Variable Frequency Drive Applications In HVAC Systems
Chapter 7Variable Frequency Drive Applications in HVAC SystemsYunhua LiAdditional information is available at the end of the ding heating ventilation and air-conditioning (HVAC) systems are designed tooperate at the peak load, which only occurs in a very short period of time throughoutthe year. One of the most effective ways to improve building energy efficiency is toutilize the variable frequency drives (VFDs). They are widely used in the HVAC field,including fans, pumps, compressors, etc. In a VFD-equipped system, the VFD adjuststhe speed of one or more motors based on the system load requirements and operationschedule, resulting in a dramatic cut in energy consumption.This article systematically introduces the application of VFDs in HVAC systems,including heating systems, ventilation systems, cooling systems, and refrigerationsystems in commercial and industrial buildings. First, the principles are introducedfor VFDs, variable speed fans, pumps, and compressors. Next, the control applicationof VFDs on each type of system (equipment) is summarized. In this section, theschematic diagram of each system as well as the detailed control strategy for eachapplication is presented. In addition, the application of VFD on fault detection anddiagnosis (FDD) is introduced. Lastly, some technical issues and concerns arediscussed with potential solutions provided.Keywords: Variable frequency drives, HVAC systems, control, energy efficiency, savings1. IntroductionElectric motor-driven systems (EMDS) are the largest electrical end users and account for 43–46% of all global electricity consumption [1]. In the United States, HVAC and refrigerationapplications consume 91% of motor-driven energy use in the residential sector and 93% in thecommercial sector [2]. Reducing unnecessary energy consumption is the most direct and 2015 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative CommonsAttribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution,and reproduction in any medium, provided the original work is properly cited.
168New Applications of Electric Driveseffective way to improve building energy efficiency. The increasing advancement of electronicand control technology greatly improves the performance of variable speed drives. Variablefrequency drives (VFDs) are being used in the HVAC industry more frequently and in moreapplications. They can modulate the motor speed very smoothly within a wide range. Reducedmotor speed provides a significant reduction in motor power.In general, a VFD can be used in a variety of applications where the load is variable, such asfans, pumps, and compressors. The energy savings for fans and pumps are about 30–50% overconventional speed applications, and up to 35% for compressors. In the following sections, theworking principle of the VFD is introduced and its applications on HVAC systems arepresented. Lastly, the current issues and concerns about VFDs are discussed with potentialsolutions provided.2. Principles2.1. VFDA VFD is an electrical device used to control the rotation speed of an alternating current (AC)electric motor by adjusting the frequency of the electrical power supplied to the motor. It isalso called pulse-width-modulated drive (PWM drive), adjustable-speed drive (ASD),adjustable-frequency drive (AFD), AC drive, inverter drive [3], or variable voltage variablefrequency (VVVF) drive.Most VFDs used in HVAC applications are inverters using sine-coded PWM technology. Asshown in Figure 1, a VFD works by converting the incoming AC power to DC power using adiode bridge rectifier, then passing the filtered, smoothed the voltage onto the invertingsection, and finally controlling voltage and frequency sent to the motor by high-speed bipolartransistors [4].Figure 1. Schematic diagram of a variable frequency drive [4]The output voltage is adjusted by changing the width and number of the voltage pulse asshown in Figure 2, whereas the output frequency is varied by changing the length of the cycle.
