Hi
air conditioning has two parts to it, an inside and an outside bit - you will need both. The inside bit and the outside bit are connected by pipes and both need electricity to work. Inside bit is heat pump etc and outside bit is heat exchanger and they are connected by gas filled pipes ( gas that gets cold not gas that can go on fire !!)
Pre installation means that the pipes etc are alreay there so you wont need to chisel out the walls and then replaster once the a/c is installed. Basically it saves you having to redecorate.
If you have vents in your house it usually means you have a ducted system that sends the cold air to all parts of the house. The ducts will be alredy installed in your ceilings, again saving you the hassle of redecorating. One of your ceilings - usually the bathroom - will be a false one alowing the inside bit of the airconditioning to be fitted to the ceiling and then covered over again by the false ceiling.
Things to note when buying your a/c
- you need a quiet one ask for the Db of the machines before buying, the lower the better
- make sure the a/c is man enough for the job, it should be big enough to supply the m2 of your property
- check that the gas is the latest type and that the units can be recharged if they leak. The EU specifies the type of gas to be used and some installers will try to palm you off with an out of date stock. Cant remeber the type it should be sorry
- it may be an idea to install your a/c in zones eg zone 1 bedrooms. zone 2 kitchen and living room so that you will not have to be cooling the whole house, just bits of it saving you some money on running cost
-dont get the cheapest go for a brand name such as daikin or panasonic which come with manufacturers guarantees not installers who disappear guarantees which are worthless.
hope this helps