FCU Engineering Guide

7/25/2019 FCU Engineering Guide

1/16

Please refer to the Price Engineers HVAC Handbook

for more information on Fan Coils & Blower Coils

Engineering GuideFan & Blower Coils

S E C T I O N F 1


2/16F1-2All Metric dimensions ( ) are soft conversion. Copyright Price Industries Limited 2011.Imperial dimensions are converted to metric and rounded to the nearest millimetre.

Product Fundamentals

Fan Coils and Blower Coils

Engineering Guide

Fan coils are a type of air handling unitdesigned to supply conditioned air to aroom or zone. The basic components thatmake up a fan coil unit are a finned-tubeheat exchanger, fan section and filter. Thefan produces forced convection across theheat exchanger, which circulates either hotor cold water to provide conditioned air tothe space. Individual zone thermostats arecoupled to the fan coils fan speed controllerand hydronic controls to maintain roomtemperature. A well-designed fan coilunit will have low air and water pressuredrops across the coil to reduce fan andpump power requirements as well as anefficient fan and motor assembly for quiet

operation. Also, any fan coil unit equippedwith a cooling coil should have a drain paninstalled to capture condensate, regardlessof whether or not the entering air is pre-conditioned. Fan coils are located in ornear the space to be conditioned for freedelivery of air into the zone or with minimalduct work. Units generally operate with ablow-through arrangement where the coil isdownstream of the fan. Most fan coil unitsare supplied with a direct drive fan/motorassembly.

Most manufacturers certify their fan coilunits cooling performance to the Air-Conditioning, Heating, and RefrigerationInstitute standard AHRI Standard 440-2008: Performance Ratings for Room Fan

Coils. The purpose of the standard is toprovide classifications, test requirements,and minimum data requirements for thepublished ratings of fan coil units deliveringup to 1500 cfm.

Fan coils can be used in decentralized HVACsystems or in conjunction with a centralair handling unit. The major advantagesof using fan coil units are that they allowfor local control of individual zones andreduce the overall footprint of the systemby replacing ductwork with water pipingin a large portion of the system. They alsoreduce the amount of cross-contaminationbetween zones and allow for unused areasto be shut down. To receive ventilation air,fan coils can either be ducted to a centralair handler or to a mixing plenum. Whenattached to a mixing plenum, care mustbe taken as fan coils do not typically haveprovisions for controlling the amount ofoutdoor air admitted, and the coil must beprotected from freezing in cold climates.

Fan Coil Components

Access Panel Removable sheet metal section allows access to internal mechanicaland electrical components.

Belt Drive The motor turns the blower by a belt connected to pulleys on each shaftend. Each motor revolution will usually not be equal to one blower revolution.

Blower/Fan Multi-bladed, driven rotor enclosed so that air from an inlet iscompressed to a higher discharge pressure.

Casing Structural sheet metal box or shell to which all components are secured.

Coil A heat exchanger in which liquid is circulated to provide heating or cooling tothe air which passes through the heat sink fins.

Control Enclosure Sheet metal shroud which houses the electrical connections,speed controller and transformer. The enclosure cover prevents accidental electricalshock as well as protects the contents from the environment.

Direct Drive The motor shaft is directly secured to the blower shaft. Each motorrevolution is equal to one blower revolution.

Discharge Collar Rectangular fitting attached to the unit outlet allowing for quickattachment of downstream ductwork.

Drain Pan Pan located under the cooling coil to catch condensate formed duringcooling.

Filter Rack Tray in which a filter can be pulled out for maintenance or replacement.

Liner Internal blanket adhered to the casing that is used to reduce the radiated and/or discharge sound levels. Materials used vary based on application and performancerequired.

Motor Electrical component of an air movement device that provides work to turnthe blade assembly.

