How to solve these warnings regarding VRF HVAC?

asked 2020-09-09 10:54:50 -0600

rainbow's avatar

updated 2020-09-09 17:42:23 -0600

I'm working with the OpenStudio Plugin to generate an IDF in order to use it as input in an EnergyPlus simulation.

I'm working with a 1-story building, with 5 rooms, a VRF System and 3 VRF Terminals.

After exporting the IDF, when I run the simulation I obtain these three warnings (all of them about the VRF System):

  1. VRFCOOLCAPFT output is equal to 1.136 at rated conditions (instead of 1.0):

    ** Warning ** GetVRFInput: AirConditioner:VariableRefrigerantFlow="VRF SYSTEM" curve values
*   ~~~   ** ... Cooling Capacity Ratio Modifier Function of Low Temperature Curve Name = VRF SYSTEM 
VRFCOOLCAPFT 1 output is not equal to 1.0 (+ or - 10%) at rated conditions.
**   ~~~   ** ... Curve output at rated conditions = 1.136

  2. COOLINGEIRLOWPLR minimum value of X = 0.500 is out of range.

    It must be <= Minimum Heat Pump Part-Load Ratio = 0.250.

    ** Warning ** GetVRFInput: AirConditioner:VariableRefrigerantFlow="VRF SYSTEM", invalid
**   ~~~   ** ...Cooling Energy Input Ratio Modifier Function of Low Part-Load Ratio Curve Name = VRF SYSTEM 
COOLINGEIRLOWPLR 1 has out of range value.
**   ~~~   ** ...Curve minimum value of X = 0.500 must be <= Minimum Heat Pump Part-Load Ratio = 0.250.

  3. HEATINGEIRLOWPLR minimum value of X = 0.500 is out of range.

    It must be <= Minimum Heat Pump Part-Load Ratio = 0.250.

    ** Warning ** GetVRFInput: AirConditioner:VariableRefrigerantFlow="VRF SYSTEM", invalid
**   ~~~   ** ...Heating Energy Input Ratio Modifier Function of Low Part-Load Ratio Curve Name = VRF SYSTEM 
HEATINGEIRLOWPLR 1 has out of range value.
**   ~~~   ** ...Curve minimum value of X = 0.500 must be <= Minimum Heat Pump Part-Load Ratio = 0.250.

So, finally, after the fatal error below (caused by the three warnings above):

**  Fatal  ** GetVRFInput: Errors found in getting AirConditioner:VariableRefrigerantFlow system input. 
** Preceding condition(s) causes termination.

EnergyPlus terminates.

Is there anyone who could help me?

PS: If useful, I could attach here the IDF.

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Comments

2

I had the same issue when modeling a VRF system. Issue 2 and 3 that you listed were preventing a successful simulation because the minimum value of x for the two OS::Curve:Cubic that define the Cooling and heating Energy Input Ratio Modifier Function for Low Part Load Ratio Curves was 0.5. This was out of the acceptable boundary. It had to be <= the minimum heat pump part load ratio, which was defined as 0.25 as default. I changed the minimum values for x for the two curves to match the heat pump part load ratio (0.25) and the simulation ran without any issues.

Draza's avatar Draza  ( 2020-09-09 17:44:38 -0600 )edit

Hi Draza, thanks for your interest. I solved in your same manner, despite the fact I don't know if it's the best way to handle this warning. In other words, now the simulation is successfull, but I don't know if this work-around has any drawbacks. Anyway, thank you for your help!

PS: if you'll write your comment as an "answer", I could give you the upvote you deserve!

rainbow's avatar rainbow  ( 2020-09-10 08:28:26 -0600 )edit

I didn't write it in the answer section because I am also unaware of any potential drawbacks to fixing the issue this way. I posted a similar question here but haven't heard back.

Draza's avatar Draza  ( 2020-09-11 12:33:10 -0600 )edit

Okay, got it, it's a safer solution.

rainbow's avatar rainbow  ( 2020-09-11 15:24:36 -0600 )edit
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