Civil Engineering Reference
In-Depth Information
possible, and to reduce the risk of different thermal behaviours in each cubicle due
to slight variations in the thermal bridges, infiltrations, etc., that are inevitable in
the manual process of mounting a window.
Figure
9
and Table
3
present the results of the controlled temperature experi-
ments using a set point of 24 C for a week in August of 2008. The accumulated
energy consumption of the Reference cubicle is by large higher than all the other
cubicles, with about twice the consumption of the other cubicles. The RT27+PU
cubicle is the one with the lowest energy consumption while the SP25+Alveolar
cubicle is the second one, consuming even less energy than the PU cubicle.
Finally, the Alveolar cubicle is the one that consumes more energy after the
Reference cubicle.
Both PCM cubicles reduced the energy consumption compared with the same
cubicle without PCM. The RT27+PU cubicle achieved a reduction of 14.75 %
compared with the PU cubicle, while the SP25+Alveolar cubicle reached 17.12 %
of energy savings compared with the Alveolar cubicle (Table
3
). These are con-
siderable energy consumption reductions, which show the synergistic effect of
combining thermal insulation with increased thermal inertia due to the PCM
inclusion. Furthermore, these savings may be higher, as several aspects of the
PCM benefits are not optimised. On the one hand, for optimal PCM behaviour, the
set point should be equal to the PCM phase-change temperature and, in this case,
should be between 2 and 4 C lower (or said in other words, the selected PCM has
a rather high melting point for the desired comfort conditions in the summer
period). On the other hand, a complete recharging of the PCM during the night is
needed so it can absorb the maximum heat at day hours, and this is only partially
the case in most of the days, as explained before.
One option is to add PCM in Trombe walls; several authors have proposed the
inclusion of PCM in walls (Sharma at al.
2009
). The most recent development in
this topic is the use of PCM in ventilated façades presented by de Gracia et al.
(
2013a
,
b
and
c)
. These authors studied experimentally (Fig.
10
) and by simulation
the thermal performance of a ventilated facade double skin facade (DSF) with
PCM in its air channel. The studies in the heating season (winter) showed that this
concept reduces significantly the electrical energy consumptions of the installed
HVAC systems, but these savings depend strongly on the mode of operation and
the weather conditions.
3.2 Active Systems
Active systems using PCM in nearly zero energy buildings would have the aim to
decrease the operational energy of the building by decreasing the use of fossil fuels
in heating, cooling and domestic hot-water production. Again, some systems can
only be included in refurbishment if major works are carried out.
In solar water heating systems, the use of PCM can be an advantage since the
volume of the necessary water storage tank can be decreased (Cabeza et al.
2006
).
