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Investigation on the flow and thermal behavior of impinging jet ventilation systems in an office with different heat loads
Linköping University, Department of Management and Engineering, Energy Systems. Linköping University, The Institute of Technology. Department of Building, Energy and Environmental Engineering, Faculty of Engineering and Sustainable Development, University of Gävle, Gävle, Sweden.
Linköping University, Department of Management and Engineering, Energy Systems. Linköping University, The Institute of Technology. Department of Building, Energy and Environmental Engineering, Faculty of Engineering and Sustainable Development, University of Gävle, Gävle, Sweden.
Department of Building, Energy and Environmental Engineering, Faculty of Engineering and Sustainable Development, University of Gävle, Gävle, Sweden.
2013 (English)In: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 59, 127-144 p.Article 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. Vol. 59, 127-144 p.
Keyword [en]
Impinging jet ventilation, Chilled ceiling, Heat sources, Air movement, Turbulence models, Measurement
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:liu:diva-89812DOI: 10.1016/j.buildenv.2012.08.014ISI: 000314371900014OAI: oai:DiVA.org:liu-89812DiVA: diva2:609782
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
In thesis
1. Experimental and numerical investigations of a ventilation strategy – impinging jet ventilation for an office environment
Open this publication in new window or tab >>Experimental and numerical investigations of a ventilation strategy – impinging jet ventilation for an office environment
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

A well-functioning, energy-efficient ventilation system is of vital importance to offices, not only to provide the kind of comfortable, healthy indoor environment necessary for the well-being and productive work performance of occupants, but also to reduce energy use in buildings and the associated impact of CO2 emissions on the environment. To achieve these goals impinging jet ventilation has been developed as an innovative ventilation concept.

In an impinging jet ventilation system, a high momentum of air jet is discharged downwards, strikes the floor and spreads over it, thus distributing the fresh air along the floor in the form of a very thin shear layer. This system retains advantages of mixing and stratification from conventional air distribution methods, while capable of overcoming their shortcomings.

The aim of this thesis is to reach a thorough understanding of impinging jet ventilation for providing a good thermal environment for an office, by using Computational Fluid Dynamics (CFD) supported by detailed measurements. The full-field measurements were carried out in two test rooms located in a large enclosure giving relatively stable climate conditions. This study has been divided into three parts where the first focuses on validation of numerical investigations against measurements, the second addresses impacts of a number of design parameters on the impinging jet flow field and thermal comfort level, and the third compares ventilation performance of the impinging jet supply device with other air supply devices intended for mixing, wall confluent jets and displacement ventilation, under specific room conditions.

In the first part, velocity and temperature distributions of the impinging jet flow field predicted by different turbulence models are compared with detailed measurements. Results from the non-isothermal validation studies show that the accuracy of the simulation results is to a great extent dependent on the complexity of the turbulence models, due to complicated flow phenomena related to jet impingement, such as recirculation, curvature and instability. The v2-f turbulence model shows the best performance with measurements, which is slightly better than the SST k-ω model but much better than the RNG k-ε model. The difference is assumed to be essentially related to the magnitude of turbulent kinetic energy predicted in the vicinity of the stagnation region. Results from the isothermal study show that both the SST k-ω and RNG k-ε models predict similar wall jet behaviours of the impinging jet flow.

In the second part, three sets of parametric studies were carried out by using validated CFD models. The first parametric study shows that the geometry of the air supply system has the most significant impact on the flow field. The rectangular air supply device, especially the one with larger aspect ratio, provides a longer penetration distance to the room, which is suitable for industrial ventilation. The second study reveals that the interaction effect of cooling ceiling, heat sources and impinging jet ventilation results in complex flow phenomena but with a notable feature of air circulation, which consequently decreases thermal stratification in the room and increases draught discomfort at the foot level. The third study demonstrates the advantage of using response surface methodology to study simultaneous effects on changes in four parameters, i.e. shape of air supply device, jet discharge height, supply airflow rate and supply air temperature. Analysis of the flow field reveals that at a low discharge height, the shape of air supply device has a major impact on the flow pattern in the vicinity of the supply device. Correlations between the studied parameters and local thermal discomfort indices were derived. Supply airflow rates and temperatures are shown to be the most important parameter for draught and stratification discomfort, respectively.

In the third part, the impinging jet supply device was shown to provide a better overall performance than other air supply devices used for mixing, wall confluent jets and displacement ventilation, with respect to thermal comfort, heat removal effectiveness, air exchange efficiency and energy-saving potential related to fan power.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2014. 92 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1606
Keyword
Impinging jet ventilation, room air distribution, thermal comfort, ventilation performance, turbulence modelling, CFD
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-106483 (URN)10.3384/diss.diva-106483 (DOI)978-91-7519-299-4 (ISBN)
Public defence
2014-06-12, ACAS, Hus A, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
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Available from: 2014-05-15 Created: 2014-05-09 Last updated: 2014-05-27Bibliographically approved

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Chen, HuijuanMoshfegh, BahramCehlin, Mattias

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