| 1. |
- Berggren, Karolina, et al.
(författare)
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Hydraulic impacts on urban drainage systems due to changes in rainfall, caused by climatic change
- 2012
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Ingår i: Journal of hydrologic engineering. - 1084-0699 .- 1943-5584. ; 17:1, s. 92-98
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Tidskriftsartikel (refereegranskat)abstract
- The changes in climate were of a growing concern in the last decade, and will be even more so in the coming years. When investigating impacts on urban drainage systems due to changes in the climate, two challenges are (1) what type of input rainfall data to use, and (2) what parameters to measure the impacts. The overall objective of this study is to investigate the hydraulic performances ofurban drainage systems related to changes in rainfall, and through these hydraulic parameters describe impacts of climate change. Input rainfall data represents today's climate, as well as three future time periods (2011-2040, 2041-2070, and 2071-2100). The hydraulic parameters used were water levels in nodes (e.g. as the number of floods, frequency and duration of floods), and pipe flow ratio. For the study area, the number of flooded nodes and the geographical distribution of floods will increase in the future, as will both the flooding frequency and the duration of floods.
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| 2. |
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| 3. |
- Borris, Matthias, et al.
(författare)
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Continuous simulations of urban stormwater runoff and total suspended solids loads: influence of varying climatic inputs and catchment imperviousness
- 2014
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Ingår i: Journal of Water and Climate. - : IWA Publishing. - 2040-2244 .- 2408-9354. ; 5:4, s. 593-609
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Tidskriftsartikel (refereegranskat)abstract
- Potential implications of climate change for future stormwater management were addressed by undertaking continuous simulations of runoff and total suspended solids (TSS) loads for three urban catchments, with imperviousness varying from 23 to 63%, which were exposed to five rainfall regimes during the snow-free part of the year: the current climate and four climate change scenarios projecting higher rainfalls. Simulated runoff volumes increased in all the future scenarios, particularly in the sub-arctic climate and the fixed uplift scenario (plus20) indicating appreciable rainfall increases. Simulated runoff volumes increased depending on the projected increases in rainfall and increasing runoff contributions from pervious areas when more intense future rainfalls exceeded hydrologic abstractions. The increased runoff volumes then contributed higher TSS loads, which were highly variable for the rainfall regimes tested. In cold climate regions, residues of solids from winter road maintenance may contribute to high initial accumulations of TSS on the catchment surface and high washed off loads. In general, the study suggests that intermediate design-life stormwater management facilities require flexible design allowing for future step-wise adaptation by gradually increasing design capacities and modifying treatment trains.
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| 4. |
- Borris, Matthias, et al.
(författare)
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Modelling the effects of changes in rainfall event characteristics on TSS loads in urban runoff
- 2014
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Ingår i: Hydrological Processes. - : Wiley. - 0885-6087 .- 1099-1085. ; 28:4, s. 1787-1796
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Tidskriftsartikel (refereegranskat)abstract
- The effect of changes in rainfall event characteristics on urban stormwater quality, which was described by total suspended solids (TSS), was studied by means of computer simulations conducted with the Storm Water Management Model for a climate change scenario for northern Sweden. The simulation results showed that TSS event loads depended mainly on rainfall depth and intensity, but not on antecedent conditions. Storms with low-to-intermediate depths and intensities showed the highest sensitivity to changes in rainfall input, both for percentage and absolute changes in TSS wash-off loads, which was explained by the contribution of pervious areas and supply limitations. This has significant implications for stormwater management, because those relatively frequent events generally carry a high percentage of the annual pollutant load
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| 5. |
- Borris, Matthias, et al.
(författare)
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Simulating future trends in urban stormwater quality for changing climate, urban land use and environmental controls
- 2013
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Ingår i: Water Science and Technology. - : IWA Publishing. - 0273-1223 .- 1996-9732. ; 68:9, s. 2082-2089
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Tidskriftsartikel (refereegranskat)abstract
- The effects of climatic changes, progressing urbanization and improved environmental controls on the simulated urban stormwater quality in a northern Sweden community were studied. Future scenarios accounting for those changes were developed and their effects simulated with the Storm Water Management Model (SWMM). It was observed that the simulated stormwater quality was highly sensitive to the scenarios, mimicking progressing urbanization with varying catchment imperviousness and area. Thus, land use change was identified as one of the most influential factors and in some scenarios, urban growth caused changes in runoff quantity and quality exceeding those caused by a changing climate. Adaptation measures, including the reduction of directly connected impervious surfaces (DCIS) through the integration of more green spaces into the urban landscape, or disconnection of DCIS were effective in reducing runoff volume and pollutant loads. Furthermore, pollutant source control measures, including material substitution, were effective in reducing pollutant loads and significantly improving stormwater quality
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| 6. |
- Borris, Matthias, et al.
