| 1. |
- Akander, Jan, et al.
(författare)
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Assessing the Myths on Energy Efficiency When Retrofitting Multifamily Buildings in a Northern Region
- 2017. - 1
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Ingår i: Sustainable High Rise Buildings in Urban Zones. - Cham : Springer Publishing Company. - 9783319177557 - 9783319177564 ; , s. 139-161
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- In the light of EU’s requirements to achieve a major cut in energy use by 2050, Sweden has the same target. The built environment must by 2020 reduce energy use by 20 and 50 % by 2050. The size of the future building stock will naturally increase and regardless of how energy efficient future buildings will be, the energy performance of the old stock must be improved in order to reach those goals. In major renovation projects involving multifamily buildings in large residential areas in the cities, 50 % reduction can be achieved. This is cost-effective and profitable even if the rent is increased.Gävleborg is a sparse region in the North, with few cities. Multifamily buildings are generally much smaller than in large cities and owners are reluctant to impose changes that increase rents due to the housing situation in the region. In consequence, the Regional Council and the University of Gävle set out to assess the potential and feasibility of reducing energy use and carbon dioxide emissions in this region’s multifamily buildings. Eleven real buildings were investigated, each having various ownership forms, different technical attributes and heating sources. Energy audits and measurements were conducted to assess the condition of each building. Performances of the buildings and proposed improvements were simulated with building energy simulation programs, whilst life cycle cost analyses were conducted to study viability. Carbon dioxide emission (CO2) reductions were estimated for each improvement.Based on the results, a concluding discussion is made on whether or not some myths on energy use and retrofitting are true. The following is concluded: It is possible to reach a 50 % reduction, but it is not economical with the costs involved and with today’s energy prices and moderate price increase over time.Retrofitting or improvements made in the building’s services systems (HVAC) are more economical than actions taken to improve performance of building by constructions. HVAC improvements give about 20 % reduction in energy use. However, mechanical ventilation systems with heat recuperation are not economical, though these may or may not substantially reduce use of thermal energy.Solar energy is, despite the latitude of the region, economically viable—especially PV solar energy. Photovoltaic panels (PVs) are becoming viable—the combination of PVs and district heating is beneficial since saving electricity is more important than thermal energy in district-heated areas.
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| 2. |
- Alvfors, Per, et al.
(författare)
-
Forskarskolan Program Energisystem : Kunskapsutveckling genom samverkan mellan teknik- och samhällsvetenskap : slutrapport 2016, Forskningssyntes för konsortiet Byggnader i energisystem
- 2016
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Denna rapport ger en kortfattad översikt och syntes av tvärvetenskapliga forskningsresultat från verksamheten i konsortiet Byggnader i energisystem inom forskarskolan Program Energisystem. Tonvikten ligger på tiden från forskarskolans start 1997 till dess 15-årsjubileum 2012, men hänvisningar görs även till forskning publicerad därefter. Utgångspunkten har varit att lyfta fram det tvärvetenskapliga inom forskningen för att visa hur forskarskolan har bidragit till tvärvetenskaplig kunskaps- och metodutveckling.I rapporten ges en översikt över fallstudier och avhandlingar inom konsortiet och de tvärvetenskapliga forskningsresultaten sammanfattas inom tre huvudsakliga tematiska områden: (1) Passivhus: boende och energieffektiva byggnadstekniker,(2) Energieffektivisering: processer och aktörer, samt (3) Energianvändning, vardagsaktiviteter och småskalig solenergi i hushåll. Tvärvetenskapliga metoder och resultat sammanfattas och utvecklingen av samarbeten och angreppssätt beskrivs. Rapporten avslutas med några sammanfattande reflektioner kring hur framgångsrik tvärvetenskaplig forskning bör bedrivas.
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| 3. |
- Alvfors, Per, et al.
(författare)
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Forskarskolan Program Energisystem : kunskapsutveckling genom samverkanmellan teknik- och samhällsvetenskap : slutrapport 2016, Forskningssyntes för konsortiet Lokala och regionala energisystem
- 2016
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Forskarskolan Program Energisystem har med sina fem deltagande forskningsavdelningar från Chalmers tekniska högskola, Linköpings universitet, KTH och Uppsala universitet varit banbrytande inom tvärvetenskaplig energisystemforskning och dess tre konsortier har spelat en viktig roll för forskarskolans utveckling. Konsortierna är inriktade på byggnader i energisystem, industriella energisystem samt lokala och regionala energisystem. I varje konsortium har doktorander och seniorer från minst två av de deltagande avdelningarna bedrivit tvärvetenskaplig forskning.I det lokala och regionala konsortiet har forskningsfrågorna kretsat kring aktörer och processer av betydelse för energisystemen i svenska kommuner, län och regioner. Inom konsortiet har frågeställningar om miljömässigt, socialt och ekonomiskt hållbara lokala och regionala energisystem bland annat studerats genom att analysera aktörers agerande och politiska processer inom de tekniska, ekonomiska och institutionella villkor som utgör begränsningar och möjligheter för energisystemen. En tydlig trend inom konsortiets forskning under forskarskolans arton år är att inriktningen gått i riktning från lokal till regional och från stationära till mobila energisystem. Den förskjutningen följer också den ökande betydelse som regioner i form av länsstyrelser har fått för samordningen av energi- och klimatplaneringen i Sverige under det senaste decenniet. Kommunerna har fortfarande en dominerande position genom den energirelaterade infrastruktur som de förfogar över men en förskjutning mot ett mer regionalt inflytande är tydlig.Totalt har 26 doktors- och en licentiatexamen avlagts av konsortiets doktorander och dessa alumner är nu verksamma inom energirelaterade verksamheter Sverige. Den främsta representationen finns inom myndigheter och akademier.
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| 4. |
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| 5. |
- Alvfors, Per, et al.
(författare)
-
Forskarskolan Program Energisystem : kunskapsutveckling genom samverkanmellan teknik- och samhällsvetenskap : slutrapport 2016, Huvudrapport
- 2016
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Idén att samhällsvetenskaplig och teknisk energisystemforskning måste vävas samman för att utveckla ny kunskap och få ökad samhällsnytta var utgångspunkt när Program Energisystem startade år 1997.Program Energisystem identifierade tidigt kärnvärden som visades vara viktiga framgångsfaktorer:Energisystem med tyngdpunkt på användarsidanTvärvetenskaplig, universitets- och fakultetsöverskridandeforskning och forskarutbildningSammanhållen forskarskolaFinansiering av hela doktorandprojektSamarbeten i tematiska forskningsområdenKontinuerlig tvärvetenskaplig utvecklingLångsiktig finansiering av samordningsstrukturProgram Energisystems arbete har kännetecknats av:Val av samhällsrelevanta projekt av hög vetenskaplig kvalitetGemensamma tvärvetenskapliga kurser och projektarbetenTvärvetenskaplig handledningKontinuerligt arbetande fora för diskussionoch kontakter över ämnesgränserForskningssamarbeten mellan seniorer i olika ämnenAktivt doktorand- och alumninätverkForskarutbildningens målsättning har varit att utbilda bättre samhällsvetareoch bättre ingenjörer, inte att göra samhällsvetare av ingenjörerna eller ingenjörerav samhällsvetarna.I den kontinuerliga utvecklingen av Program Energisystem har ett förtroendefullt samarbete utvecklats som möjliggjort kontinuerliga förbättringar av forskningen och forskarutbildningen.Arvet från Program Energisystem har förts vidare i den nya Forskarskola Energisystem. Forskarskola Energisystem har en delvis annan struktur men bygger innehållsmässigt vidare på centrala idéer från Program Energisystem. Det finns ett fortsatt stort behov av tvärvetenskaplig kunskapsutveckling på energiområdet som främst handlar om att förstå komplicerade samband och processer och hur dessa kan påverkas.
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| 6. |
- Alvfors, Per, et al.
