New Sequencing Control Strategy for Air-Handling Units.
New Sequencing Control Strategy for Air-Handling Units.
(1609 K)
Seem, J. E.; Park, C.; House, J. M.
HVAC&R Research, Vol. 5, No. 1, 35-58, January 1999.
Keywords:
air handling unit; control strategy; digital controller;
sequencing control; simulation
Abstract:
Air-handling unit (AHU) controllers commonly use
sequencing logic to determine the most economic way to
use the componems of the AHU to maintain the supply, air
temperature at a setpoint value. The objective of this
paper is to introduce the finite state machine (FSM)
sequencing control strategy for AHUs and to compare this
strategy with a traditional split-range sequencing
control strategy. The FSM control strategy represents a
paradigm shift in the way sequencing logic is developed,
illustrated and implemented for the control of HWC
systems. Simulation results obtained from representative
weather data for each month of the year are presented to
demonstrate the performance of the two sequencing
strategies with respect to the controller gains
(proportional gain and integral time) used for the
heating coil, cooling coil, and mixing box dampers.
Simulation results demonstrate that in comparison to the
split-range control strategy, the FSM control strategy
leads to more stable operation of the AHU when the
feedback, controller(s) used to control the supply air
temperature is (are) poorly tuned.
Building and Fire Research Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899