Stellenbosch University

1. Theoretical modeling and experimental verification of a passive downdraught evaporativecooling tower Stellenbosch University Energy Postgraduate Conference 2013

2. Introduction Motivation PDEC 2D Model CFD Conclusion Introduction • HVAC accounts for substantial amount of energy use in buildings (4000 gWh annually in S.A.) • Greenhouse gases (GHG) emissions from HVAC account for up to 22% of total GHG emissions. • Reducing the total HVAC load would result in a reduction in operating costs, GHG emissions and related environmental impacts

3. Introduction Motivation PDEC 2D Model CFD Conclusion Motivation • Adequate ventilation for buildings is needed • Air-conditioning and mechanical ventilation expensive running cost • Natural ventilation cheap or with no running cost • PDEC (Passive Downdraught Evaporative Cooling) efficient method of passive cooling in arid regions • Design Strategies include: • CFD • Empirical Methods • 2D Axisymmetric Theoretical Model

4. Introduction Motivation PDEC 2D Model CFD Conclusion PDEC Principle Psychrometric Chart

5. Introduction Motivation PDEC 2D Model CFD Conclusion PDEC Principle

6. Introduction Motivation PDEC 2D Model CFD Conclusion PDEC in practice

7. Introduction Motivation PDEC 2D Model CFD Conclusion 2D Model of PDEC Control Volume Grid

8. Introduction Motivation PDEC 2D Model CFD Conclusion 2D Model of PDEC • Conservation of Mass • Mass diffusion • Conservation of energy • Conservation of momentum

9. Introduction Motivation PDEC 2D Model CFD Conclusion CFD Model of PDEC Transport Equations In the air Change = Convection + Diffusion + Source • where  may be • 1 (continuity) • velocity components u, v • turbulent kinetic energy k • turbulent dissipation rate  • temperature • water vapour concentration The standard solver can be customized to meet the requirements unique to a particular application by using the user-defined functions

10. Introduction Motivation PDEC 2D Model CFD Conclusion CFD Model of PDEC PDEC laminar flow in room

11. Introduction Motivation PDEC 2D Model CFD Conclusion Conclusions • Important to understand the fundamentals of the down-draft evaporative cooling • PDEC tower can’t maintain a constant performance due to a strong climatic dependency • PDEC towers may not be suitable to humid climates without significant advancement • CFD tools have been extensively used to simulate flow and thermal fields for a variety of applications. • Climatic data with Theoretical models could benefit the design and implementation of PDEC towers

12. Thank you