Civil Engineering Reference
In-Depth Information
processes, the excess thermal energy that is available from these systems can be
effectively stored during specific time periods of the design day operations.
Precisely, the cooling or the heating energy demand in buildings can be shifted
from the on-peak to the part-load conditions; thereby the levelling of the load
demand is achieved in a much efficient way. The storing of the useful energy in a
particular operating period (part-load conditions) of the cooling/heating system and
retrieving back the same amount of energy at a later time period (on-peak conditions)
gives rise to the well-established concept of the thermal energy storage (TES).
Thermal energy can be stored as a change in internal energy of a material in the
form of sensible heat, latent heat and thermochemical or combination of these. The
TES systems can be sensible heat storage (SHS) or latent heat storage (LHS) or
combination of both. In the SHS, the temperature of the storage material increases
as the energy is stored, while the LHS makes use of the energy stored when a
substance changes from one phase to another. Thermochemical energy storage also
forms a part of the TES, wherein the heat energy can be stored and released by
virtue of the reversible chemical reactions occurring between two or more reactive
components or materials.
TES systems are more suitable for buildings requiring refurbishment, wherein
they can act as an interface between different building elements or components for
conserving the useful energy being spent on cooling/heating requirements. Ther-
mal energy can be stored as part of the building structures as well as in a separate
enclosure, which purely depends on the method of cooling/heating being provided
in the existing building envelope. For instance, TES systems can be incorporated
in the fabric elements such as bricks, concrete wall, ceiling and floor slab com-
ponents, roof structures, glazing and so on.
The TES systems are basically classified into two broad segments, namely, the
passive and the active TES systems. In the passive TES systems, the heat energy is
stored and retrieved by the heat interactions between the heat storage elements of
the building and the indoor air or the ambient air, without the aid of any mechanical
equipment like fans, blowers, pumps, etc. On the other hand, the active TES
systems utilize the mechanical assistance of equipments to transfer the heat and to
store or release the thermal energy based on the fluctuating load demand in
buildings.
The other forms of TES systems includes the diurnal, short-term and long-term
storage, which basically depends upon the thermal load demand persisting in the
building as well as on the type and availability of the energy source. The diurnal
and short-term TES systems are preferred for sharing the energy requirements
between the TES system and the cooling/heating system only for a short duration
of time, the thermal load peaks would occur in the conditioned spaces.
On the other hand, the long-term storage systems makes use of the seasonal
conditions for capturing and releasing the thermal energy, depending upon the heat
load conditions existing in buildings. In short, the seasonal TES systems utilize the
heat energy from the environment or from other renewable energy sources (e.g.
solar energy) for storing during one season and retrieving it back during the other
seasonal condition.
