Page 67 - Analysis and Design of Energy Geostructures

Energy geostructures 37

heat pumps can be employed. These machines are not present in all applications and
when heating or cooling functional modes are targeted without them, the resulting
energy geostructure operations are called ‘free heating’ or ‘free cooling’ (or geocool-
ing), respectively. The need to use heat pumps or reversed heat pumps depends on
the significance of the temperature difference between the primary circuit (i.e. the
ground) and the secondary circuit (i.e. the built environment). In fact the temperature
difference between the two circuits makes the heat exchange between them more or
less favourable.
The operation of ground source heat pump systems can involve sufficiently
high and low temperature levels for the heating and cooling of built environ-
ments, respectively, but also insufficient temperature levels for the same purposes.
When the temperature level in the ground is sufficient for the aforementioned
purposes, heat pumps or reversed heat pumps are not needed and ‘free’ operations
can be achieved. Otherwise, heat pumps or reversed heat pumps are employed to
increase and decrease the temperature level (and associated energy input), respec-
tively, in those cases in which the heat originally exchanged with the ground may
not be sufficient for heating or cooling purposes. In other words heat pumps or
reversed heat pumps allow overcoming the apparent restriction involved with the
use of a cooler ground to heat built environments or a warmer ground to cool
built environments, respectively. The reason for this is that the quoted situations
defy the second law of thermodynamics, for which heat flows from hot to cold,
if left to itself (Narsilio et al., 2014). Typically heat pumps are employed to raise

the temperature level from 10 C 15 Cto40 C 45 C for the heating of
superstructures.
It is worth noting that, even though the term free is used for operations that do
not employ heat pumps or reversed heat pumps, pumping machines using electrical
energy are required to transfer the thermal energy from the ground to the superstruc-
ture or the opposite. Fig. 2.8 presents a schematic of a typical ground source heat
pump system for the heating of a superstructure.

2.4.2 The primary circuit

Heat exchange between the ground and energy geostructures occurs via the heat car-
rier fluid circulating in the pipes embedded in such geostructures (i.e. the ground heat
exchangers) and allows exploiting the large thermal storage capabilities of the ground
for heating and cooling purposes.
One or more header and manifold blocks are generally present to collect all the
pipes arising from the energy geostructure(s). Resilience of these systems is fundamen-
tal. Hence, submanifolds are generally employed to affect only a minor portion of the
energy geostructure system if there are any problems related to the installation or