Office of Physical Plant
Operations Division
Engineering Services
The Pennsylvania State University
Physical Plant Building
University Park, PA 16802-1118
SEQUENCE OF OPERATION
HEAT EXCHANGER w/ TWO VALVES, ⅓ - ⅔
Standard control of a heat exchanger served by two steam valves in a “1/3 - 2/3” configuration.
1. Upon a call to run, the “1/3 - 2/3” steam valves will be modulated by a PID control loop to
maintain the required hot water temperature setpoint. The valves will be controlled in the
following manner:
a. The 1/3 valve will be modulated first.
b. If the output of the PID control loop exceeds 25% (adjustable) for more than 2
minutes (adjustable), the 2/3 valve will become the first valve modulated making
the 1/3 valve control range switch to the 66% to 100% output range of the PID
control loop.
c. If the output of the PID control loop exceeds 60% (adjustable) for more than 2
minutes (adjustable), the 1/3 valve will become the first valve modulated (the 1/3
valve will be 100% open at this time) making the 2/3 valve control range switch to
the 33% to 100% output range of the PID control loop (the 2/3 valve will be
modulating at this time).
d. The reverse sequence shall occur at the 40% (adjustable) and the 25%
(adjustable) points as steam demand decreases.
e. The sequence shall also reset anytime the output of the PID control loop equals
zero.
See Sample program below.
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