| 1. |
- Pettersson, Kaj, 1990, et al.
(författare)
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Contribution of dynamic capillary pressure to rainfall infiltration in thin homogeneous growth substrates
- 2021
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Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694. ; 603
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Tidskriftsartikel (refereegranskat)abstract
- The use of green roofs to help mitigate storm water contributions to urban flooding has been gaining popularity but is hindered by the limited data on the performance of such roofs with regard to storm water runoff mitigation. The underlying issue stems from the inherent complexity of modeling subsurface multiphase flow. Modeling of this phenomena requires calculating the contributions of substrate microstructure characteristics, the influence of the wetting and non-wetting phases upon each other, and the effect of the microstructure on the wetting phase. Previously we have observed how the microstructure can affect detention, however the quantification of this relationship is still missing. In the present paper we present numerical simulations of wetting phase infiltration of a thin monodisperse packed bed in order to understand and quantify the impact of microstructure geometry on storm water infiltration of a green roof substrate. For a slightly hydrophilic case, (θ=82°), we find that a dominant mechanism underlying this relationship is the microstructure-induced dynamic behavior of the capillary pressure. We determine that at larger packing ratios (ratio of packed bed depth to particle size), the influence of hydraulic head diminishes and behaves conversely for thinner layers, particularly when larger pores are present. Indeed, thin beds composed of large particles can exhibit high flow velocities that in turn affect the capillary pressure within the substrate. We observe that the capillary pressure can shift from negative values denoting capillary suction to positive ones which cause valve-like blocking effects on the flow; dependent upon the flow velocity as determined by the microstructure. In particular, we find that the capillary pressure depends on the value of the pore-scale gravity-induced flow velocity, quantified through a characteristic Capillary number. The provided quantification of this relationship can be invaluable from a design perspective to understand the behavior of capillary pressure of different substrates under a variety of flow rates prior to testing substrate candidates. In addition, a comparison of the behavior of the dynamic component of capillary pressure to other works is undertaken. Flow homogeneity is also found to be linked to the flow velocity, and consequently to the microstructure.
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| 2. |
- Pettersson, Kaj, 1990, et al.
(författare)
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On the impact of porous media microstructure on rainfall infiltration of thin homogeneous green roof growth substrates
- 2020
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Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694. ; 582
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Tidskriftsartikel (refereegranskat)abstract
- Green roofs are considered an attractive alternative to standard storm water management methods; however one of the primary issues hindering their proliferation is the lack of data regarding their ability to retain and reduce storm water under a variety of climatic conditions. This lack of data is partly due to the complexity of physical processes involved, namely the heterogeneous microscopic behavior that characterize flows in unsaturated porous media. Such an anomalous behavior is difficult to predict a priori, especially in the presence of layered structures. This paper examines water infiltration of a green roof at the pore-scale with the aim to evaluate the effect of the porous microstructure in thin substrate layers. In such layers, the thickness of the medium and the particle size are within the same order of magnitude and the effect of the packing arrangement on the flow dynamics can be pronounced. In this study, three packing arrangements and two different hydraulic heads, analogous to extreme rainfall events typical of Scandinavia, are investigated by means of direct numerical simulations based on the lattice Boltzmann method. The results show that a wider variability of pore sizes in a thin medium can be linked directly to flow pathing preference and consequently less homogenized flow in the primary flow direction. This situation corresponds to intermittent flow behavior at the pore-scale level and reduced macroscopic infiltration rates. This observation unveils the possibility of designing innovative green roof growth substrates: by tuning the particle size and thickness of the layers composing the medium the desired green roof detention time can be attained.
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| 3. |
- Bankvall, Claes, 1942, et al.
(författare)
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Air transport in and through the building envelope
- 2004
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Ingår i: Thermal Performance of the Exterior Envelopes of Whole Buildings. - 2166-8469.
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Konferensbidrag (refereegranskat)abstract
- A national R&D program dealing with air transport in and through the building envelope is presented, including some overviews of results. The program develops predictive models for evaluating air movements in and through the building envelope. These models are coupled to the outside climate and pressure situation and to the inside climate through the interaction with models defining the building services system. A major aim of the program is to analyze problems of relevance to the building process. This includes site inventory, modeling of typical situations, and laboratory testing for input data and to validate the models. The objective is to develop tools to help design and evaluate building elements and to give the necessary foundation for estimating the convective transport of heat and moisture in the envelope, which is decisive for the indoor climate, the consumption of energy, and the durability of the construction. The research program is ongoing and this presentation is to invite communication with others.
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| 4. |
- Bergel Gomez, Ramon, 1992, et al.
