3 ms·

What this and the box fans seem to miss is that prop fans have very little ability to generate static pressure. You will move more volume over the static pressu

What this and the box fans seem to miss is that prop fans have very little ability to generate static pressure. You will move more volume over the static pressure loss of the filters if you use a centrifugal type of fan. A little looking on Amazon shows those at about 3x the price of the prop boosters for the same rated cfm. If you add even a little bit of duct to extend approximately 3 duct diameters on the outlet it will make the fan a lot more efficient by allowing the airflow to stabilize and lower buffeting noise at the outlet. There athere are some of the centrifugal fans that include a noise suppressor for more money that's basically a short duct that's double walled and perforated on the inside.

londons_explore 3y ago
Having tried both, prop fans seem to beat centrifugal fans for the pressure drop across typical filters, and deliver more air per watt through a filter. I suspect the pleated nature of the filter means that the static pressure drop isn't all that much. Haven't got a manometer to measure it though.
- rainbowzootsuit 3y ago
  Thanks for the feedback. Thinking about it some more, a general purpose 1" HVAC filters are rated at about .12 in. water column at 300 feet per minute. If you're running them a lot slower by having 4x-6x area, then I could see that your tests would bear out. I often reference this manufacturer when designing a duct system and selecting filter sizes. This is for their MERV10 filter. MERV8 is lower initial pressure. They have a velocity vs pressure chart on page 4. At 50 FPM it's down to about 0.03 in. w.c. https://www.glasfloss.com/product/zl-hv/ https://www.glasfloss.com/product/zl-hv/ I think a centrifugal could still be an advantage for noise while having a reasonable dimension, but your feedback is sincerely appreciated.
  - londons_explore 3y ago
    I kinda wish all filtering was done with a greatly increased surface area. A 10x increase in surface area would mean far far less powerful fans are needed, and the filters could last a decade before needing to be replaced.
    - rainbowzootsuit 3y ago
      In a ducted system the ductwork and air terminals reach an economic happy medium that does not really balance with trying to make the filter pressure loss the driving factor.

londons_explore 3y ago

Having tried both, prop fans seem to beat centrifugal fans for the pressure drop across typical filters, and deliver more air per watt through a filter. I suspect the pleated nature of the filter means that the static pressure drop isn't all that much. Haven't got a manometer to measure it though.

rainbowzootsuit 3y ago
Thanks for the feedback. Thinking about it some more, a general purpose 1" HVAC filters are rated at about .12 in. water column at 300 feet per minute. If you're running them a lot slower by having 4x-6x area, then I could see that your tests would bear out. I often reference this manufacturer when designing a duct system and selecting filter sizes. This is for their MERV10 filter. MERV8 is lower initial pressure. They have a velocity vs pressure chart on page 4. At 50 FPM it's down to about 0.03 in. w.c. https://www.glasfloss.com/product/zl-hv/ https://www.glasfloss.com/product/zl-hv/ I think a centrifugal could still be an advantage for noise while having a reasonable dimension, but your feedback is sincerely appreciated.
- londons_explore 3y ago
  I kinda wish all filtering was done with a greatly increased surface area. A 10x increase in surface area would mean far far less powerful fans are needed, and the filters could last a decade before needing to be replaced.
  - rainbowzootsuit 3y ago
    In a ducted system the ductwork and air terminals reach an economic happy medium that does not really balance with trying to make the filter pressure loss the driving factor.