© fraunhofer ibp auf wissen bauen victor norrefeldt, thierry nouidui, christoph van treeck, gunnar...

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Auf Wissen bauen

Victor Norrefeldt, Thierry Nouidui, Christoph van Treeck, Gunnar GrünFraunhofer Institute for Building Physics – Valley, Germany

Isothermal 2D zonal air volume model

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Goal of zonal models

quick estimation of airflow patterns

quick estimation of local distributions of

heat

moisture

contaminants

…

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Idea of zonal modeling

single-zone multi-zone CFD

zonal

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Principles of zonal modeling

Subdivision of a room into zones (volumes)

Volume model:

Mass Conservation

Conservation of thermal energy

Other particle / contaminant conservations possible(moisture, CO2, VOC, …)

Flow Model

Links two volume models

Calculates mass flow rate from pressure difference

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State of art

Volume 1p1

Volume 2p2

Flow

ρ

Δp2ρACm d

• Link many volumes → room• Cd approximately 0.83 (Jiru and Haghighat, 2006, Wurtz et al., 1999)

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Basic Zonal Model

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Basic Zonal Model

Source

Sink

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Application examples of Zonal Models

Prediction of temperature stratification in an experimental atrium in Kanagawa, Japan (Heiselberg et al., 1998)

Calculation of refrigeration load of an ice-rink in Canada(Daoud et al., 2007)

Modeling of a ventilated double-skin façade (Jiru et al., 2008)

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Difficulty with state-of-the-art zonal model:Small pressure differences

Current solution: Linearization (Boukhris et al., 2009)

New solution: Calculate acceleration of air flow

Inifinte gradient at zero

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Difficulty with state-of-the-art zonal model:Dissipation of airflow velocity in volumes

Current solution: Jet- or plume correlations for regions with driving air flows (e.g. Wurtz et al., 2006)

New solution: Air flow velocity as a property in volumes

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Difficulty with state-of-the-art zonal model:Number of zones influences the total pressure drop

Current solution: None found

New solution: Size of a zone taken into account

u0 u0

u0 u0

4 pressure drops

2 pressure drops

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Formulation of the new zonal model

Forces on flow path → acceleration of air flow

Use of apparent µ → losses

Steady State → acceleration = 0, velocity = constant

distance

xv

xv

zgvp

v

2

PressureImpluseGravitationViscous losses

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Application example: Nielsen-Room

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Zoning

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Comparison of results (µ = 0.001)

+ Maximal velocity

+ Recirculation point

- Recirculating air flow

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Comparison of results (µ = 0.001)

Maximal velocity

+ Recirculation point

- Recirculating air flow

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Conclusion

New formulation of zonal models

Incorporated impulse conservation

Quick prediction of air flow pattern in rooms

Next steps

Extension to non-isothermal cases

Validation with own measurements

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References

Jiru, T.E. and Haghighat, F., 2006. A new generation of zonal models. ASHRAE Transactions. Vol. 112. Part 2. pp 163-174

Heiselberg, P., Murakami, S., Roulet, C.-A. 1998. Ventilation of large spaces in buildings, Analysis and prediction techniques. IEA Annex 26

Daoud, A., Galanis, N., Bellache, O. 2008. Calculation of refrigeration loads by convection, radiation and condensation in ice rinks using a transient 3D zonal model. Applied Thermal Engineering. Vol. 28. pp 1782-1790

Jiru, E., Haghighat, F. 2008. Modeling ventilated double skin façade—A zonal approach. Energy and Buildings. Vol. 40. pp 1567-1576

Wurtz, E., Mora, L., Inard, C. 2006. An equation-based simulation environment to investigate fast building simulation, Building and Environment. Vol. 40. pp 1571-1583

Boukhris, Y, Gharbi, L, and Ghrab-Morcos, N. 2009. Modeling coupled heat transfer and air flow in a partitioned building with a zonal model: application to the winter thermal comfort. Building Simulation. Vol. 2. pp 67-74

Nielsen, P.V. 1990. Specification of a two-dimensional test case. International Energy Agency. Energy conservation in buildings and community systems, Annex 20: Air flow patterns within buildings.

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Thank you for your attention

Questions?

in discussion or to

victor.norrefeldt@ibp.fraunhofer.de