Page 150 - Analysis and Design of Energy Geostructures

122 Analysis and Design of Energy Geostructures

sand, assuming it is fully saturated with water. Comment on the results and on
the impact of the different values of λ on the heat exchange characterising an
adjacent energy pile.
n. Calculate the effective thermal conductivity, λ, of a saturated clay characterised by
a porosity n 5 0:42 and a value of thermal conductivity of solid particles

λ s 5 0:15 W/(m C). Compare the value of thermal conductivity with that calcu-
lated above for the saturated sand. In which condition is heat exchange favourable
for an adjacent energy geostructure?
o. Which is the typical range of values of thermal conductivity for concrete?
p. Describe the two mechanisms characterising the convection heat transfer mode.
q. Discuss the difference between forced and natural convection.
r. What is radiation and which are its units?
s. What is the emissivity?
t. Which is the principal heat transfer mode that characterises the heat exchange in
the pipes of energy geostructures?
u. Which is the principal heat transfer mode that characterises the heat exchange
between the pipes and the reinforced concrete of energy geostructures?
v. Consider the case of an energy pile socketed in a uniform soil deposit charac-
terised by negligible groundwater flow. What are the main heat transfer modes
that occur when the pile is in function, neglecting the phenomena that may occur
at the ground surface?
w. Consider an energy pile socketed in a given soil deposit and connected to a rein-
forced concrete base slab of underground car parking. Assume that no thermal
insulation has been foreseen for the slab. Describe the heat transfer phenomena
occurring in the problem.
x. Consider a generic energy pile. Why are the first metres of pipes beyond the sur-
face thermally insulated? Which are the main effects of radiation on this kind of
system and, in general, of the seasonal weather changes?
y. Consider a dry sandy soil deposit. Which are the main heat transfer modes that
occur? What about a saturated soil layer with significant groundwater flow?
z. An underground metro station energy wall is thermally insulated from the sur-
rounding soil fully saturated with water, so that the heat exchange characterising
the wall predominantly occurs between the pipes embedded in the geostructure,
the grouting material and the metro station environment. Describe the heat trans-
fer phenomena occurring in the problem. What happens if no insulation may be
foreseen between the wall and the soil?
aa. Consider the following form of the Fourier heat conduction equation:

2 @T
λr T 1 _q 5 ρc p
v
@t