I have a 10×20’ hoop house in NJ zone 7a.
I calculated that I need ten 55gallon drums of water for thermal mass to keep the interior warm on cold nights. However I also like the idea that it will keep things cool on hot days. Water tends to maintain temps avoiding his and lows.
My question is do I paint them black or keep them blue?
I have 3 fans moving 3,000 cfms and I also plan to get a small heater for the really cold nights.
I am leaning towards painting them black since it’s more expensive to heat than to cool and I already have fans.
I only plan to use the hoop house in fall and spring to extend my growing season.
Any suggestions are welcome. Thanks!
by Tronracer
5 Comments
We did the same thing. Didn’t paint them black. It works. Don’t fill to the top with water in case they freeze. You can also put an aquarium heater in the barrels to keep the water warmer in the winter. Get a mesh screen that lets the right amount of UV light thru for the plants for summer. Super hot without it. Good luck
Paint them black for maximum winter gain, in summer cover them with a white tarp to minimize summer gains.
Black!!
Painting them black does nothing. But the real mistake is sealing the barrels. You want the barrels open, and the water moving, for best heat exchange. Get a jig saw, cut the tops of the barrels open. Make sure you only cut the tops, not the sides or the seam edge. Now get a decent air pump, one that will let you run a bunch of airstones. One air stone in each barrel, and suddenly you have worthwhile heat exchange. It will work.
If you’re ambitious, connect them in sequence using pvc pipe and uniseals. Then put a small pond pump in the first one, and have the water recirculate through each one until it returns to the first barrel. Since your greenhouse seems to have a dirt floor, it wouldn’t hurt to sink them into the ground about a foot, to take advantage of the persistent ground warmth
https://www.amazon.com/UNISEAL-Flexible-Tank-Adapter-bulkhead/dp/B093X14RHR/ref=sr_1_1?
I measured blue versus black barrels with a thermometer, and the black was definitely warmer. I don’t remember how much. Black barrels do, also strangely absorb daytime high temps. i do the white tarp thing in summer and it helps…
For cooling, definitely put any shade cloth on the outside. Aluminet is best but 2x the cost of black… it seems funny, but it also keeps the greenhouse a little warmer at night.
Your greenhouse looks great – I bet if it’s well sealed, it will escape freezing in your climate.