DischargeOpening Coils

Discharge Panel

Fan AssemblyCoil Connections

Filter Rack

Drain Pan

Figure 1: View of Fan Coil Unit


3/16

Copyright Price Industries Limited 2011. All Metric dimensions ( ) are soft conversion .Imperial dimensions are converted to metric and rounded to the nearest millimetre. F1-3

Fan Coils and Blower CoilsEngineering Guide

Fan Coils with Dedicated Outdoor Air Systems (DOAS)

Often fan coil units are applied in adedicated outdoor air system (DOAS). In thisconfiguration the air handler is selected todehumidify and condition the outdoor airas well as to handle the space latent load.The fan coil unit provides sensible coolingor heating at the zone (Figure 2). Thisconfiguration has several advantages overa conventional VAV system. Decoupling thesensible and latent loads ensures properhumidity control at each zone. Additionally,the exact outdoor air requirements to eachzone can be maintained, eliminating over-ventilation and ensuring compliance withASHRAE Standard 62-2001Ventilation forAcceptable Indoor Air Quality (IAQ). Energy

savings can be realized due to reducedterminal reheat and reduced outdoor air.Additionally, the DOAS system can beturned off during unoccupied hours with thefan coils maintaining local zone temperaturecontrol.

In Figure 2 the outdoor air is delivereddirectly to the space through a separatediffuser, independent of the fan coil unit.This allows the fan coil unit to be turnedoff or run at low speed during part loadconditions. Note that if a low supply airtemperature (less than 55 F) is requiredfor dehumidification, a high inductiondiffuser should be selected to preventdrafts. Another option is to duct the

outdoor air into the fan coil unit (Figure 3).In this case the fan coil must run during partload, however ductwork is minimized.

Figure 2: Outdoor air ducted through separate diffusers

Figure 3: Outdoor air ducted into fan coil unit

Supply Air Outdoor

Air

Return Air Relief Air

Zone 1

CLASSROOM

Zone 2

CLASSROOM

AHU

Fan

Coil

Unit

Fan

Coil

Unit

T T

Outdoor

Air

Relief Air

Zone 1

CLASSROOM

Zone 2

CLASSROOM

AHU

Fan

Coil

Unit

Fan

Coil

Unit

T T



Figure 7: Vertical Exposed Fan Coil

Figure 6: Horizontal Concealed Fan Coil

Low Pressure Fan Coils

Low pressure fan coils are generallylocated in or adjacent to the space to beconditioned. They are usually selected forfree delivery of air into the zone or withminimal ductwork having a static resistanceof less than 0.25 in. w.g. A well-designedunit should be equipped with an easilyremovable filter, drain pan and fan/motorassembly to reduce maintenance costsand improve indoor air quality. Theyare normally offered in nominal air flowsizes up to 1200 cfm and use multispeed,high-efficiency motors. Units commonlyhave single point power connections andthree position (plus shutdown) fan speedcontrollers. Units are available in vertical orhorizontal configurations for exposed andconcealed applications as shown in Figure4and Figure 5.

Concealed Units

Concealed units can be furred into a wall orinstalled in a ceiling plenum and then aretypically ducted to a single discharge grilleor diffuser as shown inFigure 6.

Exposed Units

Exposed units are generally installed ina visible location and therefore have anattractive painted finish and return andsupply air grilles as shown Figure 7. Unitsuse fully insulated casings to reduce the

amount of noise delivered to the occupiedspace, and the footprint is designed to besmall to minimize the amount of occupiedspace they require.

Typical Applications

Low pressure fan coils are ideally suitedfor applications where individual zonetemperature control is required. Thismakes them an ideal candidate for hotels,apartment buildings and office buildings(ASHRAE, 2008a). In many cases verticalunits are installed so that the supply airwashes the window and helps lower thethermal impact of the glass. Fan coils can beused in health care facilities, but care shouldbe taken because of their low-efficiency

filters and because they are designed mostlyfor re-circulated air which is not permittedin certain types of spaces.


Fan Coil Unit Types

Figure 4: Vertical Updraft Fan CoilArrangement

Figure 5: Horizontal Fan CoilArrangement

Filter

Fan

Coils

Discharge Air Opening

Return Air Opening

Cross Section View

FilterDuct Ceiling FanCoils

Cross Section View


5/16


Figure 8: Classroom installation


Fan Coil Unit Types

High Performance Fan Coils

High performance fan coils are designedfor higher air volumes, higher staticpressures, low noise levels and better roomtemperature control. To achieve the lowersound levels the high performance fancoils typically utilize larger fan blowers toreduce outlet velocity and fully enclose thefan/motor assembly in an insulated casing.They are normally offered in a horizontalconcealed configuration as shown in Figure9and are ducted to one or more supplyair grilles. Because of their higher staticpressure capabilities, high performance fancoils can be equipped with higher efficiencyfilters and more rows of heating-cooling

