March/April 2024 - 113
A regular column showcasing successful
best practices for sustainable foundations
FOUNDATIONS FOR A SUSTAINABLE FUTURE
Deep Foundations BOGO
The previous edition of this column
used the amended commercial slogan
" building green is saving green " as the
theme. As I wrote that column, I also
thought of another sales promotion,
usually referred to by its acronym
BOGO (buy one get one), which is a great
way to describe energy foundations.
Geothermal energy - that is energy
obtained from the heat generated by the
earth - is nothing new: the ancient
Romans used it 2,000 years ago for space
heating. Today it is still used, and in the
U.S. close to 4 gigawatts are generated,
according to the International Energy
Agency, mostly in California and Nevada
and enough to cover the energy use of
more than 3 million homes. At the same
time this is just a mere fraction (less
than 1%) of the potential geothermal
energy in the U.S.
A common way to capture this
source of energy is through geothermal
boreholes: vertical holes, generally between
0.125-0.2 m (5-8 in) in diameter,
with a high-density poly-ethylene
(HDPE) thermal loop installed after
drilling and before filling the hole with
grout (usually a water, sand and
bentonite mixture). If we assume an
0.2 m (8 in) diameter borehole that is
100 m (330 ft) deep, the geothermal
energy generated could easily be 3,500
watts or slightly more than 30 MW,
equivalent to the energy use of approximately
three homes.
But the same can be achieved in an
even more sustainable manner, by
installing a thermal loop in a foundation,
at little extra cost, to turn a
foundation into an energy foundation
and to eliminate the need to install a
geothermal borehole. This way, the
AUTHORS Gerald Verbeek, Allnamics USA
DEEP FOUNDATIONS * MAR/APR 2024 * 113
foundation gets an additional function.
Not only does it support the superstructure,
but it also generates energy
that can be used to cool or heat that
superstructure (in other words, you buy
one function and get the second
function at minimal cost).
Using the geothermal borehole
described above as a starting point, the
same geothermal energy can be generated
by converting four 0.6 m (24 in)
diameter drilled shafts with a length
of 25 m (82 ft). And converting these
four shafts will actually cost less than
the construction of the geothermal
borehole.
While an energy foundation may
not be the right solution for every
project, each project team should at
least consider whether an energy
foundation makes sense for its project.
It might just be that they can take advantage
of the BOGO opportunity
and in doing so increase the
use of the geothermal energy.
Geothermal loops installed
within foundations
Geothermal loop installation in a pile
March/April 2024
Table of Contents for the Digital Edition of March/April 2024
TOC
March/April 2024 - Intro
March/April 2024 - 1
March/April 2024 - 2
March/April 2024 - TOC
March/April 2024 - 4
March/April 2024 - 5
March/April 2024 - 6
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