electricity use compared to full-speed operation.
Application Details
Potential Applications include: Distribution centers, warehouses, manufacturing facilities, exhibition halls, sports halls, green houses, etc.
There are two approaches to this concept:
1. Install small diameter fans that produce high velocities, but a lower volume of air. These fans are ideal for smaller areas with many obstructions.
2. Install Large diameter fans that produce low velocities, but a higher volume of air. These fans are ideal for larger, open areas, and are suited for summer cooling by inducing a subtle draft across the skin.
The end result may be a combination of the two types of fans to fully implement a de-stratification strategy.
Issues and Concerns
There may be some obstructions hanging from the ceiling, such as lights, service lines, venting, high bay storage racks, sprinkler heads, unit heaters, which limits the available locations for installation.
Access for service maintenance may be problematic if the fans are installed in awkward locations or highly elevated areas.
References
www.savenergycanada.ca - Focused column small diameter de-stratification fans
www.enviranorth.com - 8-24 food diameter down-draught fans.
Analysis
The temperature profile in a room increases approximately 1ºC per meter. Areas with a high internal load, such as manufacturing plants, increase the profile.
*BTUh = (Area x DeltaT) / R
BTU's = The maximum amount of heat loss through the ceiling
Area = Square footage of the ceiling
Delta T = Room Temperature - Lowest Design Temperature (xxxºF-0ºF)
R = Insulation (R Value)
Example 1:
In a 30 meter high room, the temperature at the ceiling is 100ºF, the R value is expected to be R-8, and the room is 1000 square feet. What is the impact of a de-stratification fan?
BTUh = 1000 x 100 / 8
= 12500 BTUh
A de-stratification fan will essentially equalize the temperatures in the room
BTUh = 1000 x 70 / 8
= 8750 BTUh
12500 - 8750 = 3750 BTUh savings
OR
= 1000 x 1 / 8
= 125 BTUh per heating degree day.
With Approximately 4000 HDD/year, that equals 500 MBTU/year
ENBRIDGE Example:
A $40,000 investment in 5 large de-stratification fans serving approximately 40 000 square feet of a manufacturing facility proved to have net savings of over $6,000 annually. Enbridge provided $1,000 of incentive money for the project.