Greenhouse Grain Sprouting in Freezing Weather

We have been struggling with the ability to sprout grain for the animals in this consistently freezing weather.  When the really cold weather hit in December, we had foot long icicles INSIDE the greenhouse! Naturally that was not conducive to sprouting grain... not to mention the constantly frozen pipes and broken valves.

But finally we have arrived at a decent setup that is working. Our average nighttime low is still 25 degrees, and yet the greenhouse has stayed just above freezing at night, and rising to the 60's day times.  THAT is conducive to sprouting :)

Here is a good example of the weather swings... you can see around 5am that the supplemental heat kicked in to give it a needed bump before freezing. (might need to expand the graphic)

The rundown:

Water Line
We insulated the incoming water feed and added an electric heat strip. Yes yes.. i know they are not rated for water hose but... it works. In a pinch you do what is necessary. When things calm down I will remove the water hose entirely and replace with an underground pipe and spigot into the greenhouse itself.

The insulated water hose coming into the greenhouse

Here you can see at the bottom, the electric connection to the pipe heater strip (among the flurry of hoses for the internal sprinkler system)

Thermal Mass
We added six 40 gallon trash cans full of water, spread out in the middle and the sunny side of the greenhouse.  These black cans of water have high thermal mass and the black soaks up heat energy more efficiently. So during the day they soak up whatever heat there may be coming in, then give off that heat slowly through the night. slowing the tempo swings to more of an average. On cold nights you can see the water in these buckets steaming!

Here are some of the full black trash cans for thermal mass. the blue buckets are full of sprouting grain

Backup Heat
As a last resort, there is a propane heater ready to kick in at the edge of freezing. We don't want to heat the greenhouse as that would be too expensive. This is just an emergency measure to prevent freezing.  as you can see from the chart above, it does kick in just a few hours past hitting 32 degrees.  this one was QUITE a challenge! the heater I chose was a non-electric propane model from mr heater. It does not take an external thermostat. It was designed for room temps, so the first night we tried it, with the thermostat set as low as it would go, it ran all night and emptied a bottle of propane.  After dismantling it, and exploratory resetting the thermostat... through hours of trial and error,  i finally got it adjusted down the the range needed.

The modified heater... you cant tell any difference, but the mechanical thermostat is set about 30 degrees colder than it was intended for. 

And of course ... every heater needs a fuel source. This is the old tank from the milking barn.