HVAC Inputs by Team ABS Air Tech Gurgaon

HVAC Systems – Understanding the basis

Table of Contents

1. Introduction to HVAC Systems2. HVAC System Types3. HVAC Piping System4. HVAC Air Distribution Equipments5. Fans and Pumps6. HVAC Instrumentation and Control7. HVAC System Commissioning

1www.absairtech.in || www.abscleanroom.com || www.absventilation.com || www.abscoldroom.com

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, day lighting, 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, hedonic 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


•Purpose of an air handling system

Air Handling System

RoomWith

DefinedRequirements

SupplyAir

OutletAir

Air Handling Systems


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


+

Room/Cabin

Exhaust air treatment

Central air handling unit

Terminal air treatmentat production room level

Fresh air treatment (make-up air)

Main subsystems


FilterSilencer

Terminal filter

Weather louvre Control damper

FanFlow rate controller

Humidifier

Heating coil

Cooling coil

with droplet

separator

Production Room

Overview components

+

Prefilter

Exhaust Air Grille

Heater

Secondary Filter

Re-circulated air


• Weather louver

• Silencer

• Flow rate controller

• Control damper

• To prevent insects, leaves, dirt and rain from entering

• To reduce noise caused by air circulation

• Automated adjustment of volume of air (night and day, pressure control)

• Fixed adjustment of volume of air

Components (1)


• Heating unit •Cooling unit /dehumidifier

•Humidifier

•Filters

•Ducts

• To heat the air to the proper temperature

• To cool the air to the required temperature or to remove moisture from the air

• To bring the air to the proper humidity, if too low

• To eliminate particles of pre-determined dimensions and/or micro-organisms

• To transport the air

Components (2)


+

Production Room

Exhaust air

Return air(re-circulated)

Fresh air(make-up air)

Supply air

Air types


Filter classes

Dust filters

Standard Aerosol

FineCoarse ULPAHEPA

10 µ m > Dp > 1 µ mDp > 10 µ m Dp < 1 µ m

F5 - F9G1 - G4 U 14- 17H 11 - 13

EN 1822 StandardEN 779 Standard


Primary panel Primary panel filterfilter

Secondary Secondary filterfilter

HEPA or tertiaary filter


Duct heaters Room Heters

SilensersSilensers


Volume control damper

De-humidification

Filter Pressure Gauges

AHU with fan Variable Speed

Controller

Humid room air

Air heater

Regeneration air

Humid room air Adsorber wheel Dry air

FireFire DampersDampers


Annex 1, 17.26

Regulation of room pressure – pressure differentials concept

Room pressure gauges

Room pressure indication panel


Pressure cascade injectables Protection from micro-organisms and particles

N ote : D irection of door opening relative to room pressure

15 Pa

0 PaA ir

Lock30 Pa PassageD

C

A

B

D LF

A ir LockA ir Lock

45 Pa

Room 3 Room 2 Room 1

45 Pa60 Pa30 Pa


Pressure cascade solidsProtection from cross-contamination

N o te : D ire c t io n o f d o o r o p e n in g re la t iv e t o ro o m p re s s u re 1 5 P a1 5 P a1 5 P aE3 0 P a Pa s s a g e 0 P aA irLo ck R o o m 3 R o o m 2 R o o m 11 5 P a A ir Lo ckA ir Lo ck

N ote : D irection of door opening relative to room pressure

15 Pa

15 Pa15 Pa

E30 Pa

Passage0 Pa

A irLock

Room 3 Room 2 Room 1

15 Pa

A ir LockA ir Lock






Fan Coil Unit


Self Contain Unit


HVAC Air Distribution Equipments• Diffusers

4 Way Diffusers Two Way Diffusers One Way Diffuser

Round Diffusers34www.absairtech.in || www.abscleanroom.com || www.absventilation.com || www.abscoldroom.com

Cabin Units


• Return / Exhaust Grilles


Contents

• Fan Design• Fan Performance• Fan-duct Systems• Duct Construction• Air Duct Design

Fans and Pumps


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 and axial fan components

AXIAL FANSCENTRIFUGAL FANS


Propeller Tube-axial

Tube-vane

AXIAL FANS


Tubular centrifugal fan Centrifugal roof ventilator

CENTRIFUGAL FANS

(* Note the airflow paths and impeller design.)41www.absairtech.in || www.abscleanroom.com || www.absventilation.com || www.abscoldroom.com

