Development of a flow pattern selection algorithm for unmixed airflow

This paper presents an exploratory study on flow pattern selection in unmixed flows, resulting in aset of rules that are used to decide between flow regime during and before a simulation. The development of this set of decision rules had several goals: to define simple criteria to distinguish between flows, to assist non-expert users in the selection of the correct flow pattern model and finally to automate the choice of models during numerical simulations in energy simulation software. This last point is particularly important in simulation of naturally driven ventilation systems where flow conditions can change several times per day, often leading to changes in airflow pattern. A set of unmixed flow models and a flow pattern selection algorithm are integrated in an existing whole building thermal simulation tool: EnergyPlus. The flow pattern selection method uses simpleroom geometry and flow scaling criteria to distinguish between: mixing, displacement and cross-ventilation flows. An example of the automated use of the flow pattern selection rules in an EnergyPlus simulation of a low energy cooling system is presented.