The major difference between the $500 AC unit and the second unit is that the $500 one pulls air from within the house across the cooling coils and dumps the hot air outside. The more expensive one will be much more efficient as it intakes from outside and dumps to outside (no smell transfer). Unit #2 would be best suited for warmer climates and a room that uses CO2 as it would reduce smell and increase overall efficiency. I personally live in the Emerald Valley in Oregon. I run a single tube AC unit and it struggles to keep up cooling duel 1KW HPS air cooled hoods (outside intake to outside dumb)... I am really hoping that this winter will be easier on the electric billl... If you have the extra and intend to run CO2 then I would strongly suggest the higher priced AC or that you look into purchasing a mini-split system.
