Outside air intake filters

[dynamo78]

The place is a facility with a 24/7 electronics equipment running, so I would say its a critical area.
Backgrounder: They have the AHUs and ducts investigated for dust, molds and fungus, the result is negative, no signs of micro organism growths,aside from the accumulated dust in the return plenum filters, to me that's normal after some time of operation, which is good. the laboratory suggested OAI filter (like a pre filter. I told him no, because we already have in the plenum.aside from additional cost of stock filters and manhour for maintenance,yes,I agree that the filter in the plenum will be cleaner, just because dust is being shared with the proposed OA filters. what else can I say.
He compared it to other facilities but configuration are different because they heve preheater coil in the OAI before it riches the air plenum. so th pupose is to protect that coil. Any inout Brothers?

 

[MintJulep]

Sounds like a good application for if it aint broke don't fix it.

 

[Drazen]

I would always put at least rough filter on any pressure ductwork.

 

[dynamo78]

Thanks Guys.
I have to brush up my HVAC knowledge learned many years ago. here are some more issues that I think has merits.

Those filters are an added restrictions, no matter how you enlarged the filter area to minimize the effect of filter PD and then reduced it to the original duct size. It follows that the flow rate will be reduced because of the added filter PD, then to a certain extent air distribution will be affected. I may need a new Testing and balancing, considering that this is a critical area. As an engineer I am not inclined to do it. no substantial benefits and the cost(construction, TAB and maintenance) is too much.
yes Guys! what ya think!! I appreciate the inputs. Thanks

 

[cdxx139]

I dont completely understand the issue, but...

you have a return air plenum and outdoor air. You have filter at return air but not outdoor air? Can you relocate the filter so it filters both return air and outdoor air?

If not, the outdoor air really needs to be filtered, especially since as you say it is a critical area.

What pressure drop is the OA 30% filter adding to the system? If your concerned with PD, then change the filters more often. Also, I think your over concerned about the maintenance. Is changing cheap 30% filters every three months really a hardship?


knowledge is power

 

[dynamo78]

@cdxx, yes OA and return air goes back to the return plenum where there is a common filter for them. similar to what you suggested.
that's where I am coming from, I don't need additional filter since there is already a common filter for them.
Thanks for the input.

 

[Compositepro]

There is an argument to be made for filtering the outside air. How important is it to keep the conditioned space clean? Unless you are using HEPA filters, the capture efficiency of most air conditioning filters is quite low - like 80%. After many passes through such a filter, most of the particles will be removed. The Outside air is likely much dirtier than return air and passes through a filter only once before entering a room. When you want to remove particles from air, you generally do not want to dilute (mix with return air) before concentrating (filtering). So an dedicated outside air filter will keep things cleaner.

 

[dynamo78]

I am slowly drilling down to solve my issue.Thank you Guys!

@Composite pro
After the mixing box filter, there are three more filters banks, next is 90%,Gas absorbent and a 30% filter. all of these filters are clean and also provided with PD alarm indicator incase it operates outside the effective range. I hope I'm justified now that I dont need a new filter.if filter is dirty then its doing its job(LOL)