(författare)
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Forskarskolan Program Energisystem: Kunskapsutveckling genom samverkanmellan teknik- och samhällsvetenskap : Slutrapport 2016, Forskningssyntes för konsortiet Industriella energisystem
- 2016
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Denna syntesrapport är en sammanfattning och analys av den forskning som bedrivits inom ramen för det Industriella konsortiet från år 1997 (konsortiets verksamhet startade 1999) inom ramen för forskarskolan Program Energisystem. Under denna tid har 25 doktorsavhandlingar och en licentiatavhandling producerats inom det Industriella konsortiet. Avhandlingarna sammanfattas och analyseras i denna syntesrapport och arbetet avgränsas då till att studera avhandlingarnas Problemområde, Verktyg/Metod/Teori, Systemgräns, studerad Sektor och Övergripande resultat. Vidare ges, med utgångspunkt från dessa forskningsresultat, förslag på fortsatt forskning för hållbara och effektiva energisystem.Många viktiga problemområden har studerats inom ramen för forskarskolans Industrikonsortium. Ett flertal avhandlingar behandlar möjligheter att minska utsläppen av växthusgaser från industrin och här har flera sektorer studerats, bland annat massa- och pappersindustrin, järn- och stålindustrin, kemiindustrin och oljeraffinaderiindustrin. Ett centralt tema i avhandlingarna är potentialer för energieffektivisering i industrisektorn, inte minst vid införande av bioraffinaderikoncept i framtiden. Här analyseras t.ex. tekniska potentialer, kostnadseffektivitet för energieffektiviseringsåtgärder, samt betydelsen av energiledning och styrmedel.I avhandlingarna har en mängd olika metoder och verktyg använts. Den i särklass mest använda vetenskapliga metoden är intervjuer (15) följt av scenarioanalys (10), dokumentstudier (9), simuleringsberäkningar (9), pinchanalys (9) och optimering (8). Fallstudiemetodik där mer än en metod används för att studera ett specifikt fall, t.ex. ett företag, förekommer i flera avhandlingar. En grundtanke i forskarskolan Program Energisystem har varit att forskaren måste vara medveten om att resultat från energisystemanalyser kan påverkas av vilka systemgränser som valts. I flertalet av Industrikonsortiets avhandlingar har Europas elsystem utgjort systemgräns då effekter av förändrad elanvändning eller elproduktion analyserats.Industrikonsortiets forskningsresultat visar på många intressanta slutsatser. Det påvisas att det finns energieffektiviseringspotentialer både i nya investeringar och i energiledningsåtgärder, som att justera driftsbetingelser för befintlig teknisk utrustning och ändra beteenden. Det konstateras också att energisamarbeten mellan industri och energibolag med syfte att öka användningen av industriell överskottsvärme i många fall är en hållbar lösning som minskar regioners behov av primärenergi och reducerar utsläppen av växthusgaser. Hinder mot sådana samarbeten kan vara att detta inte är en del av industrins kärnverksamhet. Det konstateras även att energisamarbeten mellan närliggande anläggningar i ett industrikluster kan leda till avsevärt större energieffektiviseringspotentialer än om var och en av de ingående industrierna arbetar enbart med interna åtgärder. Hinder mot denna typ av samarbete är brist på etablerade affärsmodeller. Forskningen visar på ett behov av fortsatta studier kring begreppet kärnverksamhet och dess påverkan på energifrågan i svensk industrin. Avskiljning och lagring av koldioxid (CCS) från industrin har studerats och här konstateras att denna lösning inte är ekonomiskt lönsam med dagens förutsättningar. Det rekommenderas därför att framtida forskning bedrivs för att studera vilka styrmedel som skulle behövas för att CCS ska bli ekonomiskt intressant för industrin. En annan viktig fråga är hur energitjänsteföretag ska formulera affärsmodeller och strategier kring CCS, samt hur de kan samarbeta med industrin för att på affärsmässiga grunder få till stånd CO2– avskiljning, transport och lagring. Även framtida forskning kring styrmedel, t.ex. energitjänster, för ökad energieffektivitet i industrisektorn förordas. Resultat från Industrikonsortiets avhandlingar visar att processintegrationsverktyget pinchanalys kan kombineras med optimeringsverktyg (i detta fall MIND) vid analys av industriella energisystem. Denna metodkombination ger intressanta resultat varför fortsatt forskning förordas kring kombinationer av olika processintegrationsmetoder. I flertalet avhandlingar har företagsdata använts som indata vid exempelvis modellering och processintegrationsstudier. Detta har accentuerat behovet av ett standardiserat protokoll vid insamling av företagsdata. Ett sådant protokoll kan öka reliabiliteten på indata och förslagsvis användas vid fallstudier.Avslutningsvis kan konstateras att trots närmare 20 års tvärvetenskaplig forskning mellan samhällsvetare och teknikvetenskaperna finns det fortfarande mycket mer att beforska och utveckla.
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| 7. |
- Amiri, Shahnaz, et al.
(författare)
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Assessment of the natural gas potential for heat and power generation in the County of Ostergotland in Sweden
- 2009
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Ingår i: Energy Policy. - : Elsevier BV. - 0301-4215 .- 1873-6777. ; 37:2, s. 496-506
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study is to investigate the potential use of natural gas for heat and power production for the municipality of Linkoping, Norrkoping and Finspang in the County of Ostergotland, Sweden. The results of the study revealed that these three municipalities with the present heating demand can convert 2030 GWh/year of the present fuel mixed to natural gas. The expansion of natural gas provides the possibility to increase the electricity generation with approximately 800 GWh annually in the County of Ostergotland. The global emissions of CO2 reduce also by approximately 490 ktonne/year by assuming the coal condensing power plant as the marginal power plant. The total system cost decreases by 76 Mkr/year with the present electricity price which varies between 432 and 173 SEK/MWh and with 248 Mkr/year if the present electricity price increases to 37% which is approximately corresponding to European electricity prices. Sensitivity analysis is done with respect to the different factors such as price of electricity, natural gas, etc. The findings show that increased price of electricity and increased district heating demand increases the profitability to convert to natural gas using CHP plant.
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| 8. |
- Amiri, Shahnaz, et al.
(författare)
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Possibilities and consequences of deregulation of the European electricity market for connection of heat sparse areas to district heating systems
- 2010
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Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 87:7, s. 2401-2410
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Tidskriftsartikel (refereegranskat)abstract
- The objective of the study is to analyse the conditions for connection of residential buildings in heat sparse areas to district heating systems in order to increase electricity production in municipal combined heat and power plants. The European electricity market has been assumed to be fully deregulated. The relation between connection of heat sparse areas, increased electricity and heat production as well as electricity prices, fuel prices and emissions rights is investigated. The results of the study show that there is potential to expand the district heating market to areas with lower heat concentrations in the cities of Gavle, Sandviken and Borlange in Sweden, with both economic and environmental benefits. The expansion provides a substantial heat demand of approximately 181 GWh/year, which results in an electricity power production of approximately 43 GWh/year. Since the detached and stand-alone houses in the studied heat sparse areas have been heated either by oil boiler or by direct electricity, connection to district heating also provides a substantial reduction in emissions of CO(2). The largest reductions in CO(2) emissions are found to be 211 ktonnes/year assuming coal-fired condensing power as marginal electricity production. Connection of heat sparse areas to district heating decrease the system costs and provide a profitability by approximately 22 million EURO/year for the studied municipalities if the price of electricity is at a European level, i.e. 110 EURO/MWh. Sensitivity analysis shows, among other things, that a strong relation exists between the price of electricity and the profitability of connecting heat sparse areas to district heating systems.
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| 9. |
- Andersson, Harald, 1987-, et al.
(författare)
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A numerical and experimental investigation of a confluent jets ventilation supply device in a conference room
- 2022
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Ingår i: Energies. - : MDPI. - 1996-1073. ; 15:5
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Tidskriftsartikel (refereegranskat)abstract
- In this study, confluent jets ventilation (CJV) supply devices with three different nozzle arrays (1 × 19, 2 × 19, 3 × 19) were investigated both numerically and experimentally at two different airflow and supply air temperature set-ups. The performance of the CJV supply devices was investigated concerning thermal comfort, indoor air quality (IAQ), and heat removal effectiveness in a conference room environment. A comparison between the experimental and numerical results showed that the v2−f model had the best agreement out of the investigated turbulence models. The numerical results showed that the size of the array had a great impact both on near-field development and on the conditions in the occupied zone. A larger array with multiple rows and a lower momentum conserved the inlet temperature and the mean age of the air better than a single-row array with a higher momentum. A larger array with multiple rows had a higher IAQ and a greater heat removal effectiveness in the occupied zone because the larger array conserved the mean age of air better and the buoyancy driven flow was slightly better at removing the heat. Because of the lower inlet velocities, they also had lower velocities at ankle level, which decreased the risk of draft and thermal discomfort.
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| 10. |
- Andersson, Harald, 1987-, et al.
