HVAC Systems Understanding
the basis
Table of Contents
1. Introduction to HVAC Systems
2. HVAC System Types
3. HVAC Piping System
4. HVAC Air Distribution Equipments
5. Fans and Pumps
6. HVAC Instrumentation and Control
7. HVAC System Commissioning
Introduction to HVAC Systems
This article introduces the heating, ventilating and air-conditioning
(HVAC) systems. The primary function of HVAC systems is to provide
healthy and comfortable interior conditions for occupants; well-
designed, efficient systems do this with minimal non-renewable
energy and air, and water pollutant emissions.
Introduction to HVAC Systems
The purpose of HVAC design is both high indoor air quality and energy
efficiency. These dual considerations require an integrated design
approach. Rigs heating,
ventilation, and air conditioning
system (HVAC) creates a climate
that allows for maximum comfort by
compensating for changing climatic
conditions.
Though more costly to install and more complicated to operate, a chiller plant
offers a number of benefits over a large number of individual packaged
cooling units, including greater energy efficiency, better controllability,
cheaper overall maintenance, and longer life. Using a comprehensive
approach to building design, designers around the world have succeeded at
creating highly efficient air-conditioning systems that provide excellent
comfort at significant savings.
Introduction to HVAC Systems
Heating, ventilating and air-
conditioning (HVAC) systems
reduce the environmental
impact of rigs/buildings in several
key ways. The most important
function of a HVAC systems is
to provide the rig/buildings occupants
with healthy and comfortable interior
conditions. A carefully designed, efficient
system can do this with minimal non-
renewable energy and air and water pollutant emissions to minimize the
environmental impact.
Cooling equipment that avoids chlorofluorocarbons and hydro-
chlorofluorocarbons (CFCs and HCFCs) eliminates a major cause of
damage to the ozone layer.
Introduction to HVAC Systems
Even the best HVAC equipment and systems cannot compensate for a
faulty rig design. Problems of this type cause inherently high cooling and
heating needs and consume unnecessary resources and should be
corrected if possible. Conservation of non-renewable energy through an
intelligent architectural design offers the greatest opportunity for savings.
The most important factors in these designs are careful control of solar gain,
while taking advantage of passive heating, daylighting, natural ventilation
and cooling. The critical factors in mechanical systems' energy consumption
- and capital cost - are reducing the cooling and heating loads they must
handle.
HVAC System Types
Types of System Designs - There are several major heating, ventilating, and air
conditioning system types in wide spread use today. These are air systems, hydronic
and steam systems, and unitary type systems. Most systems in use today fall into one of
these categories, or are a combination or variation of them. Each type of system has
advantages and disadvantages.
Air cooled
- Air cooled Chillers
Air Cooled Chiller Advantages
Lower installed cost
Quicker availability
No cooling tower or condenser pump required
Less maintenance
No mechanical room required
Water Cooled
- Sea Water cooled Chillers
- Fresh Water cooled Chillers
Water-Cooled Chiller advantages
Higher efficiency
Custom selection in larger sizes
Large tonnage capabilities
Indoor Chiller location
Longer life
Air Handling Systems
