Greenhouse night heat idea

  New to the site and figured this would be the place to bounce ideas off of.   I have looked around and have not found any thing on this idea of heating a greenhouse. I know the use of thermal mass 55 gallon water barrels is not new but what about super heating the barrels with pass through air style solar collectors the ones using window screen. My thought was to build a plenum behind a barrel wall on the north side of the greenhouse and pump the hot air generated by the solar collectors into it and back to the collector.

Hi Tony, welcome to permies!

Would the hot air collectors be inside the greenhouse or outside?  Would the plenum just heat the north side of the barrels or would the warm air get more surface contact somehow?

Another idea would be to pump the water out of the barrels and through 100' of 3/4" black poly tubing (in the sun) before returning to the barrels.  That should heat them up nicely...

 The collectors will be out side the greenhouse and be used to only heat the barrels. I’m looking at putting 14 to 18 barrels in and stacking them 2 high.  The plenum will only be on the north side of barrels between them and the wall

Welcome, Tony.

I think it has possibilities. A squirrel cage fan can move a lot of air very economically.

One thought is that moisture in the warm air will condense as it cools. It could build up a water "plug" cutting off airflow, or possibly mold/algae issues. So there could be a bit of monitoring and periodic maintenance required.

Douglas, about the condensation, if the system is not a closed loop, it shouldn't be a problem. If closed loop, then a large plenum on the "return" would allow condensation without plugging.
Greenhouse air--->fan--->solar collector--->bubblers in barrels--->exhaust to greenhouse.
The drawback of an "open" system, is the potential to overheat the greenhouse during the day. Possibly humidity control issues?

Mike's suggestion of moving the water to the collector and back might be more efficient than a bubbling air--->water system.
There's a hybrid collector type, a Khanh collector, which has a large air collector section to boost performance of a smaller water collector.

Mike, you built system inside your greenhouse with a radiator, fan, pump, and storage barrels... did it perform well? It seems as if an external solar hot water collector could be added, or maybe even a hot air collector?

My water system froze when I wasn't expecting it.  Getting enough antifreeze into it to prevent that would have been cost prohibitive.  I've had notions of moving the wet part of my system into a mini-greenhouse within the main greenhouse but haven't moved forward with that yet.

Would the collector be on the north side?  Not sure you'd get enough heat there, especially when it's not summer.  I doubt you'll get anywhere near super-heated.  But maybe evacuated pipes would get you better results.  I've considered that.