How to Model a Portable Air Purifier?

[김수]

Hello CONTAM team,

I want to model a portable air purifier (no ducts in reality) and I’m unsure which modeling pattern is best in CONTAM.
I saw Lisa Ng’s note that we can either (a) use a ducted fan with a filter (both inlet & outlet in the same zone) or (b) an AHS with 100% recirculation and the filter in the recirculation path. Could you advise which approach you recommend for my case and how to set it up step-by-step?

My scenario

• Building: [ multi-zone building; food court in B1]

• Target zone volume: [3000m³]

• Questions

1. Approach choice. For a multi-zone model (air cleaner recirculates air only within one zone), is the AHS with 100% recirculation preferable to the ducted-fan + filter method? Any pros/cons (mass balance, solver robustness, reporting)?

2. Exact steps, ducted-fan method.

   • Do I place a Return Point and a Supply Point both in the same zone and connect them with a Fan and a Filter?

   • Should the fan be set to fixed design flow = rated fan flow or to match CADR?

   • Where exactly do I attach the filter so that species removal uses the filter efficiency table?

3. Exact steps, AHS method.

   • Create an AHS with 100% recirculation, add Fan + Filter in the recirc branch, and place both Return and Supply points in the same zone—correct?

   • How should I set the AHS flow so that room-level “clean air” equals CADR and not just raw fan flow?

4. CADR vs. filter efficiency. If the vendor gives CADR, do I:

   • (a) keep rated fan flow as the AHS/Fan flow and tune the filter efficiency curve so that “fan flow × average efficiency ≈ CADR”, or

   • (b) directly set the flow to CADR and use the manufacturer’s HEPA efficiency as is?

   • Any recommended practice to avoid double counting of deposition/settling when matching CADR?

5. Particles setup. For PM2.5:

   • Should I define size bins and give the filter penetration/efficiency vs. diameter?

   • Any default deposition coefficients you recommend for indoor surfaces so that results don’t over-estimate removal by the purifier?

6. Multiple devices. If I have [n] identical purifiers in the same zone, is it valid to duplicate the unit n times, or should I aggregate to one larger AHS? Any stability tips?

7. Validation. What output(s) should I check (e.g., zone mass balance, AHS flows, filter capture rate) to confirm the model is behaving like the device’s datasheet?

8. Example file. If possible, could you share a tiny sample (.prj) showing either method with a PM2.5 species and a HEPA filter?

I can attach the datasheet (efficiency vs. particle size and ΔP vs. flow), floor plan, and my current .prj if that helps.

Many thanks for any guidance!

Best regards,
Suhan Kim

[William Dols]

Hello Suhan,

Please refer to the FaTIMA tool that Lisa referenced in her note.

https://www.nist.gov/services-resources/software/fatima

You can obtain a CONTAM project via the FaTIMA tool that implements such an air cleaner via a simple AHS (there is no major difference between using a Simple AHS or Duct).

Further, the FaTIMA documentation addresses CADR and deposition and provides references that address many of your questions.

As for "Particles setup", that is at your discretion and depends on the goals of your analysis.

I would suggest that you start simple, as done with the FaTIMA tool, and work your way from there.

Happy Modeling,

- Stuart