Abstract
Improvement of the energy efficiency of residential buildings must ensure compliance with cost optimality criteria, assuming a specific lifespan of the building. At the same time, the energy retrofit of buildings ought to preserve their intrinsic architectural and heritage value. Portuguese residential buildings constructed before 1960 did not follow any energy efficiency rules. They represent 29% of the housing stock in the country and there is a high potential for increasing their energy efficiency. However, it costs more to implement envelope energy efficiency measures through retrofitting works than to provide for them in new buildings. An evaluation based on cost optimality criteria should therefore be performed. This work evaluates the energy performance of a Portuguese reference building typical of the pre-1960 building stock for different thicknesses of thermal insulation retrofit solutions (roof, facade, and ground floor) and systems. The study describes a sensitivity analysis that took a range of climate data, intervention costs, energy prices, discount rates, and energy needs into account. An energy needs factor dealt with the occupants’ habits and the effective reduction of energy consumption compared with the estimated energy needs.
Highlights
The construction industry and the use of buildings are important sources of carbon dioxide emissions, with buildings having an impact on long-term energy consumption
In Portugal, the housing sector accounted for about 18% of final energy consumption in 2010, of which 30% related to electricity consumption
About a quarter of the building stock in Europe was built in the last century and is older than the age specified as a theoretical lifespan in European countries, which is usually 50 to 60 years (United Nations Environment Programme 2007)
Summary
The construction industry and the use of buildings are important sources of carbon dioxide emissions, with buildings having an impact on long-term energy consumption. The study involved assessing the variability of results according to the following parameters: climate data, combination of energy efficiency measures, intervention costs, the variation of the useful energy requirements as a function of consumption habits, different energy costs, and discount rates. In 2011, Statistics Portugal (INE) and the Directorate General for Energy and Geology (DGEG) published the Inquérito ao Consumo de Energia no Sector Doméstico (Survey on Energy Consumption in Households, ICESD) (National Statistics Institute 2011) It showed that the heating and cooling habits of the Portuguese result in useful energy consumption significantly below the nominal needs estimated by the seasonal method. Based on the data provided by the national energy surveys, we concluded that the effective final energy consumption is 13.4% of the energy needs given in energy certificates This percentage expresses the heating habits of occupants and reflects both the real occupancy pattern of the dwellings and the level of household economic resources. We decided to apply this percentage as a reduction factor of the heating energy needs
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