Coldsink

Hi, newby here.
Ever since I read Mike Oehler"s book on passive solar greenhouses, one thing about his design stood out for me: The Coldsink. A place under a walkway for cold air to gather and be re-heated by the earth. It seems to make perfect sence to me, and if it works I see tons of opportunities to work with one.
But when  I search the inernet for one in action, all I ever get are references to the principle and design. There doesn't seem to be just one in the whole wide beautifull world (apart from his original one) wich  really surprises me. They seem to make perfect sence and offer possibilies for connection with mushroom-growing, chicken coops, compost production, wildlife corridor, air intake and so on...
Does anyone know about a functioning example, or of any reason why they never get implemented?

Thanks a lot,
Michiel (the Netherlands)

Hi Michiel, welcome to Permies!  I haven't seen one "officially" called a cold sink but I've seen many examples where they were used.  Any greenhouse with raised beds would use the floor as the cold sink.  Having it sunken deeper would probably help more but I think it gives the same benefits.  

I did see an awesome greenhouse build video on Youtube but I can't find it now.  It was a guy in Bulgaria or a nearby country who dug a walipini greenhouse into the side of a hill.  He heated it with a charcoal retort furnace and had a hole dug down a hell of a long ways down into a root cellar.  It was something like 8' deep and looks like it was out of a medieval monastary's basement.  It kept veggies cold (temperature of the earth), allowed the coldest air in the greenhouse to drop down into it and also allowed the heat of the earth to rise up and help the greenhouse on cold nights.  Or at least I'm imagining it did all that.  I wish I could find the video....

Hi Mike, thanks for the reply.

I am aware that a raised bed provides  some sort of coldsink. But of course Mike Oehler's idea is to extend that principle. If it is deeper it would be more effective and could offer more gradients and possibilities.More edge-effect if you will.
My idea roughly is to have a raised bed on the south side of the greenhouse. Mainly for annuals, propagation, slide-out coldframes and so on, with some sort of entrance through it  for a deep litter chicken coop. Then a walk way with cold sink (coop underneath), on the east-west axis of course. North of that could have some more annuals but mainly perennials, food forest style. Pretty standard, I'd say.
According to what I understand from Eliot Coleman, a 5% slope of a  terrain towards the south would "move"it about 480 kilometers (300 miles) south, by simulating a higher sun angle.That idea might work inside a greenhouse and would also enhance the coldsink-effect, I think.
Now I'd actually like to pack as many functions into the sink as possible (a tourist destination could be one of them, thank you very much)
Connected to the chicken coop inside the sink would be a closed composting system with subsoil drainpipe exhaust, providing heat, water vapor and CO2 into the soil directly under the plants. The New Alchemy Institute has an extensive report on such a compost exhaust system and it looks very promising. Of course the chickens (and maybe mushroom production) would also provide a certain amount of this heat and CO2. Exterior air intake for this system would be preheated by earth tubes or cellar-vent. I did think of connecting a cellar to the coldsink, but I don't know exactly how to deal with the fact that the cold air from the sink into the cellar might clash with the venting of that cellar, wich normaly would be situated on the north side of a building. Leaving it as a separate unit outside to pre-heat air into the greenhouse (via a small sauna as back-up?) might be a better option. Have to think about it, will search for the video you mentioned...
Thermal insulation around the perimeter of a greenhouse (extending to at least under the frost line) makes a lot of sense to me, but does provide a problem. It also totally isolates it from the soil food/fungal web outside. And we don't want that, do we? Here the cold sink could have yet another function. We could somehow create a corridor for the web, I think. Let''s say we slope the ends of the coldsink (east and west) towards the soil level of the greenhouse . Into the (also mulched) coldsink we could make a small but decent opening to the outside world into a "dry" pile of mulch, that we thouroughly protect from the weather . It would have to be large enough to give ample R-value. That could be calculated, I think it will have to be something like Huge! The moist bottom of the pile would provide the corridor for soil life, the dry mulch on top insulation. You'd have to top it off every fall or so.. Oxigenation of the pile could be done by a trombe wall, if needed. Does that make sense? Any ideas anyone?

