Page 93 - Analysis and Design of Energy Geostructures

Energy geostructures 63

m. When an energy geostructure is cooled as a consequence of its geothermal opera-
tion, the building is:
i. Cooled
ii. Heated
iii. Heated and cooled
iv. None of the above
n. Describe the rationale of using heat pumps or reversed heat pumps, and the com-
ponents of basic heat pumps.
o. Define mathematically the coefficient of performance and specify the meaning
and unit measure of each factor involved in this definition. What does the coeffi-
cient of performance physically represent?
p. How is the seasonal factor of performance defined and in which situations may its
use be more convenient than resorting to the coefficient of performance?

Solutions

a. To couple the role of the structural support with that of the geothermal
heat exchanger. Conventional geostructures serve only for the former
role.
b. The purposes of the heat exchange that can be established with energy
geostructure consists of (i) heating and cooling superstructures to
reach comfort levels in the built environment; (ii) contributing to the
production of hot water for anthropogenic, agricultural or tank-
farming uses; (iii) providing heat to prevent the icing of pavements
and decks of infrastructures such as roads, bridges, station platforms
and airport runways; and (iv) storing the heat in the subsurface for a
successive use.
c. Energy geostructures are typically made of reinforced concrete. Pipes are
fixed along their reinforcing cage or are placed within the filling material.
Pipes are usually made of high-density polyethylene and characterised by
a diameter of 20 40 mm with a wall thickness of 2 4 mm. Two or more
pipe loops can be installed in series or in parallel and fluid is used as a
thermal energy carrier. The heat carrier fluid usually consists of water,
water with antifreeze (glycol) or a saline solution.
d. Examples of pipe configurations for energy piles include the single
U-shaped, bent U-shaped, parallel double U-shaped, series double
U-shaped, multi U-shaped, indirect double, W-shaped, spiral (or helix)
and coaxial pipe configurations.