Is there some really compelling reason why you want to keep this DC air-conditioner? I'm guessing if you bought a new 120VAC air-con at the hardware store it would perform as good or better, and you'd have all the perks a new unit would give you, like remote control, a timer, ect.
Secondly, why are you so hesitant to go with 48V? I think any safety concerns about utilizing higher voltage are grossly overblown. I've operated a 48V system for years now without a single issue. Keep in mind that going from 24V to 48V means you can purchase somewhat lighter, smaller batteries to equal the sample Wh