Harvesting Heat

I have had a hell of a 2020! The county health nurse says i was likely on my second go around with covid in November... Which makes sense
because I'd been fighting fatigue all year!

I was able to build a 20x30 greenhouse while dealing with a pile of projects and the fatigue... I'm almost done with the set up!

The layout is 275 gallon totes of water on the north wall (6)

2- 20 amp circuits to a double gang box inside the gh
14' x 10' jean pain pile next to the greenhouse 6' tall with 350' of pex coiled inside
 55 gallon drum with 110v submersible pushing water into the heat exchanger coils in the pile
 Heat exchanger flows into a cleaned auto radiator then to a 15 gallon header tank 8' high(also the gravity feed blue mat irrigation supply)
 From the header tank the water overflows to the 55 gallon main (insulated) res...

Im registering 140 degrees in the center of the pile
My plumbing is in and functioning
I have a double layer poly inflated cover on the gh

I live at 5200' and have snow on the ground almost all winter. Winter goals are to grow broccoli, lettuce, cabbage, carrots, onions and radish.
Next year I want to winter my peppers and some tomatoes over, as blight in Northern Utah is not an issue.

I'll eventually run this off grid with a power wall, solar and wind...

As for now I need to run fans and pumps in the middle of the night to keep my temps between 40 an 55 (early tomato growing)

I have 12 volt auto fans (3) what would you guys use to control them automatically? I'd like for them to go on below 50.... And during the day above 80.
My pumps are on timers as I need to keep the water flowing
in order to keep it from freezing

Hopefully I can get my header tank and auto venting rams in this week

There are certainly industrial thermostats that activate on a high and low setpoint. I'm not sure that's cost effective for a temporary setup though.

Are you using a 120VAC-->12VDC transformer to run the fans? If so, maybe a 24hr mechanical timer would do the job. I have one that lets you set 15-minute increments of on or off in each hour. You pretty well know when the warmest parts of day and the coolest parts of the night will be anyway.

I have a timer for my main circulation pump currently. I'm hoping to find a power supply suitable for the fans... I guess I can grab another timer for the fans and set it up ahead of the 12vt supply.