## 2 Research in Sustainable Energy Systems at DTG: Main Results and Discussion
### LCA and LCC of Building Insulation Materials in Italy  
The case study simulated by Trnsys(r) was a typical Italian two-story house with an area of 135 m\({}^{2}\), a volume of 363 m\({}^{3}\) and an external surface area of 327 m\({}^{2}\). Roofs and walls were covered with insulating material. Some parameters for the analysis were fixed: Set-point temperatures, global electrical efficiency of 39%, natural gas boiler with average seasonal efficiency of 75%, electric air conditioning system with average coefficient of performance (COP) of 2.5. The cooling and heating thermal loads as primary energy (PE) were determined for three different climates (Figure 1). In PE consumption of Rome and Crotone was definitely lower than that of Milan (\(-\)33 to 41%). This was mainly due to the heating contribution, whereas the cooling load increased in the southern resort, but it remained a reduced part, less than 10%. The LCA analysis for Crotone is reported in Figure 2 for a fixed building life of 50 years. Assuming that energy was not recovered at the end of the material life (that is, the feed stock energy was included), some insulating materials featured a minimum of PE consumption. For example, the optimum thickness of expanded polyurethane foam was 17.5 cm while it was 20 cm, and 18.5 cm, respectively, for the cities of Milan and Rome. This means that no advantage was reported by increasing the insulation thickness from the LCA point of view, as the energy saving during the lifetime was not sufficient to compensate for the energy used to produce the insulation panels. Other materials did not feature any minimum point in total PE consumption in the thickness range considered (0-32 cm). For example, since the stone wool batts featured a low value of feedstock energy (16%), the total requirement did not vary significantly. As a matter of fact, the energy savings produced in the lifetime climatization allowed the energy cost of the material to be always paid back. Even in the most unfavorable conditions (cork panels, i.e., the material with the highest energy requirement per functional unit, and the climate of Crotone that had the lowest annual load), a payback energy lower than three months was calculated. Figure 1: Primary energy consumption for annual climatization varying the insulation (stone wool batts) thickness. In terms of LCC, the authors compared the results of three different cases: Stone wool (with a cost equal to the base cost \(\times\) 2, approximately 11 \(\upxi\) per functional unit); flax (base cost \(\times\) 2 fixed at 55 \(\upxi\) per functional unit, the most expensive material); paper wool (base cost \(\times\) 2 fixed at 5 \(\upxi\) per functional unit, the less expensive material) (Figure 3). Using flax rolls, no economic benefit was produced in both Milan and Crotone: In fact, for any thickness greater than the minimum of 2 cm available on market, the net present worth (NPW) was higher than without insulation. Instead, the curves featured a minimum NPW only with a thick insulation when using paper wool (7 cm in Crotone, 11 cm in Milan). These are thicknesses that are fully consistent with the current standard of Directive (EU) 2018/844 [48], but very high for the requirements set by the previous Italian law 412/93 [49]. The sensitivity analysis developed by the authors highlighted that, differently from the natural gas cost, the optimal thickness did not vary considerably with the electricity cost, both in Milan and in Crotone, due to the low weight of cooling requirements in relative terms. Figure 3: NPW of insulation (flax rolls, stone wool batts, paper wool granulated, base cost \(\times\) 2). Figure 2: Primary energy consumed in Crotone (feed stock energy included). As the main conclusion and novelty of the study, the authors stated that the most advantageous choice to minimize the energy cost of building management was the insulating material that had the lowest cost per functional unit.