(författare)
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Energy Performance Modelling: Introducing the Building Early-stage Design Optimization Tool (BeDOT)
- 2019
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Ingår i: Building Simulation Conference Proceedings. - : IBPSA. - 2522-2708. - 9781713809418 ; , s. 278-285
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Konferensbidrag (refereegranskat)abstract
- Aiming to aid the design process of buildings, their mechanical systems and materials from the perspective of building performance this paper presents the Building Early-stage Design Optimization Tool (BeDOT), a new set of tools for building early-stage design analysis, currently focused on energy performance modelling. The tool, programmed in Python and built upon ISO 13790:2008, has been implemented within Rhino/Grasshopper interface, which opens many possibilities for result visualization and optimization, besides easy geometry editing. BeDOT has been developed focusing on modularity, flexibility, fast processing and on the constant and unlimited cooperation of professionals. BeDOT has been tested against IDA-ICE for over 800 cases. Energy results lie within a range of 15% accuracy, with a slight tendency towards underestimation. Also, BeDOT has shown a better efficacy in the process of modelling buildings from geometry to results. The tool shows faster processing as well as a clearer path to build the geometry and attach information to every zone of the building(s). BeDOT’s process and accuracy are suitable for early design stages. Further development is needed to improve the handling of data and the program’s user-friendliness.
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| 5. |
- Bonakdar, Farshid, et al.
(författare)
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An optimum renovation strategy for Swedish single-family house envelopes: The implication of climate zones and the age of the houses
- 2017
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Ingår i: ECEEE summer study proceedings.
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Konferensbidrag (refereegranskat)abstract
- As a result of EU’s legislations for reducing energy demands in buildings, a large number of studies have been done about cost-effective renovation of building stocks in EU. To complement the available results, in this work we take into account the microeconomic perspective of building owners, whose major challenge is to decide about limited budget allocation for energy renovation. Therefore, this work presents results of optimal and cost-effective energy renovation of single-family houses in Swedish building stock.The houses are categorised based on the year of construction (about 1970s, 1980s and 1990s) and their location (i.e. four Swedish climate zones). The space heat demand of representative houses for each age category and climate zone is simulated to analyse optimum renovation. A reformed method of NPV is employed in order to, simultaneously, analyse the cost-optimum renovation measures of the house envelope and their cost-effectiveness.The results indicate that the space heat demand in the representative house of 1970 is reduced from 28 % in climate zone 1 to 25 % in zone 4, when all measures are implemented to a cost-optimal level. The results of similar exercise for the houses of 1990 suggest “do nothing” scenario for energy renovation to cost-optimal level, considering discount rate of 3 %. However, if the necessity of renovation is determined, then the reduced space heat demand is from 13 % in climate zone 1 to 8 % in zone 4. As far as the cost-effectiveness is concerned, the optimum renovation of attics for the houses built during early 1970s appears to be the most cost-effective component followed by the attics of the houses built during 1980s. Renovation of exterior walls and windows to a cost-optimal level are not cost-effective, regardless the year of construction. The findings suggest strategy to prioritise the energy renovation of envelope components in existing single-family houses of Sweden, built between 1965 and 1995 in different climate zones.
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| 6. |
- Bonakdar, Farshid, 1977-, et al.
(författare)
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The Implications of Climate Zones on the Cost-Optimal Level and Cost-Effectiveness of Building Envelope Energy Renovation and Space Heat Demand Reduction
- 2017
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Ingår i: Buildings. - : MDPI AG. - 2075-5309. ; 7:2
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Tidskriftsartikel (refereegranskat)abstract
- The cost-optimal level of energy performance for buildings shall be identified according to the European directive of 2010. The Swedish building stock needs comprehensive knowledge and an overall strategy for the cost-optimal level of renovation. This paper studies the contribution of Swedish climate zones to the cost-optimal level of renovation on a multi-story residential building in Sweden from the building owner perspective. The building space heat demand is simulated for four Swedish climate zones. The net present profit (NPP) method is defined and used in this study in order to analyze the cost-optimal level and the cost-effective renovation of building envelope components (e.g., attic floor, basement walls, exterior walls and windows). The implication of different discount rates is studied, as well. The results show that the optimum renovation of the building envelope offers 51% more energy savings for space heating when the building is in a northern climate zone compared to a southern zone. The study suggests that different renovation strategies for the building stock renovation need to be identified, separately, for each climate zone. The NPP analysis identifies the minimum required investment and maximum achievable energy savings that are needed to have a cost-effective renovation. The broad range of studied climate zones provides the opportunity to apply the obtained results to other climate zones by either interpolation or extrapolation of NPPs for the buildings with similar characteristics.
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| 7. |
- Dahlström, Emmy, et al.
(författare)
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Optimization of Night Cooling of Commercial Premises Using Genetic Algorithms and Neural Networks
- 2018
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Ingår i: Proceedings for the 2018 International Building Physics Association Conference. - Syracuse, New York : International Association of Building Physics (IABP).
