Titel "Korte inhoud" "Numerical and Experimental Analysis of Passive Cooling through Night Ventilation (Numerieke en experimentele analyse van passieve koeling door nachtventilatie)" "Nowadays, the application of active cooling in office buildings is hardly questioned in building practices. Also in temperate climates, active cooling is often assumed to be a necessary condition for a good thermal comfort. However, an optimal building design can go a long way towards reducing the cooling load. For example, night cooling can maintain thermal comfort during the day, by pre-cooling the building at night using cool exterior air at high air change rates. By day, the thermal mass buffers the heat released in the building, thereby reducing and delaying air temperature peaks.To address this, a thorough study is made of the transient behaviour of a room with night ventilation. The methodology can be subdivided into three main parts, a first part being numerical, a second part experimental and a third part focussing on implementation in BES models. The numerical CFD study focusses on obtaining a better insight in the transient surface heat transfer during night ventilation. In particular, the study takes into account the influence of thermal mass by including concrete slabs as floor and ceiling in the model. Furthermore, the transient behaviour of the air-mass system is simulated for different air change rates and initial indoor-outdoor temperature differences. The influence of excluding radiation from the model is investigated, as well as the impact of geometrical variations. Interesting conclusions could be drawn regarding the unsteady flow pattern. Three flow patterns were observed: buoyant flow, forced flow and transition flow, which is the intermediate regime between the first two flow regimes. The flow pattern strongly influenced the corresponding local surface convection. However, as this numerical study is limited to 2D with simplified geometry and constant boundary conditions, only qualitative conclusions can be drawn. An experimental study is required to confirm the observed phenomena.The second part of the study will therefore discuss the measurements conducted in a full scale test room under realistic climatic boundary conditions. As was the case in the numerical model, the thermal mass is also provided in the experimental set-up, by including two 15 cm thick concrete slabs as floor and ceiling. The room has dimensions close to a one-cell office, and is exposed to the climate through a SW-oriented façade with automated hopper window. The room is provided with more than 200 sensors for a detailed monitoring of air, surface and mass temperatures, along with surface heat flux, air velocity and pressure difference. Apart from the mechanical ventilation, the room is free floating. The measurements provide a detailed insight into the phenomena occurring during night ventilation under realistic circumstances. They allow confronting the assumptions made in BES models with reality and confirm the tendencies that were observed in the numerical study, such as the three flow regimes. The determination of the air change rate proved challenging and was investigated with tracer gas experiments. Furthermore, a detailed analysis was made of the thermal response of the room. Though determination of convective heat transfer coefficients was not possible with sufficient accuracy, the assumptions used in BES models could be confronted with the measurement results. Smoke visualisation experiments were conducted to determine a correlation between thermal parameters and flow behaviour. These findings are confronted with literature. Finally, a number of selected nights are simulated with CFD as well, illustrating that CFD must be used with extreme care.The final part of the study focusses on the implementation in BES models. The room is simulated in TRNSYS 17, using the results of a four week measurement campaign as boundary conditions and verification data. The influence of included multiple air nodes in one thermal zone is investigated, illustrating the difficulty of an accurate modelling of the intra-zonal" "Cost-efficient cooling of buildings by means of geothermal borefields with active and passive cooling" "Louis Hermans, Wouter Peere, Lieve Helsen" "Novel design optimization for passive cooling PCM assisted battery thermal management system in electric vehicles" "Rekabra Youssef, Md Sazzad Hosen, Jiacheng He, Mohammed Al-Saadi, Joeri Van Mierlo, Maitane Berecibar" "Recently, the phase change material (PCM) battery thermal management system (BTMS) attracted attention. However, enhancement and optimization for the BTMS are required due to volumetric system design and low thermal conductivity. This study provides a novel design optimization to improve the environmental aspect of the cooling system and reduce its weight. Jute fibers as a planet-system, available, cheap, and weightless material is combined with the PCM battery thermal management based. The thermal behavior of large lithium-ion batteries (LIB) under different load protocols including fast discharge, periodic load, and real drive cycle are investigated. The results with the periodic load profile confirm that the maximum temperature for the cooling strategies of no-cooling, PCM cooling and PCM with jute reaches 39.22 °C, 38.22 °C and 35.09 °C, respectively. Moreover, applying aggressive high constant discharge current leads to further reduction in maximum temperature, where the maximum temperature reaches 47.27 °C, 41.06 °C, and 36.29 °C with the no-cooling, PCM cooling and PCM with jute cooling strategies, respectively. This article represents the first attempt to use a combination of jute and PCM in order to maximize temperature efficiency enhanced. Thus, this research contributes to further design optimization in battery thermal management system simplicity, environmental friendliness, energy and weight saving." "Feasibility assessment of passive cooling for office buildings in a temperate climate through uncertainty analysis" "Wout Parys, Hilde Breesch, Hugo Hens, Dirk Saelens" "In this paper, the feasibility of passive cooling in newly built office buildings in the temperate climate of Belgium is assessed using the standardized adaptive comfort