Is it acceptable to filter mixed return and outdoor air instead of outdoor air only? In our case, huge industrial ventilation systems provide fresh air to a yarn factory. The ventilation systems have very large outdoor air inlets (240 x 240 cm) directly connected to the mixing chamber where return air is mixed with the outdoor air. Then, the mixture is sent to the humidification compartment and finally delivered to the air distribution ducts. The only appropriate place for the F7 filters are the air distribution ducts. Would it be acceptable? Any thoughts on that?
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Nagaraj Sankar
1 thumbs up
June 6, 2024 - 11:50 am
Hi Zenep,
Yes, it is acceptable when it has high static pressure. Only then does the fresh air pass through the filter medium located in the duct.
Andrey Kuznetsov
ESG consultant, LEED AP BD+CSelf Employed
18 thumbs up
June 7, 2024 - 12:38 am
Hello!
Epigraph: brevity - the sister of talent, but not of mine talent.
I suppose that you are talking about option 1 for mechanically ventilated spaces. In that case the only issue that I see - is from where the return air comes from.
Since it's a yarn factory, I suppose that supplied air in that amount is going to the main area where main working process occures and main place of staff circulation / working places.
I believe that such area is classified as "General manufacturing (excludes heavy industrial and processes using chemicals)" per Table 6-1 of ASHRAE 62.1-2010. Air in such areas is class 3 per the same table.
Since per p. 5.16.3.3.1 the recirculation of Class 3 air within the origin space is permitted, it's ok if:
Otherwise I don't see limitations for mix air filtering. Just be sure that all requirements for the filtering media from maintenance point of view are also met.
I hope it helps.
Zeynep Cakir
LEED AP BD+C, WELL AP, Sustainable Building ConsultantECOBUILD
13 thumbs up
June 7, 2024 - 3:41 am
Dear Nagaraj and Andrey,
Thanks for your comments.
Nagaraj, if I understood correctly, in our system the supply air fan is capable of overcoming the pressure to pass the air mix through the filter. So, I think that complies with your point.
Andrey, the return air is coming completely from the production area and supply air is also delivered completely to the same production area. Before mixing with the outdoor air, the return air is passed through a rotary drum filter to eliminate dust and fabric. It complies with Class 3 air recirculation conditions you mentioned above.
Thank you both for your help
Andrey Kuznetsov
ESG consultant, LEED AP BD+CSelf Employed
18 thumbs up
June 7, 2024 - 5:52 am
Looks fine to me.