Managing Stack Effect in Tall Buildings · Managing Stack Effect in Tall Buildings Copyright© 2019...

Managing Stack Effect in Tall Buildings

Copyright© 2019 by RWDI. All rights reserved.

MANAGING STACK EFFECT IN TALL BUILDINGS


This program is registered with AIA/CES for continuing professional education. As such, it does not include content that may be deemed or construed to be an approval or endorsement by the AIA of any material of construction or any method or manner of handling, using, distributing, or dealing in any material or product.

Questions related to specific materials, methods, and services will be addressed at the conclusion of this presentation.

American Institute of Architects


This course explores stack effect impacts in tall buildings. Stack effect represents an uncontrolled energy loss and can cause irritating noise, infiltration of humidity or odor, drafts and thermal discomfort, etc. Viewers will have an increased awareness of how to control and manage stack effect through passive strategies.

Course Information




1. Describe physics of stack effect and what it means for sustainable, efficient building design and occupant comfort

2. Discuss how to control location of neutral plane, and its importance for stack effect and natural ventilation

3. Articulate role of ventilation system in managing stack effect impacts

4. Illustrate methods of controlling stack effect to meet sustainable building and energy reduction goals through use of case study examples

Learning Objectives


Duncan Philips, Ph.D., P.Eng

Principal

Presented By

Duncan is RWDI’s Global Practice Leader for Building Performance, heading up a talented pool of building performance engineers and scientists as they develop climate-responsive design strategies for individual buildings and masterplans. Clients benefit from Duncan’s ability to solve tough building physics problems by analyzing air flow and heat transfer phenomena.

Duncan has been involved in the design of tall and supertall buildings across the planet, in both hot and cold climates. He has assisted in stack effect mitigation for existing buildings in cities ranging from Dubai to Chicago and presented at multiple conferences on stack effect.


1. Introduction to Stack Effect

2. Criteria for Assessment of “Problematic” Conditions

3. Locating the Neutral Plane

4. Effects of Building Pressurization

5. Managing Stack Effect in Buildings

Agenda




Introduction to Stack Effect


It does not happen because “hot air rises”• Can exist in all buildings

• Induced by buoyancy force originating from indoor-outdoor temperature differences

What is Stack Effect?

Winter Stack-Effect Driven Airflow


Benefits• Natural ventilation

• True in all climate types


+25 °C(77 °F)

+15 °C(60 °F)





Stack Effect

Stack EffectDriving Force(Pressures)

Stack EffectIssues/Impacts

Cannot get rid of driving force

Can reduce issues and impacts through design


Frequently asked question…

“How can I get rid of stack effect in my building?”



The right question…

“How can I reduce the frequency of stack effect issues/impacts in my building?”





Denver, Colorado

• 44 stories

• Height: 548 ft (166 m)

• Outdoor temperature: 10 °F (-12 °C)

• Indoor temperature: 70 °F (21°C)

• Moderately tall

• Cold winter day (not extreme)

Case Study

1999 N Broadway


Visualizing Stack Effect in a Tall Building

Video copyright: Dave McGrail, “Stack Effect Demonstration.”


Visualizing Stack Effect in a Tall Building




Whistling airflow through doors & cracks

Complex issue driven by:

• Shape and configuration of crack / opening

• Flow rate through the crack

Sound can range from whistle to hum

Potential Stack Effect Impacts


Difficulty opening & closing doors

A nuisance… and a safety issue

Choice of door openers and closers is important



Difficulty controlling temperatures on floors with excessive infiltration

A space can be too cold – such as residential lobby in cold climate

Upper part of a building can be too hot in warm climates





Elevator door operability issues & whistling

Difficult to define, tends to be intermittent

Different elevator door manufacturers have different mitigation methods



Increased building energy costs

Due to uncontrolled airflow from outdoors

Unclear how much energy is lost via stack effect



Ingress of odors from outdoors & migration of odors indoors

Controlling odor migration in buildings is critical





How Does Stack Effect Get Setup

Tub

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Tub

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Tub

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Tub

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Tub

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Water instantly turned into air

Air instantly turned into water


Stack Effect Driving Force: Winter

+21 °C70 °F

-17 °C0 °F

400 m(1300 ft)

350 Pa

350 Pa

Indoors

H 400 m

T +21 °C

p 1.20 kg/m3

(0.075 lb/ft3)

Outdoors

H 400 m

T -17 °C

p 1.38 kg/m3

(0.086 lb/ft3)

For a 400 m column of air…

480 kg/m2

4700 Pa(98.2 psf)

Total Pressure Difference = 700 Pa

(14.6 psf)

550 kg/m2

5400 Pa(112.8 psf)


Stack Effect Driving Force: Summer

+21 °C70 °F

+35 °C95 °F

400 m(1300 ft)

Indoors

H 400 m

T +21 °C

p 1.20 kg/m3

(0.075 lb/ft3)

