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heating demand, the main goal of these studies was to understand how
transwalls behave with regard to thermal lag and the ability to provide
heat to the indoor environment during the night. It was common to use a
third glass pane on the outdoor side of the transwall in addition to the
double glazing in order to avoid heat loss to the outdoor environment. In
some cases, the installation of an opaque and insulating plate outside the
transwall during the night was even considered (
Nayak, 1987a
).
5.1.1.2. Classical transwalls. In publications on classical transwalls the
authors propose more accurate thermal and optic numerical models and
the absorbing plate is excluded from the WBW profile, leading to a single
water gap with double glazing (
Fig. 3
, profile iii).
Papersenos (1983)
produced a thesis
that made an important
contribution to the understanding of the multiple reflection phenome-
non of the transwall surfaces, their effect on solar absorption by sub-
strates and the attenuation of indoor direct heat gain. Laboratory
experiments validated the accuracy obtained using the Nusselt number
for TTWMs without fluid exchange in thermal simulation. In order to
prevent the growth of algae in the enclosed fluid, the use of 100 ppm
CuS0
4
and 150 ppm disodium ethylenediamine tetraacetate has been
suggested On the other hand, several points clarified by Papersenos that
characterize a breakthrough in the topic were not considered in subse-
quent publications. A possible explanation
is because no article was
published from this thesis, and therefore did not appear in certain sci-
entific databases.
An evaluation of the performance of transwalls on adding dye solu-
tions to increase the solar radiation absorbance of the WBW (
Nisbet and
Kwan, 1987; Nisbet and Mthembu, 1992
) is carried out.
Nisbet and
Kwan (1987)
reports an annual energy savings simulation, using water
in clear plastic bags to seal horticultural glasshouses and release heat at
night, performed in western Scotland and southwest England. This was
the first study where liquid solutions were used, in this case red dye
(Lissamine red 3GX), to increase the water absorption coefficient.
Annual savings were in the range of 15% to 20% and water-dye sections
with a thickness of 15–20 cm were found to provide the best perfor-
mance in the cold-climate regions.
Nisbet and Mthembu (1992)
second
study involved laboratory
measurements to access the thermal performance of transwalls with
absorptive glazing or the use of water with a gelling agent. Experimental
results validated the numerical model used to compare the performance
of a water-dye double-glazed transwall with a 15 cm gap with that of a
transwall with solar absorptive glazing in the rear face and water with
gelling agent. Both modules where considered to be behind a double-
glazed window for the month of March in the west of Scotland. It was
observed that the gelling agent and solar
absorbing glazing system
transmitted more heat during solar irradiance. On the other hand, the
water-dye module was 30% more efficient at releasing heat to the indoor
environment after sunset. A year-round simulation of the transwall
indicated that energy savings of 23% and 62% could be achieved for a
water-dye transwall installed in a house sited in the west of Scotland and
in
the south of France, respectively. This clearly demonstrates the
impact of the building location in transwall energy efficiency. However,
the overall thermal assessment of these researches is not associated with
the same rigor and simulation capacity
as contemporary studies,
resulting in possible uncertainties in the energy savings values achieved.
