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E+, error message "GetDXCoils: Coil:Cooling:DX:VariableRefrigerantFlow"

asked 2018-08-27 20:13:51 -0500

Alexis's avatar

updated 2018-08-28 19:37:21 -0500

I have done a simulation with a vrf system and 4 vrf zones. When I simulate my model, I have this warning message which appears :
"GetDXCoils: Coil:Cooling:DX:VariableRefrigerantFlow="BUILDING 20 SECOND FLOOR ROOM 4 VRF COOLING COIL" curve values
Cooling Capacity Ratio Modifier Function of Temperature Curve Name = BUILDING 20 SECOND FLOOR ROOM 4 VRF COOLING COIL CAP-FT output is not equal to 1.0 (+ or - 10%) at rated conditions.
Curve output at rated conditions = 1.136

Same message for the VRF system and for each of my zones. I have a result but I would like to know how to fix it and if there is an impact on my result ?

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answered 2018-08-29 08:09:09 -0500

This message says that the Cooling Capacity Ratio Modifier Function of Temperature Curve does not output a 1.0 at the rating conditions of 19.44 C indoor wet-bulb temperature and 35 C outdoor dry-bulb temperature. The correction is to check this performance curve as to why the cooling capacity modifier is not 1.0 at these conditions. It may be that the curve is correct, but likely there is an issue since input data (capacity, airflow, etc.) is usually at the rating point. The curve output = 1.136, does the cooling capacity input data multiplied by 1.136 equal the rated capacity of the unit at these rating conditions?

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Thank you for your answer. I just have begun with energyplus. So, I dont really understand everything, Your answer is little bit complicated for me.
How can I check the curve ? With dview ?
For the input of the vrf system / zone, for the moment, everything is "autosize" or defaut value

Alexis's avatar Alexis  ( 2018-08-29 08:39:52 -0500 )edit

What I typically do for performance curves is to plot the results in a spreadsheet. All you need to do is compare 1.136 multiplied by the VRF cooling capacity (look in the eio file) and see if it matches the manufacturers data at the rating condition of 19.44 indoor wet-bulb and 35 outdoor dry-bulb. If they don't match then the performance curve is suspect. Open your input file in a text editor (WordPad or other) and search for Cooling Capacity Ratio Modifier Function of Temperature Curve and find the name of the curve. Then search for that curve name and review the coefficients.

rraustad's avatar rraustad  ( 2018-08-29 08:45:36 -0500 )edit

So if I summarize : - I copy/paste in a excel sheet the cooling capacity and the temperature (dry and wet bulb) and make a curve
- I check the value of my cooling capacity at 19,44C and 35C
- I multiply these values per 1,136
- I compare with the manufacturers data -> this step, I dont really understand, I set a "default" VRF so I dont have manufacturers data

Am I wrong ?

Alexis's avatar Alexis  ( 2018-08-30 09:14:19 -0500 )edit

No, your not wrong. What you are simulating here is a VRF system that has 13.6% more capacity at the rating point then what is defined in the VRF system as the rated capacity. Since you are defaulting the performance I wouldn't worry about it too much. If you get more specific and want to simulate an actual VRF system where you do have manufacturers data, then you would want the CAPFT curve to output 1.0 at the rating point. You also may be using my curves from the VRF example file that I never went back and corrected.

rraustad's avatar rraustad  ( 2018-08-30 10:14:56 -0500 )edit

"You also may be using my curves from the VRF example file that I never went back and corrected." Which VRF example ? "HVACTemplate-5ZoneVRF" ? If I am not wrong, in E+, there is no link between a HVAC templates VRF system / zone and a curve

Alexis's avatar Alexis  ( 2018-09-03 19:58:41 -0500 )edit

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Asked: 2018-08-27 20:13:51 -0500

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Last updated: Aug 29 '18