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 INTRODUCTION 1 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 NATURALLY VENITLATED TALL BUILDINGS 2 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) NATURALLY VENITLATED TALL BUILDINGS 3 Deutsche Post Tower/ Bonn, Germany/ 163m (41 stories) Atriums and skygardens as air exhaust / double façade admits cross ventilation Source: H. Jahn (2003) 4th skygarden level 3rd skygarden level Sky gardens as spent-air shaft Double-skin façade as supply-air shaft 2nd skygarden level Air exhaust ventilation grilles (spent air extracted to sky gardens via vents located at slab level 1st skygarden level Spent-air exhaust through vents at topmost level of the skygarden Source: H. Jahn (2003) Air intake ventilation grilles Source: R. Salib (2008) NATURALLY VENITLATED TALL BUILDINGS 4 Commerzbank/ Frankfurt, Germany/ 259m (53 stories) limited stack effect by segmented atrium space / individual cross-ventilation via ventilated cavity Central atrium ventilation Winter sky garden ventilation summer sky garden ventilation 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? 5 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 6 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 7 METHOD—Air flow network modelling 8 1) To discretize the building into zones by nodes. 2) Components are defined to represent leakage paths and pressure drops associated with openings. Boundary node Component_door 3) The nodes are linked together through components to form connections which establish a flow network. Boundary node zone node Component_window 4) A mass balance is expressed for each node in the building. Criteria for ventilation performance 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 9 Building bioclimatic charts (BBCCs) 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% 10 The prototype building with advanced natural ventilation strategies A current design of Taipei, Taiwan 11 11 The base cases 12 Proposed naturally ventilated tall office models Conceptual air flow pattern Lower inlet Central Atrium Atrium-vent 13 Individual office space DSF-vent DSF cavity Top outlet RESULTS & DISCUSSIONS The probability for ventilated cooling: 14 The buoyancy-alone(R) and wind & buoyancy combined (L)ventilation strategies RESULTS & DISCUSSIONS The worst case scenario 15 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. 16 THANK YOU FOR YOUR ATTENTION Any questions/comments ?