Educational Package Ventilation

Lecture 1 :Typical ventilation

design concepts and strategies
Zoltn MAGYAR, PhD
Department of Building Energetics and Building Service Engineering

Summary
Ventilation background
Why ventilate?

Two ways of building ventilation

Ventilation and Air Quality
Insulation, Air tightness and Ventilation
The two natural mechanisms of ventilation
Three-pronged recommended strategy for ventilation

Energy impact of ventilation

Evaluation of required ventilation rate
2

Ventilation background
Insulated
Airtight housing
Ventilation system

JUST insulated roof

Double glazing
NOT insulated
NEITHER airtight

Insulated
Airtight housing

Tomorrow

1996
1985

Before 1973

1973
Petroleum
crisis

Thermal
Regulations

Reinforced
thermal
regulations

Man is a funny creature

When its hot he wants it cold
When its cold he wants it hot
Always wanting what is not
Man is a funny creature
ASHRAE Journal, unknown author

Why ventilate?
To provide
fresh air to
occupants

Heating
and
Air-Conditioning

To distribute
heating or
cooling

Why
Why
Ventilation?
Ventilation?

To provide
natural passive
cooling

Air
Quality

To dilute
and
remove
pollutants

TWO ways of building ventilation

Natural ventilation

Mechanical ventilation

Single sided ventilation

Mechanical supply ventilation

supply and extraction through the

same openings

a fan supplies air to spaces

openings ~4% of floor area

less efficient
internal door remain closed
Cross ventilation
supply and extraction at the same level
in the building
good result when wind exists

internal doors opened or equipped with

ventilation grilles
Stack ventilation
air supply through louvers and
extracted through chimneys
wind not needed

ventilation openings in buildings

envelope are used for extraction
usually used where high ventilation
rates are needed and air has to be
heated before entering the room
Mechanical extract ventilation
a fan draws air from spaces
fresh outdoor air enters into rooms
either through the leakage routes of
building envelope or through ventilation
openings in the building envelope
Mechanical extract & supply ventilation
a balanced ventilation system
it must always include a supply and a
return air fan
an air heater is almost always installed
in the supply air side

Ventilation and Air Quality

A Solution:

Required:

VENTILATION

AIR QUALITY
COMFORT
HEALTH

CAN REMOVE POLLUTANTS

STUFFY
ODOUR
TOXIC
SICK BUILDING
HOT
COLD
DRAUGHTY

CAN REMOVE HEAT

A Problem:
LOSS OF CONDITIONED AIR
FAN ENERGY

ENERGY

Insulation, Airtightness and Ventilation

To achieve high
performance in terms
of thermal comfort,
energy savings and
air quality, it
becomes necessary
to control the
ventilation.

Thermal
Insulation

Reduce energy
consumption

Increase the
thermal comfort

To reduce heat loss

through the walls, in
addition to the
installation of
insulation, delete air
leakage through the
building envelope.
The airtightness
solves this problem.

Improve IAQ

Controlled
Ventilation
Ventilation solves
this problem.

Airtightness

The realization of
an airtight
envelope -> no
longer a sufficient
air renewal.

The two natural mechanisms of ventilation

Objectif

The objective of a good ventilation strategy is to

ensure a balance between energy efficiency and
indoor air quality.
build tight ventilate right

In other words:

Minimize the amount of air leakage through the building

envelope
Install a controlled ventilation system to provide the
necessary level of ventilation where and when necessary.
8

The two natural mechanisms of ventilation

1. Wind Driven Ventilation
Negative
pressure
region

Wind
WindTower
tower

Wind

Yazd, Iran

Wind driven flow

Badgir (WindCatcher)
Fig.3

Fig.1 (a,b,c)
Fig.2
Cross Flow Wind
IUT building La Runion Island

Fig.5

Fig.4

p w C p v 2 / 2
F. ALLARD- CHAMPS Seminar Nanjing 20-22/03/2011

Natural ventilation cross

tropical climate

Natural ventilation system

single sided type
tropical climate

The two natural mechanisms of ventilation

2. Stack Driven Ventilation

Neutral
pressure plane

Pressure of air
increases closer
to the ground due
to the extra amount
of air above.

Temperature driven flow

'Neutral' Pressure
Plane

The pressure
gradient of air
increases indoors
because warmer
air is less dense.
'Stack' pressure
between openings
is given by A + B

Stack (Flue)

Air Pressure

(Courtesy M. Liddament)
Stack (Atrium)

Fig.6
Stack height

F. ALLARD- CHAMPS Seminar Nanjing 20-22/03/2011

10

Three-pronged recommended strategy for ventilation

Extract
ventilation in
wet rooms

Remove these pollutants directly to outside

Minimize their spread into the rest of the building

Whole building
ventilation

Provide a continuous supply of fresh air from outside

Dilute and disperse water vapor and pollutants that are either not
removed by extract ventilation or are generated in other rooms from
the building

Purge
ventilation
throughout the
building

Aid removal of high concentrations of pollutants and water vapor

released from occasional activities such as painting and decorating
Opened windows

11

Energy impact of ventilation

Industry

Agriculture

17.9%

1.3%

Transport

25%

38.9%

Dissipation through Air:

-Ventilation
-Infiltration
-Venting

Buildings
Europe
Other countries
6%
18%
USA
34%

Fig.7

41.9%

Japan
19%
China
23%

Fig.8
Honk Kong, China*

Fig.9

Air-conditioner world market

(in volume) in 2000*

New York City, USA*

Huge demand to reduce the

energy impact of ventilation!

F. ALLARD- CLIMA 2010-Antalya .

Stockholm, Sweden *

12

Energy impact of ventilation

Air exchange

Power supply

Energy saving control

devices

Specific fan power

Improving
airtightness

Heat recovery units

Most common air leakage paths
1.
2.
3.
4.

5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.

Under-floor ventilator grilles.

