Geo thermal Cooling

Its been extremely hot outside this week, and were suffering a significant drought in much of the country. The chart above shows the levels of streams compared to their historical levels for this time of month. Though some regions are getting a lot of rain (the deep blue dots), much of the center of the country is experiencing drought conditions reminiscent of those over sixty years ago. The Dustbowl, as the period from 1934-1936 became known, was a drought characterized by Roland Dewing as the "most extreme natural event in 350 years."

Back to the heat, I got thinking about the Underground Heating Exchange Systems (UHES) the Chinese developed a while ago. The idea to pump air underground was first patented in the United States in the wake of the oil crisis in the 1970s. But the Chinese picked up on this technology and highlighted it as part of an integrated agricultural approach to feeding the Cold North East.

When I saw the Chinese paper (republished on the UN FOA website), I thought it was amusing that theyd used clay pipes for their experiment. After all, folks in the US typically use plastic drainage tubing for this sort of heat exchange system.

Then I got thinking last night - a problem with the plastic is getting it to simultaneously drain the water that condenses and keep out roots and pests. Clay pipe didnt sound bad, after all. Then the light bulb went off.

What if I used cinder blocks underground for the heat exchange "tubing?" At $1.65 per linear foot, it is more expensive than the HDPE drainage pipe. But I wouldnt have to worry about water draining through the blocks (it would) and I wouldnt be worried about the "tube" getting crushed.

That took me on another little adventure of the mind, as I tried to figure out how deep to run the "pipes" underground. The Chinese used half a meter, but what if one went deeper?

The ground temperature at 30 feet below the surface is constant - which is why caves are cooler than outside in the summer and warmer than outside in the winter. How far below the surface do I need to go to get to that constant heat, I wondered?

Then I found out something really fun at the Build it Solar website. It turns out the temperature profile of the ground lags the air temperature profile. Air temperatures peak in July (in my area), but the soil temperature peaks in August.

Then comes the cool part. That peak heat migrates slowly down towards the earths heat skin, so that the date of peak heat level at deep depths lags the temperature of the surface soil by weeks and months.

So not only will deep Underground Heat Exchange Systems access a larger thermal mass, the ground around that thermal mass will actually be heating up when the rest of the world is cooling down.

Im not sure how practical it is for a home owner to dig down 6 feet or more, but this kind of effort would be within the reach of a minor business. I would love to experiment with this next summer, if I can find a lot where I could dig deep...

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Q A Keeping fish waste from clogging the sump pump

From time to time someone tracks me down and asks a great question. I usually end up spending a minor chunk of time answering. Heres a recent question I thought might be of interest:

Hello Meg,

Thanks for 365 Aquaponics. I find it very informative for my future plans in aquaponics. I had some quick questions- How do you keep fish waste from cloggin up the sump pump?

Thank you very much! Regards, R

Heres what I do:

• I have relatively narrow pipes taking overflow water from my fish tank to my sump. This is not a good thing - if I were doing this over again, Id make sure my drain to the sump was at least 2 inches in diameter. Its a solids lifting overflow, so its supposed to suck the fish tank wastes out, and it does, to a certain extent.
  
  
• I dont have a swirl filter. This is also not a good thing. I really like the swirl filter in the HD Aquaponics youtube videos (episodes 28 and 29 show it, as I recall. I have all the parts to implement a swirl filter constructed out of a 5 gallon water bottle sometime soon.
  
  
• I have goldfish in my sump tank. They love to munch on stuff. So they keep the sump tank pretty clear. I also have a cover over my sump tank.
  
  
• My pump is slightly elevated. I originally put it on a 1 inch thick plastic mesh pad (repurposed the internal pump filter) because I wanted to reduce the noise of the pump. But elevating the pump does three other great things:

1. The plastic mesh isnt inside my pump. Leaving the plastic mesh filter inside the pump can leave you with a nasty slimy mess that you have to clean frequently. If you still want to have some waste filtration, put an external mesh bag filter over your pump.
   
   
2. The waste that is in the system falls to the bottom of my sump. Since the pump is ever so slightly elevated, chunks of gunk are less likely to get sucked into the pump.
   
   
3. If the water level in my sump tank gets low, the pump stops emptying the tank when theres still an inch or so of water in the tank. My goldfish who live in the sump tank are still able to get around and remain in water, so Im pretty happy about that "accident."

Good luck!

Meg

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