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This paper examines the thermal and luminous performance of single-glazed windows with and without solar control films (SCFs) and a venetian blind in actual working conditions. SCF is a passive solution to modify the solar-optical properties of glazing systems, in order to reduce the solar gains and the energy use and to increase the indoor comfort conditions. An experimental campaign was carried out simultaneously in both cooling and heating seasons in two similar office rooms, one with a SCF applied on the internal surface of the glass and the other without any SCF. The experimental data was used to calibrate a model in EnergyPlus and to assess the energy performance of several SCFs with different thermal and optical characteristics for different orientations of the façade. A decision-making framework was applied to identify the potential use of SFCs as retrofitting solutions for single-glazed windows based on energy performance criteria. The results show that SCFs have a real impact in reducing the cooling energy use for South, East and West solar orientations (SCFs with low solar transmittance coefficients show reductions of the cooling energy use up to 86%) due to the reduction of solar gains, while there is an increase in the heating and lighting energy use., Department of Civil Engineering (DECivil) - CERIS Research Institute -, Instituto Superior Técnico, Universidade de Lisboa, in particular to the occupants of the office rooms. Also, the authors would like to extend their thanks to MSc student Duarte Oliveira for the support during the experimental campaign and to the IMPERSOL company for their technical support. The first author wishes to acknowledge the support of FCT (Foundation for Science and Technology) Ph.D Grant FCT PD/BD/127848/2016

The global increase in energy needs and environmental awareness for a more efficient energy use have boosted building rehabilitation to decrease energy consumption. The installation of solar control films (SCFs) in buildings with large glazing façades makes it possible to reduce excessive solar gains through the glazing. The main purpose of the work is to assess, with field experimental data, the thermal and luminous performances of double-glazing units with SCFs installed in office rooms, in Lisbon. An experimental campaign was carried out simultaneously in three adjacent offices: one with a highly reflective SCF (external installation), one with a reflective SCF (internal installation) and one without an SCF. The exterior SCF showed the best thermal performance with reductions in the peak indoor air temperature of up to 6.9 and 2.3 °C during the representative days of the heating and cooling periods, respectively, increasing thermal comfort mainly during the cooling period. The interior SCF had a poorer thermal performance since it contributed to solar radiation absorption that is then emitted as heat into the indoor environment, increasing the greenhouse effect of the office. The presence of SCFs reduced the indoor illuminance levels, having a positive impact on thermal comfort and glare reduction in the cooling period.

Worldwide, buildings have been presented as one of the main energy consumers and, for that matter, there is an increased tendency to invest in policies and measures that promote more efficient buildings. Among the chosen strategies, the need to promote the use of passive solutions and retrofit the existing building stock is often pointed out. Portuguese building stock has proven to be obsolete in terms of thermal comfort, which can directly affect the energy demand for climatization purposes. Considering the great solar availability in the country, when compared to other European locations, building retrofit with solar passive technologies can be a suitable solution. This paper aims to review studies on the application of solar passive technologies to retrofit façades in the Mediterranean climate context, with a special focus on Portugal. Four retrofit passive solar technologies were reviewed, namely glazing, sun shading, sunspaces and Trombe wall technologies.

The main goal of the paper is to describe and provide a preliminary discussion of the performance of a large diameter earth -air heat exchanger used in cooling and heating of a small office building located in Alentejo, Portugal. The sole energy consumption associated with this system is that required to operate two fans that move outdoor air into the office spaces. There are no mechanical moving parts inside the office building and the heat exchanger is designed in combination and complementing principles of natural ventilation in the office spaces. Post-occupancy results show the large diameter design of the earth-air heat exchanger is capable of removing up to 30 kW of heat from the outdoor air using just 2,2 kW of fan power. Despite the significant cooling requirements in Alentejo, Portugal, earth air heat exchanger outflow air temperatures can be 10 K lower than outdoor temperatures, allowing the removal of office space loads in the morning period and supplying offices in the afternoon with air at temperatures that seldom exceed 27°C, despite outdoor air temperatures of 40°C. info:eu-repo/semantics/publishedVersion

Buildings are responsible for 40% of energy consumption and 36% of CO₂ emissions in the European Union. To bring these levels down, governments are striving to promote a more efficient use of energy resources and an increase adoption of renewable energy technologies, as photovoltaic panels and solar collectors on the building envelopes. To fully exploit the potential of these technologies, a detailed analysis of the incident solar radiation on buildings roofs and facades is mandatory taking into account the geographical and urban environments. Three solar radiation tools, in association with two different modelling approaches (2.5D and 3D) handled by a 3D GIS tool, were applied to a city block of downtown Lisbon for both the winter and summer solstices and for different levels of detail of the surrounding context. The study showed that both built surroundings and topographic relief have an important impact on solar potential of buildings in urban areas. An average difference of about 30% in the results was observed between the simulations with and without the geographical and the urban environments included. The study also showed that the 3D approach has high potential to fully evaluate solar access in complex urban layouts, for accounting the irradiation of all sun-exposed surfaces of the buildings.

