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Building Performance Curves for Coil:Cooling:DX:VariableSpeed

asked 2017-12-22 13:57:19 -0600

RobSalcido's avatar

updated 2017-12-23 13:08:12 -0600


I am trying to build performance curves for the speeds of a variable speed air conditioner. Specifically, for the Field: Speed <x> Total Cooling Capacity Function of Temperature Curve Name, the documentation states that the curve must be normalized to the cooling capacity at Speed<x> from the Reference Unit data, and have the value of 1.0 at the rating point.

Does anyone have guidance on how to create this curve normalized to the cooling capacity at said speed? This will help me with the remaining curves as well.

As a reference, here is the documentation for this curve:

This alpha field defines the name of a bi-quadratic performance curve for Speed <x> (ref: Performance Curves) that parameterizes the variation of the gross total cooling capacity as a function of the both the indoor wet-bulb and source side entering air temperature, from the Reference Unit. The output of this curve is multiplied by the gross rated total cooling capacity at the speed to give the gross total cooling capacity at specific temperature operating conditions (i.e., at an indoor air wet-bulb temperature or outdoor entering air temperature different from the rating point temperature). It should be noted that the curve is normalized to the cooling capacity at Speed<x> from the Reference Unit data, and have the value of 1.0 at the rating point.

Thank you,

Rob Salcido

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answered 2017-12-22 15:00:46 -0600

Jon W's avatar

Hi Rob,

I've developed many of the performance curves utilized by BEopt EnergyPlus for central, variable-speed air conditioners and mini-split heat pumps. However before I can help answer your question, I need to know what does the data look like for the unit you're trying to model. Do you have expanded performance data at specific speeds?

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Hi Jon - thanks for your reply.

I do not yet have any performance data, but have made a request. Is there specific data I should request?

In the meantime, I am hoping to find practice data to learn the normilization process for these curves so I can be ready when I do get the performance data.


RobSalcido's avatar RobSalcido  ( 2017-12-22 16:55:51 -0600 )edit

The EnergyPlus documentation on the cooling coil inputs is pretty good. You can also consult a report from several years ago that outlines the process for determining performance curve inputs using manufacturer data. link text. The crux is performing a linear regression on the data. The data provided by the manufacturer will likely be net cooling performance. You'll first need to convert the data to gross performance using fan data and then normalize it. The linear regression for the biquadratic coefficients can be performed in Excel using LINEST

Jon W's avatar Jon W  ( 2018-01-02 09:52:55 -0600 )edit

You'll need data for a minimum of two speeds (minimum and maximum) from the manufacturer.

The end of Section 2.3 in the referenced NREL report above briefly describes the steps to normalize the data.

Hope that helps some. After giving Section 2 of that report a quick read, post additional questions. Jon

Jon W's avatar Jon W  ( 2018-01-02 09:55:59 -0600 )edit

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Asked: 2017-12-22 13:57:19 -0600

Seen: 623 times

Last updated: Dec 22 '17