Intake filter
Intake filter
(OP)
Hi,
I am designing a ventilation system for an electrical room. The room is at the outside wall and a simple ventilation system is enough. The setup (from intake to exhaust) is like this:
1. Intake drainable louvre
2. Insect screen
3. Backdraft damper
4. Filter
5. Plenum
6. Transition and short straight duct run
7. Flex. duct connection
8. Inline centrifugal fan (BSQ)
9. Flex. duct connection
10. Short duct run
11. Louvered supply grille
12. Room
13. Motorized damper
14. Insect screen
15. Exhaust louvre
My question is:
a. Is the motorized damper needed? Or do I just need two backdraft dampers?
b. For the filter, I am going to need 30% filters, but will I need a pressure differential gauge to indicate the filter change? If so, what kind of pressure differential should it be?
c. For a simple setup like this, do I need a filter bank (zig-zag type), or a single pleated filter just perpendicular to the flow?
d. Is there any other problem you can see in this setup?
Thanks.
I am designing a ventilation system for an electrical room. The room is at the outside wall and a simple ventilation system is enough. The setup (from intake to exhaust) is like this:
1. Intake drainable louvre
2. Insect screen
3. Backdraft damper
4. Filter
5. Plenum
6. Transition and short straight duct run
7. Flex. duct connection
8. Inline centrifugal fan (BSQ)
9. Flex. duct connection
10. Short duct run
11. Louvered supply grille
12. Room
13. Motorized damper
14. Insect screen
15. Exhaust louvre
My question is:
a. Is the motorized damper needed? Or do I just need two backdraft dampers?
b. For the filter, I am going to need 30% filters, but will I need a pressure differential gauge to indicate the filter change? If so, what kind of pressure differential should it be?
c. For a simple setup like this, do I need a filter bank (zig-zag type), or a single pleated filter just perpendicular to the flow?
d. Is there any other problem you can see in this setup?
Thanks.





RE: Intake filter
Potential issue: fan is sucking in OA directly, which is usually an uneven intake profile and can draw in snow/rain etc.
Suggest instead a very similar setup to what you have but use a large intake opening/plenum with motorized dampers and your 30% filters, set back from the intake as much as space allows. This should be low velocity <500 fpm and will help to promote a longer filter life. Turn the fan around and blow air out a smaller louver (make room ventilation draw through vs. push through).
A backdraft damper alone on the fan outlet, before the louver should be fine in lieu of a motorized damper.
Don't bother with filter DP gauges etc. unless it's a super critical application and your client has extra budget (not too common today).
-CB
RE: Intake filter
Motorized dampers seem like overkill to me. Yeah a back-draft damper might rattle when the wind blows - is that an issue in this application?
Filter arrangement is simply a matter of how long do you want to go between filter changes. Since the filters will probably never get changed anyway, may as well keep it simple.
RE: Intake filter
That leads me to two questions:
1. if the filter do get dirty and blocked, will the fan just stall and overheat? Isn't that going to be a problem?
2. Instead of using centrifugal fan, can I use wall mount propeller fan? The flow is about 400cfm, and obviously with the filter and louver, the initial SP is going to be around .3 and goes up to .55+ when the filter is clogged. I can't find a propeller fan that can take that kind of SP for such low flow. Do you have any suggestion? We wanted to use propeller fan to save the ductworks and labors.
RE: Intake filter
No, it just won't move any air.
RE: Intake filter
This is usually a setup for a 12,000 cfm type elec. space.
Is there a building system anywhere nearby where you could tap a 400 cfm VAV box? Then forget the louvers, just undercut the doors...
RE: Intake filter
Do you think propeller fan will work here??
RE: Intake filter
Did you consider a mini split DX system?
RE: Intake filter
Use an exhaust fan near the ceiling where the hot air is. A thermostat will save some energy.
RE: Intake filter
RE: Intake filter
RE: Intake filter
RE: Intake filter
I do like using a T'Stat to avoid getting the room too cold.
Monitoring dP on the filters is something that is dependent on the end user. If there is a maintenance staff to use it, fine. If not, doing so only makes yourself feel better for doing the right thing.
RE: Intake filter
Actually, do you really need filter for electrical room or a MCC room? Do you usually put in filter or no?
RE: Intake filter
What about when the outside air temp is higher? Even in the great white north our outdoor gets around 90F in the summer, incidentally when transformer loads are typically the highest.
Typically, I get the maximum temp rating on the equipment and design the fan for a deltaT from summer design. If that is too much, a small mini-split is usually the way to go.