Page 65 - European Energy Innovation - Summer 2016 publication

Summer 2016 European Energy Innovation 65
systems, energy thermoactive
geostructures or energy geostructures
are recently experiencing exponential
growth. This category includes all the
ground-embedded structures, such as
tunnels, anchors and linings, shallow
foundations, piles and diaphragm walls,
used to exchange heat with the ground.
In general, a geotechnical structure can
be thermally activated by embedding
polyethylene pipes in its concrete
body. The fluid flowing in the pipes
constitutes the means to transfer heat
from the ground to the buildings or
vice versa thanks to heat pumps.
Since the beginning of the 1980s,
geothermal energy has been
increasingly obtained from foundation
elements, at first from base slabs,
then from piles, diaphragm walls and
tunnels. Energy geostructures have
been increasingly constructed in
Europe. The design of these energy
systems is inherently interdisciplinary
and involves geology, hydrogeology,
geotechnical engineering and
thermal engineering. A vast amount
of information across several fields
is needed for a successful design:
thermal, mechanical and hydraulic
properties of the soil, as well as
the concrete, assessment of local
atmospheric conditions, definition
of the operating system thermal
action, and overall energy demand
for the building or the facility to be
conditioned. Integration of all these
aspects is required to optimize the
system performance.
The energy efficiency performance
of these systems depends on the
exchange mode between the ground
and the thermoactive geostructure.
Currently, heat exchange is estimated
based on operating assumptions,
but accurate modelling needs to
be substantially improved to allow
a precise calculation. The thermo-
mechanical effects also need to be
assessed in order to ensure system
operation without affecting safety and
functionality. Indeed, due to expansion
and contraction of the thermoactive
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GEOTHERMAL ENERGY
Working principles
of energy piles
Heat
pump
Heat
exchanger
piles
geostructures induced by temperature The disparities highlight the need
variations, structural aspects should be to synthesize research and practice-
to be considered as well. based knowledge from across national
and disciplinary boundaries in order
Despite the significant number of develop better understanding
operating energy geostructures in and more widespread use of this
Europe, the development of specific technology. In the future, the deeper
design rules and dimensioning understanding of heat exchanges in
approaches has been slow. Attempts the ground and their application to a
to provide a set of recommendations wide range of geotechnical structures
for piles subjected to temperature can improve this technology for more
variations were carried out starting from efficient and streamlined application.
2005 in Switzerland, Germany, United One of the critical contributions
Kingdom and France. However, most expected is a better methodology to
of this documentation provides only assess interaction among multiple
general indications and does not allow thermoactive geostructures within
the adoption of this technology across urban districts. City managers
Europe for a wider range of projects. need methods to predict the effect
An international comprehensive of multiple systems operating
document addressing in detail concurrently to minimize interferences
the mechanical design of energy and provide a planning guidance for
geostructures is much needed. permitting purposes. It is expected
that the COST Action GABI will foster
The heterogeneous development the development of thermoactive
of applications and research on geostructures and will be a big step
thermoactive geostructures in towards future market development
European countries is the main and widespread usage of this
reason to launch a COST Action. innovative technology. l
OTHER INFORMATION
COST Association web page: http://www.cost.eu/COST_Actions/tud/TU1405
COST GABI web page: http://www.foundationgeotherm.org
LinkedIn address: https://www.linkedin.com/in/gabi-cost-action-69aa26100
Facebook address: https://www.facebook.com/GABITU1405