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 ?