hig.sePublications
Change search
Refine search result
1 - 30 of 30
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard-cite-them-right
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • sv-SE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • de-DE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the 'Create feeds' function.
  • 1.
    Akander, Jan
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Cehlin, Mathias
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Moshfegh, Bahram
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. Department of Management and Engineering, Division of Energy Systems, Linköping University.
    Assessing the Myths on Energy Efficiency When Retrofitting Multifamily Buildings in a Northern Region2017In: Sustainable High Rise Buildings in Urban Zones: Advantages, Challenges, and Global Case Studies / [ed] Ali Sayigh, Cham: Springer Publishing Company, 2017, 1, 139-161 p.Chapter in book (Other academic)
    Abstract [en]

    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.

  • 2.
    Angele, Kristian
    et al.
    Vattenfall Research & Development AB, Älvkarleby, Sweden.
    Cehlin, Mathias
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering. Vattenfall Research & Development AB, Älvkarleby, Sweden.
    Högström, Carl-Maikel
    Vattenfall Research & Development AB, Älvkarleby, Sweden.
    Odemark, Ylva
    Vattenfall Research & Development AB, Älvkarleby, Sweden.
    Henriksson, Mats
    Vattenfall Research & Development AB, Älvkarleby, Sweden.
    Tinoco, Hernan
    Forsmarks Kraftgrupp AB, Östhammar, Sweden.
    Lindqvist, Hans
    Forsmarks Kraftgrupp AB, Östhammar, Sweden.
    Hemström, Bengt
    Vattenfall Research & Development AB, Älvkarleby, Sweden.
    Flow Mixing Inside a Control-Rod Guide Tube: Part 2—Experimental Tests and CFD-Simulations2010In: 18th International Conference on Nuclear Engineering: Volume 4, Parts A and B, 2010, 655-663 p.Conference paper (Refereed)
    Abstract [en]

    Alarge number of control rod cracks were detected during therefuelling outage of the twin reactors Oskarshamn 3 and Forsmark3 in the fall of 2008. The extensive damage investigationfinally lead to the restart of both reactors at theend of 2008 under the condition that further studies wouldbe conducted in order to clarify all remaining matters. Also,all control rods were inserted 14% in order to locatethe welding region of the control rod stem away fromthe thermal mixing region of the flow. Unfortunately, this measureled to new cracks a few months later due toa combination of surface finish of the new stems andthe changed flow conditions after the partial insertion of thecontrol rods. The experimental evidence reported here shows an increasein the extension of the mixing region and in theintensity of the thermal fluctuations. As a part of thecomplementary work associated with the restart of the reactors, andto verify the CFD simulations, experimental work of the flowin the annular region formed by the guide tube andcontrol rod stem was carried out. Two full-scale setups weredeveloped, one in a Plexiglass model at atmospheric conditions (inorder to be able to visualize the mixing process) andone in a steel model to allow for a highertemperature difference and heating of the control rod guide tube.The experimental results corroborate the general information obtained through CFDsimulations, namely that the mixing region between the cold crud-removalflow and warm by-pass flow is perturbed by flow structurescoming from above. The process is characterized by low frequent,high amplitude temperature fluctuations. The process is basically hydrodynamic, causedby the downward transport of flow structures originated at theupper bypass inlets. The damping thermal effects through buoyancy isof secondary importance, as also the scaling analysis shows, howevera slight damping of the temperature fluctuations can be seendue to natural convection due to a pre-heating of thecold crud-removal flow. The comparison between numerical and experimental resultsshows a rather good agreement, indicating that experiments with plantconditions are not necessary since, through the existing scaling lawsand CFD-calculations, the obtained results may be extrapolated to plantconditions. The problem of conjugate heat transfer has not yetbeen addressed experimentally since complex and difficult measurements of theheat transfer have to be carried out. This type ofmeasurements constitutes one of the main challenges to be dealtwith in the future work.

