Dynamic coupling of the transient system simulation and fire dynamics simulation programs

Multi-zone building heat load prediction models are a useful tool for designing heating, ventilation and air conditioning (HVAC) systems and for assessing annual HVAC energy consumption. However, zone models are not able to account for detailed local flow-field effects. When these local flow-field effects are important, it is desirable to use computational fluid dynamics (CFD). Unfortunately, computation at the fine temporal and spatial scales used in CFD simulations is extremely time consuming, both in terms of the user input and the computational solving process, and so is often unsuitable for transient whole-of-building thermal simulations. The ideal tool would combine the benefits of both of these modelling techniques to simulate macro-scale outcomes which are influenced by complex building design features. In this study, an easy to implement and relatively efficient modelling technique is proposed which combines (i) the multi-zone and HVAC system simulation software TRNSYS with (ii) the CFD building simulation program FDS. Implementation of this technique requires the creation of a dynamic coupling procedure between the CFD and the multi-zone simulation components. Three test cases are used to check the validity of the coupling procedure. An example simulation is also provided to demonstrate the usefulness of the new technique for modelling the performance of a desiccant cooling HVAC system, with feedback control, in a shop with an open entrance. The coupling component source code and TRNSYS library files are available for download upon request.