| 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. |
- 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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| 3. |
- 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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| 4. |
- 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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| 5. |
- 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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| 6. |
- 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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| 7. |
- 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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| 8. |
- 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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| 9. |
- 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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| 10. |
- 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
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Ingår i: IEEE transactions on components and packaging technologies (Print). - : IEEE Press. - 1521-3331 .- 1557-9972. ; 30:4, s. 875-885
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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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