Cool roof

The effect of Phase Change Materials (PCMs) to optimize indoor thermal comfort conditions and reduce cooling energy requirement when included in envelope components and materials is demonstrated by an extensive scientific literature (Zhou et al., 2012. Orò et al., 2012). In this view, this research consists of the development and prototyping of an innovative passive cooling polyurethane based membrane with PCMs inclusion for roofing applications (Pisello et al., 2015).

Cool roof is a well-documented passive cooling strategy for buildings in several climate conditions. The mechanism consists of the reduction of the heat load entering the roof, which is characterized by high solar reflectance and high thermal emittance. The purpose of this paper is to study the coupled effect produced by such a technology. First, the passive cooling contribution is quantified, then, the “active” contribution is investigated.

Solar reflectance is the key performance parameter of cool roof and cool pavement materials. For its assessment, the measured spectral reflectivity of the sample is weighted by a reference spectrum of solar irradiance. Several standard and non-standard spectra are however available, taking into account different climate conditions, angle of incidence of the solar beam, contribution of the diffuse radiation content.  

Our recent study has shown that the acrylic silicon polymer is useful to formulate self-cleaning topcoat which may maintain the thermal insulation effect of cool roof effectively. 
A 2K self-cleaning topcoat was formulated with a water-borne type acrylic silicon polymer. Its effect to maintain high solar reflectance was confirmed by outdoor exposure test in comparison with coatings having no self-cleaning function. The solar reflectance performance was well maintained regardless of installation angle, lightness of colour or pigment type. 

Few studies focus on commercial low-rise buildings which are often characterized by low-cost constructions materials and weak energy performances. For these large volumes, the heat transfers with the roof and the ground are prevalent. In this article, we show how the analysis of heat transfers through both the roof and the ground can achieve their thermal performance. The roof design and its opening systems is a key factor of the thermal and lighting performance.

Energy saving in the building sector is one of the key issue to achieve environmental targets at national and EU levels. Even if characterised by a large number of different climatic conditions, Italy energy policies were aimed at reducing the energy consumption related to space heating in buildings, neglecting other relevant energy uses as space cooling, which has dramatically increased in the past years. The recent EU Directive for the State Members is to assess the energy quality of buildings taking into account all the relevant energy uses. 

Clay roof tiles are widely used as roofing materials because of their good mechanical and aesthetical properties. The exposure to atmospheric agents and, most of all, to pollutants and smog affects negatively the solar reflectance of a tile surface. The aim of this study is to analyze the influence of ageing on the solar reflectance of clay roof tiles. We studied samples provided by manufacturer in Greece and USA. Samples were coated with either organic or inorganic coatings.

Utilizing a cool roof is an efficient way to reduce the cooling energy use of a building. Cool roofs, however, may increase heating energy use in winter. In cold climates, during the winter the sun angle is lower, days are shorter, sky is cloudy, and most heating occur during early morning or evening hours when the solar intensity is low. In addition, the roof may be covered with snow for most of the heating season. All these lead to a lower (than what is commonly thought) winter time heating penalties for cool roofs. 

The treatment of roof space with cool paint or vegetation is a widely employed urban heat mitigation strategy. As the allocation of roof space for social activity becomes more prevalent in the urban environment, there is a need to understand how cool roofs and green roofs can affect the outdoor thermal comfort of its users.