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Olofsson, Thomas
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Publications (10 of 94) Show all publications
Cheng, X., Yang, B., Liu, G., Olofsson, T. & Li, H. (2018). A total bounded variation approach to low visibility estimation on expressways. Sensors, 18(2), Article ID 392.
Open this publication in new window or tab >>A total bounded variation approach to low visibility estimation on expressways
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2018 (English)In: Sensors, ISSN 1424-8220, E-ISSN 1424-8220, Vol. 18, no 2, article id 392Article in journal, Editorial material (Refereed) Published
Abstract [en]

Low visibility on expressways caused by heavy fog and haze is a main reason for traffic accidents. Real-time estimation of atmospheric visibility is an effective way to reduce traffic accident rates. With the development of computer technology, estimating atmospheric visibility via computer vision becomes a research focus. However, the estimation accuracy should be enhanced since fog and haze are complex and time-varying. In this paper, a total bounded variation (TBV) approach to estimate low visibility (less than 300 m) is introduced. Surveillance images of fog and haze are processed as blurred images (pseudo-blurred images), while the surveillance images at selected road points on sunny days are handled as clear images, when considering fog and haze as noise superimposed on the clear images. By combining image spectrum and TBV, the features of foggy and hazy images can be extracted. The extraction results are compared with features of images on sunny days. Firstly, the low visibility surveillance images can be filtered out according to spectrum features of foggy and hazy images. For foggy and hazy images with visibility less than 300 m, the high-frequency coefficient ratio of Fourier (discrete cosine) transform is less than 20%, while the low-frequency coefficient ratio is between 100% and 120%. Secondly, the relationship between TBV and real visibility is established based on machine learning and piecewise stationary time series analysis. The established piecewise function can be used for visibility estimation. Finally, the visibility estimation approach proposed is validated based on real surveillance video data. The validation results are compared with the results of image contrast model. Besides, the big video data are collected from the Tongqi expressway, Jiangsu, China. A total of 1,782,000 frames were used and the relative errors of the approach proposed are less than 10%.

Place, publisher, year, edition, pages
MDPI, 2018
Keywords
total bounded variation, image spectrum, low visibility estimation, piece stationary, fog and haze
National Category
Environmental Analysis and Construction Information Technology Remote Sensing
Identifiers
urn:nbn:se:umu:diva-144176 (URN)10.3390/s18020392 (DOI)000427544000075 ()29382181 (PubMedID)
Available from: 2018-01-24 Created: 2018-01-24 Last updated: 2018-06-09Bibliographically approved
Cheng, X., Yang, B., Liu, G., Olofsson, T. & Li, H. (2018). A variational approach to atmospheric visibility estimation in the weather of fog and haze. Sustainable cities and society, 39, 215-224
Open this publication in new window or tab >>A variational approach to atmospheric visibility estimation in the weather of fog and haze
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2018 (English)In: Sustainable cities and society, ISSN 2210-6707, Vol. 39, p. 215-224Article in journal (Refereed) Published
Abstract [en]

Real-time atmospheric visibility estimation in foggy and hazy weather plays a crucial role in ensuring traffic safety. Overcoming the inherent drawbacks with traditional optical estimation methods, like limited sampling volume and high cost, vision-based approaches have received much more attention in recent research on atmospheric visibility estimation. Based on the classical Koschmieder's formula, atmospheric visibility estimation is carried out by extracting an inherent extinction coefficient. In this paper we present a variational framework to handle the nature of time-varying extinction coefficient and develop a novel algorithm of extracting the extinction coefficient through a piecewise functional fitting of observed luminance curves. The developed algorithm is validated and evaluated with a big database of road traffic video from Tongqi expressway (in China). The test results are very encouraging and show that the proposed algorithm could achieve an estimation error rate of 10%. More significantly, it is the first time that the effectiveness of Koschmieder's formula in atmospheric visibility estimation was validated with a big dataset, which contains more than two million luminance curves extracted from real-world traffic video surveillance data.