coils. A well-designed unit should still becapable of quietly and efficiently deliveringmaximum flow when fully equipped withcoils and filter at 0.5 in. w.g. of external staticresistance. Another benefit of the higherstatic pressure capability is that the unitcan accommodate longer discharge ductruns with multiple air outlets. This allowsthe fan coil to be mounted farther from theoccupied space reducing acoustic concerns.As an example for a classroom application,the fan coil unit can be located abovethe hallway where noise levels are lesscritical. Additionally, the longer length ofdownstream ductwork can be acousticallylined for further noise reduction. Due to theirhigher air flow capacity and static pressure

capability, larger rooms or spaces can besupplied with high performance fan coilunits.

To achieve the higher flows and staticpressures and still maintain efficiency, highperformance fan coils are often equippedwith electronically commutated motors(ECM). ECMs also allow for full rangedigital speed controllers and constant flowprogramming. Full range speed controlallows the fan speed to be optimized atthe setting which meets the room loadand acoustic design goals. Constant flowprogramming ensures the fan flow will bemaintained even as the filter resistanceincreases due to dust buildup.

When coupled with electronic or DDCcontrols ECMs can also be operated toprovide variable volume of both cooling andheating fan flows, contributing to furtherenergy savings and enhanced comfort. Seepage 608 for details.

High performance fan coils can beperformance certified up to 1500 cfmunder the AHRI Standard 440-2008. Unitsoperating beyond the scope of this standardshould still be tested and rated underthe same conditions to ensure reliableperformance in the field.


High performance fan coils are an excellentchoice for applications where a high level of

individual zone temperature control and lownoise is required. This makes them an idealcandidate for schools, hotels, apartmentsand office buildings. Higher air volume andstatic pressure capability also make themideal for larger spaces and applicationsrequiring longer duct runs and multiple airoutlets such as labs, meeting rooms, halls,lecture theaters, etc.

The high cooling capacity available withhigh performance fan coils meets the needsof high load spaces such as labs, perimete

zones with high solar loads, and highoccupancy spaces. High performance fancoils are also well-suited for hospitals andlaboratories because of their constant flowprogrammability and their ability to usehigher efficiency filters. The high efficiencyand VAV capability of ECM technologycoupled with the energy efficient benefitsof hydronic cooling or heating and theIAQ benefits of a DOAS system lends welto LEED certification and green buildingdesign.

Figure 9: Horizontal High Performance Fan Coils

CLASSROOM

Supply

Return

Duct

High PerformanceFan Coil Unit

Corridor


6/16


7/16


Discharge Opening

Heavy GaugeInsulated Casing

Access PanelsBelt DriveFan Assembly

Coil & DrainConnections

Insulation

Filter RackCoils

Blower Coil Unit Types

Access Panel

Removable sheet metal section allows

access to internal mechanical and electricalcomponents.

Belt Drive

The motor turns the blower by a beltconnected to pulleys on each shaft end.Each motor revolution will usually not beequal to one blower revolution.

Blower/Fan

Multi-bladed, driven rotor enclosed so thatair from an inlet is compressed to a higherdischarge pressure.

Casing

Structural sheet metal box or shell to whichall components are secured.

CoilA heat exchanger in which liquid is circulatedto provide heating or cooling to the air whichpasses through the sink fins.

Control Enclosure

Sheet metal shroud in which houses theelectrical connections, speed controller, andtransformer. The enclosure cover preventsaccidental electrical shock as well as protectsthe contents from the environment.

Direct Drive

The motor shaft is directly secured to the

blower shaft. Each motor revolution is equato one blower revolution.

Discharge Collar

Rectangular fitting attached to the unit outleallowing for quick attachment of downstreamductwork.

Filter Rack

Tray in which a filter can be pulled out fomaintenance or replacement.

Liner

Internal blanket adhered to the casing that isused to reduce the radiated and/or dischargesound levels. Materials used vary based onapplication and performance required.

MotorElectrical component of an air movemendevice that provides work to turn the bladeassembly.

While blower coils may be rated for anominal flow, they are not restricted bya limited number of incremental motorspeeds. They are capable of operating atany flow and static pressure within theiroperating range. This ability, coupled witha large number of coil combinations andaccessories such as electric reheat, mixingplenums and UV lights, means that blowercoils, like other air handlers, can be morecomplicated to specify or order.