Gaps in and around suspended timber
floors.
Leaky windows or doors.
Pathways through floor/ceiling voids
into cavity walls and then to the
outside.
Gaps around windows.
Gaps at the ceiling-to-wall joint at
the eaves.
Open chimneys.
Gaps around loft hatches.
Service penetrations through ceilings.
Vents penetrating the ceiling/roof.
Bathroom wall vent or extract fan.
Gaps around bathroom waste pipes.
Kitchen wall vent or extractor fan.
Gaps around kitchen waste pipes.
Gaps around floor-to-wall joints
(particularly with timber frame).
Gaps in and around electrical fittings
in hollow walls.

F. ALLARD-HealthVent WP5 Seminar

Brussels 7-8/09/2010

F. ALLARD- CLIMA 2010-Antalya .

13

Evaluation of required ventilation rate

for office spaces...

for residential buildings...

Fig.11

Fig.10

1 cfm=1,7 m3/h
Brief Ventilation Rate History

Ventilation Rates 1955-2003 (cfm/person)

Fig.12
History And Background of Ventilation Rates, Kansas City Seminar 4
June 29, 2003; Fred Kohloss Consulting Engineer, Honolulu, Hawaii

14

References
F. ALLARD Natural Ventilation in Buildings, James & James London NW1 3ER UK

C. Ghiaus, F. Allard, Y. Mansouri, J. Axley, Natural ventilation in urban context

HEALTHVENT HEALTH-BASED VENTILATION GUIDELINES FOR EUROPE, WORK PACKAGE 5, EXISTING
BUILDINGS, BUILDING CODES, VENTILATION STANDARDS AND VENTILATION IN EUROPE FINAL
DRAFT REPORT, Coordination of work: Olli Seppnen, Secretary General of REHVA, Project group: Nejc
Brelih, Guillaume Goeders, Andrei Litiu
lecture F. Allard, AERAULIQUE DES BATIMENTS
F. ALLARD- CHAMPS Seminar Nanjing 20-22/03/2011
F. ALLARD- CLIMA 2010-Antalya
F. ALLARD-HealthVent WP5 Seminar, Brussels 7-8/09/2010
History And Background of Ventilation Rates, Kansas City Seminar 4, June 29, 2003; Fred Kohloss
Consulting Engineer, Honolulu, Hawaii

15

Educational Package Ventilation

Lecture 2 : Natural ventilation

Zoltn MAGYAR, PhD
Department of Building Energetics and Building Service Engineering

Summary
Natural ventilation principles
Natural Ventilation strategies
Technical solutions for natural ventilation

Case study :
BRE Office Building, Watford, UK;

Conclusion

to maintain acceptable levels of oxygen in air and to remove odours,

moisture, and internal pollutants;

it may also remove excess heat by direct cooling or by using the building
thermal mass;
35

Indoor air temperature [C]

20

Ventialtion rate [l/person]

Natural ventilation principles

Role of ventilation

15
10
5
0

1850

1900
Year

(a)

1950

2000

Natural ventilation
Air conditioning

30
25
20
15

0
10
20
30
40
Mean monthly outdoor air temperature [C]

(b)

Performance criteria: a) minimum ventilation rates used in USA for indoor air quality (Awbi 1998); b) thermal
comfort in natural ventilation (Brager 1998) and air conditioning (ASHRAE 1993).
Source: Natural ventilation: principles, solutions and tools; Cristian Ghiaus, Francis Allard, James Axley, Claude-Alain Roulet

Natural ventilation principles

Bases of
+ attractive because it is seen as a cost
effective alternative to conventional mechanical
ventilation with air conditioning;
+ steady improvements in design, material and
control methods means that the range of
buildings in which this approach is applicable
continues to grow;
+ in practice natural ventilation is most suited
to buildings located in mild to moderate
climates away from inner city locations;
natural ventilation is the use of wind and
temperature differences to create airflows in
and through buildings;

these airflows may be used both for ventilation

air and for passive cooling strategies;
natural ventilation is often strongly preferred
by building occupants, especially if they have
some control over it, as with operable windows.
.

Natural ventilation principles

Bases of

Subject to climate and outside noise

constraints, typical building types include:

and

pollution

Dwellings (individual and apartments);

Small to medium sized offices;
Schools;
Small to medium retail premises;
Recreational buildings;
Warehouses;
Industrial premises.

Specialised natural ventilation may be applicable to a

wider range of climatic conditions and buildings examples
are included in the accompanying resource module.
5

Cooling sensation deg. C

Natural ventilation principles

Cooling sensation from airflow

10
8
6
4
2
0
0

0.5

1.5

2.5

Airflow (m/s)

In a mild summer, natural ventilation can reduce the

apparent temperature (e.g.up to 60C at an airflow of 1.5
m/s or so)
Source: Natural Ventilation in Buildings, Tony Rofail, NEERG seminar, 31 Aug 2006, Windtech Consultants

3.5

Natural ventilation principles

Effect of Air Movement on Occupants

Air Velocity

Probable Impact

Up to 0.25 m/s

Unnoticed

0.25 to 0.5 m/s

Pleasant

0.5 to 1 m/s

Generally pleasant, but causes

a constant
awareness of air movement

1 to 1.5 m/s

From slightly drafty to

annoyingly drafty

Above 1.5 m/s

Requires corrective measures

if work and
health are to be kept in high

Source: Victor Olgyay, Design with Climate, Princeton University Press, 1963

30
Temperature (deg C)

Natural ventilation principles

Summer Example

20

10

Outside
temperature
6am

12noon
day

6pm

midnight
night

Source: Natural Ventilation capabilities and limitations (comfort and energy efficiency in domestic dwellings), ATA Melbourne Branch
presentation, April 2008, Jim Lambert

6am
time

30
Temperature (deg C)

Natural ventilation principles

Summer Example

20
Inside
temperature

10

Outside
temperature
6am

12noon
day

6pm

midnight
night

Source: Natural Ventilation capabilities and limitations (comfort and energy efficiency in domestic dwellings), ATA Melbourne Branch
presentation, April 2008, Jim Lambert

6am
time

Comfort
range with
moving air

30
Temperature (deg C)

Natural ventilation principles

Summer Example

20
Inside
temperature

10

Normal
comfort
range

Outside
temperature
6am

12noon
day

6pm

midnight
night

Source: Natural Ventilation capabilities and limitations (comfort and energy efficiency in domestic dwellings), ATA Melbourne Branch
presentation, April 2008, Jim Lambert

