Portuguese Residential Buildings Research Articles

Strategies and Actions for Achieving Carbon Neutrality in Portuguese Residential Buildings by 2050

As a crucial step in addressing the climate emergency and enhancing energy security, the European Union has set ambitious targets to decarbonise its economy by 2050. While the building sector plays a pivotal role in this transition, being accountable for 36% of the EU’s total carbon emissions, it shows a renovation rate below 1% per year, which is clearly insufficient. To address this challenge, this study uses the cost-optimal methodology from private and social perspectives to assess the cost-effectiveness and environmental impact of five renovation packages with passive and active solutions currently available on the Portuguese market. The results demonstrated that from both perspectives, optimal combinations of market solutions were generally cost-effective and could lead to a 90–99% reduction in energy needs and even to zero carbon levels. Nevertheless, beyond cost-effectiveness, consideration of co-benefits, e.g., social and health improvements, is also crucial, requiring government action. To drive these essential changes, effective policy measures are imperative. Recommendations encompass robust regulatory frameworks, financial support mechanisms, knowledge dissemination, and a shift towards broader-scale renovation. For carbon reduction to be economically attractive, fostering innovative business models and leveraging legal instruments to tackle complex scenarios are needed.

Primary energy saving potential of a solar-driven ejector cooling system: a case study for a Portuguese residential building

The seasonal energy performance of a cooling system based on an innovative variable-geometry ejector (VGE) is numerically investigated by using TRNSYS. The VGE-based system is mainly driven by solar energy, collected through solar thermal collectors, and is coupled to a residential building located in Porto. A biomass boiler is used as back-up heater. The energy performance of the investigated cooling system is compared with that of a conventional solution, based on a commercial air-to-water chiller. Results point out that, almost 75% of the generator heat demand can be supplied by solar collectors and about 90% of the overall energy input of the ejector-based system is satisfied by renewables. Moreover, numerical simulations confirm how the capability to vary the ejector geometry on the basis of current operating conditions allows to strongly improve the ejector seasonal efficiency. A second series of simulations aimed to further enhance the system performance. A master control logic which extends the VGE operation time in correspondence of favourable ambient conditions was introduced, in order to store additional cooling energy in the cold buffer tank. This strategy has proved to be effective, since the energy consumption of the biomass boiler could be reduced up to 35%.

Solar Bridge Retrofit System: An innovative solution to renovate structural thermal bridge areas

The structural components of load-bearing concrete frame buildings, such as concrete beams and columns, are critical elements of the facades which often act as a thermal bridge. To reduce the impact of structural thermal bridge areas in non-retrofitted Portuguese residential buildings, a new innovative solar passive retrofit solution, named Solar Bridge Retrofit System (SBRS), is proposed. This concept relies on the principles of unvented Trombe wall systems and consists in using an external transparent skin in front of the structural areas of the envelope in combination with the traditional ETICS in the remaining area. Contrary to the traditional Trombe walls, this innovative design enables the heavy structure of the building to absorb solar radiation and conduct the heat slowly inward or to the adjacent structure.To evaluate the thermal performance of the SBRS, an experimental setup was developed. The field results obtained during February and March 2020 for two different configurations, showed that the double-glazing configuration in combination with ETICS has the potential to improve thermal comfort and reduce energy consumption. This paper addresses both the design of the SBRS and the obtained results from the experimental work.

Multivariate Data Analysis of the Thermal Performance of Portuguese Residential Building Stock

The purpose of this study is to explore the relationship between solar orientation, age (constructive characterization) and energy performance of Portuguese residential building stock and to assess the usefulness of exploring the Portuguese National System for Energy and Indoor Air Quality Certification of Buildings (SCE) database through multivariate analysis techniques. By using principal components technique, it was possible to condense the residential units’ features to only four principal components (PC): solar orientation; constructive characterization; geometry and energy performance, making information more workable. Grouping the entities into Clusters with favourable and unfavourable solar orientation and old buildings allowed to dilute the particularities of each entity, facilitating the interpretation of the data through generalization. A regression model was generated in order to explore/confirm which factors influence summer comfort the most. Using this approach, it was illustrated that the exploration of the SCE database through multivariate data analyses has an enormous potential to convert data into knowledge.

