Fan Energy Consumption too high

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Short Answer:

PTAC that cycles the fan on during heating/cooling load, and does not provide OA:

1. Use a PTAC (ZoneHVAC:PackagedTerminalAirConditioner in EnergyPlus) with a Fan:OnOff so that the fan can cycle.

2. Zero-out the fields Outdoor Air Flow Rate During Cooling Operation, Outdoor Air Flow Rate During Heating Operation, and Outdoor Air Flow Rate When No Cooling or Heating is Needed so that the PTAC will never provide OA.

3. In the field Supply Air Fan Operating Mode Schedule, put a schedule that with a value of 0 (zero) for the whole year to tell the fan to cycle on only when heating or cooling is needed.

Background:

The EnergyPlus documentation for the ZoneHVAC:PackagedTerminalAirConditioner can be found here. In particular, these two fields are the key:

Field: Supply Air Fan Object Type This alpha field defines the type of fan used by this PTAC. The only valid choices are Fan:OnOff and Fan:ConstantVolume. A fan of type Fan:OnOff is used with cycling fan operating mode, and a fan of type> Fan:ConstantVolume is used with continuous fan operating mode (see Supply Air Fan Operating Mode Schedule field below). The input requirements for these fan objects are described elsewhere in this document.

and

Field: Supply Air Fan Operating Mode Schedule Name This alpha field specifies the name of the supply air fan operating mode schedule. The supply air fan operating mode may vary during the simulation based on time-of-day or with a change of season. Schedule values of 0 denote that the supply air fan and the heating or cooling coil cycle on and off together to meet the heating or cooling load (a.k.a. AUTO fan). Schedule values other than 0 denote that the supply fan runs continuously while the heating or cooling coil cycles to meet the load.

In OpenStudio:

The PTAC currently in the OpenStudio library has a Fan:ConstantVolume in it, so it will not cycle. I have filed an issue so that we will add a cycling PTAC to the library for 1.7.0. In the meantime, as a workaround, you can manually add it to your library like this:

1. Close OpenStudio
2. Go to C:\Program Files\OpenStudio 1.6.0\share\openstudio-1.6.0\OSApp\hvaclibrary' and make a backup copy of 'hvac_library.osm in case you mess it up in the next step.
3. Open hvac_library.osm in a text editor (like Notepad, etc.)
4. Copy/paste the following text into the bottom of hvac_library.osm, then save the file.
   
   • Make sure to only copy/paste the text once.
   • In 1.5.0, the resulting file should be 7106 lines long, in 1.6.0 it should be 7135 lines long.
   • Since the file lives in /Program Files/, you may need to have admin rights to save changes.
5. When you re-open OpenStudio, you should see a PTAC called "Cycling PTAC..." in the Library. It will be setup to cycle. (You'll still need to zero-out the OA fields if you ...