6am
time

30
Temperature (deg C)

Natural ventilation principles

Summer Example

Comfort
range with
moving air

Open all
windows

20
Inside
temperature

10

Normal
comfort
range

Outside
temperature
6am

12noon
day

6pm

midnight
night

Source: Natural Ventilation capabilities and limitations (comfort and energy efficiency in domestic dwellings), ATA Melbourne Branch
presentation, April 2008, Jim Lambert

6am
time

30
Temperature (deg C)

Natural ventilation principles

Summer Example
Open all
windows

Comfort
range with
moving air

Close all
windows

20
Inside
temperature

10

Normal
comfort
range

Outside
temperature
6am

12noon
day

6pm

midnight
night

Source: Natural Ventilation capabilities and limitations (comfort and energy efficiency in domestic dwellings), ATA Melbourne Branch
presentation, April 2008, Jim Lambert

6am
time

30
Temperature (deg C)

Natural ventilation principles

Summer Example
Open all
windows

Close all
windows

Start
internal
fan

Comfort
range with
moving air

20
Inside
temperature

10

Normal
comfort
range

Outside
temperature
6am

12noon
day

6pm

midnight
night

Source: Natural Ventilation capabilities and limitations (comfort and energy efficiency in domestic dwellings), ATA Melbourne Branch
presentation, April 2008, Jim Lambert

6am
time

30
Temperature (deg C)

Natural ventilation principles

Summer Example
Open all
windows

Close all
windows

Start
internal
fan

Open all
windows

Comfort
range with
moving air

20
Inside
temperature

10

Normal
comfort
range

Outside
temperature
6am

12noon
day

6pm

midnight
night

Source: Natural Ventilation capabilities and limitations (comfort and energy efficiency in domestic dwellings), ATA Melbourne Branch
presentation, April 2008, Jim Lambert

6am
time

Open all
windows

Close all
windows

Start
internal
fan

30
Temperature (deg C)

Natural ventilation principles

Summer Example

Open all
windows

Comfort range
with moving
air

Gentle forced
ventilation
overnight

20
Inside
temperature

10

Normal
comfort
range

Outside
temperature

6am

12noon
day

6pm

midnight
night

Source: Natural Ventilation capabilities and limitations (comfort and energy efficiency in domestic dwellings), ATA Melbourne Branch
presentation, April 2008, Jim Lambert

6am
time

Natural ventilation principles

Natural Ventilation Driving Forces

Air moves through an opening (e.g. window) when there
is a pressure difference across the opening:
greater pressure difference = higher airflow
larger opening area = higher airflow
Natural ventilation pressure differences driven by
two mechanisms:
air density difference (stack effect)
warm air is less dense than cool air (more
buoyant)
works when indoor air is warmer than
outdoor air
harder to achieve stack airflow in summer
wind
creates varying surface pressures around
the building
16
Source: Erik Kolderup, Saving Energy with Natural Ventilation Strategies, September 2008

Natural ventilation principles

Stack effect

z
g

,T
dz

P(z)

P0

dP(z) = - g dz
then:
P(z) = P0 g z (hydrostatic pressure)

Source: Erik Kolderup, Saving Energy with Natural Ventilation Strategies, September 2008

17

Natural ventilation principles

Stack effect

Source: Erik Kolderup, Saving Energy with Natural Ventilation Strategies, September 2008

18

Natural ventilation principles

Stack effect

Airflow through an opening

with P1 > P2,
Theoretical airflow (m3/s) will be:
A
P1, T1, 1

P2 , T 2 , 2

Qth = V *A

Real airflow < theoretical

airflow

V is calculated using Bernoullis equation

Qv = Cd Qth

P1 P2 = 1 V2

with Cd<1 (surface

pressure coefficient)

then: Qth = A ( 2 (P1-P2)/1) 0,5

Source: Erik Kolderup, Saving Energy with Natural Ventilation Strategies, September 2008
Source: F. Allard, Aeraulique des batiments et ventilation naturelle

19

Natural ventilation principles

Flow Through Gaps and Cracks Air Infiltration

flow rate through less well defined openings such as infiltration
openings is represented by the Power Law Equation:
Cd
= flow coefficient;
n
Qv Cd p n = flow exponent;
p = pressure difference across the opening.

Fig.2

Cd is related to the size of the

opening (i.e. it increases with opening
size)
n characterises the flow regime
and varies in value between 0.5 (fully
turbulent flow) to 1.0 (fully laminar
flow).
quadratic equation is recommended
in which the laminar and turbulent
terms are separated. This form of
the equation is given by:

p Q Q 2

20

Natural ventilation principles

Stack effect

Source: Erik Kolderup, Saving Energy with Natural Ventilation Strategies, September 2008

21

Natural ventilation principles

Wind Driven Ventilation

Wind Pressure
Distribution
Air Density
(Kg/m3)

Wind Velocity (m/s)

(at Building Height)

p w 0.5C p v r

(Pa)

Evaluation:
Wind Pressure
(Pa)
- Tabulated Data
Wind Pressure
- Wind Tunnel Tests
Coefficient
- CFD
Source: AM10: 2005, Natural Ventilation in Non-Domestic Buildings, CIBSE
F. Allard - CHAMPS Seminar Nanjing 20-22/03/2011

22

Natural ventilation principles

Wind Driven Ventilation

Wind pressure distribution for various building shapes and orientations

Source: VENT Dis. Course, Distant learning vocational training material for the promotion of best practice
23
ventilation energy performance in buildings, Module 1: Natural and Hybrid Ventilation

Natural ventilation principles

Combining Wind and Stack Driven Ventilation

total pressure, pti, acting at an opening, i, due to the combined impact of wind
and stack effect, is given by:

pti pwi psi

! summing the pressures due to stack and wind effect at each opening is not the
same as summing the flow rates determined by calculating the flow rates due to
wind and stack pressure separately
! summing the flow rates would lead to an erroneous result

Calculating Natural Ventilation Rate Using the Flow Equations, Wind

Pressure and Stack Pressure Equations
involves:
identifying the ventilation openings;
determining the pressures acting on each opening;
applying the flow equations at each opening;
obtaining a flow balance so that the air entering the building (and individual
zones in a building) is balanced by the outgoing air.
Source: VENT Dis. Course, Distant learning vocational training material for the promotion of best practice
24
ventilation energy performance in buildings, Module 1: Natural and Hybrid Ventilation

Natural ventilation principles

Advantages of Natural Ventilation

Suitable for many types of buildings located in mild or moderate
climates;
The 'open window' environment associated with natural ventilation is
often popular, especially in pleasant locations and mild climates;
Natural ventilation is usually inexpensive when compared to the capital,
operational and maintenance costs of mechanical systems;
High air flow rates for cooling and purging are possible if there are
plenty of openings;
Short periods of discomfort during periods of warm weather can usually
be tolerated;
No plant room space is needed;

Minimum maintenance;
Can be less expensive to install and operate than HVAC but this need not
always be true;
No fan or system noise.

