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