  • 3.
    Angele, Kristian
    et al.
    Vattenfall Research & Development AB, Älvkarleby, Sweden.
    Odemark, Ylva
    Vattenfall Research & Development AB, Älvkarleby, Sweden.
    Cehlin, Mathias
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering. Vattenfall Research & Development AB, Älvkarleby, Sweden.
    Hemström, Bengt
    Vattenfall Research & Development AB, Älvkarleby, Sweden.
    Högström, Carl-Maikel
    Vattenfall Research & Development AB, Älvkarleby, Sweden.
    Henriksson, Mats
    Vattenfall Research & Development AB, Älvkarleby, Sweden.
    Tinoco, Hernan
    Forsmarks Kraftgrupp AB, Östhammar, Sweden.
    Lindqvist, Hans
    Forsmarks Kraftgrupp AB, Östhammar, Sweden.
    Flow mixing inside a control-rod guide tube: Experimental tests and CFD simulations2011In: Nuclear Engineering and Design, ISSN 0029-5493, E-ISSN 1872-759X, Vol. 241, no 12, 4803-4812 p.Article in journal (Refereed)
  • 4.
    Arghand, Taha
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering.
    Karimipanah, Taghi
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering.
    Awbi, Hazim
    School of Construction Management and Engineering, University of Reading, United Kingdom.
    Cehlin, Mathias
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering.
    Larsson, Ulf
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering.
    Linden, Elisabet
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering.
    An experimental investigation of the flow and comfort parameters for under-floor, confluent jets and mixing ventilation systems in an open-plan office2015In: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 92, 48-60 p.Article in journal (Refereed)
    Abstract [en]

    There is a new trend to convert the workplaces from individual office rooms to open offices for motivating money saving and better communication. With such a shift the ability of existing ventilation systems in meeting the new requirements is a challenging question for researchers. The available options could have an impact on workers' health in terms of providing acceptable levels of thermalcomfort and indoor air quality. Thus, this experimental investigation focuses on the performances of three different air distribution systems in an open-plan office space. The investigated systems were: mixing ventilation with ceiling-mounted inlets, confluent jets ventilation and underfloor air distribution with straight and curved vanes. Although this represents a small part of our more extensiveexperimental investigation, the results show that all the purposed stratified ventilation systems (CJV and UFAD) were more or less behaving as mixing systems with some tendency for displacement effects. Nevertheless, it is known that the mixing systems have a stable flow pattern but has the disadvantage of mixing contaminated air with the fresh supplied air which may produce lower performance and in worst cases occupants' illness. For the open-plan office we studied here, it will be shown that the new systems are capable of performing better than the conventional mixing systems. As expected, the higher air exchange efficiency in combination with lower local mean age of air for corner-mounted CJV and floor-mounted UFAD grills systems indicates that these systems are suitable for open-plan offices and are to be favored over conventional mixing systems.

  • 5.
    Cehlin, Mathias
    University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för energi- och maskinteknik.
    Visualization of Airflow, Temperature and Concentration Indoors: whole-field measuring methods and CFD2006Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

     

    The thermal indoor climate is a complicated combination of a number of physical variables, all of which strongly affect people’s well-being. The indoor climate not only heavily affects people’s health and life quality, but also their productivity and ability to work efficiently.

    One of the reasons why so many problems are associated with indoor climate is that it is more or less invisible; it is hard to understand something that cannot be seen. In particular, the near-zone of supply air diffusers in displacement ventilation is very critical. Complaints about drafts are often associated with this type of ventilation system.

    The main aim of this research is to improve the knowledge of the whole-field techniques used to measure and visualize air temperatures and pollutant concentrations. These methods are explored with respect to applicability and reliability. Computational Fluid Dynamics (CFD) has been used to predict the velocity and temperature distributions and to improve the current limitations.

    Infrared thermography is an excellent technique for visualization of air temperature and airflow pattern, particular in areas with high temperature gradient, such as close to diffusers. It is applicable to both laboratory and field test environments, such as in industries and workplaces. For quantitative measurements the recorded temperatures must be corrected for radiation heat exchange with the environment, a complicated task since knowledge about the local heat transfer coefficients, view factors and surrounding surfaces are needed to be known with good accuracy.

