Installing air-conditioners successfully takes practice and skill.
Rating the cooling capacity too high will result in uncomfortable drafts and will also lead to an increase in costs.
Installing an air-conditioner that is too small may seem more cost effective at first, but can mean a greatly reduced cooling capacity.
It is very common in Spain, due to the low electricity prices, to install air conditioners, as these can also to provide central heating.
Please do not hesitate to contact me for a consultation. I look forward to advising you on the best possible solution.