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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

Buildings with a high window-to-wall ratio tend to suffer from excessive solar gains/losses that usually result in high energy demand and discomfort for occupants. Solar control films (SCFs) are a passive solution with the potential to increase the performance of new or refurbished glazing they are applied to. This paper presents a comprehensive literature review of the performance of SCFs applied to glazing systems of buildings. Research studies with experimental, analytical and computer simulation approaches were gathered and analyzed, identifying glass and film systems, climatic conditions, energy savings and comfort performance. The research approaches and main findings of existing research studies were compared and discussed. The presence of SCFs significantly reduced indoor solar radiation and illuminance levels, particularly with reflective films applied to south-oriented glazing (northern hemisphere). Glazing systems with SCFs were reported to promote cooling energy savings compared with clear glazing in hot climates. Few studies have explored the visual and thermal comfort performance of SCFs, concluding that these films promote thermal comfort, and reduce excessive illuminance and potential glare. Furthermore, this paper helps to highlight areas of guidance for future studies on the topic.

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.

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.

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.

Cavity walls are often proposed in the building envelope design as a solution for improving the thermal comfort of the occupants and reducing the adverse condensation effects on the building fabric. Although the behaviour of a non-ventilated cavity wall is well-known, more studies are required when cavity ventilation is allowed. In order to consistently predict the thermal behaviour of a naturally ventilated cavity wall, a convective model based on the integral equations of motion and enthalpy was developed and applied in the present study. The model is presented as a combination of two limiting cases of a steady laminar flow into the channel gap: fully developed flow and boundary layer flow. Conduction effects across the system are also included through a proper limiting case and then combined with the convective model. In addition a numerical CFD model was developed that provides solution for free convective flow configurations between two parallel conducting vertical walls. For comparison purposes, some test cases were simulated with the two models and a general good agreement was found between results. Finally, the integral model was applied to assess the thermal performance of a ventilated cavity wall for winter and summer conditions. Copyright © 2009 John Wiley & Sons, Ltd.

This paper presents the results of a program of wind tunnel model tests on pressure distributions for irregular-plan shapes (L- and U-shaped models). The experiments were carried out in a closed-circuit wind tunnel and a multi-channel pressure measurement system was used to measure mean values of loads on 1:100 scale models. The same tests were carried out on a cube-shaped model as an experimental validation. The effectiveness of the model shape in changing the surface pressure distributions is assessed over an extended range of wind directions. The experimental data for the L- and U-shaped models showed different wall pressure distributions from those expected for single rectangular blocks. Furthermore, a Computational Fluid Dynamics (CFD) code was used to illustrate some particular cases and to provide a better understanding of the flow patterns around these irregular-plan models and of the pressure distributions induced on their faces. Computed pressure coefficients have also been compared with wind tunnel results for normal and oblique wind incidence. A general good agreement has been found for normal wind incidence whereas some differences have occurred for other directions.

Solar-air collectors installed on the south-facing walls of school buildings have been tried out in Portugal as a passive means of improving indoor air quality without prejudice to thermal comfort requirements. A numerical investigation of the behaviour of these systems, typified as vertical channels opened at both ends, is presented for typical geometries and outdoor conditions. The study is carried out with natural convection and assumes that the induced flow is turbulent and two-dimensional. The fully averaged equations of motion and energy, added to a two-equation turbulence model, are discretized and solved following the concepts of TEF (Transfer Evolution Formalism) using a finite volume method. Flow and temperature fields are produced and results presented in terms of temperature and velocity distributions at the exit section of the duct. These enable a better understanding of the developing flow and can be helpful in the design phase of this type of system.

Vertical solar-air collectors that are used for providing natural ventilation can be a viable solution in buildings where higher ventilation rate requirements for better indoor air quality cannot be met by traditional natural ventilation methods. Indoor air quality problems have been experienced in Portuguese school buildings where a study revealed that the CO2 concentrations in classrooms in winter were higher than the recommended health limits. To improve the environment in these classrooms, solar-induced ventilation has been suggested. In the design of these solar ventilators, simple models can only predict the main features of the flow but they can be useful tools in the first stages of the design process. However, CFD models can produce microscopic information about the state of all flow parameters and thus are recommended when a high degree of accuracy is needed. In this paper, a simplified model based on the integral equations of motion and heat transfer is developed for a vertical solar-air collector and applied to different boundary conditions. The results are compared and discussed with those computed from a CFD code specially designed for room ventilation.

This paper concerns to the post-occupancy monitoring of a building sited in Lisbon with transparent double-skin façades (DSF). This is the first of an enlarged monitoring program covering other buildings and weather conditions aiming to clarify under which climate and performing conditions this architectural solution is acceptable. Within this campaign an enlarged set of parameters were measured, covering from outdoor conditions to indoor comfort. The present paper focus is the thermal behaviour of the façade. 111-116pp Vol. 3 DE/NESDE