An innovative system of pre-cast high performance concrete pre-walls, combined with low-cement cast-in-situ lightweight concrete core, is studied experimentally from the standpoint of the thermophysical properties of the concrete compositions under various hygroscopic conditions. Thermal conductivity, volumetric heat capacity and thermal diffusivity are experimentally determined, by a transient method, for eight concrete compositions in the dry state, hygroscopic and over-hygroscopic ranges. The incorporation of lightweight aggregates in the concrete mixture allowed to reduce the thermal conductivity (up to 53%) and thermal diffusivity (up to 41%), in comparison to normal weight concrete. The moisture content, regardless of the composition of the concrete, impacts negatively the thermal performance, with a rise of both thermal conductivity and diffusivity, which was also captured by analytical expressions. An application study of the pre-walls system to a swimming pool showed reductions of thermal conductance of up to 38% when combining high mechanical performance concrete in the pre-walls with lightweight aggregate concrete with high thermal performance in the core. These results highlight the importance of assessing thermophysical properties in service conditions, with the moisture content effect included, and selecting the types of concrete in composite pre-walls systems to enhance both mechanical and thermal performance.

Classrooms in Southern Europe are traditionally ventilated with manual opening of windows. This is an energy-sparing and perfectly appropriate way of ventilating classrooms when weather conditions are warm, however, as outdoor air temperatures drop, teaching staff and students tend to leave windows closed and, as a consequence, ventilation rates fall leading to poor indoor air quality. To safeguard classrooms' indoor air quality and promote energy conservation, understanding the conditions for which manual window-airing is appropriate is of great relevance. Yet, given the stochastic nature of window-airing, it is difficult to get hold of this understanding. The main objective of this paper is to find out when manual window-airing of classrooms is appropriate. To achieve this objective, four free-running classrooms of a Portuguese public secondary school were monitored during a two-year period. Ventilation rates were determined and it is concluded that manual opening of windows provides appropriate ventilation for outdoor running mean temperatures larger than 19 °C. When outdoor running mean temperatures are lower than 16 °C, manual window-airing becomes inappropriate and, for outdoor running mean temperatures between 16 and 19 °C, appropriate manual window-airing depends on the indoor air temperature. For the studied classrooms, these results translate into appropriate ventilation for approximately a quarter of the academic year. Because of the significance of this finding, the paper concludes with a review of the ventilation strategy used in the studied classrooms.

The incorporation or the replacement of materials in buildings may decrease the energy use during the operational stage but increase the embodied energy in a building's life cycle. In this study, three different solar control films (SCFs A, B and C) with application on the existing windows of a building are investigated through an energy, environmental and economic perspective over a defined life cycle period. The full replacement of the existing window with a new one is also analyzed as an alternative retrofitting solution. Retrofitting solutions with higher light-to-solar gain ratios showed higher energy savings during the use stage by decreasing the solar gains in a higher proportion than the decrease of the visible transmittance. The best retrofitting solution, SCF C, showed a life cycle energy (LCE) (embodied plus operational energy) and a carbon footprint of 4447 MJ/m2/40 y and 380 kgCO2eq/m2/40 y, respectively, whereas the least performant solution, new window, showed a LCE 1.5 times higher than the average of the three SCFs. The higher LCE value of the new window was found to be related to the higher value of the embodied energy when compared to that of the three SCFs (∼9 times higher than the average of the films).

Hospitals, by the nature of their function, are high energy consumers and thus buildings where the potential of energy saving is high. In hospitals built prior to the implemented European directives on energy performance of buildings the compliance with the current energy standards is difficult to achieve. This work performs a holistic experimental and numerical study to assess the thermal behavior and energy retrofitting potential of medical offices of a hospital building prior to these directives. The nursing school Francisco Gentil building of the Portuguese Oncology Institute in Lisbon, was chosen as case study. For thermal behaviour assessment, field monitoring of two typical medical offices, in opposite facades , was carried out in terms of temperatures, heat flows and irradiances in the heating and cooling seasons. Thermal comfort and U-values evaluation and a frequency-domain approach were complementary analyses performed. Finally, an experimentally calibrated building energy simulation was performed to obtain solutions that enhance the energy performance of the offices. By implementing as retrofit solutions double reflective glass in windows, 6 cm of extruded polystyrene on the exterior walls and 7 cm on the roof, energy savings up to 53% can be achieved in the medical offices.

