Civil Engineering Reference
In-Depth Information
The borehole structures are integrated to the building through the heat
exchanger hydronic networks, which can be either an open-loop or a closed-loop
configuration. In the open-loop configuration, the cold or heat energy being
extracted from the underground through the heat transfer fluid (mostly under-
ground water) is transferred to the indoor heat exchanger. The warm or cold water
from the heat exchanger is routed back to the underground through the same
borehole structure.
The water that is used for energy extraction is discharged into the underground
and is not reused again for the next cycle of system operation. On the other hand,
the closed-loop system utilize the brine solution (glycol or antifreeze) as heat
transfer medium for extracting the heat energy from the underground, by which the
overall thermal performance and heat exchange efficiency of the BTES system can
be enhanced.
The heat transfer fluid remains always inside the system and can be reused for
several thousand repeated thermal cycles. The BTES system with more borehole
structures has a higher TES performance and heat transfer output.
The closed-loop BTES systems can be further classified into horizontal, vertical
and slinky loop systems. These systems still offers a much better heat storage
performance when compared to the ATES systems. For high-temperature thermal
storage, the heat energy captured by efficient solar collectors can be stored in the
ground during sun brilliance conditions (especially hot summer days).
During winter seasons, the stored heat energy can be retrieved back from the
ground and supplied to the indoor environment, which offsets the net heating
demand and heating losses in buildings. Thus, the BTES systems, like the ATES
systems, are much favourable enough to store and release the thermal energy,
based on the load requirements in buildings on a seasonal manner.
However, the initial capital costs involved in drilling boreholes of considerable
depth, the thermal disturbances in hydrogeological structures and heat imbalances
taking place in the underground thermal masses can collectively accentuate their
consideration to the low- and medium-temperature-profile building cooling and
heating applications.
4.3 Earth-to-Air Thermal Energy Storage
The earth-to-air type of thermal storage system is relatively preferred for small
residential and commercial buildings, where the temperature of earth is stable at
specific depth from the surface of the ground. The earth-to-air energy storage
system comprises of an array of plastic pipes or a single lengthy pipe, room
air-handling unit or heat exchanger with necessary accessories. The functioning of
this system takes place by energizing (charging) the earth soil material by the
buried tubes at a depth of 3-4 m beneath the ground level.
During summer season, the outdoor cold air either at night-time or early morning
period is directly fed into the room for accomplishing free cooling. In daytime, the
