Passive cooling

[GCrumb]

No fans required. Less than two metres deep will still bring in cooler-than-outdoor-ambient air. Drill holes in the bottom of the pipe, condensation will happen in there.

 

[Jenni Hen]

How deep must the pipe be buried to be effective? Even 2 feet deep would require a lot of digging and piles of earth.
How do you stop the air vent from getting blocked? Should it stand above ground level?
The high vents in the coop are important. I've been looking at polytunnels and they don't have high vents for letting hot air escape. I've been using one for winter protection but it'll have to come off in summer (if summer arrives!).

 

[GCrumb]

How deep must the pipe be buried to be effective? Even 2 feet deep would require a lot of digging and piles of earth.

It depends on where you are on the earth, what your soil is like, and how effective you need it to be to consider it effective.

Somewhere between about ten and forty feet deep, the soil will be a constant temperature that is the average of the yearly temperature on the surface. The shallower you are, the shorter the the time period of the average. So if you have hot days and cool nights, a shallow trench will work. If the days are warm and the nights balmy, you'll need to go deep.

There's also an issue of how long the pipe is -- air needs to be in it long enough to cool off. Just a straight tube like in the diagram won't work as well as a zig-zagging mat. Also issues of what you use for the tube -- clay will transfer heat faster than PVC.

It will work much better if the tube is buried in a shady location. Moist soil will transfer the heat better than dry sandy soil.

How do you stop the air vent from getting blocked? Should it stand above ground level?

You put a U-bend on the top so that the opening faces down to stop water getting in at the one end and bedding at the other. Above ground/floor level, yes.

The high vents in the coop are important. I've been looking at polytunnels and they don't have high vents for letting hot air escape. I've been using one for winter protection but it'll have to come off in summer (if summer arrives!).

The high vents are what made me think of this -- this kind of thing requires high vents to work best. The traditional (from Ancient Egypt 'til they fell into disuse in the early 20th century) ones would have a tower so the wind would help create more draft.

The thing about the high vents in chicken coops, like two big vents on the gable ends, is that they'll vent the hot air, but they're essentially creating a draft along the ceiling and leaving the air below more or less still, not moving cool air into the building much.

 

[aart]

Yep, it's true...not sure many would employ it for a chicken coop.

 

[Red Mangrove]

Why would the cool air rise though? Does it warm up in the ground or does air pressure push it out?

 

[GCrumb]

Why would the cool air rise though? Does it warm up in the ground or does air pressure push it out?

Warm air inside the building rises and escapes through the high vents, reducing pressure inside, so cool air from the tunnel is drawn up into the building, and outside air is drawn into the tunnel, where it is cooled because it's colder underground. You can get the inside of the building cooler than the outside without electricity.

How practical it is for a chiccken coop probably has lots to do with how hard it is to dig there.

 

[Jenni Hen]

The high vents are what made me think of this -- this kind of thing requires high vents to work best. The traditional (from Ancient Egypt 'til they fell into disuse in the early 20th century) ones would have a tower so the wind would help create more draft.

Isn't that the purpose of the cupola? I guess they're expensive/awkward to install and a fan is easier to obtain.
We shouldn't lose the knowledge of how to manage without electricity but most people couldn't dig to those depths in the sub-soil. Do you know any good methods that use evaporation for cooling? e.g. when you put the milk in a bowl of water with a cloth over, and the cloth constantly wicks up the water which evaporates and cools the milk. There must be some method to collect the evaporated water, maybe trapping the vapour and letting it condense overnight.

 

[GCrumb]

@Jenni Hen Well, you wouldn't necessarily have to dig that deep. This data I am looking at from soil probes in N. Dakota is showing that two feet down it's close to ten degrees F cooler than it is two inches down, which will be cooler than the air.

Those amazing wind-tower-cooled palaces directed air-flow over fountains and cisterns for evaporative assistance with the cooling.

The ordinary sort of evaporative cooler is a fan with a water-reservoir and a pump that lifts water to dribble it down through a pad attached to the back of the fan. For some reason this is called a 'swamp cooler' but it won't work in a swamp or any place else that's too humid. Probably all of the UK, since my UK friends find mine novel.

 

[aart]

How practical it is for a chiccken coop probably has lots to do with how hard it is to dig there.

.....and you wouldn't a big hole on the floor of a coop.

Long length and/or zigzag configuration would be even more excavation.

Wonders what diameter pipe would be best?

For some reason this is called a 'swamp cooler' but it won't work in a swamp or any place else that's too humid.

I've always wondered that too.
Maybe it means it will make the space feel like a swamp?
I've always thought that using sealed ice packs would be better, no added humidity.

 

[Ridgerunner]

The thing about the high vents in chicken coops, like two big vents on the gable ends, is that they'll vent the hot air, but they're essentially creating a draft along the ceiling and leaving the air below more or less still, not moving cool air into the building much.

Having only vents up high create a noticeable draft along the ceiling when the wind is blowing. The friction between the moving air at the top and the air in the building will create turbulence in the air in the building. The stronger the wind, the more the turbulence. But that is not what provides the cooling. You have to have a source of cool air to cool it off. Even high up and with no wind one vent may be cooler than the other just because it is on the shady side. It may not be a lot but with trees or other buildings it may be more than you think.

Even vents high up can provide air cooler than what is in the coop. Some coops can heat up from sunlight, either the greenhouse effect from widows or clear panels or maybe the walls on the sunny side getting hot and radiating heat. The more difference in the temperature of the air inside and the air coming in, the greater the effect.

So where can you find cooler air? Generally, in the shade. Sometimes trees or other buildings create cool spots but generally in the northern hemisphere the north side of the coop will be in the shade while in the southern hemisphere the shade is on the south side. The east side is generally cooler than the west side after noontime when it gets the warmest. Since cool air is heavier than warm air it sinks so in the shade it is most likely your air at ground level is your coolest. So have an inlet for cool air at that spot if you don't want to bury a pipe.

The advantage of this buried pipe is that the air is cooled even more, basically thermal-powered air conditioning. Even if the air temperature is the same at the inlet and outlet of the buried pipe you will get some advantage but if the inlet is cooler (in the shade) than the air at the outlet in the coop you get an additional driving force to move the cooler air where you want it.