AIRHANDLING PROCESSES Chapter 9

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AIR-HANDLING PROCESSESChapter 9

• ERIC F. CURD
• JORMA RAILIO
• JAN GUSTAVSSON
• JAAP HOGELING
• MAMDOUH EL HAJ ASSAD
• JAN EMILSEN
• SANTE MAZZACANE
• RALF WIKSTÉN

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Contents of Chapter 9

• INTRODUCTION
• Scope and Purpose
• Linking with Other Chapters
• Aims of an Air-Handling System, Including the
  Unit and Ductwork
• AIR FILTERS
• Why Air Filters?
• Atmospheric Air and Dust
• Filters and Test Methods
• Filters in Operation
• LifeCycle Issues
• Summary
• References
• HEAT EXCHANGERS AND HEAT-RECOVERY UNITS
• General Theory of Heat Exchangers
• Plate FinandTube Heat Exchangers
• References

• AIR-HANDLING PROCESSES
• Air-Heating Equipment
• Humidification and Dehumidification
• Air Distribution
• FANS
• General
• Centrifugal Fan
• Axial Fans
• Effect of Speed of Revolution
• Fan and Duct Network
• Series Fan Connection
• Fan Volume Flow Regulation
• References
• AUTOMATIC CONTROL OF AIR-HANDLING (HVAC) SYSTEMS
• Methods for Automation Control
• Main Types of Control Equipment and Automation
  Level

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Contents of Chapter 9 (contd)

• General Technical Requirements
• Automation Equipment and Instrumentation
• Process
• Controller
• The Choice of Controllers
• Sensors
• Placing of Sensors in HVAC Systems
• Changing Speed by Using Frequency Converters
• Building the Control Station
• AIR DISTRIBUTION SYSTEM, DUCTWORK
• Friction Loss Calculation
• Design Methods
• Thermal Losses by Transmission
• Air Leakage from Ductwork

• SOUND REDUCTION IN AIR-HANDLING SYSTEMS
• Basic Concepts
• Free-Field Noise Transmission
• Criteria for Acceptable Air-Handling Unit and
  HVAC System Noise Levels
• FUNDAMENTALS OF ENERGY SYSTEM OPTIMIZATION IN
  INDUSTRIAL BUILDINGS
• Design Aspects of Energy-Efficient Systems
• SPECIAL CONSIDERATIONS AND SYSTEM DESIGN ASPECTS
• Aspects Related to the Quality of Extract or
  Exhust Air
• Other Questions

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DESIGN GUIDEBOOK, Chapter 9

• Air filtration for better IAQ
• Air handling processes
• Controls, ductwork, sound reduction
• Energy considerations, special questions
• Basic features of air handling processes, and
  theory behind equipment and control
• Link between CHAPTER 4 (physical fundamentals)
  and Applications (for details of equipment, and
  practical items)

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BASIC QUESTION

• What are the theoretical aspects of air handling
  units, ductwork design, and the optimisation of
  building energy systems

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AIR HANDLING UNIT, COMPONENTS

• FILTERS
• HEATERS
• COOLERS
• HEAT RECOVERY

• FANS
• SILENCERS
• HUMIDIFIERS
• DEHUMIDIFIERS

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9.4 AIR HANDLING PROCESSES
COVERS-
Selection Heat requirementsDirect fired
unitsAir heaters Coil selection
Humidification Dehumidification Methods of
Ventilation Methods of Air DistributionAir
Handling Equations examples.
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AIR HEATING EQUIPMENT
INTRODUCTION-

• Unit selection.
• Heating media.
• Air heating coils.

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AIR HEATING EQUIPMENT
HEAT REQUIREMENTS-
Fabric Loss ?f ?(AU) (?ei - ?ao) Ventilation
Loss ?v 0.33 NV(?ei - ?ao) Plant load ?p
?f ?v Use of F1 and F2 factors relating to
the mode of heating for various percentages of
convection and radiation can be used to improve
on the above solutions.
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AIR HEATING EQUIPMENT
The governing equations for Sensible Heat and
Latent Heat requirements are given. The
magnitude of energy loss resulting from one
m3.s-1 heated from an external temperature of -5
?C to 20?C is considered. This is shown to be
approximately 30kW showing the energy losses
that occur by ventilation.
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AIR HEATING EQUIPMENT

• The following media used for Air Heating Coils.
• are considered together with the design
  requirements-
• Low temperature hot water
• Steam
• Electricity

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DIRECT FIRED AIR HEATERS

• This section covers the following types of unit
  and
• the necessary selection factors. -
• Gas Fired
• Oil Fired
• Solid fuel fired

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HUMIDIFICATION DEHUMIDIFICATION

