Evaluation of buoyancy-driven ventilation in respect of exergy utilization

Our work aimed to analyze and evaluate the buoyancy-driven ventilation based on the exergy analysis. We took the exergy load as a desired output for this consumer system and used the functional exergy efficiency to evaluate the ventilation performance. Through the numerical case studies for a high-rise building with a tall atrium, we found that the results from the energy and exergy analysis are quite different from each other, but the latter reveals the real essence of energy utilization in ventilation systems. The results showed that the exergy efficiency of the buoyancy-driven ventilation system is very poor, only 16.9% of the exergy input is effectively utilized and the exergy destruction counts for 83.1% of the total input. However, the exergy efficiency of the mechanical ventilation system is 100% because the input shaft work is entirely utilized to undertake the exergy load; no extra exergy losses are produced. We also analyzed the relationships between the temperature difference and the exergy efficiency. Furthermore, we found that the total radiation-to-exergy efficiency is 3.5 and 15% for ventilation systems equipped with solar collectors and solar cells respectively, it is concluded preliminarily that the latter is more efficient to utilize solar energy to create ventilation.

[1]  A. Bejan.  Advanced Engineering Thermodynamics , 1988 .

[2]  P. Linden.  THE FLUID MECHANICS OF NATURAL VENTILATION , 1999 .

[3]  Nyuk Hien Wong,et al.  The study of active stack effect to enhance natural ventilation using wind tunnel and computational fluid dynamics (CFD) simulations , 2004 .

[4]  Nyuk Hien Wong,et al.  Enhancement of natural ventilation in high-rise residential buildings using stack system , 2004 .

[5]  Youming Chen,et al.  Investigating potential of natural driving forces for ventilation in four major cities in China , 2005 .

[6]  Richard A. Gaggioli,et al.  Available Energy and Exergy , 1998 .

[7]  Adriana Angelotti,et al.  Exergy analysis of renewable energy-based climatisation systems for buildings: A critical view , 2009 .

[8]  Michael J. Moran,et al.  Availability analysis: A guide to efficient energy use , 1982 .

[9]  M. Aboulnaga.  A roof solar chimney assisted by cooling cavity for natural ventilation in buildings in hot arid climates: An energy conservation approach in Al-Ain city , 1998 .

[10]  Qingyan Chen,et al.  Buoyancy-driven single-sided natural ventilation in buildings with large openings , 2003 .

[11]  R. Petela.  Exergy of undiluted thermal radiation , 2003 .

[12]  Karl Terpager Andersen.  Theory for natural ventilation by thermal buoyancy in one zone with uniform temperature , 2003 .

[13]  J. Tanny,et al.  Airflow and heat flux through the vertical opening of buoyancy-induced naturally ventilated enclosures , 2008 .

[14]  Qingyan Chen,et al.  Ventilation performance prediction for buildings: A method overview and recent applications , 2009 .

[15]  Bundit Limmeechokchai,et al.  Application of passive cooling systems in the hot and humid climate: The case study of solar chimney and wetted roof in Thailand , 2007 .

[16]  Xiaoqiang Zhai,et al.  Experience on integration of solar thermal technologies with green buildings , 2008 .

[17]  Gary R. Hunt,et al.  The fluid mechanics of natural ventilation—displacement ventilation by buoyancy-driven flows assisted by wind , 1999 .

[18]  Niyazi Serdar Sariciftci,et al.  Hybrid solar cells , 2008 .

[19]  Claude-Alain Roulet,et al.  Natural ventilation for passive cooling: measurement of discharge coefficients , 1998 .

[20]  Radu Zmeureanu,et al.  Comparison of environmental impacts of two residential heating systems , 2008 .

[21]  Radu Zmeureanu,et al.  Energy and exergy performance of residential heating systems with separate mechanical ventilation , 2007 .