If starting a AC business, the first thing to do is to research what is available from the vast number of manufacturers around the world and what's available in your part of the world, followed by gaining some insight into that / how / when / why you apply what's available.
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)