Refrigeration, typically. It's kinda lumped in with HVAC usually, but you wouldn't want a commercial HVAC service/installer working on a chiller tower IMO there are alot of differences between air conditioning and refrigeration equipment, just like sheet metal (what I do) gets lumped into HVAC as well, so when people say "Lucas can you replace my furnace and AC" I say no because to purchase the equipment for the refrigerant would take me 5-10 change outs to recoup my cost on it, plus I don't know how to braise, but I could buy a pro press... More money... Hahaha