Outdoors

H 400 m

T +35 °C

p 1.14 kg/m3(0.071 lb/ft3)

For a 400 m column of air…

480 kg/m2

4700 Pa(98.2 psf)

Total Pressure Difference = 200 Pa

(-4.2psf)

460 kg/m2

4600 Pa(94.0 psf)

100 Pa

100 Pa




Stack Effect Pressures

+350 Pa

-350 Pa

ΔP

Driving ForceΔP = 700 Pa

(ΔP = 14.6 psf)

(+7.3 psf)

(-7.3 psf)

+21 °C70 °F

-17 °C0 °F

400 m(1300 ft)

350 Pa

350 Pa


250 – 750 Pa1 – 3 inches water5.2 – 15.7 psf

Stack Effect Driving Force

Pressure Difference (Interior to Exterior)


Stack Effect Pressure Issues

1 set of frameless glass doors - 350 Pa on doors= approximately 80 lb force to open each door

Motorized swing door with airlock (two sets of doors)

Revolving door




Criteria for Assessment of “Problematic” Conditions


Difficulty opening and closing of swing doors

Operability threshold force to set in motion

• = 30 lbf

• ~ 130 Pa (2.8 psf)

Determining Acceptability


Elevator door operability issues

Operability threshold = 25 Pa (0.5 psf)

• Difficult to define





Whistling through doors

Define a threshold at 100 L/s = 200 cfm



Other considerations:

Difficulty balancing HVAC

Inability to deliver adequate quantities of fresh air

Struggle to maintain acceptable thermal conditions



Criteria

Ground floor pressures




Elevator door malfunctioning

Difficulty closing & opening around 25 Pa (0.5 psf) pressure difference

Elevator Operability Issues


Winter (normal) – cold outside Summer (reverse) – hot outside

Winter vs. Summer Airflow


Locating the Neutral Plane




Winter: Large Opening @ Top

Large Opening

ΔP = Indoor -Outdoor

Neutral Plane


Winter: Large Opening @ Bottom

Large Opening


Neutral Plane


Winter: Distributed Openings

Real buildings have distributed openings over height




Summer: Distributed Openings

Hot outside



Summer: Distributed Openings

Hot outside

ΔP = Indoor -Outdoor Neutral Plane


Natural Ventilation

Etheridge, Natural Ventilation of Buildings – Theory, Measurement and Design, John Wiley & Sons, 2012

Neutral Plane needs to be above inlet of highest room to be ventilated by stack effect

Neutral Plane




Effects of Building Pressurization


Building Pressurization

Fresh Air (from outdoors) Exhaust (to outdoors)Return

Net Airflow Rate = Fresh Air – Exhaust


Winter: HVAC Pressurization


Neutral Plane




Neutral Plane




Neutral Plane




Summer: HVAC Pressurization

Neutral Plane


Summer: HVAC Pressurization


Neutral Plane

Managing Stack Effect in Buildings




Reduce the frequency and severity of undesirable stack effect impacts and issues within the building

Managing Stack Effect

Design goal


Passive Mitigation

• Tighten building envelope, specific doors, vents

• Add vestibule doors or walls

• Use revolving doors

Active Mitigation

• HVAC pressurization (including seasonal control)

Managing Stack Effect

Two main options for mitigation:


Mitigation Examples




Mitigating Stack Effect

• 80 Story Building

• ~1000 ft / 300m

• Winter ground floor lobby

• Similar to an outdoor deck at the top of a building in summer


Mitigation Example

No mitigation


Mitigation Example

37 Pa across elevator doors> 25 Pa

Exceeds threshold 130 Pa (6.5 psf)

(0.8 psf)No mitigation




Mitigation Example

Improve façade air leakage specification


20 Pa across elevator doors< 25 Pa

Exceeds threshold 130 Pa

(0.4 psf)

Mitigation Example

Exceeds threshold 130 Pa (3.4 psf)

20 Pa across elevator doors< 25 Pa (0.4 psf)Adding

vestibules


Mitigation Example

201 Pa across elevator doors>> 25 Pa

Ok < 130 Pa (1.5 psf)(4.2 psf)

+++ Fresh Air

Positively pressurizing ground floor only




Mitigation Example

15 Pa across elevator doors< 25 Pa

Ok < 130 Pa (1.5 psf)(0.3 psf)Positively

pressurizing all floors


+ Fresh Air

Like trying to plug a leaky dam….

Solving one stack effect issue can cause another

Pressures and air leakage through whole building, not individual floors

Challenges with Mitigation


Challenges with Mitigation

Additional challenges associated with building type

Building Type Issue

Office buildings High occupant traffic during rush hour

Residential buildings Multiple penetrations through exterior façade

Mixed use Multiple building owners/operators

Podiums Connections to adjacent buildings or underground subway/shopping with large open areas and/ or different pressurization




Sample Mitigation Attempts


Airlock Doors RequiredShanghai World Financial Center


Revolving Door – Attention to Details

Drip tray under revolving door not partitioned

Air flows freely underneath door

Doors and enclosures have cracks / gaps




Basement Entrances are Important!

