Quote(s)..
"This drawing suggests a very compact arrangement. For example, if a 50 by 50 foot area of yard was involved (about 1/16 acre), nine parallel tubes (six feet apart, or 48 feet across all of them), and each 50 feet in functioning length as shown, a total of around 450 feet of functional tube length would dissipate house heat into the soil. You would probably need around double that amount of the sewer pipe, since they are "bundled" together on their way to and from the building, as the small cross sectional drawing shows. Our drawing does not show the three (or more) identical tubes above the top of the drawing This arrangement would represent a way of installing around 500 lineal feet of heat exchange surfaces in that fairly compact area (counting the bundles). Such a configuration makes sure that one or another of the tubes is within three feet of well over a million pounds of cool soil. (Simple engineering calculations show that that much soil represents over 10,000,000 Btus of cooling available!)"
"In case you're still skeptical, the "heat exchanger" arrangement we are describing has a coefficient U that is around 8 Btu/hr/square foot/°F difference. If you look at ONE of our nine tubes, its circumference is around one foot and it is 50 feet long, so its area is around 50 square feet. If the house air begins at 90°F and the deep soil temperature is 53°F, there is 37°F difference. Multiplying these (8 * 50 * 37) gives an effective rating of 14,800 Btu/hr. That's ONE of our tubes, and there are nine of them! This suggests that the total system is capable of about 135,000 Btu/hr cooling, around four times as much as the normal house requires! Well, it could (almost) actually do that for a few minutes, but there are a number of factors that would get it down below 100,000 Btu/hr of cooling in under an hour and within a few hours to the 36,000 Btu/hr that we designed our "standard configuration" for."
"There have been (many) other people who have said they intended to only install four tubes (mostly to save on the cost of digging the trenches) and they figured that was an "improvement". Note again that such an installation would likely only provide around 300 cfm of cooled air to the house. That is certainly enough to nicely cool two or three rooms, but not really enough airflow to give the comfort level that we spoiled Americans expect for a whole house!"
"There are many variables involved, but many installations should be able to use 4" plastic (thinwall) ABS or PVC drain/sewer pipe (called DWV), available at any local 'home' store."
