In 2006
our industry will be faced with tougher energy efficiency
standards. A combination of EU directive 2002/91/EC and Part
L of the UK Building Regulations (in itself a response to
the Government Energy White Paper – Our Energy Future
Creating a Low Carbon Economy), has ensured that this time
around higher efficiency standards are here to stay.
So with today’s requirement for ever
higher efficiency objectives, the introduction of the Climaveneta
(a division of DeLonghi) TECS chiller will assist you in
meeting these stricter efficiency demands. The Climaveneta
TECS chiller range is available in air-cooled versions from
210kW to 1080kW and water-cooled versions from 220kW to
2400kW all with multiple (two, three or four) refrigeration
circuits.
TECS 600 kW Air Cooled Chiller
New
Horizons for Efficiency
For most chiller applications the COP
value is taken for the design day selection criteria but this
only occurs for a few days a year; for the rest of the time
chillers operate at part-load condition. For this reason,
‘seasonal efficiency’ or IPLV (integrated part
load value) index is the truly determinant consumption factor.
For example, a traditional screw compressor chiller at design
will have a COP approaching 2.9 whereas a TECS chiller will
have a design COP of 3.3 – an improvement of 13%; however,
the IPLV index shows an improvement approaching 40% for the
TECS chiller over traditional screw compressor chillers, thereby
affording considerable energy running cost savings.
Sustainability
Highest efficiency leads to lowest CO2
emissions but this is not in itself enough - the performance
must be sustained over the entire life of the product. These
requirements take us to the compressor at the heart of the
TECS chiller – in it’s target capacity range there
is no other compressor that produces better efficiency in
overall operation and the Turbocor compressor uses oil-free
technology. This is the key to sustainability because it eliminates
the ability of oil to degrade the system’s efficiency.
Clearly
the selection of compressor type poses one of the most important
aspects of chiller selection; the compressor is generally
the single largest energy consumer within the HVACR system
and is the heart of the chiller. Owners and system designers
when surveyed indicate their most important considerations
to be:
1. Reliability
– key is simplicity of design.
2. Low
Maintenance – needs to be minimised whenever and wherever
possible.
3. Energy
Efficiency – ensure COP is high at both full and part
load conditions.
4. Sound
– so quiet you cannot hear it.
5. Capacity
Control – ideally infinite, with wide range and, more
importantly, stable operation.
The
Turbocor Compressor
The Turbocor oil-free compressor is
combined with industrially proven magnetic bearings, variable
speed inverter drive, centrifugal compressor and digital electronic
technology.
A digitally controlled magnetic-bearing system, consisting
of both permanent magnets and electro-magnets, replaces
conventional lubricated bearings. The frictionless compressor
shaft is the compressor’s only moving component. It
rotates on a levitated magnetic cushion (fig 1). Magnetic
bearings – two radial and one axial – hold the
shaft in position (fig 2).
fig1
fig 2
When the magnetic bearings are energised,
the motor and impellers, which are keyed directly to the
magnetic shaft, levitate. Permanent-magnetic bearings do
the primary work, while digitally controlled electromagnets
provide the fine positioning. Four positioning signals per
bearing hold the levitated assembly to a tolerance of less
than 7 micron. As the levitated assembly moves from the
centre point, the electromagnets’ intensity is adjusted
to correct the position. These adjustments occur 6 million
times a minute. The software has been designed to automatically
compensate for any out-of-balance condition in the levitated
assembly.
Low Maintenance
Oil management, particularly as it pertains
to the lubrication of compressor bearings, is a critical
issue in refrigeration system design. But with magnetic
bearings, this issue is avoided. Avoiding oil management
systems means avoiding the capital cost of oil pumps, sumps,
heaters, coolers, and oil separators, as well as the labour
and time required to perform oil-related services. Reports
indicate that for many installations, compressor maintenance
costs have been cut by more than 50 percent.
