In the EnergyPlus Example files for Chilled Water Storage-Mixed vs Stratified(5ZoneVAV-ChilledWaterStorage-Mixed.idf & 5ZoneVAV-ChilledWaterStorage-Stratified.idf), the Secondary chiller is present in the Mixed storage idf while only Primary in stratified idf file. What is the logic or rule to configure the plant loops and when we should consider using two chillers vs only one with TES implemented?