[Equest-users] Induction Units vs. VAV

[Josh Doherty]

I am trying to build an energy model for an office building that uses a chilled beam HVAC system.  In this system, there is a main central air handler with heating and cooling coils to condition the air to 55 F.  The supply air to each zone is then further conditioned to meet the individual zone thermostats via a 2 pipe active chilled beam with heating and cooling coils.  Cooling is supplied through a chilled water loop tied to a ground source heat exchanger and heating is supplied through a HW loop from the boilers.  Unfortunately, eQuest does not have a chilled beam HVAC system type.  So, I am trying to model the system with 2-pipe induction units.  I know these active chilled beams are more efficient than a standard VAV with reheat system.   However, to get a better idea of how "much" more efficient the active chilled beams are, I built a model with a VAV system and compared the results.   Everything in the models is the same, except for the HVAC system type (either induction unit or VAV) and I had to enter the reheat delta T on the VAV system for it to work correctly.  Finally the results...drum roll please...

The induction unit model used far more energy than the VAV system.  For whatever reason, the heating energy required in the induction unit model is more than 3X that needed in the VAV model.  I can not make sense out of this.

Does anybody have a clue what could be going on?  Is the induction unit really the closest eQuest can get to active chilled beams?  Thank you all for your help and time.  Your knowledge is greatly appreciated!

Josh Doherty





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