air conditionning systems.pdf
TRANSCRIPT
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Thermal exchange guide
Air conditioning systems
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Themal exchange guide
Air conditioning systems
Chapter 1 : Definitions
Chapter 2 : All-air systems
Chapter 3 : All-water systems
Chapter 4 : Air-water systems
Chapter 5 : Direct-expansion systems
Chapter 6 : Computer room systems
Chapter 7 : Energy storage
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Page 1/1
Thermal exchange guideVersion 1.0
Preamble
Having been informed of the type of problem to be solved and after analysis of the consequences,the designer will try to outline the type of installation which will guarantee the best results.
In order to carry out the air handling installation, the designer has at his disposal some basic
elements to be used alone or in association with others.
However the choice or implementation of these various elements will take into account the
following factors :
Nature of the enquiry :
room cooling,
comfort air conditioning,
precision air conditioning
. Nature and use of spaces to be treated :
new or existing,
number and respective locations
Presence or absence of equipments which could be used :
Heating generator,
Cooling generator,
Distribution networks
Summer-winter thermal reports concerning spaces to be treated.
This appraisal determines the choice of a system.
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Contents
Introduction............................................................................................................... 3
Space cooling ........................................................................................................... 4
Definition..................................................................................................................... 4
Aim ............................................................................................................................. 4
Parameters taken into account ................................................................................... 4
Fields of application.................................................................................................... 4
Comment .................................................................................................................... 4
Comfort air conditioning.......................................................................................... 5
Definition..................................................................................................................... 5Aim ............................................................................................................................. 5
Parameters taken into account ................................................................................... 5
Fields of application.................................................................................................... 5
Air conditioning ........................................................................................................ 6
Definition..................................................................................................................... 6
Aim ............................................................................................................................. 6
Parameters taken into account ................................................................................... 6
Fields of application.................................................................................................... 7
Systems..................................................................................................................... 8Definition..................................................................................................................... 8
Potential system components..................................................................................... 9
System identification................................................................................................. 10
Method 1: Local systems .......................................................................................... 11
Method 1: Central systems ....................................................................................... 12
Heating and refrigeration equipment .................................................................... 13
Definition................................................................................................................... 13
Heating equipment.................................................................................................... 13
Refrigeration equipment............................................................................................ 16
Fresh-air conditioning............................................................................................ 21
Definition................................................................................................................... 21
Heat recovery units................................................................................................... 26
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Introduction
This chapter defines the various terms used in the industry to address the field of
air handling: space cooling,
comfort air conditioning,
air conditioning.
It also defines what is meant by a system and its components, and identifies the
criteria for categorising systems.
The types of heating and refrigeration equipment are also redefined.
Last but not least, it discusses fresh-air conditioning and examines the energy
savings afforded by various aspects of heat recovery.
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Space cooling
Definition Cooling is the simplified conditioning of ambient air in order to lower the
temperature by a few degrees.
Aim Provide a feeling of coolness in the summer.
Parameters takeninto account
Only temperature is taken into account. The system must maintain it two or
three degrees lower than the outdoor air (for calculations at least).
Note:
Relative humidity is not taken into account. Occupants may therefore
occasionally experience a feeling of discomfort.
Fields ofapplication
They remain rather varied in cases where cost outweighs technical aspects.
Comment This conditioning method must be used with precaution. It is not suitable forsites where significant amounts of moisture are released.
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Comfort air conditioning
Definition The term comfort air conditioning encompasses all the conditioning processes
applied to ambient air to obtain an indoor environment that is comfortableinterms of temperature and relative humidity.
Aim Obtain, all year round, conditions that are favourable to occupants, their healthand well-being or even improve their conditions.
Comfort can mean two things:
In homes, comfort targets the well-being of occupants,
In businesses, it targets:
improved worker productivity,
increased customer satisfaction.
Parameters takeninto account
Air conditioning takes into account the following parameters:
temperature,
relative humidity,
air cleanliness (impurities, odours),
noise level,
quality of diffusion (air motion, velocity).
Fields ofapplication
Comfort air conditioning applies to:
single-family and multi-family housing,
businesses (shops, offices, public buildings).
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Air conditioning
Definition Air conditioning encompasses all the processes applied to the air in a space to
obtain specific temperature and humidity levelsfor: an activity,
a process,
product storage conditions.
Aim Obtain specific, constantand reliable conditionsall year round for the activityor process being carried out in the space.
Example:
Abattoir cutting room:
temperature of +12C, dew point temperature: +4C to prevent moisture forming on carcasses
taken out of coolers at +4/+5C,
Operating theatre:
highly efficient filtration (HEPA filter), no return air,
temperatures of +20C to +22C (or even 18C),
relative humidity greater than 50% (static electricity).
Parameters takeninto account
The parameters vary by activity:
air cleanliness (impurities, odours),
temperature,
relative or absolute humidity,
drying (or dehumidification) capacity.
In most cases, more or less stringent requirements must be met to maintain these
parameters:
result accuracy:
temperature C C (e.g. 25C 1C),
humidity % % (50% RH 10%),
result stability:
over time,
in the space,
controlled atmosphere:
cleanrooms.
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Air conditioning (continued)
Fields of
application
Air conditioning is used in:
industries: microelectronics,
avionics,
optics,
clockmaking,
micromechanics,
automotive,
paints,
biology:
food processing: beverages, dairy products, meat products, pharmaceuticals and cosmetics,
biotechnology: research laboratories,
hospitals: operating theatres, sterile rooms,
high-tech industries:
fine chemicals,
space (miniaturisation),
packaging,
glassware,
plastics.
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Systems
Definition Whether used for comfort or process applications, the air conditioning system
is the backbone or flow chart connecting all the basic components used tosolve the problem at hand.
The components listed in detail on the following page are divided into four main
categories:
energy production,
air conditioning,
coolant supply (air, water, refrigerant),
air diffusion.
waterchiller
recycling
fan
chilled watercoil
filter
filter
energy recoverydevice
heating coilhot watergenerator
CIATCOOLERI T OOLER
humidifier
fan
In the example opposite:
Cooling and heating energy is generated by awater chiller and a water boiler,
Air, distributed by a system of ducts, is used asthe coolant,
The air is conditioned in an air handling unit(filter, recovery unit, cooling coil, heating coil,
humidifier, forced-draught fan),
The air flows out of ceiling registers,
And is drawn out of the space by the exhaust fan.
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Systems (continued)
Potential system
components
The potential components of a system are the basic elements:
hot water production: independent boiler,
exchanger (from a distribution system),
heat pump,
heat transfer cooling unit (heat recovery condenser),
chilled water production:
independent chiller,
exchanger (from a distribution system),
direct-expansion refrigeration:
packaged, split,
multisplit,
air conditioning:
air handling unit,
terminal units,
ductwork:
distribution,
return,
supply of fresh air,
removal of stale air,
air diffusion equipment:
supply registers,
return grilles.
