I've been doing some reading on geothermal cooling systems. If soil temps are constant 4 or 5 feet below the surface...couldn't you bury a remote reservoir and pump the nute solution in from there to a grow and back out again to return and cool?
In my part of the world they say 5 feet down the temp is a constant 55 degrees or so.
it'll help for sure; plants love water cooler than ambient... i've gone so far as to create a well with a 55gal drum hooked up to a carbon filter and 1/10hp chiller set at 68f.... i feel like jack from jack and jill but my plants love it
just monitor the temp of your res; you don't want it too cold
@ 5ft down that temp will be roughly the same in most parts of the globe all year round, good use of knowledge there bro. changes by about 3-4 degreees through the seasons if that.
it would need to be sealed very well, as in air tight. besaides the obvious leakages underground water sitting is the best way to bread microbes that cause legionaires disease - not sure about plants but very nasty if your a human!
I can pick up a food grade 60 gallon plastic barrel for 15 bucks around my parts. It comes completely sealed except for 2 screw in bungs on the one end.
I would run an inlet to the top through one bung with a hose connection for polyethyelene tubing and another at the opposite end (bottom) for the supply line.