I am about to address res temps with a cabinet upgrade, so I thought it might be helpful here.
I am running a single DWC bucket in a 24x36 cabinet. I already have an upper chamber for extracting the heat. I am switching to LEDs and need some more height in the growth chamber. I am going to install a lower chamber that will house the res. I noticed on my last grow that once the scrog filled in the bottom of my cab stayed nice and cool. My cab sits in a garage, so there is no AC. It is in the 90's now(In the garage), and will surely be 100+before the summer is over.The canopy temp is around 84 today with the current setup. I expect the LEDs to cool that down significantly.
I bring air into the cabinet from a closet inside the house via a passive air intake. Temps in there stay between 66 and 71.
The plan is to create an insulated lower area that is only semi-open at the top, which is at the level of the top of the bucket. The intake points at the floor, and the air pump sits right at the intake. There is a good fan in the lower chamber to get good air circulation. The top will be made so that it can serve to allow the fan to create circulation in the lower chamber while still releasing air upward into the growth chamber.
The goal is to maintain 70 or less in the bottom of the cabinet by using shade, air circulation, and a separation of different temperature zones inside the cabinet as well as possible.
Anyway, here is the design. It's crude, but I will be adding this cool chamber onto the cabinet sometime in the next couple of weeks.