Keywords
Atmospheric visibility estimation, Variational approach, Piecewise stationary time series, Computer vision, Fog and haze
National Category
Other Environmental Engineering
Identifiers
urn:nbn:se:umu:diva-144561 (URN)10.1016/j.scs.2018.02.001 (DOI)000433169800020 ()
Available from: 2018-02-06 Created: 2018-02-06 Last updated: 2018-09-05Bibliographically approved
Nordlund, A., Nair, G., Hudson, C. & Olofsson, T. (2018). Att utveckla en stadsdel på ett hållbart sätt: en fråga om energi, transporter och människor. Umeå: Transportforskningsenheten, Umeå Universitet
Open this publication in new window or tab >>Att utveckla en stadsdel på ett hållbart sätt: en fråga om energi, transporter och människor
2018 (Swedish)Report (Other academic)
Place, publisher, year, edition, pages
Umeå: Transportforskningsenheten, Umeå Universitet, 2018. p. 59
Series
TRUM, ISSN 1403-6924 ; 2018:1
Keywords
Hållbar stadsutveckling, Universitetsstaden, Attityder och beteende, Energianvändning, Resbeteende, Åtgärder, Samhällsplanering
National Category
Social Sciences Interdisciplinary
Identifiers
urn:nbn:se:umu:diva-147957 (URN)
Projects
Umeå – En testbädd för hållbar stadsutveckling
Funder
Swedish Energy Agency
Available from: 2018-05-23 Created: 2018-05-23 Last updated: 2018-06-19Bibliographically approved
Nair, G., Olofsson, T., Nordlund, A. & Hudson, C. (2018). Comparative evaluation of city dwellers’ perspectives on household energy use based on housing tenure: survey results from Northern Sweden. In: Proceedings of the 9th International Cold Climate Conference, Sustainable new and renovated buildings in cold climates: . Paper presented at 9th International Cold Climate Conference, Sustainable new and renovated buildings in cold climates, Kiruna – Sweden 12-15, March 2018.
Open this publication in new window or tab >>Comparative evaluation of city dwellers’ perspectives on household energy use based on housing tenure: survey results from Northern Sweden
2018 (English)In: Proceedings of the 9th International Cold Climate Conference, Sustainable new and renovated buildings in cold climates, 2018Conference paper, Published paper (Refereed)
National Category
Civil Engineering
Identifiers
urn:nbn:se:umu:diva-152727 (URN)
Conference
9th International Cold Climate Conference, Sustainable new and renovated buildings in cold climates, Kiruna – Sweden 12-15, March 2018
Available from: 2018-10-21 Created: 2018-10-21 Last updated: 2018-10-21
Azizi, S., Nair, G. & Olofsson, T. (2018). Comparative Study of Influential Factors on Implementation of Energy Efficiency Measures in Single-Family Houses in Cold Climate. In: : . Paper presented at 2018 ACEEE Summer Study in Energy Efficiency in Buildings.
Open this publication in new window or tab >>Comparative Study of Influential Factors on Implementation of Energy Efficiency Measures in Single-Family Houses in Cold Climate
2018 (English)Conference paper, Published paper (Refereed)
Abstract [en]

A combination of factors, which include occupants and building related aspects, could motivate homeowners to implement energy renovation (ER). This study applies a comparative approach to assess perspectives of single-family homeowners towards different energy efficiency measures (EEMs). The aim is to unveil the factors that are effective on the residents’ attitude and decision making to implement an EEM or a set of EEMs. The analysis is based on a questionnaire survey conducted during spring 2017 among1550 owners of single-family houses in seven municipalities in northern Sweden. Approximately, 35% of respondents expressed their interest to install energy efficient household appliances and solar photovoltaic (PV) systems. The analysis suggests significant relations between the homeowners’ interest to implement thermal envelope measures and the quality of the house such as age and indoor environmental problems such as cold surfaces. The group of respondents, who reported their heating cost to be high, are more likely to be interested in implementing thermal envelope measures than other measures such as HVAC. Several socio-economic factors are found to be significantly related with homeowners’ interest to implement EEMs.