Variable Frequency Drive Applications in HVAC Systemshttp://dx.doi.org/10.5772/61782Figure 2. Sine-coded PWM waveform [4]A VFD can provide the follow benefits: Soft-start capability reduces the inrush current when motors start up, and thereby reducesthe mechanical stress on the motor and improves the motor reliability. Step-less regulation for motor speed electrically. Reduces the motor power consumption significantly with proper controls. Improves the power factor of the entire drive system including VFD and motors. Metering and monitoring system performances.These advantages boost the widespread utilization of VFDs in a variety of industrial processesincluding the HVAC field. Although equipping a VFD in a new system or existing systemincreases the initial investment, the reduced VFD cost combined with the increased energysavings derived from a VFD result in short payback period, which is usually less than threeyears.2.2. Variable speed fans and pumpsVariable speed fans and pumps are the fans and pumps equipped with VFDs. Since theirspeeds vary as the frequency of supply power changes, these pumps and fans are also calledvariable frequency fans and pumps. The operating characteristic of centrifugal fans and pumpsmakes them the excellent candidates for VFD applications. According to the fan and pumpaffinity laws, the fan or pump power has a cubic relationship with the motor speed. Therefore,significant power savings could be achieved by reducing the motor speeds with the propercontrols.The variables related to the fan or pump performance are impeller diameter D, rotation speedN, gas/water density ρ, volume flow rate Q, pressure P, power W, and mechanical efficiencyη. In a typical application, the fan or pump diameter is constant. The airflow or water flow,fan or pump head, and power solely relies on the speed. These relations are presented by thefollowing equations [3] (where equations (1) and (2) denote two working conditions):169
170New Applications of Electric DrivesQ1 N1 Q2 N 2P1 æ N1 ö ç P2 çè N 2 ø(1)2W1 æ N1 ö ç W2 çè N 2 ø(2)3(3)Equation (3) clearly indicates how the speed change affects the power change. For example,50% speed reduction results in 87.5% power reduction theoretically. There are several typesof air and water systems including the single-duct variable air volume (SDVAV) system, dualduct variable air volume (DDVAV) system, single-zone system, multi-zone system, primaryand/or secondary chilled water system, and the hot water system. Each type of system requiresspecific control strategy rather than a fixed low-speed operation without modulation.2.3. Variable speed compressorsVariable speed compressors or variable frequency compressors are compressors equippedwith VFDs. In the HVAC industry, there are several types of compressors associated with therefrigeration systems: reciprocating, screw, scroll, and centrifugal. All of them are viablecomponents for a VFD application. The commonly used working media includes air andrefrigerant. Air compressors are frequently used in industrial processes as a power source forpneumatic control systems. Refrigerant compressors are typically used in air conditioners,unitary air-handling units (AHU), or chillers in residential and commercial buildings. Signif‐icant progresses on the theoretical study and applications on variable speed compressors weremade during the past thirty years. As early as 1982, Itami et al. [5] conducted an experimentalstudy on the performance and reliability of a rotary compressor and reciprocating compressorcombined with frequency inverters. In 1996, Qureshi and Tassou [6] presented a review ofapplication of variable speed capacity control on refrigeration systems. It pointed out that VFDapplications on compressors were largely restricted to small-capacity air-conditioning unitsthus far, with only a small amount of applications to medium-range capacity units. Moreresearch work was still required. Since then, dramatic studies were conducted on applicationsof variable speed drives in HVAC systems [7–9].Unlike other types of compressors, centrifugal compressors have similar energy performanceas centrifugal fans and pumps. A scroll compressor is especially suitable for a VFD due to itsintrinsic structural design. Scroll compressors and reciprocating compressors are the mostcommonly used types on rooftop units (RTUs) and heat pumps (HPs) units. For the majority
VFD due to its intrinsic structural design. Scroll compressors and reciprocating compressorsare the most commonly used types on rooftop units (RTUs) and heat pumps (HPs) units. ForVariableFrequency DriveApplicationsin HVACSystems 171the majority of existing constant speed compressors,installinga VFDon thecompressorishttp://dx.doi.org/10.5772/61782the most feasible way. In recent years, some original equipment manufacturers (OEMs) ofcompressors,such asspeedEmersonand Danfoss,manufacturedvariablespeedof existing constantcompressors,installinghavea VFDalreadyon the compressoris the mostfeasiblecompressors.Severalsuch as Trane,McQuay,Lennox,way. In ipment manufacturers(OEMs)Carrier,of compressors,suchasEmersonandDanfoss,have alreadyvariable nufacturedequipping variablespeedcompressors.compressorsin theirHVAC manufacturers, such as Trane, Carrier, McQuay, Lennox, AAON, York, and Emerson,products,such as RTUs, HPs, computer room air‐conditioning (CRAC) units, or chillers.started equipping variable speed compressors