Flow-acoustic concept modelling of HVAC duct networks using a Dymola/Modelica frame work

A Modelica framework for the joint calculation of acoustic and flow quantities in HVAC ducts is presented. Modeling the sound propagation in ducts by one dimensional acoustic two-port methods is a well-established technique for the acoustic characterization of large HVAC duct networks. Two different approaches of acoustic modeling are implemented in the framework: When resonant phenomena are insignificant, it is often sufficient to apply band-averaged models to predict the sound power level and the transmission loss within the individual components of the duct network as well as the sound pressure level at the listener´s position, as proposed in the guidelines of ASHRAE or VDI. For the low frequency range where linear plane wave propagation is valid, acoustic two and multi-ports models based on a transmission matrix formulation of the sound pressure can be applied for high frequency resolution and phase accurate calculations. For the prediction of the mean air flow in the duct network pressure loss models are applied. Their coupling permits the simulation of flow acoustic phenomena. Setting up large networks a smooth work flow is vital for the user: The simulation is easily set up using the GUI provided by Dymola; external parametrization ensures persistent data management. The resulting system of equations is automatically pre-processed and solved by Dymola. In this paper an overview of this new software tool is given together with exemplary applications.