1. Isothermal 2D zonal air volume model
Victor Norrefeldt, Thierry Nouidui, Christoph van Treeck, Gunnar Grün Fraunhofer Institute for Building Physics – Valley, Germany

2. Goal of zonal models quick estimation of airflow patterns
quick estimation of local distributions of
heat
moisture
contaminants …

3. Idea of zonal modeling
single-zone
multi-zone
CFD
zonal

4. 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

5. State of art Volume 1 p1 Volume 2 p2 Flow Link many volumes → room
Cd approximately 0.83 (Jiru and Haghighat, 2006, Wurtz et al., 1999)

6. Basic Zonal Model

7. Basic Zonal Model
Source
Sink

8. 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)

9. Inifinte gradient at zero
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

10. 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

11. 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
4 pressure drops
2 pressure drops

12. 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
Pressure
Impluse
Gravitation
Viscous losses

13. Application example: Nielsen-Room

14. Zoning

15. Comparison of results (µ = 0.001)
+ Maximal velocity
+ Recirculation point
- Recirculating air flow

16. Comparison of results (µ = 0.001)
Maximal velocity
+ Recirculation point
- Recirculating air flow

17. 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

18. References
Jiru, T.E. and Haghighat, F., A new generation of zonal models. ASHRAE Transactions. Vol Part 2. pp
Heiselberg, P., Murakami, S., Roulet, C.-A Ventilation of large spaces in buildings, Analysis and prediction techniques. IEA Annex 26
Daoud, A., Galanis, N., Bellache, O Calculation of refrigeration loads by convection, radiation and condensation in ice rinks using a transient 3D zonal model. Applied Thermal Engineering. Vol. 28. pp
Jiru, E., Haghighat, F Modeling ventilated double skin façade—A zonal approach. Energy and Buildings. Vol. 40. pp
Wurtz, E., Mora, L., Inard, C An equation-based simulation environment to investigate fast building simulation, Building and Environment. Vol. 40. pp
Boukhris, Y, Gharbi, L, and Ghrab-Morcos, N 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 Specification of a two-dimensional test case. International Energy Agency. Energy conservation in buildings and community systems, Annex 20: Air flow patterns within buildings.

19. Thank you for your attention
Questions?
in discussion or to