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NaturalNatural Ventilation: Theory Ventilation: Theory
Hal LevinHal Levin
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Natural Ventilation: Theory
DefinitionsPurpose of ventilation What is ventilation?Types of natural ventilation (Driving forces): Buoyancy (stack effect; thermal) Pressure driven (wind driven; differential pressure)
Applications Supply of outdoor air Convective cooling Physiological coolingIssues Weather-dependence: wind, temperature, humidity Outdoor air quality Immune compromised patients Building configuration (plan, section) Management of openings
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Natural and Mixed Mode Ventilation Mechanisms
Courtesy of Martin Liddament via Yuguo Li
Mixed Mode Ventilation
Sketch of school system
Sketch of B&O Building
Natural Ventilati on
Cross Flow Wind
Mixed Mode Ventilation
Wind Tower Stack (Flue) Stack (Atrium)
Fan Assisted Stack
heated/cooledpipes
heated/cooledceiling void
Top Down Ventilation
chilled pipes
Buried Pipes
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Climate Typology (oversimplified!)Not in handout materials to be completed by class
BogotCold dry
Cold humid
San
FranciscoMt. Fuji
Temperate
seasonal RH
Montreal,Canada
LimaBostonTemperateseasonal -- Temp
Quito, Ecuador High desertTemperate dr y
Milan, ItalyLondonTemperate humi d
Low desertHot dry
SingaporeHot humid
No seasonalvariation
Seasonalvariation
Steady d ailycycle
Diurnalswing
Climate type
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What is ventilation?
Definitions covering ventilation and the flow of air into andout of a space include:
Purpose provided (intentional) ventilation: Ventilationis the process by which clean air (normally outdoor air)is intentionally provided to a space and stale air isremoved. This may be accomplished by either natural ormechanical means.
Air infil tration and exfil tration: In addition to intentional
ventilation, air inevitably enters a building by the processof air infiltration. This is the uncontrolled flow of air intoa space through adventitious or unintentional gaps andcracks in the building envelope. The corresponding lossof air from an enclosed space is termed exfiltration.
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Three elements of ventilation(source: Yuguo Li, personal communication)
Element Des cr ip ti on Req ui rem en ts /Guideline
Design orOperation
Buildings
Primary External airflow rate
Minimum ACHMinimum L/s
Fan, duct,openings orstreets
ASHRAE62
1-12 ACH
Secondary Overall flowdirectionbetween zones
Flow clean todirty spaces
PressurecontrolthroughairflowimbalancePrevailingwinds
Positive/negative2.5-15 PaIsolation/smokecontrol
Tertiary Airdistributionwithin a space
Ventilationeffectiveness,no short-circuiting
Use of CFDSmokevisualization
Ventilationstrategies
Cities
?
Dirty industrydownwind
Buy upwind
Urbanplanning
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Courtesy of Yuguo Li
Isolation room ventilationGoal: ~12 ach or 160 l/s-p (?)
23oC 23 oC 23 oC
The purpose is Not to h ave a 2.5 Pa negative pressure, but no air leaks to the cor ridor !
23 oC
C o r r i d o r
A
n t e r o o m
T o i l e t / b a t h r o o m
Cubicle
Suspended ceilings
Recommended negative pressure is 10 Pa with wind, -2.5 Pa without wind
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Types of natural ventilation
Stack effect (buoyancy) Warm air is lighter (less dense)
than cold air Warm air rises, cold air falls Intentional chimneys (stacks)
can create larger differencesbetween top and bottom,increasing the air flow rate
Wind-driven (pressure) Pressure differences result in
air mass movement Packets of air flow from
higher to lower air pressureregimes
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Wind driven vs. Stack effect
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Natural Driving Mechanisms Pressure:Wind-driven air flow
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Natural Driving Mechanisms Pressure:Wind-driven air flow
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Natural driving mechanisms -- BuoyancyStack effect
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Hot air = buoyancy
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Natural driving mechanisms -- BuoyancyStack effect
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Applications: Supply of outdoor air
Supply of outdoor air removal of pollutants In air changes per hour (AER or h -1) or liters per person per
second (l/s-p) What happens if you have a very tall space?
