Hi Russel,
What other sizes do you need apart from 36" wide and 24" high? If you need inlet / outlet nozzle sizes, you need to know the fluid you are cooling / heating (water, oil, refrigerant,...), specific heat, air wet bulb temperature (America, Europe, Africa...), wind or stagnant air, etc...For 11 gpm water, you'll be loking perhaps for 1"-1 1/2" NPS nozzles, depending on temperature also, but that's not engineering, is only a quick estimate on your information. Sorry, but you have to provide a lot more information to get a specific answer.
Cheers,
gr2vessels