Technical Development Program - Sigler...

COMMERCIAL HVAC EQUIPMENTCentral Station

Air Handlers

PRESENTED BY:

Rodrigo L Valdez, Jr.

Sigler

Technical Development Program

• Identify different types of air handlers

• Categorize air handler construction methods

• Identify major air handler components

• Compare the difference between indoorand outdoor units

• Identify coil types

• Recognize types of fans used

• Identify unit accessory sections and theiruse

Objectives

Section 1 – Introduction

• Air Movement (Circulation)

• Cool and Dehumidified Air

• Heating

• Clean Air via Filtration

• Control of Space Humidity

• Means of Mixing Outside Air and Return Air

• Humidification in Winter

AHRI 430 Definition

EADamper

Where does the AHU fit in?

RAFan RA

Grille

Water Chiller

Water Piping

ChilledWaterPump

FilterOADamper

OUTDOORAIR

RA Damper

RA Duct

SADiffuser

COOLAIR

EXHAUSTAIR

SA Duct

AirHandler

3 Types of Air Handling Units

Packaged, Central Station, and Custom

Packaged AHU

Characteristics

• Fixed fan and coil configuration

• Limited to <12,000 cfm (30 tons)

• Split Cooling, CW or Heat Pumps

• Low-static < 2 in. ESP

• Indoor applications

Section 2 – Packaged, Central, and Custom AHU

Packaged AHU’s Lack Flexibility

Central Station AHUCharacteristics• Often referred to as “Applied”

or “Built-Up” systems.• Configured in a “Building

Block” fashion. Hundreds ofcomponent combinations

• Typical sizes range from1,500 to 50,000 cfm,although AHU”S capable ofdelivering 300,000 cfm areavailable.

• Multiple arrangements, fan,and coil types.

• Wide range of component options.• Indoor or outdoor models

AHU Building Blocks

Central Station AHU

START WITH THE FAN SECTION ANDMOVE UPSTREAM…

BUILDING BLOCK CONFIGURATION….

Central Station AHUAdd additionalmodules forcoils, filter,mixing box,plenum orother asrequired tomeet theneeds of theproject..

Central Station AHU

BUILT-UP AIR HANDLING UNIT WITH ECONOMIZER,FILTER SECTION, HEATING COIL, ACCESS SECTION,

COOLING COIL, AND FAN SECTION.

Custom Air Handler

Key Features:• Job-Specific

Design– Dimensions

– Performance

– Materials

– Flexible

– More Expensive

• Used when standard unit designs cannot be applied.

Custom Air Handler

Key Features:• Can match existing

footprint. Offergreatest flexibility.

•Aspect Ratio Changes

Custom Air Handler

Key Features:• Specialty Fans

– Multiple Fans orFan Array

– Direct Drive

– Fan Wheel Type

Custom Air Handler

Key Features:• Options not

normally found instandard centralstation airhandlers.– Factory-Installed,

job-specificcontrols

– Specialtycomponent notcataloged

Custom Air Handler

Key Features:• Used where

special casings areneeded.– Stainless steel

for corrosionprotection.

– Aluminum panelsfor weightreduction.

The relationship between airflow volume (cfm),velocity (V) and area (A) is:

cfm = V*A or A = cfm/V

Solution: A = cfm / VA = 25,000 cfm / 500 fpmA = 50 ft2 cooling coil required

Air Handler Nominal Size Selection

Where:A = H * L

Coil Size & Face VelocityDetermine Max CFM

•FCS•LCS

•AIRFLOW

•ACC•HVF•MXB

•MIXING•BOX

•HIGH•VEL

•FILTER

•ACCESS•SECTION •COIL(S)

•SECTION •FAN

•39M03 = 3.5 SQ. FT. x 550 = 1,925 CFM

•39M06 = 5.9 SQ. FT. x 550 = 3,245 CFM

•39M08 = 7.6 SQ. FT. x 550 = 4,180 CFM

Basic Construction

CENTRAL STATION AIRHANDLERS

Casing Construction - Post and Panel

Frame Rail

Double Wall Panel

Section 3 – Basic Construction

• Uses load-bearing side wall panels• Individual panels may generally be removed, but not all at once• Allows manufacturers to vary wall thickness more easily