    Computed tomography together with optical sensing is a promising tool in order to study the dispersion of airborne pollutants in buildings. However, the design of the optical sensing configuration and the reconstruction algorithm has a major influence on the performance of this whole-field measuring technique. A Bayesian approach seems to be a rational choice for reconstruction of pollutant concentration indoors, since it avoids the high noise sensitivity frequently encountered with many other reconstruction methods. A modified Low Third Derivative (LTD) method has been proposed in this work that performs well particular for concentration distributions containing steep gradients and regions with very low concentrations.

    CFD simulation is a powerful tool for visualization of velocities, airflow pattern and temperature distribution in rooms. However, for predictions of the absolute value of the physical variables the CFD model have to be validated against some reference case with high quality experimental data. CFD predictions of air temperatures and velocities close to a complex supply diffuser are very troublesome. The performance of CFD prediction of the airflow close to a complex supply diffuser depends mainly on the accuracy of the diffuser, turbulence and wall treatment modeling

  • 6.
    Cehlin, Mathias
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Karimipanah, Taghi
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Prediction of indoor airflow close to a supply device using SST-SAS Model2015In: Ventilation 2015 - Proceedings of the 11th International Conference on Industrial Ventilation / [ed] Taipale A., Li Z., Li X., and Zhang X, International Conference on Industrial Ventilation , 2015, Vol. 2, 681-688 p.Conference paper (Refereed)
    Abstract [en]

    Modern diffusers applied in the field of ventilation of rooms are often complex in terms of geometry, including perforated plates, dampers, guide rails, curved surfaces and other components inside the diffuser, with the intention to create satisfying thermal comfort for the occupants. Also connecting ducts can be different for the same diffuser in different situations, affecting the supply velocity profile. It is obvious that simulation of airflow and air temperature particularly in rooms with displacement ventilation is very troublesome, particularly if the near-zone of the diffuser is of interest. Experiments commonly indicate very high turbulence intensities in the near-zone of displacement ventilation supply devices, especially close to the floor where high mean flow gradient occurs. This indicates that the air flow from inlet devices designed for displacement ventilation might be very unsteady; the position of the stream leaving the diffuser and entering the room is changing with time, hence diffusion of momentum and temperature are increased. Also Kelvin-Helmholtz instabilities occurs, resulting in mixing and entrainment of surrounding air into the gravity current. These effects are not captured correctly in RANS simulations, since it is performed with the assumption of time-independent conditions. In this paper URANS simulations were performed for prediction of velocity and temperature distribution close to a complex air supply device in a room with displacement ventilation. The presented study show that URANS with the SST-SAS ᅵᅵ - ᅵᅵ turbulence model predicts the air velocities and air temperatures very well close to the air supply device. The URANS computation using the SST-SAS model seems to successfully contribute to the reproduction of large-scale unsteady flow patterns in the near-zone of the supply device, and therefore enable more accurate prediction of the velocity and temperature distributions compared to the steady-RANS computation and dissipative URANS models.

  • 7.
    Cehlin, Mathias
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering.
    Karimipanah, Taghi
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering.
    Larsson, Ulf
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering.
    Unsteady CFD simulations for prediction of airflow close to a supply device for displacement ventilation2014In: Indoor Air 2014 - 13th International Conference on Indoor Air Quality and Climate, 2014, 47-54 p.Conference paper (Refereed)
    Abstract [en]

    Modern diffusers applied in the field of ventilation of rooms are often complex in terms of geometry, including perforated plates, dampers, guide rails, curved surfaces and other components inside the diffuser, with the intention to create satisfying thermal comfort for the occupants. Also connecting ducts can be different for the same diffuser in different situations, affecting the supply velocity profile. It is obvious that simulation of airflow and air temperature particularly in rooms with displacement ventilation is very troublesome, particularly if the near-zone of the diffuser is of interest. Experiments commonly indicate very high turbulence intensities in the near-zone of displacement ventilation supply devices, especially close to the floor where high mean flow gradient occurs. This indicates that the air flow from inlet devices designed for displacement ventilation might be very unstable; the position of the stream leaving the diffuser and entering the room is changing with time, hence diffusion of momentum and temperature are increased. This effect is not captured in RANS simulations, since it is performed with the assumption of time-independent conditions. In this paper URANS simulations were performed for prediction of velocity and temperature distribution close to a complex air supply device in a room with displacement ventilation. The presented study show that unsteady simulations with the realizable turbulence k-ε model generates too high eddy viscosity and therefore damps out the unsteadiness of the flow especially inside the diffuser.