25

Natural ventilation principles

Disadvantages of Natural Ventilation

Inadequate control over ventilation rate could lead to indoor air quality
problems and excessive heat loss;
Air flow rates and the pattern of air flow are not constant;

Fresh air delivery and air distribution in large, deep plan and multiroomed buildings may not be possible;
High heat gains may mean that the need for mechanical cooling and air
handling will prevent the use of natural ventilation;

Natural ventilation is unsuited to noisy and polluted locations;

Some designs may present a security risk;
Heat recovery from exhaust air is technically feasible (Shultz, 1993)
but not generally practicable;

Natural ventilation may not be suitable in severe climatic regions;

Occupants must normally adjust openings to suit prevailing demand;
Filtration or cleaning of incoming air is not usually practicable;
Ducted systems require large diameter ducts and restrictions on
routing.
.

26

Natural ventilation strategies

Natural Ventilation Approaches

Advantages:
Single sided ventilation is popular because openings are located
on one face only.
Disadvantages:
No defined exit route for air;
Net driving forces may be small resulting in poor ventilation;
Depth of penetration of air restricted to approximately
2.5 x ceiling height.
Single sided natural ventilation should be avoided!

Single Sided Ventilation

Cross Flow Ventilation

Advantages:
Open air flow path presents minimum resistance to air flow and
hence provides good ventilation to a space;
For equivalent size of openings, cross flow will provide more
reliable ventilation than single sided.
Disadvantages:
Cross flow of used air into further occupied spaces should be
avoided;
Design of interior layout etc. can be more complex than for single
sided solutions.
Cross flow designs form the basis of best practice in natural and
mixed mode ventilation systems. The majority of designs are
based on cross flow.

Source: VENT Dis. Course, Distant learning vocational training material for the promotion of best practice
27
. ventilation energy performance in buildings, Module 1: Natural and Hybrid Ventilation

Natural ventilation strategies

Wind Tower or
Wind Catcher

Advantages:
Air is drawn in at high level where pollutant concentration is usually lower than at
street level;
Can be integrated with a mixed mode fan to ensure reliable operation under low wind
speed conditions;
Possible to supply air into deep plan spaces.
Disadvantages:
Reliable wind force is required unless combined with mixed mode;
Can usually only provide fresh air to single or two storey buildings;
Possible conflict with stack driven ventilation;
Cold draughts are possible in winter periods.

Stack Ventilation

Atrium Ventilation

Advantages:
Provides good winter driving force in cold climates;
Can relieve the problem of single sided ventilation by providing stacks
in the interior of the building;
Can be used in conjunction with wind induced ventilation by locating the
roof termination in the negative pressure region generated by the wind
(See Section 5).
Disadvantages:
Each room should be individually ducted since Shared ducts may result
in cross contamination between zones;
Potential for reverse flow (downdraught) if the column of air in the
stack becomes cold;
Requires a temperature differential between inside and outside.

Advantages:
Provides an extract driving force on the core of the building to drive cross flow ventilation through
surrounding offices.
The zone above the occupied area can trap waste heat which can be further used to add to the stack
driving force.
Disadvantages: Flow can be upset by wind forces.
28

Source: VENT Dis. Course, Distant learning vocational training material for the promotion of best practice ventilation energy
performance in buildings, Module 1: Natural and Hybrid Ventilation

BRE Office Building, Watford, UK

Case studies

Year of completion:1996
Type of building: Office
Site: Urban
Project Manager: Bernard Williams and Associates
Architect : Feilden Clegg Bradley Architects
Services Engineers: Max Fordham and Partners

Key Features:
Single sided, cross flow and stack
ventilation for air quality and cooling;

Fig.18

Optional occupant controlled openable windows;

Solar heated fan assisted stack and wind driven design for first two floors;
Good internal air contact with thermal mass through hollow sinusoidal concrete
ceiling elements;
BEMs controlled openings of stack vents to control cooling and air quality;
Cellular and open plan offices;
Daylighting and low energy lighting;
Active external solar shading;
Some groundwater cooling;
BEMS system controls air quality and night cooling ventilation;
Air change rates as high as 30 h-1 could be achieved to meet cooling needs;
The top floor of the building was separately ventilated by cross flow, wind and
stack action.
Source: http://www.feildenclegg.com
Source: The Environmental Building, Case Study by Clayton Harrison, Spring 2006

29

BRE Office Building, Watford, UK

Case studies

Ventilation & Cooling

five cooling stacks towering over the south side of the building which hint at the
building's complex ventilation system that takes advantage of the buildings narrow
layout for cross-ventilation purposes;
the curved, hollow, concrete floor slabs also aid in the buildings ventilation by
drawing air in through the passages in the floor/ceiling on hot, windy days;
cooling can be managed also by circulating water through the passages in the
curving slab;
this cold water is supplied by a 70-meter-deep bore hole where the temperature is
a constant 10 Celsius.
this cold water is used in heat exchangers to chill circulatory water;
the floor can also then use the water to store coolness from the
night for the next day. In the winter time, the water is heated by
condensing gas boilers that are 30% more efficient than traditional
boilers by recovering heat lost in flue gases. All heating and cooling
systems are managed by the Trend building management system
(BMS).