Natural ventilation plays an important role on the thermal and energy performance of a building. The present study aims to analyze the natural ventilation conditions of a dwelling in a Mediterranean climate and their impacts on the thermal and energy performance using an advanced building energy simulation tool. Several multi-zone simulations were carried out. In the summer, the simulations were performed under free-floating conditions, whereas in the winter they were carried out under controlled temperature conditions. In the summer, ventilation scenarios with windows opened during certain periods of time and with or without permanent openings in the facades were analyzed. The existence of permanent openings proved to be an important factor of temperature control by lowering the average indoor zone temperatures during the day. Cross-ventilation also showed to be e ective. In the winter, we simulated the existence or absence of permanent openings for room ventilation and their surface area. The results showed that the stack e ect plays an important role in the ventilation and that in general it outperforms the wind e ect. Sizing permanent openings according to the standard guidelines proved to be adequate in providing the expected ventilation rates on an average basis. info:eu-repo/semantics/publishedVersion

A ventilação de salas de aula é habitualmente feita por abertura de janelas. Esta é a solução tradicional sendo perfeitamente adequada para tempo quente, porém, quando as temperaturas exteriores baixam, estudantes e professores deixam as janelas fechadas reduzindo substancialmente os caudais de ventilação, resultando na deterioração da qualidade do ar interior. Este artigo tem por objetivo compreender as condições em que a ventilação com abertura manual de janelas é adequada. Para isso usam-se 2 anos de dados de monitorização de 4 salas de aula de uma escola básica e secundária nacional (um antigo liceu com projeto da Junta das Construções para o Ensino Técnico e Secundário – Ministério das Obras Públicas e Comunicações, reabilitado pela Parque Escolar na segunda metade dos anos 2000). Analisam-se os caudais de ventilação nas salas concluindo-se que a abertura de janelas é adequada com temperaturas exteriores diárias superiores a 19ºC. Quando estas temperaturas são inferiores a 16ºC a ventilação por abertura de janelas torna-se insuficiente e, entre 16 e 19ºC, a adequabilidade vai depender da temperatura interior. Para as salas de aula monitorizadas e condições exteriores observadas conclui-se que a ventilação por abertura manual de janelas permite ambientes interiores adequados (não só sob o ponto de vista da ventilação e qualidade do ar interior, mas também do conforto térmico) durante aproximadamente 25% do ano letivo.

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.

In recent years, Energy Performance Building Directives have been published and adopted by all EU member states in order to promote the improvement of the energy performance of buildings within the EU, and thus coping with the growing comfort needs and consequent increase in energy consumption for space heating and cooling. Structural lightweight aggregate concrete (SLWAC), due to its thermal properties, presents itself as an alternative to normal weight concrete (NWC) to reduce the thermal bridging effects as well as the building energy needs to maintain thermal comfort levels in buildings. In this paper, the potential of SLWAC to improve the energy performance of buildings was assessed. An experimental study was carried out in order to determine the thermal properties of five different concrete mixtures, four SLWAC and a reference NWC for comparison purposes. These thermal properties were then used in the two-dimensional heat transfer program Therm and in the whole-building energy simulation program EnergyPlus to assess the impact of SLWAC on the thermal bridge heat losses and building energy needs of a case study. Results showed that SLWAC can improve the energy efficiency of buildings and thus be an attractive alternative to the use of the traditional NWC.

Buildings with large window areas tend to have more heat gains/losses through the glazing systems, which increase the cooling and heating loads. Applying solar control films (SCFs) on glazing systems can reduce the heat gain, annual energy consumption and peak demand load. The main objective of the present study is to assess the (thermal and visual) comfort, energy and environmental performance of different types of SCFs applied on glazing systems. Three adjacent office rooms located in a university building in Lisbon were used as case study. A building energy simulation model, calibrated from experimental results, was used to simulate the performance of the glazing systems. The most reflective SCF ( τ v i s = 16%; g = 0.15) has the highest thermal and optical performance due to its low visible transmittance and solar heat gain coefficient, making it possible to achieve temperature and glare comfort during 41% and 43% of working hours. The spectrally selective film with τ v i s = 63% and g = 0.40 has the highest energy performance, enabling to achieve an annual reduction of 38% of energy consumption and CO2 emissions. From a multi-criteria evaluation approach, the best alternative is the most reflective film when assigning preferred importance to thermal and visual comfort, and the most spectrally selective film when energy cost saving and CO2 emission reduction are taken as the decision criteria.

