NEW TECHNOLOGYNEW TECHNOLOGY

The Turbocor TT300compressor won an

Energy InnovationAward at the 2003

AHR Expo in Chicago for its

new technology.Here’s an inside view

of how the compressorwas designed and

how it works

The Turbocor TT300compressor won an

Energy InnovationAward at the 2003

AHR Expo in Chicago for its

new technology.Here’s an inside view

of how the compressorwas designed and

how it works

B Y R O N C O N R Y

The Turbocor TT300 compressor was designedfrom scratch and was not limited by traditionalconcepts, manufacturing infrastructures, tech-nologies or ideologies. As all the key technologies

were developed without any preconceived limitations, tra-ditional development methods were not followed and astrong in-house engineering development team wasassembled to develop all aspects of the compressor.

The end product is a compact, efficient, oil-free, high-speed, infinitely variable-capacity centrifugal compressordesigned to operate with R-134a refrigerant. The firstgeneration compressor is designed for rooftop units andair-, water- and evaporative-cooled chillers with a capacityranging from 60 tons to 400 tons.

The compressor was designed to be fully integratedboth mechanically and electrically and is unlike any otherin the market. It is, however, designed from a range ofproven and existing technologies.

Because of the compressor’s smooth and quiet opera-tion, noise is not an issue. The compressor operates atless than 70dBa at 3 meters when fully loaded and canoperate at less than 50dBa when operating in a low-loadsituation. The compressor emits virtually no vibrationdue to the electronic dynamic-balancing feature.

The magnetic bearing systemMagnetic bearings have been used in specialized applica-tions in aerospace and large industrial machinery and haveto date been limited to high-end applications where costwas not a consideration. The technology has proven overthe years to be a highly reliable concept and has been usedin applications where energy efficiency is an issue or whereconventional lubricants are not desirable.

With magnetic bearings, there is no mechanical fric-tion as the rotating shaft is suspended in a magnetic field,and its static position and dynamic vibration are con-trolled electronically. Typically, these bearing systemshave been extremely expensive to develop and manufac-ture and have not been used in mass-produced products.

As part of the overall product development, theTurbocor engineering team has developed its own mag-netic bearing system for the TT300 compressor. A typicalbearing-control system is housed in separate electronicenclosures and is large and expensive. In this case, thesystem has been miniaturized and is housed within thecompressor itself, thus increasing reliability while greatlyreducing costs.

The bearing system consists of a five-axis active con-trol and permanent-magnet-biased design where the bear-ing uses permanent magnets to do the primary work anddigitally controlled electro-magnets are used as a second-ary trim system. The shaft’s position is sensed and isrepositioned six million times every minute.

Each radial bearing operates with four separate mag-netic coils that are controlled with a digitally controlled,pulse-width modulation (PWM). The digital control

responds to separate signals sent to it from built-in prox-imity sensors that are sensitive to shaft movement of lessthan 0.00005 inches.

As the shaft moves from the center point, varyingstrength magnetic fields are applied to the shaft to bringit back into its required position. Typically, maximumrun-out of the shaft is confined to less than 0.0005 inches.

The axial position of the shaft is similarly controlled.However, the shaft’s position is controlled from the impellerend of the compressor, while the magnetic actuators applythe appropriate force to the opposite end of the shaft.

The software has been designed to automaticallycompensate for any out-of-balance the compressor

Compressor specificationsCompressor type Two-stage centrifugalCapacity range 60-400 tons

Capacity control guide Variable speed and inlet vanes control

Inlet guide vanes Built-in

Refrigerant R-134a model currently available, R-22 model available 4th quarter 2003

Lubrication system Oil free

Bearing type Permanent magnet biased, active control magnet

Motor type Permanent magnetsynchronous

Operating speed range 18,000-48,000 rpm

Drive type DirectTransmission NoneDischarge non-return valve IncludedSpeed control Built-inBearing control Built-inElectronic dynamic balancing Built-inPower failure soft touchdown Built-inCompressor control Built-inSoft-starter Built-inPressure transducers Built-inMotor cooling RefrigerantElectronics cooling RefrigerantElectronic expansion valve control Built-inStarting gear Not requiredChiller control Not requiredWeight 265 poundsPower factor correction coil Required

The Turbocor TT300’s benefits include its oil-free operationwith R-134a.

may experience.In the case of a power outage, the bearings’ power is

fed from onboard capacitors that are primarily used tosmooth out voltage ripple on the DC link to the motordrive. Within a millisecond of the compressor losing itspower, the motor switches into generator mode. Power isfed back into the DC bus supplying the necessary powerto levitate the bearings and feed the various control sys-tems on the compressor.

Auxiliary touchdown bearings also are included in thecompressor’s design to protect the compressor in the caseof a catastrophic failure, such as a printed circuit boardor actuator failure.

The magnetic bearings are extremely efficient and use180 watts of energy compared to 10,000 watts if a con-ventional lubrication system had been used. Additionalenergy savings are made by the eradication of oil fromthe heat exchange surfaces and the elimination of costlyoil recovery systems that are used in conventional refrig-eration installations.

The motor and variable-speed driveVariable-speed drives (VSD) are commonly used in allareas of hvac installations and are well proven in theirability to cut energy costs. Typically, as in the case withmagnetic bearings, these systems are separately housed inelectrical enclosures and are expensive to purchase. TheTurbocor engineering team has developed its own inverter

speed control and has fully inte-grated it into the compressor’shousing.

