VRF temp control jumps around like a chipmunk

asked 2020-07-13 15:21:34 -0500

updated 2020-07-13 17:58:53 -0500

The back story is this:

  1. Using EnergyPlus v8.9
  2. Lots of latent load, which is being handled by ZoneHVAC DX dehumidifiers (2 in each zone)
  3. There's a lot of sensible load from lighting and it's continuous during a 12 hour period
  4. VRF HVAC for sensible load. 2 VRF terminal units are in each zone, operating in sequence with each other via the :EquipmentList' s priorities for cooling
  5. Using 12 timesteps per hour, temperature is at setpoint for about 2 timesteps, then starts bouncing. Both VRF terminal units operate at 90% maximum capacity in one timestep, then go to very low capacity in the next timestep. Then it keeps doing the same thing and temperature control becomes erratic, bouncing up and down about 2C each direction.
  6. 6 timesteps per hour does the same thing, but it's a bit more evident when using 12 timesteps.

I'm stuck trying to figure out what causes the instability. Can you point me in a direction?

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