fan coil units that sometimes a colony of the bacteria will fluorish.

there is no difference between a water cooled "fan coil unit" and a "normal aircon unit" as far as condense water is concerned. both have formation of water at the heat exchanger which has to be drained.

Good point....makes me think that both types of air con units would harbor the bacteria or that the problem is not in the condensate. One point is that in many parts of the world fan coil units are used for both heating and cooling...wonder if this might point to the fan coil to the exclusion of the "normal" air con units...don't know. I googled a bit and found lots of references that mostly more or less said that the exact way that the disease is contracted from mechanical installations in large buildings is not understood. They also mostly indicated that the bacteria likes a warm moist environment which makes cooling units as a source sort of surprising to me.

Chownah

the problem is in the condensate Chownah as the kind of bacteria we are talking about need water/humidity. there is also a bunch of bacteria which like filters and the accumulated dirt but the real dangerous ones need water. to avoid formation or building up bacteria one has to make sure that condensate is drained properly and filters are cleaned regularly.

by the way, an old trick to keep evaporator coils rather clean and assist good drainage is to stick a few small pieces of soap (from left overs) between the fins of the heat exchanger which reduces even the low surface tension of condensated water.

a big problem (especially in hospitals) are central aircon units which might spread bacteria/viruses from one ward to another. since the early 80s one is aware of this danger ("hospitalitis" in connection with airconditioning) and it has been taken care of.

once the bacteria is in the water it can get airbourne

usually i enjoy technical discussions Karl. however i try hard to refrain from discussing the colours and the brush stroke of van Gogh or Rembrandt with a blind person.

I just follow the H & S code for the UK thats all

now i do like the one where the brush strokes go from right to left

by the way, an old trick to keep evaporator coils rather clean and assist good drainage is to stick a few small pieces of soap (from left overs) between the fins of the heat exchanger which reduces even the low surface tension of condensated water.

Do you mean a sliver of soap between each vertical fin toward the top? I could see where that would work, but sure would be tedious work. :-)

With that technique in mind, there should be a retail market for some sort of spray-on solution that would coat the fins and achieve the same effect -- a slow melting, "slippery," antibacterial coating. Or, are modern a/c units' evaporator fins pre-coated with such a substance? If not, sounds like a decent market for an inventor.

Do you mean a sliver of soap between each vertical fin toward the top? I could see where that would work, but sure would be tedious work.

not each fin as that would be of course quite tedious. 4-5 small pieces are enough to improve drainage especially the drip pan.

any additional coating of the fins would reduce the efficiency of the evaporator fins. in corrosive environments (chemical factories, refineries) the fins of the condenser are quite often coated with a polyurethane lacquer.