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          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
   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
trol and the low-voltage DC/DC power supply.

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