(författare)
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Using urban runoff simulations for addressing climate change impacts on urban runoff quality in a Swedish town
- 2012
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Ingår i: Urban Drainage Modelling. - Belgrade : Faculty of Civil Engineering, University of Belgrade. - 9788675181569
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Konferensbidrag (refereegranskat)abstract
- The effect of climate change on urban stormwater quality was studied by means of computer simulations conducted with the Stormwater Management Model (SWMM) for common climate change scenarios developed for northern Sweden. The simulation results showed that stormwater quality depended on rainfall characteristics; a climate scenario implying increased rainfall depths and intensities produced higher pollutant loads carried by stormwater, but reduced concentrations, particularly for medium to high intensity storm events. This type of stormwater quality response was explained by pollutant supply limited transport processes and the resulting dilution of such pollutants. Medium intensity events showed the highest sensitivity to climatic changes, since such events strongly affected the contributions of pervious surfaces. This has significant implications for stormwater management, because those relatively frequent events generally carry a high percentage of the annual pollutant load.
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| 7. |
- Gustafsson, Anna-Maria, et al.
(författare)
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CFD-modelling of natural convection in a groundwater-filled borehole heat exchanger
- 2010
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Ingår i: Applied Thermal Engineering. - : Elsevier BV. - 1359-4311 .- 1873-5606. ; 30:6-7, s. 683-691
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Tidskriftsartikel (refereegranskat)abstract
- In design of ground-source energy systems the thermal performance of the borehole heat exchangers is important. In Scandinavia, boreholes are usually not grouted but left with groundwater to fill the space between heat exchanger pipes and borehole wall. The common U-pipe arrangement in a groundwater-filled BHE has been studied by a three-dimensional, steady-state CFD model. The model consists of a 3 m long borehole containing a single U-pipe with surrounding bedrock. A constant temperature is imposed on the U-pipe wall and the outer bedrock wall is held at a lower constant temperature. The occurring temperature gradient induces a velocity flow in the groundwater-filled borehole due to density differences. This increases the heat transfer compared to stagnant water. The numerical model agrees well with theoretical studies and laboratory experiments. The result shows that the induced natural convective heat flow significantly decreases the thermal resistance in the borehole. The density gradient in the borehole is a result of the heat transfer rate and the mean temperature level in the borehole water. Therefore in calculations of the thermal resistance in groundwater-filled boreholes convective heat flow should be included and the actual injection heat transfer rate and mean borehole temperature should be considered. (C) 2009 Elsevier Ltd. All rights reserved.
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| 8. |
- Gustafsson, Anna-Maria, et al.
(författare)
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Heat extraction thermal response test in groundwater-filled borehole heat exchanger : Investigation of the borehole thermal resistance
- 2011
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Ingår i: Renewable energy. - : Elsevier BV. - 0960-1481 .- 1879-0682. ; 36:9, s. 2388-2394
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Tidskriftsartikel (refereegranskat)abstract
- In groundwater-filled borehole heat exchangers (BHEs) convective flow influences the heat transfer in the borehole. During heat extraction thermal response tests (TRTs) the effect of the changing convective flow is more dominant than during heat injection tests. Water is heaviest around 4 °C and when exceeding this temperature during the test, the convective flow is stopped and restarted in the opposite direction resulting in a higher borehole thermal resistance during that time. Just before 0 °C the convective flow is the largest resulting in a much lower borehole thermal resistance. Finally, during the freezing period phase change energy is released and material parameters change as water is transformed into ice, resulting in a slightly higher borehole resistance than at a borehole water temperature of 0 °C. The changes in borehole thermal resistance are too large for ordinary analysis methods of thermal response tests to work. Instead another method is introduced where the borehole thermal resistance is allowed to change between different time intervals. A simple 1D model of the borehole is used, which is matched to give a similar mean fluid temperature curve as the measured one while keeping the bedrock thermal conductivity constant during the whole test. This method is more time-consuming than ordinary TRT analyses but gives a good result in showing how the borehole thermal resistance changes. Also, a CFD-model with a section of a simplified borehole was used to further study the effect of convection and phase change while the temperature was decreased below freezing point. The test and the model show similar results with large variations in the borehole thermal resistance. If the knowledge of changing borehole thermal resistance was used together with a design program including the heat pump and its efficiency, a better BHE system design would be possible.
