pretty standard for central systems here honestly. the fresh air intake on commercial hvac in bangkok usually just has a coarse mesh filter, catches leaves and bugs but not pm2.5. your building's chiller setup prob has a damper that pulls in like 10-15% outside air for ventilation and that's your culprit.

few things you can try. check if your room has a separate fresh air grille, sometimes they have a manual damper lever you can close. also look at the return air filter in your ceiling or wall unit, some newer buildings in thonglor or asoke have started upgrading to merv 13 filters but most still use the cheap fiberglass ones. if yours is the washable type, replacing it with a proper pleated filter helps a bit.

the real move though is sealing the room. get a door sweep from homepro for like 150 baht and cover any window gaps. then run your purifier on turbo for 15 mins with the ac off, then turn the ac back on and keep the purifier running. you'll land somewhere around 15-20 which isnt perfect but way better than 37 outside.

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The short answer is that most central aircon systems in Bangkok buildings are not designed to filter PM2.5. The standard filters they use catch dust and larger particles but let the fine stuff through. Your building's chiller system is likely just recirculating indoor air with a small percentage of fresh air intake, and that fresh air is unfiltered for PM2.5.

Your experience is pretty typical. The aircon unit's fan is constantly moving air around the room, which stirs up whatever particles are already in the space and pulls in that unfiltered fresh air. That is why your levels jump when you turn it on. If you have a window unit or a split type, the story is the same they do not have HEPA filtration built in.

What works for a lot of people here is to seal the room as tight as you can, run the air purifier on high for 20 minutes before turning the aircon back on, and then keep the purifier running alongside it. Also check the seal around your door. In a condo building, a surprising amount of hallway air can leak in under the door, especially when the hallway itself is not filtered. A cheap draft stopper can make a noticeable difference.

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Honestly, that sounds normal for a building with central AC here. Most systems just have those basic mesh filters that are useless for PM2.5, and that fresh air intake is bringing in whatever is outside unfiltered. Your air purifier is doing the right thing, but the AC fan keeps cycling air through, so it's a losing battle.

What I'd do is check if there's a damper on your room's fresh air vent you can close, sometimes it's just a little lever on the grille itself. Also make sure your door is sealed tight, a lot of

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yeah Krua Dok Mai Kao is solid but if you're up for a detour, try Som Tum Nua near Siam Square. their som tam pu pla ra is insane if you like the fermented fish sauce kick. way more pungent than the On Nut spot, just less grilled chicken options

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