Structural Panel Construction

Casing Design and Materials

• Galvanized steel most common.– Indoor units use a minimum of G-60– Outdoor units use a minimum of G-90

• Painted galvanized steel is recommendedfor outdoor air handlers, and optional forindoor units

• Alternate inner casing materials areavailable and used in response to indoorair quality concerns.

• 1-inch foil-faced insulation reducesthe potential for mold or bacteriaand is easier to clean

• 1-inch matte-faced fiberglass

Insulation - Single Wall Units

Double-Wall

Thermal-Break ConstructionAn air handler construction feature thatprevents a conduction path of heat transferfrom the inside to the outside of the unit.Without this, sweating can occur at pointswithout thermal breaks.

PVC Panel FramePVC Panel Frame(no conduction path)

Casing Thermal Break

No metal-to-metal contactbetween frame and panelNo metal-to-metal contactbetween inner and outercasing

Casing Strength

MAX Deflection (D/L) = 1:200

Casing Strength = Leak-Tight Integrity,

Unit should have high quality seals on allpanel joints, section flanges, doors andaccess panels.

Seals:l Minimize air leakagel Prevent dirt and contaminants

from being drawn into the systeml Save energyl Reduce noise

Casing Seals

Unit Types

AHU - Horizontal, Vertical, Stacked

Section 4 – Unit Types

Suspended units• Locate units over NON-critical spaces

to prevent:– Water leaks that could damage

sensitive equipment or materials– Sound that could be

objectionable– Restricted service

access

Floor-mounted units• AHU must be elevated enough to

allow for condensate drain trapping• Factory-supplied base rails

(full perimeter recommended)

Base Rail or Housekeeping Pad

Unit Mounting Considerations

RecommendedInline Beam Mount

Outdoor UnitsDesign Features:

• Painted casings• One-piece design• Sloped roof with overhangs• Double-wall with 2-inch minimum

wall thickness to minimize thermalheat transfer and casing sweating Outdoor

Air Hood

SlopedRoof

Draw-Thru• Fan downstream of cooling coil• Fan motor heat travels to

conditioned space, becomingroom load

Advantages:• Even airflow assured over the coil• Shortest length required

Draw-Thru and Blow-Thru

Horizontal Draw-Thru Horizontal Blow-Thru

Vertical Draw-Thru

Blow-Thru• Fan upstream of cooling coil• Fan blows air through coil• Diffuser plate needed – which

adds length

Advantages:• Motor heat becomes coil load

– NOT ROOM LOAD• Less cfm required with

smaller ducts andless fan energy

CoilCoil CoilCoil

CoilCoil

Cooling Coil Section

Mounting Rails

Sloped Drain Pan

WaterConnections

Section 5 – Coils

Cooling Coils• Types

– Chilled water (CW)– Direct expansion (DX)– Variety of rows,

fin spacing, and splits• Materials (Common)

– Plate fins• Aluminum• Copper

– Copper tubes• Multiple wall thicknesses

• Casings– Galvanized steel– Stainless steel

Section 5 – Coils

• Multiple circuiting options:– Quarter, full, half, double– Allow a wide application range– Allow proper oil return at part load

• Coil Splits– Intertwined Row– Face Split– Allow flexibility for part load control

Feeder Tubes

Suction Headers

RefrigerantDistributors

DX Coil Details

Section 5 – Coils

Plate Fin Chilled Water CoilCooling Coils

• Plate fins mechanically bonded to tubes– Copper Tubes– Aluminum or Copper fins

• Multiple row options: 4 to 10 row typical• Fin spacing options: typically 8 to 14 fins/inch