Purpose of an air handling system
Air Handling
System
Room
Supply With Outlet
Air Defined Air
Requirements
Objectives
In the following slides, we will study the components of
air handling systems in order to:
1. Become familiar with the components
2. Know their functions
3. Become aware of possible problems
Main subsystems
Exhaust air treatment
Fresh air treatment
(make-up air) Terminal air treatment
+
at production room level
Room/Cabin
Central air handling unit
Overview components
Exhaust Air Grille Flow rate controller
Silence Fan Filter
r
Weather louvre Control damper
Heater
+
Humidifier
Prefilter Terminal filter
Cooling Secondary Filter Production Room
coil
with
Heating droplet
coil separator Re-circulated
air
Components (1)
Weather To prevent insects, leaves,
louvre dirt and rain from entering
Silencer To reduce noise caused by air
circulation
Flow rate Automated adjustment of
controller volume of air (night and day,
pressure control)
Control Fixed adjustment of volume
damper of air
Components (2)
Heating unit To heat the air to the proper
temperature
Cooling unit To cool the air to the required
/dehumidifier temperature or to remove moisture
from the air
Humidifier To bring the air to the proper
humidity, if too low
Filters To eliminate particles of pre-
determined dimensions and/or
micro-organisms
Ducts To transport the air
Air types
+ Exhaust
Fresh air Supply air
(make-up air) air
Production Room
Return air
(re-circulated)
Filter classes
Dust filters
Standard Aerosol
Coarse Fine HEPA ULPA
Dp > 10 m 10 m > Dp > 1 m Dp < 1 m
G1 - G4 F5 - F9 H 11 - 13 U 14- 17
EN 779 Standard EN 1822 Standard
HEPA or tertiaary filter
Primary panel
filter
Secondary
filter
Duct heaters Room Heters
Silensers
Volume control damper
Fire Dampers
Adsorber wheel Dry air
Humid room air AHU with fan
Variable Speed
Controller
Regeneration air Humid room air
Filter Pressure
Gauges
Air heater
De-humidification
Regulation of room pressure pressure
differentials concept
Room pressure
gauges
Room pressure indication panel
Annex 1, 17.26
Pressure cascade injectables
Protection from micro-organisms and
particles
Room 1 Room 2 Room 3
30 Pa 60 Pa A 45 Pa
LF
D
A ir L o c k A ir L o c k
45 Pa B C
15 Pa
A ir
30 Pa D Passage 0 Pa
Lock
N o te : D ir e c tio n o f d o o r o p e n in g r e la tiv e to r o o m p r e s s u r e
Pressure cascade solids
Protection from cross-contamination
Room 1 Room 2 Room 3
15 Pa 15 Pa Rom215Pa Rom315PaaE
AirLock30PasgeNote:Dircnfdpglavmsu 0PaAirLock15
15 Pa
A ir L o c k A ir L o c k
A ir
Lock
30 Pa E 0 Pa
Passage
15 Pa
N o te : D ir e c tio n o f d o o r o p e n in g r e la tiv e to r o o m p r e ss u r e
Fan Coil Unit
Self Contain Unit
HVAC Air Distribution Equipments
Diffusers
4 Way Diffusers Two Way Diffusers One Way Diffuser
Round Diffusers
Cabin Units
Return / Exhaust Grilles
Fans and Pumps
Contents
Fan Design
Fan Performance
Fan-duct Systems
Duct Construction
Air Duct Design
Fan Design
Common types of fans
Centrifugal fans: radial, forward curved, air
foil (backward curved), backward inclined,
tubular, roof ventilator
Axial fans: propeller, tube-axial, vane-axial
Fan arrangements
Motor location, air discharge orientation, drive
train type (direct drive or pulley drive)
Centrifugal: single width single inlet (SWSI),
double width double inlet (DWDI)
CENTRIFUGAL FANS AXIAL FANS
Centrifugal and axial fan components
AXIAL FANS
Propeller Tube-axial
Tube-vane
CENTRIFUGAL FANS
Tubular centrifugal fan Centrifugal roof ventilator
(* Note the airflow paths and impeller design.)
