Energy Postgraduate Conference EPC2013, 11-14 Aug 2013 iThemba LABS SAHPA ® South African Heat Pipe Association Inlet and Outlet Shape-Optimization of.

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

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South African Heat Pipe Association Energy Postgraduate Conference EPC2013, 11-14 Aug 2013

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Preface

What is a Natural Circulation Building Ventilation System?

Source: Natural draft cooling flow diagram (Cunningham, Mignon and Thompson 1987)

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South African Heat Pipe Association Energy Postgraduate Conference EPC2013, 11-14 Aug 2013

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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

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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

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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

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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

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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

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South African Heat Pipe Association Energy Postgraduate Conference EPC2013, 11-14 Aug 2013

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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.

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South African Heat Pipe Association Energy Postgraduate Conference EPC2013, 11-14 Aug 2013

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Department of Mechanical Engineering,University of Stellenbosch,

Stellenbosch, Western Cape Province, South Africa

[email protected]

Thank youJJ Swiegers