É reconhecido o mérito da ventilação natural de edifícios residenciais e de serviços não só do ponto de vista da poupança energética como também da qualidade do ar interior. Contudo, para projetistas e gestores de edifícios, a incerteza associada à ventilação natural introduz dificuldades e riscos acrescidos. Neste artigo apresenta-se um método para determinar renovações de ar em condições não-estacionárias, como as que se observam em espaços ocupados de modo intermitente, sujeitos a variações no ambiente exterior (e no interior) e na forma como são operados os dispositivos de ventilação natural. O método usa dados de ocupação e de concentração interior de CO2 em conjunto com um Filtro de Kalman para estimar variações dos caudais de ventilação. Após aplicação deste método a uma sala de aula ventilada por abertura manual de janelas, discute-se a utilidade do método para o reconhecimento por projetistas e gestores de edifícios do mérito da ventilação natural.

This paper describes a method for estimating ventilation rates in a window-aired room considering “in-use” conditions and uncertainty in occupancy (CO2 release) and in measurements of indoor air CO2 concentration. Estimates are drawn from indoor air mass conservation principles and an Extended Kalman Filter, serving as state observer. The modelling procedure is described and tested against synthetic time series generated from pseudorandom values of occupancy and ventilation rate. Additionally, data collected from a case study (a window-aired classroom) is used to illustrate how the procedure is applied and its practical interest. Test results confirm the state observer’s tracking capability and confirm its ability to reconstruct ventilation rates in the presence of sudden changes caused by window opening/ closing and intermittent occupancy. Results for the case study highlight the benefits to designers and ultimately to occupants, derived from knowledge of ventilation rates in window-aired rooms. info:eu-repo/semantics/submittedVersion

An accurate assessment of the airflow in naturally ventilated double skin facades (DSF) is crucial for a correct design and performance evaluation. Measuring and predicting DSF airflow is not a straightforward task, given the stochastic nature of the wind, which can assist or oppose the buoyancy force. The present paper resumes the results of airflow measurements inside a naturally ventilated double skin facade using a tracer gas technique. The tests were performed on an outdoor air curtain (OAC) DSF test cell with a movable slat venetian blind. Measurements with no active shading and at night were also performed. Outdoor and test cell air gap temperatures were continuously measured and wind pressure coefficients were determined from wind tunnel tests. Experimental results were then compared to those obtained by a simple model taking into account both thermal and wind effects on the facade. From this comparison discharge coefficients were estimated, which can be used for characterizing the DSF behaviour.

Instantaneous or tankless gas-fired water heaters are widely used in residential buildings to heat water for domestic use. For the combustion can process properly, a minimum amount of air is required, which can be obtained directly from outdoors or from inside the room. This latter case corresponds to the operation mode of the atmospheric-vent water heater, which is one of the most frequently encountered appliances to heat domestic water. As the room where the water heater operates is generally a living area, the installation design should account for the health and comfort requirements. Increasing the room airflow rates reduces the risk of harmful products from incomplete combustion but, as counterpart, important impacts on the thermal and energy performance of the room can occur. In this paper the natural ventilation conditions of a room with an atmospheric-vent water heater are investigated. Moreover, the effects on energy demand for thermal comfort are assessed. The study was conducted through the EnergyPlus simulation program, whose applicability to the problem was first tested. The results obtained are consistent with the expectations, allowing for a better insight into the level of compliance of the combustion air requirements and respective impacts on energy performance.

Shading devices are used to reflect direct sunlight, reduce glare and prevent overheating. A correctly designed shading system will strongly influence the entire building energy consumption, peak loads and indoor comfort. The use of the venetian blinds is particularly common due to its relatively low cost and high versatility. The present study focuses on the algorithms for calculating both short-wave (solar) and long-wave (infrared) transmittance, absorptance and reflectance of the venetian blinds. The model is based on the net radiation method, allows for different slat discretization schemes and is suitable for integration into the building energy simulation tools. Once the effective optical properties are computed, the system can be regarded as an additional layer in a multilayer glazing system. Computed blind solar transmittance has been compared with other numerical models and in situ experimental results. A general good agreement has been found, except in cases where incident radiation is mostly diffuse. In this study, the effect of different design parameters on effective optical properties of the venetian blinds is also investigated: (a) the sun profile angle, (b) the slat angle and (c) the venetian blind geometry. Moreover, the effect of the discretization of each slat is examined.