Natural home cooling

[Moontanman]

According your info the temps near my house should be about 75 degrees F, that's a little warmer than I thought but still within reason. I think you are reading the info backward, the temps are higher near the surface not deep under ground.

[Nitack]

Originally Posted by Moontanman

According your info the temps near my house should be about 75 degrees F, that's a little warmer than I thought but still within reason. I think you are reading the info backward, the temps are higher near the surface not deep under ground.

That depends entirely on the specific location and the geological activity of the location. However, the majority of the locations that I have looked at get warmer the deeper you go. However, the temperature drops after 3-5 feet below ground and then climbs.
http://rglsun1.geol.vt.edu/data/kn1bnc.well

Temperature (deg C) Depth (m)


11.272 1.300
11.361 1.809
11.568 2.318
11.904 2.827
12.323 3.336
12.872 3.845
13.090 4.354
13.442 4.863
13.770 5.372
14.263 5.881
14.656 6.390
15.085 6.899
15.238 7.408
15.458 7.917
15.643 8.426
15.808 8.935
15.875 9.444
16.008 9.953
16.140 10.462
16.215 10.971
16.262 11.480
16.301 11.989
16.334 12.498
16.366 13.007
16.388 13.516
16.409 14.025
16.429 14.534
16.445 15.043
16.463 15.552
16.487 16.061
16.512 16.570
16.542 17.079
16.577 17.588
16.604 18.097
16.630 18.606
16.666 19.115
16.690 19.624
16.713 20.133
16.735 20.642
16.756 21.151
16.777 21.660
16.798 22.169
16.814 22.678
16.834 23.187
16.852 23.696
16.866 24.205
16.881 24.714
16.894 25.223
16.907 25.732
16.922 26.241
16.933 26.750
16.945 27.259
............................
23.085 310.263
23.093 310.772
23.101 311.281
23.109 311.790
23.114 312.299
23.119 312.808
23.128 313.317
23.137 313.826
23.145 314.335
23.150 314.844
23.159 315.353
23.166 315.862
23.173 316.371
23.180 316.880
23.187 317.389
23.197 317.898
23.203 318.407
23.212 318.916
23.222 319.425
23.227 319.934
23.232 320.443
23.246 320.952
23.254 321.461
23.261 321.970
23.268 322.479
23.274 322.988
23.282 323.497
23.290 324.006
23.294 324.515
23.306 325.024
23.313 325.533
23.321 326.042
23.331 326.551
23.337 327.060
23.342 327.569
23.350 328.078
23.360 328.587
23.367 329.096
23.375 329.605
23.383 330.114
23.392 330.623
23.399 331.132
23.406 331.641
23.413 332.150
23.422 332.659
23.429 333.168
23.436 333.677
23.443 334.186
23.448 334.695
23.457 335.204
23.465 335.713
23.477 336.222
23.482 336.731
23.489 337.240
23.496 337.749
23.502 338.258
23.509 338.767
23.516 339.276
23.520 339.785
23.533 340.294
23.542 340.803
23.550 341.312
23.559 341.821
23.565 342.330
23.572 342.839
23.579 343.348
23.586 343.857
23.592 344.366
23.600 344.875
23.609 345.384
23.615 345.893
23.624 346.402
23.632 346.911
23.634 347.420
23.643 347.929
23.657 348.438

[Moontanman]

Interesting Nitack, evidently the temperature gradient is quite different where you than where i live. It drops here until about 12 or 13 meters then begins a very slow rise and doesn't equal the surface temps until about 230 meters much deeper than any local wells go. How deep will your system be? Here is the depth vs temp in my area

24.1758 2.1000
23.2576 2.6037
22.5935 3.1074
21.8717 3.6111
21.2999 4.1148
20.7954 4.6185
20.3075 5.1222
19.8425 5.6259
19.4874 6.1296
19.1454 6.6333
18.8681 7.1370
18.6333 7.6407
18.4578 8.1444
18.3079 8.6481
18.1953 9.1518
18.1035 9.6555
18.0463 10.1592
18.0065 10.6629
17.9818 11.1666
17.9771 11.6703
17.9804 12.1740
17.9883 12.6777
18.0023 13.1814
18.0201 13.6851
18.0398 14.1888
18.0613 14.6925
18.0824 15.1962
18.1346 15.6999
18.1534 16.2036

23.8951 225.2391
23.9043 225.7428
23.9276 226.2465
23.9392 226.7502
23.9699 227.2539
23.9877 227.7576
24.0074 228.2613
24.0277 228.7650
24.0486 229.2687
24.0689 229.7724
24.0856 230.2761
24.1053 230.7798
24.1245 231.2835
24.1461 231.7872
24.1591 232.2909
24.1696 232.7946
24.1913 233.2983
24.2025 233.8020
24.2248 234.3057

[Nitack]

Originally Posted by Moontanman

Interesting Nitack, evidently the temperature gradient is quite different where you than where i live. It drops here until about 12 or 13 meters then begins a very slow rise and doesn't equal the surface temps until about 230 meters much deeper than any local wells go. How deep will your system be? Here is the depth vs temp in my area

Well the table I posted before was actually a North Carolina location. My table follows:

USG-1 A RESTON lat 38 49.50 long 77 42.13 11/29/79 MCCL

Temp (C) Depth (m)