criteria. This is done through Monte Carlo uncertainty analysis of the simulated weighted exceeding time for different building designs with varying insulation level, glazing-to-wall-ratio, glazing type and air tightness. Two passive cooling schemes are studied: diurnal manual window operation and the combination of diurnal manual window operation and passive night ventilation. Additionally, two possible measures to limit heat gains, external solar shading and daylighting, are considered. The integration of a detailed model of window operation, establishing a real-time coupling between the thermal model and the behavioural model and thus allowing simulating adaptive behaviour, is shown to impact the results significantly and is therefore recommended by the authors. The uncertainty analysis shows that it is possible to cool office buildings solely by diurnal manual window operation, even for highly insulated and air tight buildings. This requires minimizing heat gains to about 900 kJ/m 2 per working day during summer months. When a combination of diurnal window operation and night ventilation is available, limiting the heat gains to about 1500 kJ/m 2 per working day suffices. © 2012 Elsevier Ltd." "Performance evaluation of passive cooling in office buildings based on uncertainty and sensitivity analysis" "Hilde Breesch" "Natural night ventilation is an interesting passive cooling method in moderate climates. Driven by wind and stack generated pressures, it cools down the exposed building structure at night, in which the heat of the previous day is accumulated. The performance of natural night ventilation highly depends on the external weather conditions and especially on the outdoor temperature. An increase of this outdoor temperature is noticed over the last century and the IPCC predicts an additional rise to the end of this century. A methodology is needed to evaluate the reliable operation of the indoor climate of buildings in case of warmer and uncertain summer conditions. The uncertainty on the climate and on other design data can be very important in the decision process of a building project.The aim of this research is to develop a methodology to predict the performance of natural night ventilation using building energy simulation taking into account the uncertainties in the input. The performance evaluation of natural night ventilation is based on uncertainty and sensitivity analysis.The results of the uncertainty analysis showed that thermal comfort in a single office cooled with single-sided night ventilation had the largest uncertainty. The uncertainties on thermal comfort in case of passive stack and cross ventilation were substantially smaller. However, since wind, as the main driving force for cross ventilation, is highly variable, the cross ventilation strategy required larger louvre areas than the stack ventilation strategy to achieve a similar performance. The differences in uncertainty between the orientations were small.Sensitivity analysis was used to determine the most dominant set of input parameters causing the uncertainty on thermal comfort. The internal heat gains, solar heat gain coefficient of the sunblinds, internal convective heat transfer coefficient, thermophysical properties related to thermal mass, set-point temperatures controlling the natural night ventilation, the discharge coefficient Cd of the night ventilation opening and the wind pressure coefficients Cp were identified to have the largest impact on the uncertainty of thermal comfort.The impact of the warming climate on the uncertainty of thermal comfort was determined. The uncertainty on thermal comfort appeared to increase significantly when a weather data set with recurrence time of 10. years (warm weather) was applied in the transient simulations in stead of a standard weather data set. Natural night ventilation, designed for normal weather conditions, was clearly not able to ensure a high probability of good thermal comfort in warm weather. To ensure a high probability of good thermal comfort and to reduce the performance uncertainty in a warming climate, natural night ventilation has to be combined with additional measures. Different measures were analysed, based on the results of the sensitivity analysis. All the measures were shown to significantly decrease the uncertainty of thermal comfort in warm weather. The study showed the importance to carry out simulations with a warm weather data set together with the analysis under typical conditions. This approach allows to gain a better understanding of the performance of a natural night ventilation design, and to optimize the design to a robust solution. © 2010 Elsevier Ltd." "Determination of boundary conditions for passive schools: impact on net energy demand for heating and cooling" "Barbara Wauman, Ralf Klein, Ruben Baetens, Hilde Breesch, Dirk Saelens" "In Flanders (Belgium), the government decided to subsidize the additional costs of 24 pas-sive school buildings as pilot projects. Performance requirements were set, showing strong correspondence to the requirements for passive houses. However, the characteristics of school buildings differ strongly from those of residential buildings. Furthermore, they are affected by the use and typology of schools. Depending on regional customs and regulations, the boundary conditions may even differ between regions or countries. To evaluate the requirements set for passive school buildings, simplified calculation methods for assess-ment of the annual heating and cooling based on EN ISO 13790 are used. As these calculations are strongly affected by the boundary conditions, they can only offer representative results for evaluation of the perfor-mance level of the design if the boundary conditions are defined properly. Therefore, to reassure objective and unambiguous evaluation, a large variety of parameters is defined specifically for Flemish school build-ings. The paper gives an overview of these boundary conditions and clearly amplifies the effects of these properties on the energy demand for heating and cooling. Therefore, a comparison is made between the cur-rently applied boundary conditions and the newly defined properties implemented in the existing monthly cal-culation methods PHPP and EPB. In addition, a comparison