Question-and-Answer Resource for the Building Energy Modeling Community
 | 1 | initial version |
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).