in their new products, such as RTUs, HPs,computer room air-conditioning (CRAC) units, or chillers.Unlike fans and pumps, the scroll and reciprocating compressors usually do not have aUnlike fans and pumps, the scroll and reciprocating compressors usually do not have a cubicrelationship between power and frequency. Figure 3 shows an approximate linear relationshiprelationshipbetweenandforfrequencyfor witha 5‐tonRTUcompressor,with a scrollcompressor,basedbetween powerandpowerfrequencya 5-ton RTUa scrollbasedon the exper‐imentalstudy [10].studyThis relationshipdemonstratesthe compressorpoweron theexperimental[10]. This clearlyrelationshipclearlyhowdemonstrateshowthe changescompressorwith frequency. The linear correlation is also helpful to develop a new, simpler compressorpower changes with frequency. The linear correlation is also helpful to develop a new,model [11].cubic relationship between power and frequency. Figure 3 shows an approximate linearsimpler compressor model [11].5Wcomp (kW)43210203040506070Frequency (Hz)Figure 3 Relationship between compressor power and frequency for a 5‐ton RTUFigure 3. Relationship between compressor power and frequency for a 5-ton RTU3. VFD applications3.1. Air systems3.1.1. Single-zone Variable Air Volume (VAV) systemSingle-zone VAV system is the simplest air system. The VAV system mainly includes outdoorair and return air dampers, filter, heating and cooling coils, and a supply fan. Some units mayalso have a preheat coil, bypass damper, and return fan. Figure 4 presents a typical single-zoneVAV system.
172New Applications of Electric Drivesunits may also have a preheat coil, bypass damper, and return fan. Figure 4 presents atypical single‐zone VAV system.Figure 4 Typical single‐zone VAV systemFigure 4. Typical single-zone VAV systemTypically, a single‐zone air‐handling unit is operated to control the temperature of only oneTypically, a single-zone air-handling unit is operated to control the temperature of only onespace. The conventional method is to integrate the cooling and heating valve to control thespace. The conventional method is to integrate the cooling and heating valve to control thespace cooling and heating temperature set point. For a VFD‐equipped supply fan, the fanspace cooling and heating temperature set point. For a VFD-equipped supply fan, the fan speedspeed can be modulated to maintain the space temperature set point, whereas the coolingcan be modulated to maintain the space temperature set point, whereas the cooling and heatingand heating coil valves are used to control the supply air temperature (SAT).coil valves are used to control the supply air temperature (SAT).Since the 2010 edition of ASHRAE Standard 90.1 [12], some requirements were added forSince the 2010 edition of ASHRAE Standard 90.1 [12], some requirements were added forsingle‐zone VAV system control. It required that single‐zone AHU and fan coil units withsingle-zone VAV system control. It required that single-zone AHU and fan coil units withchilled water cooling coil and supply fan with motor greater than 5 hp shall have supplychilled water cooling coil and supply fan with motor greater than 5 hp shall have supply fansfans controlled by two‐speed motors or VFD. Similarly, all the AHUs and AC units withcontrolled by two-speed motors or VFD. Similarly, all the AHUs and AC units with directdirect‐expansion (DX) cooling coil and a capacity 110,000 Btu/h that serve single zones shallexpansion (DX) cooling coil and a capacity 110,000 Btu/h that serve single zones shall havehave their supply fans controlled by the two‐speed motor or VFD. These requirements aretheir supply fans controlled by the two-speed motor or VFD. These requirements are manda‐mandatory.tory.There are many successful case studies on VFD applications for single‐zone units in projects.There aremany successful case studies on VFD applications for single-zone units in projects.et al. [13] applied the VFD technology to a dozen single‐zone systems by installing a VFDLi et al.Li[13]applied the VFD technology to a dozen single-zone systems by installing a VFDof them. They demonstrated that installing VFDs on supply fans in a series ofon eachonofeachthem.They demonstrated that installing VFDs on supply fans in a series of singlesingle‐zone units can save much more energy than running half of the units at constantzone units can save much more energy than running half of the units at constant speeds andspeeds and shutting off the remaining half.shuttingoff the remaining half.3.1.2. Single‐DuctVAV System3.1.2. Single-ductVAV systemThe single-duct VAV system is the most popular system, which comprises a main AHU,ductwork and a number of terminal boxes. The air-handling units are comprised of an outdoorair damper and return air damper, filter, preheating coil, cooling coil, and safety devices. Figure5 shows a typical SDVAV system.In a single-duct VAV system, VFDs are installed on the supply fan and return fan. Typically,the supply fan speed is modulated to maintain the duct static pressure at its set point. As thesystem load is reduced, the VFD speed decreases to maintain the same set point. Meanwhile,the set point need not be kept at a constant value. With the system load reduced, less airflowis needed to deliver to the space. The static pressure set point could be reset to meet thecondition. This set point can be reset based on the VFD speed or supply fan airflow [14].
