Tri-Stack Systems Provide Significant Performance, Reliability, and Cost
Advantages Over Conventional Centrifugal Exhaust Fans
Tri-Stack™ vs. Centrifugal Cost Comparison
Strobic Air Tri-Stack TM
- 7 year motor warranty, an industry first
- No need for unsightly guy wires
- Long bearing life L 10 up to 364,000 hours 6
- Belts and pulleys not needed
- Maximum Entrainment provided
- Flexible connection and spring isolation not needed
- Stack and nozzle loss already built into fan curves
- Lower stack height provides lower roof profile and center of gravity
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Typical Centrifugal
- Standard motor warranty offered
- Additional stack height requires use of guy wires
- With a bearing life L 10 = 40,000 hrs (pillowblock), and L 10 = 40,000 hrs (motor bearings), the belt-driven centrifugal has a 5x greater chance of motor or bearing failure, requiring change-out
- Losses through belts and pulleys require more energy
- Minimal or no entrainment provided
- Flexible connection required on the inlet and outlet of fan are prone to failure
- In order to match the outlet velocity of the tri-stack, a nozzle is needed, which requires an additional 1.12” of static pressure and more energy
- Larger footprint requiring more valuable space on the roof
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Tri-Stack Model |
Centrifugal Fan |
| |
TS4L400A12 |
81" SWI-BC |
| Housing Diameter |
54” |
81” |
| Flow Rate (CFM) |
33253 |
33253 |
| Inlet SP (In. W.G.) |
3.00 |
3.00 |
| Outlet Velocity (FPM) |
6239 |
6239 |
| Inlet Duct Size |
57"SQ |
42" DIA |
| Inlet Velocity (FPM) |
1474 |
3456 |
| Changes in Static Pressure 1 |
| 90 Deg. Inlet Elbow |
NOT REQ'D 2 |
0.60 |
in. |
| Inlet Flex Connection |
NOT REQ'D 2 |
0.20 |
in. |
| System Effect |
NOT REQ'D 2 |
0.20 |
in. |
| 45 Deg. Outlet |
NOT REQ'D 2 |
0.21 |
in. |
| Stack Loss |
NOT REQ'D 3 |
0.03 |
in. |
| Nozzle Loss |
NOT REQ'D 3 |
1.12 |
in. |
| New Static Pressure |
3.00 |
5.36 |
in. |
| Required Horsepower |
| Fan HP |
33.89 |
46.75 5 |
| Belt % Loss |
NO LOSS 4 |
5% |
| Belt Loss |
NO LOSS 4 |
2.34 |
| Motor HP |
33.89 |
49.09 |
| Motor Required |
40HP |
50HP |
| Cost Analysis |
| Annual Energy Cost @ $0.12/KWH 7 |
$33,213.33 |
$48,862.58 |
| Maintenance Required/ Month (Belt Maint. Per ANSI Z9.5) |
0 |
4 |
| Annual Maint. Cost @ $65/MH |
$0.00 |
$3,120.00 |
| Annual Operating Cost/Fan |
$33,213.33 |
$51,982.58 |
| Annual Savings Per Fan |
$18,769.25 |
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| Table 1: Centrifugal Pressure Loss Details |
| Loss Type |
Pressure Loss (in. w.g.) |
Source |
Parameters |
| 90º Elbow |
0.60” |
Fig. 6-9, SMACNA I |
1Ø duct length, 1.0 R/D ratio (“S” Curve) |
| Inlet Flex Connection |
0.20” |
Table 6-3, SMACNA I |
95% unobstructed area (“V” Curve) |
| Outlet Duct- Effective Length |
0.20” |
Fig. 6-3 & Table 6-2, SMACNA I |
50% Effective Duct Length, 1.0 Blast Area/ Outlet Area ratio (“V” Curve) |
| 45º Bend (Outlet) |
0.21” |
Table ED5-6, ASHRAE Fundamentals II |
1.0 Area ratio, C b = 0.64 |
| Straight Stack Friction Loss |
0.03” |
Figure 14-1, SMACNA I |
3564 fpm outlet velocity, 40ӯ Duct, 10' duct length |
| Nozzle Loss |
1.12” |
Leading Centrifugal Manufacturer's Published Loss Data |
Venturi Cap, 9.33 ft 2 outlet area, 5.33 ft 2 nozzle area, 6239 fpm outlet velocity |
Notes
- See table 1 for loss details.
- Not required due to Tri-Stack™ configuration.
- Stack and nozzle losses are already built into the Tri-Stack™ curve, each fan has been tested as a system.
- Tri-Stack™ fans are direct drive, with the motor outside the air stream. So, belts are not needed!
- Centrifugal fan horsepower taken from a leading centrifugal fan manufacturer's catalog.
- Motor bearing life based on published bearing life from motor manufacturer.
- Annual energy cost evaluated using the formula: Cost = (HP X .746)(1/Eff)(1/PF)(8760 HRS/YR)(KWH Rate)
I. “HVAC Systems Duct Design, 3 rd ed.” SMACNA, 1990.
II.
“Fundamentals- 1997 ASHRAE Handbook I-P Edition.” ASHRAE, 1997. Strobic Air has been refining
the technology of mixed flow fans
for more than two decades, and has pioneered many aerodynamic concepts associated with
mixed flow fan technology. Mixed flow fans–originally developed for low pressure, high flow applications–provide optimum performance in virtually all configurations of low pressure and high flow, and high pressure and low flow. They offer substantial advantages over centrifugal-type fans such as higher efficiency performance for lower horsepower requirements for comparable pressures and flows, as well as energy efficient operation. The constant acceleration ratio of mixed flow fan blades permits both the leading and trailing edges to perform equal work, maximizing efficiency and providing a stable performance curve without stall or unstall sections.
Because Tri-Stack
fume exhaust systems require little or no maintenance, health and safety considerations of maintenance people (on the roof) are eliminated, while freeing them for more productive work. In addition, the need for rooftop penthouses to protect maintenance workers is also eliminated, reducing costs and weight on the roof structure.
On a direct operating cost basis, use of Tri-Stack mixed flow fan technology reduces energy consumption as indicated in the chart. When combined with accessory heat recovery systems, Tri-Stack systems dramatically lower overall energy costs for building climate control. |
