Dynamic Modeling of Mechanical Draft Counter-Flow Wet Cooling Tower with Modelica

Cooling towers are important equipments for the HVAC systems in commercial buildings, rejecting the process heat generation to the atmosphere. Dynamic modeling of cooling towers is beneficial for control design and fault detection and diagnostics of the chilled-water systems. This paper proposes a simple and yet effective dynamic model for a typical mechanical draft counter-flow wet cooling tower. The finite volume method is applied to the one-dimensional heat and mass transfer analysis. With control volumes defined separately for the water and air sides, the dynamic equations are constructed with the mass and energy balances. The steady-state performance of the proposed model is evaluated with experimental data from literature. The transient behavior is also simulated under the changes of tower inlet conditions, with the performance to be evaluated in the future with field test data.