Air Distribution and Airconditioning Apparatus.pdf

Unit-5:
Air Distribution and
Air conditioning Apparatus
Prepared by:
Ankur Sachdeva
Assistant Professor, ME

Transmission of Air
• In an AHU, air is transmitted through various ducts and other
components with the help of fans.
• Since the fan motor consumes a large amount of power, and
the duct system occupies considerable building space, the
design of air transmission system is an important step in the
complete design of air conditioning systems.
• In the end the success of any air conditioning system depends
on the design of individual components as well as a good
matching between them under all conditions.
• In order to design the system for transmission of air, it is
important to understand the fundamentals of fluid (air) flow
through ducts.
Ankur Sachdeva, Assistant Professor, ME

What are Ducts
• Ducts are conduits or passages used in heating, ventilation,
and air conditioning (HVAC) to deliver and remove air.
• The needed air flows include, for example, supply
air, return air, and exhaust air.
• Ducts commonly also deliver ventilation air as part of the
supply air.
• As such, air ducts are one method of ensuring
acceptable indoor air quality as well as thermal comfort.
• Ducts work on the principle of air pressure difference. If a
pressure difference exists, air will flow from an area of high
pressure to an area of low pressure.
• The larger this difference, the faster the air will flow to the
low-pressure area.

Classification of Ducts
1. According to the pressure of air
- Low Pressure : Static Pressure <50 mm of water
- Medium Pressure : 50 mm< Static Pressure< 150 mm of water
- High Pressure: 150 mm< Static Pressure< 250 mm of water
2. According to the velocity of air
- Low Velocity: Velocity of air < 10 m/s
- High Velocity : Velocity of air > 10 m/s
3. According to the type of air
- Fresh Air : carries outside air
- Supply Air : carries conditioned air to the space to be conditioned
-Return Air : carries recirculated air from the conditioned space

Schematic Air-flow diagram for an
Air-conditioning system

AHU and its purposes
• In air conditioning systems that use air as the fluid in the
thermal distribution system, it is essential to design the Air
Handling Unit (AHU) properly.
• The primary function of an AHU is to transmit processed air
from the air conditioning plant to the conditioned space and
distribute it properly within the conditioned space.
• A typical AHU consists of:
(i)A duct system that includes a supply air duct, return air
duct, cooling and/or heating coils,
humidifiers/dehumidifiers, air filters and dampers.
(ii)An air distribution system comprising various types of
outlets for supply air and inlets for return air.
(iii)Supply and return air fans which provide the necessary
energy to move the air throughout the system

Requirements of Air Distribution
System
1) There should be enough entrainment of room air with
the supply air , so that upon reaching the occupied zone,
the air stream attains desired temperature.
2) The temperature throughout the occupied zone of the
room should be within ± 1ºC of the design temperature.
3) Only minor horizontal or vertical temperature variation
should be there in occupied zone.
4) Noise level should be below the objectionable level.
5) Effect of natural convection and radiation within the
room should be minimum.
6) The desirable air velocity is 9.1 mpm at the occupancy
level.

Terms used in Air Distribution System
1. Draft: It is defined as any localized feeling of coolness or warmth
of any portion of the body due to air movement and
temperature, with humidity and radiation considered constant.
2. Blow or Throw: The distance travelled by the supply air stream
in the horizontal direction on leaving the air outlet and reaching
a velocity 15 mpm.
3. Drop:- It is the vertical distance that the lower edge of the
horizontally projected air stream drops between the outlet and
the end of its throw.
4. Induction or Entrainment ratio: It is defined as the ratio of total
air to primary air.
5. Spread: The angle of divergence of an air stream after it leaves the
outlet.

Throw and Drop

Terms used in Air Distribution System
1. Outlet :- It is an opening through which air is supplied to the
conditioned space.
2. Intake :- It is an opening through which air is return from the
space.
3. Grills :- Grills provide decorative covering for an outlet or inlet
4. Diffuser :- It is an outlet grille designed to guide the direction of
the air.
5. Register :- It is a grille provided with a damper or control valve.