Pollutant concentration = source strength/removal rate Removal rate includes dilution/exhaust plus deposition on
surfaces or chemical interactions/transformation Chemicals: source strength expressed as mg of pollutant / m 2-h
or mg/h Dilution/exhaust rate expressed as dilution ventilation (air
changes per hour) Deposition: gcm -1s -1
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Pollutant concentration as a function of outdoor airexchange rate
0
1
2
3
4
5
6
7
8
0 1 2 3 4 5
Ventilation air changes per hour (ach)
C o n c e n t r a t i o n
( g
/ m 3 )
EF = 1g/m2 hr
EF = 5 g/m2 hr
EF = 10 g/m2 hr
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Applications: Convect ive cooling convection /convection/ (kon-vekshun) the act of conveying or
transmission, specifically transmission of heat in a liquid or gas bybulk movement of heated particles to a cooler area.
Air flow person can be caused by the higher temperature of thepersons skin relative to the air around it, giving rise to an air flowknown as the thermal plume, air movement predominantly in anupward direction.
Or, it may be caused by forced air movement, as from a fan orwind.
Temperature variation in an objectcooled by a flowing liquid
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Convective cooling
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Physiological cool ing
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Appl ications: Physiological cooling
Ectothermic cooling Vaporization:
Getting wet in a river, lake or sea. Convection:
Entering a cold water or air current. Building a structure that allows natural or generated air flow for cooling.
Conduction: Lie on cold ground. Staying wet in a river, lake or sea. Covering in cool mud.
Radiation: Find shade.
Enter a cave or hole in the ground shaped for radiating heat (Black boxeffect). Expand folds of skin. Expose skin surfaces.
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Convective + Physiological cooling
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Physiological cool ing
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Impact of wind and temperaturedifference on natural ventilation
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Concept of the neutral level
Externalpressuregradient
Internalpressure
gradienth
1
h 2
T iT 0
Neutralplane
Externalpressuregradient
Internalpressure
gradienth
1
h 2
T iT 0
Neutralplane
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Single-sided ventilation
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Influence of wind and temperature (stackeffect) on ventilation and air flow pattern
(source: AIVC, 2009)
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Cross flow ventilation(source: AIVC, 2009)
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Stack ventilation (dwellings)(source: AIVC 2009)
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Stack ventilation (atrium)(source: AIVC 2009)
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Stack driv ing flows in a building
Neutralpressureplane
+
+
_
_
+
+
_
_
_
_Indoor air
temperatureis greater
thanoutdoor
Neutralpressureplane
+
+
_
_
+
+
_
_
_
_Indoor air
temperatureis greater
thanoutdoor
Neutralpressureplane
+
+
+
_
_
+
+
+_
_Indoor air
temperatureis less than
outdoor
Neutralpressureplane
+
+
+
_
_
+
+
_
_
+
+
+_
_+
+_
_Indoor air
temperatureis less than
outdoor
(A)
I n d o o r a i r w a r m e r I n d o o r a i r c o o l e r
t h a n o u t d o o r t h a n o u t d o o r
(B)
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Wind floor 18F
Memorial Hall
Entrance Hall
LectureRooms
Graduate School
Offices
Library Car Parking
Roof Garden
119.5m
Heat Storage TankRain Water Tank
Canteen
Roof Garden
Stack effect in ahigh ri sebuildingLiberty Tower,Meiji University,
Tokyo
Stack effect
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Wind Floor for HybridVentilation
Gross Floor Area: 59000 m 2
completed in 1998
Meiji University L iberty Tower, Tokyo, Japan(source: Professor Toshihara Ikaga, Keio University)
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Natural ventilation in bui ldingsFrancis Allard, Mat Santamour is, Servando Alvarez, European
Commissio n. Directorate-General for Energy, ALTENER Progr am
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Natural ventilation in buildingsBy Francis Allard, Mat Santamouris, Servando Alvarez, European Commission.
