Installation Instructions

Document No. 588-150 Page 5 of 11
In cold climates, to prevent mechanical equipment freeze up, there is a need to keep the
air handler warm even when the fan is off. The Predator can cycle or modulate an
optional hot water valve to keep the mixed air temperature (or discharge temperature)
within a desired range while the fan is off.
The Predator can initiate a warm-up sequence for the zones. When the zone
temperature and the outdoor temperature are both below adjustable limits and
occupancy is due to start soon, the Predator switches to warm-up mode. It issues a
network command for the zone controllers to put them in warm-up mode. The only
inputs required are the zone temperature and the LonMark compatible schedule
variable.
Adaptive Control of Outdoor Air Damper
Past history has proven that tuning for economizer control loops poses problems. For
example, when it is particularly cold outside, a small damper movement can cause a big
change in the mixed air temperature. The control loop is likely to overshoot or even
oscillate which can cause big problems in the air-handling unit. To prevent oscillation, it
is necessary to tune the loop specifically for the cold-weather case. Then when warmer
weather arrives, the cold-weather tuning leads to sloppy control and an ineffective air
conditioning system.
The Predator addresses this dilemma directly by automatically adjusting the economizer
control loop tuning to suit the outdoor temperature. Without any attention or
maintenance, the loop is always fast, stable and accurate, making the economizer truly
economical.