ACE Turbine Technology
Carrier Corporation released our patented 19XT turbine
assisted centrifugal chiller in January of 1995. This introduction
was a technology breakthrough in changing the basic vapor compression
cycle to achieve even higher operating efficiencies. In the conventional
vapor compression cycle, refrigerant exits the condenser, passes
through a throttling valve and enters the evaporator at reduced
temperature and pressure. With Carrier's revolutionary new technology
, a patented turbine will receive positive pressure HFC-134a refrigerant
from the condenser and use energy from the refrigerant to supplement
energy furnished by the chiller's motor. The use of the turbine
assisted centrifugal was possible due to the use of chlorine free
HFC-134a positive pressure refrigerant. The differential pressure
between the evaporator and condenser of the 19XT drives the impulse
turbine which is mounted on an extension of the motor shaft. The
turbine operates at 3600 RPM for 60 Hz applications and 3000 RPM
for 50 Hz applications. This operating speed combined with the
properties of HFC-134a are ideal for the application of an energy
recovery turbine.
This new technology adds very little complexity to
the proven 19XL compressor that we've been building since 1992.
The simplicity of this breakthrough, however, is somewhat deceptive.
The major technical challenge was to design a turbine system which
could accommodate a refrigerant stream in two states - liquid
and vapor. To enlist expertise in this niche application of fluid
mechanics, we partnered with Biphase Energy Company, a California
based engineering firm which has designed two-phase turbines for
power generation from geothermal wells. Carrier has been granted
an exclusive license from Biphase to use the turbine technology
in air conditioning and refrigeration applications.
In order to properly feed the refrigerant to the
turbine, nozzles are placed around the turbine rotor, and positioned
so that refrigerant is directed at the inlet side of the blades.
The nozzles are secured in a housing called the nozzle block,
which surrounds the rotor. A circumferential space called the
inlet plenum surrounds the nozzle block, so that each nozzle is
fed equally. Under normal operating conditions, this space is
filled with subcooled liquid from the condenser. Pure liquid refrigerant
enters the converging section of the nozzles and gains velocity
as the flow area converges. In the diverging section, the refrigerant
begins to expand, or flash, as the pressure is dropped. The refrigerant
leaving the nozzle is a mixture of liquid and vapor, and it is
the relative high velocity of the liquid that provides the energy
that is recovered by the turbine rotor. When the refrigerant
leaves the turbine rotor, it is still in a mixed phase condition
- partly liquid and partly vapor. It then enters a large chamber
called the discharge plenum, where the flow is stabilized prior
to being piped to the evaporator.
The 19XT turbine assisted centrifugal chiller using
chlorine free HFC-134a can achieve operating efficiencies in
the .56 to .60 IKW/TON range. Although this efficiency level is
significantly better than conventional centrifugal chillers which
use HFC-134a refrigerant it still did not equal efficiency levels
achievable with chlorine based refrigerants.
In January 1996 Carrier introduced our improved turbine assisted centrifugal, model 19XRT. Because the aerodynamic parts of the 19XL/XT compressor were originally designed for operation with HCFC-22 refrigerant, when operated with HFC-134a peak compressor operating efficiencies were not obtainable. Our engineers went to work to optimize the compressor speed and aerodynamic components for use with HFC-134a. The result is 19XRT operating efficiencies approaching the .50 IKW/TON level. Now our customers are no longer forced to compromise when it comes to choosing between environmental responsibility, safety, high efficiency, and assurance of a supply of refrigerant for the life of their chiller. Carrier Corporation is the only centrifugal chiller manufacturer that can offer all of these benefits to our customers.