Directorate-General for Energy, ALTENER Program
http://books.google.com/books?hl=en&lr=&id=1tdQMyhPA2gC&oi=fnd&pg=PR9&dq=Natural+ventilation+theory&ots=mFzmfd4mct&sig=XA3zksH_OBkkS8tILbxmwJqbWyo
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Natural ventilation in bui ldingsFrancis Allard, Mat Santamour is, Servando Alvarez, European
Commissio n. Directorate-General for Energy, ALTENER Progr am
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Indoor air velocities for naturally ventilated spacesunder different wind directions and different number of
apertures and locations
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Effects of inlet / outlet sizes in cross-ventilatedspaces with openings on opposite walls
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Velocity as percent of wind velocity: openingson opposite walls, wind perpendicular to inlet
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Effect of oblique wind direction withopenings on oppos ite walls
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Velocity as percent of wind velocity: Openingson opposite walls, wind oblique to inlet
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Effects of inlet / outlet sizes in cross-ventilatedspaces, openings on adjacent walls
Wind perpendicular Wind oblique
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Effect of inlet and outlet sizes, openings onadjacent walls, wind perpendicular to inlet
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Simple formulation for Vent Calculation
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Single-sided ventilation
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Single-sided ventilation
4949
Natural and Mixed Mode Ventilation Mechanisms
Courtesy of Martin Liddament via Yuguo Li
Mixed Mode Ventilation
Sketch of school system
Sketch of B&O Building
Natural Ventilati on
Cross Flow Wind
Mixed Mode Ventilation
Wind Tower Stack (Flue) Stack (Atrium)
Fan Assisted Stack
heated/cooledpipes
heated/cooledceiling void
Top Down Ventilation
chilled pipes
Buried Pipes
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Natural Ventilation Issues
Weather-dependence: wind, temperature,humidity
Outdoor air quality Immune compromised patients Building configuration (plan, section) Management of openings Measurement of ventilation rate(s)
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Outdoor air quality becomes indoor airquality at high ventilation rates
The higher the outdoor air ventilation rate, the higher theindoor/outdoor pollutant concentration
The effect of the building on reducing outdoor pollutantsvaries by pollutant and by building ventilation pathways
Where outdoor air pollution is high, natural ventilationmust be considered not only as a means for reducingconcentrations from indoor sources (infectious airborneagents as well as chemicals emitted indoors), but also asa means of delivering un-cleaned outdoor air.
With highly susceptible health care facility occupantpopulations, consideration must be given to the effects ofoutdoor pollutants on the occupants health.
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Chapter 2.
Global ambient airpollutionconcentrations andtrends
Bjarne Sivertsen
http://www.who.int/phe/health_topics/outdoorair_aqg/en/
WHO, 2005. Air Quali ty Guidelines:Global Update
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Ranges of annual average concentrations of
outdoor air pollutants by continent based onselected urban data
120300100250
120310150380150350200600
10100665
317935836
4070
35652075
1128357018573082
4015035220
2812720602070
30129
Africa Asia
Australia/New ZealandCanada/United StatesEuropeLatin America
Ozone(1-hour maximum
concentration)Sulfur
dioxideNitrogendioxidePM 10Region
(source: World Health Organization, 2005. Air Quality Guidelines: Global Update)
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Where are the people who will arrive innaturally ventilated health care facilities?
