Page 56 - Analysis and Design of Energy Geostructures

26 Analysis and Design of Energy Geostructures

2.2 The energy geostructure technology
2.2.1 Roles of energy geostructures
Energy geostructures, more properly defined from a theoretical perspective as thermo-
active geostructures, are an innovative, multifunctional technology that can be used
for energy transfer applications as well as for providing structural support to any type
of built environment. This technology includes all ground-embedded structures that
can be used as structural supports while exchanging heat with the ground. Similar to
other shallow geothermal systems, energy geostructures deal with low enthalpy and
take advantage of the relatively constant temperature field in the shallow subsurface
throughout the year for their heat exchanger role (Batini et al., 2015).
Energy geostructures can involve deep foundations (e.g. piles, piers and barrettes),
earth retaining structures (e.g. diaphragm walls and sheet pile walls), shallow founda-
tions (e.g. footings, base slabs), tunnel linings and anchors. Deep foundations enable
massive constructions to be supported with a limited use of subsurface, such an aspect
representing a great advantage in dense urban areas compared, for example, to shallow
foundations. Earth retaining structures can be used to generate useful space for human
activity below the underground. Tunnels are typically used to contribute to transpor-
tation in the underground. In this framework, the geostructures resulting from cou-
pled energy transfer and structural support purposes are so-called energy piles, energy
walls, energy slabs, energy tunnels, etc. (cf. Fig. 2.1).
There are various purposes of the heat exchange that can be established with
energy geostructures. These purposes can consist of (1) heating and cooling superstruc-
tures to reach comfort levels in the built environment, (2) contributing to the produc-
tion of hot water for anthropogenic, agricultural or tank-farming uses, (3) providing
heat to prevent the icing of pavements and decks of structures and infrastructures such
as roads, bridges, station platforms and airport runways and (4) storing heat in the sub-
surface for a successive use.
The use of energy geostructures for heating and cooling superstructures to reach
comfort levels in the built environment can be achieved with the broadest range of
energy geostructures, such as energy piles, energy walls, energy slabs and energy tun-
nels (the latter located close e.g. within 400 600 m to the superstructure they
supply with thermal energy).
The use of energy geostructures for contributing to the production of hot water
for anthropogenic purposes can nowadays be achieved via the lower temperature levels

needed for this aim (e.g. 45 C 55 C) compared to those needed in constructions

built during the 20th century to a few decades ago (e.g. 75 C 85 C). Typical energy

geostructures that can be employed for this purpose, as well as for contributing to the
production of hot water for agricultural or tank-farming purposes, are energy piles
and energy walls, but also energy tunnels located in the vicinity of agricultural or