Types of Supply Air-Outlet
1. Grill Outlet
• These outlets have
adjustable bar grills which
are the most common
types with vertical and
horizontal vanes.
2. Ceiling Outlet
• They are mounted in the
Grill Outlet
ceiling. Multi-passage
round, square or
rectangular are most
common type
Ceiling Outlet

Types of Supply Air Outlet
3. Slot Diffuser
• It is an elongated outlet with an
aspect ratio 25 : 1 and maximum
height of 7.5 cm. They are used in
side walls but at a higher height
of the floor.
4. Perforated Ceiling
Slot Diffuser
• In this case, confined space above
the ceiling is used as supply
plenum.
• The air from the plenum is
supplied to the room through
small holes or slots.
• The air is supplied at the rate of
0.3 to 4.5 m³/m² of the floor area.
• They are specially suited to large
zones
Perforated Ceiling

Mechanism of flow of Air
through Duct Outlet
• The mechanism of flow of air from the duct and through the outlet to the
room is shown in Fig.
• Ac is the core area or the area of grille opening in which the air flows with a
velocity Cc.
• Afa is the free area of the grille through which air can pass.
• The ratio Afa/Ac is Rfa so that Cfa = Cc/Rfa.
• A0 is the area at the vena-contracta formed outside the grille.
• If Cd is the discharge coefficient of the outlet, and C0 is the velocity at the
vena contracta,

The zone of interest is at 25 to 100 times the diameter or width of the outlet in
the x direction. In this zone, the velocity at any x is given by
through Duct Outlet
where Q is the volume delivered by the outlet and K = 1.13 K.

through Duct Outlet
The tested values of K are given in Table below. The equation can also be used to calculate
the throw L by putting Cx = 15 mpm = 0.25 m/s.

through Duct Outlet
• As far as the entrainment ratio R is concerned, it is given by the following empirical
relations in which Q x represents the volume of the total air at any distance x from the
outlet and Q is the volume of primary air.

Considerations for Selection and
Location of Outlets
1. The amount of air to be delivered by the outlet should be proportional to the load of
the part of the space for which it is installed.
2. The selection of the type of outlet is governed by the ceiling height, nature of room
occupancy, etc.
3. The location of the outlet should be governed by the condition of uniform air
distribution and rapid temperature equalization.
4. The selection of size of the outlet can be made from the manufacturer’s catalog data
according to the air delivery, core velocity, distribution pattern, sound levels, throw,
drop, spread etc.
• As a corollary to this, the outlets should be located so as to neutralize the concentrated
loads, such as those that result from exterior windows, electronic equipment, etc.
• In buildings in which the lighting load is heavy, i.e., more than 55 W/m2 and the ceiling
height is more than 4.5 m, it is desirable to locate the outlets below the lighting load.
• In such and similar cases of concentrated loads, the return grilles or inlets can be located
adjacent to these loads so that warm air (in the case of cooling) is withdrawn from the
source instead of being dissipated in the conditioned space.

Considerations for Selection and
Location of Outlets
• This arrangement is also suitable to remove the fumes, pollutants, etc., from their
sources in the space.
• In their distribution pattern, the outlets may have characteristics in between the
behaviour at the two extremes.
• At one extreme are ceiling diffusers with radial flow. As a result of the large perimeter
area of the primary air, they will have a high entrainment rate and rapid temperature
equalization in the room. The air will, however, quickly slow down and will have a
short throw.
• At the other extreme are slot diffusers. They have a low entrainment rate and slow
temperature equalization. But they have a long throw.
• Thus, generally speaking, ceiling diffusers can deliver more air to a space than grilles
and slot diffusers. Because of their high entrainment, ceiling diffusers may also be
used in systems with low supply air temperatures. In spite of the low supply air
temperature, induction will result in rapid temperature equalization.
• The same cannot be done in the case of slot diffusers and grilles. In their case, this
temperature difference may not exceed 11°C. They are used only when the throw
required is very long.

