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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

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.

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.

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.

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.

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.

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.