As far as projects to transition to the winter greenhouse, I installed two 55-gallon metal drums filled with water to act as a heat sink and thermal mass, but also to provide water for our watering needs. It was gratifying to fill these from our rain barrels, and this begins the winterizing of our rain barrels and their transition to downspouts for the winter.
Unlike the plastic olive barrels we use for rain water harvesting, the barrels we re using in the greenhouse are metal (for thermal conductance), black (for solar gain), and also act as good shelving and work surfaces. These are reused drums (clean) and are about $20 from Axmen
We’ll see how these work, only having 110 gallons of water will not provide nearly enough BTU’s to maintain the greenhouse above freezing alone, but coupled with other features, hopefully it is enough to provide benefits. Water, though a good heat sink, would need to be in a volume close to 500 gallons, based on the square feet of glazing and insulative value of my greenhouse, to have a significant effect if that was the only thing I was relying on to keep temperatures moderate. If nothing else, however, the metal drums do act as shelving and storage for water.
Other changes for the winter:
I disconnected the solar window opener on the east window, and covered the east and north window with 2” rigid insulation, the silver film will also reflect a bit more light to the greenhouse.
Install storm door