N
Natural Ventilation in Built
Environment
Tong Yang1 and Derek J. Clements-Croome2,3
1
Department of Design Engineering and
Mathematics, Faculty of Science and Technology,
Middlesex University, London, UK
2
School of Construction Management and
Engineering, University of Reading, Reading, UK
3
School of Engineering and Materials Science,
Queen Mary University of London, London, UK
Article Outline
Glossary
Definition of the Subject
Introduction
Vernacular Architecture
Natural Ventilation Principles
Natural Ventilation Design Requirements
Design Guidelines for Natural Ventilation
Mixed Mode: The Selection of Ventilation
Strategies
Natural Ventilation and Mixed-Mode Case
Studies
Future Directions
References
Glossary
Advanced natural ventilation system (ANV)
Integration of basic natural ventilation strategies such as cross ventilation and stack effect
with smart controls.
Air changes per hour (ACH) The volumetric
flow rate of supply air, divided by the volume
of the ventilated space.
BEMS Building energy management system.
BREEAM Building research establishment
environmental assessment method – UK
origin.
Exfiltration/infiltration Air flows through
unintended leakages out/into buildings.
Hybrid ventilation Combined natural and
mechanical ventilation (also called mixedmode ventilation).
Indoor air quality (IAQ) Broadly defined by
the purity of the air but often CO2 is used as
an indicator.
Mixed-mode ventilation See hybrid ventilation.
Natural ventilation Use of natural forces, i.e.,
pressure differences generated by wind or air
temperature, to introduce and distribute outdoor air into or out of buildings.
Night cooling The use of night air to cool the
building using wind towers or a fan to circulate
the air.
Thermal comfort The state of mind that
expresses satisfaction with the surrounding
thermal environment.
# Crown 2018
R. A. Meyers (ed.), Encyclopedia of Sustainability Science and Technology,
https://doi.org/10.1007/978-1-4939-2493-6_488-3
2
Ventilation Provides fresh air into a building to
ensure good air quality for occupant health and
well-being.
Ventilation effectiveness The ability of a ventilation system to exchange the air in the room
and also the ability to remove airborne
contaminants.
Ventilation flow rate The amount of air per unit
time into the ventilated space (liter per second
or l/s, cubic meters per hour or m3/h).
Well-being Healthy mind and body.
Definition of the Subject
Natural ventilation uses the natural forces of wind
and buoyancy to introduce fresh air and distribute
it effectively in buildings for the benefit of the
occupants. Fresh air is required to achieve a
healthy, fresh, and comfortable indoor environment for people to work and live in. Natural ventilation can ensure or support the supply of
adequate breathing air, adequate ventilation of
contaminants, and adequate thermal conditioning
and moisture dissipation and contribute to wellbeing through a connection to the dynamics of
nature. For natural ventilation to be effective,
there has to be a close relationship between the
architecture and the air circulation system. This
includes the relationship between the built form,
the site environment in a particular location, and
the layout within the building.
The Natural History Museum in London,
designed by Alfred Waterhouse in the Victorian
age, is an excellent example of design for natural
ventilation. The architect designed the built form
to encourage the flow of air through each space in
the building by the use of two ventilation towers at
the back of the building to induce airflow through
stack ventilation [1]. Buildings should be
designed to take full advantage of the prevailing
natural forces such as wind, outdoor temperature,
and sunlight, incorporating building elements
such as towers, atria, and thermal mass to ventilate
and cool occupied spaces. In many climates there
is a growing proportion of naturally ventilated
buildings using natural features and forces to
Natural Ventilation in Built Environment
reduce a building’s environmental or carbon
footprint.
Introduction
The reasons for ventilating a space with air are as
follows:
1. Ventilation air provides oxygen that is needed
for human life processes; it takes about 4 s for
inhaled air to pass through the respiratory system and transfer oxygen to the blood and then
to the brain; poor-quality air that is deficient in
oxygen with consequent high CO2 levels
impedes clear thinking and concentration.
2. Ventilation air dilutes; the contaminants may
be CO2 from respiration, odors secreted
through the human skin, cigarette smoke, or
emissions from other processes such as dust,
allergens, aerosols, toxic gases, and particulates in general.
3. Ventilation promotes and directs air movement
in the space, removing excessive heat and/or
moisture essential for comfort and well-being.
Traditional vernacular architecture has taught
us the best of sustainable architecture and ecologically sensitive adaptation, using passive features
ranging from building orientation and form to
appropriately sized and oriented openings that
are linked with vertical spaces, to ensure the benefits of natural ventilation, including the use of
local materials and mass for night cooling, and the
siting of buildings in context to ensure effective
airflows.
Vernacular Architecture
Vernacular architecture blends buildings into their
specific settings, so that there is a natural harmony
between the climate, architecture, and people.
Vernacular architecture learned from the environmental variations of place relating to local variations in temperature, humidity, sun, wind, rain,
earthquakes, and storms. In climates where the
diurnal range may be 17 C, vernacular buildings
Natural Ventilation in Built Environment
reduce the variation in indoor temperature to 4 C
through time lag and night cooling. In climates
where humidity may be 90%, vernacular buildings support human comfort by allowing air to
flow over the many thermoreceptors on the human
body. Vernacular architecture is also adapted to
ensure indoor air quality through natural ventilation with the careful design and placement of
indoor pollutant generators from stoves to commodes. Four vernacular solutions are further
described: wind towers, courtyards, termite
mounds, and igloos, each integrating the conditioning power of natural ventilation in unique
responses to local climate.
Wind Towers
The wind towers or bagdirs are a distinctive and
ancient feature of Islamic architecture. It has been
used for centuries to create natural ventilation in
buildings. Examples of wind towers (Fig. 1) can
be found throughout the Middle East, Pakistan,
and Afghanistan and now are sometimes incorporated into Western architecture.
Wind flowing around a building causes a separation of flows which creates a positive pressure
on the windward side and a negative pressure on
the leeward side of the building. Due to its height,
the wind tower enhances the positive pressure on
the windward side; it is then directed through the
tower into the building. Airflow follows the pressure gradients within the structure and exits
through purposely designed openings and through
the leeward side of the tower. The size and location of openings (e.g., windows, doors, etc.) and
distribution of internal party walls have a great
impact on encouraging cross flow and mixing of
the indoor air.
In addition to the pressure-induced flows, the
principal factor in wind towers is buoyancy which
depends on the temperature difference and the
height. During the day the sun heats up the structure warming the internal air which then rises
through the wind tower, as illustrated in Fig. 1.
At night the cool night air lowers the temperature
of the structure and the internal air and the heavier
air then flows downward, cooling the internal
spaces after the heat of the day. Figure 2 shows
3
how wind towers can also provide natural cooling
for underground water cisterns.
Courtyards
Courtyards are one of the oldest plan forms for
dwellings going back thousands of years and
appearing as a distinctive form in many regions
in the world. Examples exist in Latin America,
China, the Middle East, Mediterranean, and in
Europe. Preserving the basic typology of the
courtyard, local climate, and culture has created
a unique style for each region.
The courtyard house called siheyuan is a typical form in ancient Chinese architecture, especially in Northern China. It offers space,
comfort, quiet, and privacy. A siheyuan consists
of a rectangle with a row of houses bordering each
side around a courtyard, normally with a southern
orientation and having the only gate usually situated in the southeast side. Walls protect the houses
from the harsh winter winds and from the spring
dust storms that frequently occur in Northern
China from the Gobi Desert in Mongolia. The
house’s deep eaves provide cooling shade and
protection from the summer rains while allowing
the winter sun’s warmth to be captured in the
rooms. Their design reflects the traditions of
China, following the rules of feng shui and Confucian tenets of order and hierarchy.