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Systems (continued)
System
identification
Depending on the criteria used, there are two methods of categorising air
conditioningsystems (see note): Method 1:
The cooling of one or more spaces is the main criterion. It does not take into
account the type of system:
individual air conditioning, or local system,
shared air conditioning, or central system,
Method 2:
The main coolant is the main criterion.
If Then
the system is an all-AIR system air is the coolant
the system is an all-WATER system water is the coolant
the system is an AIR-WATER system both water and air are used
the system is a DIRECT EXPANSION system the refrigerant is the coolant
Note:
These two categorisation methods are the most common.
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Systems (continued)
Method 1:
Local systems
Definition Each space is served by self-contained equipment containing:
a refrigeration and/or heating unit,
air conditioning and diffusion components.
Generally, the equipment is either packagedor split, low or medium capacity,
and direct expansion.
INDOOR UNIT
HEAT EXCHANGER
REFRIGERANT/INDOOR AIR
EXPANSION VALVE
REFRIGERANT LINE
OUTDOOR UNIT
COMPRESSOR
HEAT EXCHANGER
REFRIGERANT/OUTDOOR AIR OR WATER
Use Local systems are generally used in existing single-family homes and smallbusinesses.
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Systems (continued)
Method 1: Central
systems
Definition Each space is supplied with airconditioned in a central unit containing:
an air handling unit (AHU),
heating equipment (+),
refrigerationequipment (-),
the necessary ductwork
Exhaust air
Fresh air
Hotwater
Chilledwater
Supply
Return
A H U
DuctworkAir handling unit
Water boiler
Water chiller
Use As old buildings were not designed with air conditioning in mind, this type ofsystem is found more often in new or recent buildings. A buildings design takes
into account the entire system, i.e. mechanical room and duct runs.
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Heating and refrigeration equipment
Definition The following equipment is needed in order for air to be conditioned:
water (coolant, humidifier),
electricity (to power the motors),
heating equipment,
refrigeration equipment.
This section will discuss local heating and refrigeration equipment.
Heatingequipment
The term encompasses a number of items of equipment:
boiler,
heat exchanger, heat pump,
transfer unit.
Boiler A self-contained vessel used to heat water. Electricity, gas or fuel oil may beused as a heating source. The temperature of the hot water can vary from 50 to
80C.
SUPPLY
BOILER
RETURN
SUPPLY
RETURN
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Heating and refrigeration equipment (continued)
Heating
equipment(continued)
Heat exchanger Actual production is centralised (district heating or the boiler room in a factoryor for a group of buildings),
A heat exchanger is used locally to raise the hot fluid to the desired temperature.
The operating temperature can vary from 50 to 80C.
EXCHANGER
SUPPLY
RETURN
DISTRICT HEATING
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Heating and refrigeration equipment (continued)
Heating
equipment(continued)
Heat pump Heat pumps draw heat from a cold source and transmit it to a heat source.
The cold source may be:
Water: ground water, river, lake, sea, process cooling water,
Air: outside air, exhaust air (buildings, processes).
The temperature of the hot water (heat source) is between 40 and 55C.
SUPPLYRETURN
WATER - WATER
DISCHARGE
HEAT PUMP
SUPPLYRETURN
AIR - WATER
air
Transfer unit Transfer units are found on cooling systems that operate all year long (processcooling).
The refrigeration circuit may be equipped with an additional water-cooled
condenser known as a heat recovery condenser.
No heat is produced unless refrigeration is also produced.The temperature of
the hot water is between 40 and 50C.
SUPPLYRETURN
WATER-cooled heatrecovery condenser AIR-cooledcondenser
Evaporator
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Heating and refrigeration equipment (continued)
Refrigeration
equipment
The term covers a number of items of equipment:
water chiller,
direct-expansion refrigeration unit,
heat exchanger,
cooling tower,
drycooler.
Water chiller A water chiller is a machine that cools water, which is used as a refrigerant.
Temperature of the chilled water:
5 to 12C depending on the operating conditions,
mean inlet/outlet temperature difference: 5C,
Freezing temperatures:
An antifreeze such as glycol or similar is added to the water.
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Heating and refrigeration equipment (continued)
Refrigeration
equipment(continued)
Direct-expansion
refrigerationunit
The evaporator is removed from the central system and placed inside the air
handling unit, where it cools the air that will be supplied to each space.
Direct expansion coil
Thermostaticexpansion valve
Air flow
Water-cooled condenser(or air-cooled)
Motor compressor
Heat exchanger Actual production is centralised (district cooling or factory system).
More and more large cities are turning to chilled water district cooling systems.
In industry, heat exchangers are used in applications requiring water at
temperatures different from that in the distribution system.
EXCHANGER
SUPPLY
RETURN
DISTRICT HEATING
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Heating and refrigeration equipment (continued)
Refrigeration
equipment(continued)
Cooling tower A cooling tower is a specific type of cooling device. It uses humidified ambientair to produce chilled water. The air is cooled to its wet bulb temperature.
Example: Air at a temperature of 30C with 40% RH is cooled to its wet bulb
temperature of +20C. It serves as a refrigerant.
There are two types of cooling tower:
Closed-circuittowers, in which heat is exchanged between air and water by asprayed heat exchange coil. The air and the water in the condenser circuit
do not enter into contact.
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Heating and refrigeration equipment (continued)
Refrigeration
equipment(continued)
Cooling tower(continued)
Open-circuit towers, in which air and water come into direct contact. Dropsof water run along a distribution panover which air flows. The water in the
condenser circuit and the air are in direct contact with each other.
The diagram below shows a water chiller operating on an open-circuit cooling
tower.
Fan
Spray nozzle
Air inlet
Drain pan
Wet deck
Gutter
Droplet separator
Cleaning tap
Makeupwater
Bypassvalve
pump
Treated makeup water inlet
Overflow
Screen filter
Drain
Water-cooled condenser
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Heating and refrigeration equipment (continued)
Refrigeration
equipment(continued)
Drycooler A drycooler is a type of cooling device that uses dry air as a refrigerant.
Example: When the air temperature is 30C with 40% RH, the temperature taken
into account is +30C (not +20C, as in the case of the cooling tower). Heat is
transferred from water to air by a dry heat exchanger.
As with a closed-circuit cooling tower, the water in the condenser circuit of a
drycooler never enters into contact with the air.
This eliminates the risk of spreading Legionellosis.
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Fresh-air conditioning
Definition Before discussing the subject of fresh-air handling, one should understand what
is meant by the following terms: pollution,
removal of stale air,
supply of fresh air,
fresh-air handling,
heat recovery units.
