PRINCIPLES OF AIR AND CONTAMINANT MOVEMENT INSIDE AND AROUND BUILDINGS Chapter 7

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PRINCIPLES OF AIR ANDCONTAMINANT MOVEMENTINSIDE
AND AROUND BUILDINGSChapter 7

• ALEXANDER ZHIVOV
• HÅKON SKISTAD
• ELISABETH MUNDT
• VLADIMIR POSOKHIN
• MIKE RATCLIFF
• EUGENE SHILKROT
• ANDREY STRONGIN

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Contents of Chapter 7

• INTRODUCTION
• CONTAMINANT SOURCES
• Classification
• Nonbuoyant Contaminant Sources
• Emission from Heat Sources
• Sources of Dust
• Sources of Moisture Emission
• Explosive Gases, Vapors, and Dust Mixtures
• AIRFLOW
• Factors Influencing Room Airflow
• Airflow in Rooms Dominated by Supply Jets
• Airflow Dominated by Thermal Plumes

• Unidirectional Flow
• Spiral Vortex Flow
• Airflow Created by Exaust Performance
• AIR JETS
• Introduction
• Classification
• Isothermal Free Jet
• Non-isothermal Free Jets
• Jets in Confined Spaces
• Jet Interaction

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Contents of Chapter 7 (contd)

• PLUME
• Natural Convection Flows
• Nonconfined and Nonstratified Environments
• Plume Interaction
• Plumes in Confined Spaces
• Plumes in Rooms with Temperature Stratification
• AIRFLOW NEAR EXHAUSTS
• Introduction
• Capture Velocity
• Air movement near sinks
• AIR CURTAINS
• Introduction
• Types of Air Curtains and Their Applications

• Principle of Calculation
• Operation of the Air Curtain
• Design of an Air Curtain Device
• AIR MOVEMENT AROUND BUILDINGS AND THROUGH A
  BUILDING ENVELOPE
• Airflow around Buildings
• Infiltration and Exfiltration
• Airflow through Large Openings and Gates
• Controlled Airflow through an Envelope
  Principles of Natural Ventilation.
• Air and Contaminant Movement between Building
  Zones.
• REFERENCES

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INTRODUCTION

• Proper selection and sizing of ventilation
  systems require knowledge of emissions from
  internal contaminant and heat sources and an
  understanding of the mechanisms and
  characteristics of air and contaminant movement.
• Major factors affecting air and contaminant
  movement inside ventilated space can be
  classified as
• Sources of heat and contaminants
• Air currents produced by process equipment and
  moving people
• Forced convection or supply air jets introduced
  into the room by mechanical or natural
  ventilation systems, or their combination
• Free convection flows along heated and cooled
  vertical surfaces and above heat sources
• Airflow created in the vicinity of local and
  general exhausts
• Airflow through intended and unintended openings
  and cracks in the building envelope (Section
  7.8.2), and aerodynamic means of the large
  opening protection, described in Section 7.7
• Airflow around the building under the influence
  of natural winds (Section 7.8.1) and
• Airflow between different building zones caused
  by pressure and temperature differences, or
  turbulent exchange, addressed in Section 7.8.5.

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CONTAMINANT SOURCES

• Classification
• Knowledge of the process or operation and
  contaminant sources is essential before
  ventilation systems can be selected and designed.
  
• Contaminant sources affecting the working
  environment may be external, associated with the
  elements of HVAC systems, or internal.

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AIRFLOW

• Factors Influencing Room Airflow
• Air and contaminant movement and turbulent
  intensity in the ventilated space are affected by
  different external and internal forces, such as
• Supply air jets forced into the room by
  mechanical systems
• Free convection currents generated by air heating
  or cooling by surfaces (process equipment,
  external walls)
• Airflow in the vicinity of local exhausts (hoods)
  or general exhaust (due to negative pressure in
  the duct produced by mechanical systems)
• Airflow forced through intended and unintended
  openings in the building envelope, which depends
  on the pressure difference across the opening
  resulting from wind pressure on the building
  envelope, temperature difference between the
  indoor and outdoor air, and an imbalance in the
  mechanical exhaust ventilation system performance
  versus the mechanical air supply (positive or
  negative pressure building)
• Air currents produced by process equipment or
  moving people (e.g., high-speed rotating machines
  such as pulverizers, high-speed belt material
  transfer systems, falling granular materials, and
  escaping compressed air from pneumatic tools)