Keywords
Energy efficient renovation
National Category
Energy Engineering
Identifiers
urn:nbn:se:umu:diva-151878 (URN)
Conference
2018 ACEEE Summer Study in Energy Efficiency in Buildings
Funder
European Regional Development Fund (ERDF)
Available from: 2018-09-14 Created: 2018-09-14 Last updated: 2018-09-14
Allard, I., Olofsson, T. & Nair, G. (2018). Energy evaluation of residential buildings: Performance gap analysis incorporating uncertainties in the evaluation methods. Building Simulation, 11(4), 725-737
Open this publication in new window or tab >>Energy evaluation of residential buildings: Performance gap analysis incorporating uncertainties in the evaluation methods
2018 (English)In: Building Simulation, ISSN 1996-3599, E-ISSN 1996-8744, Vol. 11, no 4, p. 725-737Article in journal (Refereed) Published
Abstract [en]

Calculation and measurement-based energy performance evaluations of the same building often provide different results. This difference is referred as "the performance gap". However, a large performance gap may not necessarily mean that there are flaws in the building or deviations from the intended design. The causes for the performance gap can be analysed by calibrating the simulation model to measured data. In this paper, an approach is introduced for verifying compliance with energy performance criteria of residential buildings. The approach is based on a performance gap analysis that takes the uncertainties in the energy evaluation methods into consideration. The scope is to verify building energy performance through simulation and analysis of measured data, identifying any performance gap due to deviations from the intended design or flaws in the finished building based on performance gap analysis. In the approach, a simulation model is calibrated to match the heat loss coefficient of the building envelope [kWh/K] instead of the measured energy. The introduced approach is illustrated using a single-family residential building. The heat loss coefficient was found useful towards identifying any deviations from the intended design or flaws in the finished building. The case study indicated that the method uncertainty was important to consider in the performance gap analysis and that the proposed approach is applicable even when the performance gap appears to be non-existing.

Place, publisher, year, edition, pages
Tsinghua University Press, 2018
Keywords
performance gap, energy signature, calibration, simulation, design criteria
National Category
Energy Engineering
Identifiers
urn:nbn:se:umu:diva-150666 (URN)10.1007/s12273-018-0439-7 (DOI)000435421700008 ()2-s2.0-85048691979 (Scopus ID)
Note

Originally included in thesis in manuscript form with title A methodology to investigate the building energy performance gap

Available from: 2018-08-20 Created: 2018-08-20 Last updated: 2018-11-13Bibliographically approved
Olofsson, T., Nair, G. & Azizi, S. (2018). Enkät om renovering och energieffektivisering [Review]. Energi & Miljö (1)
Open this publication in new window or tab >>Enkät om renovering och energieffektivisering
2018 (Swedish)In: Energi & Miljö, no 1Article, book review (Other (popular science, discussion, etc.)) Published
Place, publisher, year, edition, pages
Stockholm: , 2018
National Category
Energy Systems
Identifiers
urn:nbn:se:umu:diva-145549 (URN)
Available from: 2018-03-09 Created: 2018-03-09 Last updated: 2018-09-14
Nordwall, U. & Olofsson, T. (2018). Hållbara hus i kallt klimat / Sustainable buildings in a cold climate. Svensk byggtjänst
Open this publication in new window or tab >>Hållbara hus i kallt klimat / Sustainable buildings in a cold climate
2018 (Swedish)Book (Other academic)
Abstract [sv]

Boken beskriver hur hållbar arkitektur kan vara utformad i subarktiskt och arktiskt klimat. Detta visas genom 31 exempel på hållbart byggande i Finland, Sverige, Norge, Svalbard, Island, Grönland, Kanada och USA. Projekten presenteras ur sex hållbarhetsperspektiv - energi, material, återbruk, platsen, klimat och funktion. Varje hus presenteras med bilder och arkitektens beskrivning av huset.Varje projekt har även text på engelska.

