Earth cooling tubes or earth warming tubes (also known as ground-coupled heat exchangers) utilize the earth's near constant subterranean temperature to warm or cool air for residential, agricultural or industrial uses. They are often a viable and economical alternative to conventional heating, cooling or heat pump systems since there are no compressors, chemicals or burners and only blowers are required to move the air.
Most systems are usually constructed from 100 to 600mm (4 to 24 inch) diameter, smooth-walled (so they do not easily trap condensation moisture and mold), rigid or semi-rigid plastic, plastic-coated metal pipes or plastic pipes coated with inner antimicrobial layers, buried 1.5 to 3m (6 to 10 feet) underground where the ambient Earth temperature is typically 10 to 23 °C (50-73 °F ) all year round in the temperate latitudes where most humans live. Smaller diameter tubes require more energy to move the air and have less Earth contact surface area. The higher the ambient temperature of the Earth, the less effective they are for cooling and dehumidification.
Whether using Earth tubes with or without antimicrobial material, it is EXTREMELY IMPORTANT that the underground cooling tube have an excellent condensation drain and be installed at a 2-3 degree grade to ensure the constant removal of condensed water from the tubes. When implementing in a house without a basement on a flat lot, an external condensation tower can be installed at a depth lower than where the tube enters into the house and at a point closes to the wall entry. The condensation tower installation requires the added use of a condensate pump in which to remove the water from the tower. For installations in houses with basements, the pipes are graded so that the condensation drain located within the house is at the lowest point. In either installation, the tube MUST continually slope towards either the condensation tower or the condensation drain. The inner surface of the tube, including all joints must be smooth in which to aid in the flow and removal of condensate. Corrugated or ribbed tubes and rough interior joints must not be used. Joints connecting the tubes together must be tight enough to prevent water or gas infiltration. In certain geographic areas, it is important that the joints prevent Radon gas infiltration. Porous materials like uncoated concrete tubes cannot be used. Ideally, Earth Tubes with antimicrobial inner layers should be used in installations in which to inhibit the potential growth of molds and bacteria within the tubes.
Earth cooling tubes vary widely depending on the location latitude, altitude, ambient Earth temperature, climatic temperature-and-relative-humidity extremes, solar radiation, tube diameter / length / depth, soil type (thermal conductivity), soil moisture content and the efficiency of the building's exterior envelope design / insulation. Generally, dry-and-low-density soil with little or no ground shade will yield the least benefit, while dense damp soil with considerable shade should perform well. A slow drip watering system may improve thermalperformance. Damp soil in contact with the cooling tube conducts heat more efficiently than dry soil.
In the context of today's diminishing fossil fuel reserves, increasing electrical costs, air pollution and global warming, properly-designed earth cooling tubes offer a sustainable alternative to reduce or eliminate the need for conventional compressor-based air conditioning systems, in non-tropical climates. They also provide the added benefit of controlled, filtered, temperate fresh air intake, which is especially valuable in tight, well-weatherized, efficient building envelopes.