Pollution People, their health and activities, as well as processes are all sources ofpollution:
dust,
germs,
water vapour,
carbon dioxide, etc.
The concentration of contaminants that can endanger health and adversely affect
processes rises quickly in enclosed rooms.
Removal ofstale air
The concentration of contaminants must be reduced to a safe level. This is
accomplished by extracting all or part of the stale air.
Supply of freshair
The extracted air is replaced with air from the outside. This air is often referred
to as fresh air. This outside air is assumed to be of better quality than the
extracted air. This is not always the case however. This is why fresh air must be
conditioned before it is introduced into a space.
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Fresh-air conditioning (continued)
Definition
(continued)
Fresh-airconditioning
Fresh air is conditioned in a number of ways:
It is filtered to ensure the right level of cleanliness,
It is heated or cooled to ensure the right temperature,
It is either humidified or dehumidified to ensure the correct level of humidity.
These processes are energy consuming.
Fresh air
+32C
Stale air
discharge
Forced-draught fan
-10C
+20Cor
+25C
ExtractionfanFilters
Preheating or precooling coil
or both if need be
to
Winter : ambient +20Cair supply +30C
Summer : ambient +25Cair supply +15C
ENERGY-
CONSUMING
SYSTEM
Fresh air can be conditioned:
For specific environmental conditions. In this case it is not used to heat orcool the space,
For specific air flow conditions in a space. In this case a portion is usedfor heating and cooling. As the volume of fresh air is small, it is simply
an addition.
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Fresh-air conditioning (continued)
Definition
(continued)
Heat recoveryunits
The phenomenon is most flagrant in winter. Fresh air drawn in from outdoors is
at low temperature (e.g. -10C) and stale air discharged outdoors is at high
temperature (+20C at comfort levels).
A heat recovery unit is a device used to transfer heat without any direct contact
between both types of air. More specifically, a portion of the heat in the exhaust
air is transferred to the supply air. This exchange of heat results in lower energy
consumption.
Exhaustair
Freshair
Outdoors
-10C/90%32C/40%
Air-conditionedspace
20C/50% (winter)25C/50% (summer)
Energy recoverysystem
A H U
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Fresh-air conditioning (continued)
Air purification:
the No concept
The No concept is based on the combination of an adsorbent such as
activated carbon and photocatalysis.
Polluted air
mineralization byphotocatalysis
Contaminant retention Purified air
NEO operation principle
Contaminant removal
ACTIVATED
carbon
ULTRAVIOLETradiation
desorptionabsorption
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Fresh-air conditioning (continued)
Air purification:
the No concept(continued)
The activated carbon [Navarri et al., 2001] absorbs large quantities of
contaminants along its surface (it has a specific surface area ofapprox. 1000 m/g). These contaminants are trapped by low-intensity
electrostatic forces, called van der Waals bonds, with interaction energies of
5 to 40 kJ/mol. The main drawback of this kind of filter is the saturation
point of activated carbon. Known as the breakthrough point, this threshold
is very difficult to predict in cases where concentrations and flow rates vary.
Once this point is reached, the filter can no longer achieve the desired
concentration efficiency. Titanium dioxide (TiO2) photocatalysis in the gas
phase [Nguyen, 2001] is a heterogeneous catalysis process in which the
solid catalyst is activated only by ultraviolet radiation. Under certain
conditions, the heterogeneous photocatalysis process is capable of
mineralising pollutants completely. It is split into five phases:
transfer of gaseous reagents to the photocatalytic surface,
adsorption of the gaseous reagents on the photocatalytic surface,
photochemical reaction between the adsorbed gaseous reagents and thephotocatalytic surface; mineralisation of organic compounds,
desorption of gaseous photocatalytic reaction products,
diffusion of the gaseous products off the photocatalytic surface.
The main drawback of photocatalysis used on its own is the low adsorption
capacity of the catalyst (titanium dioxide) which prevents it driving down
high pollution levels. Pollutants are thus only partially mineralised when
concentrations and/or flow rates are high. Combining a filter containing anadsorbent such as activated carbon with a photocatalysis system eliminates
the drawbacks inherent to each process and also significantly cuts down on
maintenance.
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Fresh-air conditioning (continued)
Heat recovery
units
The term heat recovery unit, or HRU, covers various types of equipment:
dual-coil recovery units,
plate heat exchangers,
heat pipes,
heat recovery wheel.
Dual-coilrecovery units
As is implied by its name, a dual-coil recovery unit consists of two standard
finned coils connected by a circuit through which refrigerant (antifreeze if
necessary) is circulated by a circulator pump.
One coil is placed in the exhaust air circuit and the other in the supply air circuit.
The air and water circuits are arranged for counter-current circulation.
Safety valve
HEAT
RECOVERY
COIL
HEAT
RECOVERY
COIL
Circulator
+20C
50%
-10C90% Drain
Circuit
filling
Preheate
d
freshair
Exhausta
ir
Expansionvessel
Freshair
Cooled
exhaust
air
Drain valve
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Fresh-air conditioning (continued)
Heat recovery
units (continued)
Dual-coilrecovery units
(continued)
This system allows for much flexibility, and the coils can be integrated inside the
air handling unit.
Water
Exhaustair
Freshair
Outdoors
AHU+/-
+/-
Return air
Supplyair
Air-conditionedspace
In more complex cases where an air extraction system cannot be installed in the
same space as a fresh-air conditioning system, both can be connected
hydraulically.
Forced-draughtfan
Extractionfan
Conditionedsupply air
Pump
Glycol/water heat transfer circuit
Airextrait
Freshair
Exhaustair
Water
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Fresh-air conditioning (continued)
Heat recovery
units (continued)
Heat pipe A heat pipe is a metal tube usually with fins on its outside and containing a fluidin the form of two balanced phases:
a liquid phase,
a gas phase.
It transfers heat through a cycle of evaporation and condensation.
1. The fluid evaporates in the hot end (evaporator).
2. The vapour thus formed condenses on the cold end (condenser).
3. The fluid from the cold end returns to the hot end:
By gravity, in which case the condenser section must be above theevaporator section,
Via a capillary (or wick) structure lining the inside wall of the tube. Theheat pipe can also operate horizontally in this case; a slight angle of 7-8
will promote movement.
HORIZONTAL HEAT PIPE
Liquid
Vapor
Liquid
Evaporation section Condensation section
Capillary
structure
Extracted warmair enters
Warmed
air exits
Cooled airexits
Cool freshair enters(cold source)
Partition
Heat transfer
(hot source)
Heat
recovery
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Fresh-air conditioning (continued)
Heat recovery
units (continued)
Heat pipe(continued)
Condensed
liquid
Heat transfer
(hot source)
Heat
recovery
Vapour
Capillary
structure
Extracted
warm air
enters
Cooled air
exits
Warmed
air exits
Cool fresh
air enters(cold source)
The pipes are arranged in arrays split into two by a sealed partition separating the
two streams of air.