Section 5 – Coils

Sloped Drain Pan• ASHRAE 62 requires

sloped drain pans thatdrain completely withno standing water

• Can be galvanizedor stainless steel

• Can be coated withantimicrobial compounds

Cooling Coil Sections

Section 5 – Coils

Fan Characteristics and Performance

Supply Fan

SA Fan

Draw-ThruCoilCoil

Blow-Thru

CoilCoil

SA Fan

Section 6 – Fan Characteristics and Performance

DiffuserPlate

Return Fans

• Prevents excessive building pressurization• Used in systems with high return duct pressure drops• Generally controlled by building pressure sensor or

tracks the supply fan on VAV systems

RA Fan SA Fan

CoilCoil

• Prevent excessive building pressurization

• Operates only during “economizer mode” or when ahigh percentage of ventilation air is being drawn in

Exhaust Fans

EXH Fan SA Fan

CoilCoil

Characteristics:• Most commonly used wheel in HVAC• Light weight – lowest cost• Operates at static pressures up to 5 in. wg max.• Low rpm (800 to 1200 rpm)

Forward-Curved Wheel Design

Characteristics:• Aerodynamically designed – double thickness airfoil shape for maximum

efficiency• For medium to high air capacity and pressure applications (4 to 10 in. wg)• Higher cost

Airfoil Wheel Design

Characteristics:• Pressurize a plenum chamber.• Operates at static pressures up to 10 in. wg• Flexibility to connect multiple outlet ducts

FanWheelGuard

InletCone

Plenum Fans (SWSI)

• Inlet Guide Vanes

• Discharge Dampers

• Variable Frequency Drives

VAV Airflow Control Options

Inlet Guide Vanes

Actuator Shaft(actuator not

shown)

Fan BearingLube Line for

Bearing

Inlet Vanes

•Dampers on inlet reduce fan capacity

Discharge DampersDampers are typically mounted close to or right off the fan discharge.

Remote DuctStatic Pressure

Sensor

DischargeDampers

Variable Frequency Drives (VFDs)

Fan Modulation Methods

% Design Airflow

Inlet GuideVanes

VFD Speed Control

Discharge Dampers

VAV Applications

• It’s important to checkyour VAV fanselections at theminimum operatingpoint for stability.

AMCA Fan Construction Class

Outlet Velocity (fpm)

Based onSP andoutletvelocity.

Fan Components

• Fan Mounting

• Discharge Isolation

• Bearings

• Drives

• Motors

Standard 2-inchSteel Spring Isolator

Fan Spring Isolation

Discharge Isolation

Traditional Canvas Connector

Fan Discharge Vibration Isolation

Hours and Years

How long is 200,000 hours? The following tableconverts hours to years based on different daily usage.

HoursYears

8 hoursper day

16 hoursper day

Continuousduty

40,000 13.7 6.8 4.6

100,000 34.2 17.1 11.4

200,000 68.4 34.2 22.8

400,000 137 68.4 45.8

500,000 171 85.6 57.0

1,000,000 342 171 114

Bearings

Typical Pillow Block Bearing

Grease Fitting

Operating Life Rating

Example = L50, L10…

• Belt drive is most commonon central station units– Adjustable pitch for low bhp– Fixed-pitch for bhp >15

• Drive losses typically 3 to 5%

• More AHU’s today are usingdirect drives to reduce thecost of maintenance andeliminate belt residue

Motor and Drive Arrangement

Totally EnclosedFan-Cooled

(TEFC) Motor

Open Drip Proof(ODP) Motor

Fan Motor Types

Unit Accessories

Accessory Sections• Filters• Access & Plenum• Mixing Box• Exhaust and Economizer Box• Humidifier• UV-C Germicidal Lights

Section 7 – Unit Accessories

• Most common.