Variable Frequency Drive Applications in HVAC Systemshttp://dx.doi.org/10.5772/61782Figure 5 Typical single‐duct VAV systemFigure 5. Typical single-duct VAV systemIn a single‐duct VAV system, VFDs are installed on the supply fan and return fan. Typically,For the returnfan,fanthereseveral controlmethods:modulatingreturnfanthespeed tothe supplyspeedareis modulatedto maintainthe duct staticpressure attheits setpoint. Asmaintain (a)returnstatic pressure(b) buildingHowever,thesesystemloadductis reduced,the VFD orspeeddecreases differentialto maintain pressure.the same setpoint.Meanwhile,the setpointneednot be keptat a constant Avalue.the systemloadcontrols arenot reliabledueto thepressuremeasurement.newWithcontrolmethodis using areduced, methodless airflowneeded to deliverto the space.The staticpressure theset pointcouldandbe returnvolume trackingtoismaintainthe airflowdifferencebetweensupplyreset to meet the condition. This set point can be reset based on the VFD speed or supply fanfans.airflow [14].3.1.3. Dual-duct VAV systemFor the return fan, there are several control methods: modulating the return fan speed tomaintain (a) return duct static pressure or (b) building differential pressure. However, theseA dual-duct variable air volume (DDVAV) system handles hot and cold air separately andcontrols are not reliable due to the pressure measurement. A new control method is using adelivers them through hot and cold ductwork. The hot air and cold air are mixed at the terminalvolume tracking method to maintain the airflow difference between the supply and returnbox and then supplied to the space. There are two types of DD system: the single-fan dualfans.duct system and the dual-fan dual-duct system. The first one has a supply fan delivering theairflow to both hot and cold decks. The second one has a dedicated supply fan in each deck.3.1.3. Dual‐Duct VAV SystemThe cold deck includes a cooling coil, whereas the hot deck is equipped with a hot water orsteam coil.AFigure6 showsschematicdiagramofhandlesa single-fansystem. anddual‐ductvariabletheair volume(DDVAV)systemhot andDDVAVcold air separatelydelivers them through hot and cold ductwork. The hot air and cold air are mixed at theterminal box and then supplied to the space. There are two types of DD system: the single‐fan dual‐duct system and the dual‐fan dual‐duct system. The first one has a supply fandelivering the airflow to both hot and cold decks. The second one has a dedicated supplyfan in each deck. The cold deck includes cooling coil, whereas the hot deck is equipped witha hot water or steam coil. Figure 6 shows the schematic diagram of a single‐fan DDVAVsystem.Figure 6. Single-fan DDVAV system schematic diagramFigure 6 Single‐fan DDVAV system schematic diagramIn a single‐fan dual‐duct VAV system, a VFD is installed on the supply fan. For a dual‐fandual‐duct VAV system with separate supply fans for the hot and cold deck, a VFD isinstalled on each fan. If there is return fan in this system as well, a VFD is also equipped onreturn fan.Typically, for a single‐fan dual‐duct system, the supply fan is modulated to maintain the173
174New Applications of Electric DrivesIn a single-fan dual-duct VAV system, a VFD is installed on the supply fan. For a dual-fandual-duct VAV system with separate supply fans for the hot and cold deck, a VFD is installedon each fan. If there is a return fan in this system as well, a VFD is also equipped on the returnTypically, for a single‐fan dual‐duct system, the supply fan is modulated to maintain thefan.cold deck static pressure, whereas the hot deck main damper is modulated to maintain theTypically, for a single-fan dual-duct system, the supply fan is modulated to maintain the coldhot deck static pressure set point. For a dual‐fan dual‐duct system, each supply fan speed isdeck static pressure, whereas the hot deck main damper is modulated to maintain the hot deckmodulated to maintain its own static pressure set point. Similarly, with single‐duct VAVstatic pressure set point. For a dual-fan dual-duct system, each supply fan speed is modulatedsystem, the return fan speed is modulated to maintain the airflow difference between theto maintain its own static pressure set point. Similarly, with single-duct VAV