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| 9. |
- Gustafsson, Anna-Maria, et al.
(författare)
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Influence of natural convection in water-filled boreholes for GCHP
- 2008
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Ingår i: ASHRAE Transactions. - 0001-2505. ; 114:1, s. 416-423
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Tidskriftsartikel (refereegranskat)abstract
- In groundwater filled borehole heat exchangers (BHE), convective flow inside the borehole water will affect the heat transfer. Since the convective flow is dependent of the temperature gradient, different injection rates and ground temperatures will result in different borehole thermal resistance. This paper describes the influence of natural convection in water-filled boreholes in impermeable bedrock for ground-coupled heat pump (GCHP) systems. An overview of groundwater-filled boreholes and the influence of groundwater movements are presented followed by numerical simulations and field measurements to further investigate the influence. The results from the simulations of the three-dimensional, steady-state model of a 9.8 ft (3 m) deep BHE are compared to evaluated results from performed thermal response test (TRT). The results show that convective flow in groundwater-filled BHE results in 5-9 times more efficient heat transfer compared to stagnant water when heat carrier temperatures are in the range of 50-86°F (10-30°C). The size of the convective flow depends on the temperature gradients in the borehole. This shows the importance of on-site investigation of thermal properties using appropriate power injection rates similar to those in the system to be built. This research is part of an on-going project to find ways to estimate the heat transfer including convective flow and to incorporate the findings into the design of GCHP systems. TRT are today a common way to determine heat transfer properties for a BHE and its surroundings. Performing TRT measurements with several injection rates is a way to evaluate the dynamic thermal response including the change in convective flow due to changes in temperature levels. If this dynamic response would be included in design tools a more thorough design of the BHE system is performed. Here, the early result of this research is presented
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| 10. |
- Gustafsson, Anna-Maria, et al.
(författare)
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Metoder för att undersöka extrema regnhändelsers påverkan på dagvattensystemet
- 2014
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Rapport (refereegranskat)abstract
- Detta projekt har genomförts av Luleå Tekniska Universitet i samarbete med 5 kommuner; Arvika, Skellefteå, Sundsvall, Trelleborg samt Växjö. Projektets syfte har varit att studera hur olika metoder kan användas för att utvärdera dagvattensystemets påverkan av extrema regnhändelser. Rapporten har skrivits i syfte att ge en övergripande bild av olika metoder och de osäkerheter som finns när de olika metoderna används. Materialet i rapporten är hämtat från aktuellt projekt samt från parallella studier vid forskningsgruppen Stadens vatten, LTU och från internationella och nationella studier för att ge ett så brett perspektiv på olika metoder som möjligt. De metoder som beskrivs i rapporten går från en väldigt enkel analys baserat på vanliga dimensioneringsekvationer som kan utföras i ett excelark eller för hand till analyser som kräver komplexa modeller som simulerar vattenföringen i ledningsnätet samt ytavrinning kopplat till infiltration. Alla metoder kräver någon form av nederbördsinformation och därför inkluderas i rapporten ett avsnitt om regn och framtida regn kopplat till klimatförändring. För att genomföra en analys krävs även parametrar att studera effekterna av olika körningar och i slutet presenteras ett kort avsnitt om indikationer som är lämpliga att använda vid utvärdering av dagvattensystemet. När en metod ska väljas är det viktigt att syfte med undersökning och resurser i form av tid, existerande data och pengar ställs mot varandra. En avancerad modell har ett större krav på indata, datakapacitet och på mätdata som den kan verifieras mot. I vissa fall är det bättre att använda en enklare modell med kontinuerligt, historiskt regndata medan i andra fall krävs en komplex modell som inkluderar t.ex. infiltration i permeabla ytor och att då använda sig av designregn för att klara av de begränsningar som ev. finns i datakapacitet och simuleringstid. Innan beslut tas om modell eller metod bör det noggrant funderas över varför modellen ska tas fram, hur den ska användas samt vilka data som finns tillgängliga eller kan tas fram med nya mätningar. Om metoderna beskrivna i rapporten används på korrekt sätt och verifieras med tillräckligt data kan dessa utvärderingar av dagvattensystemet ge en bra bild av hur systemet fungerar samt hur det påverkas av olika scenarier.
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