Earthtubing

a non-electric, passive geothermal
solar heating & solar cooling system

Earthtubing utilizes conventional, thin wall, plastic pipe to passive solar pre-heat your home's air intake. Fresh air enters a system of these pipes which are laid around the exterior and interior of your home's foundation. (Or even down the driveway!) You can let the air draft naturally through your earthtubes for a truly sustainable, non-electric, passive geothermal system or add fans and filters to supplement the home's back-up heating and cooling system. Be careful with Earthtube details, though ... while architects are warming-up to the idea, they are making very elementary mistakes, like using large concrete (cement) pipe that is impossible to clean.

Earth tubing (fresh air return tempering) is not suggested for low/zero energy, sustainable applications in humid climates where the designer is concerned about air quality. There have been numerous designs over the years that attempt to deal with the issues, but they invariably are forced to develop high-energy, mechanical systems to deal with lowering humidity and sterilize air prior to passage through the tempering earth tubes. Every low-tech passive energy system we have ever encountered fails to properly address the air quality issue. Hybrids tend to rely upon UV treatment of the air, which is sketchy, at best.

Conventional homes are typically High R value and "airtight", so all of the heating and cooling effect is stored within the air temperature (convection). If you let the air escape, you lose all your comfort.

"High thermal mass" building materials allow the heating and cooling effect to be stored within the home's walls and floor (radiant). This allows you to vent the inside air of an HTM without "losing" all your heating or air conditioning comfort. Constant venting in the winter is common to HTMs, with fresh air being pre-heated or pre-cooled before it enters the home.

Please note that Earthtubing is not meant as a summer cooling system in hot, humid climates where moisture would reach dewpoint and collect in the tubes. Weep holes are drilled in the bottom of corner fittings, but these drains can be quickly overwhelmed in a very humid climate. If you must alter your indoor climate in the summer for personal comfort level, you will need mechanical means. There really is no truly healthy passive method to de-humidify.

The Earth is like a "solar battery" absorbing nearly half of the sun's energy. The ground stays a relatively constant temperature throughout the seasons, providing a warm heat source in the winter and a cool heat sink in the summer.

The typical number of earthtubes is four, which is enough to supply average household air volume. One pipe is generally considered to carry enough air for one room. In theory, you could have as many earthtubes as you wish, but the slower the draw-time, the warmer the air moving through it (or cooler in the summer).

Cleaning earth tubes is an easy matter - simply lay nylon cord in the pipes while constructing and use it to pull a bleach or disinfecting solution soaked towel through the tubes. Tie a second cord to the towel so that you leave a cord in the pipes after the towel has been pulled through. We suggest installing a standard furnace filter at the earthtubing inlet grate to prevent dust and insects from entering the pipes. Keep in mind that mold only grows on surfaces with fuel to support it - clean pipes will not support mold growths. Many people worry about keeping the earth tubes clean, but you rarely see folks cleaning their home heating and cooling ducts.

Earth tubes are nothing more that air intake pipes - and round pipes are much, much easier to clean than rectangular duct work. Earthtubing is a very simple and cost-effective means to temper air intake for any home. They are especially important for high thermal mass homes, which can be very aggressively vented, ensuring quality indoor air (versus air-tight conventional construction).

Please note that earthtubing technology is not geothermal heat pumping. Earthtubes are sustainable, non-electric, passive heating and cooling systems. Unlike geothermal heat pumps, earthtubes do not involve any exotic machinery or special type of pipe that we are trying to sell you. In the picture at right, we have left the earthtubes exposed for better illustration (normally they are hidden in wall or floor). The two pipes seen at right (top of photo below log) are entering from outside. They drop down to the base of the frostwall and encircle the home giving fresh air plenty of time to warm up or cool down before it vents into the HTM. In the lower right corner shadows you?ll see the two grated pipes where air finally enters. These two pipes originated at the opposite end of the planterbed. Earthtubes are a very simple, low-tech system without any moving parts. Passive solar at its best. And see how well the Cannas are blooming in the middle of the winter.

The most important factor to successful earthtubing is DRY EARTH. Wet earth acts as a constant heat sink pulling energy away from your foundation walls. Dry earth under and around an HTM stores an amazing amount of energy. Earthtubes utilize this energy by allowing fresh, incoming ventilation air to passively gain or lose heat energy before it enters your home. This sustainable ventilation system exchanges indoor air more often, keeping your home's environment fresh without the drawback of "losing all that energy".