The evaporation and condensation temperatures are highly similar and the
operation is virtually isothermal. The transfer occurs only through the latent heat
of the change in state.
gravity causes liquidto flow back down
condensation
vaporisation
vapour
Warmedair exists
Liquid
Extracted warmedair enters
C
ondensation
section
Evaporation
section
Heat
recovery
Cooledair exits
Cool freshair enters
(cold source)
Heat transfer
(hot source)
VERTICAL HEAT PIPE
Vapor
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Fresh-air conditioning (continued)
Heat recovery
units (continued)
Heat pipe(continued)
partitionheat pipe
coolai
r
warm
air
warmedair
cooled
air
The figure below illustrates a constant-flow model of a ClimaCIAT dual-flow
AHU with heat pipes:
Exhaust air
Fresh air-10C
Exhaust air+20C
Air supply
The figure below illustrates a ClimaCIAT dual-flow AHU with variable-flow
heat pipes and a mixing box:
Freshair
-10C
Exhaustair
+20CExhaust
air
Airsupply
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Fresh-air conditioning (continued)
Heat recovery
units (continued)
Plate heatexchanger
In this type of heat exchanger, horizontal and vertical streams of air flow
between thin plates stacked in parallel:
The exhaust air transfers its heat to the air flowing between the plates.
There are two types of flow arrangement:
cross-flow,
counter-flow.
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Fresh-air conditioning (continued)
Heat recovery
units (continued)Plate heat
exchanger (continued)
Cross-flowexchanger
Counter-flowexchanger
Exhaustair
Fresh air
Exhaustair
Cooledexhaust
air
Inside
Outside
Fresh air
Preheatedfresh air
Platethickness
Gap
This figure illustrates a ClimaCIAT dual-flow AHU with a plate heat exchanger
but no mixing box:
constant flow of exhaust air,
constant flow of fresh air.
Fresh air-10C
Exhaustair
+20C
Exhaust air
Air supply
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Fresh-air conditioning (continued)
Heat recovery
units (continued)
Plate heatexchanger
(continued)
The figure below illustrates a ClimaCIAT dual-flow AHU with a plate heat
exchanger and a mixing box. The flow of air over the plate heat exchanger can
be adjusted.
exhaust air+20C
exhaust air
fresh air-10C
supply air
Example of an air handling process: fresh air in with recovery of heat from
exhaust air by a plate exchanger.
Dual-flow AHU
exhaustair
AIR-TO-AIRheat exchanger
frost protection dampers freshair
supply
air
exhaust
air
R
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Air conditioning systemsVersion 1.0
Fresh-air conditioning (continued)
Heat recovery
units (continued)
Heat recoverywheel
A heat recovery wheel is a low-speed wheel (10-20 rpm) with many small
channels through which air passes. A little less than half the front surface is
connected to the exhaust air circuit. A little less than half the surface is
connected to the supply air circuit. A small surface is used as the purge sector.
As the wheel rotates, the section heated by the warm air gives up its heat to the
stream of cool air flowing through it.
The two air streams thus flow through the channels alternately.
motor
fresh
air
exh
aust
air
purge sector
drive belt
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Air conditioning systemsVersion 1.0
Fresh-air conditioning (continued)
Heat recovery
units (continued)
Heat recoverywheel
(continued)
Apurge sectoris usually built over the wheel to minimise carryover from the
exhaust air. To facilitate this, the pressure of the exhaust air must be lower than
that of the supply air.
direction of
rotation
purge sector
P4
P1
P1>P4 exhaust air
fresh air
duct exhaust air
exhaust air
supply air fresh air
seal
purge sector
purge stream
whell
direction ofrotation
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Air conditioning systemsVersion 1.0
Fresh-air conditioning (continued)
Heat recovery
units (continued)
Heat recoverywheel
(continued)
The figure below illustrates a ClimaCIAT dual-flow AHU with a rotary heat
exchanger without amixing boxbypass:
constant flow of exhaust air,
constant flow of fresh air.
fresh air-10C
exhaustair
exhaust air+20C
supplyair
The figure below illustrates a ClimaCIAT dual-flow AHU with a rotary heat
exchanger, mixing box and adjustable air flow:
fresh air-10C
supply air
exhaust air+20C
exhaust air
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Air conditioning systemsVersion 1.0
Fresh-air conditioning (continued)
Heat recovery
(continued)
Importantinformation
Choosing the right fresh-air conditioning method is part of the design process.
It depends on the type of air handling equipment that will be used:
When the air in a large number of spaces is to be handled by standardterminal units (e.g. fan coil units), fresh air should be handled completely by
one central unit,
When the air in a space is handled by an AHU, a single or double mixing boxmay be added to help to condition fresh air.
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Air conditioning systemsVersion 1.0
CCChhhaaapppttteeerrr222:::AAAllllll---aaaiiirrrsssyyysssttteeemmmsss
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Contents
Contents .................................................................................................................... 2
Basic concept ........................................................................................................... 3
Definition..................................................................................................................... 3
Air handling unit .......................................................................................................... 5
Possible solutions....................................................................................................... 6
Local air handling unit.............................................................................................. 7
Concept ...................................................................................................................... 7
Operation.................................................................................................................... 8
Mollier chart ................................................................................................................ 9
Single-zone air handling unit................................................................................. 10Concept .................................................................................................................... 10
Operation.................................................................................................................. 11
Mollier chart .............................................................................................................. 13
Field of application.................................................................................................... 14
Dual-duct AHU ........................................................................................................ 15
Concept .................................................................................................................... 15
Operation.................................................................................................................. 16
Mollier chart .............................................................................................................. 17
Field of application.................................................................................................... 17
Multizone unit.......................................................................................................... 18
Concept .................................................................................................................... 18
Operation.................................................................................................................. 19
Mollier chart .............................................................................................................. 21
Field of application.................................................................................................... 21
Air handling unit with variable-volume diffusion boxes for each space ........... 22
Concept .................................................................................................................... 22
Operation.................................................................................................................. 23
Field of application.................................................................................................... 25
Impulsair ................................................................................................................... 25
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Basic concept
Definition Air is preconditioned by an air handling unit then supplied to a space via a duct.
All the heatneeded to cool a space is carried by air:
Air conditioning is generally centralised,
The mechanical room contains:
refrigeration equipment,
heating equipment,
an air handling unit in which air, including fresh air, is conditioned,
The ductwork contains:
return ducts running from each space,
stale air exhaust ducts,
fresh air supply ducts, supply ducts running to each space.
