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mattie

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Old McDonald

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It has taken me a while to get around to following up on this video. It is an interesting concept, an extension of a few things I have seen before, but never set up inside a "grow house". I would be suspicious of overheating in the daytime. 

Not long before I left Australia (1992) I came to know an Eastern European who liked his cold summer vegetables, but where he lived was too hot so he designed a grow house from heavy shade cloth. It did not heat up because of the sun blocking effective of the cloth and he could grow his vegetables in there. Where it was situated had cold (for Australia) winters with a little snow, and although he did not use it in winter, I think it would have been good for crops that would be overwinter in slightly warmer climes, like where I am now - onions, garlic, beans and peas.

There must be many places in the US where either the Gondar design or the shade house could be used.
JohnGuest

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I have no experience of gardening in the desert, but on the face of it i doubt it would provide much water. Overheating could be solved by driving the moist daytime air underground. Assuming the desert ground temperature was capable of driving the air temperature down to dewpoint, the vapour will condense out in the rootzone where it is directly available to the plants and being underground, its less likely to evaporate.
At night when the air temperature drops, the same fan is used along with a heat exchanger to remove both sensible and latent heat (water vapour) from the ground. This warms the greenhouse air at night and also replenishes the grounds cooling capacity for the following day. The latent heat in the airstream condenses out in the heat exchanger and is returned to the ground as liquid water. The sensible heat released in the process is transferred to the greenhouse. Typically 50% of the total energy returned at night will be in the form of latent heat. Latent heat raises RH% but doesnt raise the air temperature.
Old McDonald

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JohnGuest, Gondar is in the mountains in Ethiopia and the area around about is at an elevation in the region of 2200m/7000ft and since this is a University inspired project (I have used internet info from there for farming purposes) assume that they did achieve success with their trials in collecting sufficient water. They do receive some rainfall too, although I do not have the info to hand. I just know they describe the area as arid.

The explanation of how the system works is not good, but I gained the impression that the air inside the house is moist during the day because of the water stored in the tank and not because the atmosphere outside is moist. The tank is topped up from dew (they say) when the temperature falls at night. It could be condensation forming on the plastic funnel. 

I like the concepts you put forward, with reservations about withdrawing moisture from the soil overnight, but do not understand how you would do it.

JohnGuest

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The loss of water from the soil would be an issue in the arid greenhouse where water is limited. I`m not sure how much dew it could supply unless the dry air is constantly replaced with fresh moist air.
I`ve used a shcs system (buried tubes and fan) in my greenhouse for the past 7 years. On a sunny day running the entire air volume underground 40x an hour can easily condense out 30L of water, a greenhouse full of transpiring plants produces a staggering amount of water vapour [wink]  A fair percentage of the water is returned to the greenhouse at night in latent form which isnt very useful as it only serves to raise the humidity not the greenhouse air temperature.
   
Old McDonald

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I checked the climate info for Gondar http://www.gonder.climatemps.com/ and cold night temps appear not to be a problem. In the absence of what is we are only guessing at possible improvements. The rainfall is high given the temperatures, and like I said, it is guessing, but I cannot see any reason other than very poor soil - or lack of any reasonable soil at all. The rainfall is well above my average here, with temps higher in the summer and a bit lower in winter, and also way above the long term average for my Australian property. Previous owners had passed down their records and they went back to the early 1920s. With temps well in the 40sC, and that land was far from arid.
mattie

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Reply with quote  #7 
I did not have any evidence of proof of concept in this and it was me who used the arid land term here,it was a food for thought more than anything else,often one idea triggers another thought which can lead to something even more useful in the end.
Old McDonald

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I agree with you that it is indeed "food for thought". It is a shame there is not more info about what they were doing. I thought perhaps they were experimenting with the design for use in an area that does not receive as much rain as Gondar, but I could not find anything. Because you opened the thread on here, it will serve as a reminder for me to check from time to time if more info is provided. As previously posted, I have used other info from the same source.
stmbtwle

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Reply with quote  #9 
As long as there is SOME moisture it should work. It would also recapture moisture lost by the plants themselves, so even if you needed to add water you'd need a lot less. Overheating might be prevented by storing the heat for nighttime use. Several setups on here and BIS for that.
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Willie, Tampa Bay
Old McDonald

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Willie, As I said at #6, moisture/rainfall at the site is not a problem, and I am baffled as to why this thing has received publicity. I will delve into it from time to time to try and find out. If I find anything I will post here. 
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