Buoyancy-driven Ventilation in respect of Tall Office Buildings in a
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Transcript Buoyancy-driven Ventilation in respect of Tall Office Buildings in a
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
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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
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?
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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
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METHOD—Air flow network modelling
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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
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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%
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The prototype building with advanced
natural ventilation strategies
A current design of Taipei, Taiwan
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The base cases
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Proposed naturally ventilated tall office models
Conceptual air flow pattern
Lower inlet
Central
Atrium
Atrium-vent
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Individual office
space
DSF-vent
DSF
cavity
Top outlet
RESULTS & DISCUSSIONS
The probability for ventilated cooling:
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The buoyancy-alone(R) and wind & buoyancy combined (L)ventilation strategies
RESULTS & DISCUSSIONS
The worst case scenario
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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.
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THANK YOU FOR YOUR ATTENTION
Any questions/comments ?