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Basic concept (continued)
Definition
(continued)
The drawing below illustrates the basic design of an all-air system.
exhaust air
fresh air
hotwater
chilledwater
supplyair
retrurnair
A.H.U.
ductworkair handling unit
water boiler
water chiller
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Basic concept (continued)
Air handling unit The flow of the air handled by the unit is determined by:
thermal loads,
the acceptable t between the supply and return air (see comfort airconditioning and air handling).
For obvious reasons of economy, the supply of fresh air is limited (unless
required otherwise for safety) to minimum healthy levels set out by regulations.
The type of handling needed is defined by the influencer, who then buildsthe air
handling unit to fit the needs of the space.
For example, the AHU below contains the following equipment:
1 return air fan,
2 exhaust air/recirculated air mixing
dampers,
3 prefilter,
4 cooling coil and heating coil,
5 humidifier,
6 forced-draught fan,
7 f inal filter.
exhaust air
return air
fresh air
1
2
3
supply air
45
6
7
In some cases (such as cleanrooms; see our document on filtration) the final filter
may be placed at the entrance to a space instead of inside the AHU to allow
for potential pollution from ductwork.
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Basic concept (continued)
Air handling unit
(continued)
The drawing below shows an air handling system with a heat recovery unit
installed on the fresh air/exhaust air circuits.
heat recovery unit on exhaust air circuit
exhaust
air
return air from
served spaces
supply airfresh
air
128
43 5 6 7
mixes exhaust air and
recirculated air
Possible solutions The solutions depend on the type of space and changes in loads, as well as
investment possibilities and the requirements for each space.
The most common solutions include:
individual space equipment: a separate AHU and ducts for each space,
multispace equipment: a unit with ducts for a series of spaces,
a single unit connected to two ducts, one for hot air and the other for cool air.A mixing box ensures the adequate mix of air for each space,
a multizone AHU with separate ducts for each space,
basic equipment (air handling unit) with, for each space, a variable-volume
air diffusion box.
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Air conditioning systemsVersion 1.0
Local air handling unit
Concept Each space is supplied with conditioned air by its own specific unit:
constant flow of air,
fresh air (suction) is usually conditioned in the AHU which also extracts staleair,
the components (filter, cooling and heating coils, humidifier) are determinedbased on the requirements of each space.
Heating and refrigeration equipment is with the unit in the mechanical room or
outside (cooling system with air-cooled condenser).
exhaustair
Example of a unit with electric heating coil and chilled-water
cooling coil with temperature control only
freshair
volume = constantT = f (space requirement)
R
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Local air handling unit (continued)
Operation The unit adjusts conditions based on the space loads. It:
regulates the temperature (summer and winter),
regulates the humidity (winter),
and, in certain cases, dehumidifies the air (summer).
In the drawing below, regulation occurs with the following sequences:
Sensors Effect on
Temperature cooling coil (chilled water) (1)
heating coil (hot water) (2)
Relative humidity cooling coil (chilled water) (1)
humidifier (3)
Occupancy fresh air damper
Outdoor temperature free cooling (energy savings)
room
supply air
A
exhaustair
extraction air
T : Temperature sensorH : Humidiy sensorO : Occupancy meter
O
T
T
S
EFM C
H
freshair
(1) and (2) 2-way or 3-way modulating or on/off valve(3) 2-way on/off valve
(1) (2) (3)
R
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Local air handling unit (continued)
Mollier chart Changes in air temperature and humidity are plotted in the following manner on
what is called aMollier chart.
O
M
t
wq'
HM
space linesegment
summer operation
O : outdoor airI : indoor environmentM : mixing
S : supply airC : supply from cooling coil
H : supply from heating coil Ssummer line segment
Hwinter line segment
winter operation
S
I
I
SS
W
C
100%
O
H
Field ofapplication
This type of system is generally used for:
large-volume spaces,
low-tolerance environmental controls,
spaces with heavy load conditions that vary,
meeting rooms,
theatres and concert halls.
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Single-zone air handling unit
Concept Air is supplied to several spaces by a single air handling unit:
the air flow for each individual space is constant and calculated based on itsmaximum heat load,
fresh air (suction/extraction) is generally conditioned in the AHU beforebeing supplied to all the spaces,
the components (filter, cooling and heating coils, humidifier, etc.) aredetermined based on the needs of each space,
heating and refrigeration equipment is generally located in the mechanicalroom,
detection devices (temperature and humidity sensors) are arranged in acontrol room.
exhaust air
fresh air
hot
water
chille
dwater
supp
lyair
retur
nair
A.H.U.
ductworkair handlingunit
water boiler
water chiller
This type of system is also called a simplified all-air system.
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Single-zone air handling unit (continued)
Operation This system is used for spaces where the following loads are identical:
distribution of sensible heat and latent heat, changes and variations in the same direction and proportions,
The properties of the air supplied to each space are the same,
Fresh air is distributed based on the total load, not on the density of occupantsin the space.
The control devices and temperature and humidity sensors may be installed:
In a control room (e.g.
A1)
The other spaces (A2, A3etc.) are governed by the A1
law.
In the main return airsection
All the spaces (A1, A2, A3etc.) are governed by thelaw of averages.
Space conditions cannot be adjusted to personal preferences,
As a matter of fact, spaces rarely experience the same changes in heat.Deviations occur in environment parameters on account of the fact that the air
supply conditions are the same for all spaces. The system would not be an
adequate choice for precision air conditioning.
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Single-zone air handling unit (continued)
Operation
(continued)
The figure below shows an installed single-zone air handling unit.
SA3
A2
A1
S
(1) and (2) 2-way or 3-way modulating or on/off valve(3) 2-way on/off valve
S
(1)(2)(3)
T
T H
exhaustair
fresh
air
R
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Single-zone air handling unit (continued)
Mollier chart Changes in the air supplied to the spaces are plotted on the Mollier chart.
S
2
A3
A1=A
A2
3
1
t
wq'
This diagram does not show the various handling/conditioning processes the air
undergoes in the unit. It shows changes in the air in each space based onsensible and latent heat.
1, 2, and 3 are the line segments. A is the space setpoint. When the same
amount of air S is distributed to all the spaces, it is clear that the space
conditions A cannot be controlled when their loads are different,
the space line segments 1, 2, 3 are rarely completely identical,
all pass by the same supply air point.
The indoor environment A1, A2, A3, should have the same value A, but as the
loads are not really identical, the value of A is controlled only for the space
where the sensors are installed (i.e. space A1for which A1will equal A).
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Single-zone air handling unit (continued)
Mollier chart
(continued)
To sum up:
The simplified all-air system is adequate only if the thermal loads in each zoneare identical and vary in the same direction and proportions,
The balance and stability of the air flows are deceptive for branched orlengthy systems.
fresh air
zone 1 zone 2 zone 3 zone 4
return air
duct
supply air
duct
no means ofregulation
supply air conditions are
the same for every zone
Field ofapplication
Because it is economic, the system may be used for spaces with identical thermal
loads and where conditions do not need to be adjusted to personal preferences.
