Preparing to Back-fill, more components - part 3

I attached another barrel with the top cut out, to the inlet and outlet plenums of the underground heat storage tubing using strips of scrap plastic, self tapping #12 x 1 inch screws, and foam pipe insulation for a gasket between the barrels. The barrels were attached upside down and I didn't cut holes in the bottom (now the top) so that as I back-filled the dirt, I wouldn't get dirt down in the plenum distribution area.

When the area is completely back filled, the ground level should be at or slightly higher than where the tops of the barrels come to now. The 650 feet of underground tile pipes will be four to seven feet below the surface! That is where the hot day-time air from the greenhouse will be circulated and the heat stored for later extraction or radiating to the surface.

I bought the remaining 20 cyclone fencing top-rails from Home Depot this afternoon, I already had 10, they were $9.41 each. The hoop house ribs will be made from three, 10 foot 6 inch, top rails bent in an arch that begins 5 foot from the end. This will make the width of the greenhouse about 16 feet wide and 11 feet high. I chose Home Depot over Menard's for the top rails because Home Depot had 17 gauge and Menard's rails were 18 gauge. The lighter rails from Menard's were $8.97 only $.41 cheaper, so I went with the heavier 17 gauge. The ribs should be no more than four feet apart so these 10 ribs are enough for a 36 foot long greenhouse. My total cost for for 30, 10'6" x 1 3/8 top rails, is $282.30.

Another item I bought today was the main circulation fan. I purchased a Master Flow Best Pro 3, Attic ventilator fan for $93.00 from Home Depot. It's rated at 1600 cubic feet per minute and came with an automatic thermostat adjustable from 60 to 120 degrees. Since I want it to kick on in the day-time when the temperature is 80 or above this should work great but I don't know how I can make it turn on at night when the temperature drops to 60 degrees or below? I think it will require a whole different set-up.

The fan housing measures 15 inches across. I thought I would use smaller 15-gallon barrels to house the fan and extend from the blue 55-gallon drums to near the ceiling of the green house but they are only 14 inches across, about an inch too small, but still may work.

Should the fan draw the air through the system or blow it through?

I think blowing it through would be best because it would seem more apt to force the hot air out the slotted drain tile pipe and into the ground. I'll have to go back and read some of the plans to see what they suggest. I think the fan would run quieter if it were mounted near the ground or even below the surface in the inlet blue barrel with just the intake barrels extending upwards toward the ceiling. I suppose it should also be located near the north wall barrel so the inlet barrels don't cast a shadow over the plants.