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The results show that theapplication of this coating reduces the number of hours when theattic operative temperature is greater than 26 ◦C by about 18% insummer, while the worsening in winter is negligible.In California and Florida, the American Society for Testing andMaterials (ASTM) introduced, for roofs and almost horizontal build-ing surfaces, the solar reflectance index (SRI), which combinesfar-infrared emissivity and solar reflectance. In temperate and hotclimates, the use of coatings with high SRI reduces the energydemand for summer cooling by 10–60% [18]. Cool roofs (roofswith coatings characterized by high infrared emissivity and solarreflectance) are widely promoted in the U.S.In Europe, materials with colour similar to those of historicaland traditional buildings are frequently used for existing build-ings, so the solar reflectance is partially sacrificed. Nowadays, tilestreated superficially with “cool colour” finishes are also considered;this kind of finishes has the same spectral response of terracottatiles in the visible range (43% of the solar radiation), but reflectsmuch more radiation in the near infrared spectral band (betweenabout 700 nm and 2500 nm), which characterizes more than 52% ofthe solar radiation. Therefore, these cool paints show much greatersolar reflectance compared to traditional materials, but the samecolour [19].In Mediterranean climates the use of flat white roofs is quitefrequent, but in historical centres the buildings are characterizedby pitched roofs, sometimes not insulated, with low thermal inertiaand coated in brick tiles with low solar reflectance s (minor than0.3–0.4). Therefore, these attics show high energy costs for heatingand cooling.In the present paper, the energy requirements of an attic ofan existing building, with typical HVAC systems, are evaluated.Then, after the application of innovative internal and external fin-ishes on roof and walls of the attic, a yearly energy, economic andenvironmental analysis is performed. The proposed energy retrofitmeasures are characterized by low cost and simple installation;moreover, they preserve the architectural and chromatic charac-teristics of the building. The study refers to various Italian andEuropean cities with different climates, i.e.
Palermo, Seville, Rome,Milan, Paris, London, Berlin and Stockholm. The obtained results,at least in terms of energy impact, could be related also to non-European locations with climates similar to those of the consideredEuropean cities.The main aim of this paper is the improvement of energy effi-ciency of existing attics, without sacrificing the little living spacesand available heights (as occurs when considering internal insula-tion panels).External and internal innovative coatings on existing buildingenvelopes are applied, so obtaining optimal radiative characteris-dynamic building simulation software [20] based on EnergyPlus.The payback period and CO2 emissions are also evaluated.The importance of the surface finishes has been already shownin previous articles, but the energy effects related to the describedretrofitting measures have not been completely analysed, mainlyregarding the yearly primary energy requirements and the combi-nation of internal and external surface finishes. Moreover, this typeof investigation is missing when referred to pitched roofs insteadof flat roofs.2. Research approach and case studyAs said, the research activity is carried out by using a dynamicbuilding simulation software [20] based on EnergyPlus as calcula-tion engine. EnergyPlus was validated by means of measured datain Europe [21]; moreover, extensive validation procedures for dif-ferent locations and buildings are available. Currently, three majortypes of tests are conducted: analytical tests; comparative tests;release and executable tests. EnergyPlus testing reports are avail-able for many of these test suites, for example for building envelope[22] and HVAC equipment [23]. In [24], EnergyPlus was also com-pared to other simulation codes, and the detected deviation of theobtained results was almost always lower than 10%.The analysis of the present work is conducted on a building rep-resentative of the typical residential buildings built in the period1920–1960 in some European towns, above all in historical centres[25]. The main geometrical and thermal–physical characteristics ofthe case study attic are reported in Fig. 1 and Tables 1 and 2. It canbe noted that the Swedish reference building shows much betterU-values compared to other cases.For the considered European cities, an attic with the samedimensional characteristics is modelled, but with different charac-teristics regarding U-values of the building envelope components,efficiencies and operating hours of the HVAC systems and main cli-matic characteristics (Tables 2 and 3) [26]. For all the cases, theenergy, economic and environmental analysis of the attic is carriedout.For each case, four retrofit measures are analysed: dependingmainly on the climatic conditions, each of these actions resultsadvantageous or not from energy, economic and/or environmentalpoint of view. The four retrofit actions are the following:(1) red tile cool paint on traditional tiles of the pitched roof;(2) red tile paint on pitched roof and innovative white plaster onoutside surface of uncoated walls;(3) low emissivity plaster (with ceramic nanospheres) on internalsurface of roof and walls;(4) red tile cool paint on pitched roof and low emissivity plaster oninternal surfaces.The main radiative parameters of the innovative and traditionalsurface finishes are described in Section 3.The main characteristics and operating hours of the HVAC sys-tems are shown in Tables 2 and 3. These traditional systems,as occurs in urban residential attics, are constituted by simpleautonomous systems: radiators served by a typical hot water boilerfor heating; split systems for cooling. Regarding the heating sea-son, a seasonal global efficiency ( gl) equal to 0.66 has been used,considering Eq. (1): gl = g · d · r · e (1) – d is the distribution efficiency, equal to 0.98 when water pipesare installed into external walls;– r is the regulation (or control) efficiency, equal to 0.85 for asimple on-off control on the boiler;– e is the emission efficiency, equal to 0.90 in presence of simpleradiators installed on the external uninsulated walls.Eq. (1) and values of the efficiencies are those reported in theItalian technical specification UNI TS 11300-2 [27].It can be noted that the application of a reflective internal plaster(third retrofit action) causes the rising of the emission efficiency( e) from 0.90 to 0.95 [27]; therefore, the seasonal global efficiencyof the heating system increases from 0.66 to 0.70 and the energydemand of the heating system reduces.