All the rooms around the courtyard have doors
and large windows facing onto the yard and small
windows high up on the back wall facing out onto
the street. Ridged roof tops provide shade in the
summer and retain warmth in the winter. The
verandah divides the courtyard into several big
and small spaces that are closely connected, providing a common place for people to relax whatever the weather. The courtyard is an open-air
living room and garden with plants, rocks, and
flowers, for family members to chat and gather.
In cold Northern China, courtyards are built
broad and large to increase the exposure to sunlight, and there are more open areas inside the
courtyard walls for daylight, fresh air, and rainwater capture for plants and gardens. In hot Southern China, the courtyard houses (Fig. 3) are built
with multiple stories to encourage cross ventilation flow incorporating natural cooling effects.
4
Natural Ventilation in Built Environment
1
Air Flow(Day)
2
Roof
3
4
Hall
5
Ground
Level
6
Air
Flow
(Night:No Wind)
Basement
Natural Ventilation in Built Environment, Fig. 1 Bagdir in Dubai, in United Arab Emirates [2]
Wind
Ground
Wind
Door
Wind
Tunnel
Foundation basement
Combination of sensible and evaporative cooling
Natural Ventilation in Built Environment, Fig. 2 Wind towers in Yazd, Iran, to ventilate houses, are also constructed
to cool underground cisterns (water reservoir) [3]
The orientation of houses is not strictly northsouth aligned, but follows the local topology of
hills and easy access to water sources.
Lessons from Nature: Termite Mounds or
Termitaries
Termites are an outstanding example in the animal
kingdom of ingenious animal architects as master
Natural Ventilation in Built Environment
Natural Ventilation in Built Environment, Fig. 3 A
typical courtyard house in Southern China (Image credit:
Beifan Yang, Tianjin Weland Landscape Architecture
Design Co., Ltd.)
builders. Over 2000 species of termites live in
tropical and subtropical regions and have shown
us by analogy the art of designing for living in a
variety of dwelling styles with natural ventilation.
Termites build their nest so as to achieve automatic ventilation to regulate the internal temperature, as well as constantly managing control of gas
exchange and moisture level. They do not keep a
set temperature, but allow a gradual change
between the seasons determined by the external
environmental temperature.
In Australia, compass termites build largesized mounds in the form of huge, flat chiselshaped blades, with their long axis pointing
north-south. This arrangement exposes the minimum possible area to the midday sun but allows
the mounds to catch the rays of the early morning
and late evening sun, when the termites need
warmth, especially in the cold season; peak temperatures can be lowered by about 7 C with N-S
orientation and thus maintain a preferred temperature of 30–32 C [4].
There are two main types of termite mounds:
(1) the open ventilation mounds which let air flow
into or out through chimneys or holes built into
5
the mounds and (2) the completely enclosed
mounds in which gases are exchanged through
the porous thin-walled tunnels.
The nest of a termite species Apicotermes
gurgulifex is shown in Fig. 4a. It is embedded in
the soil but clothed by a mantle of air. The nest is
constructed from the excrement of the termites so
is well insulated. Its outer wall has a pattern of
raised, ring-shaped configurations which surround an array of precisely spaced and shaped
ventilation slits. These slits link the external and
the internal spaces.
The termitary of the fungus-cultivating termites, Macrotermes bellicosus in Fig. 4b, may
reach a height of 3 or 4 m and contain more than
two million termites. The fungus chambers are
built into complex spongelike structures with
numerous supporting ridges with air ducts. The
air in the fungus chamber is heated by fermentation processes and the metabolic heat generated
by the termites. The hot air rises and enters the
duct systems in the ridges, the walls of which are
porous, allowing carbon dioxide to escape from
the dwelling and oxygen to enter. The cooler air
flows down to the cellar and replaces the rising
warmer air.
Igloos
The Inuit people build igloos as shelters from the
extreme weather conditions in the Arctic. The
igloo (Fig. 5) has excellent thermal performance
without mechanical equipment. The hemispherical shape of the igloo provides the maximum
resistance to winter gales from all directions,
while simultaneously exposing the minimum surface area to heat loss. The dome uses packed snow
blocks, some 500 mm thick, 1000 mm long, and
150 mm wide, which are laid in a continuously
sloping pile. Effectively, the shape encloses the
largest volume with the least material, so it can be
heated by a blubber lamp. Coated by a glaze of ice
on the interior surface, the finished dome is made
stronger and windproof. The interior surface is
also draped with animal skins and furs to prevent
radiant and convective heat loss to the cold floor
and the walls. Measurements have shown that
with no heat source apart from the small blubber
6
Natural Ventilation in Built Environment,
Fig. 4 Ventilation of termite molds. (a) Nest of a termite
species Apicotermes gurgulifex [4]. (b) Longitudinal
Natural Ventilation in Built Environment
section through the nest of Macrotermes bellicosus from
Ivory Coast showing the air being circulated by buoyancy
[4]
Airholes
Cold sink
Sleeping
platform
Natural Ventilation in Built Environment, Fig. 5 Illustration of an igloo (Image credit: Bin Zhang, Tianjin Weland
Landscape Architecture Design Co., Ltd.)
lamp, internal air temperatures are held at levels of
6 to 4 C with external temperatures of 24 and
40 C [5]. At the same time, the combination of
a cold sink inlet and airhole outlets provides critically needed breathing air.
These four illustrations show that traditional
building technologies have evolved and been
adapted over time by people and animals in all
climates to meet thermal comfort and ventilation
needs, accommodating the values, economies,
and the culture-inspired ways of life. However
versatile, they all reflect the basic principles
described in the next section.
Natural Ventilation Principles
The natural forces that drive ventilation can be
wind pressure driven or buoyancy driven where
pressure is generated by the density differences
between indoor and outdoor air.
Wind-Driven Ventilation
Wind is caused by pressure differences in the
atmosphere. The general flow of wind close to
the Earth’s surface is subjected to boundary layer
effects, called the atmospheric boundary layer, in
which wind speed is influenced by the surface
Natural Ventilation in Built Environment
7
Natural Ventilation in Built Environment, Fig. 6 Wind speed variation with height and terrain conditions [7] (Image
credit: Jin Zhang, JINT Design Consultants Ltd.)
Direction of wind
Direction of wind
Roof pitch >30°
Roof pitch <30°
Plan
Section
Section
Section
Natural Ventilation in Built Environment, Fig. 7 Wind pressure distribution on buildings. (a) Wind pressure on
building. (b) Wind pressure on roof [8]
friction of the ground. The variation of wind speed
at different heights and in different terrains is
illustrated in Fig. 6. Wind speed correction coefficients for different terrain conditions in the UK
are listed in the British Standards Institute document BS 5925 [6].
When the path of the wind is impeded by
obstacles, such as trees and buildings, then an
energy conversion takes place. Velocity pressure
is converted to static pressure, so that on the
windward side, an overpressure is produced
(about 0.5–0.8 times the wind velocity), whereas
on the leeward side, an under-pressure results
(about 0.3–0.4 times the wind velocity). The pressure distribution on the roof varies according to
pitch. Figure 7 shows areas of positive and
negative pressures generated by wind normal to
building front: wind-driven flow through inlets on
positive pressure faces and outlets on negative
pressure faces [8]. The pressure differentials arising across a building cause infiltration of air
through window cracks and other openings.
