Civil Engineering Reference
In-Depth Information
Therefore, the gap between the energy need for the base case A related to the
method applied for thermal transmittance is negligible. In the following analyses,
case A0.a is used as a reference for intervention simulations, while case A0.b is
omitted.
The performance indicators for case A.0a are as follows:
• EP
H, env
= 282.08 kWh/(m
2
year);
• EP
H
= 474.40 kWh/(m
2
year);
• EP
gl
= 498.40 kWh/(m
2
year).
In case B0.a, which represents the existing building, keeping constant all the
calculation parameters, with a thermal transmittance value U = 0.90 W/(m
2
K),
the corresponding value of the energy performance indicator in the heating season
of the envelope, EP
H,env
, is 108.10 kWh/(m
2
year), instead of 121.32 kWh/(m
2
year), for case B0.b with U = 1.1 W/(m
2
K)), with a gap of 10.9 % as shown in
Fig.
5
. In particular, the same trend can be noted in the energy performance
indicator for the heating season EP
H
and for the global performance index (which
is the sum of EP
H
and the performance indicator EP
w
for domestic hot water
production). In fact, the simplified calculation of the thermal transmittance gen-
erally introduces an overestimation of the heat transmission through the opaque
element. Finally, it should be noted that, for the hollow bricks, it is possible to use
the thermal conductivity value of 0.3 W/(m K) derived from Appendix B or from
UNI 10351 (corresponding to a thermal resistance of 0.4 (m
2
K)/W) or, alterna-
tively, the thermal resistance value of 0.31 (m
2
K)/W drawn directly from UNI
10355. Therefore, choosing one value or another one can bring further differences
in thermal transmittance and energy performance values.
7.2 Thermal Bridges: Simplified and Analytical Calculation
The first kind of refurbishment action is the thermal insulation of external enve-
lope: in this section, the energy performance for both case studies is investigated.
For the detached house, the effects of external thermal insulation have been
Fig. 5 Energy performance
indicators
300
B0.a
B0.b
255.54
250
228.68
232.46
205.6
200
150
121.32
108.1
100
50
0
EPH,env
EPH
EPgl