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Dual-duct AHU
Concept This system offers the following features:
A singleair handling unit that is simplified for air preconditioning. It is madeup of:
a mixing box,
a preheating coil for winter,
The supply air duct leaving the AHU is split in two:
warm air duct with preheating coil and humidifier,
cool air duct with cooling coil,
Three ducts are routed to and from spaces:
cool air supply duct,
warm air supply duct,
extraction duct.
The unit is generally operated at high speed (V >6 m/s) for reasons of space.
Each space contains a motorised mixing box controlled by the space sensor.
The supply air is delivered at a constant rate but the proportions of cool and
warm air vary.
C
F
S
spacesensor
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Dual-duct AHU (continued)
Operation Contrary to what might be thought, the system is not particularly energy
consuming: Most often (in spring and autumn, amongst other periods) only one of the
ducts (heating or cooling) is supplied with air that has been conditioned
simply by mixing the outdoor air with the recirculated air,
When both ducts are needed, the hot water is delivered by the condenser in thewater chiller unit (the condenser then becomes a heat transfer unit).
Fresh air is introduced when the outdoor temperature drops below room
temperature and cooling is needed.
A3
S3
A2
A1
T
T
exhaustair
freshair
S2
T
S1
T
(1) and (2) 2-way modulating or on/off valve
(3) 2-way on/off valve
(2) (2)(1)(3) R
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Dual-duct AHU (continued)
Mollier chart Changes in air temperature and humidity are plotted on the Mollier chart.
O
M
H
C
t
w
q'
C
M
I
I
SS
W
C
E
S
O : outdoor airI : indoor air
M : mixingH : warm air stream properties
S : supply airC : cool air stream properties
Ssummer line segment Wwinter line segment
Field of
application
This system is advantageous for handling the air in spaces with heavy load
conditions that vary.
It is often used with laminar-flow ceilings:
business spaces,
exhibition halls,
upscale spaces: large glazed surfaces subject to varying loads.
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Multizone unit
Concept This system offers the following features:
The conditions of the supply air are adjusted by mixing the cool and warm air,
Both air types are mixed inside the unit and occupants in each space (or zone)choose the level they want,
Each space has its own separate supply air duct:
constant air flow,
variable supply air temperature,
The return air ducts may be shared.
The AHU has a different design.
recirculatedair
filter fan
thermostat
heating
coil
cooling coil
freshair
warm air
cool air
zone 3 (H)zone 2 (H)
zone 1 (H)
zone 3 (C)zone 2 (C)
zone 1 (C)
R
(1) and (2) 2-way or 3-way modulating or on/off valve
(1)
(2)outdoor sensor
R
R
outdoor sensor
The heating and cooling coils are installed in parallel (not in series) on the aircircuit. This creates a stream of warm air and a stream of cool air,
The fan is installed upline and blows air on the coils,
Two rows of dampers downline of the coils (one on the warm stream, theother on the cool stream) are used to mix warm air and cool air,
Vertical barrier walls are used to divide the free areas (i.e. volumes of air) andcreate zones inside the unit. The air flows at work are a function of the thermal
balances. A unit is typically split into no more than four or five zones.
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Multizone unit (continued)
Operation The figure below shows a multizone unit.
recirculated air
return air A
freshair
limit swich for : 3 rooms 3 zones 3 air supply ducts the return air duct may be shared
A3A2A1
T1
T2
T3
S1 S2 S3
T
exhaustair
M3
M2
M1
M3M2
M1
C
F
The sets of dampers are used to mix air in all types of proportions possible for each zone :Warmed air (H) mixed with conditioned air (M) by the mixing box in winterCooled air (C) mixed with conditioned air (M) by the mixing box in summer
M
(2)
(1)
(1) and (2) 2-way or 3-way modulating or on/off valve
R
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Multizone unit (continued)
Operation
(continued)
the coils ensure constant cool-air and warm-air temperatures,
servomotors controlled by the space thermostat adjust the dampers foradequate air mixing:
a detection unit measures the outdoor air temperature and controls themixing box servomotor (free cooling),
limit switches (servomotors zone) also participate in regulating air flows.Closing all the zones during heating will cause the heating coil supply to
close.
Note:
as stated previously, the energy-efficient operation described below isfrequently observed:
only one coil (cooling C or heating H) is supplied and the air delivered bythe mixing box (M = mix of fresh air and recirculated air) is divided
between the supplied coil and the unsupplied one.
this gives a new mix:
C + M or H + M depending on the need,
when adjusted correctly, this type of system is relatively energy efficient,
by using refrigeration equipment such as a heat transfer unit, heat from thecondenser can be used in cases where both cooling and heating are necessary.
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Multizone unit (continued)
Mollier chart Changes in the air supplied to a given space are plotted on the Mollier chart.
O
O
MH
M
C
t
w
q'
CC
S
W
S1
I1
S1
I1
O : outdoor airI : indoor airM : mixingH : supply from heating coilS : supply airC : supply from cooling coil
Ssummer line segment Hwinter line segment
Field ofapplication
The systems advantage lies in its quick responsiveness and the ability to adjust
spaces to individual needs:
Groups of spaces with load conditions that vary quickly,
Series of spaces, each with occupancy loads that are never the same or varyfrom zone to zone (this makes it possible to lower the total installed capacity).
It is therefore well-suited to spaces such as:
company canteens, dining halls, homes (day zone, night zone).
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Air handling unit with variable-volume diffusion boxes for eachspace
Concept This system offers the following features:
variations in thermal loads are handled by adjusting the flow of conditionedairsupplied to each space,
a single air handling unit for all spaces,
the AHU may be equipped with a flow control system (suction deflectors orspeed control),
it may be constant volume; if so, each space is equipped with a bypass.
variable-volumebox
variable-speedforced-draught fan
variable-speedreturn air fan
air handlingunit
return air
exhaust air fresh air
air outlet
return airgrille
System with variable volumes of air per zoneUnit equipped with a flow controller
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Air handling with variable-volume diffusion boxes for eachspace (continued)
Operation How the system operates:
air is regulated in the air handling unit to ensure a constant supply airtemperature. The AHU operates in either heating or cooling mode; differing
needs cannot be met,
the flow of supply air to each space is modulated by the space sensor based onthe heat load.
In the example below:
Air is delivered to Type A spaces by the variable air volume system; the returnair flows along passageways (halls),
Type B spaces are equipped with their own individual units. Stale air is drawnout by a separate extraction unit.