Country residential building stock electricity demand in future climate – Portuguese case study

The future residential energy demand is expected to be significantly affected by increasing electrification rates and climate change. This study uses a Monte Carlo-based approach and an ensemble of climate models to address potential changes in electricity demand in this sector. The whole Portuguese residential building stock in 2050 is used as a case study. It is performed a sensitivity analysis for the retrofitting and new construction, floor area of new buildings, electrification of domestic hot water and cooking and, finally, adoption of heat pumps for space heating and cooling. Results show a potential increase of 5 to 60% of the total electricity consumption in the sector. Space heating is expected to decrease by 33% while space cooling shows a possible 20-fold increase. The electrification of domestic hot water and the development of housing stock characteristics are the factors with the largest impact on the overall electricity consumption changes.

Harvesting big data from residential building energy performance certificates: retrofitting and climate change mitigation insights at a regional scale

The reduction of energy consumption and the increase in energy efficiency is currently an important cornerstone of EU policy. Energy performance certificates (EPCs) were implemented as one of the tools to promote this agenda, and are used for the energy performance assessment of buildings. In this study, the characteristics of the Portuguese dwelling stock are regionally analysed using data from approximately 523,000 Portuguese residential EPCs. Furthermore, a bottom-up building typology approach is used to assess the regional energy needs impact of retrofitting actions and to estimate the heating and cooling energy performance gaps of the whole dwelling stock, as well as the potential CO2 emissions resulting from the gaps’ potential offset due to increase thermal comfort. The results show that Portuguese residential buildings have very low energy performance, with windows and roofs being identified as the most energy inefficient elements. Roof retrofitting has the highest potential for the reduction of energy needs. The estimated heating and cooling energy performance gap amount to very significant percentages, due to the poor performing building stock but also very low energy consumption levels, with probable consequences for the thermal comfort of occupants. Assuming the current energy mix, carbon emissions would be 9.8 and 20.2 times higher associated with heating and cooling, respectively, if the actual final energy consumption were to match the estimated theoretical values derived from building regulation. This study demonstrates several application cases and leverages the potential of the individual EPC, increasing the detail in the dwelling stock characterization and energy performance estimation, revealing its value for energy retrofit and climate change mitigation assessments, as well as establishing the ground for future work related to building retrofits, energy efficiency measure implementation, climate change mitigation, thermal comfort, and energy poverty studies.

A sensitivity analysis of a cost optimality study on the energy retrofit of a single-family reference building in Portugal

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.

Phase Change Materials as a solution to improve energy efficiency in Portuguese residential buildings

The buildings sector contributes to 30% of annual greenhouse gas emissions and consumes about 40% of energy. However, this consumption can be reduced by between 30% and 80% through commercially available technologies. The consumption of energy in the dwellings is mostly associated with the heating and cooling of the interior environment. One solution to reduce these consumptions is the implementation of technologies and Phase Change Materials (PCMs) for Thermal Energy Storage (TES). So, the aim of this work is to analyse the advantages, in terms of decreasing energy consumption, associated with the application of PCMs in Portuguese residential buildings. For this, eight PCMs with different melting ranges were analysed. These materials were analysed through a dynamic simulation performed with EnergyPlus software. The results achieved, showed that the materials studied allow to reduce up to 13% of the heating needs and up to 92% of the cooling needs of a building located in the North of Portugal, at an altitude higher than 100m.

An Analytical Approach to the Ventilation Effectiveness of Mediterranean Buildings. Case Study: Existing Residential Building, Portugal

Building airtightness assumes an important role in the energy saving and the indoor thermal comfort. Ventilation rates bring significant impacts on energy usage in the constructions and indoor contaminant concentrations and also setting them as the key parameters in building performance.Ventilation rate have been measured in building for a long time, and there are some developed measurement methodologies related to it in the research domains. However, most of the investigations in recent years have been done usually in the cold climate conditions, while Mediterranean construction are not deeply investigated in the literature.In this paper, the authors present the obtained results of an experimental research which is carried out on the Portuguese residential buildings. The investigation is done by fan pressurization methods, also known as “Blower Door Test (BDT)” as the measurement method as well as Design Builder (DB) as the simulation software. The airtightness measurement of the existing buildings and the influence of air leakage on energy consumption and indoor comfort in different Portuguese construction typologies are focused on the aim of the research.The important parameters of the building such as whole-building air change rates, building infiltration rates, and ventilation effectiveness rate in the residential building are also considered in this research.

