Cooling Tubes

A metre or two below the surface the ground barely notices the weather. It stays cooler than the summer air above it and warmer than the winter air, because a change at the surface takes months to reach that depth. A cooling tube uses that steadiness: outside air is pulled along a pipe buried down there and arrives at the building already part-conditioned, with no compressor. The air only moves toward the temperature of the soil and never past it, so the result is tempered air rather than comfort.

Two things set how much it delivers: how deep the pipe sits and how long the run is. Depth is usually decided by the machine on hand - a walk-behind trencher may reach only 0.8 to 0.9 m (2.5 to 3 ft) where a backhoe reaches 1.8 m (6 ft), and the shallower run sits in ground that still follows the weather. Documented installations use 10 and 15 cm (4 and 6 in) pipe over about 20 m (65 ft) of buried run, sized to change roughly half the building's air each hour. No published practice standard covers it. The tube moves nothing by itself: a high opening above it or a small fan has to pull air through, and any pipe that comes back above ground wants insulating or it gives back what the soil just took.

Because the incoming air is cooled past the point where its moisture condenses, water forms inside the pipe. The run has to fall to a low point that can be pumped out, or the fresh air supply sits above a puddle nobody can reach once the trench is filled. The same suction that draws air along the pipe can also pull soil gas in through a joint, so solid pipe and watertight joints are used rather than perforated ones, the ground is tested for radon before anything is buried, and the tube is never the only way air enters the building. Upkeep is pumping out that low point and keeping the intake covered against rain and pests.