Source: http://www.feildenclegg.com
Source: The Environmental Building, Case Study by Clayton Harrison, Spring 2006

30

BRE Office Building, Watford, UK

Case studies

Solar Control and Daylighting

the buildings glazing is optimized by a louvered exterior shading

system that is designed to allow maximum daylighting while minimizing
glare;
the louvers in the shading system have a translucent ceramic coating
on their underside to filter direct sunlight as it reflects off it;
the louvers change position corresponding to the time of day and
season; they are controlled by the automated functions of the BMS,
but can be overridden by occupants via a remote control;
the louvers are oriented so the views of the occupants are not
obstructed while either seated at desks or standing in circulation
spaces.
Fig. 19 a,b

Source: The Environmental Building, Case Study by Clayton Harrison, Spring 2006

31

Case studies

BRE Office Building, Watford, UK

Statistics and Studies

Building Area: 2,200 m2

Site Area: 6,400 m2
Density: 100 people @ 12 m2 /person
Energy Use Predicted Total:
83 KWhr/ m2 /annum
(0.3GJ/m2/annum)
Heating: 47 kW/h/ m2 /annum
Artificial lighting: 9 kW/h/ m2 /annum
Cooling: 2-3.5 kW/h/ m2 /annum
Mech Vent: 0.5 kW/h/ m2 /annum
General elec: 23 kW/h/ m2 /annum

Monitoring in winter and

summer showed that design
conditions were fully satisfied;
During hot weather the
inside
air
temperature
remained
at
between
approximately 3-5 K below the
outdoor peak temperature;
The inside peak design
temperature of 28C was not
exceeded.
Source: The Environmental Building, Case Study by Clayton Harrison, Spring 2006

32

Lecture 3 : Mechanical
(forced) ventilation
Zoltn MAGYAR, PhD
Department of Building Energetics and Building Service Engineering

Summary
Supply-Only ventilation system (SOV)

Extract-Only ventilation system

A- Mechanical extract ventilation (MEV)
B-Intermittent extract fans and background ventilators

Balanced ventilation system

A-Single room heat recovery ventilators (SRHRVs)
B-Whole house mechanical ventilation with heat recovery (MVHR)

Fans
Design criteria
Air filters

Supply-Only ventilation system

4 basic types of ventilation systems

Natural exhaust
No.
Type of air
in fig
1
outdoor air
Natural

Natural

SupplyOnly

Mechanical
supply

supply
ExtractOnly

Mechanical

Balanced

2
3
4
5
6
7
8

exhaust
Various air
flows in a
mechanical
ventilation
system (EN
13779).

9
10
11
12

Definition

air taken into the air handling system or

opening from outdoors before any air
treatment
supply air
airflow entering the treated room, or air
entering the system after any treatment
indoor air
air in the treated room or zone
transferred indoor air which passes from the treated
air
room to another treated room usually
adjacent rooms
extract air
the airflow leaving the treated room
recirculation extract air that is returned to the air
air
treatment system
exhaust air airflow discharged to the atmosphere.
secondary
airflow taken from a room and returned to
air
the same room after any treatment
(example: fancoil unit)
leakage
unintended airflow through leakage paths
in the system
infiltration
leakage of air into the building through
leakage paths in the elements of structure
separating it from the outdoor air
exfiltration leakage of air out of the building through
leakage paths in the elements of structure
separating it from the outdoor air
mixed air
air which contains two or more streams of
air

Source: VENT Dis.Course, Distant learning vocational training material for the
promotion of best practice ventilation energy performance in buildings
Module 3: Energy Efficient Mechanical Ventilation

Supply-Only ventilation system

SOV or
Positive input ventilation (PIV)

Particularities:
PIV consists of a fan to
supply air to spaces and
ventilation openings in
building envelope to
allow air to flow out of
the building;
Filtration of the
incoming air;
Can be used in a
polluted and noisy
environment
Adequate when the
occupants are
sensible of exterior
contaminates

house

Fig.1

apartment building

office building

Source: Guide pratique La ventilation mchanique des habitation

Supply-Only ventilation system

Description
A fan, typically mounted in the roof space, supplies
air into the dwelling via central hallway or landing.
This creates a slight positive pressure in the dwelling

Control
The systems deliver a continuous flow of air to the
dwelling;
Fan speed can be increased by occupant, or
automatic switching;

Installation
If the fan draws air directly from the roof space,

Fig.2

it will depressurize the roof space relative to the rest of the house

upstairs

ceiling has to be airtight;

the roof space needs to be adequately ventilated from outside

Maintenance
occasional cleaning is necessary;
intake filters (fitted to most units) will need occasional cleaning/replacement.
Source: Energy efficient ventilation in dwellings a guide for specifiers (2006 edition)

Extract-Only ventilation system

A - Mechanical extract ventilation (MEV)

(MEV) continually extracts air
single-point exhaust systems
multi-point exhaust systems

Advantages
easy to install;
provides continuous low-level
background ventilation;
small negative pressure in
building
prevents moisture
mitigation into the constructions
of external walls and prevents
condensation and consequently
the mould growth;

Disadvantages

Fig.4

requires ducting from wet rooms;

air infiltration through the building envelope creates easily
draught in winter in cold climate;

heat recovery from the exhaust air is not easy to implement;

as the exhaust is usually from kitchens, bathrooms, and
toilets ventilation supply air flow is not evenly distributed in the
bed rooms and living rooms.
Source: Energy efficient ventilation in dwellings a guide for specifiers (2006 edition)
Source: Dr. Sam C. M. Hui, Department of Mechanical Engineering, The University of Hong Kong, lecture
Mechanical and Natural Ventilation, 2011

Extract-Only ventilation system

A - Mechanical extract ventilation (MEV)

SINGLE-POINT EXHAUST
SYSTEMS

System Components:
1) quiet, efficient exhaust ventilation fan
2) several passive wall or window vents
3) programmable timer with speed switch
System Operation:
1) exhaust ventilation fan operates continuously
2) spot fans exhaust air from kitchen and
bathrooms
3) residents can temporarily boost the ventilation
rate.

