Difference between revisions of "Earth Tubes"

Revision as of 10:20, 27 May 2009

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What is It?

• A brief description of what it is.
• If it is part of a system-level pattern put a link to it in here.

Why is it Important?

Describe how it:

• strengthen our relationship to the earth...all are connected (sun, wind, water, plants and animals)
• helps restore the planet's eco-systems (plant, animal, water, air)
• builds strong communities.
• creates equal economic opportunities and energy.
• creates One Earth patterns of living

When to Use It?

• Need available land to hold the length of tubes.
• Avoid areas with high water tables.
• Best where there are extreme highs and lows. The high difference between the ambient temperatures and the indoor temperatures create the best opportunity for the earth tubes to produce better results.

Green Garage Example

Sustainability Goals

The sustainability goals for the Green Garage Earth Tubes are:

• Promotes a stronger connection with the earth. "The earth warms our air in the winter and cools it in the summer...naturally."
• Output temperatures: Winter = 40F; Summer = 70F
• Dehumidification: Output Summer RH 60%
• Air Volume: 800cfm. Commercial building code requirement for air exchange for 40 people.
• Air Quality the same as ambient air
• Easy to maintain

Strategy and Conceptual Design

• 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.
    • Temp of earth in Detroit MI is approx 50F at 30ft.
    • At 8' below the surface the soil temp will vary approximate +/- 10F.
    • At 8' the earth low temp will be in late March and high temp in late Sept.
  • Slope the tube at a 2% grade
  • Allow a drain at the bottom...with one-way material.

• Tube Material
  • General Guidelines
    • Surprisingly the material of tubes matter little, as long as they are not insulated. This is because the thickness of the material absorbing the heat is actually the tube plus the ground around the tube. When this is put in the thermal equations, the thickness of the tube is such a small part of the whole area of absorbtion that it's conductance doesn't amount to much.
    • Avoid materials with ridges that may hold water without drainage approach. If it has ridges...it will need drains.
    • Select tubing that is rigid so there are not any dips to trap water. If it is flexible it will need drains.
    • Select a material that has a long life and has a low chance of fracturing or corroding.
    • Allow water to only pass out of the tubes, but not in.
  • Green Garage
    • Two Options
      • Black Rigid tubing
        • Positives: simple, cheap, available, no seams, can't break, flexible, won't corrode, creates air turbulence, high surface area, continuous drainage (cut at seam)
        • Negatives: high pressure loss, potential flooding from ground water
      • Concrete Pipe
        • Positives: medium price, available, higher conductivity
        • Negatives: Can fracture, seams could leak (could minimize), need to develop drainage approach, large-heavy pipe
• Tube Size
  • Use 3 - 10in diameter tubes (235 sq in...approx 1.63 sf results in air velocity = 8.2 ft/sec)

• Tube Location
  • Ideal area is shaded, moist and clay soil.
    • Place the tube in the backyard of the Green Garage because the
  • Locate 3 feet away from any buildings.

• Inlets
  • Provide an inlet with a screen/filter (.3 - .5 microns)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.)
  • Develop a manifold on each end...insulate the upper 4ft of the tube and the manifold.

• Construction Recommendations
  • Tamp the clay soil firmly around the tube to eliminate all air pockets.

• Drainage Design - to avoid mold / bacteria
  • "open to air" catch basins that have their bottom in the gravel drainage level.
  • Additionally drill down through the clay layer to provide a drain.
  • Slope the tube / drainage
  • Continuous drain

Proposed Materials / Suppliers

• Product Suppliers: Timewell Pipe, ADS Products...there are many more.

Related Internal Links

• Help people find other related Green Garage pages that may help them. Keep it tight.

Resources

• Provide valuable links to help make it easier for others to pursue this pattern.