Digging a grave

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Painley

 
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Digging a grave

by Painley » Fri Apr 05, 2019 8:14 pm

So I was thinking about buying a chest freezer to make a kick ass highlands setup. Then I thought about what my mother would do to me if I bought a chest freezer.... might as well start digging a grave now. Oh boy, it's going to be dark and cold down there. Then the epiphany hit "dark and COLD". Geothermal is used all the time to heat greenhouses during the winter or cool them in the summer. The ground is a steady 50° all year around wich is a perfect way to store up some cold air or cool off some water to make a nice highlands system. Anybody ever considered this? Why not keep a reservoir of cool air to vent into a well insulated box.

Any thoughts would be appreciated.

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TheTrapper

 
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Re: Digging a grave

by TheTrapper » Fri Apr 05, 2019 11:46 pm

It would be possible but you would run into a mountain of engineering problems to overcome. First you have to consider location and soil. Some soil is home to a host of wild fungi which produce billions of spores and other thing that you wouldn't really want coming into your setup also you may have to worry about flooding as the water will enter the pit one way or another and you would likely need a pump to pump out flood water. You will also need support braces to make sure that the wall do not collapse in. Additionally the soil temperature varies quite a bit depending on depth, thermal conductivity, water table activity, underground springs and other temperature variables. Then you will also have to call up the pipeline service to make sure that there are no underground pipes around and then check your city's ordinances to see if it is legal. Other than that it is a very good idea but I would say not really worth it unless your looking for an interesting build. An easier way would be to build a peltier cooling unit. It is cheap to build, easy, and parts are readily available. Also you can customize it however you like and add a thermostat for precise temps and temp cycles, and it has the added bonus of adding nice circulation in your grow unit without lowering humidity. You could also build an AC reservoir unit which works quite well. Finally the easiest route is to buy a wine cooler and with a few simple modifications have a great unit. Hope this helps. Good growing.
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Re: Digging a grave

by Copper2 » Sat Apr 06, 2019 6:28 pm

You know, a peltier cooler connected to some heat sinks would cool a terrarium. Probably need a few for a well insulated large tank. Get a thermometer and arduino...
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Re: Digging a grave

by Painley » Sat Apr 06, 2019 6:41 pm

Copper2 wrote:You know, a peltier cooler connected to some heat sinks would cool a terrarium. Probably need a few for a well insulated large tank. Get a thermometer and arduino...
I am unfamiliar with peltier coolers. How do they work?

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Re: Digging a grave

by Copper2 » Sat Apr 06, 2019 6:56 pm

The peltier cooler is a thin wafer with wires coming out. You connect the wires to a power source- I think it runs on 12 volts but I’ll check later. So once the peltier is on, one side becomes burning hot, and the other becomes cold. So it sucks the heat from the air surrounding the cold side and transfers it to the hot side. That’s why the hot side gets hot. You need one heat sink to dissapate the heat on the hot side, and it will cool more efficiently if you add a heat sink to the cold side. People use it to cool coolers for trips
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Painley

 
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Re: Digging a grave

by Painley » Sat Apr 06, 2019 7:06 pm

Copper2 wrote:The peltier cooler is a thin wafer with wires coming out. You connect the wires to a power source- I think it runs on 12 volts but I’ll check later. So once the peltier is on, one side becomes burning hot, and the other becomes cold. So it sucks the heat from the air surrounding the cold side and transfers it to the hot side. That’s why the hot side gets hot. You need one heat sink to dissapate the heat on the hot side, and it will cool more efficiently if you add a heat sink to the cold side. People use it to cool coolers for trips
So you can cook more effectively by cooling off the warm side of the peltier so that it can draw more heat?

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Re: Digging a grave

by Copper2 » Sat Apr 06, 2019 7:38 pm

Painley wrote:
Copper2 wrote:The peltier cooler is a thin wafer with wires coming out. You connect the wires to a power source- I think it runs on 12 volts but I’ll check later. So once the peltier is on, one side becomes burning hot, and the other becomes cold. So it sucks the heat from the air surrounding the cold side and transfers it to the hot side. That’s why the hot side gets hot. You need one heat sink to dissapate the heat on the hot side, and it will cool more efficiently if you add a heat sink to the cold side. People use it to cool coolers for trips
So you can cook more effectively by cooling off the warm side of the peltier so that it can draw more heat?

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Yes, that is how it works. Another reason you need to have the heat sink for the hot side is because it will overheat and stop working. A heat sink allows it to dissipate excess heat quickly
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Painley

 
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Re: Digging a grave

by Painley » Sat Apr 06, 2019 7:40 pm

Increases surface area to cool it off ehh?

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Copper2

 
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Re: Digging a grave

by Copper2 » Sat Apr 06, 2019 8:24 pm

Or you can use a chest freezer.
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Re: Digging a grave

by bananaman » Sat Apr 06, 2019 9:55 pm

Painley wrote: The ground is a steady 50° all year around wich is a perfect way to store up some cold air or cool off some water to make a nice highlands system. Anybody ever considered this? Why not keep a reservoir of cool air to vent into a well insulated box.

It's not 50° everywhere -- the ground is going to be pretty close to whatever your average annual air temperature is. Here, that's about 68-70°. Not really cold enough to build a cooling system for highlanders!
Here's a US map of average annual air temperatures. Ground temperatures are going to be pretty close to that.

The other issue is obviously logistics. How do you cool the air to that temperature? All the geothermal solutions I know of for heating and cooling involve huge projects including laying lots and lots of pipe into the ground to circulate with a heat exchanger.

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Painley

 
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Re: Digging a grave

by Painley » Sat Apr 06, 2019 10:08 pm

After 4 foot below frontline ground temperatures are relativly stable in the 50s. That's why caves and springwater are so cold and if you have ever visited one. I'm sure it would be a project and quite expensive but surely it couldnt be that diffucult to cool a 4x4x4ft box if this method is used often for whole greenhouses and homes. It's just a thought. Maybe one day I will experiment with it

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Re: Digging a grave

by bananaman » Sun Apr 07, 2019 6:36 pm

Painley wrote:After 4 foot below frontline ground temperatures are relativly stable in the 50s. That's why caves and springwater are so cold and if you have ever visited one.

Again, groundwater and deep temperatures are approximately the average annual temperature. It’s a common misconception that it’s in the 50s everywhere.

Groundwater and springwater here is right around 70 all year, as are temperatures even in deep caves. Here’s a map of groundwater temperatures in the US. See how closely it parallels average annual temperatures?

FWIW, what you are talking about is used to help augment the heating and cooling of buildings. They’re called geothermal heat pumps — effectively, instead of moving heat in the summer into the atmosphere and heat in the winter from the atmosphere inside, they move heat into and from the ground — because in winter, it’ll be warmer than the air, and in the summer, it’ll be cooler. The way they do this is by laying pipe at a depth where the ground temperature is fairly constant (ranges from 3-20m depending on ground composition). They run fluid through the pipes that connects with a heat exchanger on the heat pump.


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