Fig.5 a,b

Example of a single-point local exhaust

system with makeup air inlets (Oikos
Green Building Source, 1995). Air inlets
are needed only for tight building
envelope

Source: Judy A. Roberson, Richard E. Brown, Jonathan G. Koomey, Steve E. Greenberg, Recommended ventilation strategies for energyefficient production homes, 1998
Source: Marion Russell, Max Sherman and Armin Rudd, Review of Residential Ventilation Technologies , Ernest Orlando Lawrence
Berkeley National Laboratory, 2005

Extract-Only ventilation system

A - Mechanical extract ventilation (MEV)

MULTI-POINT EXHAUST
SYSTEMS

System Components:
1) quiet, efficient multi-port exhaust fan
2) several passive wall or window vents
3) 3-4" diameter ventilation ductwork, grilles
4) programmable timer with speed switch
System Operation:
1) exhaust fan operates continuously on low.
2) bathrooms have exhaust ports instead of spot
fans
3) residents can temporarily boost the ventilation
rate.
Fig.6 a,b,c

Short circuiting
Exhaust

Bedroom
Kitchen

Hall

Perfect mixing

Livingroom

Bedroom

Example of the short

circuiting ventilation
in an apartment with
mechanical exhaust
ventilation

Bathroom
Bad ventilation

Inline exhaust fan with make-up trickle vents

Exhaust

Source: Judy A. Roberson, Richard E. Brown, Jonathan G. Koomey, Steve E. Greenberg, Recommended ventilation strategies for energyefficient production homes, 1998
Source: Marion Russell, Max Sherman and Armin Rudd, Review of Residential Ventilation Technologies , Ernest Orlando Lawrence Berkeley
National Laboratory, 2005
Source: VENT Dis.Course, Distant learning vocational training material for the promotion of best practice ventilation energy performance in
buildings, Module 3: Energy Efficient Mechanical Ventilation

Balanced ventilation system

Balanced ventilation uses a supply fan and an

exhaust fan to regularly exchange indoor air;
both fans move similar volumes of air, so indoor
pressure fluctuates near neutral or "balanced.
From a safety and health perspective, balanced
pressure is better than negative indoor
pressure, but not as beneficial as positive
indoor pressure, which helps keep outdoor
pollutants outdoors !
Particularities:
controlled air flow rates (inlet and outlet)
A Balanced ventilation system
filtration of the inlet air
Types:
possibility of heat recovery
Fig. 7 a,b
With heat recovery
used in a polluted and noisy environment
Without heat recovery
1)

Both can be:

Centralized
Decentralized

Source: Marion Russell, Max Sherman and

Armin Rudd, Review of Residential
Ventilation Technologies , Ernest Orlando
Lawrence Berkeley National Laboratory,
2005
Source: VENT Dis.Course, Distant learning
vocational training material for the
promotion of best practice ventilation
energy performance in buildings, Module 3:
Energy Efficient Mechanical Ventilation

1)Exhaust air
2)Extract air
3) Supply air Ventilation
air in normal operation
4) Heat recovery
exchanger
5)Kitchen exhaust
6) Sound attenuator
7)Outdoor air intake for
ventilation.

7)

6)

2)
2)
5)

4)

Principle of mechanical exhaust and supply

system in a house
9

Balanced ventilation system

Balanced Ventilation with Heat Recovery

Ventilation System Components:
1) HRV unit containing exhaust and
supply fans, and air-to-air heat
exchanger
2) exhaust and supply ducts and
grilles
3) programmable timer with speed
switch

Fig. 8 a,b

Ventilation System Operation:

1) air is supplied to bedrooms, exhausted
from bathrooms;
2) sensible heat is recovered from exhausted
indoor air;
3) residents can temporarily boost the
ventilation rate.
Source: Judy A. Roberson, Richard E. Brown, Jonathan G. Koomey, Steve E. Greenberg, recommended ventilation strategies for energyefficient production homes, 1998
Source: VENT Dis.Course, Distant learning vocational training material for the promotion of best practice ventilation energy performance in
buildings, Module 3: Energy Efficient Mechanical Ventilation

10

Balanced ventilation system

Centralized mechanical supply

and exhaust system with heat
recovery in an apartment
building

Decentralized mechanical supply

and exhaust ventilation system
with heat recovery in an
apartment building
Fig.10 a,b

ventilation is easier to control

by demand
the number of components
requiring maintenance is higher

better heat recovery

efficiency
more complex control

Source: Jacob Verhaart, Balanced Ventilation System Part of the problem or part of the solution?, Final Report, 2010
Source: VENT Dis.Course, Distant learning vocational training material for the promotion of best practice ventilation energy
performance in buildings, Module 3: Energy Efficient Mechanical Ventilation

11

Balanced ventilation system

B-Whole house mechanical ventilation with

heat recovery (MVHR)

the most common ones are cross-flow and counterflow air to air HE;
in cross-flow exchangers, the airflows through the different layers flow perpendicular to each
other;
more effective then a cross-flow exchanger is the counterflow HE; the two streams flow in opposite
directions
temperature difference as large as possible; disadvantage
the pipes have to cross
at one end and the inlet as well as the exit pipes need to be connected with the exchanger in between;
when designing a BVS, there is always a trade-off between heat transfer, which needs to be as high
as possible, size (preferably as compact as possible to reduce costs) and electricity use;
electricity use by the ventilators is related to the drag of the HE;
more drag with a finer mesh of channels, but a finer mesh also means a more effective heat
transfer;
there is a disadvantage in using a direct air-to-air HE; warmer air can contain more moisture, before
it is saturated. When this air is cooled off in the HE, moisture can condense inside the exchanger!!
this can cause damage, because the walls in heat exchangers are thin for maximum efficiency, which
make them fragile;
in older systems, the ventilation air by-passes the HE, when there is a risk of freezing;
in modern systems outside air is mixed with air from inside the house, to pre-heat it till there is no
risk of freezing.
Fig.11 a,b,c

Fig. 12

Source: Jacob Verhaart, Balanced Ventilation System Part of the problem or part of the solution?, Final Report, 2010
Source: Energy efficient ventilation in dwellings a guide for specifiers (2006 edition)
Source: Chiel BOONSTRA, Loes JOOSTEN, TREES Training for RenovatedEnergyEfficient Social housing, Intelligent Energy-Europe
programme, contract nEIE/05/110/SI2.420021, Section 1 Techniques 1.3 Ventilation