The design engineer needs to specify manyparameters such as supply air temperatureand volume, outside air requirements, fluidtemperatures and flow rates, external staticresistances and more, before an equipment

supplier can provide the proper blower coilunit.

Manufacturers can certify their blower coilunits fan performance to the AHRI Standard430-2009: Performance Rating of CentralStation Air-Handling Units. The purpose ofthe standard is to provide classifications,test requirements and minimum datarequirements for the published ratings ofcentral station air-handling units. Watercoils used in blower coil units should alsobe AHRI certified to AHRI 410-2001: ForcedCirculation Air-Cooling and Air-HeatingCoils. By using equipment that is certifiedto these standards, the design engineer canbe confident that units will function properlyunder the conditions that are specified.


Blower coils are an excellent choice forapplications where high cooling capacitiesor external static pressures cannot be metwith standard or high performance directdrive fan coil units. This makes them an idealcandidate for schools, hotels, apartmentsand office buildings. Also, with their abilityto operate with up to 100% outdoor air and avariety of options such as mixing boxes, UVlights and solid metal liner, blower coils arealso well-suited for hospital and laboratoryapplication.

Fan coil system and zone piping can beconfigured in several ways to meet therequirements and priorities of the systemdesigner. System efficiency, flexibility andfirst cost are the primary drivers of thesystem piping design. The entire system(fan coils, piping, pumping, chillers andboilers) needs to be considered to confirmthat appropriate compromises are made tomeet the system goals.


Figure 13: Fan Coil/ Blower Coil Product Components (Exploded View)



Series and Parallel Piping

The piping system can be designed with twobasic piping concepts series or parallelpiping. In a series type system, a single pipeloop is utilized to supply water in a loop. Theindividual fan coils take water from this loopand discharge back to the loop. As more fancoils take from and return water to the seriesloop, the temperature in the loop is changed.It progressively increases in a chilled waterloop and progressively decreases in a hotwater loop. The fan coils at the end of theloop see water temperatures that provideless potential capacity than the fan coil atthe beginning of the loop. These fan coils atthe end of the loop will require larger coils

to provide similar capacity. The benefit ofthis type of system is the elimination of thereturn piping and the cost associated withit, but must be weighed against the cost oflarger coils in the fan coils that are later inthe loop.

In a parallel system, there is a supply pipeand a return pipe. Each fan coil unit receiveswater at the same temperature giving eachthe same capacity opportunity. Coils canbe selected with similar temperaturecharacteristics providing for more consistentsmaller coils.

Load Pumps

In a series piping system, load pumps isa way to pull water from the water flow in

the series piping and supply it to the coilin the fan coil unit. As capacity is requiredto meet the load, the pump pulls waterfrom the loop to provide the heating orcooling capacity required. This type ofdesign provides simple design and controlof the loop and the loads. The loop pipingexperiences constant flow and pressure.The load pump and piping at each fan coilunit is designed to only meet the pressureand flow requirements of the loop. Eachoperates and is controlled independently ofthe other. In some cases, control valves areprovided in the loop piping to confirm thatthere is no flow in the loop system when theloop system is shut down. See Figure 14.

Fan Coil Piping


Figure 14: Piping Systems

Series System With Load Pumps

Fan Coil Unit

Fan Coil Unit

Fan Coil Unit

Paralled System

Fan Coil Unit

Fan Coil Unit

Fan Coil Unit


9/16


Direct & Reverse Return

An important consideration in designingthe system is ensuring that each fan coilcan receive the desired chilled water or hotwater flow rates during system operation.Two types of systems can be utilizeddirect return or reverse return. In a directreturn system, as shown below, the pipingis run in the shortest method possible andbalancing valves are used to manipulate thepressure drop through each piping zone toensure each fan coil receives the requiredwater flow. This requires the system tobe balanced. These valves must be setthrough an iterative process to verify theflow through each coil. As each valve is

changed the rest of the system is affectedand they must be adjusted until the systemachieves steady state flow at each fan coil.See Figure 15.

In a reverse return system, the pipe lengththrough each piping zone is laid out to beequal. This ensures that the pressure dropthrough the piping system is equal for eachfan coil unit. This works well if the pressuredrop through each coil and piping loop isvery similar. This can be accomplished byusing the same pressure drop criteria for thecoils, and the same pressure drop criteriaper foot of pipe. While more piping needsto be installed, the balancing requirementof the system is eliminated. See Figure 16.