Distribution Patterns of Outlets
The distribution patterns follow differently for cooling and heating.
The best distribution pattern is one in which the whole room air is set in motion, and there
are neither any stagnation zones nor zones of draft at the occupancy level.
The representation for primary air, total air, natural convection air, and stagnant zone is
shown below:

High Sidewall Grilles Discharging Air
Horizontally
Distribution patterns for high sidewall grille
• The variation of the vane setting may affect the flow to some extent but the general
pattern will be the same for both cooling and heating.
• It is seen that during cooling, the total air drops on the occupied zone at some
distance from the outlet, depending on Q , Cc, (ti – ts), deflection setting, ceiling
effect, and type of loading in space.
• It may be noted that the throw is about three-fourths of the room width, and in no
case should the air overthrow otherwise draft conditions will result.
• During heating, the total warm air tends to rise. This results in a large stagnation
zone. A degree of over-blow may be helpful in minimizing the stagnation zone.

Ceiling Diffusers Discharging
Air Horizontally
Distribution patterns for ceiling diffusers projecting air horizontally
The general pattern for ceiling diffusers projecting air horizontally is similar though
symmetrical on the two sides as shown in Fig. (a) and (b).
There is hardly any stagnation zone for cooling application though the same cannot be said for
the case of heating.
During heating, cold air from the walls tends to drop but warm air tends to remain near the
ceiling. A large stagnation zone results. An attempt must be made to direct the air towards the
cold walls.

Floor Registers
Discharging Air Vertically
Floor registers normally discharge primary air in a straight vertical jet as shown in the figure.
Ultimately the total air, after reaching the ceiling, fans out.
In the case of cooling, it falls out soon after travelling a short distance.
The cooling diagram shows the stagnation region above the terminal point of the total air. In a
large space, this stagnation zone may extend much farther and to a lower level.
In the case of heating, the total air follows the ceiling and then descends down if flowing along
the cold exterior walls.
There is a better temperature equalization for heating than for cooling. In these outlets, generally,
an increase in the supply air velocity will improve the air distribution.
These outlets are more suited for heating only.

Floor Diffusers Discharging Air in a
Spreading Jet
• Floor diffusers are similar to floor registers. The only difference is in the nature of the jet
which is spreading in this case, instead of being nonspreading as seen from the figure.
• Although the characteristics are similar, the stagnation zone is much larger during cooling
but smaller during heating.
• These outlets are suitable when the heating requirement is severe and primary, and the
cooling requirement moderate and secondary.
• Floor outlets are not permissible when people are seated such as in theatres. But where
people are moving, as in stores, they are quite permissible.
• However, a very low dehumidified rise, say, not more than 8°C should be used. This will
require a large volume flow.
• One disadvantage of floor outlets is that they become dust collectors.

Low Sidewall Outlets
Discharging Air Horizontally
• As is seen from the figure, the total air during cooling remains near the floor level resulting in
low temperature in the occupied zone and a large stagnation zone above.
• During heating, the warm air rises and temperature equalization takes place except in the
region of total air.
• These outlets discharge air directly into the occupied zone with high velocity. They are not
recommended for comfort air conditioning.

Ceiling Diffusers
Discharging Air Vertically
• These are ceiling diffusers which do not project air horizontally, but vertically as shown in Fig.
• During cooling, the total air drops to the floor and then fans out, finally rising along the walls.
The stagnation region is near the ceiling.
• During heating, the total air, after reaching the floor, returns back towards the ceiling. There is
no stagnation zone.
• These outlets have completely different distribution patterns for cooling and heating because of
the different throws obtained.
• They are, therefore, used either for cooling or for heating, but seldom for both.
• For cooling, we require low values of supply air volume, velocity and temperature difference,
whereas for heating, the same should be high to get proper throw.
• Nevertheless, ceiling diffusers can be conveniently applied to ducts or plenums in the ceiling in
large spaces and halls/auditoriums.,

