1. Energy Postgraduate Conference EPC2013, 11-14 Aug 2013 iThemba LABS SAHPA ® South African Heat Pipe Association Inlet and Outlet Shape-Optimization of Natural Circulation Building Ventilation Systems Department of Mechanical Engineering, University of Stellenbosch, Stellenbosch, Western Cape Provence, South Africa Energy Postgraduate Conference 2013

2. SAHPA ® South African Heat Pipe Association Energy Postgraduate Conference EPC2013, 11-14 Aug 2013 iThemba LABS 2 Preface What is a Natural Circulation Building Ventilation System? Source: Natural draft cooling flow diagram (Cunningham, Mignon and Thompson 1987)

3. SAHPA ® South African Heat Pipe Association Energy Postgraduate Conference EPC2013, 11-14 Aug 2013 iThemba LABS 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. SAHPA ® South African Heat Pipe Association Energy Postgraduate Conference EPC2013, 11-14 Aug 2013 iThemba LABS 4 Introduction (cont.) Example of such a natural circulation ventilation system is a Solar Chimney Augmented Passive Downdraught Evaporation Cooling (SCAPDEC) system.

5. SAHPA ® South African Heat Pipe Association Energy Postgraduate Conference EPC2013, 11-14 Aug 2013 iThemba LABS 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. SAHPA ® South African Heat Pipe Association Energy Postgraduate Conference EPC2013, 11-14 Aug 2013 iThemba LABS 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. SAHPA ® South African Heat Pipe Association Energy Postgraduate Conference EPC2013, 11-14 Aug 2013 iThemba LABS 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. SAHPA ® South African Heat Pipe Association Energy Postgraduate Conference EPC2013, 11-14 Aug 2013 iThemba LABS 8 Results 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 1 Test 2 Test 3

9. SAHPA ® South African Heat Pipe Association Energy Postgraduate Conference EPC2013, 11-14 Aug 2013 iThemba LABS 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. SAHPA ® South African Heat Pipe Association Energy Postgraduate Conference EPC2013, 11-14 Aug 2013 iThemba LABS 10 Department of Mechanical Engineering, University of Stellenbosch, Stellenbosch, Western Cape Province, South Africa 15664155@sun.ac.za Thank you JJ Swiegers