Relative to the static pressure of the free wind,
the pressure on any point on the surface of a
building façade pw can be approximated by the
equation:
pw ¼ 0:5rCp vz 2 ðPa Þ
(1)
where
• Cp
=
wind
(dimensionless)
pressure
coefficient
8
Natural Ventilation in Built Environment
• nz = local wind speed at a specific reference
height z (m/s)
• r = air density (kg/m3)
In order to calculate the ventilation rate due to
the wind, a knowledge of the wind speed and
direction is necessary as well as information
about the nature of wind-stream patterns developed around the building. A summary of the
façade-averaged wind pressure coefficient data
for simple rectangular-plan low-rise buildings in
varying degrees of shelter and wind directions is
given in the AIVC Application Guide: A Guide to
Energy Efficient Ventilation [9].
For buildings with a simple layout, the natural
ventilation airflow rate by wind effect can be
determined as in the following case, with more
examples given in CIBSE Applications Manual
AM 10 [10]:
(a) Wind effect alone for a zone with multicross
flow openings (Fig. 8):
DCp
q ¼ A Cd U 2
0:5
(2)
where
• U is the wind speed measured at the same
height as the building (m/s)
• A is the total ventilation area (m2) – assuming
the four openings are identical
• Cd is the discharge coefficient (typical value
0.6)
• DCp is the difference between wind pressure
coefficient (C p1 and C p2)
Buoyancy-Driven (Stack) Ventilation
Warm air in a room tends to rise because of its low
density. It is replaced by cooler, denser air from
outside. There is a neutral pressure plane where
the pressure difference is zero as shown in Fig. 9.
Since the pressure at the outlet or inlet can be
affected by the wind, the extent to which the
stack effect operates is governed partly by the
wind pressure and partly by the design of the
openings and the internal layout.
U
A/2
q/2
q/2
A/2
Cp2
Cp1
Natural Ventilation in Built Environment,
Fig. 8 Cross ventilation driven by wind effect alone
For buildings with a simple layout, the natural
ventilation airflow rate by buoyancy effect can be
determined as illustrated in the following example
[10]:
Buoyancy effect alone for a single-opening
zone (Fig. 10):
q¼h
A Cd
i0:5
ðT i þ273Þ
DTgh
(3)
where
• q is the ventilation flow rate (m3/s)
• Ti is the internal temperature ( C)
• DT is the difference between the internal and
external air temperature (K)
• A is the opening area (m2)
• h is the opening height (m)
• Cd is the discharge coefficient (0.25 for
single-opening)
• g is acceleration due to gravity (m/s2)
In spaces where cross ventilation is not feasible, stack ventilation works best with high ceilings, atria, or chimneys (Fig. 11).
An atrium is a variant of stack ventilation principle (Fig. 12). It draws air from both sides of the
building toward a central extract point, doubling
the natural ventilation effective width in the
building.
A well-designed double-skin façade provides
buildings with additional protective layers from
the outdoor environment, improves thermal and
Natural Ventilation in Built Environment
Natural Ventilation in
Built Environment,
Fig. 9 Stack pressure
distribution between two
vertically placed openings
[9, p. 214]
9
A
Text
H2
Tint
Neutral pressure
plane
B
H1
Natural Ventilation in
Built Environment,
Fig. 10 Single-sided
ventilation, single-opening,
driven by buoyancy alone
Pressure
Internal
pressure
gradient
External
pressure
gradient
ΔT
q
A
h
q
visual comfort for occupants, and reduces intrusive noise. The double skin can also enclose the
circulation, integrating the internal and external
spaces in the building and providing views to
outside to achieve the harmonious integration of
people and nature.
The Gherkin building (see Fig. 13), 30 St Mary
Axe in the city of London, is naturally ventilated
most of the year through its exterior cladding
consisting of triangular- and diamond-shaped
glass panels. The glazing system contains a
double-glazed outer layer and a single-glazed
inner layer with solar control blinds in the central
ventilated cavity. Fresh air is drawn up through
spiraling light wells enclosed by the openable
double-glazed panels, which also effectively
reduce the need for additional heating and
cooling. The circular tapering shape of the
building and the light wells maximize the amount
of natural light throughout the building and provide views out across the city from deep inside.
When natural forces cannot provide the
required indoor environment conditions, mechanical systems – e.g., fans for increasing ventilation
rate and/or heat exchangers for cooling
(or heating) at peak summer (or winter) times –
can be used to enhance the thermal conditioning
and natural ventilation through purposely
installed openings in the building envelope. This
is known as a mixed-mode or hybrid ventilation
system with pressure sensors and motor-driven
dampers used to give control. Careful considerations in the design and operation as well as enduser education are needed to deliver effective
environmental control with ventilation in hybrid
systems.
10
Natural Ventilation in Built Environment
below 10 l/s per person result in lower air quality
and increased health problems. Ventilation rates
for acceptable indoor air quality are currently
assessed by using the ASHRAE Standard 62.1
[17]. In this standard there are two procedures
for estimating the amount of fresh air required.
The first is referred to as the ventilation rate and is
a prescriptive approach stating a requirement of
10 l/s per person of fresh air in nonsmoking office
environments. The second is a performance
approach, with more detail available given in the
ASHRAE Handbook of Fundamentals [18].
Natural Ventilation in Built Environment,
Fig. 11 Stack ventilation from vertical chimneys [11]
Natural Ventilation for Indoor Air Quality
To obtain breathing air and remove pollutants
from internal spaces, adequate outdoor air
exchange rates are critical. To establish these
rates, a range of pollutants must be addressed
including odors, tobacco smoke, metabolic carbon dioxide, and VOCs.
Body Odors
Natural Ventilation in Built Environment,
Fig. 12 Stack ventilation from atrium [11]
Natural Ventilation Design
Requirements
Fresh Air
Indoor CO2 source is primarily generated through
human metabolism. Human respiration requires a
fresh air rate of 0.1–0.9 l/s per person depending
on the activities (metabolic rate) and clothing
insulation of the occupants [14]. Seppänen et al.
[15] and Wargocki et al. [16] have made a comprehensive review of over 20 studies with over
30,000 persons and found that ventilation rates
A human being’s sense of smell permits very low
concentrations of odors. The sensitivity varies
between individuals. In a typical indoor environment, around 500 out of 6000 compounds of
concern are human bioeffluents [19]. Poor-quality
air is usually referred to as being stuffy, stale,
close, heavy, or lacking in freshness. Inhaled air
comes into contact with the nasal passages and
then the respiratory tissue; in each case the motion
of the olfactory hairs, and of the cilia on the
respiratory membrane, is affected by temperature,
humidity, dirt, odors, and also ions [20]. Body
odors are often the indication of poor ventilation
to building occupants.
Environmental Tobacco Smoke
Environmental tobacco smoke contains more than
4000 chemicals, and at least 50 of these chemicals
are known to be cancer-causing substances [21]. It
generates about 2 ppm CO, leads to irritation and
discomfort among 20% of those exposed, and is
also suspected to increase the risk of lung cancer
[22]. Based on a study on the rates of hospital
admissions for heart attacks before and after the
smoking ban was introduced in England on July
01, 2007, there was a clear association between
Natural Ventilation in Built Environment
11
Natural Ventilation
Blinds intelligently automatically
controlled by BMS
40.0
49.0
38.0
37.0
36.0
35.0
34.0
33.0
32.0
31.0
30.0
29.0
28.0
27.0
26.0
25.0
24.0
23.0
22.0
21.0
20.0
30 1/s/m
Extract Rate
Temp°C
45
Predicted performance:
40
85% solar protection
35
50% light transmission
30
0.8 W/m2K thermal insulation
25
60 1/s/m
Extract Rate
20
Fresh air
left over
Natural Ventilation in Built Environment,
Fig. 13 Gherkin, London, and ventilation through light
wells and double-skin façade. (a) Gherkin façade [12] and
natural ventilation concept [13]. (b) Gherkin double-skin
façade design [13] (Source: Matt Kitson, Hilson Moran)
the smoking ban and a 2.4% reduction (or 1200
fewer admissions due to a heart attack) in the
12 months following the ban [23].
produces approximately 0.0051 l/s (18 l/h) of
CO2 by respiration when performing light office
duties [6]. Younger people such as infants and
primary school children have lower emission
rates, but they are likely to be more active and
may well have CO2 production at similar levels
[22]. Normally, in buildings, CO2 concentrations
Metabolic Carbon Dioxide
An average sedentary adult (metabolic rate
M = 70 W/m2 and body area A = 1.8 m2)
12
below 0.1% (1000 ppm) are required to avoid
discomfort and headaches [24]. According to the
Canadian Centre for Occupational Health and
Safety [25] and ASHRAE standards [17], health
effects can become acute at higher exposure
levels.
