fan speed

[mitch1075]

hi, does anyone know what percentage of air movement i will loose when the carbon filter is attached to the fan???

[dontknownuttin]

I run mine at 100% at all times 747 CFM rated

[oldjarhead100]

if its a straight shot you will only loose what the filter blocks but adding turns in your duct work will reduce cfms by alot so keep it as straight as possible

[mitch1075]

thans mate but what approx percentage will i loose from the filter so i can then work out the size of my inlet fan without getting too much or too little negative pressure??

[PuravidaC]

I read somewhere that carbon filters can reduce air flow as much as 20%. Like OJH said, keep bends in air duct to a minimum and make intake larger than exhaust. I used solid metal duct elbows for turns thinking it would cause less resistance, but that is just my overactive imagination!!

[DW2]

Howdy mitch1075,
If the manufacturer does not list the pressure drop thru their filter, the only way to determine it is with a Magnahelic gage (from Dwyer instruments and they are very expensive). The filter to test would be set up with a long (5 to 6 times the diameter of the ductwork) with a fan at one end pushing the air thru the filter. A velocity pressure reading is taken before the filter to test and another downstream of the filter. The difference in the readings is the pressure drop or loss. As stated before, all turns, changes in diameter and the type of duct work will affect the flow and efficiency of the fan. A smooth walled duct is much better than the flexible wire reinforced ducting when it comes to air flow.
Good luck with Your grow.

[mitch1075]

thanks mate

[OzBud]

I don't know how accurate this is but I like it as a bit of a guide.

http://botanical.com/hydro/air/calcu...uirements.html

It says about 20% for a carbon filter.

[Zativa]

Ventilation systems are difficult to design by calculation unless you are a real expert with lots of experience. Manufacturer's ratings like airflow for a particular fan are based on how it performs in free air (with no restriction at either inlet or outlet). How much air it actually moves in your setup depends on a lot of details which are very difficult to estimate or measure. As DW2 points out, the tools to do it 'right' cost a bundle. Go with the bottom line: If what you have is not removing enough heat and/or smell, you need more or larger cooling components.

[PigSquishy]

When I was learning HVAC stuff, ductwork, fans, etc.... one of the most important things I learned was in my researching the carbon filter manufacturers will often tell you what to expect for air flow drops through their filter, some will drop more airflow than others. just as company companies are more trusted than others on the professional level. Not only do you have to worry about the duct work itself leaking and slowing the air down, but the type of ductwork also makes a difference. Ridged ductwork will allow for better air flow vs the flexible duct, the bends will also affect air flow, as will the proper setup... If you have a run of multiple manifolds to dump air at various locations, but leave the end of the pipe wide open you won't get the proper air movement to anything, you have to cap the end so far away from the last vent point; unless of course you are just doing a straight run of ductwork. Air flow is also determined by the type of fan you have, if you have a lot of bends in your pipe you would need a Mixed Flow Fan, all in all you need to look up and understand the different types of fans Centrifugal Fans Inline Flow Fans, Mixed Air Flow Fans... because having the right fan for the job can make a big difference. The proper placement of the fan in the ductwork can also make a huge difference too... The best place to start is always with looking to the manufacture of the fan or carbon filter to see what they say about what it will do and decide for yourself if that is what you need.