Many good, well functioning greenhouse systems exist. But many of them seem to be depending on mechanical and electric (and digital) inputs. That's all fine really, but I think I want to learn more about biological, physiological and hydrological possibilities first. They actually represent the "passive" aspect of a greenhouse (or any house), don"t  they? And they fascinate me...

Anyway, thanks. I think now I"m going to read every permie-post on greenhouses thrice. And then some...

Salut,
Michiel

You have some neat ideas, it will be great to see them put together!  The only comment that comes to mind at this time is to consider shallow foundation insulation.  Instead of having a deep foundation and deep insulation, I went with a shallow footer foundation and insulation that went 1' down into the ground and then 3' horizontally away from the greenhouse.  I didn't do it to allow the soil web to extend out of the greenhouse but that could be a way to address that concern.  

My greenhouse is in a field of grass so I'm counting on the soil web inside to be more beneficial than the web outside anyway.  But I'm aiming for tropical perennials and other strange things.

Thanks, Mike.
Good thinking about the insulation. I'm going to ponder on that... It might very well be part of the solution.

It"ll be a while before I can put my ideas to work. Don't even have a place yet, nor money to do a lot. I'm just exploring ideas and principles...
Very much interested in the concept of PAHS. Passive! Trying to figure out how that would work in a greenhouse.

Greetings, M.

Have you drawn things on a piece of paper to see how the ideas overlay each other, that may help.
I will need to study your comments to make them clearer to myself. And then I will add to the conversation

Mike Jay wrote:
I did see an awesome greenhouse build video on Youtube but I can't find it now.  It was a guy in Bulgaria or a nearby country who dug a walipini greenhouse into the side of a hill.  He heated it with a charcoal retort furnace and had a hole dug down a hell of a long ways down into a root cellar.  It was something like 8' deep and looks like it was out of a medieval monastary's basement.  It kept veggies cold (temperature of the earth), allowed the coldest air in the greenhouse to drop down into it and also allowed the heat of the earth to rise up and help the greenhouse on cold nights.  Or at least I'm imagining it did all that.  I wish I could find the video....

I watched that too! I swear it was just last weekend or the one before.... IIRC, you commented about it, something like "I thought it was a little hollow in the wall, but I almost pooped myself when he kept going down into the ground!!"
He said in the video he was 9M underground!!

John C Daley wrote:Have you drawn things on a piece of paper to see how the ideas overlay each other, that may help.
I will need to study your comments to make them clearer to myself. And then I will add to the conversation

test

This is picking up an old post.  My water table is only about 4-5 ft down on sandy soil 7km from the beach.  The grass can dry brown, but the fruit trees in the orchard will still bear, and I have never watered them.

Twice in five years, the water table has flooded 90% of the property including under the house, and sat for months.  The town council has finally put a ditch down our road where it flows down and into our property, but much of our property is still lower than the ditch.  The flooding takes months to build up in paddocks about a km away before it floods down our road and into our property, so we need to wait another few years to see what effect it will have if it drains the source of the flooding early enough.

What will happen if there is a heat sink and it gets flooded, will it still work?

The lowest it ever gets in winter is -4C as we as so close to the sea.  On an average winter there a frosts several times in winter.  In such temperatures is a heat sink so important?

Annie, can I ask a few questions?
- are both properties in a natural flood plain?
- Does the new drain direct flood waters directly to you property?
- IF so, are you happy with that?

As I understand it, the idea of a cold sink is based on the simple fact that warm air rises and cold air sinks. So a cold sink is simply a place to channel the coldest air away from plants. It would be better named as a "cold sump."

But this is an air system, based on stratification of warm air vs. cold air.

I think it would be better to split flooding issues into a new thread. This is a different beast, and worth exploring.

Annie, have you thought to use earthworks to improve the quality of your road so that this does not happen?

Ditches and swales would work.

Then once the water problem has been solved maybe a coldsink might work for you.