Increased CO2 content of the external atmosphere causes the decreased pH value of the blood
[26]. Metabolism is very sensitive to body fluid
pH value. The health concerns of CO2 is another
reason besides global warming, for why the atmosphere CO2 concentration should be limited to
<426 ppm [20].
Volatile Organic Compounds (VOCs)
Thousands of chemical compounds have been
identified in the indoor environment. The most
common pollutants are given in ASHRAE Standard 62.1-2010 and Health and Safety Directives
[17, 27]. Contaminants such as formaldehyde,
toluene, volatile organic compounds (VOCs),
allergens, and radon can accumulate in poorly
ventilated buildings, causing health problems.
Complex mixtures of organic chemicals in indoor
air also have the potential to invoke subtle effects
on the central and peripheral nervous system,
leading to changes in behavior and performance
[28]. The latest overview on knowledge and
research outcomes concerning the relationships
between indoor air pollutants and health effects
by Brown, Holmes, and Harrison highlights critically needed research directions [29]:
• Development of validated measuring methods
• Establishment of dose-response relationships
• Development of risk indicators for multiple
exposures
Ventilation Effectiveness
Ventilation effectiveness is an indicator of how
efficiently supplied fresh air is mixed and distributed in the occupied space, related to both the
dilution and removal of indoor airborne contaminants [30]. Gan [31] used airflow pattern, air temperature, and local mean age of air (i.e., the
average time for air to travel from an inlet to any
point in a room set equal to the room volume
divided by the air supply rate) to determine the
Natural Ventilation in Built Environment
effective depth of fresh air distribution in a naturally ventilated space. CFD predictions show that
the width and height of window openings, room
heat gains, and outdoor air temperature have combined effects in determining the maximum room
depth for effective fresh air distribution in singlesided natural ventilation. For summer cooling
requirements, thermal comfort may displace
indoor air quality as the determining factor in
design. Instead of contaminant concentrations
for effectiveness measures [32], Coffey and Hunt
[33] proposed to measure the active buoyancy
(e.g., the heat or coolth) removal in natural displacement and natural mixing flows within a
space for evaluating the ventilation effectiveness.
Practical design guidance for naturally ventilating performing arts buildings in an urban context has been outlined by Short and Cook
[34]. Specific space features and operating
requirements in designing auditoria were
addressed and demonstrated through the presentation of three case studies. The technical guidelines beyond typical natural ventilation space
design include:
• Sizing larger inlet and outlet areas
• Managing acoustic attenuation
• Configuring building management system to
cater for all levels of occupancy density
• Ensuring the stratification of warm, stale air
remains above the breathing zone in theaters
with raked seating
• Avoiding airflow imbalance generated by wind
pressure
For hospital environments, natural ventilation
system design needs to pay special attention to
eliminate the spread of biological (i.e., fungi, bacteria, and virus), chemical, and other
contaminants [35].
Natural Ventilation for Cooling
In addition to natural ventilation for breathing air,
there is significant benefit for natural ventilation
for convective cooling of the human body and
thermal cooling of the air. Design of the natural
cooling system can be optimized considering
Natural Ventilation in Built Environment
parameters involved, such as thermal mass, window size, and local environmental conditions.
Convective cooling is achieved whenever airflow
can effectively lift heat and moisture from the
skin. To obtain thermal cooling of the air and
remove heat from internal spaces, the incoming
air from the surroundings must be cooler than
indoor temperature. Water, earth, and concrete
have high capacity to store heat; providing inertia
against temperature fluctuations, they are referred
to as high thermal mass materials. The potential
sources for the cool air may be from a shaded or
landscaped space or from over a body of water, a
labyrinth with high thermal mass, underground
channels, or other sources of cooling.
In cold climates and locations with high diurnal temperature range, nighttime ventilation can
be applied to passively cool the building structure
and provide a heat sink during the daytime occupancy period to achieve good thermal comfort.
Evaporative downdraft cooling techniques
[36, 37] involve introducing fresh ambient air at
the top of a central light well and providing atomized water for evaporatively cooling the air as it
flows downward, filling the space with a static
reservoir of denser, cooler air.
Air Movement in Rooms
It has been well established that air movement is
one of the important factors influencing people’s
perception of thermal comfort [38]. Air movement is a combination of a momentum-induced
airflow and buoyancy-induced airflow [32]. A jet
airflow is caused by a momentum source, which
can either be a fan or the pressure difference
across an opening caused by the wind or temperature difference. Buoyancy-driven airflow is
caused by density differences. This type of motion
is also called natural convection. The research
work of Linke [39], Mullejans [40], and van
Gunst [41] has given clear descriptions of the air
patterns produced by air streams at various velocities and temperatures, when directed through different types of outlet, and also their interaction
with the natural convection currents in the space.
Design should ensure that the optimum air and
temperature distribution as well as satisfactory
13
sound levels will be provided from the air stream
outlet.
• Air movement should vary in space and time
without giving drafts, recognizing that some
parts of the body (i.e., ankles, back of the
neck) are more susceptible to drafts.
• Temperatures should vary within the vertical
gradient for comfort, recognizing that a higher
level of warmth is preferable below knee level
rather than at head level.
• For freshness, higher air velocities are required
at higher temperatures, with an air velocity
change of 0.15 m/s being equivalent to a
change of about 1 C in temperature. Air at a
lower temperatures and relative humidity of
40–60% (i.e., air with a lower enthalpy) is
perceived as fresher than air with a higher
enthalpy [42, 43]).
• Above the head, the convection air velocities
can be 0.25 m/s or higher depending on the
occupancy density.
• Air movement helps to dispel a sense of
stuffiness.
Cross ventilation is normally the primary strategy for passive cooling. Operable windows are
the most commonly used vents in natural ventilation systems. There are four common types of
windows – sliding (sash), horizontal-vane opening, vertical-vane opening, and combination tilt
and turn windows, as illustrated in the BSRIA
guide [44]. Window selection, integrated with
building form and orientation, façade details, and
internal layout design, contributes to create different indoor airflow patterns and provide different
options for the control of direction and volumetric
flow. In certain conditions windows can cause
localized discomfort, i.e., local drafts, cold radiant
surfaces in winter, or solar gain in summer. However, occupants of naturally ventilated buildings
are generally willing to accept a wider range of
internal temperatures as satisfactory and prefer the
greater control they are given over their
environment.
In addition to cross ventilation, buoyancy or
stack ventilation can be effective at increasing the
14
Natural Ventilation in
Built Environment,
Fig. 14 Natural cooling in
traditional Malacca
Mosque, Malaysia [45]. (a)
A traditional Malacca
Mosque in Malaysia with
typical floor plan. (b) Cross
ventilation design. (c)
Stack-effect design
Natural Ventilation in Built Environment
a
qiblat
qiblat
N
mihrab
serambi
Prayer
hall
serambi
serambi
b
Northeast
Southwest
c
airflow rates for convective cooling of the occupants. Stack ventilation can be further assisted by
wind-induced stack airflow and by solar chimneys. Solar chimneys are constructed to capture
solar radiation to increase the difference in temperature between incoming and outflowing air to
enhance stack ventilation.
