Difference between revisions of "Earth-air tube design"

From Green Garage Detroit
Jump to: navigation, search
Line 27: Line 27:
 
** Tamp the clay soil firmly around the tube to eliminate all air pockets.
 
** Tamp the clay soil firmly around the tube to eliminate all air pockets.
  
* Avoiding Mold / Bacteria
+
* '''Avoiding Mold / Bacteria'''
 
** Slope the tube
 
** Slope the tube
 
** No ridges in tube
 
** No ridges in tube

Revision as of 23:03, 26 January 2009

This is the design ideas for the Green garage Earth-Air Tube

  • Tube Length
    • It seems that the temp transfer occurs in about 100ft of tube.
  • Tube Depth
    • Place the tube at least 8 feet below the surface of the earth.
    • Slope the tube at a 2% grade
    • Allow a drain at the bottom...with one-way material.
  • Tube Material
    • Studies have shown that any material is just as good at transferring the temperature.
    • Avoid materials with ridges that may hold water.
    • Select tubing that is rigid so there are not any dips to trap water.
    • Select a material that has a long life and has a low chance of fracturing.
    • Avoid water leaks.
  • Tube Location
    • Place the tube in the backyard of the Green Garage because the area is shaded, moist and clay soil.
    • Locate 3 feet away from any buildings.
  • Inlets
    • Provide an inlet with a screen to keep bugs and small animals out of the tube.
    • Provide a secondary inlet near the building to bypass the earth tube when needed or the ambient air is preferred (e.g. Air temp is 65 degrees and the ground is 50 degrees in the spring.)
  • Construction Recommendations
    • Tamp the clay soil firmly around the tube to eliminate all air pockets.
  • Avoiding Mold / Bacteria
    • Slope the tube
    • No ridges in tube


I have seen one and built one at the residential scale of construction. Factors to consider include the soil moisture content as mentioned by others because this significantly affects the thermal conductivity of the soil, heat load, and other similar engineering concerns. The temperature difference between the soil and the surface is a function of the depth, both in the magnitude and the time lag compared to the surface temperature. I suggest you look at some reference materials on earth sheltered construction for more detail on this, but at 30' (9m) depth, the time lag is typically 6-months and the delta-T over the year is close to 1-deg C.

Practical concerns are: Introduction of toxins, unwanted odors, etc. from the soil (so probably a lined earrth tube is better). Control of water condensation during humid warmer weather along with the probability of mold growth if water is standing (continuous slope to appropriate type of drain). Ability to clean if needed. Protection from entry of unwanted animals, insects, etc. And, preservation of the air entrance location from damage or removal by people in the future who may not know its purpose.

My empirical one was with 10" dia (254 cm) PVC pipe with rubber gasket joints so it would remain flexible in the soil (SDR-35 in the USA), encased in compacted clay about 5' (1.6m) below the surface, 80' (26m) long. It started outside with an above-ground vent in the corner of the building, insulated from it, ran out into the yard where it turned and came back under the basement floor, and ended inside by connecting to the return air plenum of the central heating and cooling unit. Thus, whenever the air was being circulated in the building, there was a mild positive pressure equal to the pressure loss due to friction in the return air system. All air leakage points in the building were therefore exfiltration only. All exhaust fans had a generous source of earth tempered fresh air into the building. The low point in the earth tube had a small drain pipe attached, which went to a nearby sump pump pit.

Thre are many methods of passively heating or cooling buildings, but the local climate you have will be the biggest concern in deciding which one(s) to use. Best wishes in your work. Contact me, if you want at jmueller245@yahoo.com.

John Mueller, Kansas City, USA