Balanced ventilation system

Large Heat Recovery Systems

heat is stored in solid heat batteries
metal (mostly
aluminium or copper) mesh of small channels, through which the
air can flow
the smaller the channels, the larger the surface area for heat
transfer, and the larger the aerodynamic drag;
heat wheel
a honeycomb mesh made of heat storing
material rotates through the two airflows. First heating up in
the flow out and then releasing that heat in the incoming flow;
a Kantherm system
two heat batteries are stationary and
the airflow through them is alternated via a valve. The valve
changes the direction of the airflow every 50 s. the first 50
seconds, one of the batteries is loading and the other is
releasing heat. The next 50 seconds the roles reverse and the
loaded battery releases its heat and the other battery heats up.
larger systems use solid material in the
heat batteries to temporarily store
heat and reverse the airflow from cold
to hot
the chance of the exchanger
getting damaged by freezing of
condensation
is
much
lower!
Condensation and ice can only built-up
for the period of half a cycle!
installations using solid heat batteries
have typically a lower overall efficiency,
but are better suited for larger
ventilation capacities.

Heat wheel

Fig.13

Kantherm system

Source: Jacob Verhaart, Balanced Ventilation System Part of the problem or part of the solution?, Final Report, 2010

Fig.14

13

Fans and Blowers

Fans
provide air for ventilation and industrial processes that need air flow
The factors to consider when
selecting a fan include:
Redundancy a single fan or
multiple fans;
Duty CFM and static
pressure at design conditions;
First cost more efficient
fans are often more
expensive;
Space constraints a tight
space may limit fan choices;
Efficiency varies greatly
by type and sizing;
Noise different fan types
have different acoustic
performance;
Surge some fan selections
are more likely to operate in
surge at part-load conditions.

Turning Vanes
(typically used
on short
radius
elbows)

Outlet
Diffusers

Heat
Exchanger
Baffles

Filter

Inlet
Vanes

Motor
Controller
Centrifugal Fan

Variable Frequency Drive

Motor

Belt Drive

Fig.15

Source: Advanced Variable Air Volume System design Guide, 2007

Source: www.energyefficiencyasia.org

Fans and Blowers

Fans laws

Fig.16
Source:

Fans & Blowers, Presentation from the Energy Efficiency Guide for Industry in Asia, www.energyefficiencyasia.org

Fans

Fans and Blowers

the performance of a fan is described by a FAN CURVE that relates the

static pressure increase across a fan to the airflow rate through the fan at
a constant fan speed in revolutions per minute (rpm).
Fig.17 a,b
Set of Fan Curves

System Curve

Air pressure decreases through the ventilation system, and this pressure
drop is equal to the total airflow resistance of all the system components
and the ductwork. This pressure drop depends on the airflow rate and is
described by a SYSTEM CURVE
The SYSTEM CURVE is affected by changes in damper position, dirty
filters, condensation on coils, holes in ductwork and obstruction of outlets or
inlets.

Source: Andrew K. Persily, Manual for Ventilation Assessment in Mechanically Ventilated Commercial Buildings, 1994, Building and Fire Research
Laboratory National Institute of Standards and Technology, Gaithersburg, MD 20899

Systems functioning

Fans and Blowers

The intersection of the system curve and the fan performance curve defines the point at
which the pressure across the fan and through the system are equal, and thereby defines the
airflow rate;
If the airflow resistance of the system is accurately estimated during the design and the fan
is properly selected and installed, then the point of intersection will be at the design airflow
rate of the system;
If the system resistance increases, then a new system curve S replaces the original system
curve S; the fan and system curves will intersect at a higher pressure difference and a lower
airflow rate; the airflow rate can be returned to its design value by increasing the fan speed,
such that a new fan curve F is in effect.
Interaction Between System and Fan Curves
Fig.17 c

Source: Andrew K. Persily, Manual for Ventilation Assessment in Mechanically Ventilated Commercial Buildings, 1994, Building and Fire Research
Laboratory National Institute of Standards and Technology, Gaithersburg, MD 20899

Fans and Blowers

Fan classification

Backward inclined
Forward
inclined
Fig.18 a,b,c,d,e,f

Roof-top
Axial
Mixed flow

Source: Advanced Variable Air Volume System design Guide, 2007

Design criteria

BASIC DESIGN TECHNIQUES

1. Design the air distribution system to minimize flow resistance and

turbulence. High flow resistance increases the required fan pressure, which
results in higher noise being generated by the fan. Turbulence increases the
flow noise generated by duct fittings and dampers in the air distribution
system, especially at low frequencies.
2. Select a fan to operate as near as possible to its rated peak efficiency
when handling the required quantity of air and static pressure. Also, select a
fan that generates the lowest possible noise but still meets the required
design conditions for which it is selected. Using an oversized or undersized
fan that does not operate at or near rated peak efficiency can result in
substantially higher noise levels.
3. Design duct connections at both the fan inlet and outlet for uniform and
straight air flow. Failure to do this can result in severe turbulence at the fan
inlet and outlet and in flow separation at the fan blades. Both of these can
significantly increase the noise generated by the fan.
4. Select duct silencers that do not significantly increase the required fan
total static pressure. Duct silencers can significantly increase the required
fan static pressure if improperly selected. Selecting silencers with static
pressure losses of 87 Pa. or less can minimize silencer airflow regenerated
noise.
5. Place fan-powered mixing boxes associated with variable-volume air
distribution systems away from noise-sensitive areas.
19
Source: Chapter 46 of the 1999 ASHRAE Handbook Applications

