BTW, do be advised that such a contraption would be very much louder than the Samsung AX40 that I have been recommending (it's really very quiet in the air purifier world). Centrifugal fans do have an advantage in the air pressure exerted (pascals) and noise and also "shaping" the airflow.
Smartfilters did say that it's quite loud, they did some testing on their site.
I can confirm for you right here that you won't be able to sleep with that much white noise.
The NUS - AiRazor "system" I think does not have a pre-filter. Correct me if I am wrong.
That said, it might not be using HEPA. HEPA is MERV16-MERV18 grade.
The 3M Filterete Elite Allergen filters I posted and used before in my Sharp KC-840 is MERV-13. They do let through quite a bit more air, at the expense of a wee bit drop in filtration power.
The taobao ones have prefilter, either comes as a set with the HEPA or you get it separate for like $1 or so.
I posted a few times liao. Here it is :
Various diameters, 25mm thickness. But more expensive than others.
Ô²ÐÎDIY·çÉÈÓøßЧHEPA¹ýÂËÍø£ü´øÄÚ¿×HEPAÔ²ÐιýÂËÍø£ü³§¼ÒÖ±¹©-ÌÔ±¦Íø
29cm, 20mm thickness. Cheaper.
Ô²ÐÎHEPA¹ýÂËÍø DIYÖÆ×÷HEPA¿ÕÆø¾»»¯Æ÷PM2.5¹ýÂËÍø HEPA¹ýÂËÍø-ÌÔ±¦Íø
Just go to ABC shop (not sure if Japan home got or not) and buy for S$2.
You want small medium big size, all got. Actually my mother in law bought like 3 of them, not sure where I chucked them coz this netting disrupted the airflow (mainly the intake side) and made quite a lot of noise.