Drive arrangements and motor positions
Single- and double-width centrifugal fans
Fan Performance
Major parameters
Fan volume flow rate (m3/s or l/s), Vf
Fan total pressure ptf, fan velocity pressure
pvf & fan static pressure psf (Pa)
Fan power & efficiency
Fan power or air power (W) = ptf x Vf
Fan power input on the fan shaft (brake
horsepower), Pf
Fan total efficiency: t = ptf x Vf / Pf
Combined aerodynamic, volumetric & mechanical
efficiencies
Fan static efficiency: s = psf x Vf / Pf
Air temp. increase through fan, T = p /(c )
Fan performance curves
Total pressure
Static pressure
Fan total efficiency
Fan static efficiency
Fan power input
Velocity pressure
Volume flow rate
Typical fan performance curve
Fan Performance
Fan Laws
Speed (n)
Volume flow (V)
Total pressure loss
( p )
Air density ()
For air systems that
are geometrically &
dynamically similar:
(D = impeller
diameter)
c.f.: pump laws
CENTRIFUGAL FANS
Velocity triangle at the blade inlet and outlet of a centrifugal fan
Fan Performance
Major issues causing energy losses to a
centrifugal fan:
Circulatory flow between the blades
Air leakage at the inlet
Friction between fluid particles and the blade
Energy loss at the entrance
Partially filled passage
Operating characteristics for a backward-curved centrifugal fan
Total efficiency
curves for
centrifugal fans
Fan power curves for centrifugal fans with same impeller diameter
Fan pressure curves for centrifugal fans with same impeller diameter
AXIAL FANS
Velocity triangles for a vane-axial fan
Fan pressure curves for axial fans with same impeller diameter
Fan efficiency curves for axial fans with same impeller diameter
Fan power curves for axial fans with same impeller diameter
Performance
curves for
controllable-
pitch vane-axial
fans
Fan-duct Systems
Duct pressure changes (c.f. atm
pressure)
Static pressure (SP)
Velocity pressure (VP) = V2 / 2 g
Total pressure (TP) = SP + VP
Fan: a pumping device
Fan (total) pressure = pressure difference
between fan inlet and fan discharge
At fan suction/inlet, SP = negative (c.f.
atmospheric); at discharge, SP = positive
Fan-duct Systems
Pressure characteristics
SP and VP are mutually convertible (or)
TP always decreases in the direction of
airflow
For constant-area straight duct sections
Velocity and VP are constant
TP change = SP change
When duct cross-sectional areas are reduced
Velocity and VP increase
Absolute value of both TP and SP decrease
Dynamic losses from elbow, dampers, etc.
Fan-duct Systems
Fan-duct systems
Flow resistance
o
R, pressure drop p and
volume flow rate V
p = R V 2
Duct sections in series: Rs = R1 + R2 + + Rn
Duct sections in parallel:
1 1 1 1
= + ++
Rp R1 R2 Rn
Fan-duct Systems
Fan-duct systems
Terminology
Primary air (conditioned air or makeup air)
Secondary air (induced space air, plenum air, or
recirculating air)
Transfer air (indoor air that moves from an
adjacent area)
System curve: volume flow vs pressure loss
System operating point
Fan-duct Systems
System effect pts
Its additional total pressure loss caused by
uneven or non-uniform velocity profile at the
fan inlet, or at duct fittings after fan outlet
Due to the actual inlet and outlet connections
as compared with the total pressure loss of the
fan test unit during laboratory ratings
Inlet Outlet
Fan system operating point & system effect
Fan-duct Systems
Modulation of air systems
Constant volume system
Volume flow rate remains constant
Supply temperature is raised during part load
Variable-air-volume (VAV) system
Volume flow rate is reduced to match part load
operation
Modulation curve
Fan modulation curve
Fan-duct Systems
Fan modulation methods
Damper (vary the opening of the air flow
passage)
Waste energy
Inlet vanes (opening & angle of inlet vanes)
Low cost; less efficient than following types
Inlet cone (peripheral area of fan impeller)
Inexpensive; for backward curved centrifugal fan
Blade pitch (blade angle of axial fan)
Fan speed (using adjustable frequency
drives)
Most energy-efficient; but usually cost more
Damper, inlet vanes & fan speed modulation
Inlet vane
modulation
Fan speed
modulation using
AC inverter
Fan-duct Systems
Fan surge (in centrifugal fan)
Occurs when air volume flow is not sufficient to
sustain the static pressure difference between
