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Open Source Geothermal substrate cooling - grow cold weather species in the summer heat!

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#1 Nsnail



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Posted 22 June 2017 - 09:57 PM

This projects goal is to create an environment suitable for fruiting colder weather species (50-60F) without the use of air conditioning.

This is still in the conceptual stages so feel free to give input and bounce around ideas.

Anyways I've been trying to figure out a more economic way to cool my grow area. Between Arathu, Ferather, Myc, and me we've been bouncing around a few ideas and sort of merging them into one efficient system to cool down substrate.


Here's my crude drawing of how I think this can all work.
The system could be gravity fed as per Arathu's idea but would likely still need a water pump to return water back into the loop. Fortunately the pump used will almost certainly draw under 1 amp, making it easy power through solar and battery if one desires. In theory the system itself should be much cheaper to run than an ac unit. Usually with geothermal systems for every $1 of energy used you would get 4 or 5 dollars worth of heating / cooling.

Aquarium pump
Water tank
Hdpe tubing or copper tubing ( or both)
Some sort of foam insulation
Silicone to seal everything

I have a feeling that whatever the fruiting chamber is may need to be insulated further but maybe not. The way this design works the coil in the fruiting area cools down whatever is on top of it. In this example it's an aluminum tray which works similar to a heat sink and cools the substrate considerably. I think that because any further transfers would pass through the substrate that maybe and this is still a big maybe, the substrate will remain cool even if the surrounding air is not.

At some point I will edit this from a computer and try to put everything in a more logical order, I'm just trying to cover a lot of stuff at once right now.

Let's come up with something great y'all!

Further reading:

Edited by Nsnail, 22 June 2017 - 09:59 PM.

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#2 Gnomesayin


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Posted 23 June 2017 - 01:37 AM

Got the gnomes attention.
Pulling up a chair.
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#3 Arathu



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Posted 23 June 2017 - 03:43 AM

I'm going to try and sink a heat exchanger down into the sump pit, temperature measures 57F in the pit, in my basement and then run that water through a a second one making a water cooled shelf. First experiments of course. If I can I want to use gravity feed and rain water as much as possible and then if necessary a 12 VDC bilge pump on a deep cycle marine battery and solar panel for return to the reservoir.


I'm still kicking it around some. Proof of principal tests coming up in I have to get the spending change for a couple of things first........... :biggrin: 


I like it..........



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#4 Nsnail



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Posted 25 June 2017 - 10:47 AM

Let's talk tubing

The best options in my opinion are hdpe and copper

- passes heat quickest
- sensitive only to nitric acid
- not recommended in acidic soil

- plastic is an insulator so more length is required for desired effects
- rated for something like 100 years in ground
- used in commercial geothermal applications
- cheap

That being said I think the in ground heat exchanger should be hdpe and inside the greenhouse can be copper for maximum cooling.
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#5 Nsnail



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Posted 27 June 2017 - 12:13 AM

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While not geothermal, this device (peltier cartridge) is capable of serious heating or cooling and can run off a USB. It would be another great option for solar and to my understanding there's tons of off grid refrigeration types builds out there using it.

Another neat option for this open source project.
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#6 Nsnail



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Posted 12 July 2017 - 12:48 AM

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Here's this concept in action using a pond instead of a buried coil, still a form of geothermal.

I think my cooled greenhouse will consist of a chest freezer which follows this same setup. Is there a good way to keep a chest freezer protected from the elements outdoors? Otherwise this project will be confined to my garage.
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