Hi there from Chiangmai Thailand.....first post.
First before you throw up your hands in horror at the unprofessionality of what i am going to suggest and ask about remember this is a country where earth wires are almost non-existent, I have installed practically the only SAFE-T-CUT wiring in CM. Also bear in mind I did Physics at university and was qualified in the UK as a registered gas boiler repairman, entailing knowledge of gas/elec/instruments//plumbing, so I may not be the complete buffoon I sound (though don't rely on it!).
That said get ready for a laugh.
Here in Chiangmai we get really dirty air for three months a year when all the farmers in the region burn their fields. It's now illegal but will take decades to change. I'm just about to renovate a place, and I thought I could be the first around with a simple air filtration system built in for the bad months.
I thought about pumping air in the above ceiling space to avoid ducting and a few things like that. Then I started looking at the existing aircon units, National CS2400 which are 24500btu.
It seems to me if I build a really nice white casing around a wall unit (I have the cabinet maker) with appropriate grille and interior sealing and well fitting slots for a pair of 30mm thick HEPA filters which I can have a regular supply of, I could use the fan function of the unit to filter the air clean. The cooling could be on or off as required, and I could run simple controls down to a wall unit, perhaps dumping the swing fan function, and perhaps only allowing lower speed setting so the HEPA filter does it's thing properly. The area of 2 cartridges side by side is 25% over the original area of the air intake grille which seems a perfect redundant fit, and the present grille position, flat and on the front, is, unlike the latest units, ideally suited.
One or two questions:
1. The units are 24500 btu, and I am reducing the room sizes to 27m2 and 21m2.....what size BTU do I actually need bearing in mind they are older units and it's hot here?
2. If it is less, say 15000, this would fit well with the lower fan setting. Could I simply replace the old outside units with smaller without doing anything to the indoor units? Would this in fact be a simple way of reducing my BTU?
3. To get a HEPA rating requires standards to be met. Is it true the only difference between say 4in cartridges and the 30mm like I could obtain would be the surface area and thus the interval between replacements?
Hope this will stimulate some minds and thanx in advance, remember this is Thailand where we just try to get practical solutions and don't worry about rules and regs. There are none.