Water Source VRF System Curve

asked 2017-06-07 13:25:47 -0500

970 ●1 ●8

I created VRF system from OS then export the IDF and changed the condenser type as water cooled, condenser inlet and outlet node name is updated as well.

However, when I try to update the performance curve, eg Cooling/Heating Capacity Ratio Modifier Function of High/Low Temperature Curve or Cooling/Heating Energy Input Ratio Modifier Function of HIgh/Low Ratio curve, those functions require coil entering wet bulb temp and condenser air dry-bulb temp as variables. For condenser type:water cooled, it is condenser water entering temp available not condenser airy dry-bulb temp.

How can I update the performance curve since they require different independent variables ? Will the E+ automatically assume it is condenser water entering temp if water cool is selected ? image description

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answered 2017-06-07 14:51:07 -0500

Aaron Boranian

13830 ●76 ●24 http://bigladdersoftware.com/

You should use the performance curve coefficients for condenser water entering temperature if you are modeling a water-cooled condenser.

From the Input-Output Reference for the AirConditioner:VariableRefrigerantFlow object:

image description

From the Engineering Reference for the same object: image description

That information leads me to believe that EnergyPlus has the capability to model water-cooled condensers for VRF systems. I agree with you that the documentation for the Cooling Capacity Ratio Modifier Function of Low Temperature Curve Name input field you referenced is not clear and makes it seem like it will only use outdoor air dry-bulb. However, after digging around in the source code, I am confident in telling you that the VRF condenser inlet will use the water node you assign and not outdoor air dry-bulb IF you have specified WaterCooled in the Condenser Type input field.

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@Aaron Boranian Thank you very much, Aaron !

BL ( 2017-06-07 14:54:58 -0500 )edit

I have been working on a water-cooled VRF model in E+ and finding issues with heating at low outdoor air temperatures. It seems like the system should be using the condenser water node, but the heating capacity is decreases significantly at low OA temps. Modifying the capacity curve does not seem to help. Any ideas?