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Computational investigation on the factors influencing thermal comfort for impinging jet ventilation
Linköping University, Department of Management and Engineering, Energy Systems. Linköping University, The Institute of Technology.
Linköping University, Department of Management and Engineering, Energy Systems. Linköping University, The Institute of Technology.
Linköping University, Department of Management and Engineering, Energy Systems. Linköping University, The Institute of Technology.
2013 (English)In: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 66, 29-41 p.Article 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. Vol. 66, 29-41 p.
Keyword [en]
Computational fluid dynamics (CFD), Response Surface Methodology (RSM), Draught discomfort, Temperature stratification, Impinging jet ventilation
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:liu:diva-92744DOI: 10.1016/j.buildenv.2013.04.018ISI: 000321423500004OAI: oai:DiVA.org:liu-92744DiVA: diva2:622050
Available from: 2013-05-20 Created: 2013-05-20 Last updated: 2017-12-06
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, Mathias

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