(författare)
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An Investigation Concerning Optimal Design of Confluent Jets Ventilation with Variable Air Volume
- 2023
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Ingår i: The International Journal of Ventilation. - : Taylor & Francis. - 1473-3315 .- 2044-4044.
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Tidskriftsartikel (refereegranskat)abstract
- This parametric study aims to predict the performance of confluent jets ventilation (CJV) with variable air volume (VAV) from four CJV design parameters. A combination of computational fluid dynamics (CFD), and response surface method (RSM) has been used to predict the energy efficiency, thermal comfort and IAQ for the four expected vital design variables, i.e., heat load (XH), number of nozzles (XN), airflow rate (XQ) and supply temperature (XTS). The RSM was used to generate a quad-ratic equation for the response variables exhaust temperature (TE), sup-ply temperature (TP), PMV, DR, eT and ACE. The RSM shows that the TE, TP and PMV were independent of the number of nozzles. The proposed equations were used to generate setpoints optimized for thermal com-fort (PMV) for summer, spring and winter cases with different CLO fac-tors and different TS under a scenario where the heat load varied between 10-30W/m2. TE was used as setpoint to regulate the airflow rate to keep the PMV values close to zero. The results show that by adapting the TS to the CLO factor both thermal comfort and the energy efficiency can be improved. Further energy reduction can be gained by downregulating the airflow rate to keep the TP at a fixed setpoint when the heat load is decreased. This means that a CJV can effectively be combined with VAV to improve environmental performance with good thermal comfort (-0.5
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| 11. |
- Andersson, Harald, et al.
(författare)
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Energy-Saving Measures in a Classroom Using Low Pressure Drop Ceiling Supply Device : A Field Study
- 2016
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Ingår i: 2016 ASHRAE Winter Conference Papers. - : ASHRAE. - 9781939200136
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Konferensbidrag (refereegranskat)abstract
- Between 1990 and 2006 the energy use by ventilation systems in Swedish schools doubled. This is explained by high airflows in schools because of the high occupant density. Studies show that 87% of Swedish schools use constant air volume (CAV), and it is estimated that a change to variable air volume (VAV) could save 0.12-0.33 TWh (4.1*10(12) - 1.1*10(13) Btu) per year. Therefore the aim of this study is to investigate whether it is possible to replace displacement ventilation (DV) with mixing ventilation (MV) to create a comfortable indoor climate in a typical classroom and at the same time decrease the energy use by using VAV and Low Pressure Drop Ceiling Supply Device (LPDCSD). The study used two LPDCSDs which consist of circular channels with 190/228 round jets placed in an interlocking pattern, with a horizontal one/two-way-direction. The field study was carried out in a school which is intended to be extensively renovated. The school currently has DV and CAV. The study was carried out by installing MV with LPDCSD in one of the typical classrooms. Several different air-flow rates were investigated using tracer-gas technology to measure the local mean age of the air in the occupied zone. Simultaneously, thermal comfort and vertical temperature gradients were measured in the room. The results show nearly uniform distribution of the local mean age of air in the occupied zone, even in the cases of relatively low air-flow rates. Since the mixing of air is more or less the same in the entire occupied zone VAV can be used to reduce air-flow rate based on the desired CO2-level. Because of the number of students in each classroom and the fact that changes in air-flow rates have no significant effect on the degree of mixing, it is possible to reduce the air-flow rates for extended periods of time. Finally, since the LPDCSD has a lower pressure-drop than the currently used supply devices and it is possible to use VAV to lower the airflows in cases with reduced heat loads, it is possible to significantly reduce the energy usage in the school while maintaining the IAQ, increasing the thermal comfort and the available floor area of the occupied zone.
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| 12. |
- Andersson, Harald, et al.
(författare)
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Experimental and numerical investigations of a new ventilation supply device based on confluent jets
- 2018
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Ingår i: Building and Environment. - : Elsevier BV. - 0360-1323 .- 1873-684X. ; 137, s. 18-33
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Tidskriftsartikel (refereegranskat)abstract
- In developed countries, heating, ventilation, air conditioning (HVAC) systems account for more than 10% of national energy use. The primary function of a HVAC system is to create proper indoor environment. A number of ventilation strategies have been developed to minimize HVAC systems’ energy use whilst still maintaining a good indoor environment. Among these strategies are confluent jet ventilation and variable air volume. In this study, an air supply device with a novel nozzle design that uses both of the above-mentioned strategies was investigated both experimentally and numerically at three different airflow rates. The results from the numerical investigation using the SST k - ω turbulence model regarding velocities and flow patterns are validated by experimental data carried out by Laser Doppler Anemometry. The results from both studies show that the flow pattern and velocity in each nozzle is directly dependent on the total airflow rate. However, the flow pattern does not vary between the three different airflow rates. The numerical investigation shows that velocity profiles for each nozzle have the same pattern regardless of the airflow rate, but the magnitude of the velocity profile increases as the airflow increases. Thus, a supply device of this kind could be used for variable air volume and produce confluent jets for the airflow rates investigated.
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| 13. |
- Andersson, Harald, 1987-
(författare)
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Numerical and experimental study of confluent jets supply device with variable airflow
- 2019
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In recent years, application of confluent jets for design of ventilation supply devices has been studied. Similarly, numerus studies have been made on the potential and application of variable air volume (VAV) in order to reduce the energy demand of ventilation systems. This study investigates the combination of supply devices based on confluent jets and VAV, both in terms of the nearfield flow behavior of the device and the impact on thermal comfort, indoor air quality and energy efficiency on a classroom-level space when the airflow rate is varied.The method used in this study is an experimental field study where the confluent jets-based supply devices were compared to the previously installed displacement ventilation. The field study evaluated the energy efficiency, thermal comfort and indoor air quality of the two systems. In the case of the confluent jets supply devices, airflow rate was varied in order to see what impact the variation had on the performance of the system for each airflow rate. Furthermore, the confluent jets supply devices were investigated both experimentally and numerically in a well insulated test room to get high resolution data on the particular flow characteristics for this type of supply device when the airflow rate is varied. The results from the field study show nearly uniform distribution of the local mean age of air in the occupied zone, even in the cases of relatively low airflow rates. The airflow rates have no significant effect on the degree of mixing. The thermal comfort in the classroom was increased when the airflow rate was adapted to the heat load compared to the displacement system. The results lead to the conclusion that the combination of supply devices based on confluent jets can reduce energy usage in the school while maintaining indoor air quality and increasing the thermal comfort in the occupied zone.The results from the experimental and numerical study show that the flow pattern and velocity in each nozzle is directly dependent on the total airflow rate. However, the flow pattern does not vary between the three different airflow rates. The numerical investigation shows that velocity profiles for each nozzle have the same pattern regardless of the airflow rate, but the magnitude of the velocity profile increases as the airflow increases. Thus, a supply device of this kind could be used for variable air volume and produce confluent jets for different airflow rates.The results from both studies show that the airflow rate does not affect the distribution of the airflow on both near-field and room level. The distribution of air is nearly uniform in the case of the near-field results and the room-level measurement shows a completely uniform degree of mixing and air quality in the occupied zone for each airflow rate. This means that there is potential for combining these two schemes for designing air distribution systems with high energy efficiency and high thermal comfort and indoor air quality.
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| 14. |
- Andersson, Harald, 1987-, et al.
(författare)
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On the ventilation performance of low momentum confluent jets supply device in a classroom
- 2020
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Ingår i: Energies. - : MDPI. - 1996-1073. ; 13:20
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Tidskriftsartikel (refereegranskat)abstract
- The performance of three different confluent jets ventilation (CJV) supply devices was evaluated in a classroom environment concerning thermal comfort, indoor air quality (IAQ) and energy efficiency. The CJV supply devices have the acronyms: high-momentum confluent jets (HMCJ), low-momentum confluent jets (LMCJ) and low-momentum confluent jets modified by varying airflow direction (LMCJ-M). A mixing ventilation (MV) slot jet (SJ) supply device was used as a benchmark. Comparisons were made with identical set-up conditions in five cases with different supply temperatures (TS) (16–18 °C), airflow rates (2.2–6.3 ACH) and heat loads (17–47 W/m2). Performances were evaluated based on DR (draft rating), PMV (predicted mean vote), ACE (air change effectiveness) and heat removal effectiveness (HRE). The results show that CJV had higher HRE and IAQ than MV and LMCJ/LMCJ-M had higher ACE than HMCJ. The main effects of lower Ts were higher velocities, DR (HMCJ particularly) and HRE in the occupied zone as well as lower temperatures and PMV-values. HMCJ and LMCJ produce MV conditions at lower airflow rates (<4.2 ACH) and non-uniform conditions at higher airflow rates. LMCJ-M had 7% higher HRE than the other CJV supply devices and produced non-uniform conditions at lower airflow rates (<3.3 ACH). The non-uniform conditions resulted in LMCJ-M having the highest energy efficiency of all devices.
