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
The MEGS Christmas Seminar, 15th December 2010
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 .
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The sick building skin
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Liberty Tower of Meiji University/Tokyo, Japan/ 119m (23 stories)
Central core for stack effect / Wind Floor opens to 4 directions
NATURALLY VENITLATED TALL BUILDINGS
Source: S. Kato & T. Chikamoto (2002)
4NATURALLY VENITLATED TALL BUILDINGS
Source: R. Salib (2008)
4th skygarden level
3rd skygarden level
2nd skygarden level
1st skygarden level
Spent-air exhaust through vents at topmost level of the skygarden
Source: H. Jahn (2003)
Deutsche Post Tower/ Bonn, Germany/ 163m (41 stories)
Atriums and skygardens as air exhaust / double façade admits cross ventilation
Sky gardens as spent-air shaft
Double-skin façade as supply-air shaft
Air intake ventilation grilles
Air exhaust ventilation grilles(spent air extracted to sky gardens via vents located at slab level
Source: H. Jahn (2003)
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Commerzbank/ Frankfurt, Germany/ 259m (53 stories)
limited stack effect by segmented atrium space / individual cross-ventilation via ventilated cavity
NATURALLY VENITLATED TALL BUILDINGS
Winter sky garden ventilation summer sky garden ventilation
Central atrium ventilation
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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?
RESEARCH QUESTIONS
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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
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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
METHOD—Air flow network modelling9
Component_window
Boundary node
Component_door
Boundary node
zone node
1) To discretize the building into zones by nodes.
2) 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.
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
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Building bioclimatic charts (BBCCs) 11
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%
12A current design of Taipei, Taiwan
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The prototype building with advanced natural ventilation strategies
The base cases13
Proposed naturally ventilated tall office models
Conceptual air flow pattern
Central Atrium
DSF cavity
Atrium-vent
DSF-vent
Lower inlet
Top outlet
Individual office space
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RESULTS & DISCUSSIONS
The probability for ventilated cooling: The buoyancy-alone(R) and wind & buoyancy combined (L)ventilation strategies
16RESULTS & DISCUSSIONS
The worst case scenario
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Natural
EXPECTED OUTCOMES
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.
THANK YOU FOR YOUR ATTENTION
Any questions/comments ?