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Pollutant concentrations by national levelof development
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U.S. EPA National Ambient Air QualityStandards (NAAQS) http://www.epa.gov/air/criteria.html
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Average annual PM10
concentrations inselected cities world wide (part 1)
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Average annual PM 10 concentrations inselected cities world wide (part 2)
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Average annual PM 10 concentrations inselected cities world wide (part 3)
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Average annual PM 10 concentrations inselected cities world wide (part 4)
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NORTH AMERICA
Average annual PM10
concentrations inselected cities world wide (part 5)
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Average annual PM 10 concentrations inselected cities world wide (part 6)
Europe
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EUROPE
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Ultrafine particle number concentrationsmeasured in urban and roadside environments
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Mean afternoon (13:00 to 16:00) surface ozone
concentrations calculated for the month of July(comment: where are people living?)
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Highest (1-hour average) ground-level ozoneconcentrations measured in selected cities
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Modeled surface ozone concentrations (ppb) overEurope during July for the years 2000 2009
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Indoor O 3 concentration as a function ofoutdoor concentration and ventilation rate
180162144126108907254361820
16014412811296806448321612
132119106927966534026136
1109988776655443322114
75676052453730221572
50454035302520151051
AER(h -1)
20018016014012010080604020
Outdoor Air Ozone Concentration (parts per billion)
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Wind: direction and velocity are neitherstable nor consistent Selected data from almost any city will show daily cycles
and variations in wind direction and velocity Seasonal variations are more reliable, but daily
variations are still the rule rather than the exception Even with many predictable situations, wind direction will
change over the diurnal cycle California coast is anexample.
Relying on wind alone can result in both under and over-ventilation relative to a design objective.
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Lima, Peru: May 1, 2008
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Lima, Peru: September 1, 2008
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Lima, Peru: January 1, 2009
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Lima, Peru: March 1, 2009
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Boston, MA: July 24, 2009
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Boston, MA: March 1, 2009
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Boston, MA: January 1, 2009
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Boston, MA: October 1, 2008
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Grantham Hospital Study, Hong KongYuguo Li
0
90
180
270
Test 4:Wind speed= 3.0 m/s
Test 17:Wind speed=4.5m/s
(A)
10 15 200
5
10
15
20
25
30
35
10 15 20 10 15 20 10 15 20 10 15 200
50
100
150
200
250
300
350
Aug 28,2006Nov 10,2005Nov 09,2005Nov 07,2005
W i n d d i r e c t
i o n (
o )
S p e e d
( m / s )
T e m p e r a
t u r e
( o C )
Time (hours)
TemperatureWind speed
Nov 06,2005
Wind direction
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Natural Ventilation: TheorySummary - Review
Purpose of ventilation What is ventilation?Types of natural ventilation (Driving forces): Buoyancy (stack effect; thermal) Pressure driven (wind driven; differential pressure)
Applications Supply of outdoor air Convective cooling Physiological coolingIssues Weather-dependence: wind, temperature, humidity Outdoor air quality Immune compromised patients Building configuration (plan, section) Management of openings
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Natural Ventilation: TheoryReferences
Karl Terpager Andersen, 2003. Theory for natural ventilation by thermal buoyancy in onezone with uniform temperature Building and Environment 38: 12811289.
Yuguo Li 2000. Buoyancy-driven natural ventilation in a thermally stratifed one-zonebuilding. Building and Environment 35: 207-214.
Francis Allard, Mat Santamouris, Servando Alvarez, Natural ventilation in buildings.European Commission. Directorate-General for Energy, ALTENER Program. Can beread on-line athttp://books.google.com/books?hl=en&lr=&id=1tdQMyhPA2gC&oi=fnd&pg=PR9&dq=Natural+ventilation+theory&ots=mFzmfd4mct&sig=XA3zksH_OBkkS8tILbxmwJqbWyo
WHO, 2005. Air Quality Guidelines, 2005 Update . Geneva: World Health Organization.http://www.who.int/phe/health_topics/outdoorair_aqg/en/
Heiselberg, P., Ed., 2002. Principles of Hybrid Ventilation . IEA-ECBS Annex 35 report.Downloadable from http://hybvent.civil.auc.dk/