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Bill Lantry said:
Best way to get it? Water! If you have a pond in there, the water will absorb the daytime heat and release it at night. You probably won't even need a heater, if the house is well sealed.
Dig down a couple feet, build a frame one foot above ground. I use stacked two by fours, staple the plastic to the top of the frame *after* it's fill with water, and finish it with 1x2s nailed into the frame. Line it with six mil black plastic from the borg. Make it fit across the back, and about 2 feet wide. An 8x2x3 foot pond will be enough. You can build a greenhouse bench over it. Put a cheap aquarium bubbler in there to recirculate the water.
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Got any pictures Bill? I'm picturing a trench along the back side that goes down into the ground and comes up about a foot above?

That might be doable...
 
You know, As far as the passive solar goes, I'm thinking I can get several plastic trash cans and fill them with water and set them under the back bench.
 
Brent,

Rob's links are good, but there a a few disadvantages to that solution. First, and most importantly, they take up space. Great solution in a large greenhouse, but in a small one, every square foot counts. Second, they won't conduct any of the heat from the ground. I'm betting the ground doesn't freeze 24" down in your area! ;)

Third, it's both good and bad those barrels are sealed. It's good, *if* you have separate humidity controls. Most small greenhouses don't. There are two reasons, well, three, for that bubbler I mentioned. First, it recirculates the water, bringing up heat from the ground when it's cold out, pushing it down when it's warm. Second, the air warms as it goes through the water, and then rises. Doesn't seem like a big deal, but in a well sealed greenhouse, it makes a big difference. Third, believe it or not, humid air holds more heat than dry air. Or at least it's more stable.

Sorry I don't have pics, they're on an old disk. Forget the greenhouse for a second, and picture building a level bottomless box out of two by fours. Stacked three high on each side, and bolted or nailed together. Now imagine digging a hole two feet deep, and lining it with a couple layers of six mil plastic (the stuff comes in hundred foot rolls). Put the plastic in, fill it with water. Then nail down 1 x 2s on top of the frame, just to hold the plastic and make it look nice. Presto, a pond.

Now translate that idea to inside the far end of the greenhouse. You can put in a few goldfish or guppies if you're worried about mosquitoes. You won't need to feed them, they'll eat the bugs that fall in! ;)

Thanks,

Bill
 
Thanks Bill.

That's food for thought. Certainly makes sense about picking up some heat from the ground.

We are rated for a 2' frost depth around here, but I seriously doubt it get's down 1/2 to 1/3 that far.

Certainly digging the hole isn't a big deal anymore...

Hmm...
 
The 6 mil plastic is probably all you'd need, but another option would be rubber based pond lining. Considerably more expensive, but also considerably more durable.
 
My dad added a 2 story "sunspace" to the south end of one of the houses we lived in. We had probably 50 15 gallon plastic jugs filled with water and painted black and the floor was brick to store up the heat. That was 30yrs ago...but it worked pretty well. As Bill said it work great as it was really big and space wasn't an issue. It heated the house probably 70% of the time too via blowers and duct work thru the attic. Wish I had some pics of that...
 
Well Doggone it Bill, Look what you made me go and do on my lunch break. Gorgeous day out here, 53 degrees, sunny, didn't want to waste it.

So I went and dug a hole on the north side of the greenhouse, and made a couple of extra holes for some additional hold down concrete.

Looks like I kind of exposed one of the sonotubes, so will need to figure out a way to fix this up... I'm figuring a little pressure treated cribbing or something.

Anyhow, just figured it's way easier to dig the hole now, than it would be once the green house is up.I figure the hole is at least 2.5 feet deep at the middle.

(Have I mentioned lately how fun it is to have a bobcat with a backhoe attachment.... :D )

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Rennie Heuer said:
NORTH side? :huh:
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Well, All the designs I've seen generally put the heat sinks at the back and save the front (south side) for the growing things.

This will have a 1' tall wood surround anyway, so it wouldn't really pick up much heat directly anyway. I'll put some reflective insulation on the lower back (north) side of the green house at any rate to insulate things an reflect a little light/heat back in.

As I understand this system, it takes advantage of the natural temperature of the earth as well as soaking up some heat during the day.

Bill Lantry said:
Make it fit across the back, and about 2 feet wide.
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Bill Lantry said:
Now translate that idea to inside the far end of the greenhouse.
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Bill Lantry said:
You can put in a few goldfish or guppies if you're worried about mosquitoes. You won't need to feed them, they'll eat the bugs that fall in!
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Quick word of caution here. Apparently they can breed really well. I have a small pond in the backyard, keep some goldfish in it no problems. A friend had a pond that had a bit of a mosquito problem and I suggested "hey put a few goldfish in there" :thumb: He does and then a few months later comes back and says "umm so I have about 500 goldfish and my pond smells like Saurons back yard and my dog LOOOVES swimming in it" :blackeye: Turns out the difference is I have a recirculating pump which sucks in and destroys the eggs, he didn't. Something to keep in mind anyway.


