Environmental Engineering Reference
In-Depth Information
Table 5.1
Results of the Passivhaus concept translated to the Mediterranean area (end use
Efficiency Research Group, eERG
2007
)
Location
Air permeability of
building (n
50
)(h
-1
)
Transmittance of the building
envelope (U-value) (W/m
2
Insulation levels (cm)
K)
Roof
Walls
Basement
Glass
Roof
Walls
Basement
Milan
1
0.134
0.135
0.134
1.400
25
25
25
Rome
1
0.200
0.300
1.000
1.400
16
10
1
Palermo
1
0.540
0.420
1.340
1.400
5
6
0
average winter temperature: 2.8 C; average summer temperature: 21.7 C) it is
possible to satisfy the standard with less thick coatings both on external walls,
basement and on roofs (25 cm). In Palermo (the capital of Sicily, latitude:
386'43
00
56 N; heating degree days: 751; cooling degree days: 642; average
winter temperature: 13.9 C; average summer temperature: 25.5 C) such
thickness can be reduced up to 5-6 cm, if the mechanical ventilation with heat
recovery is kept, or alternatively the mechanical ventilation can be eliminated
using a thicker coating (about 25 cm). In what follows the Table
5.1
below
summarizes the results of the Passivhaus concept translated to the Mediterra-
nean area.
The study concluded in 2006 shows values of external insulation and air per-
meability required to achieve the Passivhaus Standard in Milan, Rome and
Palermo,
using
a
thermal
insulation
with
conductivity
0.037 W/mK
and
mechanical ventilation with heat recovery.
• The airtightness of building
16
: the standard and best practice of central Europe
require that the building coatings limit the air exchange to a maximum of 0.6
volumes per hour for a pressure difference of 50 Pa (n50 \ 0.6 h
-1
). But the
limit for Milan and Rome of n50 equal to 1 h
-1
(referring to optimal tightness)
is even too conservative in southern cities such as for example Palermo since
the winter external design temperature overcomes 0 C (according to the norm
UNI 5364 in Palermo it is equal to 5 C) and as it is well known the air loss,
namely an uncontrolled air flow through the walls, doors, the windows and the
16
Measured with the airtightness test (Blower Door Test) allowing to define the equivalent air
flow for infiltrations at a pressure difference of 50 Pa (V
50
).The number of air turnovers per hour
at the pressure of 50 Pa is indicated with the index n
50
. Such values allow to evaluate the quality
of the building coating under the airtightness profile. The lower the value the more efficient the
coating. Indeed a cold air infiltration from outside or the leakage of hit air from the inside, due to
not perfect sealing, become a concentrated flow of water and steam. As a result the condensation
inside different components such as walls, node wall-subframe, node subframe shutters, thermal
insulation, roofs, etc.). The effects are quite negative: the thermal conductance of a material
increases with the internal increased humidity and the retention of condensed water in the
structures damages the materials, favours the upcome of mold, causes a decay of the living
comfort. Moreover molding phenomena in wooden structures can take place or the fast deteri-
oration of insulating materials (Ronchini
2012
).