discharge & suction
Discharge pressure is reduced momentarily
Volume flow & pressure fluctuations
Create noise & vibration
Surge region: shall avoid operation in it
Fan stall (in axial fans)
When smooth air flow suddenly breaks & pressure
difference across the blades decreases
The fan loses pressure capability drastically
Stall and stall region of an axial fan
Fan-duct Systems
Fan selection
Select fan type + determine fan size
Important factors:
Pressure-volume flow operating characteristics
Fan capacity modulation
Fan efficiency
Sound power level
Airflow direction
Initial cost
Duct Construction
Types of air duct
Supply air duct
Return air duct
Outdoor air duct
Exhaust air
Duct sections
Header or main duct (trunk)
Branch duct or runout
Duct Construction
Duct systems
Max. pressure difference (between air inside
the duct and the ambient air)
125, 250, 500, 750, 1000, 1500, 2500 Pa
Commercial buildings
Low-pressure duct system: 500 Pa, max 12 m/s
Medium-pressure system: 500-1500 Pa, max 17.5
m/s
Residential buildings: 125 Pa or 250 Pa
Industrial duct system: P can be higher
Duct Construction
Duct material: e.g. UL (Underwriters
Laboratory) standard
Class 0: zero flame spread, zero smoke
developed
Iron, galvanized steel, aluminum, concrete,
masonry, clay tile
Class 1: flame spread 25, smoke
developed 50
Fiberglass, many flexible ducts
Class 2: flame spread 50, smoke
developed 100
Duct Construction
Shapes of air duct
Rectangular
More easily fabricated on site, air leakage
Round
Less fluid resistance, better rigidity/strength
Flat oval
Flexible
Multiple-ply polyester film w/ metal wire or strips
SMACNA (Sheet Metal and Air
Conditioning Contractors National
Association) standards
Rectangular duct Round duct w/ spiral seam
Flat oval duct Flexible duct
(Source: Wang, S. K., 2001. Handbook of Air Conditioning and Refrigeration)
Transverse joint reinforcement
(Source: Wang, S. K., 2001. Handbook of Air Conditioning and Refrigeration)
Duct Construction
Duct specification
Sheet gauge and thickness of duct material
Traverse joints & longitudinal seam
reinforcements
Duct hangers & their spacing
Tapes & adhesive closures
Fire spread and smoke developed
Site-fabricated or factory-/pre-fabricated
Duct Construction
Duct heat gain or loss
Temperature rise or drop
Duct insulation (mounted or inner-lined)
Reduce heat gain/loss, prevent condensation,
sound attentuation
Minimum & recommended thickness
See ASHRAE standard or local codes
Temperature rise curves
Depends on air velocity, duct dimensions &
insulation
Temperature rise from duct heat gain
(Source: Wang, S. K., 2001. Handbook of Air Conditioning and Refrigeration)
Duct Construction
Frictional losses
Darcey-Weisbach Equation
Hf = friction head loss, or pf = pressure loss
f = friction factor (dimensionless)
L = length of duct or pipe (m)
D = diameter of duct or pipe (m)
v = mean air velocity in duct (m/s)
>
<
Mode of airflow when air passes over and around
surface protuberances of the duct wall
Duct Construction
Duct friction chart
Colebrook formula
Roughness & temperature corrections
pf = Ksr KT Kelpf,c
Ksr = correction factor for surface roughness
KT = correction factor for air temperature
Kel = correction factor for elevation
Friction chart for round duct
Duct Construction
Circular equivalent
Hydraulic diameter, Dh = 4 A / P
A = area (mm2); P = perimeter (mm)
Rectangular duct:
Flat oval duct:
Duct Construction
Dynamic losses
Result from flow disturbances caused by duct-
mounted equipment and fittings
Change airflow paths direction and/or area
Flow separation & eddies/disturbances
In dynamic similarity (same Reynolds number
& geometrically similar duct fittings), dynamic
loss is proportional to their velocity pressure
Duct Construction
Local or dynamic loss coefficient
Ratio of total pressure loss to velocity
pressure
Duct Construction
Duct fittings
Elbows
Converging or diverging tees and wyes
Entrances and exits
Enlargements and contractions
Means to reduce dynamic losses
Turning angle, splitter vanes
ASHRAE duct fitting database
Fitting loss coefficients
Region of eddies and
turbulences in a round elbow 5-piece 90o round elbow
Rectangular elbow, smooth radius, 2 splitter vanes
Mitered elbow and its secondary flow
Airflow through a