The design of traditional mosques in Malacca,
Malaysia (Fig. 14), demonstrates the combination
of cross ventilation with stack or heat
stratification-induced ventilation to achieve
cooling with natural ventilation.
Design for Daylighting with Natural
Ventilation
The design of windows for natural ventilation
must also consider effective daylighting opportunities. Daylight is good for health and saving
energy. Natural light has a balanced spectrum of
colors and wavelengths which vary over the day
depending on latitude and seasons (Fig. 15) with
measurable benefits over artificial light sources in
regulating circadian rhythms and maintaining
overall health [46].
The daylight penetration depends on the room
geometry as does the air distribution. In order to
Natural Ventilation in Built Environment
15
Natural Ventilation in Built Environment,
Fig. 16 Urban canyon – the magnificent Mile in Chicago
[49]
Natural Ventilation in Built Environment,
Fig. 15 Design to maximize daylight throughout the
year [47]
create stimulating high-quality interior environments, lighting design must consider source intensities, distribution, glare, color rendering, and
surface modeling [47]. Improved daylight metrics
can be applied in a practical, real-world context to
take into account the temporal and spatial aspects
of daylight, as well as meeting design standards
for energy and occupant comfort [48].
Urban Pollution and Noise with Natural
Ventilation
The design of windows for natural ventilation
must also consider the effects of outdoor pollution
and noise. In the built-up urban environment,
buildings and roads make up the basic geometric
form of street canyons. Similar to a natural canyon, which is a steep gorge with very high sides
and a minimal valley floor, an urban canyon has
narrow street space bordered by very high buildings. One example of an urban canyon is the
Magnificent Mile in Chicago as shown in the
picture (Fig. 16).
It is important to understand how these topographic places affect wind patterns, pollution, and
noise. An urban boundary layer rises above the
canopy (see Fig. 17). The potential for natural
ventilation is seriously affected by the reduction
of wind speed, complicated turbulent dispersion
patterns, elevated day- and night-time ambient
temperatures due to the urban heat island effect,
and increased external pollutants as well as noise
level.
Based on neural network methodologies, an
algorithm calculating the optimum sizes of openings for naturally ventilated buildings located in
urban canyons for single-sided and stack-effect
configurations was derived by Ghiaus and Allard
[51]. They identify that mitigation of the urban
heat island effect can be accomplished through the
use of green roofs and the use of lighter-colored
surfaces in urban areas, which reflect more sunlight and absorb less heat. Green roofs protect the
roof materials from intense solar radiation and
prolong the service lifetime. Plants that retain
and absorb rain improve the microclimate and
also reduce the runoff water to drainage systems.
Plants and soil provide for a level of acoustic
absorption and pollution reduction for incoming
streams of natural ventilation.
Embracing nature, even in urban settings, has
been long-term inspiration and challenge for
architects and engineers. In Japan, the Osaka
Gas Corporation has sponsored an experimental
“Open Building” (Fig. 18) project NEXT21 since
1994. The structural and building services are
challenged to use resources more effectively
through systemized construction [53]. A variety
16
Natural Ventilation in Built Environment
Natural Ventilation in
Built Environment,
Fig. 17 Cross section of
the urban atmosphere [50]
Natural Ventilation in Built Environment, Fig. 18 Open building in Japan [52]
of residential units have been designed by different architects’ practices to accommodate varying
households. Substantial natural greenery was
planted on the “3D streets” formed by different
levels of building service pathways connecting
different apartments in a high-rise structure.
Green plants can reduce pollution and create
healthier microclimate in/around the building,
also connecting people to nature above street
level in urban settings. Innovative designs could
tackle the noise issue when utilizing natural
ventilation [54–57]. Energy-efficient measures
include fuel cells and behavior – encouraging
occupants to become more aware of how to lead
a comfortable life possible without increasing
energy consumption.
A 1993 study by Clausen et al. in a climate
chamber revealed that a change of 2.4 decipol in
the perceived air quality or a change of 3.9 dB in
the noise level has the same effect on thermal
comfort as 1 C change in the operative temperature [58]. Recently, a number of newly built
Natural Ventilation in Built Environment
schools in the UK with different ventilation strategies have shown that the complex interactions
between thermal comfort, ventilation, and acoustics are major challenges for designers [59].
The shape of the room and surface finishes
affect the sound distribution. The optimum balance of direct and indirect sound depends on the
shape of the space and the boundary surface sound
absorption. Combined acoustic and airflow design
chart and equations could help designers to
achieve both adequate acoustical insulation and
airflow rates requirement, especially in the early
stages of the design process [60]. The newly completed broadcast center in London has showcased
a range of sustainable technologies to achieve the
world’s first naturally ventilated television studios
(see details in case study).
Humidity and Condensation Prevention with
Natural Ventilation
Natural ventilation is typically associated with
higher ventilation rates, especially when outdoor
conditions are cooler than indoors. In Nordic residential buildings, monitoring data has shown
health risk for the residents with ventilation rates
below 0.5 ACH. Low ventilation rates may lead to
high indoor relative humidity and indoor pollutant
concentrations. Low ventilation rates and moisture accumulation may lead to increased dust
mites in residential dwellings linked to asthma.
Moisture in buildings can lead to mold formation
also associated with exacerbation of asthma and
upper respiratory disease in both children and
adults [3, 61].
Studies of ventilation rate and health effects in
public buildings [62] indicate that ventilation rates
below 10 l/s per person have significantly associated with health risks and perceived air quality
complaints. On the other hand, increased ventilation rates between 10 and 20 l/s per person
reduce sick building syndromes (SBS) and
improve perceived air quality. A relative humidity
range of 40–60% is generally considered acceptable. High humidities over 60% gradually
increase the risk of mold growth, and other fungal
contamination, which may cause asthma and
other respiratory health concerns. Increased
humidity may also enhance other emissions in
17
buildings, e.g., formaldehyde from furnishings
[63]. On the other hand, low humidity (<30%)
may cause dryness and irritation of the skin, eyes,
and airways of some occupants [22] including
increased throat infections. Contact lens wearers
often experience discomfort in dry environments.
A set amount of background ventilation (e.g.,
trickle vents formed passive stack) will provide
sufficient fresh air and also work with all types of
ventilation strategies (either natural or mechanical) to ensure a healthy atmosphere and reduce the
potential for condensation and mold.
Fire Safety with Natural Ventilation
In the event of a fire, flames and smoke will follow
the paths of natural ventilation. As a result, the
natural ventilation system must integrate fire
safety strategies and provide solutions which
facilitate safe occupancy, warning, escape, and
increased visibility for the fire service
[6]. Smoke ventilation designs utilize the buoyancy of hot smoke to automatically open vents
(AOVs) on the fire floor in conjunction with an
AOV at the top of the smoke ventilation system to
naturally extract smoke from the common escape
routes. Depending on the building envelope and
structural configuration, automatically open vents
(AOVs) should be placed in natural/mechanical
smoke shafts, atria, internal glazed screen/
façades, and fire stairs to achieve the prime objective of keeping common escape routes clear of
smoke. Standby fans should be installed as an
emergency safety precaution.