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| 15. |
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| 16. |
- Anton, Raul, et al.
(författare)
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Modelling of EMC Screens for Radio Base Stations : Part 2: Evaluation of Turbulence Models
- 2004
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Ingår i: Proc. 9th InterSociety Conf. on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm 2004), Las Vegas, NV, USA. - : IEEE Press. - 0780383575 ; , s. 471-478
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Konferensbidrag (refereegranskat)abstract
- The objective of this paper is to investigate the performance of five well-known turbulence models and 2 wall treatments, in order to predict the details of the flow patterns through an EMC (ElectroMagnetic Compatibility) screen. The employed turbulence models are investigated in the present study is four different eddy-viscosity models; the standard k-ε model, the renormalization group (RNG) k-ε model, the realizable k-ε model and the k-ω model, as well as the Reynolds stress model, RSM. The commercial finite volume code Fluent 6.1 was used for simulation. A steady-state three-dimensional model, which serves as the most accurate representation of the model, was used in order to predict the details of the air flow paths and pressure field. The flow was assumed to be isothermal, turbulent and incompressible. The numerical predictions were validated experimentally by using wind tunnel measurements and smoke visualization. The performances of the turbulence models are discussed and the RSM results are compared with other two-equation turbulence models. The result shows that choosing the right turbulence model and wall treatment does not have a great influence on the prediction of pressure drop and the velocity field. The pressure field is over predicted about 15% and the velocity average deviation at several locations before and after the screen is less than 10%. Simulations using a hydraulic impedance surface, i.e. without a detail modeling of the EMC screen, show that the pressure field is also over predicted and great differences are observed in the velocity field.
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| 17. |
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| 18. |
- Anton Remirez, Raul, et al.
(författare)
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Compact CFD modeling of EMC screen for radio base stations : A porous media approach and a correlation for the directional loss coefficients
- 2007
-
Ingår i: IEEE transactions on components and packaging technologies (Print). - : IEEE Press. - 1521-3331 .- 1557-9972. ; 30:4, s. 875-885
-
Tidskriftsartikel (refereegranskat)abstract
- A methodology to obtain the directional pressure loss coefficients in a porous media model of an electromagnetically compatible screen of a radio base station model is presented. The directional loss coefficients of this compact model are validated against a detailed computational fluid dynamics model not only by comparing the total pressure drop, but also by evaluating the flow pattern after the screen. The detailed model was validated in an earlier article by the authors. A parametric study is conducted for 174 cases. Seven parameters were investigated: velocity, inlet height, screen porosity, printed circuit board (PCB) thickness, inlet-screen gap, distance between two PCBs and screen thickness. Based on the compact model parametric study, two correlations for the directional loss coefficients are developed as a function of the Reynolds number and the above geometrical parameters. The average disagreement between the compact model that uses the directional loss coefficients from the correlations and the detailed model was of 3% for the prediction of the total pressure drop and less than 6.5% and 9.5% for two coefficients that accurately characterize the flow pattern. © 2007 IEEE.
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| 19. |
- Anton Remirez, Raul, et al.
(författare)
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Detailed CFD Modelling of EMC Screen for Radio Base Stations : A Conjugate Heat Transfer Problem
- 2007
-
Ingår i: International Journal of Heat Exchangers. - : R.T Edwards Inc.. - 1524-5608. ; 8:1, s. 95-116
-
Tidskriftsartikel (refereegranskat)abstract
- The objective of this paper is to perform an experimental as well as CFD investigations of the conjugate heat transfer problem in a sub-rack slot model. A steady-state three-dimensional detailed model, which serves as the most accurate representation of the model, was used in order to evaluate the details of the airflow paths and temperature field. A general model that covers a considerable range of velocities, screen porosities and heat fluxes was validated experimentally by wind tunnel measurements. The result shows that the RNG k-ε model used with correct y+ and mesh strategy accurately predicts the temperature field. The average temperature deviation at several locations is less than 4% compared to experimental data. The influence of the velocity, screen porosity, heat flux and presence of the EMC screen on the PCB temperature field is commented.
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| 20. |
- Anton Remirez, Raul, et al.
(författare)
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Detailed CFD modelling of EMC screen for radio base stations : a parametric study
- 2009
-
Ingår i: IEEE transactions on components and packaging technologies (Print). - 1521-3331 .- 1557-9972. ; 32:1, s. 145-155
-
Tidskriftsartikel (refereegranskat)abstract
- The objective of this paper is to make a parametric study of the hydraulic resistance and flow pattern of the flow after an electromagnetic compatibility screen and between two printed circuit boards (PCBs) in a model of a 90° subrack cooling architecture. The parametric study is carried out using a detailed 3-D model of a PCB slot. The detailed model was experimentally validated in a previous paper by the authors. Seven parameters were investigated: velocity, inlet height, screen porosity, PCB thickness, distance between two PCBs, inlet-screen gap and screen thickness. A correlation for the static anddynamic pressure drop, the percentage of dimensionless wetted area, Aw*, and the RMS* factor (a function of the flow uniformity along the PCB) after the screen is reported as a function of six geometrical dimensionless parameters and the Reynolds number. The correlations, that are based on 174 three dimensional simulations, yield good results for the total pressure drop, in which the values are predicted within the interval of ±15%. For the, Aw* all the predicted values are within the interval of ±22% of the observed values. Finally, for the RMS* factor, the majority of the values also have a disagreement of less than 20% of the observed values. These last two parameters are believed to provide a correct insight about the flow pattern after the screen.
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| 21. |
- Anton Remirez, Raul, et al.
(författare)
-
Detailed CFD modelling of EMC screen for radio base stations : a benchmark study
- 2007
-
Ingår i: IEEE transactions on components and packaging technologies (Print). - 1521-3331 .- 1557-9972. ; 30:4, s. 754-763
-
Tidskriftsartikel (refereegranskat)abstract
- The objective of this paper is to investigate the performance of five well-known turbulence models, in order to find a model that predicts the details of the flow patterns through an electromagnetic compatibility (EMC) screen. The turbulence models investigated in the present study are five different eddy-viscosity models; the standard k-ε model, the renormalization group (RNG) k-ε model, the realizable k-ε model, the standard k-ω model, as well as the shear stress transport k-ω model. A steady-state 3-D detailed model, which serves as the most accurate representation of the model, was used in order to evaluate the details of the airflow paths and pressure field. The flow was assumed to be isothermal, turbulent and incompressible. A general model that covers a considerable range of velocities and geometries was validated experimentally by wind tunnel measurements. The result shows that for most of the k-ε models used with correct y+ and mesh strategy, the pressure drop and the velocity field deviation is small compared to experimental data. The k-ω models overpredict the overall pressure drop. When using the RNG k-ε model, the total static pressure drop predicted differs around 5%-10% and the average velocity deviation at several locations before and after the screen is around 5%.
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| 22. |
- Broström, Tor, et al.
(författare)
-
A method to assess the potential for and consequences of energy retrofits in Swedish historic buildings
- 2014
-
Ingår i: The Historic Environment. - : Maney Publishing. - 1756-7505 .- 1756-7513. ; 5:2, s. 150-166
-
Tidskriftsartikel (refereegranskat)abstract
- Tor Broström is a Professor in Conservation at Uppsala University, Campus Gotland, Sweden. With a background in engineering, his research focuses on indoor climate and energy conservation in historic buildings. He is coordinator of the Swedish national research programme on energy efficiency in historic buildings. Petra Eriksson, is a lecturer and PhD candidate in conservation at Uppsala University, Campus Gotland, Sweden. Petra has a background in the applied field of conservation and her research is in the field of heritage conservation in relation to energy efficiency. Linn Liu is a PhD candidate in the Division of Energy Systems, Department of Management and Engineering at Linköping University, Sweden. Her research area is within energy efficiency and cost efficiency of multifamily buildings and historic buildings. Patrik Rohdin is Associate Professor in the Division of Energy Systems, Department of Management and Engineering at Linköping University, Sweden. Patrik is conducting research related to energy efficiency in the built environment and building simulation and is active within the national interdisciplinary research programme, program energy systems. Bahram Moshfegh is a Professor and Head of the Division of Energy Systems, Department of Management and Engineering at Linköping University, Sweden. Professor Moshfegh has been active in the following research areas: mathematical modelling and measuring techniques for air and energy flow in buildings, energy-efficient HVAC systems and local and regional energy systems. Fredrik Ståhl is Senior Researcher in the Department of Energy Technology at SP Swedish Technical Research Institute. Currently, his research is focused on energy efficiency in historic buildings. The Swedish research project 'Potential and Policies for Energy Efficiency in Swedish Historic Buildings' aims to investigate the interdependency between political energy targets and effects on the built heritage. The fi rst part of this paper presents an iterative and interactive method to assess the potential for and consequences of improving the energy performance in a stock of historic buildings. Key elements in the method are: categorisation of the building stock, identifying targets, assessment of measures, and life-cycle cost optimisation. In the second part of the paper, the method is applied to a typical Swedish building. The selected case study shows how the method allows for an interaction between the quantitative assessment of the technoeconomic optimisation and the qualitative assessment of vulnerability and other risks. Through a multidisciplinary dialogue and iteration it is possible to arrive at a solution that best balances energy conservation and building conservation in a given decision context.