• Required for the following reasons-
• Control of air moisture content within
• a space for the well being of human, animal
• or plant life
• Control of air moisture content within
• a space for the control of a process or product
  
• storage
• A table is included relating the various effects
• that high and low humidity have on given factors

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HUMIDIFIER TYPES

• The various methods by which controlled
• humidification can be achieved is covered.
• By a fine mist or spray
• Absorbent pad evaporation
• Water vaporization
• Steam injection

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HUMIDIFICATION UNITS

• With water storage-
• Spray type
• Pan-type
• Mechanical pan
• Steam generated pan
• Without water storage-
• Spinning disk
• Steam jet
• Ultrasonic atomisation
• Air Washers
• Selection factors for the above

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PSYCHROMETRICS
Moisture content.kg.kg-1
100 Saturation
KEY. 1.Humidification only 2.Heating
humidification 3.Sensible heating
only 4.Dehumidification heating 5.Dehumidificati
on only 6.Cooling dehumidification 7.Sensible
cooling only 8.Evaporative cooling only
1
2
8
7
3
4
6
5
Dry bulb temperature.
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AIR WASHER
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CAPILLARY AIR WASHER


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DEHUMIDIFICATION

• Required for the following reasons-
• Reducing moisture content of a gas to aid
• the manufacture of hygroscopic material
• To stop fouling of heat exchanges
• To stop fine dusts or salts being discharged into
  a
• conditioned space

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DEHUMIDIFICATION

• Dehumidification is achieved by either-
• Compression
• Refrigeration
• Liquid sorption
• Solid sorption
• A combination of the above

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LIQUID SORPTION
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SOLID SORPTION
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AUTOMATIC ROTARY REGENERATION
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AIR DISTRIBUTION

• REQUIRED TO-
• Provide Oxygen for life
• Remove odours
• Reduce bacteria count
• Remove toxic gases, dusts and vapours
• Remove explosive gases and dusts
• To provide adequate air for combustion
• Reduce the moisture content
• Reduce mold growth
• Add or remove heat from the space

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VENTILATION METHODS

• Ventilation of a space is achieved by-
• Natural Ventilation.A combination of(wind
• thermal forces)
• Mechanical extract - induced input
• Mechanical input - Forced Extract (Plenum)
• Mechanical input- Mechanical extract

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NATURAL VENTILATION THERMAL FORCES

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NATURAL VENTILATIONWIND FORCES
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MECHANICAL - EXTRACT INDUCED INPUT
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PLENUM SYSTEM
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MECHANICAL INPUT -MECHANICAL EXTRACT
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METHODS OF AIR DISTRIBUTION

• Achieved by either-
• Upward ventilation (displacement)
• Downward Ventilation
• Crosswise
• Mixed Upward-Downwards

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UPWARD VENTILATION DISPLACEMENT
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DOWNWARD SYSTEM
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CROSS WISE

Laminar Flow Room Arrangement is shown above,
however many other arrangements are possible
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MIXED UPWARD-DOWNWARD SYSTEMS
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AIR HANDLING EQUATIONS
Air Mixing. Considering any two gas streams A
and B which when combine produce a mixed
condition C
Flow Stream A
qvA qmA ? A m
WA h A Mixed conditions
C
qvC qmC ? C m WC h C Flow
Stream B qvB qmB ? B m WA h B
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MASS FLOW
For Mass Flow. Assuming no flow losses occur, the
total mass of a gas introduced into and out of
the system must be constant hence - qm A q m.B
qm C
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MOISTURE CONTENT
For Moisture Content Similarly the total quantity
of moisture in the system will be the same before
and after mixing. However the amount of moisture
per unit mass of the gas will change, hence in
this case the equation must include mass. qmA x
m wA qmB x mw B qmC m w C
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ENTHALPY
For Enthalpy. Provided that no gain or loss of
heat takes place during the mixing process, then
the total heat in the two air streams before
mixing must equal that of the combined air stream
after mixing. qmA x hA qmB x hB qmC x hC
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TEMPERATURE
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TOTAL ROOM AIR MOVEMENT
Primary air leaving the grille, secondary
entrained air from the room,entrainment is
related the leaving jet velocity. Total air is
the combined air stream. Induction expressed by
the momentum equation - qmP vp q ms vs
(qVP qVS) vT The induction ratio (R) is the
ratio of the total air to the primary air.
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SENSIBLE HEAT AIR REQUIREMENTS

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DUCTWORK

• MAIN ITEMS
• design principles
• balancing
• air leakages
• BASIC THEORIES IN CHAPTER 4 (fluid flow)

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ENERGY ISSUES

• FAN EFFICIENCY
• HEAT RECOVERY OPTIMISATION
• DIMENSIONING
• DEMAND-CONTROLLED VENTILATION