• Minimum filtration capability

• Up to MERV 13

• Throw-away:– Cardboard frames (shown)– Pleated media available

• Permanent– Cleanable– OSA intake hoods

Panel Filters

Panel filters arranged in a “V” bank

• Reduced velocity through filters– Better filtration efficiency– Lower pressure drop vs. high velocity (flat)

filter section

Angle Filters

• Medium to high efficiency

• Up to MERV 15

• Removes “fine” dust particles

• Greater filter area– Lower velocities– More dirt absorption

• Use with pre-filters

Bag Filters

Box or Cartridge – MERV 15Box filters will not sag at reduced cfms in VAV systems.

Up to 95% Eff.

HEPA / ULPA FilterHigh Efficiency Particulate Air

Both types are high efficiency (above 99%).

RigidRigidFrame

Ultra Low Penetration Air

• Service access• Field-installed components

– Humidifiers– Sound attenuators– Controls, VFD.– UVC Lights

• Discharge Plenums– Provide duct outlet for

blow thru units

Blow-thru plenum with safety grate

Access and Plenum SectionsProvide space between components

• Plenum with two air inlets– Outdoor air– Return air

• Provides– Ventilation air– Free cooling (economizer)– Indoor air quality (CO2)

Mixing Box

Exhaust and Economizer Box

• Used downstream of return fan• Provides outlet to relieve excess air from building• Maintains space pressurization• Dampers are controlled by space pressure

sensor, or linked to mixing box dampers

Exhaust Box Mixing Box

ECONOMIZERSECTION

Steam Grid

Atomizing

Humidifiers

• According to BOMA(Building Owners & Managers Assoc.),the average condensate drain pan is cleanedonly 3.5 times per year

• Condensate drain pan and evaporator coilmay be sources of mold/bacteria growthunder certain conditions (68 to 86° F)

• Limits biological growth onevaporator coil and condensatedrain pan

– Maintains design air pressure drop– Helps reduce maintenance costs

• General rule of thumb sizing:– 1 lamp per 12 ft2 of coil surface

@ 12” distance from coil

UV-c Germicidal Lamps

Motor / System Controls

• Motor disconnects, starters, VFDs offered as options

• DDC control systems and components offered

• Factory installation– Reduces field labor costs– Minimizes mistakes and setup time

Additional Configurations

Dual-Duct Unit• Blow-thru arrangement• Normally a constant volume system• Coil section with cooling and heating coils in parallel

– Coils referred to as “cold “ and “hot” decks, respectively– Provide simultaneous cooling and heating– Separate cooling and heating supply air ducts throughout building– Zone mixing boxes blend air from both ducts to meet space requirements

Section 8 – Additional Configurations

Constant Volume, Blow-thru variation of Dual Duct System• Zoning dampers mounted on dual coil section in lieu of zone mixing boxes

– Opposed dampers mix air from cold and hot decks into a common duct– Dampers controlled by space temperature– Separate supply air ducts to each zone

Multizone Damper Arrangement

Multizone variation• Adds a third “neutral” deck

between cold and hot decks– Neutral air is unconditioned return/outdoor air

Zoning dampers• Opposed Dampers can mix cold, hot,

and neutral air to meet zone needs• Minimizes reheat (mixing of cooled and heated air)

Triple-Deck Multizone

• Identified different types of air handlers

• Categorized air handler construction methods

• Identified air handler components

• Compared the difference between indoorand outdoor units

• Identified coil types

• Discussed the types of fans used

• Identified typical unit accessory sectionsand specified their use

Summary

Section 10 – Summary

Summary

Work Session

CENTRAL STATION AIR HANDLERS

Work SessionQuestions may have more than one correct answer. Include all correct answers in your re-

sponse to the questions below.

1. List the seven functions of a central station air handler as defined by ARI.

______________________ ______________________

______________________

2. True or False? A packaged air handler offers a wider size range with more features andflexibility than a central station air handler. ___________________

3. The size of a central station air handler is usually based on _______

the unit.

TDP-611 Central Station Air HandlersArtwork from Symbol Library used by permission ofSoftware Toolboxwww.softwaretoolbox.com/symbols

Technical Development Program - Sigler...

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