Duct Design
• A duct system is also called ductwork.
• Duct Design of a system involves:
– Planning (laying out),
– Sizing,
– Optimizing,
– Detailing, and
– Finding the pressure losses

Aspect Ratio
• Aspect Ratio is the ratio of the dimensions of
the two adjacent sides of a rectangular duct.
• Mathematically, Aspect ratio = a/b
b
a
A rectangular duct section with an aspect ratio close to 1 yields the most
efficient rectangular duct shape in terms of conveying air. A duct with
an aspect ratio above 4 is much less efficient in use of material and
experiences great pressure losses.

Material of the Duct
Type Advantages
Galvanized Iron Zinc coating of this metal prevents rusting and avoids
cost of painting
Aluminium Lightweight, Quick to install, Easily fabricated into
different shapes
Flexible Plastic Convenient for attaching supply air outlets to the rigid
ductwork
Fiber-Glass Built-in thermal insulation and the interior surface
absorbs sound
Wood Used in applications where moisture content is less in
air

Recommended Thickness of GI
Sheets for the Ducts

Duct Design Methods
• There are mainly three methods which are
commonly used for duct design.
1) Velocity reduction method
2) Equal friction loss method
3) Static regain method

Velocity Reduction Method
• In this method the duct designed in such a
way that the velocity decreases as flow
proceeds.
• The pressure drops are calculated for this
velocities for respective branches and main
duct.
• The duct size are determined for assumed
velocities and known quantities of air to be
supplied through the respective ducts

Recommended maximum duct velocity
for low-velocity system (mpm)

Equal Friction Method
• In this method, the frictional pressure drop
per unit length of duct is maintained constant
throughout the duct system.
• The procedure is to be select a suitable
velocity in the main duct from the sound level
consideration.
• Knowing the air flow rate and the velocity in
the main duct, the size and friction loss are
determined from the friction chart.

Static Regain Method
• For the perfect balancing of the air duct layout system,
the pressure at all outlets must be made same.
• This can be done by equalizing the pressure losses in
various branches.
• This is possible if the friction loss in each run is made
equal to the pressure gain due to reduction in velocity.
• Advantages :
• It is possible to design long run as well as short run for
complete regain.
• It is sufficient to design the main duct for complete
regain

Flow of Air through Ducts
• The fundamental equation to be used in the analysis of air
conditioning ducts is the Bernoulli’s equation.
• Bernoulli’s equation is valid between any two points in the
flow field when the flow is steady, irrotational, inviscid and
incompressible.
• The equation is valid along a streamline for rotational,
steady and incompressible flows.
• Between any two points 1 and 2 in the flow field for
irrotational flows, the Bernoulli’s equation is written as:

Flow of Air through Ducts
• The above equation implies that for frictionless flow through
a duct, the total pressure remains constant along the duct.
• Since all real fluids have finite viscosity, i.e. in all actual
fluid flows, some energy will be lost in overcoming friction.
• This is referred to as head loss, i.e. if the fluid were to rise
in a vertical pipe it will rise to a lower height than
predicted by Bernoulli’s equation.
• The head loss will cause the total pressure to decrease in
the flow direction. If the head loss is denoted by Hl then
Bernoulli’s equation can be modified to:

Fan Total Pressure (FTP)
• To overcome the fluid friction and the resulting head, a fan
is required in air conditioning systems.
• When a fan is introduced into the duct through which air
is flowing, then the static and total pressures at the section
where the fan is located rise.
• This rise is called as Fan Total Pressure (FTP). Then the
required power input to the fan is given by:

Fan Total Pressure (FTP)
• The FTP should be such that it overcomes the pressure drop
of air as it flows through the duct and the air finally enters
the conditioned space with sufficient momentum so that a
good air distribution can be obtained in the conditioned
space.
• Evaluation of FTP is important in the selection of a suitable
fan for a given application