Thermal and indoor air conditions in Portuguese residential buildings: risk factors for childhood health

Thermal and indoor air conditions in Portuguese residential buildings: risk factors for childhood health

Evolution of earthquake losses in Portuguese residential building stock

The evolution of the expected earthquake losses in different Portuguese regions was studied in order to determine whether the natural regeneration of buildings could contribute to the mitigation of seismic risk, although the building exposure has increased over time in most analysed regions. To achieve this goal, five inter-related risk indicators were estimated, based on the Portuguese censuses’ surveys of residential buildings and inhabitants obtained in two different moments in time: 2001 and 2011. The FEMA (2008) approach was used to estimate the risk indicators, i.e., the Annualized Economic and Human earthquake Losses, either in absolute terms or normalised by building and population exposure. This study offers a perspective of the seismic risk in the Portuguese mainland, provides a comparison of risk levels between different epochs, and analyses the obtained results in order to compare the risk among Portuguese regions. It is important to mention that the comparison of economic losses based on the building stocks surveyed in 2001 and in 2011 took into account the Portuguese inflation rate in that time interval. The main findings of the study show that the natural regeneration of the residential housing stock contributes to the reduction of the expected seismic economic losses in Portugal, at an average rate of 14 % per 10 years, and to the reduction of the expected annualized human losses to almost one half after 10 years. The results support the conclusion that the natural regeneration of the residential housing stock contributed to the mitigation of the seismic risk in mainland Portugal, in the 10 year period under analysis, even though there was an increase of the building exposure in the region.

Cost optimality and net-zero energy in the renovation of Portuguese residential building stock – Rainha Dona Leonor neighbourhood case study

Cost optimality and nearly-zero energy buildings are two fundamental concepts within the current European Union policy related to the energy performance of buildings and consequently related to climate change mitigation and non-renewable resources consumption. While cost optimality is mainly focused on costs, nearly-zero energy buildings are focused on low energy consumption levels and on-site renewables harvesting.Using a residential building from a social housing neighbourhood, this study investigates the most cost-effective packages of renovation measures to achieve a zero energy balance building and compares these packages with those resulting from the calculation of cost-optimal levels. The investigation on the trade-offs between both approaches is relevant to achieve a smooth transition from cost-optimal levels to nearly-zero energy buildings.The results show that the measures that lead to the cost-optimal levels are very similar to the ones needed to achieve the zero energy balance and the results ...

Natural Ventilation Potential in Portuguese Residential Buildings under Winter Conditions – An Opportunity for Hybrid Ventilation

This paper presents a study of the potential for the use of natural ventilation systems in Portuguese multi-family residential buildings under winter climatic conditions. The behaviour of various natural ventilation systems is tested in a standard residential dwelling, using the TRNSYS 15 and COMIS 3.1 software programs. This study leads to the conclusion that the use of hybrid ventilation systems can save a considerable amount of the energy normally spent on continuously operating mechanical ventilation systems. Hybrid ventilation systems will not be adequate if there are no ventilation inlets in the façade and air intake is only by means of infiltration, especially in the case of certain modern windows with better seals; in such situations, the use of continuous mechanical ventilation systems is recommended. Therefore, it is essential to equip buildings with air inlets in the façades, preferably self-adjustable grilles, to ensure the best use of hybrid systems.

Cork-based mortars for thermal bridges correction in a dwelling: Thermal performance and cost evaluation

The aim of the present work was to simulate the behaviour of cork-based mortars in the minimization of energy consumption and condensation effects in an existing dwelling from the 1980s built in Lisbon, Portugal. Tests were carried out on hydraulic lime mortars and cement mortars with several proportions of cork as regards rheological characterization, thermal behaviour in and water vapour permeability. The first assessment of the behaviour of an existing dwelling showed that the power of heat dissipation in the dwellings’ thermal bridges is of the same magnitude order than heat loss in roof and much higher than in vertical opaque envelopes or openings, which enhances the need to reduce thermal bridges in the building. The selection of the most adequate mortar was then carried out in view of several scenarios. The best solution corresponds to the correction of thermal bridges using a Hydraulic lime mortar with 70% of cork granulate (CH70). An economic evaluation was also done concerning electric energy cost and its annual growing rate in Portuguese residential buildings. The results show that the use of CH70 mortar for thermal bridge correction has a payback of 3 years when compared to the simple repair of the original external plaster.

