Building Services III

Course Code: 3201941 [P] ; 3201942 [SS]

Class 3rd A
A.Y. 2022-2023

Unit 1: Natural Ventilation

1.1 : Conditions of Human thermal comfort
1.2 : Factors affecting Natural Ventilation
1.3 : Strategies to effect Natural Ventilation
Back to Basics
 Heat- Form of Energy that appears as molecular motion
or kinetic motion in substances and as electro magnetic
radiation in space
 Heat can be measured by temperature and/or Moisture
content
 Sensible Heat
 Latent Heat
 Radiant Heat.

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Modes of Heat Transfer
 Conduction

 Convection

 Radiation

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Heat Transfer in Buildings

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Building Envelope

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Incident and Reflected rays

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Heat Transfer in Building
 Outside warmer Inside cooler

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 THERMAL COMFORT

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ASHRAE Standard 55
 Defines criteria for thermal environmental conditions for
human occupancy
 Body tries to maintain 37ºC all times irrespective of
external changes in climate.
 Heat balance in body is MUST

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Heat transfer w.r.t Human Body

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Factors affecting Thermal Comfort
1. Environmental Factors
a) Air Temperature
b) Radiation
c) Air Motion
d) Relative Humidity

2. Personal Factors
a) Clothing level
b) Metabolic Rate

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Comfort Zone
 Certain combination of Air Temperature, Relative
Humidity, Metabolic rate, air motion is what most people
consider thermally comfortable condition
 This is defined as the “comfort zone”.
 In this zone: 80% of the occupants would find the
conditions thermally acceptable.

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Passive Design
 Design approach where building is designed in response to the
climate and sun.
 Objectives:
 Reduce demand for cooling.
 Reduce the energy required for cooling.

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 VENTILATION

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VENTILATION
 Process by which fresh air is introduced and used air is
removed from an occupied space.
 The primary aim of ventilation is to preserve the qualities
of air.
 Sometimes, ventilation may also be used to lower the
temperature inside an occupied area.
 Ventilation is the movement of air within a building and
between the building and the outdoors.
 Control of ventilation is most subtle yet important
concerns in building design.

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Types of ventilation
 • Natural ventilation
 • Mechanical ventilation

We will be concentrating on Natural Ventilation

Strategy

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 NATURAL VENTILATION

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What is Natural ventilation
 Natural ventilation is an ancient way of free cooling.
 It is the use of prevailing wind to achieve 2 objectives:
 to remove the heat generated inside our buildings
 to make people feel cooler by circulating air at a certain
minimum speed.
 Theoretically, natural ventilation widens the thermal
comfort zone with the increased air velocity.
 The building should have large openings on at least 2
sides for the wind to enter and exit the space.
 The operation of this method is straightforward. When
occupants feel the indoor air is too warm, they should
open their windows if the outdoor air is cooler

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 Natural ventilation is process of supplying and removing
air by means of purpose- provided aperture ( such as
openable windows, ventilators and shafts) and the natural
force of wind and temperature- difference pressures

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Principles of natural ventilation
 For air to flow in and out of a building, a pressure
difference between the inside and outside of the building
is required.
 The pressure difference is caused by
 Wind ( or wind effect)
 Difference in air density due to temperature difference
between indoor and out door air.
 Combination of both wind and stack effects.

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Wind effect & Wind flow
 When air flow is due to wind, air enters through openings
in the windward walls and leaves through openings in the
leeward walls
 Wind pressure are generally high/ positive on the
windward side of a building and low/ negative on leeward
side.
 The occurrence and change of wind pressures on building
surface depend on
 Wind speed & wind direction relative to the building
 The location and surrounding environment of building and
 Shape of the building

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External Features for Natural Ventilation
 Orientation of Buildings
 Position of Openings
 Cross Ventilation
 Size of Opening
 Opening Types

Lets see all in Details now

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Massing and Orientation of Building

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Opening Size and direction

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Size of opening

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Cross ventilation

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Requirement of Windows or vents
 The actual number of vents required and the air supply
necessary makes allowance for flow resistance based on
their exhaust and inlet coefficients.
 The positioning of the vents is also critical in order to
exhaust the smoke without mixing and cooling.

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Climate specific recommendations
 In hot and dry regions
 In warm humid regions
 In cold regions

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Energy and cost saving
 Eliminate the requirement of a cooling system.
 A well designed building can respond to the outdoor
conditions and reduce mechanical cooling when the
conditions warrant.
 natural ventilation can provide the much needed air
movement to provide comfort during humid periods.

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Techniques to achieve natural
ventilation
 Stack effect
 Wind tower
 Courtyard effect
 Solar chimney

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Stack effect

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Wind tower
 Air enters in wind tower through openings- cooled down
– becomes heavier and sink down ( presence or air
movement)
 After whole day air exchange – tower becomes warm in
the evening.
 Tower walls absorbs heat during daytime and releases at
night warming cool night air at night.

Further Reading : https://www.linkedin.com/pulse/use-wind-tower-passive-ventilation-buildings-reduce-energy-lukhi/

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Courtyard Effect
 Due to incident solar radiation in a courtyard, air gets
warmer and rises
 Cool air from Ground level flows through the lower
opening.

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Further Reading: https://gharpedia.com/blog/understanding-courtyards-housing-typology-in-houses/

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Evaporative Cooling
 Over the years, traditional wisdom has supported the idea of a
water body such as pond, lake or a fountain to provide cooling
effect to the surrounding environment.
 This effect lowers the indoor air temperature – a widely
known concept of evaporative cooling. This phenomenon is
largely witnessed in systems such as desert coolers in most
Indian households.
 Evaporative cooling lowers the indoor air temperature thus
lowers the energy cost for air-conditioning in buildings.
However, evaporative cooling is mostly effective in hot and dry
climate where the humidity is low.
 Pools, ponds and water features immediately outside windows
or in courtyards can pre-cool air entering the house. As water
evaporates it draws large amounts of heat from surrounding
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air.
Air is in direct contact
with the cooling media,
water, in direct
evaporative cooling. The
most commonly used
methods are water
bodies and water sprays.
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Reference Reading
 ASHRAE 55, Thermal Environmental Comfort Conditions for Human Occupancy.

 Kamal, M. (2012 ). An Overview of Passive Cooling Techniques in Buildings: Design

concepts and architectural interventions . Acta Technica Napocensis: Civil Engineering &
Architecture , Vol 55 (84-97).

 TERI – Guidelines for Solar passive design for new

buildings… http://passivesolar.sustainablesources.com/#heat

 MNRE – Architects Guidebook

 Integrated green design for Urban and Rural buildings in Hot- Dry climate zone –
CPWD

 Geetha , N., & Velraj, R. (2012). Passive cooling methods for energy efficient buildings
with and without thermal energy storage – A review. Energy Education Science and
Technology Part A: Energy Science and Research,Vol 29- 913 – 946.
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 ALL THE BEST !!

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