Drive arrangements and motor positions42www.absairtech.in || www.abscleanroom.com || www.absventilation.com || www.abscoldroom.com

Single- and double-width centrifugal fans43www.absairtech.in || www.abscleanroom.com || www.absventilation.com || www.abscoldroom.com

Fan Performance• Major parameters

– Fan volume flow rate (m3/s or l/s), Vf

– Fan total pressure Δptf, fan velocity pressure pvf & fan static pressure Δpsf (Pa)

– Fan power & efficiency• Fan power or air power (W) = Δptf x Vf

• Fan power input on the fan shaft (brake horsepower), Pf

• Fan total efficiency: ηt = Δptf x Vf / Pf

– Combined aerodynamic, volumetric & mechanical efficiencies

• Fan static efficiency: ηs = Δpsf x Vf / Pf

• Air temp. increase through fan, ΔTf = Δptf /(ρcpaηt)44www.absairtech.in || www.abscleanroom.com || www.absventilation.com || www.abscoldroom.com

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 (Δp )– Air density (ρ)– For air systems that are

geometrically & dynamically similar: (D = impeller diameter)

• c.f.: pump laws


Velocity triangle at the blade inlet and outlet of a centrifugal fan

CENTRIFUGAL FANS


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 fan50www.absairtech.in || www.abscleanroom.com || www.absventilation.com || www.abscoldroom.com

Total efficiency curves for

centrifugal fans


Fan power curves for centrifugal fans with same impeller diameter52www.absairtech.in || www.abscleanroom.com || www.absventilation.com || www.abscoldroom.com

Fan pressure curves for centrifugal fans with same impeller diameter53www.absairtech.in || www.abscleanroom.com || www.absventilation.com || www.abscoldroom.com

Velocity triangles for a vane-axial fan

AXIAL FANS


Fan pressure curves for axial fans with same impeller diameter55www.absairtech.in || www.abscleanroom.com || www.absventilation.com || www.abscoldroom.com

Fan efficiency curves for axial fans with same impeller diameter56www.absairtech.in || www.abscleanroom.com || www.absventilation.com || www.abscoldroom.com

Fan power curves for axial fans with same impeller diameter57www.absairtech.in || www.abscleanroom.com || www.absventilation.com || www.abscoldroom.com

Performance curves for

controllable-pitch vane-axial

fans


Fan-duct Systems

• Duct pressure changes (c.f. atm pressure)– Static pressure (SP)– Velocity pressure (VP) = ρV2 / 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 R, pressure drop Δp and volume flow

rate V

– Duct sections in series:– Duct sections in parallel:

ns RRRR 21

2VRp o

np RRRR

1111

21


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 Δpts

– 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 Outlet65www.absairtech.in || www.abscleanroom.com || www.absventilation.com || www.abscoldroom.com

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 curve68www.absairtech.in || www.abscleanroom.com || www.absventilation.com || www.abscoldroom.com

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 modulation70www.absairtech.in || www.abscleanroom.com || www.absventilation.com || www.abscoldroom.com

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 fan74www.absairtech.in || www.abscleanroom.com || www.absventilation.com || www.abscoldroom.com

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: ΔP 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 Δpf = 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 aroundsurface protuberances of the duct wall

δ >ε

δ <ε


Duct Construction

• Duct friction chart– Colebrook formula

• Roughness & temperature corrections– Δpf = Ksr KT KelΔpf,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 path’s 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 andturbulences in a round elbow 5-piece 90o round elbow


Rectangular elbow, smooth radius, 2 splitter vanes

Mitered elbow and its secondary flow


Airflow through arectangular converging

or diverging wye


Entrance Exit


Abrupt enlargement Sudden contraction


Duct Construction• Flow resistance, R

– Total pressure loss Δpt at a specific volume flow rate V

– Flow resistance in series:

– Flow resistance in parallel:

ns RRRR 21

2VRpt

np RRRR

1111

21


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

• Optimize transporting capacity (balance points often follow the sun’s position)

• Result in smaller main duct

– Compare alternative layouts & reduce fittings– For exposed ducts, appearance & integration with

the structure is important113www.absairtech.in || www.abscleanroom.com || www.absventilation.com || www.abscoldroom.com

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.


HVAC Inputs by Team ABS Air Tech Gurgaon

Environment

hvac systems heating

airconditioning hvac

air conditioning hvac

hvac instrumentation

air conditioning system

hvac piping system

hvac system commissioning

efficient systems