2 Way and 3 Way ValvesThe fan coil zone piping system can bedesigned for constant volume or variablevolume water flow. A constant volumesystem would require 3 way type controlvalves to modulate the water flow throughthe coil or around the coil to provide aconstant water flow through the zonepiping. A balancing valve is installed in thebypass to maintain constant pressure dropas the water flow is modulated around thewater coil. This type of constant flow systemwith 3 way control valves is very simplefrom a control and layout perspective, butcontinues to run the pump at full powerduring part-load conditions.

For a variable flow, 2 way control valves arerequired. In this type of system the pressurein the supply piping header is measuredand the pump output is varied to controlthe constant pressure in the system. As 2way valves are closed the system ridesthe pump curve. At lower flow the pumpincreases the pressure in the system. Thepressure control then slows the pumpdown to provide a lower flow at constantsystem pressure. As flow is lowered thepump requires significantly less power. Apump with a curve that has good predictiveperformance throughout the anticipated

Fan Coil Piping


water flow rate should be selected. Pumpswith very flat curves should be avoidedas small changes in pressure would leadto large changes in flow, creating systemcontrol issues.

Figure 17:Constant Flow

Figure 16: Reverse Return

Figure 15: Direct Return

Figure 18: Variable Flow

Fan Coil Unit

Fan Coil Unit

Fan Coil Unit

Fan Coil Unit

Fan Coil Unit

Fan Coil Unit



Figure 20: Common Coil 4 Pipe System

Capacity Control

In each of the above system and controldesigns, capacity control can be on-off ormodulation. On-off control would provideno water flow when the control system issatisfied. Often in a fan coil system the fanwould also be turned off during this satisfiedmode. When the control system calls forcapacity, the water flow would be providedat full design flow and the fan would beenergized to full air flow.

These systems can also utilize modulatingcontrol. Water flow would be varied toprovide the desired amount. In systemsdesigned to experience varying enteringconditions, the flow can be varied to maintaina constant leaving air temperature basedon a constant air volume. The water flowcan also be varied to provide less capacityby changing the leaving air temperaturebased on a constant flow. Also, variablewater flow and air flow can be provided. Theair flow is decreased as the load decreasesand the water flow is regulated to maintaina constant leaving air temperature. This isan uncommon control strategy for a fancoil system, but would provide enhanceddehumidification performance at low loadconditions.

Separate or Common Cooling andHeating Coils

Fan coil units are readily available with

either a single coil or with both a heating andcooling coils. When heating and cooling isrequired, they are most often provided withboth heating and cooling coils. In this typeof system, each coil is piped and controlledindependently. Generally there is sometype of dead band in the control systemto eliminate the possibility of heating andcooling simultaneously.

In a single coil system, where it operates ineither heating or cooling, the system canbe a 2 pipe or 4 pipe system. In a 2 pipesystem, either hot water or chilled water issupplied to the entire system depending onthe season. The fan coils are controlled tomaintain the required heating or coolingleaving air condition. In a 4 pipe system,each fan coil can be heating or cooling.This allows some parts of the system toprovide cooling while other parts provideheating. This is often required in buildingswith interior zones that require cooling allyear in all seasons. In this case 3 way valvescan be used to select either heating supplyand return or cooling supply and return.This type of system provides the greatestflexibility while lowering the first cost of thefan coil units.

Fan Coil Piping


Figure 19: Separate Coils 4 Pipe System

Heating Coil

Fan Coil Unit

Cooling Coil

Fan Coil Unit

Common Coil


11/16


Fan Coil Controls

Generally fan coils are applied to controlthe space temperature of a room or zone.A typical control system would consist of athermostat, multi speed fan, a heating coilwith control valve and/or a cooling coil withcontrol valve. Some systems may includecooling only and some heating only. Severallevels of control sophistication are availabledepending on the accuracy of temperaturecontrol and energy efficiency required.

Basic Electric Control

The simplest and most basic controlsystem would be manual adjustment ofthe fan flow and manual activation of theheating or cooling coil. In this case thethermostat has a temperature adjustmentdial, a manual switch for fan operation atone of three speeds or off, and a manualswitch for selecting either cooling or heatingmode. Figure 21 illustrates a typicalmanually switched thermostat. Generallythe thermostats are powered by line voltageand directly connected to the fan and valveactuator (Figure 22).

