Displacement ventilation systems—Convection flows and temperature gradients

Mundt, Elisabeth

doi:10.1016/0360-1323(94)e0002-9

Cited by 62 publications

(27 citation statements)

References 2 publications

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“…In practice, the actual vertical stratification of DV depends on the combined effect of various factors but largely on the characteristics of the room air supply flow and the configuration of heat source presented in the room (Mundt, 1995;ASHRAE Handbook, 2009). Since buoyancy rather than momentum is the dominant force in driving overall floor-to-ceiling air motion, DV can only be operated in cooling mode.…”

Section: Air Distribution Systemsmentioning

confidence: 99%

Experimental and numerical investigations of a ventilation strategy – impinging jet ventilation for an office environment

Chen¹

2014

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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 CO 2 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 f v  2 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. IVIn 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 ...

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Section: Air Distribution Systemsmentioning

confidence: 99%

Experimental and numerical investigations of a ventilation strategy – impinging jet ventilation for an office environment

Chen¹

2014

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“…Figure 10 shows a clear correlation between occupied zone stratification and level of internal load. We theorize that this is either due to the increased overall total airflow required to cool the zone under these conditions, as discussed in Mundt [7], or the average height at which the loads occur within the zone. Previous studies on displacement ventilation systems [6] note that the height at which the loads are located in the zone affects the height at which stratification occurs.…”

Section: Figure 5: Vertical Temperature Profiles Within the Room (Avementioning

confidence: 99%

“…Looking at specific experiments, Mundt [7] However, it should be noted that all of the compared studies above do not necessarily represent the distribution of room loads that occur in a UFAD system, where conditioned air passes through a ductless supply plenum and absorbs heat from the room before entering the occupied space through the supply diffuser in the raised floor. We found only one study that investigates a case that approximates a UFAD system with displacement ventilation.…”

Section: Figure 5: Vertical Temperature Profiles Within the Room (Avementioning

confidence: 99%

Laboratory testing of a displacement ventilation diffuser for underfloor air distribution systems

Raftery

Bauman²,

Schiavon

et al. 2015

Energy and Buildings

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Underfloor air distribution (UFAD) systems use the underfloor plenum beneath a raised floor to provide conditioned air through floor-mounted diffusers, which typically discharge cool air with both horizontal and vertical momentum components. These systems usually create a vertical temperature stratification when in cooling mode and this has an impact on energy, indoor air quality and thermal comfort. The purpose of this study was to characterize the stratification performance of a previously unstudied type of floor diffuser that discharges air horizontally, with almost no vertical velocity component, and that aims to combine the benefits of both UFAD and displacement ventilation (DV) strategies.We performed 19 full scale laboratory experiments in which we varied the number of diffusers and the internal loads over a range of values typically found in office spaces. We quantified the amount of thermal stratification by measuring the dimensionless temperature at ankle height and found a degree of stratification that is typical of DV systems -higher than is typical in UFAD systems. We developed a model based on these results that can be used to simulate these systems in whole building energy simulation tools, such as EnergyPlus, and simplified UFAD design tools.

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“…In the past it has been mainly carried out by full scale experiments and resorting to experience. However, engineering design methods and guidelines have been developed and are available in the literature [1][2][3][4][5] while numerical analysis methods have also been investigated [6]. Furthermore, displacement ventilation has been analyzed in conjuction with chilled ceilings [7][8][9] proving the effectiveness of this approach.…”

Section: Introductionmentioning

confidence: 99%