IPS - ESTS – DEM - Artigos científicos
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- The effect of occupancy and environmental physical variables on classrooms’ natural ventilation: a path modeling approachPublication . Duarte, Rogério; Rodrigues, António Moret; Pimentel, Fernando; Gomes, Maria da GlóriaIn this paper, we use a path model to study natural ventilation in classrooms and research the link between air change rate, occupancy, and both outdoor and indoor physical variables. In general, the path model is derived from the building physics and occupant behavioral considerations via structural equation modeling (SEM), and allows for the use of continuous observable and unobservable factors. The latter are often employed in behavioral and social sciences to represent personal and group attributes. The path model is validated with data gathered during two consecutive academic years from four classrooms of a Portuguese school. The results confirm indoor and outdoor air temperature as major drivers of classroom ventilation, with standardized total path coefficients of approximately 0.55. Solar energy, precipitation, and occupancy are also significant drivers of classroom ventilation, with standardized total path coefficients of 0.24, −0.18, and 0.17, respectively. These results contribute to our understanding of the relative importance of occupancy as well as to identifying the most relevant environmental determinants of natural classroom ventilation. In spite of the statistical significance of the path model as a whole and its detailed causal relationships (direct, indirect, and feedback), only 58% of classroom ventilation variance is explained by the selected input variables. Because naturally ventilated classrooms depend significantly on occupants’ interactions with the built environment, i.e., opening/closing windows and blinds, extending path modeling to include additional personal and context-related drivers of occupants’ behavior would allow for further insights into the complex multi-domain topic of natural classroom ventilation.
- Gestão de segurança e saúde no trabalho em projetosPublication . Costa, Olga; Didelet, Filipe
- Análise do processo de gestão de projetos: um estudo de caso no setor da metalomecânicaPublication . Condeixa, Rui; Costa, Olga
- Legislação de segurança contra incêndios: aplicação em edifícios anteriores ao ano de 2008Publication . Gomes, H.; Costa, Olga
- Applying computational fluid dynamics in the development of smart ripening rooms for traditional cheesesPublication . Alvarenga, Nuno; Martins, João; Caeiro, José; Garcia, João; Passáro, João; Coelho, Luis Manuel Rodrigues; Santos, Maria Teresa; Lampreia, Célia; Martins, António; Dias, JoãoTraditional ewe’s cheese producers face certain challenges caused by fluctuating envi- ronmental parameters inside the ripening room, which lead to lack of homogeneity in the final product. The present research discusses the application of computer fluid dynamics for simulating the distribution of environmental parameters, predicting the airflow pattern, and identifying critical areas where such parameters could cause reduced cheese quality. A new monitoring system was developed including presence sensors, temperature and humidity dataloggers, pneumatic actua- tors, microcontrollers, and microcomputers connected remotely for control, data visualization, and processing. The validation of the computer simulation and monitoring system was made with a batch of 40 ewe’s cheeses distributed in three different zones inside a prototype ripening room and ripened for 35 days. At 35 days, a physical, chemical, and microbiological characterization of cheeses was made for evaluation of the influence of environmental conditions on cheese quality. The comparison between simulated and local measurements showed close agreement, especially concerning air velocity inside the stacks of cheese. The results of Pearson’s correlation analysis and PCA concluded that temperature affected the appearance of the rind, hardness, number and area occupied by holes. Humidity affected aw and mFeret. Air velocity affected pH and the circularity of gas holes.
- Latent thermal energy storage application in a residential building at a mediterranean climatePublication . Coelho, Luis Manuel Rodrigues; Koukou, Maria K.; Dogkas, George; Konstantaras, John; Vrachopoulos, Michail Gr.; Rebola, Amândio; Benou, Anastasia; Choropanitis, John; Karytsas, Constantine; Sourkounis, Constantinos; Chrysanthou, ZenonAn innovative thermal energy storage system (TESSe2b) was retrofitted in a residential building in Cyprus with a typical Mediterranean climate. The system comprises flat-plate solar collectors, thermal energy storage tanks filled with organic phase change material, a geothermal installation consisting of borehole heat exchangers with and without phase change material and a ground source heat pump, an advanced self-learning control system, backup devices and several other auxiliary components. The thermal energy storage tanks cover the building’s needs at certain temperature ranges (10–17 ◦C for cooling, 38–45 ◦C for heating and 50–60 ◦C for domestic hot water). A performance evaluation was conducted by comparing the TESSe2b system with the existing conventional heating and cooling system. The systems were simulated using commercial software, and the performance of the systems and the building’s energy needs were calculated. Based on the energy quantities, an economic analysis followed. The equivalent annual primary energy consumption with the conventional system resulted in being 43335 kWh, while for the storage system, it was only 8398 kWh. The payback period for the storage system was calculated to be equal to 9.76 years. The operation of the installed storage system provided data for calculations of the seasonal performance factor and storage performance. The seasonal performance factor values were very high during June, July and August, since the TESSe2b system works very efficiently in cooling mode due to the very high temperatures that dominate in Cyprus. The measured stored thermal energy for cooling, heating and domestic hot water resulted in being 14.5, 21.9 and 6.2 kWh, respectively. Moreover, the total volume of the phase change material thermal energy storage tanks for heating and domestic hot water was calculated to be roughly several times smaller than the volume of a tank with water as a storage medium.
