Operating Principles; General Requirements; Cooling Cycle - Trane CVHE Installation, Operation And Maintenance Manual

Operating Principles

General Requirements

Operation and maintenance information for CVHE, CVHF ,
and CVHG chillers are covered in this section. This
includes both 50 and 60 Hz centrifugal chillers equipped
with the Tracer AdaptiView UC800 control system. This
information pertains to all chiller types unless differences
exist, in which case the sections are listed by chiller type as
applicable and described separately. By carefully
reviewing this information and following the instructions
given, the owner or operator can successfully operate and
maintain a CenTraVac unit. If mechanical problems do
occur, however, contact a Trane service technician to
ensure proper diagnosis and repair of the unit.

Cooling Cycle

When in the cooling mode, liquid refrigerant is distributed
along the length of the evaporator and sprayed through
small holes in a distributor (i.e., running the entire length
of the shell) to uniformly coat each evaporator tube. Here,
the liquid refrigerant absorbs enough heat from the
system water circulating through the evaporator tubes to
vaporize. The gaseous refrigerant is then drawn through
the eliminators (which remove droplets of liquid
refrigerant from the gas) and the first stage variable inlet
guide vanes, and into the first-stage impeller.
CVHE and CVHG 3-Stage Compressor
Compressed gas from the first-stage impeller flows
through the fixed, second-stage inlet vanes and into the
second-stage impeller. Here, the refrigerant gas is again
compressed, and then discharged through the third-stage
variable guide vanes and into the third-stage impeller.
Once the gas is compressed a third time, it is discharged
into the condenser. Baffles within the condenser shell
distribute the compressed refrigerant gas evenly across
the condenser tube bundle. Cooling tower water circulated
through the condenser tubes absorbs heat from the
refrigerant, causing it to condense. The liquid refrigerant
then passes 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 three stages of compression
(see Figure 33, p. 56). Notice that some of the liquid
refrigerant flashes to a gas because of the pressure drop
created by the orifice plates, thus further cooling the liquid
refrigerant. This flash gas is then drawn directly from the
first and second stages of the economizer into the third-
and second-stage impellers of the compressor,
respectively. All remaining liquid refrigerant flows
through another orifice plate to the evaporator.
56
Figure 32. Pressure enthalpy curve, 3-stage
condenser
6
P
4
high side economizer
7
P
3
low side economizer
8
P
2
evaporator
1
P
1
Figure 33. Refrigerant flow, 3-stage
CVHF 2-Stage Compressor
Compressed gas from the first-stage impeller is
discharged through the second-stage variable guide
vanes and into the second-stage impeller. Here, the
refrigerant gas is again compressed, and then discharged
into the condenser. Baffles within the condenser shell
distribute the compressed refrigerant gas evenly across
the condenser tube bundle. Cooling tower water,
circulated through the condenser tubes, absorbs heat
from the refrigerant, causing it to 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
(see Figure 35). 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,
passes through another orifice plate and into the
evaporator.
5
compressor
rd
(3 stage)
4
compressor
3
nd
(2 stage)
compressor
2
st
(1 stage)
CVHE-SVX02H-EN