converting a portable aircon to permanent

[Matthew J.E. Durkin]

Hi All, A while ago someone was talking about converting their portable air conditoiner by fitting it into the loft, and then fitting vents etc in the roof. Has anyone tried this. I have a homebase portable aircon unit which is a tad noisy in the bedroom. I'd like to put it in the loft, fitting vents for the cooling side to the ceiling, and vents for the exhaust / intake side to my outside wall. I just wondered if anyone has done this, and if so, what was required - new case etc. Could I make a new case out of plywood... Otherwise I'm not sure how I would mod the plastic one to accept the new fitings I'd need! ideas? Matthew

[Andrew Gabriel]

There are a couple of problems I can think of. Many of the portable units do not have separate air intakes for the evaporator and condenser side. Ideally you want to keep them separate so you are recirculating the room air. Otherwise you are exchanging room air at the same speed as you are cooling it, which will severely limit the cooling capability and efficiency of the system.

Secondly, transporting chilled air (or water or refrigerant) presents condensation problems, as the outside of the ducting or pipework will get cold, and can suffer from condensate dripping off. This means it all has to be very thoroughly insulated (to a much higher standard than you would normally insulate water pipes). The slightest gap in the insulation creates a cold spot which forms condensation and drips, just like the pipe was leaking. In the case of ducted air, it is possible to add control such that the air temperature in the ducting does not go below the dew point. This is done by mixing the cooled air with air which has bypassed the evaporator (cooling element) so it's not as cold but has a higher flowrate (so the cooling effect is not reduced). However, you would need computer control of this to get the temperature right, based on ambient temperature and relative humidity monitoring.

[John Rumm]

Not tried it, but how difficult it is will depend a bit on the desigh of the unit.

You really want the air intake to be from the room you are cooling, that way you get a recirculation effect that helps dehumidify the air in the room. This is in many respects the main benefit of air con in the first place - it is not just about making the air cooler.

The limitation with many mono block units is they only have one air intake. Some of the air drawn from it gets cooled, dried and fed back to the room, the rest gets blown outside with the unwanted heat. Alas this is a limit on the effectiveness, since this displaced air must be replaced which means you are sucking warm wet air from the rest of the house into the room.

A few mono blocks do have two air instakes, one for the the receirculating conditioned air, and the other for supplying the vent pipe to dump the heat. If yours is like this and you can arrange to have two internal and two external vents it could improve the effectiveness of the unit into the bargain.

Make some manifolds to fit the case in thin ply, and gaffer tape them together and to the case. Cocoon in inslation and away you go!

[Matthew J.E. Durkin]

I have separate air intakes on mine so should be able to route everything correctly. I might give it a go over winter when I don't need it, being very careful about the insulation requierments. On a related note, how would I make the large vent holes in my outside wall? Obviously I'm not going to be able to drill it. A cold chisel will take me quite some time through the outside wall!! I've seen plenty of suitable fittings, but am not sure how to make the hole!

Thanks, Matthew

[Set Square]

What size does it need to be?

You can hire core drills - along with a Kango hammer - for making clean holes through masonry, but this may be an overkill for one hole.

The alternative is to drill a ring of small (typically 8mm) holes, and then join them up with a cold chisel. In a cavity wall, I usually drill one - maybe 1/2" - hole right through on the centre-line of the desired larger hole. I then mark out a circle of the required diameter, concentric with the pilot hole, on both sides of the wall, and then drill a ring of holes from each side through to the cavity.

Whilst you *can* do all of this with an ordinary hammer drill, an SDS drill makes it a hell of a lot easier.

[John Rumm]

You coud also go for a tile vent, may be simpler to fix it you lack a suitable drill.

Failing that then a core drill like:-

?ts=40121&id=11459or:- you have a fairly powerfull drill (800W or better).

You can hire them as well if required.

Chain drill and chisel is easy with a cavity wall, bit harder with a 9" solid wall.