Table of Contents
Advertisement
O O p p e e r r a a t t i i n n g g P P r r i i n n c c i i p p l l e e s s
condense. The liquid refrigerant then flows out of the
bottom of the condenser, passing through an orifice
plate and into the economizer.
The economizer reduces the energy requirements of
the refrigerant cycle by eliminating the need to pass all
gaseous refrigerant through both stages of
compression (refer to the following figure). Notice that
some of the liquid refrigerant flashes to a gas because
of the pressure drop created by the orifice plate, thus
further cooling the liquid refrigerant. This flash gas is
then drawn directly from the economizer into the
second-stage impellers of the compressor. All
remaining liquid refrigerant flows out of the
economizer, passing through another orifice plate and
into the evaporator.
Figure 48. Pressure enthalpy curve
Condenser
P
5
3
Economizer
P
6
2
Evaporator
P
1
1
Enthalpy
Figure 49. Refrigerant flow, 2-stage
Duplex Compressor Sequencing
Four methods (two fixed-sequence methods, a
balanced start and hour's method, and a no-staging
method) are provided for order of a compressor
sequencing on Duplex™ CenTraVac™ chillers. The
desired method is selectable at startup via the service
tool. The application can decide to either balance the
wear burden among the unit's compressors, to start
the most efficient compressor, or to simultaneously
68
4
Compressor
Second Stage
3
Compressor
First Stage
2
start and stop both compressors to minimize startup
pull down time. Each method has specific applications
were it can be used advantageously. If one compressor
is locked out, in restart inhibit, or generally not ready to
start, the available compressor will be started.
N N o o t t e e : : The following description assumes
Compressor 1 is the downstream compressor.
Fixed Sequence—Compressor 1 /
Compressor 2 (Default Mode)
If the chiller is in the Auto mode and all interlocks have
been satisfied, Compressor 1 will be started based on
the leaving water temperature rising above the
"Differential to Start" setting. Compressor 2 will stage
on when the overall chiller average capacity exceeds
stage-on load point for 30 seconds. The stage-on load
point is adjustable (via service tool) up to 50 percent.
The default is 40 percent which means that a single
compressor would have to load to 80 percent (the
average would be 40 percent) before the second
compressor starts. Both compressors will run until
chiller average capacity drops below stage-off load
point for 30 seconds. The stage-off load point is also
adjustable (via service tool) (default = 30 percent, range
from 0 to 50 percent). Compressor 2 will be shut down
and Compressor 1 will run until water temperature
drops below the differential to stop. Before shutting
down, Compressor 2 will be unloaded and
Compressor 1 will be loaded to maintain the same
average capacity command. When running chilled
water temperature at selected conditions, the
downstream compressor usually will be the most
efficient compressor to operate at part load because
compressors on Duplex™ CenTraVac™ chillers are not
sized exactly the same.
Figure 50. Duplex™ chiller sequence of operation:
lead 1 / lag 2
Evap LWT Falls
Below
Differential to
Stop
Running
(Circuit 1)
Chiller Capacity
Less than 30%
(No Time Delay)
Running
(Circuit
1 and 2)
Auto
Evap LWT Rises
Above
Differential to
Start
Compressor A
Capacity Greater
than 80%
(No Time Delay)
CDHF-SVX01N-EN
Advertisement
Table of Contents