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| 23. |
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| 24. |
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| 25. |
- Carlander, Jakob, et al.
(författare)
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Effects on Energy Demand in an Office Building Considering Location, Orientation, Façade Design and Internal Heat Gains : A Parametric Study
- 2020
-
Ingår i: Energies. - : MDPI. - 1996-1073. ; 13:23
-
Tidskriftsartikel (refereegranskat)abstract
- 12.9% of the energy use in the EU originates from the commercial and public sector. It has therefore become a priority to optimize energy efficiency in these buildings. The purpose of this study has been to explore how energy demand in a new office building is affected by different internal heat gains, location, orientation, and façade design, and also to see how different indicators can change perspective on energy efficiency. The study was performed with simulations in IDA-ICE with different façade design and changes in internal heat gains (IHG), orientation, and location. Energy demand was then compared to two different indicators. Using a façade designed to lower solar heat gains had little effect on energy demand in the north of Sweden, but slightly more effect further south. The amount of internal heat gains had significant effect on energy demand. Making deeper studies on design and internal heat gains should therefore be prioritized in the beginning of new building projects so the most energy-efficient design can be chosen. When the indicator kWh/m2 was used, the cases with low internal heat gains were perceived as the most energy efficient, while when kWh/(m2 × hpers) (hpers = hours of use) was used, the cases with high occupancy and low electricity use were considered to be the most energy efficient. Therefore, revising the standardized indicator is of great importance.
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| 26. |
- Carlander, Jakob, et al.
(författare)
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Integration of measurements and time diaries as complementary measures to improve resolution of BES
- 2019
-
Ingår i: Energies. - Basel : MDPI. - 1996-1073. ; 12:11
-
Tidskriftsartikel (refereegranskat)abstract
- Building energy simulation (BES) models rely on a variety of different input data, and the more accurate the input data are, the more accurate the model will be in predicting energy use. The objective of this paper is to show a method for obtaining higher accuracy in building energy simulations of existing buildings by combining time diaries with data from logged measurements, and also to show that more variety is needed in template values of user input data in different kinds of buildings. The case studied in this article is a retirement home in Linköping, Sweden. Results from time diaries and interviews were combined with logged measurements of electricity, temperature, and CO2 levels to create detailed occupant behavior schedules for use in BES models. Two BES models were compared, one with highly detailed schedules of occupancy, electricity use, and airing, and one using standardized input data of occupant behavior. The largest differences between the models could be seen in energy losses due to airing and in household electricity use, where the one with standardized user input data had a higher amount of electricity use and less losses due to airing of 39% and 99%, respectively. Time diaries and interviews, together with logged measurements, can be great tools to detect behavior that affects energy use in buildings. They can also be used to create detailed schedules and behavioral models, and to help develop standardized user input data for more types of buildings. This will help improve the accuracy of BES models so the energy efficiency gap can be reduced.
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| 27. |
- Carlander, Jakob, 1985-
(författare)
-
On the Effect of Occupant Behavior and Internal Heat Gains on the Building’s Energy Demand : A case study of an office building and a retirement home
- 2021
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- About 12% of the greenhouse gas emissions and 40% of the total energy use in the EU derive from the buildings. User behavior, construction, and HVAC systems has a significant impact on a building’s energy use. If a building is to be energy-efficient it is important to understand how all these parameters are connected. This study is motivated by the need to decrease the energy use in buildings to reach the goals of energy use and greenhouse gas emissions. In this thesis, measurements of indoor climate and electricity use, together with time diaries was used to create input data for an energy simulation model of a retirement home. A parametric study was conducted to simulate how energy demand was affected by changes in five different parameters in an office building. Also, two different energy-efficiency indicators were used to see how indicators can affect the perceived energy-efficiency of buildings.High amount of airing and low electricity use had the most impact on the heating demand in the retirement home, and electricity use had the highest impact on the total energy demand in the office building. The model of the retirement home using data gathered on-site had 24% higher energy use than the model using standard user input data. In the office building, total energy demand for heating and cooling could be lowered with 12-31% by lowering the electricity use with 30% compared to standard user input data.For office buildings the most important thing to lower total energy demand seems to be lowering the electricity use. Using today’s standard user input data does not correspond well to using on-site gathered data in a retirement home and it is therefore important to develop the standard user input data further. The indicator kWh/m2, seems to promote buildings with low occupancy. This could lead to buildings being utilized in an in-efficient way. The indicator kWh/m2 should either be replaced or combined with an indicator that takes occupancy into consideration.
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| 28. |
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| 29. |
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| 30. |
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| 31. |
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| 32. |
- Cehlin, Mathias, et al.
(författare)
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Measurements of Air Temperatures Close to a Low-Velocity Diffuser in Displacement Ventilation Using Infrared Camera
- 2002
-
Ingår i: Energy and Buildings. - : Elsevier. - 0378-7788 .- 1872-6178. ; 34, s. 687-698
-
Tidskriftsartikel (refereegranskat)abstract
- The near zone of supply air diffusers is very critical for the indoor climate. Complaints of draft are often associated with low-velocity diffusers in displacement ventilation because the air is discharged directly into the occupied zone. Today, the knowledge of the near zone of these air supply diffusers is insufficient, causing an increased need for better measuring methods and representation of the occupied zone. A whole-field measuring technique has been developed by the authors for visualization of air temperatures and airflow patterns over a large cross-section. In this particular whole-field method, air temperatures are measured with an infrared camera and a measuring screen placed in the airflow. The technique is applicable to most laboratory and field test environments. It offers several advantages over traditional techniques; for example, it can record real-time images within large areas and capture transient events. The purpose of this study was to conduct a parameter and error analysis of the proposed whole-field measuring method applied to a flow from a low-velocity diffuser in displacement ventilation. A model of the energy balance, for a solid measuring screen, was used for analyzing the influence of different parameters on the accuracy of the method. The analysis was performed with respect to the convective heat transfer coefficient, emissivity, screen temperature and surrounding surface temperatures. Theoretically, the temperature difference between the screen and the ambient air was found to be 0.2–2.4 °C for the specific delimitation in the investigation. However, after applying correction the maximum uncertainty of the predicted air temperature was found to vary between 0.62 and 0.98 °C, due to uncertainties in estimating parameters used in the correction. The maximum uncertainty can be reduced to a great extent by estimating the convective heat transfer coefficient more accurately and using a screen with rather low emissivity.
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| 33. |
- Cehlin, Mathias, et al.
(författare)
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Numerical modeling of a complex diffuser in a room with displacement ventilation
- 2010
-
Ingår i: Building and Environment. - : Elsevier BV. - 0360-1323 .- 1873-684X. ; 45:10, s. 2240-2252
-
Tidskriftsartikel (refereegranskat)abstract
- A micro/macro-level approach (MMLA) has been proposed which makes it possible for HVAC engineers to easily study the effect of diffuser characteristics and diffuser placement on thermal comfort and indoor air quality. In this article the MMLA has been used to predict the flow and thermal behavior of the air in the near-zone of a complex low-velocity diffuser. A series of experiment has been carried out to validate the numerical predictions in order to ensure that simulations can be used with confidence to predict indoor airflow. The predictions have been performed by means of steady Reynolds Stress Model (RSM) and the results have good agreement both qualitatively and quantitatively with measurements. However, measurements indicated that the diffusion of the velocity and temperature was to some extent under-predicted by the RSM, which might be related to high instability of the airflow close to the diffuser. This effect might be captured by employing unsteady RSM. The present study also shows the importance of detailed inlet supply modeling in the accuracy of indoor air prediction.