Estimation of Pressure Drop
• As air flows through a duct its total pressure drops in
the direction of flow. The pressure drop is due to:
1. Fluid friction
2. Momentum change due to change of direction
and/or velocity
• The pressure drop due to friction is known as frictional
pressure drop or friction loss, Δpf
• The pressure drop due to momentum change is
known as momentum pressure drop or dynamic loss,
Δpd
• Thus the total pressure drop Δpt is given by:

Flow of Air in a Duct

Flow of Air in a Duct
• For Actual case,
• Where pL is the total pressure drop between
section 1-1 and 2-2
• If a fan is installed between the two sections
then, above equation changes into
• Where pTF is the Fan Total Pressure

Some Important Points
• Pressures in the duct are usually expressed in mm of water
• Properties of standard air in the duct:
– Temperature of air, Ta= 20°C,
– Pressure of air, Pa = 1.01325 bar
– Density of air, ρa, at 20°C = 1.2 (kg/m3)

Evaluation of frictional
pressure drop in ducts
• Frictional pressure drop in internal flows are
calculated using Darcy-Weisbach equation:
• Where
– f is the dimensionless friction factor,
– L is the length of the duct and
– m is the hydraulic mean depth
– Friction factor is a function of Reynolds number

Estimation of Pressure Drop
But
Therefore
For Circular Duct
For Rectangular Duct

Calculation of Friction factor

Surface Roughness of Materials

Moody’s Chart for friction factor
(Circular Ducts/Pipes)

Equivalent Diameter of a Circular
duct for a Rectangular Duct
Two cases:
(i) When quantity of air, Q , passing through the circular and rectangular duct is same
(ii) When velocity of air, V , passing through the circular and rectangular duct is same
Case (i) When Quantity of air, Q, is same

Duct for a Rectangular Duct
Pressure Loss due to friction,
Hydraulic mean depth,

Pressure loss due to friction in rectangular duct,
Since the pressure loss, friction factor, length, density and quantity of air for the circular
and rectangular duct is same , we have

Case (ii) When Velocity of air, V, is same
,
Pressure loss due to friction in circular duct,
Pressure loss due to friction in rectangular duct
Since the pressure loss, friction factor, length, density and velocity of air for the
circular and rectangular duct is same , we have

Part-2: AIR CONDITIONING APPARATUS

Introduction
• Fans and blowers provide air for ventilation and
industrial process requirements.
• Fans generate a pressure to move air (or gases) against
a resistance caused by ducts, dampers, or other
components in a fan system.
• Large capacity fan units typically consist of a bladed
rotating impeller enclosed in a stationary casing.
• The rotor system causes the motion of the air/gas and
the casing directs the airflow.
• The fan rotor receives energy from a rotating shaft and
transmits it to the air.

Difference between Fan, Blower,
and Compressor
• As per “ASME” Depending on the specific ratio and rise in
system pressure.

Types of Fans and Blowers

Centrifugal Fans
• Rotating impeller increases air velocity.
• Air speed is converted to pressure.
• This fan produces high pressure which ranges
from 550 mmwc to 1400 mmwc.
• Efficiency varies from 60-83 %.
• Used for dirty air stream conditioning and
material handling applications.
• Whenever a system has duct work, centrifugal
fans have to be used as the static pressure drop is
considerable.
• But when there is no duct work, propellers or
axial flow fans can be used.
• Nevertheless, in window-type and package
units, simple drum-type centrifugal fans are used,
whereas most exhaust fans are of the axial type,
as they occupy less space, and can handle large
volumes

Types of Centrifugal Fans
These are categorized by blade shapes as:
(a) Radial
(b) Forward Curved
(c) Backward Curved

Radial fans
Characteristics:
• Usually contains 6 to 16 impeller blades.
• High static pressures up to 1400 mm wc
can achieve with low flow rates.
• Low/medium airflow rates only.
• Efficiency ranges from 69% - 75%.
• Simple in Design.
Applications:
• Suitable for handling heavily
contaminated airstreams like dust-laden,
sawdust, etc.
• These are widely used in corrosive and
high-temperature environments.

