This indicates the possibility of coil frost/freeze(VRV System),what should I do

asked 2019-02-20 21:01:34 -0500

l1023
141 ●2

updated 2019-02-20 22:01:05 -0500

shorowit

10881 ●180 ●9 https://www.nrel.gov/b...

  ** Warning ** Coil:Cooling:DX:VariableRefrigerantFlow "LIVINGROOM1 VRF COOLING COIL" - Full load outlet air dry-bulb temperature < 2C. This indicates the possibility of coil frost/freeze. Outlet temperature = -3.32 C.
   **   ~~~   **  ...Occurrence info = SHANGHAI ANN HTG 99.6% CONDNS DB, 01/21 09:00 - 09:01
   **   ~~~   ** ... Possible reasons for low outlet air dry-bulb temperatures are: This DX coil
   **   ~~~   **    1) may have a low inlet air dry-bulb temperature. Inlet air temperature = 5.885 C.
   **   ~~~   **    2) may have a low air flow rate per watt of cooling capacity. Check inputs.
   **   ~~~   **    3) is used as part of a HX assisted cooling coil which uses a high sensible effectiveness. Check inputs.
** Warning ** ZoneHVAC:TerminalUnit:VariableRefrigerantFlow "LIVINGROOM1 VRF TERMINAL UNIT"
   **   ~~~   ** Terminal unit part-load ratio calculation failed: PLR limits of 0 to 1 exceeded
   **   ~~~   ** Please fill out a bug report and forward to the EnergyPlus support group.
   **   ~~~   **  Environment=RUNPERIOD1, at Simulation time=02/23 07:08 - 07:09

answered 2019-02-21 08:48:15 -0500

rraustad

13599 ●72 ●12 http://www.fsec.ucf.edu/

As the warning shows, the inlet air temperature to the DX cooling coil is 5.9C (42.6F). This is lower than the usual supply air outlet temperature when coil inlet temperatures are normal. The outlet air temperature is -3.3C. This will likely cause frost to build up on the coil and the VRF model does not account for INDOOR coil defrost. If this happens very few hours of the year you can likely disregard the warning, otherwise a system performance correction is warranted. So to correct this you have a couple options.

review the system and controls to determine why the HVAC system turned COOLING on when the coil inlet temperature is so low. Is outside air included? If not then that means the zone temperature is 5.9C and cooling should not be needed. If OA is included, then that means the zone needs cooling when it is very cold outside, is there a reason for the need for cooling at these outdoor conditions?
the rated cooling and air flow determine the outlet air condition (mainly temperature for this discussion). If the capacity is lower and/or the air flow is raised, the outlet air condition will rise. Check the rating information for this coil and see if there is room to make adjustments.

Likely the issue relates to why the HVAC system turns on at these cold conditions (indoor and/or outdoor).

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