AB
T
T
exhaust air
return air
discharge
outside outsidehall
distribution ofconditioned air bypass
fresh air
T
(1) and (2) 2-way or 3-way modulating or on/off valve(3) 2-way on/off valve
(1)(2)(3)
window
fan coil unit with fresh air inlet
Constant-volume unit with
space bypasses
H
R
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Air handling with variable-volume diffusion boxes for eachspace (continued)
Mollier chart Changes in the air in the AHU are plotted as follows on the Mollier chart.
O :outdoor airI : indoor airM : mixingS : supply air
Ssummer linesegment
O
M
t
w
q'
S S I
Air is conditioned in the conventional manner inside the unit. The regulation
system ensures that the temperature and humidity of the supply air are at
particular levels. However, the amount of air delivered to each space is adjusted
as needed.
Issues andprecautions foruse
Variations in flow in a given space should not disrupt the balance of the wholeor the flows delivered to the other spaces.
A system is needed to control and maintain the pressure in the distributioncircuits.
High variations and significant drops in flow rates may cause the geometry ofthe air stream introduced and its range to create uncomfortable conditions for
occupants.
As regards air change, a number of problems may arise:
The fresh air is conditioned entirely inside the unit.
Each space receives the required amount of fresh air under full load
conditions.
Losses (e.g. insulation) may cause heat load variations in the spacewhereas the occupant density (i.e. the need for fresh air) stays even. The
modulation of the flow of supply air in turn modulates the amount of fresh
air introduced.
Adjustingflow and pressure may be tricky; an adjusting device may need tobe installed to maintain the pressure inside the ducts at a constant level.
Installing ceiling registers specially designed to keep air streams horizontal isrecommended.
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Air handling with variable-volume diffusion boxes for eachspace (continued)
Field ofapplication
This system, quite rate in France, may be used in:
office buildings,
hotels.
Impulsair The impulsair is a variable-air-volume adjustment system used in the 1970s.
The Coandaeffect
The operation of the impulsair is based on a well-known aerodynamic
phenomenon known as the Coanda effect, or the extremely odd tendency of air
to adhere to the surface along which it is flowing.
Henri Coanda discovered this phenomenon in 1928 when he noticed that hot
gases from his experimental jet-propelled aircraft hugged the sides of the
fuselage, damaging the tail unit.
On closer look at this phenomenon, it can be seen that a fluid will stay attached
to a surface, even a convex one, as is moves along it.
Coanda effect
stream of fluid
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Air handling with variable-volume diffusion boxes for eachspace (continued)
Impulsair(continued)
Concept A stream of air directed towards a Y-duct can be deflected to either branch if twolateral openings A and B are placed just before the Y-duct.
Opening A and closing B will direct all the air to the right branch. Conversely,
closing A and opening B will direct all the air to the left branch.
A B A B
Variable-volume impulsair systems have the following main features:
constant supply air velocity resulting in even space temperature,
air flows are adjusted without the means of moving components such asdampers or motors (zero breakdowns or servicing),
constant volume in the air handling units, air is supplied to spaces intermittently. The supply time, not the volume
supplied, is modulated.
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Air handling with variable-volume diffusion boxes for eachspace (continued)
Impulsair(continued)
Concept(continued)
If Then
Space cooling under full load is
required.
The control damper is maintained in a position set by the
thermostat while the main damper directs the entire volume of air
to the space.
The temperature in the space
decreases, as does the need for cool
air.
The thermostat controls the impulsair. The air from the unit is
directed to either the space or the recirculation duct. At the start,
the supply time is longer than the recycling time.
Cooling requirements continue to
decrease.
The impulsair responds by gradually shortening the supply time
and extends the recycling time.
suspended ceiling
diffuser
damper
damper
damper
return air
supply air
return air grille
ceiling
T
impulsair
Operation Note:
Although it is theoretically conceivable that the entire volume of air be
recycled and that no more air be directed to the space, this possibility should be
excluded in a well-designed system. Firstly, lighting and people are a basic
cooling load. By carefully selecting the supply air temperature, however, a high
rate of air can be obtained even if the heat gain is minimal.
What occurs between 100% supply air and 100% recycling is depicted in the
figure on the following page. The surfaces at the top show the air flows
delivered to the space. The surfaces at the bottom show the flow rates of
recirculated air.
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Air handling with variable-volume diffusion boxes for eachspace (continued)
Impulsair(continued)
Operation(continued)
100% constant-volume air stream
time in seconds
spaces100
100
returnpercentageofveloc
ity
spaces100
250
100
return
p
ercentageofflow
2 HZ (max.frequency)
2 54 565248 504642 444036 3834323026 282420 221814 16128 10640
AIR VELOCITY
AIR FLOW
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Air handling with variable-volume diffusion boxes for eachspace (continued)
Impulsair(continued)
Operation(continued)
The figure below shows an installed system with impulsair units.
return air grille
impulsair
diffuser
diffuser
forced-draught fan
return air fan
airhan
dlingunit
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CCChhhaaapppttteeerrr333:::AAAllllll---wwwaaattteeerrrsssyyysssttteeemmmsss
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Contents
Contents .................................................................................................................... 2
Basic concept ........................................................................................................... 3
Definition of an all-water system ................................................................................................ 3
Possible solutions........................................................................................................................ 4
Fan coil units............................................................................................................. 5
Basic concept ............................................................................................................................... 5
Two-pipe fan coil unit .................................................................................................................. 7
Four-pipe fan coil unit.................................................................................................................. 9
Two-pipe, two-wire fan coil unit................................................................................................ 11
Air-change fan coil unit.............................................................................................................. 13Non self-contained air-handling terminal units.................................................... 15
Basic concept ............................................................................................................................. 15
Equipment type .......................................................................................................................... 15
Fan coil units .............................................................................................................................. 15
Mini air handling units ............................................................................................................... 20
Individual water-loop heat pumps......................................................................... 29
Basic concept ............................................................................................................................. 29
Advantages................................................................................................................................. 29
Heating and refrigeration equipment........................................................................................ 30
Heat pumps................................................................................................................................. 32
Field of application..................................................................................................................... 33
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Basic concept
Definition of an
all-water system
An all-water system offers the following features:
The space is equipped with a terminal unitsupplied with hot and/or coldwater by pipes (water loop).
The pipes transfer energy between the central plant(refrigeration andheating equipment) and the terminals.
All the energy needed to cool a space is carried by water.
Note: With this type of system, fresh air may be conditioned inside the terminal
unit or introduced directly in the space without being conditioned (see fan coil
unit, air change).
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Basic concept (continued)
Possible solutions The solutions generally depend on the type of space, as well as investment
possibilities and the requirements for each space.The most common solutions include:
A fan coil unit that can also be used in a number of versions (two-pipe,four-pipe, two-pipe/two-wire).
