Buoyancy-driven Ventilation in respect of Tall Office Buildings in a

Report
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.
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
THANK YOU FOR YOUR ATTENTION
Any questions/comments ?

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