Very large gap under doors between underground parking and service elevator lobby

Tend to assume basement garage is outdoor space


Case Study: Shanghai Building


• 3 Lift banks: Low rise, mid-rise, high-rise, & service

• 40 story building

• Lifts to highest floors do not work on “cold” days

Solution: Building operations put 2 lifts out of 5 on hold-open in order to get others to work

Shanghai Case Study

Building features

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Shanghai Case Study

Pressure across the lift doors

Low Rise High RiseMid-Rise

-50 -40 -30 -20 -10 0 10 20 30 40

L40

L38

L36

L34

L32

L30

L27

L25

L22

L15

L11

L07

L04

L02

Pressure Difference LR Lifts

Le

ve

l

-50 -40 -30 -20 -10 0 10 20 30 40

L40

L38

L36

L34

L32

L30

L27

L25

L22

L15

L11

L07

L04

L02

Pressure Difference MR Lifts

Le

ve

l

-50 -40 -30 -20 -10 0 10 20 30 40

L40

L38

L36

L34

L32

L30

L27

L25

L22

L15

L11

L07

L04

L02

Pressure Difference HR Lifts

Le

ve

l


Doors did not seal well

• Façade took up ~25 Pa

• Lift doors took up ~40 – 70 Pa

Shanghai Case Study

Component issues

L1 – Exterior Door Leak:Partial Seal

L1 – Gap in Rotating Door

L1 – Exterior Door Leak


Shanghai Case Study

Construction issues

L1 – Thermal Image of Façade Above Rotating Door

Mullion conduction (expected)

Cold plume at façade (not expected)

Mullion conduction (expected)

Cold plume at façade (not expected)




Seal the façade

• A clear problem, but not a definitive solution

Create a vestibule for the HR Lifts

• Solves the problem for the HR lifts

• Creates a new one for the MR lifts

Shanghai Case Study

Solutions


Shanghai Case Study

Pressure across the lift doors

Low Rise High RiseMid-Rise

-50 -40 -30 -20 -10 0 10 20 30 40

L40

L38

L36

L34

L32

L30

L27

L25

L22

L15

L11

L07

L04

L02

Pressure Difference HR Lifts

Lev

el

-50 -40 -30 -20 -10 0 10 20 30 40

L40

L38

L36

L34

L32

L30

L27

L25

L22

L15

L11

L07

L04

L02

Pressure Difference MR Lifts

Lev

el

-50 -40 -30 -20 -10 0 10 20 30 40

L40

L38

L36

L34

L32

L30

L27

L25

L22

L15

L11

L07

L04

L02

Pressure Difference LR Lifts

Lev

el


Seal the façade

• A clear problem, but not a definitive solution

Create a vestibule for the HR Lifts

• Solves the problem for the HR lifts

• Creates a new one for the MR lifts

Make a hole in the HR lift shaft wall – bypass vent

• A non-standard approach, but resolves the operational problem

• Likely would have some code issues to resolve in North America

Shanghai Case Study

Solutions




The current practice is equivalent to adding that bypass vent


Shanghai Case Study

Case Study: North American Building


North American Case Study• Two lift cores (L, H) & service lift

• 28 story office building

• Sealed façade

• Bridge to adjacent buildings on L2

• Access to exterior on L4 and L27

• Unique quirk - interior of top mechanical room was open to outdoors

• Exceptionally cold in lobby area

• Temperature drops down to -35°C (~ -32°F) ASHRAE 99.6

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Plot shows conditions at moderate temperatures

Various factors can pull the pressure plot

• High internal HVAC pressurization

• A “very” leaky lower level


North American Case Study

Measurement of ∆P Across Building

0

20

40

60

80

100

120

140

-60 -40 -20 0 20 40 60

He

igh

t A

bo

ve G

rad

e [

m]

Pressure [Pa]

Expected Measured - Stair Shaft Measured - SE - Elevator Shaft

• Improve all exterior doors - lobby level, mechanical rooms, terraces

• Rotating doors on most frequently used doors

• Adjust operational protocols to close vestibule doors on cold days

• Better seals on doors above neutral plane

• Check building mechanical pressurization

• Closing off boiler combustion air intake vent or seal mechanical room


North American Case Study

Recommendations

Conclusions




Stack effect can exist in all buildings

The driving force (strength of stack effect) depends on:

• Building height

• Temperature difference

We can’t totally get rid of the driving force but we can reduce negative impacts through design

Mitigating stack effect needs a holistic building approach rather than treating isolated symptoms

THANK YOUDuncan Phillips, Ph.D., P.EngBuilding Performance [email protected]


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Managing Stack Effect in Tall Buildings · Managing Stack Effect in Tall Buildings Copyright© 2019...

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