Abstract
This paper describes the results of simulating the dynamic behavior of the air handler unit (AHU) of a Heating, Ventilating, and Air Conditioning System. The air handler unit is identified as comprising several interconnected components. Mathematical models for each of the individual components based upon first principles and a lumped parameter approach are developed separately and then combined to provide the necessary representation for the entire unit. The resulting model of the air handler unit consists of stiff nonlinear differential equations as well as nonlinear algebraic equations which have to be solved simultaneously. An efficient procedure for solving these nonlinear mixed algebraic-differential equations is presented. Simulation results for a specific air handler unit are also presented.