Q. I have been looking at different fan options for my Air Handling Unit application. What are your thoughts on the Fan Wall technology?
The technology is called by different terms; Fan Array, Fan Wall, Fan Matrix, Multi-Fan etc. It is a combination of smaller fans built into a wall section to replace a traditional single large fan. It was initially developed by Hunt Air and now is available in some form through nearly every air handling unit manufacturer.
The marketing of this approach listed the following as the key reasons to employ this fan arrangement:
- Shorter Footprint
- Quiet Operation
- Energy Savings through Optimized Performance
- Lower Maintenance Costs
- Good for Retrofits
Now that we have access to this technology and have used it on several projects we have an opinion.
Shorter Footprint: Not really. In optimal design practice we will use use multiple fans (2 to 4 fans) to help shorten the unit . With a fan array you can save a couple of extra inches but not much more.
Quiet Operation: Yes this can be true, but……. The fan array is usually quieter because the fans can be provided inside individual acoustical enclosures. The same type of enclosures can be used with fewer fans (like a 2 to 4 fan arrangement). The acoustical enclosure decreases sound output and saves having to include a separate acoustical attenuator section.
Energy Savings through Optimized Performance: Do not agree here. Larger fans are more efficient than smaller fans, we all know that. Also, larger motors are more efficient than smaller motors, we know that too. We always opt for the most efficient design which means fewer fans. The reason we add additional fans is for redundancy. If you add more fans you pay a premium in efficiency.
Also less efficient motors add more fan-heat and increase cooling requirements.
Redundancy: Yes, the fan array will provide redundancy. But how much do you need? We typically provide the minimum amount of redundancy to match system requirements. If one fan fails you want to satisfy somewhere between 75 and 100% of the capacity with remaining fans (depending on system diversity). Anything more is really wasteful and not efficient.
Lower Maintenance Costs: In a perfect world we would provide equipment with no moving parts, then nothing would break. If you have 16 fans instead of 2 fans, where’s the maintenance savings? More moving parts (fans and motors) equals more maintenance. That’s simple to understand.
The argument that it’s easier to change out a motor in a fan array doesn’t make sense. It’s still really hard to change out a 250 pound 7.5 hp motor. OSHA will make you use two people and a chain fall (same as with a 650 pound 30 hp motor). Nobody wants to do either.
Good for Retrofits: Yes, We agree with this, but……. We have done over 100 field erected units in the past 20 years and most have been space constrained. We have used the fan array in one application. In that case the extra inches made a difference. In all others we used 4 or fewer fans.
So does the fan array make sense? We don’t think so in most applications.
Additional questions on Air Handling Unit Design; askRick?