is made between the results of both calculation methods. Although based on the same standard EN ISO 13790, important differences between the results for cooling and heating demand are concluded. Therefore, it is not only important to define exact boundary con-ditions, but to critically evaluate existing calculation methods used for performance evaluations and certifica-tion procedures." "Analysis of the predicted effect of passive climate adaptation measures on energy demand for cooling and heating in a residential building" "Twan van Hooff, Bert Blocken" "© 2015 Elsevier Ltd. Both new and existing buildings need to be adapted to climate change, in order to keep providing a comfortable and healthy indoor climate. Preferably, the adaptation measures applied at the building level scale do not require additional energy (i.e. passive measures). Previous studies showed that passive climate change adaptation measures can have a positive effect on thermal comfort in summer and its shoulder seasons in non-air-conditioned residential buildings. In this paper, the effect of these passive climate adaptation measures - applied at building component level - on the cooling and heating energy demand of a terraced house is analyzed using building energy simulations. It is shown that for this particular case the required cooling energy can be limited to a large extent (59-74%) when external solar shading or additional natural ventilation is applied. In addition, it is shown that for a well-insulated terraced house the energy cost for heating is not strongly affected by the application of passive climate change adaptation measures." "Evaluation of passive cooling in low energy police office" "Hilde Breesch, Ralf Klein, Alexis Versele" "Natural night ventilation is driven by wind and stack generated pressures and cools down the exposed building structure at night, in which the heat of the previous day is accumulated. This passive cooling technique is applied in the low energy police office Schoten (Belgium). Thermal summer comfort in the offices is analysed based on the adaptive temperature limits indicator. Design, operation and performance of natural night ventilation are also evaluated. The design is compared to design guidelines for natural night ventilation. The operation is evaluated by comparing measured opening/closing of the windows to the designed control system. The performance is analysed based on the achieved temperature drop overnight. Measured data of indoor temperatures and opening/closing of windows were collected from the building management system during short periods in the summers of 2009 and 2010. Good thermal summer comfort is noticed during normal and warm summer periods. Only when the maximum outdoor temperature exceeds 30°C, high indoor temperatures are measured. Too low temperatures in the morning are noticed in some landscaped offices in normal summer periods. This can be solved by raising the set point for indoor temperature. The users have a large impact on the achieved thermal comfort by manual opening and closing of the windows by day. A rather good agreement is found between measured and designed operation of natural ventilation. Daytime activation requirements have to be checked. The temperature drop overnight varies between 0.3°C and 2.9°C." "Exterior louvers as a passive cooling strategy in a residential building: Computational Fluid Dynamics and Building Energy Simulation modelling" "Abel Tablada de la Torre, Jan Carmeliet, Tine Baelmans, Dirk Saelens" "The implementation of shading devices is one of the passive strategies to improve indoor thermal conditions during summer. They can obstruct direct solar radiation while permitting wind flow inside the building. Therefore, its use implies two passive interventions for indoor thermal comfort: solar protection and natural ventilation. This study focuses on the implementation of exterior louver systems and the simulation, evaluation and improvement of indoor thermal comfort in an existing modern residential building in Palermo, Sicily. The implementation of the louver systems, the natural ventilation strategies and the evaluation and quantification of the (dis)comfort is performed by coupling Computational Fluid Dynamics (CFD) and Building Energy Simulation (BES) calculations. Values of indoor air speed and pressure coefficients are obtained from CFD calculations and further used as input in BES calculations and comfort analysis. The results show, for this particular case, that overheating problems could be improved by passive means by the application of several strategies like the use of existing balconies with external louver systems and whole day natural cross ventilation." "Holistic 1D Electro-Thermal Model Coupled to 3D Thermal Model for Hybrid Passive Cooling System Analysis in Electric Vehicles" "Danial Karimi, Hamidreza Behi, Mohsen Akbarzadeh Sokkeh, Joeri Van Mierlo, Maitane Berecibar" "Thermal management is the most vital element of electric vehicles (EV) to control the maximum temperature of module/pack for safety reasons. This paper presents a novel passive thermal management system (TMS) composed of a heat sink (HS) and phase change materials (PCM) for lithium-ion capacitor (LiC) technology under the premise that the cell is cycled with a continuous 150 A fast charge/discharge current rate. The experiments are validated against numerical analysis through a computational fluid dynamics (CFD) model. For this purpose, a comprehensive electro-thermal model based on an equivalent circuit model (ECM) is designed. The designed electro-thermal model combines the ECM model with the thermal model since the performance of the LiC cell highly depends on the temperature. Then, the robustness of the model is evaluated using a precise second-order ECM. The extracted parameters of the electro-thermal model are verified by the experimental results in which the voltage and temperature errors are less than ±5% and ±4%, respectively. Finally, the thermal performance of the HS-assisted PCM TMS is studied under the fast charge/discharge current rate. The 3D CFD results exhibit that the temperature of the LiC when using the PCM-HS as the cooling system was reduced by 38.3% (34.1 °C) compared to the natural convection case study (55.3 °C)."