Up Here - Explore Canada's Far North; January/February 2008

They line the Hudson Bay Railway to Churchill, Manitoba, flank the NWT Legislative Assembly building in Yellowknife, and were the first thing installed during the construction of Iqaluit's new Anglican church. They're thermosyphons - and they're uniquely Northern devices.

A thermosyphon's job is to keep permafrost frozen. Ingeniously self-powered, they're tubes imbedded in the Earth and filled with pressurized carbon dioxide that's liquid at Northern winter air temperatures.  For much of the winter, permafrost is actually warmer than the air above it, and thermosyphons are designed to make use of the difference, drawing warmth out of the ground until it's chilly enough to survive the summer without melting. 

The pool of CO2 at the bottom of the tube absorbs heat from the permafrost until it boils - at temperatures still well below freezing. The resultant vapour rises to the top of the tube, where cooling fins allow the heat to escape into the air. Sufficiently cooled, the CO2 condenses to liquid again dripping back down into the pool.

Anchorage, Alaska's Arctic Foundations is North America's largest manufacturer, making up to 800 thermosyphons a year. "If you build without them in thaw-unstable permafrost, the middle of your floor will start to settle in late winter. Then it'll just keep going down and down," says chief engineer Ed Yarmak. "I've walked into aircraft hangars where, standing at the door, my eye is level with the Cessna wings." As global warming looms, engineers design more conservatively, adding more and bigger thermosyphons. 

uphere1.gif COOL DEVICE: Inserted vertically in the ground, tubular thermosyphons contain liquid carbon dioxide at the bottom. The CO2 absorbs permafrost menacing warmth from the ground, turns to gas, rises up the tube, and offjets the heat into the atmosphere. It then cools, re-liquifies, and drips down the tube - ad infinitum.

 Written by Jessa Sinclair