Place, publisher, year, edition, pages
Svensk byggtjänst, 2018. p. 219
National Category
Building Technologies
Identifiers
urn:nbn:se:umu:diva-152719 (URN)9789173338950 (ISBN)
Available from: 2018-10-20 Created: 2018-10-20 Last updated: 2018-10-20
Brembilla, C., Östin, R., Soleimani-Mohseni, M. & Olofsson, T. (2018). Paradoxes in understanding the Efficiency Factors of Space Heating. Energy Efficiency
Open this publication in new window or tab >>Paradoxes in understanding the Efficiency Factors of Space Heating
2018 (English)In: Energy Efficiency, ISSN 1570-646X, E-ISSN 1570-6478Article in journal (Refereed) Epub ahead of print
Abstract [en]

Efficiency factors are here defined as the thermal energy performance indicators of the space heating. Until recently, the efficiency factors were assumed as one value for space heating located inany climate. This study addresses the problem of how the outdoor climate affects the efficiency factors of a space heating equipped with 1D model of hydronic floor heating. The findings show how the efficiency factors, computed with two numerical methods, are correlated with the solar radiation. This study highlights the paradoxes in understanding the results of efficiency factors analysis. This work suggests how to interpret and use the efficiency factors as a benchmark performance indicator.

Place, publisher, year, edition, pages
Springer, 2018
Keywords
Efficiency factors, Space heating, Accuracy 1D model of hydronic floor heating, Outdoor climate, Performance indicator, Solar radiation, Benchmark, Linear regression model
National Category
Building Technologies
Research subject
Technical Physics
Identifiers
urn:nbn:se:umu:diva-149931 (URN)10.1007/s12053-018-9692-y (DOI)
Projects
Reliability and robustness of efficiency factors theory of the space heating equipped with hydronic technologies
Available from: 2018-06-29 Created: 2018-06-29 Last updated: 2018-09-25
Brembilla, C., Östin, R. & Olofsson, T. (2018). Predictions' robustness of one-dimensional model of hydronic floor heating: novel validation methodology using a thermostatic booth simulator and uncertainty analysis. Journal of Building Physics, 41(5), 418-444
Open this publication in new window or tab >>Predictions' robustness of one-dimensional model of hydronic floor heating: novel validation methodology using a thermostatic booth simulator and uncertainty analysis
2018 (English)In: Journal of Building Physics, ISSN 1744-2591, E-ISSN 1744-2583, Vol. 41, no 5, p. 418-444Article in journal, Editorial material (Refereed) Published
Abstract [en]

Hydronic floor heating models provide predictions in estimating heat transfer rates and floor surface temperature. Information on the model performance and range of validity of its results are often lacking in literature. Researchers have to know the accuracy and robustness of the model outcomes for performing energy and climate comfort calculations. This article proposes a novel validation methodology based on the uncertainty analysis of input data/parameters of one-dimensional model of hydronic floor heating tested in a thermostatic booth simulator and compared with experimental measurements. The main results are: (1) prediction accuracy between 0.4% and 2.9% for Tf and between 0.7% and 7.8% for qup when the serpentine has tube spacing (p) of 0.30 m, (2) prediction accuracy between 0.5% and 1.4% for Tf and between 8.7% and 12.9% for qup with p = 0.15m and (3) Tfld mostly affects predictions with oscillations between 6.2% and 2.2% for qup. This model provides robust and reliable predictions exclusively for qup when p = 0.30m.

Place, publisher, year, edition, pages
Sage Publications, 2018
Keywords
One-Dimensional model of hydronic floor heating, thermostatic booth simulator, validation methodology, uncertainty bands, differential sensitivity analysis, robustness of model's predictions
National Category
Building Technologies
Research subject
Physics
Identifiers
urn:nbn:se:umu:diva-136486 (URN)10.1177/1744259117721002 (DOI)000429862600002 ()
Available from: 2017-06-19 Created: 2017-06-19 Last updated: 2018-09-21Bibliographically approved
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