So I have been trying to think of a cooling/warming solution system that would accumulate warmth from a copper tube loop run along the backside of LEDs and be plumbed to a holding tank with a temperate range relay that opens when the lower root system gets to a certain low and kicks off when it gets to a certain high. The lower tubing would be run underneath the pots with copper coils or something similar to act as the radiators. I don’t know.,…just sitting on my back porch enjoying this new medicine with no name apparently… Seemed intriguing… not bad. A little fluffy maybe but well taken care of.
Unless you have extensive experience or knowledge on water cooling loops, I don’t recommend this approach.
A seedling mat on a thermostatic controller would be much safer.
Or:
Credit for the following belongs to @Mr.Sparkle
“If it’s floor based, Just run a side res with an aquarium heater.”
Much safer idea and less potential deadly shocks 
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its a valid option just mount one side higher than the other side of the loop that way some natural convection starts going.
but something to consider this will work both ways, as in it can cool, so keep run distances short or less exposure to air, and insulate below it.
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Now I am thinking maybe just use the cooling loop to drive a small impeller that stores electricity to use in a seedling mat sitting on thick styrofoam sheet.hmmmm. gonna go calculate heating mat power usage. Anybody got data?
I’ve seen a lot of homebrewers make glycol chillers for fermentation. Sometimes incorporating old ac/heat units. May be something to look at.