The compressor’s variable-speed drive system consists of arectifier to convert the incomingmain power (380V-460V, 50/60Hz) to a DC current, a DC busconsisting of four capacitorsallowing for the smoothing ofvoltage ripple, an insulated gatebipolar transistor (IGBT) inverterto switch the DC current into avariable-frequency supply for themotor and a soft starter thatreduces the inrush current to atrickle (the compressor has astarting current of less than 5 amps).

The Turbocor engineering team and the CommonwealthScientific Industrial Research Organization of Australia(CSIRO) designed the permanent magnet synchronousmotor used in the compressor. Operating at speeds of up to48,000 rpm, the 160 hp motor is the same physical size asa 1-hp, four-pole induction motor and is refrigerant-cooled.

Being variable-speed, the motor allows for maximumefficiency gains as the system load decreases. Chillers usingthis technology are experiencing a coefficent of perform-ance (COP) over 5.6 (energy-efficiency ratio of 0.63 kw/tr)

Operating at speeds ofup to 48,000 rpm, the160-hp motor is the samephysical size as a 1-hp,four-pole induction motorand is refrigerant-cooled.

The Turbocor engineering team has developed its own magnetic bearing system for the TT300 compressor. The system hasbeen miniaturized and is housed within the compressor itself, thus increasing reliability while also reducing costs.

at full load in water-cooled applications, with integratedpower load value of 9.38 (EER 0.375).

The motor’s cooling circuit is integrated into the com-pressor’s design and also is used to cool the key electroniccomponents.

The aerodynamics and R-134a selectionThe two-stage fluid dynamics were developed in conjunc-tion with Concepts ETI in Vermont. This concept uses twoopen shrouded impellers and is designed to operate bothwith and without an economizer system.

During the design process, many new refrigerants wereinvestigated, but the first gas that the engineering teamselected proved to be the right one for this technology andmarket segment. R-134a has been universally adopted inthe automotive industry as the replacement for R-12 andnow is the most commonly used refrigerant in the worldand, therefore, is readily available. Using R-134a in a cen-trifugal system eliminates the need for a costly and com-plicated purge system required in R-123 machines.

As the gasenters the com-pressor, it passesthrough a set ofpre-swirl inletguide vanes (IGV)that typicallyremain open formost of the com-pressor’s operatinglife. The vanes startto close off and areappropriately adjusted to balance the system when thecompressor starts to approach a surge condition. The gasthen is directed into two investment cast impellers thatpump the gas through the system.

Between the first- and second-stage impellers is a side-stream inlet port that allows the system to use an econo-mizer circuit if required. From there, the gas passesthrough a purpose-built discharge service/non-return

The schematic shows how thecompressor’s control system hasbeen broken into two segments:the high-voltage/high-power sec-tion and the low-voltage/control/service section. The high-voltagesection is situated on top of thecompressor and houses the powerelectronics required to drive themotor, and the isolated high-volt-age DC/DC power supply for mag-netic bearings and low-voltagesystem control functions. The low-voltage section is situated onthe side of the compressor andincludes the bearing/motor control,the compressor control and thelow-voltage DC/DC power supply.

The compressor’s first-stage impelleris shown.

valve. When the compressor shuts down or is not operat-ing (when installed in parallel with other compressors),the non-return valve closes off to prevent the gas fromfeeding back through the turbine wheels causing a shortcircuit in the gas flow and eliminating shaft reversal.

The electronics integrationThe TT300 is the world’s first fully integrated centrifugalcompressor system and can be classed as an electronicmachine. It has been designed with fully integrated powerelectronics, an insulated gate bipolar transistor inverter(IGBT), IGBT control, bearing and motor control, com-pressor control, soft starter, control power supply, PWMamplifier, smoothing capacitors, multiple electronicexpansion valve control, motor and electronics coolingcontrol, inlet guide vane (IGV) control and pressuretransducers.

The electronics have been designed to be service friend-ly and were designed using a plug-and-play concept forease of service and troubleshooting.

The engineering-grade PVC covers have a sputteredmetal coating to eliminate any electro-magnetic interfer-ence. The compressor’s capacity and efficiency are main-tained with either 50Hz or 60Hz power.

The cooling system allows the electronics to operateat the optimal conditions, thus increasing componentlife and reliability.

The control system has been broken into two seg-ments: the high-voltage/high-power section and the low-voltage/control/service section. The high-voltage section issituated on top of the compressor and houses the powerelectronics required to drive the motor, and the isolatedhigh-voltage DC/DC power supply for magnetic bearingsand low-voltage system control functions. The low-voltagesection is situated on the side of the compressor andincludes the bearing/motor control, the compressor con-trol and the low-voltage DC/DC power supply.

Miniaturization has been a key part of the electronicsdevelopment work and this has allowed elimination ofmany components, wiring and PCBs.

The software was developed in-house and wasdesigned to minimize manufacturing costs while increas-ing overall compressor reliability and system efficiency.◆

Ron Conry is the executive vice president of technologydevelopment at Turbocor. For more information, call514-421-0523 or visit turbocor.com.

The TT300 is the world’s first fullyintegrated centrifugal compressor

system and can be classed asan electronic machine