Forward Curved Blade Fans
Characteristics:
• Usually contains 24 to 64 impeller blades.
• Produces low pressure up to 5 in wg.
• Large airflow rates against relatively low
static pressure.
• Efficiency ranges from 60% - 65%.
• Lighter in construction and less expensive
Applications:
• Suitable for clean air environment as blades
easily accumulate dirt
• Well suited for low-pressure HVAC such as
packaged air conditioning equipment
• Not constructed for high pressures or harsh
service.

Backward Curved Blade Fans
Characteristics:
• Usually contains 6 to 16 impeller
blades.
• Produces high pressure (40 in wg)with
high flow rates.
• More efficient than forward curved
blade efficiency ranges from 79% -
83%.
• High maintenance cost.
Applications:
•Only recommended for clean air
streams containing no condensable
fumes or vapours.
• A common application is a forced
draft.

Comparison of Characteristics of Backward
and Forward Curved Blade Fans
Forward-curved fans develop highest pressure for a given diameter and speed. They are also
available as high volume flow fans.

Backward-curved fans are commonly used in air conditioning.
However, a backward-curved fan must run at a higher speed to develop the same pressure as a
forward-curved fan. Accordingly, forward-curved fans are smaller and slower running. Thus
they tend to be quieter and cheaper for FTP up to 750 N/m2
Comparison of Characteristics of Backward
and Forward Curved Blade Fans

Axial Flow Fans
• Air is pressurized by blades which create
aerodynamic lift.
• Typically provide large air volumes at relatively
low pressures ranging from 250 mmwc to 500
mmwc.
• Efficiency varies from 45% - 85%.
• Popular in the industry as compact, low-cost, and
lightweight.
• Axial fans are frequently used in exhaust
applications with small airborne particulate sizes,
such as dust streams, smoke, and steam.
• It is categorized as,
1. Propellor Axial Fan
2. Tube Axial Fan
3. Vane Axial Fan

Propeller Axial Fans
Characteristics:
• Have two or more blades that generate
very high airflow volumes
• Produces low static pressure (20-50)
mmwc.
• Very low efficiencies of
approximately 50 %.
• Lightweight and inexpensive.
• Noise levels are higher than tube axial
and vane axial fan.
Applications:
•Air circulation within a space or
ventilation through a wall without
attached ductwork.
• Ideally used for make up or
replacement air supply.

Tube Axial Fans
Characteristics:
• Tube axial fans have a wheel inside a
cylindrical housing which improves the
air flow efficiency.
• Numbers of blades range from 4 to 8.
• Capable of developing a more useful
static pressure range(250-400 mmwc).
• Efficient up to 65 %.
Applications:
• Frequently used in exhaust applications.
• Also used in some industrial
applications such as drying ovens and
paint spray.

Vane Axial Fans
Characteristics:
• Vane-axial fans are similar to tube-
axial fans with guide vanes that
improve efficiency by directing the
flow.
• Typically have 5 to 20 aerofoil-type
blades with a large hub diameter.
• Such fans are generally used for
pressure (up to 500 mmwc).
• They can achieve efficiencies up to
85%.
Applications:
• Typically used in high-pressure
applications, such as induced draft
service for a boiler exhaust.

Tube Axial and Vane Axial Fans

Types of Fans, Characteristics and
their Applications

Blowers and their Types
• Blowers can achieve much higher pressures
than fans, as high as 1.20 kg/cm2.
• The impeller is typically gear-driven and
rotates as fast as 15,000 rpm.
• They are also used to produce negative
pressures for industrial vacuum systems.
Types:
1. Centrifugal blowers
• Typically operate against pressures of 0.35
to 0.70 kg/cm2.
• They are most often used in applications that
are not prone to clogging.
2. Positive-displacement blowers
• They are especially suitable for applications
prone to clogging since they can produce
enough pressure up to 1.25 kg/cm2 - to blow
clogged materials.