Design Guidelines for Natural
Ventilation
The parameters which affect the air velocity and
temperature at a given point in the room include:
1. Air inlet velocity (sound emission must also be
accounted for when selecting a value for this)
2. Temperature differentials of outdoor and room
air
3. Geometry and position of air supply inlets
4. Geometry and position of air extract outlets
5. Room geometry
18
6. Room surface temperatures (low surface temperature components, such as glass, tend to
promote strong convection currents)
7. Position, shape distribution, and emission of
heat sources (e.g., people)
8. Room turbulence
Natural ventilation can be difficult to control
due to the fluctuating indoor and outdoor conditions. As previously stated naturally ventilated
buildings have to be inextricably linked to architectural form and fabric; they require holistic
design and significant attention to detail. Welldesigned natural ventilation systems need to
address the following aspects comprehensively
[64–66]:
• Site design – building location, orientation, site
layout, and landscaping
• Building design – building type and function,
building form and orientation, envelope, thermal mass, natural ventilation strategy, internal
spatial division and functions, internal heat
load, solar shading, daylight, and passive
night cooling potential
• Vent opening design – position of openings,
clear path of airflow, types of openings, sizing
and choice of window opening design, effective area of multiple openings, provision of
secure, operable openings, and control strategy
The rules of thumb for effective natural ventilation can be simplified as follows [10], illustrated
in Fig. 19:
• Single-sided single-opening (mainly driven by
wind turbulence) can be effective up to a depth
of two times the floor-to-ceiling height, typically 4–6 m (Fig. 19a).
• Single-sided double-opening (mainly driven
by buoyancy forces) can be effective up to a
depth of 2.5 times the floor-to-ceiling height,
typically 7–8 m (Fig. 19b).
• Cross ventilation with ventilation openings on
both sides, generally opposite sides of a space
(mainly driven by wind), can be effective up to
Natural Ventilation in Built Environment
a
W ≤ 2H
H
W
b
W ≤ 2.5H
h approx
1.5 m
H
W
c
W ≤ 5H
H
W
d
Edge-in,
Centre-out
(E.C)
Centre-in
Edge-out
(C-E)
Edge-in,
Edge-out
(E-E)
Centre-in,
Centre-out
(C-C)
Natural Ventilation in Built Environment,
Fig. 19 Schematic diagrams of the different forms of
natural ventilation: (a) single-sided single-opening, (b)
single-sided double-opening, (c) cross ventilation, and (d)
atrium ventilation [68]
a depth of five times the floor-to-ceiling height,
typically 15 m (Fig. 19c).
Natural Ventilation in Built Environment
19
Stack ventilation
through a rooflight
Louvres
adjusted to
reject summer
radiation
Wind-assisted
external ventilator
for lower floors
Roof vent and glazing
with glare protection
Single-sided
ventilation
Air supply through
floor diffusers
Louvres
adjusted to
admit overcast
sky luminance
Air intake on
North elevation
to floor duct
Louvres
adjusted to
act as lightshelves
Transfer
grille
Manually
operable
windows in
summer with
BMS control
of fanlights
Natural Ventilation in Built Environment, Fig. 20 Illustration of combined natural ventilation strategies [44]
• Stack ventilation is mainly driven by temperature differences between the hot air in the
occupied space and the cooler external air.
The effective depth of a stack ventilation system is up to five times the floor-to-ceiling
height. Stack ventilation can also be enhanced
by the wind effect or through the use of a solar
chimney,
i.e.,
solar-driven
stack
ventilation [67].
• Different forms of atrium ventilation are illustrated in Fig. 19d [68].
Figure 20 illustrates how various natural ventilation strategies can be integrated into design.
For natural ventilation to be effective for thermal comfort, it may be critical for heat gains to be
kept below 35 W/m2 to avoid excessive overheating. This means there is a need to reduce
solar loads, daytime highs, and internal gains by:
• Solar protection
• Vented façades
• Thermal mass
• Low-energy lighting
• Plug load management including the use of
cloud computing, which can reduce computer
heat gains considerably
Benefits of Natural Ventilation
The indoor environmental advantages of natural
ventilation are predominantly gained by the elimination or reduced use of mechanical systems:
•
•
•
•
•
•
Less energy is consumed.
Less mechanical system space is needed.
Maintenance is simpler.
Durability is improved.
Mechanical noise is eliminated.
Occupants gain control of air quality and temperature using windows.
• Costs are lower.
• A higher level of daylight is provided with
well-designed windows.
The disadvantages of natural ventilation
include:
20
• The driving pressure depends on the wind
and/or the stack effect, and both are variable
and cannot be easily controlled.
• There has to be an integrated approach to
design between the architect and the engineer
with regard to built form, orientation, massing,
internal layout, selection of window types, and
their positioning in the façade.
• Internal heat gains are limited to less than
35 W/m2.
• There is no filtration or control of outdoor
pollution or moisture content.
• Outdoor noise can be an issue.
Most significantly, however, the ventilation
rate depends on the strength and direction of
wind and/or buoyancy forces and the resistance
of the flow path. The uncontrollable feature of
natural ventilation can result in the air change
rate varying significantly and being distributed
unevenly to internal spaces giving periods of inadequate ventilation, or periods of over ventilation.
Health and Productivity
There is a unique relationship between an individual, the environment, and the building they
inhabit. The complicated interaction between the
environmental stimuli, such as air and surface
temperatures, humidity, air movement, and air
purity, and the interlinked social and psychological factors of individuals and their organization
influences the sense of well-being, health, and
productivity [20, 69]. Loftness et al. [70] captures
the impact of access to the natural environment,
including natural ventilation, on health and productivity (Fig. 21a, b). In addition to the health
and productivity benefits brought by design with
access to the natural environment, there are measurable energy benefits. Effective daylighting can
yield 10–60% reductions in annual lighting
energy consumption. There is evidence of potential 40–75% reductions for cooling energy consumption when natural ventilation is interactively
supported by mixed-mode HVAC systems. Sustainable and healthy built environments result
from integrating the natural diversity of the
Natural Ventilation in Built Environment
region – its unique climate and seasons, textures,
sounds, smells, and variety of landscape and
species.
Mixed Mode: The Selection of
Ventilation Strategies
CIBSE [64] gives the following monograph to
help the decision process for selecting whether
to use natural ventilation, mechanical ventilation,
mechanical assist to cooling, and air-conditioning
(Fig. 22).
Decision-making can be substantially
improved through the use of computer-aided prediction models. Chen [71] presented an overview
of ventilation performance prediction methods,
including analytical models, empirical models,
small-scale experimental models, full-scale experimental models, multizone network models, zonal
models, and computational fluid dynamics (CFD)
models. Recent applications of these simulation
tools were examined in terms of their contributions to design practice and/or to research. CFD
applications in modeling of wind-driven natural
ventilation [72] have shown improved prediction
capability for complex naturally ventilated buildings. Not reliant on simulation alone, Walker [73]
developed a methodology to evaluate natural ventilation in a multizoned commercial office building by combining full-scale building monitoring,
reduced-scale physical experiment, and CFD simulation. Simulation that incorporates detailed thermal sensation and comfort models provides more
accurate predictions on the dynamic responses of
occupants to building environments, and
advanced coupling in simulation extends the prediction capability of CFD and brings the needs of
the human occupancy into the design of buildings
[74, 75]. The integration of CFD with dynamic
building simulation (BS) models and geographic
information systems (GIS) data would be a practical way to take advantage of the strength of the
other models for optimal natural ventilation
design and analysis. Figure 23 illustrates an application of CFD for advanced natural ventilation
design in hospitals. Lomas and Ji [76] evaluated
Natural Ventilation in Built Environment
simple natural ventilation (SNV) and advanced
natural ventilation (ANV) designs in terms of
overheating risk in healthcare buildings given
current and future climate conditions. They also
proposed an overheating risk criterion compatible
with adaptive thermal comfort – an emerging
approach to defining comfort in naturally ventilated environments (see Chapter ▶ Adaptive
Comfort and Mixed-Mode Conditioning). Both
field monitoring and modeling studies reveal that
advanced natural ventilation could offer greater
resilience to climate change, particularly as a
refurbishment strategy.