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AIR JETS

• Introduction
• Air supplied into the room through the various
  types of outlets (grills, ceilingmounted air
  diffusers, perforated panels, etc.) is
  distributed by turbulent air jets.
• In mixing-type air distribution systems, these
  air jets are the primary factor affecting room
  air motion.
• Numerous theoretical and experimental studies
  that developed a solid base for turbulent air
  jets theory were conducted concurrently in
  different countries (Germany, Sweden, Russia, the
  UK, and the United States) from the 1930s through
  the 1980s.
• Theory of air jets and air distribution design
  principles are discussed in this section.

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FIGURE 7.19 Types of diffuser jets (a) compact
(b) linear (c) radial (d) incomplete
radial (e) conical.
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FIGURE 7.20 Turbulent jet (a) schematic with
four zones (b) simplified jet schematic
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FIGURE 7.76 Schematic illustration of the airflow
pattern in a room ventilated by displacement.
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AIR CURTAINS

• Introduction
• Air curtains are local ventilation devices that
  are used in industrial buildings to reduce
  leakage of airflow through apertures in building
  enclosures and process equipment. Their operation
  is based on the damping effect of air jets that
  are supplied into the area of the open aperture.
  The advantages of air curtains include
• Improvement of working conditions near open
  apertures
• Reduction of heat (cold) consumption and
  electrical energy for heating (cooling) of
  buildings and process equipment
• Reduction of heat loss in the building by using
  overheated air from an upper zone of the room
• Reduced loss of usable working area near gates
  due to the ingress of outdoor air into the
  building

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Types of Air Curtains

• According to the application and aerodynamic
  pattern, the following types of air curtains have
  been designed
• Air curtains with heated indoor air
• Air curtains with unheated indoor air
• Combined air curtains with indoor air
• Air curtains with unheated outdoor air
• Air curtains for cooled rooms
• Air curtains for gates with long passages
• Air curtains for process equipment

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FIGURE 7.86 Schematic of shutter-type air
curtains. (a) Heated or unheated air supply. (b)
Outdoor air supply. (c) Combined air curtain.
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AIR MOVEMENT AROUND BUILDINGS AND THROUGH A
BUILDING ENVELOPE

• Airflow around Buildings
• Airflow around buildings consists of natural
  winds that travel around and possibly through
  buildings. Airflow around buildings has two
  influences on industrial ventilation
• Wind pressures exerted on the exterior building
  surfaces, which can influence air movement
  indoors
• The outdoor movement of air contaminants, which
  can degrade indoor air quality if brought indoors
  with insufficient dilution.
• This section will describe general features of
  airflow patterns and then present information on
  the dimensions and locations of recirculating
  (stagnant) zones around the building envelope,
  which determine wind pressures and contaminant
  dilution. This knowledge allows one to select the
  locations of stacks and air intakes and to
  calculate infiltration and natural ventilation
  rates.

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FIGURE 7.108 Mechanisms of contaminant movement
between zones (a) difference in static pressure
resulting from unbalanced air supply and return
(b) difference in static pressure result from
wind effect (c) buoyancy forces create vertical
air movement along the passage between zones
located on different levels (d) turbulent
exchange between air in different zones due to
energy introduced by supply air jets, moving
objects, etc.
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FIGURE 7.109 Construction, process-related, and
ventilation techniques used to separate building
zones (a) solid wall (b) unbalanced supply and
return airflow rates (c) specially arranged
local supply and return, creating an air oasis
with cleaner and cooler air in the desired zone
of the building (d) temperature and
contaminant stratification along the room height
using a natural or displacement ventilation
system (e) air curtain supplied around the
perimeter of the canopy hood, which separates the
contaminated process zone (f) an air lock
located between two zones (g) enclosing process
equipment and extracting air from the enclosure.