FAN CHARACTERISTICS
• Fan characteristics can be represented in the form of fan curve(s).
• The fan curve is a performance curve for the particular fan under a specific set of
conditions.
• Typically a curve will be developed for a given set of conditions usually
including fan volume, system static pressure, fan speed, efficiency and brake
horsepower required to drive the fan under the stated conditions.
• The intersection of the system curve and the static pressure curve defines the
operating point.
• When the system resistance changes, the operating point also changes.
• Once the operating point is fixed, the power required could be found by
following a vertical line that passes through the operating point to an intersection
with the power (BHP) curve.
• A horizontal line drawn through the intersection with the power curve will lead to
the required power on the right vertical axis

FAN CHARACTERISTICS
• The required fan work can be calculated by
knowing the flow rate and fan total pressure
using the following equation and including the
fan efficiency in it.
• Point A on the fan total pressure-volume flow curve
represents the condition of the open inlet and outlet.
• At this point FSP = 0 and FTP = FVP
• It is seen that as Q decreases, FTP increases.
• In terms of the diameter D and speed N of the
fan, it is seen that the fan total pressure, FTP or
pT is proportional to the density and square of the
velocity, which in turn is proportional to the
product DN. Thus
• Such a relation can also be obtained by
dimensional analysis. The volume flow rate is
proportional to the fan area and velocity.

Fan Arrangement
• The fan arrangements are standardized for the drive, rotation, motor position,
suction and discharge.
• Thus, there can be a belt or direct drive and bearings on one side with the
wheel overhung or bearings on both sides.
• The rotation may be clockwise or counter-clockwise.
• The discharge may be top horizontal or bottom horizontal,
• upblast or downblast, top angular down or up, or bottom angular down or up.
• The suction is commonly from one side but may be from both sides also.
• Further, a multiple number of fans may be used.
• The arrangement for the purpose will be either in series or in parallel.

Fans in Series
• When two fans are employed in a series,
• The flow rate Q through each fan is the same, and
• (ii) The overall fan total pressure pT is equal to the
sum of individual FTPs minus the losses in the
connections.
• The combined characteristic of two fans in a series
can, therefore, be drawn by adding the FTP of each
fan for each Q as shown in Fig.
• To obtain the combined characteristic, it is assumed
that the characteristic of each fan is known for
volumes greater than those that are achieved by fans
when running with suction and discharge
unconnected to the system. This information is
rarely available.
• The characteristic in this region may be extrapolated
as shown in Fig.
• Further, it is preferable to use identical fan units in
series as it is unlikely that efficient operation would
result otherwise.

Fans in Parallel
• When two fans are employed in parallel,
(i) The total pressure pT across each fan is the same,
and
(ii) The total volume handled Q is equal to the sum of
the volumes handled by individual fans.
• The combined characteristic of two fans in parallel
can, therefore, be drawn by adding Q of each fan
for the same pT as shown in Fig.
• Again, in order to draw this combined
characteristic in full, it is necessary to know the
reverse-flow characteristic of one of the fans with
the impeller running in the normal direction which
is normally not known.

Suction line, Discharge line and
Liquid line

HVAC Piping
HVAC piping or heating ventilation and air-conditioning piping delivers hot
water, cool water, refrigerant, condensate, steam, and gas to and from the HVAC
components.
HVAC Systems provide thermal comfort for the occupants accompanied by
indoor air quality. They are used in industrial, commercial, residential, and
institutional buildings for different purposes like
•To add or remove heat from the air inside the building.
•Control the humidity.
•Filter the air in the building.
•Bring fresh air into the building.

