What is the standard for laboratory fume hood exhaust?

The primary standard relating to laboratory fume hood exhaust is ANSI Z9.5 (1992). The entire standard can be ordered from The American Industrial Hygiene Association. Should you wish to familiarize yourself with the exhaust parameters of the standard, you may order an extract from Strobic Air.

How high should a stack be to avoid re-entrainment?

Stack height is determined by the height, width and length of the building, the wind currents around the building created by surrounding buildings or terrain, and the chemical make-up of the fume hood exhaust. Consult Chapter 15, ASHRAE Fundamentals Handbook for detailed formula. However, we strongly recommend you consult a professional wind consultant who is more familiar with the process.

When should you manifold laboratory exhausts?

Manifolding fume hood exhausts is recommended for all types of hoods with the exception of radioisotopes and perchloric exhaust. By combining the exhaust hoods, sufficient mass can be achieved with the proper outlet velocity from the stack, usually 3000 feet per minute or more, to create sufficient momentum to break through the recirculation zone on the roof.

What maintenance is required for Tri-Stack®?

The maintenance of your Tri-Stack® system is negligible. Motors up through a 256T frame have sealed for life bearings. Motors larger than 256T require minimal lubrication every 18 months. That's it! No other maintenance is required.

How easy is it to install Tri-Stack®?

Tri-Stack® fume hood systems install in minutes. All units are pre-assembled at the factory and line-up tags are clearly attached to mating flanges. Stainless hardware and gasketing are also placed on each component. A four-fan system on a common plenum can be completely installed in less than two hours.

How do you isolate Tri-Stack® against vibration?

Unlike most other exhaust fans the Tri-Stack®> mixed flow exhaust fan utilizes a true non-stall mixed flow impeller that is balanced to less the 0.5 mil peak to peak. Therefore, we strongly recommend that spring vibration isolation mountings are NOT used. This also eliminates the need for flexible duct connections, both of which are point failures and would require frequent maintenance. The Tri-Stack® fan can be mounted directly on a roof curb, concrete slab or steel structure, whatever is the preferred mounting for your particular application. Also, the low profile of a Tri-Stack® eliminates the need for guy wires that are otherwise necessary on taller stacks.

Can you use Variable Frequency Drives with Tri-Stack®?

Due to the non-stall feature of the mixed-flow wheel, Variable Frequency Drives are very effective when used with the Tri-Stack® fume hood exhaust system. Tri- Stacks are also balanced to below 0.5 mils peak to peak, thus minimizing vibration through critical Hertz levels during down-turn. However, you should consult your wind consultant to determine the minimum speed to safely operate your system and avoid re-entrainment back into your laboratory.

What is the initial cost of a Tri-Stack® system?

The Tri-Stack® is a system and not just a fan. Therefore, in comparing the cost of this system to the conventional centrifugal vent set, be sure to include the cost of the centrifugal elbow, flex connectors, vibration isolators inertia base, stack and reducing nozzle cone, along with the associated installation labor. You will find the Tri-Stack® system will compare favorably, as well as saving you energy dollars annually due to the increased efficiency of the system.

For additional information, please click on the links below:
•    10 Ways Tri-Stack® Systems Reduce Costs
•    Tri-Stack® vs. Centrifugal Fans

What is the Return on Investment of Tri-Stack®?

The Tri-Stack® fume hood exhaust system reduces the static pressure in your laboratory system by approximately two inches water gauge, when compared with the traditional centrifugal fan and stack combination. That translates to approximately $0.44 per cfm. Depending on the sophistication of your system, the typical Tri-Stack® can pay for itself in less than 2 1/2 years.

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