Isothermal 2 D zonal air volume model Victor

Isothermal 2 D zonal air volume model Victor Norrefeldt, Thierry Nouidui, Christoph van Treeck, Gunnar Grün Fraunhofer Institute for Building Physics – Valley, Germany Auf Wissen bauen © Fraunhofer IBP

Goal of zonal models n quick estimation of airflow patterns n quick estimation of local distributions of n heat n moisture n contaminants n… © Fraunhofer IBP

Idea of zonal modeling single-zone multi-zone zonal © Fraunhofer IBP CFD

Principles of zonal modeling n Subdivision of a room into zones (volumes) n Volume model: n Mass Conservation n Conservation of thermal energy n Other particle / contaminant conservations possible (moisture, CO 2, VOC, …) n Flow Model n Links two volume models n Calculates mass flow rate from pressure difference © Fraunhofer IBP

State of art Flow Volume 1 p 1 Volume 2 p 2 • Link many volumes → room • Cd approximately 0. 83 (Jiru and Haghighat, 2006, Wurtz et al. , 1999) © Fraunhofer IBP

Basic Zonal Model © Fraunhofer IBP

Basic Zonal Model Source Sink © Fraunhofer IBP

Application examples of Zonal Models n Prediction of temperature stratification in an experimental atrium in Kanagawa, Japan (Heiselberg et al. , 1998) n Calculation of refrigeration load of an ice-rink in Canada (Daoud et al. , 2007) n Modeling of a ventilated double-skin façade (Jiru et al. , 2008) © Fraunhofer IBP

Difficulty with state-of-the-art zonal model: Small pressure differences Inifinte gradient at zero n Current solution: Linearization (Boukhris et al. , 2009) n New solution: Calculate acceleration of air flow © Fraunhofer IBP

Difficulty with state-of-the-art zonal model: Dissipation of airflow velocity in volumes n Current solution: Jet- or plume correlations for regions with driving air flows (e. g. Wurtz et al. , 2006) n New solution: Air flow velocity as a property in volumes © Fraunhofer IBP

Difficulty with state-of-the-art zonal model: Number of zones influences the total pressure drop 4 pressure drops u 0 2 pressure drops u 0 n Current solution: None found n New solution: Size of a zone taken into account © Fraunhofer IBP

Formulation of the new zonal model Forces on flow path → acceleration of air flow Pressure Impluse Gravitation Viscous losses Use of apparent µ → losses Steady State © Fraunhofer IBP → acceleration = 0, velocity = constant

Application example: Nielsen-Room © Fraunhofer IBP

Zoning © Fraunhofer IBP

Comparison of results (µ = 0. 001) + Maximal velocity + Recirculation point - Recirculating air flow © Fraunhofer IBP

Comparison of results (µ = 0. 001) Maximal velocity + Recirculation point - Recirculating air flow © Fraunhofer IBP

Conclusion n New formulation of zonal models n Incorporated impulse conservation n Quick prediction of air flow pattern in rooms n Next steps n Extension to non-isothermal cases n Validation with own measurements © Fraunhofer IBP

References n Jiru, T. E. and Haghighat, F. , 2006. A new generation of zonal models. ASHRAE Transactions. Vol. 112. Part 2. pp 163 -174 n Heiselberg, P. , Murakami, S. , Roulet, C. -A. 1998. Ventilation of large spaces in buildings, Analysis and prediction techniques. IEA Annex 26 n Daoud, A. , Galanis, N. , Bellache, O. 2008. Calculation of refrigeration loads by convection, radiation and condensation in ice rinks using a transient 3 D zonal model. Applied Thermal Engineering. Vol. 28. pp 1782 -1790 n Jiru, E. , Haghighat, F. 2008. Modeling ventilated double skin façade—A zonal approach. Energy and Buildings. Vol. 40. pp 1567 -1576 n 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 n 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 n 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. © Fraunhofer IBP

Thank you for your attention Questions? in discussion or to victor. norrefeldt@ibp. fraunhofer. de © Fraunhofer IBP