i would bring the air duct in through the ceiling then t-y it off so it goes through the light system and the y gos through a carbon filter which would also supply cold air for the room. then on the exhaust of the light add another t-y at the top of the room to suck air out of the room and out of the light. bring the exhaust out of the top of the room and put another carbon filter to eliminate odor and a fan attached to create negative pressure to help suck the air out of your grow room. this way the room will be supplied with fresh circulating air and you can control the temperature by putting a thermostat in the room that controls the air system. and if your using your homes air system you may think about installing a zoning system to take use of one a/c system for your home and grow room. if you have any questions ill answer to the best of my ability