NEW TECHNOLOGY The Turbocor T T300 compressor won an Energy Innovation Award at the 2003 AHR Expo in Chicago for its new technology. Here’s an inside view of how the compressor was designed and how it works BY RON CONRY he Turbocor TT300 compressor was designed T from scratch and was not limited by traditional concepts, 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 a Compressor type Capacity range Compressor specifications Two-stage centrifugal 60-400 tons Variable speed and strong in-house engineering development team was Capacity control guide inlet vanes control assembled to develop all aspects of the compressor. Inlet guide vanes Built-in The end product is a compact, efficient, oil-free, high- speed, infinitely variable-capacity centrifugal compressor R-134a model currently Refrigerant available, R-22 model designed to operate with R-134a refrigerant. The first generation compressor is designed for rooftop units and available 4th quarter 2003 air-, water- and evaporative-cooled chillers with a capacity Lubrication system Oil free ranging from 60 tons to 400 tons. Permanent magnet biased, The compressor was designed to be fully integrated Bearing type active control magnet both mechanically and electrically and is unlike any other in the market. It is, however, designed from a range of Permanent magnet Motor type synchronous proven and existing technologies. Because of the compressor’s smooth and quiet opera- Operating speed range 18,000-48,000 rpm tion, noise is not an issue. The compressor operates at Drive type Direct less than 70dBa at 3 meters when fully loaded and can Transmission None operate at less than 50dBa when operating in a low-load situation. The compressor emits virtually no vibration Discharge non-return valve Included due to the electronic dynamic-balancing feature. Speed control Built-in Bearing control Built-in The magnetic bearing system Electronic dynamic balancing Built-in Magnetic bearings have been used in specialized applica- Power failure soft touchdown Built-in tions in aerospace and large industrial machinery and have to date been limited to high-end applications where cost Compressor control Built-in was not a consideration. The technology has proven over Soft-starter Built-in the years to be a highly reliable concept and has been used Pressure transducers Built-in in applications where energy efficiency is an issue or where Motor cooling Refrigerant conventional lubricants are not desirable. Electronics cooling Refrigerant With magnetic bearings, there is no mechanical fric- Electronic expansion valve control Built-in tion as the rotating shaft is suspended in a magnetic field, and its static position and dynamic vibration are con- Starting gear Not required trolled electronically. Typically, these bearing systems Chiller control Not required have been extremely expensive to develop and manufac- Weight 265 pounds ture and have not been used in mass-produced products. Power factor correction coil Required As part of the overall product development, the Turbocor engineering team has developed its own mag- The Turbocor TT300’s benefits include its oil-free operation with R-134a. netic bearing system for the TT300 compressor. A typical bearing-control system is housed in separate electronic enclosures and is large and expensive. In this case, the responds to separate signals sent to it from built-in prox- system has been miniaturized and is housed within the imity sensors that are sensitive to shaft movement of less compressor itself, thus increasing reliability while greatly than 0.00005 inches. reducing costs. As the shaft moves from the center point, varying The bearing system consists of a five-axis active con- strength magnetic fields are applied to the shaft to bring trol and permanent-magnet-biased design where the bear- it back into its required position. Typically, maximum ing uses permanent magnets to do the primary work and run-out of the shaft is confined to less than 0.0005 inches. digitally controlled electro-magnets are used as a second- The axial position of the shaft is similarly controlled. ary trim system. The shaft’s position is sensed and is However, the shaft’s position is controlled from the impeller repositioned six million times every minute. end of the compressor, while the magnetic actuators apply Each radial bearing operates with four separate mag- the appropriate force to the opposite end of the shaft. netic coils that are controlled with a digitally controlled, The software has been designed to automatically pulse-width modulation (PWM). The digital control compensate for any out-of-balance the compressor The Turbocor engineering team has developed its own magnetic bearing system for the TT300 compressor. The system has been miniaturized and is housed within the compressor itself, thus increasing reliability while also reducing costs. may experience. speed control and has fully inte- In the case of a power outage, the bearings’ power is grated it into the compressor’s fed from onboard capacitors that are primarily used to housing. smooth out voltage ripple on the DC link to the motor The compressor’s variable- drive. Within a millisecond of the compressor losing its speed drive system consists of a power, the motor switches into generator mode. Power is rectifier to convert the incoming fed back into the DC bus supplying the necessary power main power (380V-460V, 50/60 to levitate the bearings and feed the various control sys- Hz) to a DC current, a DC bus tems on the compressor. consisting of four capacitors Auxiliary touchdown bearings also are included in the allowing for the smoothing of compressor’s design to protect the compressor in the case voltage ripple, an insulated gate of a catastrophic failure, such as a printed circuit board bipolar transistor (IGBT) inverter Operating at speeds of or actuator failure. to switch the DC current into a up to 48,000 rpm, the The magnetic