In fact, the only required regular maintenance of the compressor
is the quarterly tightening of the terminal screws, the
annual blowing off of dust and cleaning of the printed circuit
boards, and the changing of the capacitors every five years
Efficiency
Among the key parameters affecting performance
are capacity and efficiency (IPLV). The compressor’s
capacity ranges from 200 kW to 320 kW depending on the operating
conditions.
Efficiency improvements stem from a combination of the centrifugal
compressor, permanent-magnet motor and magnetic bearings.
Within the compressor, efficiency is affected by the compressor
isentropic efficiency (the efficiency of the impellers)
the motor and the bearings. Typically, traditional induction
motors of this size are in the 92-percent efficiency range.
This compressor’s permanent magnet motor has an efficiency
of 96 to 97 percent.
Efficiency is further enhanced with the
use of magnetic bearings, which avoid the friction associated
with traditional oiled bearings. Conventional bearings can
use as much as 10,000 W, while magnetic bearings require
only 180 W. That amounts to 50 times less friction loss.
Motor and Inverter
Most hermetic compressors use induction motors cooled by
either liquid or suction-gas refrigerant. Induction motors
have copper windings, that when alternating current is run
through them, create magnetic fields that cause the motor
to turn. These copper windings are bulky, adding size and
weight to the compressor.
Two-pole 50-Hz induction motors operate at approximately
3000 rpm. A higher number of revolutions per minute can
be obtained by increasing the frequency. Compressors that
require higher shaft speeds tend to use gears. While gears
are proven technology, they create noise and vibration,
consume power and require lubrication.
The magnetic-bearing compressor features a synchronous permanent-magnet
brush-less DC motor with a completely integrated variable-frequency
drive (VFD).
The stator windings found on conventional induction motors
are replaced with a permanent-magnet rotor. Alternating
current from the inverter energizes the armature windings.
The stator (excitation) and rotor (armature) change places.
No commutator brushes are required. The motor and key electronic
components are internally refrigerant-cooled, so no special
cooling is required for the VFD or the motor.
The use of permanent magnets instead of rotor windings makes
the motor smaller and lighter than induction motors. Using
magnetic-bearing technology, a 250kW capacity compressor
weighs about one-fifth the weight of a conventional screw
compressor.
Control
A variable-speed drive (VSD) is required
for the motor to operate. The VSD varies the frequency between
300 and 800 Hz, which provides a compressor-speed range
from 18,000 to 48,000 rpm. This avoids a gear set. The VSD
is integrated into the compressor housing, avoiding long
leads and allowing key electronic components to be refrigerant-cooled.
The VSD also acts as a soft starter; as a result, the compressor
has an extremely low start-up in-rush current: less than
2 amps, compared with 200 amps for a traditional screw compressor
with a star-delta starter. With the integration of the motor,
VSD, and magnetic-bearing system, the capacitors required
for the motor and drive can be used as a backup power source
for the bearings in the event of a power outage or emergency
shutdown.
The new TECS chiller range features user interface and adjustment
software with a graphic display for reading and writing
control parameters. The controller also comprises a mimic
panel for real-time visualisation of compressor operating
status. Chillers can communicate with Modbus, LonWorks or
BACnet as well as other systems.
Sound
Because the rotating assembly levitates, there essentially
is no structure-borne vibration. The magnetic bearings create
an air buffer that prevents the only major moving part –
the motor rotor – from transmitting vibration to the
structure.
Similarly, sound levels are extremely low, primarily because
of refrigerant-gas movement through the compressor and the
rest of the refrigeration system. There are no tonal issues,
such as those found with some screw compressors and the
noise occurs in the higher octave bands where it is easier
to attenuate. When two magnetic-bearing compressors are
integrated into a TECS 600 kW air cooled water chiller,
the sound pressure is 68 dB(A) at 1.0 m under standard Eurovent
conditions. Click below to experiance an indication of the
sound difference for yourself.
fig1