Design criteria

BASIC DESIGN TECHNIQUES

6. Minimize flow-generated noise by elbows or duct branch takeoffs,
whenever possible, by locating them at least four to five duct diameters
from each other. For high velocity systems, it may be necessary to increase
this distance to up to ten duct diameters in critical noise areas.
7. Keep airflow velocity in the duct as low as possible (7.5 m/s or less) near
critical noise areas by expanding the duct cross-section area. Flow
separation, resulting from expansion angles greater than 15, may produce
rumble noise. Expanding the duct cross-section area will reduce potential
flow noise associated with turbulence in these areas.
8. Use turning vanes in large 90 rectangular elbows and branch takeoffs.
9. Place grilles, diffusers and registers into occupied spaces as far as
possible from elbows and branch takeoffs.
10. Minimize the use of volume dampers near grills, diffusers and registers in
acoustically critical situations.
11. Vibration isolate all vibrating reciprocating and rotating equipment if
mechanical equipment is located on upper floors or is roof-mounted. Also, it
is usually necessary to vibration isolate the mechanical equipment that is
located in the basement of a building as well as piping supported from the
ceiling slab of a basement, directly below tenant space. It may be necessary
to use flexible piping connectors and flexible electrical conduit between
rotating or reciprocating equipment and pipes and ducts that are connected
to the equipment.
20
Source: Chapter 46 of the 1999 ASHRAE Handbook Applications

Design criteria

BASIC DESIGN TECHNIQUES

12. Vibration isolate ducts and pipes, using spring and/or neoprene hangers
for at least the first 15 m from the vibration-isolated equipment.
13. Use barriers near outdoor equipment when noise associated with the
equipment will disturb adjacent properties if barriers are not used. In normal
practice, barriers typically produce no more than 15 dB of sound attenuation
in the mid frequency range.

21
Source: Chapter 46 of the 1999 ASHRAE Handbook Applications

TYPES AND PERFORMANCE

Air filters

Fig.24
VISCOUS IMPINGEMENT FILTERS
panel filters made up of coarse fibers with a high

porosity;
the filter media are coated with a viscous substance,
such as oil which causes particles that impinge on the fibers
to stick to them;
design air velocity through the media is usually in the
range of 1 to 4 m/s;
low pressure drop, low cost, and good efficiency on lint
but low efficiency on normal atmospheric dust!
this type of filter is commonly used in residential
furnaces and air conditioning and is often used as a prefilter for higher-efficiency filters.

DRY EXTENDED-SURFACE FILTERS

media of random fiber mats or blankets of varying

thicknesses, fiber sizes, and densities;
media in these filters are frequently supported by a wire frame in the
form of pockets, or V-shaped or radial pleats;
efficiency is usually higher than that of panel filters, and the variety
of media available makes it possible to furnish almost any degree of
cleaning efficiency desired;
media velocities range from 0.03 to 0.5 m/s, although approach velocities
run to 4 m/s.

Source: Chapter 24 of the 2000 ASHRAE Handbook Systems and Equipment

TYPES AND PERFORMANCE

Air filters

VERY HIGH-EFFICIENCY DRY FILTERS

HEPA (high-efficiency particulate air) filters

ULPA (ultralow-penetration air)
filters are made in an extended-surface configuration of deep space
folds of submicrometre glass fiber paper;
operate at duct velocities near 1.3 m/s, with resistance rising from 120
to more than 500 Pa over their service life;
are the standard for clean room, nuclear, and toxic particulate
applications.

MEMBRANE FILTERS

are used mainly for air sampling and specialized small-scale applications
where their particular characteristics compensate for their fragility, high
resistance, and high cost;
available in many pore diameters and resistances and in flat sheet and
pleated forms.

ELECTRET FILTERS

composed of electrostatically charged fibers;

the charges on the fibers augment collection of smaller particles by
interception and diffusion (Brownian motion) with Coulomb forces caused by
the charges;
there are three types of these filters: resin wool, electret, and an
electrostatically sprayed polymer;
efficiency of charged-fiber filters is determined by both the normal
collection mechanisms of a media filter and the strong local electrostatic
effects;.
Source: Chapter 24 of the 2000 ASHRAE Handbook Systems and Equipment

TYPES AND PERFORMANCE

Air filters

RENEWABLE-MEDIA FILTERS
(1) moving curtain viscous impingement filters
the resistance remains approximately constant as long as proper
operation is maintained. A resistance of 100 to 125 Pa at a face
velocity of 2.5 m/s is typical of this class;
(2) moving-curtain dry media roll filter
operating duct velocities near 1 m/s are generally lower than those
of viscous impingement filters
ELECTRONIC AIR CLEANERS
can remove and collect airborne contaminants with an initial
efficiency of up to 98% at low airflow velocities (0.8 to 1.8 m/s)
when tested according to ASHRAE Standard 52.1;
Efficiency decreases:
(1) as the collecting plates
become loaded with particulates
(2) with higher velocities
(3) with nonuniform velocity.
Fig.25
Source: Chapter 24 of the 2000 ASHRAE Handbook Systems
and Equipment

Air filters

SELECTION AND MAINTENANCE

the following factors should be considered:

Degree and type of air cleanliness required
Disposal of dust after it is removed from the air
Amount and type of dust in the air to be filtered
Operating resistance to airflow (pressure drop)
Space available for filtration equipment
Cost of maintaining or replacing filters
Initial cost of the system

Fig.26

The performance of different filter media is normally as follows:

Flat panel type (disposable filters): air velocity 0.11.0 m s-1, resistance 25250 N m-2,
efficiency 2035%
Continuous roll (self cleaning filters): air velocity 2.5 m s-1, resistance 30175 N m-2,
efficiency 25%
Bag filters: efficiency 4090%
HEPA filters: efficiency 99.97% for 0.3 micron particles and larger
ULPA filters: efficiency 99.9997 for 0.12 micron particles or larger
Viscous filters panel type (cloth with viscous fluid coating: washable or disposable);
plates about 500 500 mm, air velocity 1.52.5 m s-1, resistance 20150 N m-2
Viscous filters (Continuous roll - continuously moving, self cleaning). Air velocity 2.5 m
s-1, resistance 30175 N m-2
Electrostatic precipitators. Cleaned automatically, air velocity 1.52.5 m s-1, resistance
negligible, efficiency 3040%
Absolute. Dry panel with special coating: disposable or self cleaning, air velocity 2.5 m
s-1, resistance 250625 N m-2
Source: Chapter 24 of the 2000 ASHRAE Handbook Systems and Equipment
Source: B. Purushothama , Humidification and ventilation management in textile industry, Woodhead Publishing India (P) Ltd, 2009

25