Figure 23illustrates the control sequencefor a manually controlled heat-coolchangeover fan coil control system. Duringcooling mode the cooling coil will be turnedon if the room temperature rises above set-point. During heating mode the heating coilwill be turned on if the room temperaturedrops below set-point. The operation of

the cooling or heating coil is full on or off.Either a 2 pipe or 4 pipe water supply canbe accommodated.

An enhancement to the above sequence isautomatic control of heating or cooling bythe thermostat. If a 2 pipe system is used awater temperature sensor is adhered to thesupply water pipe to allow the thermostat todetect if hot or cold water is available andautomatically switched between heatingor cooling mode. With a 4 pipe systemthe thermostat will automatically activatecooling mode when the room temperatureis above the thermostat set-point andheating mode when the room temperatureis below set-point. A further enhancementto the same sequence is automatic control

of the fan. The thermostat energizes the fanat the selected speed when there is a callfor heating or cooling. The level of controlenhancement will be determined by thethermostat model selected.


Figure 21: Manually Switched Fan Coil Thermostat

Figure 22: Typical Wiring Diagram - Basic Electric

Figure 23: Sequence of operation for manually selected fan speed and manualheat-cool changeover

FanCoil

TerminalBlock

L

SR Jumpers

SR1 SR2

G1 G2 G3 W/YAutomaticTemperatureControl Valve

Neutral

Low

Med

High

Line 1

OperatingV

oltage

Thermostat Terminals

Factory Electrical Wiring

Field Electrical Wiring

FanSpeedI(Low)

FanSpeedII(Med)

FanSpeedIII

(High)

ControlOutput

Min. Air Flow

Dead Band3 Speed Fan Flow

High High

Med Med

Low Low

0.9oF 0.9oF

Valve

Signal

Tset-point

Max. Air Flow

On

Off

Heating ON Cooling ON

Cool WarmRoom Condition



Fan Coil Controls

Analog Electronic Control

Analog electronic control systemsoffer several advantages over the basicelectric package, including more preciseproportional integral (PI) control of roomtemperature, optional modulating control ofthe cooling and heating coil, and an optionalLCD display for user-friendly monitoringand selection of control parameters. Figure24 illustrates a typical analog thermostatwith LCD display. Generally the thermostatsare powered by 24 VAC from a controltransformer (Figure 25). Figure 26 illustratesthe control sequence for an automaticheat-cool changeover fan coil system withmodulating control of heating and cooling.


Figure 24: Analog Thermostat with LCD display

Figure 25: Typical Wiring Diagram - Analog Electronic

Figure 26: Sequence of operation for automatic heat-cool changeover andmodulating control of heating and cooling

Changeover SensorField Installed

+24V Hot 1+24V Hot 1

+24V Open

+24V Closed

-24V Com 2

-24VCom

-24V Com 2

Air Temperature Sensor(Not Included)

1 2 3 4 6 7 8 9 10 11 12 D1 GND

Neutral

Neutral

OparatingVoltage24VAC

3PositionValve,

OpenSignal

3PositionValve,

CloseSignal

ChangeoverSensorInput

MeasuringNeutral

ReturnAirTempInput

FanSpeedIII(High)

FanSpeedII(Medium)

FanSpeedI(Low)

Potential-FreeOperating

ModeChangeoverSwitchInput

AutomaticTemperatureControl Valve

Factory Electrical Wiring

Field Electrical Wiring Thermostat Terminals

Min. Air Flow

3 Speed Fan Flow

High High

Med Med

Low Low

3.6oF

Valve

Signal

Tset-point

Max. Air Flow

Open

Closed

Heating ON Cooling ON

1.8oF


GREEN TIPDuring occupied hours the fan shouldbe operated to maintain ventilation airto the space.

GREEN TIPPI control and modulating water valvesminimize room temperature over-shoot providing energy savings.


13/16


Fan Coil Controls

GREEN TIPReducing the supply air temperatureduring overhead heating will limitstratification and improve indoor airquality.

GREEN TIPECMs consume considerably lesspower at part load operation thanstandard PSC motors, providingfurther energy savings.

