Civil Engineering Reference
In-Depth Information
Table 4
Influence of opaque and transparent elements insulation
Case
study
Type of intervention
Calculation
method
EP
H,
env
EP
H
EP
gl
Energy
class
A2.a
Case A1.a ? high-performance
windows
Simplified
66.74
123.46
147.53
E
A2.b
Case A1.b ? high-performance
windows
Analytical
87.52
157.63
181.68
E
A2.c
A0.a ? high-performance
windows
Simplified
274.66
459.26
483.26
G
B2.a
Case B1.c ? high-performance
windows
Simplified
66.74
123.46
147.53
D
B2.b
Analytical
87.52
157.63
181.68
E
Percentage gap (%)
22.9
20.3
15.3
B2.c
B0.b ? high-performance
windows
Simplified
67.18
132.37
159.24
F
the envelope and just the insulation of the windows, without any intervention on
opaque elements, allowing the improvement of energy class from G to F.
Once again, analyzing integrated refurbishment action on opaque and trans-
parent element insulation, the choice of the calculation procedure for thermal
bridges brings significant differences in terms of energy performance: in Table
4
,
the percentage gap accounts for 15.3 % and also the energy class changes from E
to D, using the analytical and the simplified method, respectively.
7.3 Heat Transfer Via the Ground: Simplified and Analytical
Calculations
According to EN ISO 13790 and Italian National Standards, an accurate calcu-
lation of the temperature difference between the heated zone and the external
environment, accounting for the large inertia of the ground as indicated by EN ISO
13370, is required (analytical method).
Moreover, in order to account the ground effect, it is also possible to consider
the temperature difference between the building and the external air and applying
an adjustment factor b
tr,g
to the heat transfer coefficient (simplified method).
Table
5
shows the results obtained by applying these two different assessment
methods for case A: the underfloor has been insulated (10-cm EPS), and it reaches
a thermal transmittance of 0.293 W/(m
2
K). Case A3.a is characterized by a
simplified calculation of the thermal transmission via the ground using the cor-
rection factor b
tr,g
= 0.45 as established for floor close to the ground, while for
case A3.b, EN ISO 13370 has been applied. It should be noted that, keeping
constant all other conditions, the difference among the three significant perfor-
mance indicators (EP
H, env
, EP
H
and EP
gl
) in each case is negligible.
Case B was not considered since it is a dwelling positioned in an intermediate
floor, and it does not adjoin the ground.
