Civil Engineering Reference
In-Depth Information
the alternatives in question show that this construction has the lowest thermal
transmittance coefficient, one of the highest inertia values and one of the highest
prices. Since the price variation was minor, this criterion was not too determining a
factor in the overall assessment.
The group titled 'Glazing' (
http://iti.vgtu.lt/imitacijosmain/simpletable.aspx?
sistemid=428
)
comprised six standard, sun protecting, reflecting or tinned glazed
units defined by ten criteria—seven quantitative and three qualitative.
Glazed surfaces have an impact on the energy demand for lighting, heating and
cooling of buildings (Da Silva et al.
2012
), so the optical and thermal properties of
glazed units are of particular importance in hot climates. Higher energy demand
for cooling, leads to larger emissions, which in turn would exacerbate climate
change and global warming.
The alternatives in this group were defined by the following criteria: thermal
transmittance (U-value), solar heat gain coefficient (SGHC), visible light reflectance
(VLR), price, warranty time, longevity, functionality, comfort and aesthetics. All of
the quantitative criteria were available in the specifications produced by manufac-
turers. The qualitative indicators were scored in points by a group of experts.
In this particular case, the assessment trends of optical and thermal properties
correspond to the requirements laid out in SAFIERA: the lower the U-value, the
lower the SGHC value and the higher the visible light transmittance (VTT) value.
Here, the lower the U-value, the greater a window's resistance to heat flow and the
better its insulating value. The lower the SHGC value, the better glazing is at
blocking unwanted heat gain. The higher the VTT value, the more light is trans-
mitted into the room and, in turn, the better is the visual comfort indoors. The biggest
weights in this group were, therefore, attributed to SGHC (0.27) and U-value (0.2).
The system's results indicated 'Glazing 5' as the best option among the glazing
alternatives. This glazing unit has the best thermal properties with its U-value at
1 W/m
2
K., some of the best optical properties with SHGC = 33 %, but the
highest price at 175 LTL/m
2
. Since the optical and thermal properties have far
higher weights—SGHC 0.27 and U-value 0.2—than price (0.1), the latter indicator
was not the determining one.
Besides the properties of glazed units, other factors that contribute to a build-
ing's energy efficiency—such as glazed area, orientation towards the cardinal
directions and shading devices—also play an important role in hot climates. The
factors ought to be considered in early designing phases to find an optimal and
energy-efficient architectural solution.
Ouedraogo et al. (
2012
) shown that it is possible to achieve significant a 31 %
cooling load reduction by reducing the building total glazing surface area. Shading
devices can produce a cooling load reduction of up to 40 % depending on their
type and location. For East and West facing facade, the reduction in cooling load is
up to 49 % when shading devices are installed.
So our next group of objects is, therefore, eight alternatives of glazed areas
[window to wall ratio (WWR %)] (Table
1
), four orientations of the main façade
towards the cardinal directions (Table
2
) and four shading devices (Table
3
).
