Inlet and Outlet Shape-Optimization of Natural Circulation Building Ventilation Systems

1. Inlet and Outlet Shape-Optimization ofNatural Circulation Building Ventilation Systems Energy Postgraduate Conference 2013 Department of Mechanical Engineering,University of Stellenbosch, Stellenbosch, Western Cape Provence, South Africa

2. Preface • What is a • Natural Circulation Building Ventilation System? Source: Natural draft cooling flow diagram (Cunningham, Mignon and Thompson 1987)

3. Introduction • Normal air conditioning use refrigerants to cool air to desired temperatures. • It normally has a power of between 4 to 8 kW. • ESKOM currently charges a mean of 100c/kWh for electricity. • An alternative solution to achieve thermal tempering in a building is to use natural circulation Source: Amana heating and air conditioning

4. Introduction (cont.) • Example of such a natural circulation ventilation system is a Solar Chimney Augmented Passive Downdraught Evaporation Cooling (SCAPDEC) system.

5. Objectives • Develop inlet and outlet configurations for a SCAPDEC system. • Test these configurations in real atmospheric conditions, i.e. exposed to precipitation and wind. • Develop a 2 dimensional theoretically model of the system with incorporated inlet and outlet configuration loss coefficients. • Use CFD software to obtain results on the same domain. • Compare the theoretical results with the experimental results to determine optimized shapes. • Compile design guidelines for such a system.

6. Theory • Four inlet and outlet configurations have been tested. • Open-ended and extruding end configuration for comparative purposes. • Cone and DSI-design inlet configuration aimed to funnel wind into PDEC. • Whirlybird and DSO-design protects against rain and fowl. • DSO-design no moving parts. Figure 1: Inlet configurations Figure 2: Outlet configurations

7. Theory • Proposed discretization scheme of PDEC with cone inlet configuration for two dimensional theoretical model. • This domain will also be incorporated into the CFD model. • Two dimensional approach used to obtain more accurate results. • One-dimensional model could not capture subtle changes. Figure 3: Discretization scheme

8. Results Test 1 • Initial testing consisted of four tests: • High draft, no wind. • High draft, high wind. • Low drat, high wind. • No draft, high wind. • Test 1: Open ended inlet, no wind. • Test 2: DSI-design inlet, no wind. • Test 3:DSI-design inlet, with wind. Test 2 Test 3

9. Discussion and Conclusion • Open ended inlet and outlet configuration performed best, but does not protect against rain and fowl. • Initial testing shows DSI-design configurations to have significantly lower loss coefficient than cone and extruding end configurations, for all four administered tests. • DSO-design configuration and whirlybird showed similar results and are the only two viable outlet configurations. • Further optimization planned on DSI- and DSO-design configurations. • Configurations will be tested on full-scale SCAPDEC system.

10. Thank you JJ Swiegers Department of Mechanical Engineering,University of Stellenbosch,Stellenbosch, Western Cape Province, South Africa 15664155@sun.ac.za