Cassette or mini non self-contained air-handling terminal units.
Individual water-loop heat pumps.
Each of these solutions will be discussed in detail in this chapter.
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Fan coil units
Basic concept A fan coil unit is a terminal unit with:
a heat exchange coil,
a fan motor,
a filter,
a condensate drain pan.
Fan coil units can be in cased or uncased configurations, vertical or horizontal,
and withor withoutfresh air inlet.
Ceiling-mounted
horizontaluncased fan
coil unit
Fresh air inlet with mixing dampers fitted in a suspended ceiling.
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Fan coil units (continued)
Basic concept
(continued)
Vertical casedfan coil unit
with fresh airinlet
Fresh air inlet with mixing dampers attached to a partition wall.
Horizontalcased fan coil
unit
An horizontal cased fan coil unit is also called a ceiling unit.
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Fan coil units (continued)
Two-pipe fan coil
unit
Operation The unit has just one coil supplied by two pipes (supply and return).
The coil operates as follows:
The circuit is supplied with warm water for winter heating,
And with chilled water for summer cooling.
The term changeoverrefers to the changing from heating to cooling and vice
versa.
The output power is adjusted by: Turning the fan on and off on ultra-simple systems (for economical reasons).
Opening or closing an electric on/off valve on the water circuit.
Modulating valve that varies progressively the rate of water supplied to thecoil.
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Fan coil units (continued)
Two-pipe fan coil
unit (continued)
Operation(continued)
Two-pipe fan coil units
coil :air/water
exchanger
fan
filter
central plant :hot water / cold water
Principle
Energyproduction
Heating and cooling energy is produced in a central plant consisting of:
water heating equipment (e.g. furnace or exchanger),
water chilling equipment (water chiller).
An air-to-water or water-to-water heat pump can also be used to produce hot
or chilled water depending on the season.
Field ofapplication
This system is used for divided spaces, such as offices and hotels, where needs
fluctuate but are of the same type.
It does not satisfy simultaneous heating and cooling needs; heating is provided
in the winter, and cooling in the summer.
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Fan coil units (continued)
Four-pipe fan coil
unit
Operation The unit consists of two coils, one connected to a hot water loop, the other to acold water loop.
Both water loops are necessary. The flow of water is usually regulated by valves
(on/off or modulating) on each water circuit.
Energyproduction
Energy may be provided by a:
Water boiler and a water chiller.
Heat pump providing hot and cold water simultaneously. Transfer unit that recovers heat from the condenser during cooling.
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Fan coil units (continued)
Four-pipe fan coil
unit (continued)
Field ofapplication
This system is used for offices, hotels and other spaces with significant heating
and cooling needs that fluctuate and are not of the same type.
It delivers heating and cooling at the same time.
or
Four-pipe fan coil units
heatingcoil
filter
coolingcoil
fan
Principle
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Fan coil units (continued)
Fan coil units
Two-pipe, two-wirefan coil unit
Operation The unit has two coils: a two-pipe water coil and a two-wire electric heater.
Under conventional operation, the water coil is connected to the chilled water
circuit to provide cooling. There is no hot water circuit; the electric heater
serves as a heating battery.
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Fan coil units (continued)
Fan coil units
Two-pipe,two-wire fan coilunit (continued)
Energyproduction
A water chiller is located in the mechanical room.
A reversible water chiller could be installed in order to have chilled water in the
summer and hot water in the winter. In this case the unit serves as a
low-temperature hot water coil and back-up electric heater in the winter, when
no cooling is needed.
or
Two-pipe, two-wire fan coil units
electricheater
filter
cooling orheating
coil
fan
Principle
Field ofapplication
This system is advantageous for heavily insulated modern buildings, such as
offices and hotels, where heating needs are reduced.
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Fan coil units (continued)
Air-change fan coil
unit
Concept Although there are fan coil units with fresh air inlets, in most cases the air inspaces is changed by independent, central equipment:
single-flow ventilation,
dual-flow ventilation.
Single-flowventilation
Single-flow ventilation generally consists of using a roof ventilator (T) to expel a
portion of the air from a building with passageways and spaces containing
specific pollutants. Fresh air is introduced via inlets along the exterior walls.
Although inexpensive, this type of ventilation has the drawback of being unable
to adequately control air change in each separate room. Nothing guarantees that
fresh air will actually enter through the inlets and in the expected proportions. As
a result, some spaces could be under-ventilated while draughts could be created
in others.
Furthermore, the inlets along the outer walls also allow outside noise to enter
indoor spaces. This technique is therefore to be avoided in noisy environments.
It should also be avoidedin polluted environments.
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Fan coil units (continued)
Air-change fan
coil unit(continued)
Dual-flowventilation
Dual-flow ventilation makes it possible to avoid these risks:
The desired amount of fresh air is filtered (and warmed in the winter) by an airhandling unit before being introduced into each space. This conditioned fresh
air is carried through ducts:
Directly to served spaces.
Or to the return air section of terminal units . This solution makes itpossible to limit the risks of occupants being bothered by air draughts. It
also allows fresh air to be warmed at lower temperatures (energy savings in
spring and autumn). On the other hand, the fans in the terminal units mustbe left on occupancy periods.
Stale indoor air is expelled outside by an exhaust fan.
Fresh air conditioning and air extraction may be accomplished inside a single
dual-flow air handling unit. A heat recovery unit, or HRU, can also be installed
to recover heat from exhaust air.
Comment: A chilled water coil can be added to cool incoming fresh air slightly
in the summer. The aim here is not to chill the indoor air, but rather to avoid
supplying fresh air at too high of a temperature in the summer (this is not a true
chilled dual-ventilation system, which is much more elaborate).
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Non self-contained air-handling terminal units
Basic concept These units have the same components as conventional fan coil units (heat
exchange coil, fan motor, filter, condensate drain pan), but are designedspecifically for installation in ceilings, suspended ceilings and raised floors.
Equipment type There are two types of such terminal units: fan coil units and mini air handlingunits.
Fan coil unitsare designed for installation in suspended ceilings. They bothsupply air to and recirculate the air in spaces directly. They have no available
pressure and cannot be connected to ductwork.
Mini air handling unitscan be installed in false ceilings or raised floors(uncased models) or directly in spaces (cased ceiling or vertical models).
They can be connected to a mini-duct system (available static pressure).
Fan coil units There are two models of cassette type fan coil unit:
Melody fan coil units, designed specifically for installation in the centre of aspace, far from walls.
Coadis fan coil units, designed for easy installation near walls.
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Non self-contained air-handling terminal units (continued)
Fan coil units
(continued)
Melody type fancoil units
The composite drawing below shows the components of a cassette type fan coil
unit:
6 5 111
7 3 2 14
A Melody cassette type fan coil unit discharges air la