On the heat sink - you're doing something a little different than I've seen plans for.. Mostly what I've seen is more like:

S | aaaaaaaaaaaaa H| N
S |--------+ aaaa H| N
S | aaaaaa |______H| N_____
S_|cold sink|

Where
S = South
N = North
| = wall
H = Heat sink (gallon water jugs, etc...).
---+ thing = table
___ = floor/ground
[cold sink] = hole in ground for cold air to fall into. This is really not to scale at all...
a = empty air because board editor isn't honoring my spaces :dunno:

There are several things that I know of that are happening here (again I'm no expert but I've read a few books):
  • the cold sink allows cold air to well.. sink. Its being on the south side may be counter-intuitive, but that is the side you want to be warmest so allowing the cold air to fall of there makes some sense. The one book I read had a good explanation, but I would just munge it. If you search "cold sink" or "cold well" and "greenhouse" you'll find much more coherent explanations than I can give.
  • The table is just there because it was easy to "draw" :p you could also put a loose floor over the cold well and it would work just as well
  • The H heat sink is on the north side because you want to protect against northern exposure. Gallon jugs of water painted black and stacked in shelves work well for this. Water is especially effective because of the energy required to change phases (going from liquid to ice is tremendously expensive) and thus will buffer large quantities of heat. The little "water walls" you can buy work on the same principal. Its best if this is "loose" from the wall to provide an air gap on the north side. If you don't have space a blanket hung from the ceiling on that side also helps provide an air gap (and may well be more than enough in your location).
Note that I'm not saying that a pond on the north side is a bad idea or that it won't help (it very likely will).. Just passing along what I've seen (I read to much or maybe just enough, depends on if you ask loml or me :p).
There are several other advantages to having a pond though, you could use it as a watering buffer, grow cress (mmm cress :bliss:) I'm sure there are others :D
 
Ryan Mooney said:
<Bunch-o-great-advice
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Now that's some more good advice. Not sure how I would go about dealing with a cold sink, but the rational for the north side heat sink makes sense. I'm going to put some of the red colored paving stones down for the flooring. I figure that will add some thermal mass and make for a nicer floor than just gravel, or dirt.

We had a fish pond in the backyard when I was a kid. For some reason it would be my job to clean that out in the spring time and thats one of those smells that I'll never forget. All the rotting vegetation and used fish food.... With as deep as this thing is, the last thing I think I'd want is to have some sort of maintenance issue with live (or dead) critters or vegetation decaying on the bottom. Heck, I'll probably need to make sure I put some screening on top of it to keep rodents from accidently meeting their demise in it.

I originally gave some thought to doing an air based sort of thermal battery where you would have a little fan circulate hot air from the top of the greenhouse down through a pit lined with stones. Read some conflicting reports on whether or not that worked. But I can see the value of having a little pond to add humidity and hopefully buffer the temps a bit more.
 
Bill Satko said:
Well, did it pass inspection?
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I think so. The dogs don't like to jump down in these kinds of holes I've dug.

The hole is actually a bit deeper than it looks in this picture. I figure the deeper the better. Should be fun trying to get all the sharp rocks off the sides and bottom...
 
What I will say is that before I got "Bob" there's no way I could have dug that hole. I've dug a bunch of holes around here by hand, and it always involved using a shovel, a pickaxe, and an Idiot stick (spud bar). The process is to slam some heavy piece of metal into the ground to loosen up some rock, reach down, remove the rock and dirt by hand, then repeat.

So, I would have been in boot hill before that hole got dug! :D
 
Brent Dowell said:
Should be fun trying to get all the sharp rocks off the sides and bottom...
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Brent,

That plastic comes in hundred foot rolls. I usually use several layers. It's *way* easier to add extra layers now, than to have to fix a punctured liner later! Some people use newspaper or even old carpet under the bottom. I've never tried it, so can't honestly recommend it, but they swear by the idea.

By the way, I discovered this passive heat technique quite by accident, because I was using a greenhouse pond to raise tropical water lily seedlings. So all my experience is merely pragmatic... others will know far more about theory and concept.

If you do end up going with fish, whatever you do, don't feed them! That's how people end up with yucky ponds!

Wish I'd had Bob when I was digging my ponds. I had to do it the old fashioned way, just as you described. Yikes!

Thanks,

Bill
 
I actually think I have a big part of a roll of it laying around here, and some strips of carpet. Since the ground around here is so 'crumbly', I'm building a box out of PT 2x12 to put down the hole just so I can fill in the dirt around it and get the foundation finished.

Going to have to pour some more concrete to hold the foundation frame down too.

I just figured its worth a shot to see how it works, especially since digging the hole isn't a big deal now, as opposed to later. The extra humidity that it will generate has to be a good thing too.

Not planning on really using it to grow anything, or any fish at this point. A koi pond would be an interesting feature to have out here, but I'm not sure what kind of predators it would attract. Thankfully, we don't have any raccoons...

In my research, I haven't found anyone else talking much about using one for heating, so maybe this is a discovery that will be worth sharing someday... :rolleyes:

Part of my head says that even if I do want to run some heat out there, it might be more efficient to put a stock tank heater in the pond to warm up that heat sink, rather than heating the air directly...

Should be fun experiment and I thank you for the idea!
 
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