rectangular converging
or diverging wye
Entrance Exit
Abrupt enlargement Sudden contraction
Duct Construction
Flow resistance, R
Total pressure loss pt at a specific volume flow
pt = R V
rate V 2
Rs = R1 + R2 + + Rn
Flow resistance in series:
1 in parallel:
Flow resistance 1 1 1
= + ++
Rp R1 R2 Rn
Total pressure loss and flow resistance of a round duct section
Flow resistance in series
Flow resistance in parallel
Flow resistance for a Y connection
Air Duct Design
Optimal air duct design
Optimal duct system layout, space available
Satisfactory system balance
Acceptable sound level
Optimum energy loss and initial cost
Install only necessary balancing devices
(dampers)
Fire codes, duct construction & insulation
Require comprehensive analysis & care for
different transport functions
Flow characteristics of a supply duct system
Air Duct Design
Design velocity
Constraints: space available, beam depth
Typical guidelines:
Main ducts: air flow usually 15 m/s; air flow noise
must be checked
With more demanding noise criteria (e.g. hotels),
max. air velocity: main duct 10-12.5 m/s, return
main duct 8 m/s, branch ducts 6 m/s
Face velocities for air-handling system
components
Air Duct Design
Reduce dynamic losses of the critical path
Maintain optimum air velocity through duct
fittings
Emphasize reduction of dynamic losses
nearer to the fan outlet or inlet (high air
velocity)
Proper use of splitter vanes
Set 2 duct fittings as far apart as possible
Air duct leakage
Duct leakage classification
AISI, SMACNA, ASHRAE standards
Air Duct Design
Fire protection
Duct material selection
Vertical ducts (using masonry, concrete or
clay)
When ducts pass through floors & walls
Use of fire dampers
Filling the gaps between ducts & bldg
structure
Duct systems for industrial applications
Any other fire precautions?
Air Duct Design
Design procedure (computer-aided or manual)
Verify local codes & material availability
Preliminary duct layout
Divide into consecutive duct sections
Minimise local loss coefficients of duct fittings
Select duct sizing methods
Critical total pressure loss of tentative critical path
Size branch ducts & balance total pressure at
junctions
Adjust supply flow rates according to duct heat gain
Resize duct sections, recalculate & balance parallel
paths
Check sound level & add necessary attenuation
Air Duct Design
Duct layout
Symmetric layout is easier to balance
Smaller main duct & shorter design path
For VAV systems, duct looping allows feed
from opposite direction
Optimise transporting capacity (balance points
often follow the suns position)
Result in smaller main duct
Compare alternative layouts & reduce fittings
For exposed ducts, appearance & integration
with the structure is important
Typical supply duct system with symmetric layout & looping
Air Duct Design
Duct liner
Lined internally on inner surface of duct wall
Mainly used for noise attenuation & insulation
Fiberglass blanket or boards
Duct cleaning
Prevent accumulation of dirt & debris
Agitation device to loosen the dirt & debris
Duct vacuum to extract loosened debris
Sealing of access openings
Duct breakout noise
HVAC Piping System
HVAC Instrumentation and Control
HVAC System Commissioning
The key elements of commissioning include:
Installation checks. Check installed equipment to ensure that all associated
components and accessories are in place.
Operational checks. Verify and document that systems are performing as expected,
and that all sensors and other system control devices are properly calibrated.
Documentation. Confirm that all required documentation has been provided, such as
a statement of the design intent and operating protocols for all building systems.
O&M manuals and training. Prepare comprehensive operation and maintenance
(O&M) manuals, and provide training for rig operations staff.
Ongoing monitoring. Conduct periodic monitoring after the school is occupied to
ensure that equipment and systems continue to perform according to design intent.
Correctly implemented, commissioning is extremely cost-effective, and should
improve the delivery process, increase systems reliability, improve energy
performance, ensure good indoor environmental quality, and improve operation and
maintenance of the facility.