  • 8.
    Cehlin, Mathias
    et al.
    University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för energi- och maskinteknik.
    Karlsson, Fredrik
    Linköping Universitet.
    Komfort- och inomhusmiljökonsekvenser av strukturerad energieffektivisering av vårdlokaler2009Report (Other academic)
  • 9.
    Cehlin, Mathias
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering.
    Moshfegh, Bahram
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering.
    Numerical Modeling of a Complex Diffuser in a Room with Displacement Ventilation2010In: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 45, no 10, 2240-2252 p.Article in journal (Refereed)
    Abstract [en]

    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.

  • 10.
    Cehlin, Mathias
    et al.
    University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för energi- och maskinteknik.
    Moshfegh, Bahram
    University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för energi- och maskinteknik.
    Visualization of Isothermal Low-Reynolds Circular Air Jet Using Computed Tomography.2005In: Proceedings of 6 th World Conference on Experimental Heat Transfer, Fluid Mechanics, and Thermodynamics, 2005Conference paper (Refereed)
    Abstract [en]

    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.

  • 11.
    Cehlin, Mathias
    et al.
    University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för energi- och maskinteknik.
    Moshfegh, Bahram
    University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för energi- och maskinteknik.
    Karlsson, Fredrik
    Larsson, Ulf
    University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för energi- och maskinteknik.
    Analysis on Thermal Comfort for a Hospital Building by Multi-zone Modeling: Summer Condition2008In: Proceedings of World Renewable Energy Congress X, 2008Conference paper (Refereed)
  • 12.
    Cehlin, Mathias
    et al.
    University of Gävle, Department of Technology and Built Environment.
    Moshfegh, Bahram
    University of Gävle, Department of Technology and Built Environment. Linköpings universitet, Tekniska högskolan.
    Stymne, Hans
    University of Gävle, Department of Technology and Built Environment.
    Kartläggning av inneklimatparametrar i Volvo Eskilstuna: byggnad SE75 Zon 7, 10 och 122000Report (Other academic)
  • 13.
    Cehlin, Mathias
    et al.
    University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för energi- och maskinteknik.
    Moshfegh, Bahram
    University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för energi- och maskinteknik.
    Stymne, Hans
    Mapping of Indoor Climate Parameters in Volvo, Eskilstuna2000Report (Other academic)
  • 14.
    Cehlin, Mathias
    et al.
    University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för energi- och maskinteknik.
    Sandberg, Mats
    University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för inomhusmiljö.
    Computed tomography for indoor application2006In: The International Journal of Ventilation, ISSN 1473-3315, E-ISSN 2044-4044, Vol. 4, no 4, 349-364 p.Article in journal (Refereed)
    Abstract [en]

    This paper deals with tomographic techniques for two-dimensional spatially resolved concentration measurements indoors. This represents a significant advance over the traditional point measuring method for mapping tracer gas and pollutants. Methods for recording of data are stressed as well as different types of tomographic reconstruction algorithms such as the Smooth Basis Function Minimization (SBFM) and the modified Low Third Derivative (LTDm) methods. Among the reconstruction algorithms available today, SBFM and LTDm are among the most promising. These algorithms show potential for reconstruction of gas concentration in rooms, since they are regularized to converge towards smooth concentration distributions. Using the LTD method and ‘snapshot’ configuration enables the examination and real-time monitoring of transient flows.