Application of Prefabricated Panels for the Energy Retrofit of Portuguese Residential Buildings Facades: A Case Study

Abstract This article aims to evaluate the potential application of prefabricated panels in energy retrofit of facades in the Portuguese building stock. The fundamentals of this study were part of Annex 50, which was an international ECBCS IEA project, with the purpose of developing an innovative concept of building renovation for the most representative buildings based on prefabricated systems. To analyze the potential application of energy retrofit using prefabricated panels, was important to know the reality of the existing building stock and its morphology. To know the reality of the building stock, an analysis was done based on the existing statistical data and to find the most representative residential buildings, target of the study, three criteria were defined: buildings built before 1990, with 2 to 6 floors and with renovation needs in the exterior envelope.In the absence of statistical information about buildings morphology, a research work was done in the field. During the collection of data a methodology was developed in which each opening was classified according to a code with three parameters. In the end of the classification, 29 final codes were achieved and was verified that three types of panels have a higher probability of being applied.

Projections of energy services demand for residential buildings: Insights from a bottom-up methodology

Projections of energy demand are important for energy security supply and low carbon futures, and usually rely on final energy consumption trends methods, limiting the opportunity for future options. Methods supported by energy services are much preferred to estimate future energy demand, since they are better suited to accomplish end-users needs. Final energy can then be assessed through complementary tools, as technological models, resulting in deeper knowledge on the relation between energy services and technology options.This paper presents a bottom-up methodology to project detailed energy end-uses demand in the Portuguese residential buildings until 2050, aiming to identify the parameters governing energy services demand uncertainty, through a sensitivity analysis. The partial equilibrium TIMES (The Integrated MARKAL-EFOM System) model was used to assess technology options and final energy needs for the range of parameters variations for each end-use, allowing to conclude on the impact of uncertainty of energy services demand in final energy.Main results show that technology can overweight behavioral practices and lifestyle changes for some end-uses as in space heating and lighting. Nevertheless, important focus should be given to uncertain parameters related with consumer behavior, especially those on heating and other electric end-uses, as thermal comfort and equipment's use.

On the use of internal thermal insulation systems for the retrofit of buildings' exterior walls

In this paper, a quantitative analysis of internal thermal insulation systems (ITIS) is made based on three basic requirements: thermal bridges minimisation; control of temperature variations within the exterior wall; and the need for at least a minimum thermal mass. This study relies on computer simulation using different tools depending on the purpose of the calculation. The selected software applications were in compliance with the available European standards, namely for thermal bridges and dynamic parameters. The effect of different outdoor climate conditions was evaluated, taking also into account the typical indoor hygrothermal characteristics of Portuguese residential buildings such as common temperatures and ventilation rates. The results of this study quantitavely show that, for the analysed requirements, the ITIS option should not be disregarded, provided that some proper measures are guaranteed. It can be an interesting solution for retrofitting exterior walls as long as thermal bridges are corrected whenever needed; that temperature variation within the exterior wall (which depends greatly on the colour of its outer surface and on the location of thermal insulation, and less on its thickness) are compat-ible with its resistance (with or without reinforcement measures); and that the availability of a minimum thermal mass is assured.

Modelling and simulation of a ventilated double window

Double windows are a currently adopted construction system in Portuguese residential buildings to prevent air leakage and thermal discomfort. We have changed this construction system so that it could be able to pre-heat the ventilation air between the windows. Simple changes consist in introducing vents at the base of the outer window to allow a supply of fresh air. Heat that escapes from inside through the inner window and solar radiation heat up the air between the two windows. Due to wind pressure and stack effect, the air rises and enters the room through a vent at the inside top of the system warmer than the outdoor air. A simulation program was built and validated with the use of test facilities, where different configurations of the system were tested. This paper presents the mathematical model and some results of a simulation work based on it. Parametrical studies were carried out by varying the airflow rate, the outdoor air temperature and the solar irradiance to predict the temperature rise and the useful energy of the delivered air. Results indicate an encouraging thermal performance of the ventilated double window offering itself as an alternative to cold natural ventilation.

Building Sustainability Assessment

Although social, economic, and cultural indicators are of substantial importance to the concept of sustainable building, this concept is usually related to environmental characteristics. Any building level assessment method is complex and involves contradictory aspects. Moreover, emphasizing qualitative criteria only increases confusion. R&D and standardization are thus concentrated to transparency and usability of the environmental methods. Other directions of research aim at performance-based design and methods to take regional and cultural aspects into account. In this paper, the perspectives of the sustainability assessment of a whole building are presented, based on a state of the art, feasibility study on performance analysis and the development of an extended life-cycle assessment for buildings. Using various tools, and based on the case studies of building sustainability assessment, environmental indicators were often shown to be of lesser importance than the other, soft ones. The first steps in the development of a building sustainability assessment method for Portuguese residential buildings will be presented and discussed in the end.