system, the returnreturn fans.fansupplyspeedandis modulatedto maintain the airflow difference between the supply and return fans.Theenergyare ual‐duct VAVVAV systemsystem arecontrolandductClaridge peraturetemperature reset.reset. LiuLiu andand deckresetschedules,maximum potential energy savings by optimizing the hot deck and cold deck resetwhere75% in potential savings can be expected.schedules, where 75% in potential savings can be expected.3.1.4. Multi-zone system3.1.4. Multi‐Zone SystemA multi-zone system serves multiple zones with each zone having its own thermal require‐A multi‐zonesystemsystem,serves onemultiplezones systemwith eachzoneandhavingits ownthermalthement.Like a dual-ductmulti-zonehas coldhot decks.However,requirement.dual‐ductone multi‐zonehas coldunitandbeforehot deliverydecks.differenceis thatLikethe coldair andsystem,hot air mixesat the outletsystemof air-handlingdifferenceis that the systemcold airtheandhothotairairandmixesthe outletair‐handlingto However,the space,thewhereasin a dual-ductcoldatmixesat ofatypicalmulti-zonesystemwhereaVFDisinstalledunit before delivery to the space, whereas in a dual‐duct system the hot air and cold mixesonatthefan.thesupplyterminalboxes. Figure 7 shows the schematic diagram of a typical multi‐zone systemwhere a VFD is installed on the supply fan.Figure 7 Multi‐zone VAV system (three zones)Figure 7. Multi-zone VAV system (three zones)
Variable Frequency Drive Applications in HVAC Systemshttp://dx.doi.org/10.5772/61782In a multi-zone system, the supply fan speed is modulated to maintain the discharge air staticpressure or the temperature in the worst zone at its set point. The zone damper is modulatedto maintain each zone temperature set point.3.1.5. Exhaust air systemAn exhaust air system is often associated with one air-handling unit, make-up unit, or freshair unit. An exhaust air system is applicable for several types of facilities, such as kitchens,cafeterias, and laboratories in the hospital, just to list a few. They require enough fresh air andassociated exhaust air. Proper exhaust airflow should be provided to satisfy the building orspace pressure requirement. As the airflow delivered by air-handling unit is variable, theexhaust airflow is adjustable accordingly. Figure 8 shows an exhaust air system where a VFDis installed onthe exhaust fan.variable, the exhaust airflow is adjustable accordingly. Figure 8 shows an exhaust air systemwhere the VFD is installed on the exhaust fan.In this exhaust air system, the VFD is modulated to maintain the suction air pressure set point,or the differentialbetweentheVFDsupplyand exhaustair theto maintainthe requiredbuildingIn this airflowexhaust airsystem, theis modulatedto maintainsuction air pressuresetpressure. point, or the differential airflow between the supply and exhaust air to maintain therequired building pressure.Figure 8. Exhaust air systemFigure 8 Exhaust air system3.2. Water Systems3.2. Water systemsThe major water systems in HVAC system include chilled water system, condenser waterThe major waterin system.HVACEachsystemchilledsystem,condenser watersystem,systemsand hot watersystem includehas dedicatedpumpswatercirculatingwater throughclosedor ansystem.open loop.EachVFDssystemcan be installedon these systems,whichcould reducethesystem, and ahotwaterhas dedicatedpumpscirculatingwaterthrough apartialload conditions.closed or an pumpopenenergyloop.consumptionVFDs canatbeinstalledon these systems, which could reduce the pumpenergy consumption at partial load conditions.3.2.1. Chilled Water System and Condenser Water System3.2.1. Chilled Chilledwater systemand condenserwatersystemwater systemand condenserwatersystemare two independent systems in thechiller plant. Figure 9 shows a typical chiller plant comprising these two loops. A chilledChilled dentwatersystemandincludesone or morechillers,chilledwaterand coolingsystemscoils. Thein the chillercoilsa areusuallylocatedplantin thecomprisingAHUs or fan thesecoil units.are Atwotypes ofplant. Figurecooling9 showstypicalchillertwoThereloops.chilledwater em.a primaryincludes onepumpingor morechillers,chilledsystemwaterandpumps,and coolingcoils.In Thecooling coils aresystem, the chilled water pump circulates the chilled water through the evaporator ofusually locatedin the AHUs or fan coil units. There are two types of pumping system: primary-175