  • 15.
    Cehlin, Mathias
    et al.
    University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för energi- och maskinteknik.
    Sandberg, Mats
    University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för inomhusmiljö.
    Computed Tomography for Indoor Applications2006In: The International Journal of Ventilation, ISSN 1473-3315, E-ISSN 2044-4044, Vol. 4, no 4, 349-364 p.Article in journal (Other academic)
    Abstract [en]

    This paper deals with tomographic techniques for two-dimensional spatially resolved concentration measurements indoors. This represents a significant advance over the traditional point measuring method for mapping tracer gas and pollutants. Methods for recording of data are stressed as well as different types of tomographic reconstruction algorithms such as the Smooth Basis Function Minimization (SBFM) and the modified Low Third Derivative (LTDm) methods. Among the reconstruction algorithms available today, SBFM and LTDm are among the most promising. These algorithms show potential for reconstruction of gas concentration in rooms, since they are regularized to converge towards smooth concentration distributions. Using the LTD method and ‘snapshot’ configuration enables the examination and real-time monitoring of transient flows.

  • 16.
    Cehlin, Mathias
    et al.
    University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för energi- och maskinteknik.
    Sandberg, Mats
    University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för inomhusmiljö.
    Time evolution of gravity currents discharged from low velocity diffusers2007In: Roomvent 2007, 2007, 61-70 p.Conference paper (Refereed)
  • 17.
    Cehlin, Mathias
    et al.
    University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för energi- och maskinteknik.
    Sandberg, Mats
    University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för inomhusmiljö.
    Time evolution of gravity currents discharged from low velocity diffusers2007In: Roomvent 2007: 10th International Conference on Air Distribution in Rooms, 13-15 June 2007, Helsinki, Finland, 2007, Vol. 3 61-70 p.Conference paper (Refereed)
  • 18.
    Chen, Huijuan
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering. Division of Energy Systems, Department of Management and Engineering, Linköping University.
    Moshfegh, Bahram
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering. Division of Energy Systems, Department of Management and Engineering, Linköping University.
    Cehlin, Mathias
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering.
    Computational investigation on the factors influencing thermal comfort for impinging jet ventilation2013In: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 66, 29-41 p.Article in journal (Refereed)
    Abstract [en]

    Impinging jet ventilation (IN) 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.

  • 19.
    Chen, Huijuan
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering. Division of Energy Systems, Department of Management and Engineering, Linköping University.
    Moshfegh, Bahram
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering. Division of Energy Systems, Department of Management and Engineering, Linköping University.
    Cehlin, Mathias
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering.
    Investigation on the flow and thermal behavior of impinging jet ventilation systems in an office with different heat loads2013In: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 59, 127-144 p.Article in journal (Refereed)
    Abstract [en]

    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. The (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.

  • 20.
    Chen, Huijuan
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering.
    Moshfegh, Bahram
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering.
    Cehlin, Mathias
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering.
    Numerical investigation of the flow behavior of an isothermal impinging jet in a room2012In: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 49, 154-166 p.Article in journal (Refereed)
    Abstract [en]

    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. 

  • 21.
    Joudi, Ali
    et al.
    Energy and Environmental Technology, Dalarna University, Falun, Sweden .
    Cehlin, Mathias
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering.
    Rönnelid, Mats
    Energy and Environmental Technology, Dalarna University, Falun, Sweden .
    Reflective coatings for interior and exterior of buildings and improving thermal performance2013In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 103, 562-570 p.Article in journal (Refereed)
    Abstract [en]

    The importance of reducing building energy usage and thriving for more energy efficient architectures, has nurtured creative solutions and smart choices of materials in the last few decades. Among those are optimizing surface optical properties for both interior and exterior claddings of the building. Development in the coil-coating steel industries has now made it possible to allocate correct optical properties for steel clad buildings with improved thermal performance. Although the importance of the exterior coating and solar gain are thoroughly studied in many literatures, the effect of interior cladding are less tackled, especially when considering a combination of both interior and exterior reflective coatings. This paper contemplates the thermal behavior of small cabins with reflective coatings on both interior and exterior cladding, under different conditions and climates with the aim to clarify and point out to the potential energy saving by smart choices of clad coatings.

