energy postgraduate conference epc2013, 11-14 aug 2013 ithemba labs sahpa ® south african heat pipe...
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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
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)
SAHPA®
South African Heat Pipe Association Energy Postgraduate Conference EPC2013, 11-14 Aug 2013
iThemba LABS
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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
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South African Heat Pipe Association Energy Postgraduate Conference EPC2013, 11-14 Aug 2013
iThemba LABS
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Introduction (cont.)• Example of such a natural
circulation ventilation system is a Solar Chimney Augmented Passive Downdraught Evaporation Cooling (SCAPDEC) system.
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South African Heat Pipe Association Energy Postgraduate Conference EPC2013, 11-14 Aug 2013
iThemba LABS
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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.
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South African Heat Pipe Association Energy Postgraduate Conference EPC2013, 11-14 Aug 2013
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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
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South African Heat Pipe Association Energy Postgraduate Conference EPC2013, 11-14 Aug 2013
iThemba LABS
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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
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South African Heat Pipe Association Energy Postgraduate Conference EPC2013, 11-14 Aug 2013
iThemba LABS
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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
SAHPA®
South African Heat Pipe Association Energy Postgraduate Conference EPC2013, 11-14 Aug 2013
iThemba LABS
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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.
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
Thank youJJ Swiegers