Types of HVAC Piping and Material Used
• HVAC Piping system can be classified into two parts; the piping in the central
plant equipment room and the delivery piping.
• The central plant equipment room consists of the pipe networks connected to
the rotating equipment and tanks.
• They are connected to different types of equipment like heat exchangers and
pumps over the pump room from these regions the piping network transports the
process liquid to the other parts of the building using the delivery piping.
• The effectiveness of the piping is influenced by the materials used to make it.
Copper and steel are the two major types of metals used for HVAC piping.
• Copper is used mostly for smaller piping, and transporting water in AC units as
the use of copper is very expensive than that of other materials available.
• Steel on the other hand is much cheaper and is used for large sizes. It can also
withstand higher pressure than copper and is ideal for both hot and cold water. It
usually allows for a range of temperatures and pressure

Noise and Vibration in HVAC
• The building's HVAC system can manually or intelligently control the
comfort of the human living environment in the building.
• The equipment of the HVAC system generates a certain amount of vibration
and noise due to the mechanical operation during operation, which affects the
comfort of human living and the structural stability of the building.
• In building structure design, the main design types are divided into seismic
design, durability design, and fatigue design.
• In the design process of prevention and control of common problems in
buildings, the main common problem is vibration.
• The shape and frequency of vibration generated by equipment and human
activities in the building will damage the building.
• The design of the HVAC system fully considers the structure of the building,
the characteristics of the equipment, the frequency of use of the equipment,
and the form and stability of vibration.
• These are the main sources of noise and vibration in the design process and
are necessary to ensure the safety of the system.
• At the same time, it provides people with a comfortable living environment.

• The noise and vibration of the building's HVAC system are mainly caused by
air conditioning terminals, such as air conditioning units, circulating water
pumps, cooling towers, fans, and air conditioning window cabinets.
• These types of equipment are prone to noise and vibration during use.
• When the impact of noise and equipment vibration in decibels exceeds the
allowable limit, it will affect people's comfort, and the noise and vibration of
the building's heating, ventilation, and air-conditioning system will have a
significant impact on people's production and life.
• At the same time, continuous vibration can cause permanent damage to the
equipment, reduce the efficiency of the equipment, and shorten its service life.
• In addition, the noise and vibration of the building's HVAC system will
increase the cost of subsequent maintenance.
• Therefore, the personnel involved in the design and construction should pay
close attention to the noise and vibration of the building's HVAC system
Origin & Effects of Noise and Vibration

Noise and Vibration Control
• Vibration is the source of noise from HVAC systems, management of those
conditions is imperative to a quiet design.
• System design that neglects to properly address vibration may result in
malfunctioning components, noise, and, in some cases, catastrophic failure.
• There are two facets of vibration management: isolation and damping.
• Isolation is the prevention of vibration from entering the system and
dissipating it by changing kinetic energy of vibration into a different form of
energy, such as heat.
• Vibration isolation systems for mechanical components require some amount
of damping.
• Damping dissipates mechanical energy from the system and attenuates
vibrations more quickly.
• Without damping, these systems may vibrate for some time before coming to
rest.
• The fluid in automotive shock absorbers is a kind of damper, as is the
inherent damping in elastomeric (rubber) equipment mounts.

Basic Elements of HVAC Control
In simplest terms, the control is defined as the starting, stopping, or regulation of
heating, ventilating, and air conditioning systems.
Controlling an HVAC system involves three distinct steps:
1) Measure a variable and collect data
2) Process the data with other information
3) Cause a control action
Elements of HVAC Controls
An HVAC control system, from the simplest room thermostat to the most
complicated computerized control, has four basic elements: sensor, controller,
controlled device and source of energy.
1) Sensor measures actual value of controlled variable such as temperature,
humidity or flow and provides information to the controller.
2) Controller receives input from sensor, processes the input and then produces
intelligent output signal for controlled device.
3) Controlled device acts to modify controlled variable as directed by controller.
4) Source of energy is needed to power the control system. Control systems use
either a pneumatic or electric power supply

Air Distribution and Airconditioning Apparatus.pdf

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