Digital Programmable Control

Similar to the analog control system, thedigital thermostat includes proportionalintegral (PI) control of room temperature,modulating control of the cooling andheating coil, and an optional LCD display.However the addition of an on-boardmicroprocessor provides enhancedfunctionality and flexibility. Digitalthermostats typically are shipped pre-programmed for the desired sequence ofoperation but can be easily reconfiguredin the field if required. Figure 27illustrates field configuration of theprogrammable thermostat with a laptopPC and interface module.

More custom or specialized controlsequences can also be accommodated.One example is control of discharge airtemperature to a selectable set-point withthe addition of a discharge temperaturesensor. During cooling a minimumdischarge air temperature may be desiredto maintain control of humidity. Duringheating a maximum air temperature maybe desired to prevent stratification in theroom if ceiling mounted outlets are utilized.Figure 28illustrates the control sequencefor automatic heat-cool changeover andmodulating control of heating and cooling,with discharge air temperature control ofthe cooling flow.

If the fan coil is supplied with an ECM thedigital thermostat can be programmed toprovide modulating control of the fan flowduring both heating and cooling modes ofoperation. This enhanced function providessuperior comfort control, energy savings andimproved acoustics. Figure 29 illustrates thecontrol sequence for automatic heat-coolchangeover, modulating control of heatingand cooling with discharge air temperaturecontrol of the cooling and heating flow andvariable fan speed.


Figure 27: Field Programmable Thermostat

Figure 28: Sequence of operation for automatic heat /cool changeover and modulatingcontrol of heating and cooling, with discharge air temperature control of the cooling flow.

Figure 29: Sequence of operation for automatic heat /cool changeover, modulatingcontrol of heating and cooling with discharge air temperature control of the coolingand heating flow and variable fan speed.

Min. Air Flow

High High

Med Med

Low Low

2 oF

1oF 1oF

Valve

Signal

Tset-point

Max. Air Flow

10 Volts

0 Volts

HeatingON

CoolingON

2 oF

Dead Band


Min. Air Flow ECM

Valve

Signal

Tset-point

Max. Air Flow ECM

10 Volts

0 Volts

HeatingON

CoolingON

Dead Band


2 oF1oF 1oF

2 oF



Application of Fan Coil and Blower Coil Units

While blower coils and fan coils arefundamentally very similar, deciding whichtype of unit to use and in what configurationis not always straightforward. Consultationsbetween the designer and owner maybe required to weigh the benefits ofperformance, flexibility and maintainabilityversus cost.

Capacity

Blower Coils are capable of higher air flowsand static pressures than Fan Coils. For thisreason, Fan coils are typically smaller andare used to condition the room in whichthey are located, whereas Blower Coilsare moderate-sized and can be ducted tocondition several rooms. This is not alwaysthe case though as High Performance FanCoils have filled the gap between the twoproducts by offering capacities close tothose of blower coils while still retainingthe small size of a fan coil unit.

Controls

Fan coils are typically controlled by eithera thermostat or fan speed switch in theroom that they are conditioning (ASHRAE,2008a). This makes them well-suited forapplications where a high level of individualcontrol is desirable, such as hotel rooms, orwhere there are infrequent loads, such as ameeting room. Blower coils on the otherhand are typically operated as constant airflow units. If required, they can be equippedwith variable frequency drives for VAVcontrol, however the cost will be higher.High performance fan coils can be equippedwith ECMs programmed to deliver constantair flow within a range of static pressures.

Noise

Both fan coils and blower coils generatea significant amount of fan noise so theirapplication and location needs to becarefully considered. Fan coils tend tobe quieter so they can be located in theconditioned space as an exposed unit ordirectly adjacent to the space in a ceilingplenum or wall cavity. Exposed units shouldbe fully lined with fiberglass insulation toreduce radiated noise.

Fan coils by design are intended to belocated in or directly adjacent to theoccupied space. They can be installed inwalls, ceiling plenums, closets, and manyother areas close to the room they serve.Noise is a large concern as there is oftenlimited ability to provide sound attenuationtechniques in the building material betweenthe unit and the space or in the supply andreturn ductwork. The location of the fancoils needs to be reviewed to confirm thatthe sound level in the adjacent space isacceptable.



15/16


Application of Fan Coil and Blower Coil Units

Locating the fan coil unit in or over spaceswith higher sound criteria is often used tominimize the occupant objections. Locatingthem above a bathroom ceiling would bean example of this technique. Selecting theunits at lower than the maximum air flowthe unit can produce is a method of loweringthe noise produced by the fan coil unit.