176New Applications of Electric Drivesonly system and primary–secondary system. In a primary-only system, the chilled water pumpcirculates the chilled water through the evaporator of chillers and cooling coils. In a primary–secondary system, there are two loops. The primary pumps circulate chilled water throughthe chiller only, while the secondary pumps circulate the chilled water through buildings.Usually, there is one bypass pipe, which connects the primary and secondary water loops.Many investigations and case studies were conducted on the efficiency, reliability, andoptimization of primary–secondary or primary-only chilled water systems [16–18]. WhenVFDs are installed on chilled water pumps, how to operate pumps under the maximumefficiency point for single or multiple pumps are one of the study topics.In a chilled water system, as seen in Figure 9, the cooling load of each coil varies at mps area chilledwatersystem,as requiredseen in Figure9, thewatercoolingflowload variable.of each coilThevariesat differentmodulatedto maintainthe es andtimes, makingrequiredchilled pressurewater flowwhilevariable.The primary pumpsareminimumwatertoflowrequirementfor chillers.The secondarymaintainingpump speedsare equal to themodulatedmaintainthe loop deltaT while simultaneouslythe minimumprimarypumpAs thebuildingcoolingloadreduces,the requiredchilled thewater flowwaterflow speeds.requirementfor chillers.Thesecondarypumpsare modulatedto maintaindecreases.Reduced pumpflowresultsin greatpumppower savings.loop differentialpressure.As thebuildingcoolingload reduces,the required chilled waterflow decreases.Reducedpumptheflowresults in greatpumppowercirculatessavings. the condensing waterIn a condensingwatersystem,condensingwaterpumpthrough the condenser of chillers and cooling tower. When a VFD is installed on the condensingIn a condensing water system, the condensing water pump circulates the condensing waterwater pump, the pump speed is adjusted to maintain the loop differential pressure (ΔP) orthrough the condenser of chillers and cooling tower. When a VFD is installed on thetemperaturedifference (ΔT).condensing water pump, the pump speed is adjusted to maintain the loop differentialpressure (ΔP) or temperature difference (ΔT).Figure 9 Chilled water and condenser water systemFigure 9. Chilled water and condenser water systemFurthermore, the VFDs could be installed on the fans of cooling tower. The fan speed isoptimizedtheto maintainthe condensingwater leavingfrom thetower.coolingThetower.Furthermore,VFDs couldbe installedon thetemperaturefans of coolingfan speed isoptimized to maintain the condensing water leaving temperature from the cooling tower.3.2.2. Hot Water SystemThe hot water system delivers the hot water from boilers or heat exchangers to the heatingcoils of air‐handling units or terminal boxes inside the building. In traditional operation, the
Variable Frequency Drive Applications in HVAC Systemshttp://dx.doi.org/10.5772/617823.2.2. Hot water systemThe hot water system delivers the hot water from boilers or heat exchangers to the heatingcoils of air-handling units or terminal boxes inside the building. In traditional operation, thewater pumps are running at full speed. The heating valves at the end users are modulated tocontrol the airside temperature set point. Figure 10 shows a hot water system with VFDinstalled on both primary and secondary pumps. After installing of VFDs, the speed ofsecondary pump is often modulated to maintain the supply and return temperature differenceor loop differential pressure. The speed of primary pump can track that of secondary pumpand should be high enough to ensure sufficient water going through boilers.Figure 10. Hot water systemFigure 10 Hot water system3.3. Air Compressors3.3. Air compressorsCompressed air has many applications in the manufacturing process. In the HVACCompressedair airhascompressorsmany applicationsmanufacturingprocess.In thetheHVACindustry,industry,can be usedintothegeneratethe pressurizedair to drivepneumaticair compressorscandampersbe usedandto generatethe pressurizeddrive the pneumaticactuators forvalves in