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Cehlin, Mattias
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Publications (3 of 3) Show all publications
Joudi, A., Cehlin, M., Svedung, H., Rönnelid, M. & Moshfegh, B. (2017). Numerical and experimental investigation of the influence of infrared reflective interior surfaces on building temperature distributions. Indoor + Built Environment, 26(3), 355-367
Open this publication in new window or tab >>Numerical and experimental investigation of the influence of infrared reflective interior surfaces on building temperature distributions
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2017 (English)In: Indoor + Built Environment, ISSN 1420-326X, E-ISSN 1423-0070, Vol. 26, no 3, p. 355-367Article in journal (Refereed) Published
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) kε 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.

Place, publisher, year, edition, pages
Sage Publications, 2017
Keywords
Reflective interior surfaces, indoor air temperature gradient, Transient computational fluid dynamics, surface-to-surface radiation, building thermal performance
National Category
Energy Systems Building Technologies
Identifiers
urn:nbn:se:liu:diva-118289 (URN)10.1177/1420326X15609966 (DOI)000399487300007 ()
Note

Funding agencies|SSAB Europe; Dalarna University; University of Gävle; Linköping University.

At the time for thesis presentation publication was in status: Manuscript

Available from: 2015-05-25 Created: 2015-05-25 Last updated: 2017-05-05Bibliographically approved
Chen, H., Moshfegh, B. & Cehlin, M. (2013). Computational investigation on the factors influencing thermal comfort for impinging jet ventilation. Building and Environment, 66, 29-41
Open this publication in new window or tab >>Computational investigation on the factors influencing thermal comfort for impinging jet ventilation
2013 (English)In: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 66, p. 29-41Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
Elsevier, 2013
Keywords
Computational fluid dynamics (CFD), Response Surface Methodology (RSM), Draught discomfort, Temperature stratification, Impinging jet ventilation
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-92744 (URN)10.1016/j.buildenv.2013.04.018 (DOI)000321423500004 ()
Available from: 2013-05-20 Created: 2013-05-20 Last updated: 2017-12-06
Chen, H., Moshfegh, B. & Cehlin, M. (2013). Investigation on the flow and thermal behavior of impinging jet ventilation systems in an office with different heat loads. Building and Environment, 59, 127-144
Open this publication in new window or tab >>Investigation on the flow and thermal behavior of impinging jet ventilation systems in an office with different heat loads
2013 (English)In: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 59, p. 127-144Article in journal (Refereed) Published
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. 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.

Place, publisher, year, edition, pages
Elsevier, 2013
Keywords
Impinging jet ventilation, Chilled ceiling, Heat sources, Air movement, Turbulence models, Measurement
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-89812 (URN)10.1016/j.buildenv.2012.08.014 (DOI)000314371900014 ()
Note

Funding Agencies|KM Foundation|2007/0289|Formas|242-2008-835|Fresh Air AB||Kraft and Kultur AB||University of Gavle|7216-7438-181-81|Linkoping University||

Available from: 2013-03-07 Created: 2013-03-07 Last updated: 2017-12-06Bibliographically approved

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