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The summer efficiency coefficient value for split system, SEER,varies depending on the climate considered, as shown in Table 2.It can be noted that the performed analysis does not considernewer types of HVAC systems used today in new constructions,because this analysis refers only to existing residential attics, whichusually present traditional HVAC systems.The seasonal and the yearly building envelope thermal energyneeds (TE), as well as the primary energy demands (PE), are eval-uated by means of the software. The difference between values ofTE and PE depends on the HVAC systems’ efficiencies and thermal-electric efficiency, all reported in Table 2.Primary energy demand (PE) is evaluated as follows:- for heating system, TEh/ gl;- for cooling system, TEc/SEER * thermoelectricFor the economic analysis, different electricity and gas tariffs areconsidered for the various European countries (Fig. 2, from Eurostatdata for 2014 [28]).Moreover, it is noteworthy that the proposed retrofitting meas-ures are characterized by easy installation and low cost. A usefullife of 40 years is considered for the used products. To evaluate thecosts of the retrofit actions, the following components are consid-ered: capital costs, labour costs, company profit of 10%, overheadof 15% and security cost of 15%. So, the cost of the cool paint on the pitched roof is evaluated in about 5 D m−2, while 5.80 D m−2 for theapplication of the innovative internal and external plaster. There-fore, the simple and discounted payback time (SPB and DPB) arecalculated.
Also the environmental impact of the various actions proposedis evaluated. For the calculation of yearly CO2 emissions, LCA (lifecycle assessment) European emission factors are considered [29],i.e. 0.578 tCO2-eq/MWh for electricity and 0.237 tCO2-eq/MWh fornatural gas requirements. The LCA emission factors include overalllife cycle of the energy (exploitation, transport, processing stepsand final combustion). It can be noted that the emission factorfor the electricity requirements is not reported to primary energy,but to delivered energy (the contrary occurs for the natural gasemission factor).3. Characteristics of the innovative surface finishesThe solar radiation is characterized by 52% near-infrared, 43%visible and 5% ultraviolet. The solar radiation incident on opaquesurfaces is partially reflected and partially absorbed by the surface,as a function of the kind and colour of the surface finish: surfaceabsorptance (˛) and reflectance ( ) are the key factors. Anotherimportant factor of the building envelope surface is the infraredemissivity (εfar-infrared), as the delivered radiant energy depends onit [30].The modelled reference building presents traditional materi-als: red tiles on the pitched roof, characterized by high εinf (about0.9) and low s (0.3–0.4); bricks on the external surface of walls;internal white plaster with low ˛s (about 0.2) and high εinf (about0.9).In order to reduce energy requirements for winter heating, alow emissivity plaster on the inside surface of building envelope isapplied. This innovative low-emissivity internal plaster is obtainedby mixing ceramic nanospheres with a traditional plaster; it is par-ticularly suited for energy retrofitting of building opaque envelope.The nanospheres, patented in collaboration with the N.A.S.A., arethermal reflective and form a radiant barrier to reduce winter heatlosses towards the outside ambient. This finish is characterizedby high infrared reflectance; thus, most of the long-wave radia-tion coming from the indoor environment is reflected. Therefore,the U-value of the walls is reduced, because the internal surfaceresistance is increased by 26.5% and 18.5% for vertical and hori-zontal walls, respectively [31]. From laboratory studies [32], it hasbeen drawn that two layers of the innovative low-emissivity plas-ter provide an additional thermal resistance to radiant heat equalto 6 h ft2 ◦F BTU−1 = 1.05 m2 K W−1, compared with two layers of thesame painting without nanospheres.In order to minimize energy demand for summer air condition-ing, two actions on outer surface of envelope building are identified:red tile paint on pitched roof and innovative plaster on externalsurface of vertical walls. The paint is a special coating in liquidform, i.e. a water paint containing minerals, acetic acid solution,water and other components (also indicated, in the following, asthermal-reflective multi-mineral emulsion). It has the same spec-tral response of the traditional brick in the visible range, but higher