Energy Performance of Buildings: A Comparison of Standard Assessment Methods - Nearly Zero Energy Building Refurbishment - page 190

Table 5 Energy performance depending on heat transfer via the ground for case A
Case study Calculation method EP H, env EP H EP gl Energy class

A3.a Simplified (b tr,g = 0.45) 220.57 378.46 402.50 G

A3.b Analytical 222.47 381.43 405.43 G

Percentage gap (%) 0.85 0.78 0.72

7.4 Heat Transmission to Adjacent Unconditioned Spaces

The temperature of unconditioned spaces, adjacent to the heated volume, influences
heat transmission; therefore, its correct calculation is very important in the deter-
mination of building performance indicators. UNI/TS 11300-1, according to EN ISO
13790, provides two possibilities for the evaluation of the temperature difference
between the heated zone and the adjacent unconditioned spaces. The first one is
the analytical calculation of the temperature for the unconditioned space by virtue of
EN ISO 13789, while the second one is a simplified assessment using an adjustment
factor b tr,x for the temperature difference which can be derived from UNI/TS 11300-1.
The comparison between these two possibilities has been tested for both cases
A and B using, respectively, the temperature of the unheated space determined by
EN ISO 13789 and the adjustment factor b tr,x : in case A, the unheated space is the
attic and in case B the stair case.
Table 6 shows the results in terms of performance indicators for both cases, and
it is apparent that the application of the two methods can significantly influence the
heat transfer calculation. By using the adjustment factor (case A4.a), the value of
EP H,env is 13.6 % higher than by applying the calculated and accurate tempera-
tures of the unconditioned space (case A4.b).
Moreover, in case B3.a, the temperature of the staircase is determined by using
the adjustment factor, while in case B3.b, the analytical method is adopted, and in
this case, the gap between the two procedures in terms of performance indicators
accounts for 11 %.

7.5 Heat Generator Subsystem Losses

A typical action which increases the efficiency of the heating system is the sub-
stitution of the traditional old generator with a condensation one and, if possible,
with the association to radiant panels and an efficient control subsystem, such as

Table 6 Energy performance depending on the temperature of the non-heated space
Case study

Calculation method EP H, env EP H EP gl Energy class

A4.a Simplified 207.07 357.39 381.40 G

A4.b Analytical 193.00 335.29 359.30 G

Percentage gap (%) 6.79 6.18 5.79

B3.a Simplified 70.18 137.59 164.46 F

B3.b Analytical 62.00 122.73 149.60 F

Percentage gap (%) 11.7 10.8 9.0