air‐handlingunits.airThetocompressedair is stored actuatorsin afor dampersand valvesin air-handlingunits.Theis stored inpressurizedpressurizedtank, whichserves as an airsourceto compressedthe end users. airTraditionally,theapressuretank, whichservesas an airto theendofusers.the pressureof 11tank isof tankis maintainedby sourcethe on–offcontrolone or Traditionally,multiple air compressors.Figuremaintainedthe on–offcontrolof ofor multipleair compressors.Figure on11eachshows ashowsbya schematicdiagraman oneair compressorsystemwith a VFD installedschematicdiagram of an air compressor system with a VFD installed on each rolis usedto maintainthe compressedairairpressure.Typically,controlis usedto maintainthe compressedpressure.WhenWhenthetheendend usersrequire usersless anthesetpoint,require less compressed air and the compressed air pressure is higher than the set thecompressorwillshut off. Onmore onecompressorstarts whenthe endpoint, the compressorwilltheshutcontrary,off. On theonecontrary,more compressorstarts whenthe userutilizes psdownbelowthesetuser utilizes more compressed air and the compressed air pressure drops down belowpoint.This t–stops,which definitelythe set point.inefficientcontrolcauses frequentcompressorstart–stops,shortenswhich thelifetimedefinitelyof the ronthecompressorsshortens the lifeti
3.1.1. Single-zone Variable Air Volume (VAV) system Single-zone VAV system is the simplest air system. The VAV system mainly includes outdoor air and return air dampers, filter, heating and cooling coils, and a supply fan. Some units may also have a preheat coil, bypass damper, and return fan. Figure 4 pr
EV2 inverter drive to a variable speed compressor in a safe and reliable manner. The EV2 inverter drive will be referred to throughout this document as the inverter drive or simply the drive. Product Description The inverter drive has been developed specificallyfor the variable speed compressor. The drive will power
H-Max Series Variable Frequency Drive H-Max Series Variable Frequency Drive MN04008005E—May 2017 www.eaton.com i Disclaimer of Warranties and Limitation of Liability The information, recommendations, descriptions, and safety notations in this document are based on Eaton Corporation's ("Eaton") experience and judgment, and may not cover all
Variable Frequency Drive Troubleshooting Tutorial Figure 2: Variable Frequency Drive Welcome to the VFD Troubleshooting Tutorial. This guide will help you step through the processes of troubleshooting a VFD. Please note, every VFD will be different; different housings, components, locations, terminals, specifications, etc so your VFD may not
The VFD68 Drive is intended for use with variable speed motors that are rated for 40:1 operation. Note: If three-phase power is not available as supply power for the VFD68 Drive, refer to the VFD68 Variable Frequency Drive Technical Bulletin (Part No. 24-7664-3051). Selecting a VFD68 Drive for Controlling Multiple Motors
The Baker Hughes Electrospeed Advantage variable speed drive (VSD) is classified as a variable voltage inverter (VVI). It uses a six-pulse silicon controlled rectifier (SCR) front end to convert incoming AC power into variable voltage DC power. This DC power is inverted to variable voltage variable fr
Variable Frequency Drives Presented by: Greg Stark, P.E. September 10, 2014 Sponsored by: Variable Frequency Drives (VFD’s) Popular speed control devices used in industrial, commercial and residential applications. –Huge energy savings potential operating centrifugal fans, pumps and compressors Vary frequency of electrical
Unit A: Scientific Method 1. Define the following terms: Variable: a variable is any factor that can be controlled, changed, or measured in an experiment. Dependent Variable: The dependent variable is the variable that you measure or observe. Independent Variable: The independent variable is the one condition that you change in an
qualifies for the variable speed. We will check the suitability in the following sections. Note: The terms variable speed drive (VSD) and variable frequency drive (VFD) have been used interchangeably through out the text in this paper. Torque, Speed and Horsepower A drive controls two main elements of induction motor: "Speed" and "Torque".
