Mike Jay wrote:
What is the roofing material? Does snow sit on it all winter?
Can you pile snow around the base on all four sides to insulate the ground a bit?
If the block wall behind it has open cores (square holes), they may be allowing cold air to travel within the wall, cooling it down and reducing its helpfulness.
Could you insulate the North wall? You probably don't get any sunlight though it so it is a wall that gives no solar gain and a fair amount of heat loss.
Mike Jay wrote:First off, you're already doing great. A few thoughts for ways to boost your temperatures this winter would be:
Try to hold the snow on the roof during the coldest part of winter when the sun is low. Unless it blocks a bunch of light, the insulation would help hold in a ton of your heat. If it would block too much sun, maybe still try to insulate the North half. Of course you could try removable insulation that you put on in winter and remove in summer instead of relying on a layer of snow.
Digging down the 6" around the perimeter and adding some underground insulation would help keep the cold ground outside the greenhouse from transmitting under and into your greenhouse. I'm putting styrofoam in a "Swedish skirt" arrangement so it goes down a foot and then horizontally out 3 feet. I have a 4' frost depth in my area so that will keep it from encroaching under my greenhouse.
I like the compost idea and will be trying it myself. I think the recommended minimum size for it to generate good heat is 3' by 3' by 3'. I'm guessing a smaller volume would still work but need more tending and quicker addition of new material. One key is for the compost to be in a lump/ball/cube/pile. If the same volume is spread around the floor 4" deep, while it may be the same amount of compost, it won't be able to feed off its own heat to get composting.
Jerome Lee wrote:Anyone done the math on the effectiveness of water jugs for regulating temperature? (Or has some empirical data to share?)
Mike Jay wrote:Here's a thread on the topic of thermal mass: Thermal mass for hoop house
I don't have any data to share but I've read a fair bit about it. From what I recall, drums collect and distribute heat over the course of days, 5 gallon buckets do so over the course of a day or so and gallon jugs are over the course of hours. So the time span that they need to be able to help your greenhouse partially dictates their size. Painting them black or a dark color helps them absorb heat, putting them in the sun also helps.