The strengths and weaknesses of a wide range
of design simulation tools have been summarized
by governmental and professional organizations
Fig. 21 (continued)
21
in DoE and IBPSA [77, 78]. Educational
resources and practical equations for various
design stages and step-by-step guided case studies
will help multidisciplinary professions to design
and build sustainable buildings that incorporate
natural ventilation [68, 79–81]. The following
case studies showcase innovative solution to natural and mixed-mode ventilated buildings in the
built environment.
Natural Ventilation and Mixed-Mode
Case Studies
Six case studies have been selected to illustrate the
sophistication and diversity of naturally ventilated
and mixed-mode commercial building projects.
22
Natural Ventilation in Built Environment
Natural Ventilation in Built Environment,
Fig. 21 Health and productivity gains from access to the
natural environment. (a) Health gains from access to the
natural environment. (b) Productivity gains from access to
the natural environment [70]
Case Study 1: Liverpool John Moores
University, UK
The award-winning Liverpool John Moores University art and design academy was designed by
Rick Mather Architects, engineered by
Whitbybird Engineers, and built by Wates Construction. The building was designed from 2004
and opened in 2008 (see Fig. 24).
The 11,000 m2 five-story university academic
building has a number of important environmental
initiatives in the client brief including a 25%
energy savings below UK conservation of fuel
and power building regulations, a BREEAM target of Very Good, and a 10% onsite renewable
energy target. To meet these requirements, the
design team reviewed a number of architectural,
structural, and services engineering options and
concluded that a mixed-mode ventilation scheme
utilizing thermal mass with heat recovery would
be of particular benefit to the low-energy goals.
The building design team used the latest computer
modeling techniques to prove compliance with
industry standards for thermal comfort, with particular attention to the prevention of overheating
(see Figs. 25, 26, 27, and 28).
The building is designed for cross and stack
ventilation through multiple benefits from a
heavyweight thermal mass during the spring and
Natural Ventilation in Built Environment
23
Start
No
Are
max. heat
gains more than
30–40
–2
W.m ?
Yes
Can
re-design
reduce gains to
30–40
W.m–2?
No
Yes
Is
Occupancy
transient?
No
Can capacity
effects absorb
swing in temp.
and IAQ?
Yes
No
Is
seasonal
mixed-mode
acceptable?
Yes
No
Yes
Yes
Is
this a peak
season?
No
Yes
Yes
Does
the building
have a narrow
plan?
No
Can
courtyards or
atria reduce width
to less than
15 m?
No
Yes
Yes
Yes
Are
noise and
pollution levels
acceptable?
Is zonal
mixed-mode
acceptable?
No
Is
this a
perimeter
zone?
No
See also
AM13:
Mixed
mode
ventilation
Yes
No
Yes
Can
occupants
adapt conditions
with weather
changes?
Is tight
temperature
control required?
(= ±1 K)
No
Yes
Yes
Is
close control
of RH required?
(better than
±10%)
Yes
No
No
No
Is
humidification
required in
winter?
Yes
Natural
ventilation
Mechanical
ventilation
Mechanical
ventilation and
humidification
Comfort
cooling
Full air
conditioning
Natural Ventilation in Built Environment, Fig. 22 Flowchart for selecting a ventilation strategy [64]
summer, utilizes single-sided natural ventilation
with mechanical extract during peak summer with
nighttime free cooling (see Fig. 25), and during
winter operates as a sealed building with heating
provided by a biomass pellet boiler. A weather
station provides data to the BEMS to ensure the
automated windows are aligned with the ventilation strategy.
Case Study 2: Tamworth Academies –
Staffordshire, UK
Two secondary school academies were commissioned by Tamworth County Council in 2009.
Designed by Aedas architects and engineered by
WSP and CTM, the two 9000 m2 two-story buildings were completed by Willmott Dixon Construction and opened in 2010 (Fig. 29). These
24
Natural Ventilation in Built Environment
Natural Ventilation in Built Environment,
Fig. 23 Advanced natural ventilation system design in
hospital using CFD [76]
school buildings met the government’s 60% carbon reduction targets compared to 2002 UK building regulations and achieved the BREEAM
environmental target of Excellent.
It was the aim of the architectural, structural,
and services engineering teams to design a lowenergy building that was future proofed against
rising energy costs. The client team requested a
life cycle cost solution, with low ongoing costs.
The building was designed to operate as a naturally ventilated building predominantly, with a
highly efficient mechanical ventilation and thermal conditioning system during peak summer and
extremely cold winters. To extend the period of
natural ventilation and natural cooling, the project
incorporated TermoDeck by Tarmac, an integrated structural mixed-mode ventilation scheme
utilizing thermal mass free cooling with energyefficient heat recovery (see Fig. 30). The measured impact of night cooling of the thermal
mass for next day ventilation cooling is as high
as 4 C (see Fig. 31).
Other features of these two school buildings
include the use of chilled water cooling with
ground source heat pumps to manage zones with
high internal gains due to communication technologies. The seasonal operation of natural and
Natural Ventilation in Built Environment,
Fig. 24 LJMU Liverpool façade in nighttime. (a) LJMU
Liverpool exterior; (b) LJMU Liverpool façade in nighttime (Source: Rick Mather Architects)
mechanical ventilation and thermal conditioning
is communicated to the occupants alongside
weather station data on flat screen TVs.
Case Study 3: BSkyB Broadcast Center –
London, UK
Designed by Arup Associates (architects and
engineers), the BSkyB broadcast center (Fig. 32)
is located in West London and houses the world’s
first naturally ventilated television studios
[82]. Thirteen giant ventilation chimneys provide
stack ventilation, with nine lining the building’s
Natural Ventilation in Built Environment
Natural Ventilation in
Built Environment,
Fig. 25 Exposed concrete
soffit for thermal mass
benefit (Source: Lee
Hargreaves, WSP UK Ltd.)
25
WARM AIR
OUT
CONCRETE SCAB COOLED AT NIGHT TIME VENTILATION
RADIANT
HEAT
EXCHANGE
COOL AIR
IN
Natural Ventilation in
Built Environment,
Fig. 26 Sun path analysis
for external façade design
(Source: Whitbybird
Engineers)
CONVECTIVE
HEAT EXCHANGE
11
10
12
14
15
9
16
17
8
18
19
7
6
N
5
eastern elevation and another four on the west. The
construction provides a solution to eliminating
external noise as well as naturally ventilating the
studios to remove excessive heat generated by
studio lights. Fresh air is supplied through an
acoustically lined labyrinth built in between the
underside of the studio’s concrete floor and the
enclosure over the street. This configuration creates
big air paths to minimize noise from air delivery as
well as eliminating street noise (Fig. 33).
In order to prevent a common stack ventilation
problem – air cooling in the flue and dropping
back into a room – the flues are lined and insulated
on the inside. In an intermediate mode, the ventilation system will run on extract only to pull the
air up the chimney and warm it. When the right
flue surface temperature has been reached, the
air’s natural buoyancy will take over, and the
system will switch to the natural ventilation
mode automatically.
At the south end of the building, a glazed
atrium houses a series of meeting rooms, a café,
and breakout spaces, with access between levels.
