Civil Engineering Reference
In-Depth Information
This system is expected to accomplish a storage density of 124 and 100 kWh/m
3
for heating and cooling applications, with the COP for the former and latter of
0.9 and 0.8, respectively.
4.9.3 Closed Absorption Energy Storage System
The solar-based seasonal heat energy storage system operating with the closed
absorption concept was studied by the EMPA (Swiss Federal Laboratories for
Materials Testing and Research in Switzerland) in 2006 (N'Tsoukpoe et al.
2009
).
The prototype of this system is intended for heat storage on a long-term basis using
the seasonal thermal energy source. The absorbent utilized in this system is the
commonly known caustic soda or sodium hydroxide (NaOH), and the water acts as
the sorbate.
The working principle of this system is much similar to the closed adsorption
system, wherein during the charging process, the solar heat is directly supplied to
the regenerator containing the low-concentration solution (usually the NaOH
solution). This heat input drives off the water content from the solution (desorption
phase), thereby enabling the caustic soda to be concentrated for further utilization
in the discharging cycle.
The water vapour thus generated is transferred into the condenser, where it gets
cooled and condensed, and the condensate water as obtained is stored separately in
the sorbate storage tank. The excess heat is routed to the ground heat exchanger for
further utilization in winter season.
During the discharging cycle, by utilizing the low-temperature heat source from
the ground heat exchanger, the stored water is evaporated from the storage tank.
The water vapour thus obtained is absorbed by the concentrated caustic soda lye in
the absorber tank, and the stored heat energy is thus retrieved back.
Furthermore, the evaluation of this system for a single-family home in accor-
dance with the passive house standard of 120 m
2
, heating demand of 15 kWh/m
2
at 35 C, domestic hot water requirement of 50 l/day (approx.) at 60 C and
evaporator temperature of 5 C yields a total storage volume of 7 m
3
. This value
includes the tanks and heat exchangers.
With this system, the maximum absorber temperature of 95 C was attained,
and the lowest temperature at the condenser was about 13 C. These operating
temperatures correspond to the 62 wt% concentration of the lye, which is 7 %
higher than that was expected.
4.9.4 Thermo-Chemical Accumulator Energy Storage System
The importance of amalgamating the absorption storage and solar technologies
with reduced system discrepancies has been achieved by the Solar Energy
Research Centre, Sweden (SERC), and their industrial partner ClimateWell AB.
This system is developed for catering the cooling requirements in buildings