  • 22.
    Joudi, Ali
    et al.
    Energy Technology, Dalarna University, Falun, Sweden; SSAB Europe, Borlänge, Sweden.
    Cehlin, Mathias
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Svedung, Harald
    Energy Technology, Dalarna University, Falun, Sweden; SSAB Europe, Borlänge, Sweden.
    Rönnelid, Mats
    Energy Technology, Dalarna University, Falun, Sweden.
    Moshfegh, Bahram
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. Energy Systems, Linköping University, Linköping, Sweden.
    Numerical and experimental investigation of the influence of infrared reflective interior surfaces on building temperature distributions2017In: Indoor + Built Environment, ISSN 1420-326X, E-ISSN 1423-0070, Vol. 26, no 3, 355-367 p.Article in journal (Refereed)
    Abstract [en]

    Radiative properties of interior surfaces can affect not only the building heat flux but also the indoor environment, the latter of which has not been thoroughly investigated. The aim of this study is to analyse the effect of surface emissivity on indoor air and surface temperature distributions in a test cabin with reflective interior surfaces. This was done by comparing experimental and simulation data of the test cabin with that of a normal cabin. This study employs transient computational fluid dynamics (CFD) using re-normalisation group (RNG) k-epsilon model, surface-to-surface radiation model and an enhanced wall function. Boundary conditions were assigned to exterior surfaces under variable outdoor conditions. The numerical and the measurement results indicate that using interior reflective surfaces will affect the indoor air temperature distribution by increasing the vertical temperature gradient depending on the time of the day. CFD simulations with high spatial resolution results show increased interior surface temperature gradients consistent with the increased vertical air temperature gradient. The influence of reflective surfaces is potentially greater with higher indoor surface temperature asymmetry. The vertical indoor air temperature gradient and surface temperatures are important parameters for indoor thermal comfort.

  • 23.
    Karimipanah, Taghi
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering.
    Cehlin, Mathias
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering.
    Comparing the efficiency of three turbulence models with experiments conducted for a two-dimensional wall jet in a ventilated room: 2011In: Proceedings of Roomvent 2011, 11th International Conference on Air Distribution in Rooms 19 - 22 June 2011 Torendheim, Norway, 2011, 8- p.Conference paper (Refereed)
  • 24.
    Karimipanah, Taghi
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering.
    Larsson, Ulf
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering.
    Cehlin, Mathias
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering.
    Investigation of flow pattern for a confluent-jets system on a workbench of an industrial space2014In: Indoor Air 2014: 13th International Conference on Indoor Air Quality and Climate, 2014, 192-199 p.Conference paper (Refereed)
    Abstract [en]

    A new air supply terminal based on confluent jets was installed on a workbench, in vicinity of a CNC machine, of an industrial space. The flow pattern and temperature field was carried out by CFD calculations and infrared camera imaging technique. A main goal of this technique is to save energy therefore the jet should distribute the air where it is desired. This is possible because the confluent jets system uses the benefits of both mixing (high momentum for better spreading of the air jet) and displacement (cleaner air in occupied zone). The results show that thermal comfort and air quality analysis relies on consistent facts and is in good agreements with the existed standards. It was shown that the supply terminal is able to spread the fresh air to the needed work area. This is an advantage of the high momentum air distribution system used in this investigation.

  • 25.
    Lane, Anna-Lena
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. SP Technical Research Institute of Sweden.
    Cehlin, Mathias
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
    Gustavsson, Thorbjörn
    SP Technical Research Institute of Sweden.
    ByggaE – Method for Quality Assurance of Energy Efficient Buildings2017In: International Journal of Energy Production and Management, ISSN 2056-3272, E-ISSN 2056-3280, Vol. 2, no 2, 133-139 p.Article in journal (Refereed)
    Abstract [en]