- A case study for decentralized heat storage solutions in the agroindustry sector using phase change materialsPublication . Simão, Carlos; Murta-Pina, João; Oliveira, João Pedro; Coelho, Luis Manuel Rodrigues; Pássaro, João; Ferreira, Diogo; Reboredo, Fernando; Jorge, Tiago; Figueiredo, PedroThe development of thermal energy storage solutions (TES) in agroindustry allows reduc- tion of production costs and improvement of operation sustainability. Such solutions require high storage capacity and the ability to adapt to existing equipment. The use of phase change materials (PCMs), which are able to store thermal energy as latent heat, creates new opportunities for heat storage solutions (LHS, latent heat storage) with higher energy density and improved performance when compared to sensible heat storage. New architectures are envisaged where heat storage is distributed throughout the production chain, creating prospects for the integration of renewable generation and recovery of industrial heat waste. This work aims to investigate the benefits of decentralized thermal storage architecture, directly incorporating PCM into the existing equipment of an agroindustry production line. To assess the feasibility and potential gain in the adoption of this TES/LHS distributed solution, a tempering and mixing equipment for food granules is selected as a case study, representing a larger cluster operating under the operation paradigm of water jacket heating. The behavior of the equipment, incorporating an inorganic PCM, is modeled and analyzed in the ANSYS Fluent software. Subsequently, a prototype is instrumented and used in laboratory tests, allowing for data collection and validation of the simulation model. This case study presents a demonstration of the increase in storage capacity and the extension of the discharge process when compared to a conventional solution that uses water for sensible heat storage.
- Effect of fins and nanoparticles in the discharge performance of PCM thermal storage system with a multi pass finned tube heat exchangePublication . Pássaro, João; Rebola, A.; Coelho, Luis Manuel Rodrigues; Conde, J.; Evangelakis, J.A.; Prouskas, C.; Papageorgiou, D. G.; Zisopoulou, A.; Lagaris, I. E.This work studies the heat exchange process of a latent heat thermal energy storage (LHTES) system equipped with a compact finned tubes heat exchanger (HE) as this is one of the most important aspects of the storage system, the capacity for effectively delivering its stored energy. This work fills in a literature gap for 3D, transient heat transport fluid (HTF) flow models concerning storage systems with phase change materials (PCMs) with fins and nanoparticles allowing for an evaluation on the quality of heat delivered by the system. Numerical simulations, for full turbulent conditions of the HTF flow, were developed to access the influence of the fin pitch and the PCM thermal properties in the performance of the energy discharge process. Samples of commercial paraffin-wax A53 doped with graphene based nanoplatelets were tested and characterised. Different types of nanoplatelets were employed in the range of 0.5% to 6% weight. Measured data of the thermal conductivity, specific heat and fusion latent heat are presented. The simulations were developed for three fin pitch values 5 , 10 and 20 mm and for 1%wt and 6%wt nanoparticles loads. The effect of fins and combination of fins and nanoparticles in the outlet temperature and liquid fraction distribution inside the LHTES unit during the discharge process in a 3D full scale model was analysed. The system performance was evaluated based of off the outlet temperature of HTF to ascertain both the quantity and quality of the heat provided. The results show that the PCM thermal conductivity is significantly enhanced by the addition of graphene nanoparticles with a high aspect ratio. The addition of only 1%wt doubled the solid phase PCM thermal conductivity and for a 6%wt load the thermal conductivity increased by a factor of 3.5. Meanwhile, specific and latent heat values of the samples are relatively unaffected. The numerical results further show that applying thin fins is an effective approach to enhance LHTES systems discharge performance. Increasing the fin number significantly enhances the heat transfer rate and the HTF discharge temperature during solidification and has a positive impact in the useful discharge heat capacity, providing better quality heat. Combining fins and nanoparticles improves the discharge process, nevertheless the role of nanoparticles becomes secondary as the fins number increases. The results demonstrate that standardised compact finned heat exchangers ubiquitously used in the HVAC industry can successfully overcome the low thermal conductivity of common PCMs without compromising the useful heat discharge capacity or resorting to nanoparticles decreasing the discharge time between 60 and 77% with adequate fin number.
- Numeric study of geothermal borehole heat exchanger enhancement via phase change material macro encapsulationPublication . Pássaro, João; Rebola, A.; Coelho, Luis Manuel Rodrigues; Conde, J.his article addresses the theoretical effect of using geothermal boreholes enhanced with macro-encapsulated phase change materials (PCM) employed with a ground sourced heat pump (GSHP). The aim being the improvement of the heat pump performance through soil temperature stabilisation, taking advantage from the PCM inherent property of changing phase at a constant temperature, that can be matched with the temperature of the surrounding soil, contributing as well to increase the energy storage capacity underground. The numeric work studied different PCM thermal parameters with regards to their influence on the overall behaviour of the heat pump, with different operation modes (On/Off and Inverter) changing the solidus and liquidus temperatures and phase change enthalpy values. The CFD results showed that, while it underperformed having 0.15% difference in the best of cases (specifically the On/Off mode), it used in the best case scenario only 30% of the stored energy in the PCM. The application of macro-encapsulation did provide a stabilising effect to the soil and heap pump operation as it was originally intended to do, helping reduce energy expenditure by the system. Significant modifications are needed in order to improve, both concerning geometry and encapsulation techniques to overcome the PCM and other materials thermal limitations.