Interstage Pressure Limit - Trane HORIZON ABDA Manual

(16) Inter-Stage Pressure
Limit
High Interstage Pressure
A pressure transducer monitors the inter-stage vapor
pressure generated by first stage generator. This pressure
is a function of the energy input to the first stage generator,
the presence of noncondensable gases, and the
condensing temperature. The inter-stage pressure
transducer is mounted vertically on a stand off tube to
isolate it from any lithium bromide that may be carried with
the water vapor. If this pressure rises above the 3 psig
cutout of the HPC, the chiller will be shut down, protecting
the chiller and the rupture disk (~15PSIG).
The interstage pressure cutout setpoint is factory set to
3PSIG. This is adjustable within service setting: machine
configuration menu group on the CLD. The range is 0-15.
Figure 31. Example illustrating the microprocessor response to a pressure increase approaching cutout
.H
Shutdown above
.i..
g..
3 psig
h
.L.
.i
m.
Unloading
i...
t
.H
.i..
hold
g..
h
.L.
.i
Limited
m.
loading
i...
t
Unrestricted loading
Limited Loading
(Low Limit)
The limit is a proportional control that limits loading as the
Interstage Vapor Pressure approaches the UCP2 high-
pressure cutout setpoint. See the illustration below for an
understanding of the allowed loading verses interstage
pressures.
Low Interstage Pressure Limit
To avoid sensor diagnostic at startup the diagnostic is not
enabled until the Solution Temperature Leaving the LTG is
above 120 Degree F. At this point the microprocessor
monitors the inter stage pressure for a continued increase.
Low interstage pressure limit will likely be displayed as the
machine interstage pressure is brought up from the low
pressures at a cold startup.
Figure 31 identifies how the microprocessor responds to a
pressure increase as the pressure approaches cutout.
Interstage Pressure (PSIG) Interstage Pressure (PSIG)
81