bearings are extremely efficient and use variable-frequency supply for the 160-hp motor is the same 180 watts of energy compared to 10,000 watts if a con- motor and a soft starter that physical size as a 1-hp, ventional lubrication system had been used. Additional reduces the inrush current to a four-pole induction motor and is refrigerant-cooled. energy savings are made by the eradication of oil from trickle (the compressor has a the heat exchange surfaces and the elimination of costly starting current of less than 5 amps). oil recovery systems that are used in conventional refrig- The Turbocor engineering team and the Commonwealth eration installations. Scientific Industrial Research Organization of Australia (CSIRO) designed the permanent magnet synchronous The motor and variable-speed drive motor used in the compressor. Operating at speeds of up to Variable-speed drives (VSD) are commonly used in all 48,000 rpm, the 160 hp motor is the same physical size as areas of hvac installations and are well proven in their a 1-hp, four-pole induction motor and is refrigerant-cooled. ability to cut energy costs. Typically, as in the case with Being variable-speed, the motor allows for maximum magnetic bearings, these systems are separately housed in efficiency gains as the system load decreases. Chillers using electrical enclosures and are expensive to purchase. The this technology are experiencing a coefficent of perform- Turbocor engineering team has developed its own inverter ance (COP) over 5.6 (energy-efficiency ratio of 0.63 kw/tr) The schematic shows how the compressor’s control system has been broken into two segments: the high-voltage/high-power sec- tion and the low-voltage/control/ service section. The high-voltage section is situated on top of the compressor and houses the power electronics required to drive the motor, and the isolated high-volt- age DC/DC power supply for mag- netic bearings and low-voltage system control functions. The low- voltage section is situated on the side of the compressor and includes the bearing/motor control, the compressor control and the low-voltage DC/DC power supply. at full load in water-cooled applications, with integrated As the gas power load value of 9.38 (EER 0.375). enters the com- The motor’s cooling circuit is integrated into the com- pressor, it passes pressor’s design and also is used to cool the key electronic through a set of components. pre-swirl inlet guide vanes (IGV) The aerodynamics and R-134a selection that typically The two-stage fluid dynamics were developed in conjunc- remain open for tion with Concepts ETI in Vermont. This concept uses two most of the com- open shrouded impellers and is designed to operate both pressor’s operating The compressor’s first-stage impeller with and without an economizer system. life. The vanes start is shown. During the design process, many new refrigerants were to close off and are investigated, but the first gas that the engineering team appropriately adjusted to balance the system when the selected proved to be the right one for this technology and compressor starts to approach a surge condition. The gas market segment. R-134a has been universally adopted in then is directed into two investment cast impellers that the automotive industry as the replacement for R-12 and pump the gas through the system. now is the most commonly used refrigerant in the world Between the first- and second-stage impellers is a side- and, therefore, is readily available. Using R-134a in a cen- stream inlet port that allows the system to use an econo- trifugal system eliminates the need for a costly and com- mizer circuit if required. From there, the gas passes plicated purge system required in R-123 machines. through a purpose-built discharge service/non-return 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 from feeding back through the turbine wheels causing a short circuit in the gas flow and eliminating shaft reversal. The electronics integration The TT300 is the world’s first fully integrated centrifugal compressor system and can be classed as an electronic machine. It has been designed with fully integrated power electronics, an insulated gate bipolar transistor inverter (IGBT), IGBT control, bearing and motor control, com- pressor control, soft starter, control power supply, PWM amplifier, smoothing capacitors, multiple electronic expansion valve control, motor and electronics cooling control, inlet guide vane (IGV) control and pressure transducers. The electronics have been designed to be service friend- ly and were designed using a plug-and-play concept for ease of service and troubleshooting. The TT300 is the world’s first fully integrated centrifugal compressor system and can be classed as an electronic machine The engineering-grade PVC covers have a sputtered metal 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 operate at the optimal conditions, thus increasing component life and reliability. Miniaturization has been a key part of the electronics The control system has been broken into two seg- development work and this has allowed elimination of ments: the high-voltage/high-power section and the low- many components, wiring and PCBs. voltage/control/service section. The high-voltage section is The software was developed in-house and was situated on top of the compressor and houses the power designed to minimize manufacturing costs while increas- electronics required to drive the motor, and the isolated ing overall compressor reliability and system efficiency.◆ high-voltage DC/DC power supply for magnetic bearings and low-voltage system control functions. The low-voltage Ron Conry is the executive vice president of technology section is situated on the side of the compressor and development at Turbocor. For more information, call includes the bearing/motor control, the compressor con- 514-421-0523 or visit turbocor.com. trol and the low-voltage DC/DC power supply.