    Policies for energy efficiency requirements in buildings have become more stringent according to EU2020 goals. Despite policy regulations, requirements for energy efficiency are not met in many new buildings. Some of the reasons for this energy performance gap are related to the building process. The aim with this paper is to describe a purposed method for quality assurance of sustainable buildings according to energy efficiency. The proposed method is called ByggaE, where ‘Bygga’ is the Swedish word for ‘build’ and E is the first letter in ‘energy efficient’. It is a tool intended to lower the energy performance gap related to the building process by guiding the client and providers through the process to fulfill goals. The essence of ByggaE is the formulation of requirements by the client and the working process of identifying, handling and following up critical constructions and key issues. This working process involves all participants in the building project by using appropriate quality guidelines and checklists for documentation, communication and verification. ByggaE is a step forward ensuring that the building fulfills the defined functions and that conscious decisions are taken when goals have to be changed during the building project. The next steps are to ensure the usefulness of the method in practice by more testing and to spread knowledge about the method.

  • 26.
    Linden, Elisabet
    et al.
    University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för inomhusmiljö.
    Cehlin, Mathias
    University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för energi- och maskinteknik.
    Sandberg, Mats
    University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för inomhusmiljö.
    Temperature and velocity measurements on a diffuser for displacement ventilation with whole field methods2000In: The 7th International Conference on Air Distribution in Rooms, 2000Conference paper (Other academic)
  • 27.
    Linden, Elisabet
    et al.
    University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för inomhusmiljö.
    Hellström, Jennie
    Cehlin, Mathias
    University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för energi- och maskinteknik.
    Sandberg, Mats
    University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för inomhusmiljö.
    Virtual reality presentation of temperature measurements on a diffuser for displacement ventilation2001In: The 4th International Conference on Indoor Air Quality, Ventilation and Energy Conservation in Buildings, 2001Conference paper (Other academic)
  • 28.
    Liu, Linn
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering. Division of Energy Systems, Department of Management and Engineering, Linköping University.
    Moshfegh, Bahram
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering. Division of Energy Systems, Department of Management and Engineering, Linköping University.
    Akander, Jan
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering.
    Cehlin, Mathias
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering.
    Comprehensive investigation on energy retrofits in eleven multi-family buildings in Sweden2014In: Energy and Buildings, ISSN 0378-7788, E-ISSN 1872-6178, Vol. 84, 704-715 p.Article in journal (Refereed)
    Abstract [en]

    Rapidly growing energy use in the building sector is considered a serious problem by both the European Union (EU) and Sweden. Reducing energy demand in the building sector is important for Sweden in order to reach national energy goals for reduced energy use and CO 2 emissions in the future. This project aims to find energy efficiency potential in multifamily buildings in the Gävleborg region, which is a cold climate region in Sweden. Measurements and simulations have been made on eleven multifamily buildings from the whole region. The results include different energy efficiency measure packages, profitability analysis of individual measures and packages, and primary energy use analysis. The paper also includes CO 2 emissions reduction analysis based on different methods. The project shows that the multifamily buildings in the Gävleborg region have good potential to reduce their energy use by more than 50%, which in turn will contribute to 43% primary energy reduction and 48% CO 2 emissions reduction. 

  • 29.
    Sandberg, Mats
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering.
    Wigö, Hans
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering.
    Claesson, Leif
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering.
    Cehlin, Mathias
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering.
    A wind tunnel method for screening the interaction between wind turbines in planned wind farms2011In: Wrec 2011 Linköping Sweden 2011, 2011Conference paper (Refereed)
  • 30.
    Sumner, Jonathon
    et al.
    École de technologie supérieure, Department of Mechanical Engineering.
    Garcia, Bibiana
    Cehlin, Mathias
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering.
    Bechmann, Andreas
    Risø National Laboratory / Technical University of Denmark.
    Prospathopoulos, John
    Masson, Christian
    École de technologie supérieure, Department of Mechanical Engineering.
    Cabezon, Daniel
    Sanz Rodrigo, Javier
    Odemark, Ylva
    Sørensen, Niels
    Risø DTU, Wind energy departmernt.
    Politis, Evangelos
    Chaviaropoulos, Panagiotis
    RANS simulations of Bolund2011In: Wind Energy, ISSN 1095-4244, E-ISSN 1099-1824Article in journal (Refereed)
1 - 30 of 30
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard-cite-them-right
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • sv-SE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • de-DE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf