Warning Error: Cooling Capacity Ratio Modifier Function of Low Temperature Curve

asked 2019-10-14 21:12:41 -0500

Eru
91 ●1 ●6

updated 2019-10-15 04:29:57 -0500

Julien Marrec

29032 ●85 ●74 http://www.effibem.com/

Hi Fellas! I run my simulation successfully but I found a warning error message that shows below:

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

This error always in my simulation but it not severe. The question is what the error explains? It significantly affected the HVAC sizing result? Your answer will help me, thank you!

Comments

What is the impact of this warning on the simulation results? Is there any method we can choose to normalise the curve?

Shaun Wang ( 2023-05-22 05:31:40 -0500 )edit

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answered 2019-10-15 04:46:00 -0500

Julien Marrec

29032 ●85 ●74 http://www.effibem.com/

The error is pretty self-explanatory. The curve is supposed to be normalized, that is produce a value of 1.0 at the rated conditions.

If you look at the I/O reference guide for this curve here, you'll see that this is a bivariate object as a function of indoor wet-bulb temperature and condenser temperature (either air dry-bulb temperature or water temperature if watercooled).

The engineering reference here also includes more info and the equations.

What the documentation is not clear about is what these rated temperatures are, so I'll tell you what they are for an Air-cooled VRF after looking at the source code:

RatedInletWetBulbTemp: 19.44 or 67F
RatedOutdoorAirTemp: 35 C or 95F

For heating side,

RatedInletWetBulbTempHeat: 15.55 or 60F
RatedOutdoorAirTemp: 8.33 C or 47F

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Comments

Thank you Julien! From the I/O reference written that indoor WB temp is 19.44 C and outdoor DB temp is 35 C, how you can say from the source code that: RatedInletWetBulbTemp: 19.44 or 67F RatedOutdoorAirTemp: 35 C or 95F ? what source code you mean?

Eru ( 2019-10-17 22:40:21 -0500 )edit

I mean the EnergyPlus source code. Cf HVACVariableRefrigerantFlow.cc. The RatedOutdoorAiTemp and stuff are initialized in DXCoils.cc, line 158 currently.