Water jugs for thermal mass/heat sink?

[JayPoc]

Hello all. I built this little hoop house at the start of the fall, and it managed to keep my lettuce alive until the minus 5 degree F night we had a couple weeks ago.




Anyway, the thing works very well in terms of heating up during the day. It routinely would get up in the 70s and 80s even when it was in the 20s and 30s outside. My only beef is that it cools down very quickly once the sun goes down.

The house is 10 feet long, 5 feet wide and about 3.5 feet high in the middle. I was thinking of lining the house with a couple dozen gallon jugs of water to store up heat during the day and keep the house a little warmer during the overnight hours. Would that amount of water do much of anything? (In other words, would it even be worth trying it?) If it's worth doing, would it help if I spray painted the jugs black?

Thoughts? Thanks!

[rainbowgardener]

Interesting question. Water is good thermal mass. Whether 20 or so gallons of it is enough to make much difference, I really don't know. I'm sure it depends on things like how cold it gets outside, how humid your air is, etc. If you have the jugs around and don't have to buy them, it seems worth trying. And yes, I think making them black is important. Also if you could set them on some paver stones, the stones would be thermal mass too. You would want to put styrofoam or something insulating under the pavers, so they aren't sitting on the cold ground.

Keep us posted on what you try and how it works out for you! Your lettuce was looking beautiful!

[Ozark Lady]

I agree with Rainbow. To hold the heat you definitely need something that will store up the heat energy and then slowly release it overnight.

Even a few water jugs might make a difference. Stones would do the job too. Also the direction would matter, you would want to maximize the heat the jugs or stones can absorb. For me in winter the sun has a bit of a southern orientation, so lining the southern side with heat savers is important here.

You might also consider insulating the lower edges at least of the tent on the north side to help prevent heat loss.

How about compost as a heat source? Maybe some compost bins in there? You would have to play with this idea too. But I have seen articles online about compost heating homes!

[scottalot]

I'm a big fan of thermal mass. I use three 55 gallon barrels filled with h2o and sealed for mass. My greenhouse is 10'x16' and I find that it helps a lot. I plan on doing paver stones as well as soon as it warms up. That will help with next winter.