I vent to outside maintaining temps isn't too bad, fwiw I'd be happy with 28/29c I would only get mildly concerned say 31/32c+ then it'd be more for the ec than the heat itself.That's what we need in this weather. A nice cold pint of Carling lol. Are you struggling with temperature in your grow room at the minute? I've got my light dimmed down to 75% and even with my 13,000 BTU portable air conditioner running I can't get my temperature below 28c in my grow tent. I would hate to think what my temps would be without an air conditioner lol.
I use a dehumidifier to add heat I'd expect your portable aircon is adding a fair bit heat to the room, air conditioners and dehumidifiers create heat as a by product, that heat is normally lost outside with typical aircons but with portable units it adds heat to the room.