Trane AFDH, Installation Manual

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AFDH-SVN01A-EN 59
Installation
5. AF Pressure Coefficient Constant: This value is used to normalize the Pressure Coefficient
(PC) calculation within the AFDB control algorithm. The PC constant value to be entered for this
parameter must be calculated for each specific individual chiller. This calculated PC value takes
into account how specific compressor parameters such as the number of compressor stages
and average impeller diameter affect the level of speed control dictated by the control
algorithm. Refer to the Figure below for the formula used to calculate the PC constant value that
needs to be entered into this UCP2 menu parameter, and an example calculation.
Important: Using the actual specific average impeller size of the chiller is critical for determining
an accurate value for the PC constant. If the unit nameplate is missing, unreadable,
or of a vintage that did not include all of the data categories, such as impeller size,
contact Trane Technical Services through the toll-free Trane automated phone
support system at 877-788-7263 and using the menu code sequence of 4-2-7. Provide
the support person with the chiller serial number and request a copy of the shipped-
with bill of materials for this unit.
Figure 33. AF PC Constant formula and sample calculation
6. AF Re-Optimization Factor: This factor is a magnitude-based parameter for clearing the
Surge Flag. It is helpful to think of this value relative to the size of the pressure error deadband.
For example, with the recommended deadband value of 0.03 in use and the re-optimization
factor set at the recommended value of 0.30, this sets the internal algorithm calculation to 10x
the deadband. This means that when encountering a pressure error greater than 10x the
deadband during operation, it implies that the operating conditions have changed enough to
clear the Surge Flag.
a. The AF Re-Optimization Factor is adjustable from 0.03 to 1.0 in 0.01 increments. Optimal
chiller performance is most often achieved using the recommend setting value of 0.30
b. Setting a large re-optimization factor will cause this feature to operate using the time-based
parameter.
7. AF Re-Optimization Timer: This factor is the time-based parameter for clearing the Surge
Flag. The timer begins to decrement from the front panel set point as soon as surge occurs. The
timer counts down as long as the UCP2 is powered. This value determines how aggressively
the chiller will try and re-optimize for efficiency. For example, if the timer value is set to 1-hour,
the Surge Flag will be cleared 1-hour after being set.