Abstract
Social housing built in the middle of the last century in Spain suffers from poor thermal insulation conditions that cause situations of discomfort and energy poverty. For this reason, the energetic refurbishment of the envelope of this social building stock is necessary to overcome these situations and reduce energy consumption aimed at achieving interior comfort for its occupants. The goal of this work is to optimize a constructive solution that combines cool roof techniques with the use of thermal insulation applied to the refurbishment of the roof of buildings belonging to a quarter of social housing in Seville, Spain. The optimization analysis is based on the computation of the energy performance of the roofs when the energy retrofitting measure is applied, considering a variety of combinations of solar reflective coatings and insulation layer thickness, performing a dynamic analysis that accounts for the aging effect of the cool coats on the monthly roof energy performance and on the economic balance for the whole life cycle (LC) span. Economic and energy optimization analysis show that a suitable combination of cool roof emissivity and insulation layer thickness produces significant savings in the operational energy and in the economic profitability of the proposed retrofitting measure: the optimum combination obtained provides for the entire life cycle timespan an energy savings of 5.71 GJ/m2 and a cost savings equivalent to the 63.1% of the total costs when compared to the non-refurbished roof. The application of a time-dependent pattern for the changes on time produced by the aging effect on the cool roof emissivity, and its effects on the optimization of the combination of cool roof and insulation layer, can be considered novel in literature, both from an energy and an economic point of view.
Highlights
The building sector is responsible for around 40% of final energy consumption in Europe and is a major source of CO2 emissions
The cost of the roof retrofitting must be paid by all the owners of the building, while the benefit of the retrofitting would only be noticeable in the housing under the roof; in the event of damage, according Spanish law, the cost of restoring the roof is paid by all the owners of the building; so, since the owners and tenants of the dwellings taken as the case study are characterized by having low incomes, a retrofitting action on the roof is unlikely, except for the existence of some deterioration of the roof that makes such retrofitting necessary; to perform the analysis, it is assumed that the reference roof needs some kind of renovation or maintenance
The thermal performance of social building roofs under Southern Spain climate and its refurbishment by means of combining a cool roof coat and a thermal insulation layer have been analyzed in the present paper
Summary
The building sector is responsible for around 40% of final energy consumption in Europe and is a major source of CO2 emissions. In climates characterized by mild winters and very long hot seasons, such as the case of southern Spain and much of the Mediterranean area, a large amount of energy consumption is necessary to obtain the internal comfort of buildings during the cooling season. This poses a serious problem in the case of the social park housing built in southern. The energy efficiency of roofs has been object of a wide research focused on the enhancement and the optimization of its energy performance This is largely justified by the fact that the roof is the envelope component that receives the most solar radiation in summer and in winter is responsible of an important percentage of the heat losses. In the geographical context considered here, in summer, most of the time, the sky is clear, and, in winter, the temperatures are not too cold, the cool roof technique seems advisable to lower the temperature of the roof, while the combination with a layer of insulation can help to achieve indoor comfort conditions and reduce energy consumption for this purpose
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