U-Bend Coils- in 3/4", 1", and 1 1/4" pipe sizes. SDR 11 and SDR 9
Pressure Ratings-SDR 11 (160 PSI at 73 Degrees F), SDR 9 (200 PSI at 73 Degrees F)

HDPE U-Bend Coils save installers precious field time fabricating u-bends which often require larger boreholes. HDPE U-bend coils contain a very tight 180 degree radius u-bend which is factory installed. The two pieces of pipe are fused to the u-bend and the pipe is neatly packaged into a configuration which can be easily uncoiled in the field. This ends the need for field fabrication of u-bends coils. The u-bends have a unique on piece molded design which contains a space for a vent hole. An anti-buoyancy wing tube can be fitted easily into the vent hole, which minimizes the possibility of a loop assembly "floating" out of the borehole. The vent port may also be used to connect weights, stiffeners, or other devices without risking damage or compromising performance.
 

Single HDPE Coils-we offer standard polyethylene pipe coils in 500' lengths in 3/4", 1", 1 1/4", and 2" in SDR 11 and SDR 9. Other coil lengths are available by special order.

HDPE Geothermal Piping System-Key Benefits

• Cost Efficient Installation- Easy to join, lightweight, and flexible to help reduce construction and installation costs.
• Tough and Durable- Excellent impact and abrasion resistance. Pressure ratings based on long term testing. Exceptional resistance to slow crack growth and environmental stress cracking.
• Ductile and Flexible- with a bending radius equal to approximately 20 times the diameter of the pipe, HDPE piping has the flexibility, that will make trench and downhole installation easy.
• Resistant to Chemicals and Corrosion- Excellent resistance to most chemical compounds and aggressive soils.
• Thermally Conductive- HDPE pipe offers high strength resin pipe material to minimize pipe wall thickness and maximize heat transfer.
• Leak-Tight Joining- Long continuous coils or straight lengths reduce joining requirements. Properly made heat fusion joints are as strong as the pipe itself and do not break.
• Superior Flow Characteristics- HDPE pipe offers high volume flows with low flow resistance. The hydraulically smooth, non-wetting surface provides excellent flow properties. A Hazen-Williams C-Factor of 150-155 is typically used to estimate flow resistance. HDPE pipe does not rust, rot, corrode, tuberculate, or support biological growth.
• Sequential Footage Markings- Coils contain footage marker indications every 2' to assist with proper depth setting in borehole installations.

# With any earth tube system, it is key to note: the earthtubes enter wherever and drop down to bottom of footers
# after entering, they encircle the interior of the frostwalls
# a small amount of slope in the earthtubes is not vital, but nice
# drill 1/8th inch "weep" holes in corners to drain condensation
# use 45's in the corners and not 90's to allow easier cleaning
# separate pipes by 4 inch minimum to ensure maximum energy transfer
# use thin wall SCH2729 four inch diameter sewer pipe (thinner than SDR35)
# drag several nylon cords through AFTER the glue sets with a wire fish
# cover inlets and outlets ALL THE TIME during installation to keep clean
# protect inlet and outlet grates from water/dust intrusion with furnace filters

Earth Loop Options:


Or just lay down in circles, or along the driveway, just keep in mind to keep separated by 4 inches. And lay them deep enough in the ground as to be below freeze line.

It is common to bring all earthtubes into the central utility room. Terminate the pipes in a small junction box, if you wish to filter the ventilation air and/or add a fan to power draft and/or use as fresh air intake for HVAC system. The junction box can be a simple wooden cabinet sized for the filter being used. We have seen "D" Boxes (like those used for septic systems) used to create a very effective interior junction/filter box. It is also possible to simply terminate the pipes in a wooden framed "wet" wall and install standard galvanized grate/vent duct box (cold air return) for each individual room.

The outlet ends of your earth tube vent pipes can be spread out around the home or clustered in a single room. Using tempered air tubes as the "cold air return" for boiler or furnace is common commercial construction practice.

A common upgrade to any earth tube system is powered venting to assist passive draft. Your home is constantly venting out through open windows, bathroom vents, furnace, water heater, dryer and range hood This air is coming in from somewhere - the earth tube pipes (cold air return system). Earth tubes can end in a central terminus box ("plenum") and be fan powered (air handler) or you can individually fan assist each earth tube pipe.

We commonly suggest installing a 4 inch axial fan (12 VDC computer cooling fan) in the end of each earth tube pipe and covering with a protective vent grate. Common computer fans fit nicely into a four inch pipe and can be run on a small solar panel, car battery, or just use a transformer (standard 110 volt AC).

A nice touch is pulling cheesecloth across pipe end for filtration and aromatherapy (drip oils onto cheesecloth).

For a good read: Home heating from the good Earth