12.912 4.300
12.942 4.809
12.944 5.318
12.923 5.827
12.896 6.336
12.851 6.845
12.827 7.354
12.771 7.863
12.717 8.372
12.639 8.881
12.591 9.390
12.533 9.899
12.465 10.408
12.434 10.917
12.373 11.426
12.327 11.935
12.273 12.444
12.249 12.953
12.229 13.462
12.196 13.971
12.180 14.480
12.171 14.989
12.157 15.498
12.149 16.007
12.150 16.516
12.144 17.025
12.146 17.534
12.146 18.043
12.149 18.552
12.151 19.061
12.149 19.570
12.156 20.079
12.164 20.588
12.164 21.097
12.173 21.606
12.177 22.115
12.185 22.624
12.195 23.133
12.201 23.642
12.210 24.151
12.216 24.660
12.217 25.169
12.232 25.678
12.239 26.187
12.249 26.696
12.250 27.205
12.264 27.714
12.271 28.223
12.276 28.732
12.281 29.241
12.288 29.750
12.294 30.259
12.304 30.768
12.310 31.277
12.320 31.786
12.327 32.295
12.335 32.804
12.345 33.313
12.354 33.822
12.360 34.331
12.367 34.840
12.379 35.349
12.388 35.858
12.395 36.367
12.406 36.876
12.419 37.385
12.429 37.894
12.437 38.403
12.446 38.912
12.458 39.421
12.469 39.930
12.479 40.439
12.484 40.948
12.496 41.457
12.504 41.966
12.514 42.475
12.521 42.984
12.531 43.493
12.539 44.002
12.548 44.511
12.554 45.020
12.565 45.529
12.572 46.038
12.581 46.547
12.590 47.056
12.598 47.565
12.607 48.074
12.616 48.583
12.625 49.092
12.634 49.601
12.642 50.110
12.651 50.619
12.657 51.128
12.665 51.637
12.674 52.146
12.682 52.655
12.691 53.164
12.697 53.673
12.704 54.182
12.711 54.691
12.716 55.200
12.757 57.745
12.766 58.254

As you can see, it is pretty constant for at least the first 200 or so feet. The crawl space that I will be using is actually below ground level for the outside walls by seven feet or so, with no windows or southern sun exposure walls. I plan on dropping my system an additional 5 feet. That should get me definately to the stable temp zone. If I were to continually circulate air from these earth tubes to the air return I'm thinking that it will mitigate both the temperature and humidity of even the hottest days. And running a low power fan continually will require much less electricity than running the AC intermittently and we will have a more pleasant home temp level.

If this does work, I may use it as the jumping off point for incorporating a solar chimney design, and try to perfect an electricity free design. Or I was thinking of using something like this: Solar Fan with 10 Watt Solar Panel. The fan will only run with the sun is out though, so that may not be optimal for warmer nights. Perhaps I can build some batteries into the mix though.

[Moontanman]

Obviously not my NC location, your data was for Kinston NC a significant distance from me, about a 2 hour drive if I recall correctly, my old employer had a Plant there and i visited it on company business frequently. I provided a link to my location in my earlier post. I hope your idea works, My idea of a problem you might face was just a possibility due to factors about how an AC works but it might not apply to what you are doing.

[lawcat]

Theoretically, the heat transfer from air in underground pipes to ground is possible.
Practically, as Moontanman pointed out, moisture removal is the problem, as well as pipe sizes, and air quality.

What you are trying to do is essentially geothermal system.I would suggest researching water cooled geothermal system. See, e.g., http://www.climatemaster.com/index/r...eothermal+Heat.

Instead of running loops of 18" steel pipes to supply 1750 CFM of air, underground; you may want to run 1" copper water loop. It is much cheaper.

If indeed the ground temp is 53deg F, then the system may work. The water coil in the fan will remove moisturesufficiently , I believe. (Instead of collecting moisture in underground pipes.) Water system is also less susceptible to bad air quality, since air is controlled within the house environment.

(Hire an Engineer to design it, whatever you decide to do.)

[Nitack]

Well I have continued to do a lot of research, and this is by far not a new idea. Apparently this was a buzz worthy idea in the 70's and 80's but ended up busting due to environmental concerns. Mold, fungi, and bacteria ended up creating environmental concerns. The gravel drainage bed that I incorporated was specifically mentioned as having become choked with air quality hazards. Given my six month old child, I will not be doing anything that could reduce the air quality in the house.

Back to the drawing board I guess... however I am not ready to give up on the idea entirely. Perhaps an indirect system like what lawcat suggested. It would lose efficiency, but perhaps be safer.

[Nitack]

OK, as I said, not ready to give up on this idea yet. Very good points have come up about air quality, and I am not willing to sacrifice any degree of quality that may lead to illness form mold, fungi, or bacteria. So, rather than running the air underground, I have come up with a two phase system. Despite the increased complexity, we may actually find a more efficient system because the first phase will use water rather than air.

The system goes like this. We will still lay pipe below ground in order to act as a heat sink, however the pipe will be filled with water. It will be circulated using a small pump. As we really only need a very minor current in the pipe, this can be a very small pump. That system will be closed loop. At one point, that system will lead INTO the existing duct. While the majority of the loop will be PVC pipe underground, the portion of the loop inside the vent will probably be a radiator coil like you find on the back of refrigerators. The ducts will be slightly modified (I really only have to block off one piece of duct) so that they form a tunnel from one upper level air return to the other, with the chilled coil in the center. Install a fan at the air return closest to our living spaces that will pull air through the duct, and we have very low power air conditioning. If I use a DC pump and fan, and connect them to a solar panel we have no power AC. New diagram included.

Thoughts?

[lawcat]

I am not aware of any DC fans with 1500-2000 CFM output. This means that you will need AC converter. In addition, on the second heat sinks, metal pipes are recommended, because they conduct heat better. You should have: 1.5-2 gallons per minute of flow in water pipes, per ton of air conditioning (1" pipe for 5 ton system, at 5ft/100 pressure drop); 1 ton of airconditioning per 500 sq. ft. of house; 400 CFM per ton of air conditioning. Do not forget a filter in the duct.