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| 34. |
- Cehlin, Mathias, et al.
(författare)
-
Visualization of Isothermal Low-Reynolds Circular Air Jet Using Computed Tomography.
- 2005
-
Ingår i: <em>Proceedings of 6 th <em>World Conference on Experimental Heat Transfer, Fluid Mechanics, and Thermodynamics</em></em>.
-
Konferensbidrag (refereegranskat)abstract
- The intention of this paper was to demonstrate the principle and usefulness of computed tomography for concentration field measurements. Radial extinction coefficient profiles have been reconstructed using the LTD approach in the transition region of an isothermal jet of air at Reynolds number of 2 600. Reconstructed profiles were compared against velocity profiles at axial distances ranging from 2 to 20 nozzle diameters downstream. Results indicate that the width parameter of the reconstructed scalar distribution is around 23 % larger than the velocity distribution for distances between 10 and 20 nozzle diameters downstream. This finding is in good agreement with the results of other investigators. This technique has evidently yielded an accurate description of the scalar field of the round isothermal free jet. The quality of the reconstructions is very promising considering the relatively few measurement data, projection angles and low pixel resolution used in this study. Ccomputed tomography is superior for monitoring chemical concentrations over larger areas (whole room) when PMS and PLIF are unfeasible.
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| 35. |
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| 36. |
- Chen, Huijuan, et al.
(författare)
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Comparing k-ε Models On Predictions Of An Impinging Jet For Ventilation Of An Office Room
- 2011
-
Ingår i: Proceedings of Roomvent 2011, 11<sup>th</sup> International Conference on Air Distribution in Rooms 19 - 22 June 2011 Torendheim, Norway. - : tapir academic press.
-
Konferensbidrag (refereegranskat)abstract
- The objective of this study is to compare the performance of different k-ε models, i.e. the Standard k-ε, the Renormalization Group (RNG) k-ε, and the Realizable k-ε, with a two-layer model for the prediction of the mean velocity field and the temperature pattern from a newly designed impinging jet supply device for ventilation of an office room. The numerical predictions are validated against the detailed experimental measurements. The experimental investigation was performed in a test room with the dimensions 4.2×3.6×2.5 m, as a mock-up of a single-person office. Detailed velocity and temperature field measurements including the comfort zone and the jet developing region along the floor were carried out. The in-house made single-sensor hot-wire probe and the thermocouple are measuring instruments used to investigate the mean velocity, turbulence intensity and temperature. The boundary conditions for Computational Fluid Dynamics (CFD) study are obtained from the same set-up measurement. The results mainly consist of the flow field presentation, i.e., the velocity and temperature profiles in the comfort zone and the jet developing region along the floor. The comparisons between the results from the three versions of the k-ε models and measurements show generally satisfactory agreement, and better consistency is observed at the free jet region and the wall jet region that farther from the impingement zone. Among the three tested turbulence models, RNG shows the best overall performance.
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| 37. |
- Chen, Huijuan, et al.
(författare)
-
Comparisons of ventilation performance of different air supply devicesin in an office environment
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this study was to compare ventilation performance of four different air supply devices in an office environment with respect to thermal comfort, ventilation efficiency and energy-saving potential, by performing numerical simulations. The devices have the acronyms: Mixing supply device (MSD), Wall confluent jets supply device (WCJSD), Impinging jet supply device (IJSD) and Displacement supply device (DSD). Comparisons were made under identical set-up conditions, as well as at the same occupied zone temperature of about 24.2°C achieved by adding different heat loads and using different air-flow rates. Energy-saving potential was addressed based on the air-flow rate and the related fan power required for obtaining a similar occupied zone temperature for each device. Results showed that the IJSD could provide an acceptable thermal environment while removing excess heat more efficiently than the MSD, as it combined the positive effects of both mixing and stratification principles. This benefit also meant that this device required less fan power than the MSD for obtaining equivalent occupant zone temperature. The WCJSD studied in this paper behaved somewhat like the MSD, but caused higher draught discomfort at ankle level because of very high supply velocities, which was might due to small nozzle diameter of the supply device. Further studies are required for the WCJSD to make these conclusions applicable for general conditions. The DSD showed a superior performance on heat removal, air exchange efficiency and energy saving to all other devices, but it had difficulties in providing acceptable vertical temperature gradient between the ankle and head levels for a standing person.
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| 38. |
- Chen, Huijuan, et al.
(författare)
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Computational investigation on the factors influencing thermal comfort for impinging jet ventilation
- 2013
-
Ingår i: Building and Environment. - : Elsevier. - 0360-1323 .- 1873-684X. ; 66, s. 29-41
-
Tidskriftsartikel (refereegranskat)abstract
- Impinging jet ventilation (IJV) has been proposed to achieve an effective ventilation of an occupied zone in office and industrial buildings. For IJV systems, draught discomfort is the issue of most concern since it supplies cooled air directly to the occupied zone. This study investigated a number of factors influencing draught discomfort and temperature stratification in an office environment equipped with IJV. The factors considered were: shape of air supply device, discharge height, supply airflow rate and supply air temperature. The Response Surface Methodology (RSM) was used to identify the level of the significance of the parameters studied, as well as to develop the predictive models for the local thermal discomfort. Computational fluid dynamics (CFD) was employed to perform a set of required studies, and each simulation condition was determined by the Box – Behnken design (BBD) method. The results indicated that at a low discharge height, the shape of air supply device had a major impact on the flow pattern in the vicinity of the supply device because of the footprint from impinging jet, which consequently affected the draught risk level in the occupied zone. A square-shaped air supply device was found to result in lower overall draught discomfort than rectangular and semi-elliptic shapes. The RSM analysis revealed that the supply airflow rate had a significant impact on the draught discomfort, while the shape of air supply device and discharge height had moderate effects. The temperature stratification in the occupied zone was mostly influenced by the supply air temperature within the range studied.
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| 39. |
- Chen, Huijuan
(författare)
-
Experimental and numerical investigations of a ventilation strategy – impinging jet ventilation for an office environment
- 2014
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A well-functioning, energy-efficient ventilation system is of vital importance to offices, not only to provide the kind of comfortable, healthy indoor environment necessary for the well-being and productive work performance of occupants, but also to reduce energy use in buildings and the associated impact of CO2 emissions on the environment. To achieve these goals impinging jet ventilation has been developed as an innovative ventilation concept.In an impinging jet ventilation system, a high momentum of air jet is discharged downwards, strikes the floor and spreads over it, thus distributing the fresh air along the floor in the form of a very thin shear layer. This system retains advantages of mixing and stratification from conventional air distribution methods, while capable of overcoming their shortcomings.The aim of this thesis is to reach a thorough understanding of impinging jet ventilation for providing a good thermal environment for an office, by using Computational Fluid Dynamics (CFD) supported by detailed measurements. The full-field measurements were carried out in two test rooms located in a large enclosure giving relatively stable climate conditions. This study has been divided into three parts where the first focuses on validation of numerical investigations against measurements, the second addresses impacts of a number of design parameters on the impinging jet flow field and thermal comfort level, and the third compares ventilation performance of the impinging jet supply device with other air supply devices intended for mixing, wall confluent jets and displacement ventilation, under specific room conditions.In the first part, velocity and temperature distributions of the impinging jet flow field predicted by different turbulence models are compared with detailed measurements. Results from the non-isothermal validation studies show that the accuracy of the simulation results is to a great extent dependent on the complexity of the turbulence models, due to complicated flow phenomena related to jet impingement, such as recirculation, curvature and instability. The v2-f turbulence model shows the best performance with measurements, which is slightly better than the SST k-ω model but much better than the RNG k-ε model. The difference is assumed to be essentially related to the magnitude of turbulent kinetic energy predicted in the vicinity of the stagnation region. Results from the isothermal study show that both the SST k-ω and RNG k-ε models predict similar wall jet behaviours of the impinging jet flow.In the second part, three sets of parametric studies were carried out by using validated CFD models. The first parametric study shows that the geometry of the air supply system has the most significant impact on the flow field. The rectangular air supply device, especially the one with larger aspect ratio, provides a longer penetration distance to the room, which is suitable for industrial ventilation. The second study reveals that the interaction effect of cooling ceiling, heat sources and impinging jet ventilation results in complex flow phenomena but with a notable feature of air circulation, which consequently decreases thermal stratification in the room and increases draught discomfort at the foot level. The third study demonstrates the advantage of using response surface methodology to study simultaneous effects on changes in four parameters, i.e. shape of air supply device, jet discharge height, supply airflow rate and supply air temperature. Analysis of the flow field reveals that at a low discharge height, the shape of air supply device has a major impact on the flow pattern in the vicinity of the supply device. Correlations between the studied parameters and local thermal discomfort indices were derived. Supply airflow rates and temperatures are shown to be the most important parameter for draught and stratification discomfort, respectively.In the third part, the impinging jet supply device was shown to provide a better overall performance than other air supply devices used for mixing, wall confluent jets and displacement ventilation, with respect to thermal comfort, heat removal effectiveness, air exchange efficiency and energy-saving potential related to fan power.