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Konferensbidrag (refereegranskat)abstract
- This paper investigates if it is possible to optimize night cooling control setpoints and ventilation schedule regarding energy consumption and indoor climate. A retail store, located in Gothenburg, was used as a case study. The investigation was done by numerical modelling and simulations. It started with development and calibration of a building energy model for the store with data collected from the field. Afterwards, the calibrated model was used in the optimization of the night cooling. Initially, a genetic algorithm was applied to find the global minimum of the problem and further refined with a local search algorithm. The optimization speed was increased by neural networks, as they can approximate results faster than the building energy model. The study suggests that the cooling and fan energy consumption can be reduced by 16% in the studied facility, compared to the currently used trial-and-error schemes. The project concludes that the use of logged control data in combination with genetic algorithms and neural networks are an efficient way for both calibration and optimization of building energy models. The industry moves towards an increase of available logged control data. As such, it is important to be able to properly utilize the data, for improving the accuracy of building energy simulations and improving the results.
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| 8. |
- Domhagen, Fredrik, 1987, et al.
(författare)
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Modelling VOC levels in a new office building using passive sampling, humidity, temperature, and ventilation measurements
- 2023
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Ingår i: Building and Environment. - 0360-1323. ; 238
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Tidskriftsartikel (refereegranskat)abstract
- New buildings often have high initial concentrations of VOCs that, although not necessarily harmful, may be disturbing and cause discomfort among occupants. In new buildings, running the ventilation system continuously and at full rate during the first year is common practice to reduce VOC levels. However, the drawback of such an arbitrary strategy is the risk of over-ventilating with unnecessary heat losses as a consequence. In this article, a new approach, a VOC-passport, is developed where early measurements of VOCs together with a calculation model are used to find an optimized ventilation strategy. The proposed calculation model is tested on two newly built office rooms where VOCs were measured using passive samplers, together with temperature, humidity and ventilation rates, and it shows good agreement with measurements. An example of how a daily ventilation schedule may look like if optimized with the prosed model is presented. The example illustrates that in buildings where VOC levels are allowed to increase periodically, VOC levels can be kept at acceptable levels during occupancy hours if the effective storage capacity is known. The proposed method has a potential to improve the indoor air quality in new buildings without compromising energy efficiency.
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| 9. |
- Domhagen, Fredrik, 1987, et al.
(författare)
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Theoretical Threshold for Estimating the Impact of Ventilation on Materials’ Emissions
- 2024
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Ingår i: Journal of Environmental Science and Technology. - 0013-936X .- 1520-5851. ; 58:11, s. 5058-5067
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Tidskriftsartikel (refereegranskat)abstract
- In new buildings, nonoccupant VOC emissions are initially high but typically decrease within months. Increased ventilation is commonly used to improve indoor air quality, assuming it speeds up VOC off-gassing from materials. However, previous research presents inconsistent results. This review introduces a simplified analytical model to understand the ventilation-emission relationship. By combining factors such as diffusivity, emitting area, and time, the model suggests the existence of a theoretical ventilation threshold beyond which enhanced ventilation has no further influence on emission rates. A threshold of approximately 0.13 L s-1 m-2 emitting area has been found for various VOCs documented in the existing literature, with which the conflicting results are explained. It is also shown that the threshold remains notably consistent across different boundary conditions and model resolutions, indicating its suitability for real-world applications.
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| 10. |
- Eriksson, Sara, et al.
(författare)
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Numerical Simulations and Empirical Data for the Evaluation of Daylight Factors in Existing Buildings in Sweden
- 2019
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Ingår i: Energies. - : MDPI AG. - 1996-1073 .- 1996-1073. ; 12:11
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Tidskriftsartikel (refereegranskat)abstract
- Point Daylight Factor (DFP) has been used for daylighting design in Sweden for more than 40 years. Progressive densification of urban environments, in combination with stricter regulations on energy performance and indoor environmental quality of buildings, creates complex daylight design challenges that cannot be adequately solved with DFP. To support a development of the current and future daylight indicators in the Swedish context, the authors have developed a comprehensive methodology for the evaluation of daylight levels in existing buildings. The methodology comprises sample buildings of various use and their digital replicas in 3D, detailed numerical simulations and correlations of diverse DF metrics in existing buildings, a field investigation on residents' satisfaction with available daylight levels in their homes, and a comparison between the numerical and experimental data. The study was deliberately limited to the evaluation of DF metrics for their intuitive understanding and easy evaluation in real design projects. The sample buildings represent typical architectural styles and building technologies between 1887 and 2013 in Gothenburg and include eight residential buildings, two office buildings, two schools, two student apartment buildings, and two hospitals. Although the simulated DFP is 1.4% on average, i.e., above the required 1%, large variations have been found between the studied 1200 rooms. The empirical data generally support the findings from the numerical simulations, but also bring unique insights in the residences' preferences for rooms with good daylight. The most remarkable result is related to kitchens, typically the spaces with the lowest DF values, based on simulations, while the residents wish them to be the spaces with the most daylight. Finally, the work introduces a new DF metric, denoted DFW, which allows daylighting design in early stages when only limited data on the building shape and windows' arrangement are available.
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