buildings. Most structures built in Iqaluit are set on deep
pilings – not just for stability, but also to prevent snowdrifts
building up at the base and to avoid melting permafrost
underneath by transferring the heat of the building. Ingenious
methods for keeping permafrost frozen have been employed
since the 1960s, Gesret says, including refrigerated thermopiling
driven through the permafrost; the most common
system in the northern territory.
“But a building has to be slightly above ground, and
energy is lost through that void,” he said. Instead, for the
Iqaluit Airport project, Bouygues worked with Arctic
Foundations of Canada Inc., “One of very few companies
in the world doing this type of work,” to design, build and
install a passive thermosyphon system embedded in aggregate
to form a barrier between the heat of the building and the
coldness of the frozen permafrost, like “a big mattress floating
or sitting on ice.”
Thermosyphons and thermo-piling use the same principle
of two-phase passive cooling with high-pressure liquified
carbon dioxide (CO2) as the refrigerant. As CO2 has such a
low boiling point, any time the underslab temperature is
warmer than the outside temperature, even to a fraction of
a degree, that heat causes the CO2 to boil and turn into a
vapour that rises through the piping, either into radiators
PROJECT SPOTLIGHT
THERMOSYPHON
TECHNOLOGIES
Three separate applications of thermosyphon technologies
have been used in Canada for more than 35 years – the flat loop
system used under slabs such as the Iqaluit Airport buildings, a
sloped design most often used for installations such as frozencore
dams and large retention walls or to retrofit buildings that
have experienced settlement issues, and load-bearing “thermopiles”
that contain compressed liquid CO2 refrigeration systems
right in their piping. Thermopiling and thermo-helical piling are
now widely used in Alaska to augment or replace traditional
piling, according to Justin Panagapko of Arctic Foundations.
While thermopiles are more expensive per unit than traditional
piles, third-party engineering studies indicate that they can
lower overall construction costs, according to Panagapko.
“Say an engineering requirement for conventional piling comes
out at a 30 metre-depth to get the adfreeze friction required to
support the structure – a refrigerated piling system might only
require 15 metres or 12 metres of piling depth, reducing the drilling
cost as well as the installation time,” he said. Thermopiles can be
especially advantageous where freezing points and freezeback
temperatures are lower, such as in-shore communities with
alkaline ground conditions, he said, “especially in warm regions
like the Mackenzie Valley Delta and the coastal regions in the
northeast, where we’ve seen a lot higher warming rates than in
other areas of the Arctic.”
All the specialized components are premanufactured and
precharged with refrigerant in-house at Arctic Foundations of
Canada’s manufacturing plant in Elie, Man., then supervision and
construction crews go to the site to oversee their installation
with the drilling contractor.
“It’s a very sleek design,” said Panagapko, similar to a standard
pile except for ¼-inch-thick steel rings just above ground level
up to the underside of the grade beam. A surface area in the air
space that allows for radiation cooling and the CO2 phase change.
“A standard rig drills an open hole, the pile is installed and
backfilled with a sand slurry that creates a constant surface-area
contact in the annulus between the hole and the pile,” ready for
the building’s structure to be put right on top of that, he said.
JAKKREE THAMPITAKKULL / 123RF
Thermosyphon radiators at Iqaluit International Airport
ARCTIC FOUNDATIONS OF CANADA
50 Q3 2019 www.pilingcanada.ca
/www.pilingcanada.ca