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| 40. |
- Chen, Huijuan, et al.
(författare)
-
Investigation on the flow and thermal behavior of impinging jet ventilation systems in an office with different heat loads
- 2013
-
Ingår i: Building and Environment. - Oxford : Elsevier. - 0360-1323 .- 1873-684X. ; 59, s. 127-144
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents the flow and temperature field within an office using impinging jet ventilation (IJV) under different heat loads ranging from 17 to 65 W per square meter floor area. The measurement was carried out in a full-scale test room to verify the reliability of three turbulence models, i.e., the RNG k-epsilon, SST k-omega and (nu(2)) over bar - f models. It is found that all the tested models show good agreements with measurements, while the (nu(2)) over bar - f model shows the best performance, especially on the overall temperature prediction. less thanbrgreater than less thanbrgreater thanThe (nu(2)) over bar - f model is used further to investigate a number of important factors influencing the performance of the IJV. The considered parameters are: cooling effect of chilled ceiling, external heat load as well as its position, number of occupants and supplied air conditions. The interaction effect of chilled ceiling and heat sources results in a complex flow phenomenon but with a notable feature of air circulation. The appearance and strength of the air circulation mainly depends on the external heat load on window and number of occupants. It is found that with higher external heat load on window (384 W and 526 W), the air circulation has a strong tendency towards the side wall in the opposite direction to occupant, while with lower power on window (200 W) the air circulation has a strong tendency in the center of the room and extends to a larger area. When two occupants are present, two swirling zones are formed in the upper region. The effects of air circulation consequently alter the temperature field and the level of local thermal comfort.
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| 41. |
- Chen, Huijuan, et al.
(författare)
-
Numerical investigation of the flow behavior of an isothermal impinging jet in a room
- 2012
-
Ingår i: Building and Environment. - : Elsevier. - 0360-1323 .- 1873-684X. ; 49, s. 154-166
-
Tidskriftsartikel (refereegranskat)abstract
- The impinging jet concept has been proposed as a new ventilation strategy for use in office and industrial buildings. The present paper reports the mean flow field behavior of an isothermal turbulent impinging jet in a room. The detailed experimental study is carried out to validate the numerical simulations, and the predictions are performed by means of the RNG k-ε and SST k-ω model. The comparisons between the predictive results and the experimental data reveal that both of the tested turbulence models are capable of capturing the main qualitative flow features satisfactorily. It is found that the predictions from the RNG k-ε model predicts slightly better of the maximum velocity decay as jet approaching the floor, while the SST k-ω model accords slightly better in the region close to the impingement zone. Another important perspective of this study is to investigate the influence of different flow and configuration parameters such as jet discharge height, diffuser geometry, supply airflow rate and confinement from the surrounding environment on the impinging jet flow field with the validated model. The obtained data are presented in terms of the jet dimensionless velocity distribution, maximum velocity decay and spreading rate along the centerline of the floor. The comparative results demonstrate that all the investigated parameters have certain effects on the studied flow features, and the diffuser geometry is found to have the most appreciable impact, while the supply airflow rate is found to have marginal influence within the moderate flow range.
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| 42. |
- Chen, Huijuan, et al.
(författare)
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Numerical investigation of ventilation performance of different air supply devices in an office environment
- 2015
-
Ingår i: Building and Environment. - : Elsevier BV. - 0360-1323 .- 1873-684X. ; 90, s. 37-50
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to compare ventilation performance of four different air supply devices in an office environment with respect to thermal comfort, ventilation efficiency and energy-saving potential, by performing numerical simulations. The devices have the acronyms: Mixing supply device (MSD), Wall confluent jets supply device (WCJSD), Impinging jet supply device (IJSD) and Displacement supply device (DSD). Comparisons were made under identical set-up conditions, as well as at the same occupied zone temperature of about 24.2°C achieved by adding different heat loads and using different air-flow rates. Energy-saving potential was addressed based on the air-flow rate and the related fan power required for obtaining a similar occupied zone temperature for each device. Results showed that the WCJSD and IJSD could provide an acceptable thermal environment while removing excess heat more efficiently than the MSD, as it combined the positive effects of both mixing and stratification principles. This benefit also meant that this devices required less fan power than the MSD for obtaining equivalent occupant zone temperature. The DSD showed a superior performance on heat removal, air exchange efficiency and energy saving to all other devices, but it had difficulties in providing acceptable vertical temperature gradient between the ankle and neck levels for a standing person.
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| 43. |
- Choonya, Gasper, et al.
(författare)
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Experimental investigations of flow and thermal behavior of wall confluent jets as a heating device for large-space enclosures
- 2023
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Ingår i: Building and Environment. - : Elsevier. - 0360-1323 .- 1873-684X. ; 236
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Tidskriftsartikel (refereegranskat)abstract
- The study aimed to explore the effects of inlet air temperature, outdoor air temperature, inlet bulk velocity, and the number of nozzles on wall confluent jets (WCJ) propagating along an external cold wall in a large space enclosure such as a greenhouse. A combination of experimental study and Response surface methodology has been used to predict the flow and thermal behavior of the WCJ for the studied cases. Box-Behnken design was used to determine the case matrix for four of the above-mentioned vital variables for non-isothermal cases. The experimental study employed constant current anemometers to measure the velocity and temperature of the WCJ. Results showed that the WCJ attached to the wall under both isothermal and non-isothermal conditions. This flow behavior suggests that the WCJ can be used to heat the external facades of large-space enclosures. All the stated variables were critical to the decay factor and decay rate of maximum velocity, albeit at varying levels. The velocity decayed faster with an increase in the inlet bulk velocity and outdoor air temperature. It also decayed faster as the number of nozzles and inlet air temperature decreased. The external wall surface temperature and the wall-heating effect increased as the momentum of the jet increased. The surface temperature on the external wall was most influenced by the inlet air temperature and least by the number of nozzles. Correlations of the second-order polynomial for the Response surface models that estimate the rate of velocity decay and temperature on the external wall were obtained.
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| 44. |
- Choonya, Gasper, et al.
(författare)
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Heating of Cold Wall with Confluent Jets in Large Space Enclosures: Application in Greenhouse Premises
- 2023
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Ingår i: Proceedings of the 5th International Conference on Building Energy and Environment COBEE 2022. - : Springer. - 9789811998218 ; , s. 1925-1933
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Konferensbidrag (refereegranskat)abstract
- A parametrical investigation has been carried out to explore the velocity and temperature behaviour of wall confluent jets (WCJ) when used to heat and ventilate a test room, which mimics a greenhouse. This study assessed how the outdoor air temperature and supply air temperature affect the velocity and temperature profiles of the WCJ. The study also evaluated how WCJ can be used to eliminate film-wise condensation on greenhouse enclosure surfaces. Constant current anemometers (CCA) and T-type thermocouples were used to measure air velocity and temperature of the WCJ, air and surface temperature in the cooling chamber and test room. This study found that the supply air temperature affects the magnitude of the WCJ’s temperature in each region but the pattern (shape) of the dimensionless temperature is unaffected. The study also showed that both magnitude and pattern of the dimensionless temperature profiles are unaffected by the outdoor air temperature in all regions of the WCJ. The dimensionless velocity profiles under isothermal and non-isothermal were similar, but the magnitude of the profiles increased as the supply air temperature increased in the merging and impinging regions of the WCJ. WCJ formed a boundary layer of warm fluid on the nearby wall; thus, can be used to reduce condensation on the inner surfaces of the greenhouse enclosure.