The 8-m-deep office areas on the west elevation
Natural Ventilation in Built Environment
850
26
1500
top-hung opening window(no requirement for
restricted opening to be confirmed by LJMU)
1100
side-hung opening window (restricted?)
fixed transluscent panel
PART EXTERNAL ELEVATION
PART SECTION
Natural Ventilation in Built Environment, Fig. 27 External façade design (Source: Rick Mather Architects)
30
25
Temperature (C)
20
15
10
5
0
–5
Dry resultant temperature: room 214 (room 214.aps)
Dry-bulb temperature: (room 214.aps)
–10
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Date: Sun01/Jan to Sat 30/Dec
Natural Ventilation in Built Environment, Fig. 28 Thermal modeling chart (Source: Whitbybird Engineers)
are ventilated using single-side natural ventilation. The 15-m-deep office areas on the east elevation utilize three additional chimneys in the
atrium at the center of the building to help draw
air across the floor plates. Natural light through
these atriums are additional benefit of the design.
Case Study 4: Commerzbank – Frankfurt,
Germany
Norman Foster and Ove Arup’s Commerzbank in
Frankfurt, Germany (see Fig. 34), demonstrates
that sustainable urban architecture featuring natural ventilation, vast amounts of daylight, and
Natural Ventilation in Built Environment
27
Natural Ventilation in Built Environment, Fig. 29 Tamworth Landau Forte exterior (Source: WSP)
Natural Ventilation in
Built Environment,
Fig. 30 TermoDeck
concrete plank (Source:
Tarmac Termodeck)
Air supply to
hollowcore
system
Surface away
from room
Surface facing
into room
Air supply
to room
pleasant exterior views can be achieved within a
deep building at the scale of the skyscraper.
The three thin buildings laid out in a triangularshaped plan provide the rigid structural support
needed for a high-rise building alongside functional cores located at each corner of the triangle.
The central atrium that is formed by the buildings
provides light both vertically from the glass roof
at the atrium’s top and horizontally from the winter gardens that displace one of the office areas for
six floors in a spiraling pattern. These winter
gardens, which rotate around the façade of the
building, allow for natural ventilation from the
offices into six-story atria. Natural light is also
brought directly into the center providing daylight
and outdoor views to green, natural spaces. The
operable, layered façade allows natural ventilation
into the office spaces, and the winter gardens
provide controllable natural ventilation for the
building.
Case Study 5: Queen’s Building, De Montfort
University, UK
The Queen’s Building (Fig. 35), designed by
Short and Ford Associates architects and Max
Fordham LLP engineers and built in 1993, features large venting chimneys, heavy thermal
mass, shallow floor plans, operable windows,
and generous ceiling heights to facilitate natural
ventilation and daylighting. This traditional brick
28
36
Lightweight
Lightweight with
night vent
34
Internal temperature/°C
Natural Ventilation in
Built Environment,
Fig. 31 Temperature time
lag for lightweight and
heavyweight buildings
(Source: Tarmac
Termodeck)
Natural Ventilation in Built Environment
Heavyweight
Heavyweight
with night vent
32
30
28
26
24
0
6
12
Time/h
18
24
building has deep insulation-filled cavity walls
and concrete floor slabs, buffering the indoors
from outdoor temperature peaks. The glazed ventilation shafts also help to provide natural lighting.
In the auditoria fresh air enters through louvers in
the façade supplying plenums below the raked
wooden floor and wall inlets which are controlled
by the building energy management system.
Since being the Green Building winner of the
Year in 1995, the Queen’s Building has served as a
“Living Lab” to showcase innovative natural ventilation and ventilative cooling technologies and
demonstrate ways of achieving significant carbon
reductions in academic buildings.
Natural Ventilation in Built Environment,
Fig. 32 BSkyB broadcast center in West London [82]
Case Study 6: Major Refurbishment Project –
David Attenborough Building, University of
Cambridge, UK
The David Attenborough Building (former University of Cambridge’s Arup Building) was originally built in 1971 in the “Brutalist” style. The
16,000 m2 reinforced-concrete multistory building had a poorly insulted concrete façade with
ribbons of steel-framed single glazing. A fullenergy audit together with a thermal-imaging
Natural Ventilation in Built Environment
29
The integrated refurbishment strategies for the
David Attenborough Building (opened in
February 2017) are illustrated in Fig. 36 and
detailed in the following list:
Natural Ventilation in Built Environment,
Fig. 33 Natural ventilation flow within the BSkyB television studios (Source: Arup Associates)
survey of its fabric explained why the existing
building was one of the most energy-intensive
buildings on the university’s estate. An occupant
satisfaction survey also revealed that the building
was too hot in summer and too cold in winter
[85, 86].
Closely working with Nicholas Hare Architects and Cambridge Conservation Initiative
(CCI), BuroHappold pioneered an extensive Sustainability Framework beyond BREEAM to set
ambitious project-specific targets across 10 headline themes and 50 subthemes.
• Natural ventilation zoning strategies
i. Natural ventilation of all perimeter office
bays
ii. Cross ventilation for upper levels
iii. Single-sided ventilation for levels 1 and 2
iv. Window vents with temperature and carbon dioxide automated control
• Overheating prevention
i. Utilizing the thermal mass of the concrete
on the lower floors
ii. Adding phase-change materials on top
floor
iii. Adding the low-energy intelligent communication technology
• Daylight harvesting, lighting, and acoustic
control
i. New glass atrium provides daylight deep
into floor plan with BIPV for glare control
ii. Combined lighting and acoustic raft?? for
acoustic control and low energy
consumption
iii. LED lighting update in the corridors
iv. Lighting controls for daylight dimming
and occupancy sensing
• Soft landing and smart metering to ensure
sustainable occupation
i. Energy and water submetering per floor
ii. Energy displays in the foyer of the building
With a shared vision, integrated and collaborative project teams, engaging all stakeholders, and
a willingness to share lessons learned as a standard industry practice, a comprehensive handbook was produced. This set design,
construction, and post-occupancy targets to
ensure headline targets, including a 40% reduction in operational carbon emissions, a 30%
reduction in water use per person, and a 60%
total roof coverage for biodiverse green roofs
[85, 86].
30
Natural Ventilation in Built Environment
Natural Ventilation in Built Environment, Fig. 34 Commerzbank, Frankfurt, Germany. (a) Building section [83]. (b)
Winter garden and interior view design [84]
Natural Ventilation in Built Environment
Natural Ventilation in Built Environment,
Fig. 35 The Queen’s Building, De Montfort University,
Leicester, UK. (a) Exterior view and stack outlets. (b)
Exterior view and air inlets. (c) Interior view of auditorium.
31
(d) The Queen’s Building – natural ventilation strategy
(Source: Professor Malcolm Cook, Loughborough
University)
32
Natural Ventilation in Built Environment
Natural Ventilation in Built Environment,
Fig. 36 David Attenborough Building, University of
Cambridge, Cambridge, UK. (a) Perspective views of the
building model [85]. (b) Integrated refurbishment strategies [86]
Future Directions
is necessary to achieve a sustainable built environment [87, 88] and provide the optimum cost-benefit
value for all stakeholders in the building industry
[89]. Natural ventilation should be integrated in all
projects, recognizing that various factors can limit
Sustainable design requires a long-term approach to
ensure resiliency that integrates all passive conditioning strategies. Holistic design and construction
Natural Ventilation in Built Environment
its use at times. Vernacular architecture demonstrates that natural ventilation and ventilation
cooling can work effectively in many climates.
Modern solutions demand a unity of thought
between architects and the engineers, introducing
hybrid systems that allow natural ventilation to be
augmented by mechanical ventilation and cooling
as needed. These hybrid systems are common in
Europe driven by the demand for low-carbon buildings. Natural ventilation and ventilation cooling are
critical for resiliency in the face of climate change
and critical for enhancing the well-being of building
occupants through increased ventilation rates,
important environmental variability (alliesthesia),
and increased connection to the natural environment.
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