Larger fans running at slower speeds oftenprovide improved noise characteristics,but will require greater first cost of theunit. Sound data from the manufacturershould be reviewed with options to reducethe noise levels to achieve acceptable spacenoise design.

Blower coils can be equipped with integralsilencers to significantly reduce theirdischarge noise. They can then be locatedaway from the noise sensitive space andducted to the room.

Contaminant Control

Most fan coils and blower coils are equippedwith a filter, but the level of filtration variesgreatly. Low pressure fan coils are typicallyonly equipped with MERV 3 filters becausethey are not capable of overcoming the largepressure drop caused by higher efficiencypleated filters. High performance fan coilscan be equipped with medium efficiencyfilters up to MERV 13. If a high degree ofcontaminant control is required, blowercoils can be equipped with high-efficiency

filters (up to MERV 15) and UV lights. Blowercoils can also be equipped with HEPA filtersif special care is taken to seal the unit casingagainst infiltration of non-filtered air.

Outdoor Air

Fan coils should not be used to conditionoutdoor air as they are not designed tohandle high levels of humidity. They do nottypically have deep enough coils to providethe level of dehumidification required,and condensate carryover can occur inhigh humidity locations due to high facevelocities on coils caused by the typicalblow-through configuration. Blower coilson the other hand have the static pressurecapabilities required to use deep coils and

can be equipped with mixing boxes tocombine re-circulated air with outdoor air.One notable exception is that fan coils arewell-suited for heating only applicationswhere there are high infiltration rates ofoutdoor air such as using an exposedvertical fan coil to heat a vestibule or lobby(ASHRAE, 2008a).


Unit Type

Office Space,Educational Facilities

Hospitals,Clean Rooms,Laboratories

Large

Buildings

Small

Buildings

Patient

Areas

Operatin

g

Areas

Laborato

ry

Spaces

Low Pressure Fan Coils

High Performance Fan Coils - -

Blower Coils

Type Fan Cabinet cfm Ext Static

Horizontal Direct Exposed / Concealed < 2,000


16/16

References


AHRI (2001a). AHRI standard 260-2001: Sound ratings of ducted air moving and conditioning equipment.Arlington, VA: Air-Conditioning, Heating, and Refrigeration Institute.

AHRI (2001b). AHRI standard 410-2001: Forced circulation air-cooling and air- heating coils. Arlington, VA:Air-Conditioning, Heating, and Refrigeration Institute.

AHRI (2008a). AHRI standard 440-2008: Performance rating of room fan-coils.Arlington, VA: Air-Conditioning,Heating, and Refrigeration Institute.

AHRI (2008b). AHRI standard 885-2008: Procedure for estimating occupied space sound levels in theapplication of air terminals and air outlets. Arlington, VA: Air-Conditioning, Heating, and RefrigerationInstitute.

AHRI (2009). AHRI standard 430-2009: Performance rating of central station air- handling units. Arlington, VA:Air-Conditioning, Heating, and Refrigeration Institute.

ASHRAE (2001). Standard 62-2001Ventilation for acceptable indoor air quality. Atlanta, GA: American

Society of Heating, Refrigeration and Air-Conditioning Engineers.ASHRAE (2007a). ASHRAE handbookHVAC applications. Atlanta, GA: American Society of Heating,

Refrigeration and Air-Conditioning Engineers.

ASHRAE (2007b). Standard 52.2-2007Method of testing general ventilation air-cleaning devices for removalefficiency by particle size. Atlanta, GA: American Society of Heating, Refrigeration and Air-ConditioningEngineers.

ASHRAE (2008a). ASHRAE handbookHVAC systems and equipment (SI edition). Atlanta, GA: AmericanSociety of Heating, Refrigeration and Air-Conditioning Engineers.

ASHRAE (2008b). Standard 130-2008Methods of testing air terminal units. Atlanta, GA: American Societyof Heating, Refrigeration and Air-Conditioning Engineers.

ASHRAE (2009). ASHRAE handbookFundamentals. Atlanta, GA: American Society for Heating, Refrigeratingand Air Conditioning Engineers, Inc.

Price Industries (2011). Price engineer's HVAC handbookA comprehensive guide to HVAC fundamentals.Winnipeg, MB: Price Industries Limited.

Documents

FCU Engineering Guide