Modeling Sound Level and Pressure Loss in HVAC Duct Networks using a Framework in Modelica/Dymola

Introduction In the early phase of designing large HVAC duct networks the joint calculation of the sound level, air ow rate and pressure loss in the duct network as well as the prediction of the noise level in the passenger compartment gains more and more in importance. A uni ed framework for one-dimensional ow and acoustic simulation using Dymola/Modelica is introduced. As a tool for concept modeling it ful lls several requirements: The predictions methods used should be fast and computational e cient. It should use all kinds of data available, from analytic and (semi)empiric models to data obtained from measurements and acoustic and uid dynamics computer simulations to characteristic diagrams and sparse point data given by component manufacturers. The acoustic part is alternatively described by sound power based methods or plane wave two-port theory, the uid mechanic part by pressure loss models. Each component either represents the acoustic or the ow part of a duct element or can, itself, be composed of both types allowing the modeling of non-standard components. The object oriented approach provided by Modelica assures the extensibility of the models. It also allows the integration into a complete system simulation of the HVAC network. The simulation is easily set up using a GUI; an external parametrization ensures persistent data management and a smooth work ow. The resulting system of equations is automatically preprocessed and solved by Dymola.