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| 45. |
- Eriksson, Martin
(författare)
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A Statistical Approach to Estimate Thermal Performance and Energy Renovation of Multifamily Buildings : Case study on a Swedish city district
- 2022
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Several climate and energy goals have been set in the European Union, one of them being to increase energy efficiency. In Sweden, a large potential for increased energy efficiency lies in the residential and service sectors, which account for about 40% of total energy use. A large share of buildings in Sweden were built in the Million Homes Program in the 1960s and ’70s. These buildings are now in need of renovation, which enables renovation with the ambition of reducing energy use. In this thesis, the purpose is to develop an energy signature method, a bottom-up statistical method. This method has been validated using a building energy simulation software called IDA ICE, for two kinds of multifamily buildings from the Million Homes Program. The energy signature method has then been applied to a district located in Gävle, Sweden, containing more than 90 multifamily buildings with similar construction. In addition to characterizing current thermal performance of the buildings, the energy signature method is further developed so that potential for energy renovation of the district can be simulated. Simulated energy renovation is developed to comply with building energy use requirements, according to the most recent Swedish building regulations. Both on building and district level, sensitivity analysis is performed. In both cases the energy signature method is insensitive to changes in internal heat gains and indoor temperature. To investigate the effects of simulated renovation on a local district heating system, results are visualized in a duration diagram, where energy use reduction in different load periods is displayed. Thus, it is demonstrated how the energy signature method can be used as a rapid way of simulating energy renovation on district level and with readily available data.
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| 46. |
- Eriksson, Martin, et al.
(författare)
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Development and validation of energy signature method – Case study on a multi-family building in Sweden before and after deep renovation
- 2020
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Ingår i: Energy and Buildings. - : Elsevier. - 0378-7788 .- 1872-6178. ; 210
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Tidskriftsartikel (refereegranskat)abstract
- Building energy use constitutes a large part of total energy use, both in the European Union and Sweden. Due to this energy use, and the resulting emissions, several goals for energy efficiency and emissions have been set. In Sweden, a large portion of multi-family buildings were built between 1960 and 1980, which have major energy savings potential. The purpose of this paper is further development and validation of previously introduced energy signature method and its inherent parameters. The method was applied on a multi-family building where thermal energy data supplied by the district heating company was available before and after deep renovation. Using IDA ICE, a building energy simulation (BES) software model was created of the building, to aid in validation of the energy signature method. The paper highlighted the accuracy of the proposed energy signature (PES) method and a sensitivity analysis on the inherent parameters have been performed. The results showed new ways of treatment of the thermal energy data and revealed how more information can be extracted from this data.
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| 47. |
- Eriksson, Martin, et al.
(författare)
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Investigating energy use in a city district in nordic climate using energy signature
- 2022
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Ingår i: Energies. - : MDPI. - 1996-1073. ; 15:5
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Tidskriftsartikel (refereegranskat)abstract
- This paper focuses on multi-family buildings in a Swedish city district, erected between 1965 and 1973, which are now in need of renovation. For the two types of multi-family buildings in the district, tower buildings and low-rise buildings, dynamic energy use is predicted by using an energy signature method. The energy signature is then used to calculate the primary energy use number of the building stock, according to calculations methods dictated by Swedish building regulations. These regulations are also used to assess which multi-family buildings are in need of renovation, based on the buildings’ primary energy use. For buildings that need energy renovations, it is simulated so that the energy use of each multi-family building complies with these same building regulations. The proposed methodology for simulating energy renovation also determines new energy signature parameters, related to building heat loss coefficient, balance temperature and domestic hot water usage. The effects of simulated renovation are displayed in a duration diagram, revealing how a large-scale renovation affects the district’s heat load in different annual periods, which affects the local district heating system. Sensitivity analysis is also performed before and after simulated energy renovation.
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| 48. |
- Gebeyaw, Getiye Wodaje, et al.
(författare)
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Effect of spatial-temporal behavior of a newly developed cooling system on carbon and stainless steel bar properties
- 2023
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This report summaries the work within the project ”Effect of spatial-temporal behavior of a newly developed cooling system on carbon and stainless-steel bar properties”. The project was conducted from 2020-01-01 to 2022-12-31 and was co-produced by SSAB, Outokumpu and University of Gävle (UoG). The Knowledge Foundation, SSAB, Outokumpu and UoG financed the project.For the Swedish steel companies SSAB and Outokumpu producing special steels, it is very important to be able to control the cooling process in order to produce steel bars with excellent properties. Both steel companies also want to be able to control the cooling process so that the excellent steel properties become even over the bars’ spatial configuration.The aim of the present project is to reveal the spatial-temporal behavior of a newly developed cooling technology in order to produce steel bars with excellent properties and to control the phase transformation to achieve optimal performance of the steel bars.By using the special test rig at the UoG, detail temperature measurement mapping, invers solution and direct numerical simulation, the present project has identified and quantified several important aspects related to the quenching process, operating conditions, and temperature field development within the investigated products. The result from the proposed cooling process provides an outstanding cooling rate that is very crucial to obtain the required steel phase and thus the correct properties of the bar with different sizes. Results from this study have also shown that the cost per kg product can be reduced by tunning the process parameters such as soaking time and bar temperature before starting the cooling process.In addition, both experimental and numerical results of the material investigation show that the cooling technology has resulted in the desired phase transformation and subsequently the desired steel phases and material properties. The results show that the cooling technology and the control of the cooling parameters can be used to optimize the material properties of the bar materials.These good results and conclusions have been obtained via the deep collaboration between the SSAB, Outokumpu and UoG. The co-production, starting in the steering group planning the work along with the combination of research conducted at UoG and at the companies, have led to a successful project with great knowledge transfer in all direction during the duration of the project.
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| 49. |
- Gebremedhin, Alemayehu, 1962-, et al.
(författare)
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Modelling and optimization of district heating and industrial energy system - An approach to a locally deregulated heat market
- 2004
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Ingår i: International Journal of Energy Research. - : Hindawi Limited. - 0363-907X .- 1099-114X. ; 28:5, s. 411-422
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Tidskriftsartikel (refereegranskat)abstract
- Regions with densely concentration of industries and district heating systems (DHS) could be interesting study object from the light of an integrated heat market on local basis. System analysis with a widened system boundary could be used as an approach to evaluate the benefit of an integrated heat supply system. In this study, an energy system model consisting of totally seven different participants is designed and the optimization results of the system analysis are presented. With applied data and assumptions, the study shows that a significant amount of the heat demand within two sub-systems can be covered by heat supply from the heat market (the entire heat comes from two industries). Shadow prices, which can be used for heat pricing, indicate the advantage of an integrated system. The system cost reduction through integration and the availability of several actors with diverse energy supply system, makes the region under study an interesting area to prove a locally deregulated heat market.
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| 50. |
- Ghahremanian, Shahriar, et al.
(författare)
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A study on proximal region of low reynolds confluent jets : Part 1: Evaluation of turbulence models in prediction of inlet boundary conditions
- 2014
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Ingår i: ASHRAE Transactions. - New York : ASHRAE. - 9781936504701 ; , s. 256-270
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Konferensbidrag (refereegranskat)abstract
- Conventional ventilation systems (mixing and displacement) produce low air quality in industrial premises. A new air supply system (confluent jets system) may improve the ventilation efficiency and the energy efficiency. When round jets issue from co-planar nozzles with enough spacing, they converge, merge, and combine at certain downstream distances, which are called confluent jets. In order to numerically predict confluent jets, it is crucial to provide inlet boundary conditions for these jets at the nozzles' exit. Numerical prediction of inlet boundary conditions of confluent jets was chosen due to two reasons: the difficulty of measurement at the nozzles' exit, and lack of information about the shape of the employed nozzles to make artificial inlet profiles. Numerical predictions by two turbulence models (Realizable k - ε and RSM) of the supply device producing the confluent jets was verified by hot-wire measurements at 0.26 d0 downstream of the nozzles' exit in both lateral and vertical direction. The verification was carried out for different nozzles in an array by measuring axial velocity and its turbulence intensity. The axial velocity profile at the nozzles exit has a saddle-back shape with two distinct off-centered overshoots. The convergence of the velocity profile shows the existence of Vena contracta phenomena. Low turbulence intensity at the central part of nozzles was found with narrow shear layer upstream of confluent jet flow. Differences of velocity components, turbulent kinetic energy (TKE), and turbulent dissipation rate (TDR) of the studied contraction nozzle were examined with a flow issuing from a typical long pipe. Reynolds number dependency in the studied range has been carried out and Re effects were observed on TKE but not on TDR.
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