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Pei-Chun, Liu * , Brian Ford and David Etheridge

The MEGS Christmas Seminar, 15 th December 2010. Modelling on the naturally ventilated tall office buildings of a hot and humid climate: The thermally conflated mass flow network approach . Pei-Chun, Liu * , Brian Ford and David Etheridge . INTRODUCTION. Problems:

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Pei-Chun, Liu * , Brian Ford and David Etheridge

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  1. The MEGS Christmas Seminar, 15th December 2010 Modelling on the naturally ventilated tall office buildings of a hot and humid climate: The thermally conflated mass flow network approach Pei-Chun, Liu*, Brian Ford and David Etheridge

  2. INTRODUCTION • Problems: Fully air-conditioned tall office buildings in a hot and humid climate. Challenge of close control due to the dynamic nature of natural ventilation . The sick building skin

  3. NATURALLY VENITLATED TALL BUILDINGS Liberty Tower of Meiji University/Tokyo, Japan/ 119m (23 stories) Central core for stack effect / Wind Floor opens to 4 directions Source: S. Kato &T. Chikamoto (2002)

  4. NATURALLY VENITLATED TALL BUILDINGS Deutsche Post Tower/ Bonn, Germany/ 163m (41 stories) Atriums and skygardens as air exhaust / double façade admits cross ventilation Source: H. Jahn (2003) 4thskygarden level 3rdskygarden level Sky gardens as spent-air shaft 2ndskygarden level Double-skin façade as supply-air shaft Air exhaust ventilation grilles (spent air extracted to sky gardens via vents located at slab level 1stskygarden level Spent-air exhaust through vents at topmost level of the skygarden Source: H. Jahn (2003) Air intake ventilation grilles Source: R. Salib (2008)

  5. NATURALLY VENITLATED TALL BUILDINGS Commerzbank/ Frankfurt, Germany/ 259m (53 stories) limited stack effect by segmented atrium space / individual cross-ventilation via ventilated cavity Winter sky garden ventilation summer sky garden ventilation Central atrium ventilation

  6. RESEARCH QUESTIONS • How many possibilities can the naturally ventilated tall • office buildings to be applied in a hot and humid climate? • What building configurations should be adopted for the • advanced natural ventilation strategies? • How the ventilation related parameters responds to • overall thermally comfortable conditions in the occupied • spaces?

  7. Tools for ventilation assessment • The envelope flow model: MS Excel • --Size openings at the chosen design condition • --Off-design condition • Integrated building simulation tool: • ESP-r_V9 • --Thermally conflated air flow network model • --Hourly base data output for the whole year

  8. METHOD—Envelope flow model Envelope flow models solve the equations that govern the airflow through openings in the envelope of a building. An implicit method solves the equations by an iterative procedure. One equation for the building envelope One equation for each opening One equation for each opening

  9. METHOD—Air flow network modelling 8 To discretize the building into zones by nodes. Components are defined to represent leakage paths and pressure drops associated with openings. 3) The nodes are linked together through components to form connections which establish a flow network. 4) A mass balance is expressed for each node in the building. Boundary node Component_door Boundary node zone node Component_window

  10. Criteria for ventilation performance 9 • Desired airflow pattern : ---Q> 0 m^3/s when follows the conceptual design • Desired volume flow rates for ventilated cooling : Heat gains are balanced by the heat removed with ventilation air Q=H/ ρ∙Cp ∙∆T Where H=(30W/m^2) ∙400m^2 ;ρ=1.2kg/m^3 ; Cp=1006 J/kgK ; ∆T=3.3K ---Q=3 m^3/s may suffice for cooling purpose

  11. Building bioclimatic charts (BBCCs) 10 • BBCCs: A way for testing comfortable conditions in the occupied space. • Adaptive thermal comfort theory: People naturally make adjustments to themselves and their surroundings to reduce discomfort. • Comfort boundaries : Still air: 18-29˚C / 50%~80% Airflow of 1.5m/s: 18-32˚C / 50%~90%

  12. The prototype building with advanced natural ventilation strategies 11 A current design of Taipei, Taiwan

  13. The base cases Proposed naturally ventilated tall office models

  14. Conceptual air flow pattern 13 Central Atrium Atrium-vent Lower inlet Individual office space Top outlet DSF-vent DSF cavity

  15. RESULTS & DISCUSSIONS The probability for ventilated cooling: The buoyancy-alone(R) and wind & buoyancy combined (L)ventilation strategies

  16. RESULTS & DISCUSSIONS 15 The worst case scenario

  17. EXPECTED OUTCOMES Natural • To investigate the year round feasibility of natural • ventilation in a hot and humid climate with • reference to the proposed building configuration. • To identify the dominated parameters and its range • of influence to the resultant air flow rates and flow • pattern. • To suggest the possible control strategies in terms • of the identified driving forces. • To develop routes for predicting the performance of • advanced naturally ventilated tall office buildings.

  18. THANK YOU FOR YOUR ATTENTION Any questions/comments ?

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