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In historical centres, the buildings are characterized by pitched roofs, sometimes not insulated, with lowthermal inertia and coated in brick tiles with low solar reflection factor. So, the attics show high energycosts for heating and cooling.This paper analyses the energy saving obtainable by applying innovative surface finishes on interiorand exterior surfaces of opaque envelope components of existing buildings. This simple and inexpensiveretrofit action determines energy cost reductions for heating and cooling, but also benefits regardingindoor thermal comfort and useful life of buildings, because condensation problems and thermal shock arereduced; moreover, it preserves the architectural and chromatic characteristics of the building envelope.The analysis is performed by means of a building energy simulation code, considering typical HVACsystems for various Italian and European cities. A technical-economic and environmental investigationis also performed.Thermal energy needs of buildings for summer cooling can be reduced up to 60% by applying “coolpaints” on the external surface of walls and roof, while internal low infrared emissivity coatings canreduce winter thermal requirements up to 12.5%.Significant primary energy savings for heating and cooling and reductions of greenhouse gas emissions(up to 60%) can be obtained, as well as a payback value of few years in most cases. 1. IntroductionIn the last decades, the summer heat waves have increased andsimilar future weather events will be probably more severe [1].41842
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This leads to an increase of HVAC system use and of their energyrequirements.A significant part of total energy consumption and pollutant gasemissions depends on buildings [2]. In the European Union, 40% ofglobal energy consumption depends on buildings, and this sectoris on the increase [3]; moreover, in 2005, 26.6% of the final energyrequirements depended on residential sector [4].Therefore, the European Union is engaged in diminishing energyconsumption by 20%, with reference to 1990, within 2020 [5]. Tothis aim, all member states must increase the energy performanceof new buildings and related systems and provide energy retrofitmeasures for existing buildings [3]. One of the challenges consists in improving the building energy efficiency while keeping a satis-factory indoor microclimate for the occupants [6].In temperate or hot climates, the use of summer air conditioningis spreading also in residential buildings, causing the increase inpeak electric demand and blackouts [7].Energy saving in buildings is typically achieved by a com-bination of active and passive techniques. The active ones arebased on the utilization of renewable energy sources (mainlysolar) [8,9]. Simultaneously, significant savings can be achieved byimplementing passive techniques, mainly focused on the appro-priate selection of the components of the building envelope[10].Among the various passive techniques for building envelope, animportant option is the optimization of the radiative characteristicsof surface finishes. Absorptance is about 40% for external surfacefinishes with a light colour, whereas about 90% for dark finishes[11].The Albedo control allows to achieve three important effectsby reflecting to the space the shortwave incident radiation: GlobalWarming mitigation, reduction of urban heat island phenomenonand energy savings in buildings [12]. The application of cool paints on the building roof can improvealso the indoor thermal comfort of the occupants in summer, bydecreasing the mean radiant and the operative temperatures of therooms [13]; moreover, the overall energy needs of the building forspace heating and cooling can be greatly reduced [14].In [15], the authors investigated the performances of green roofsin reducing the cooling energy demands in summer. They alsoshow that cool coatings, mainly in warm European climates, arepreferable compared to green roofs, because of the great poten-tial in reducing the heat gains due to the solar radiation and therelated energy costs for cooling. Anyway, an optimization proce-dure is required to identify the best technology depending on theclimate [16].Pisello et al. reported experimental analyses on innovative coolcoatings for traditional clay tiles [17].