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Zero cooling electricity in Energy+

asked 2020-06-24 02:00:31 -0500

SJB gravatar image

updated 2020-06-24 08:57:08 -0500

i'm trying to calibrate a building model using jEPlus. i've modeled the building in DesignBuilder and used a "Cooling System: Default" with "Cooling system seasonal CoP: 2.1" for its cooling system but i can not find where the COP is defined in the .idf file. also when running the project in the jEPlus the "End Uses" table in .csv file show zero for cooling electricity. however the "District Cooling" has a value and if divide it by CoP=2.1 it would be exactly the value which DesignBuilder reports for "Cooling (Electricity)". i need to define a parameter for CoP in jEPlus so i can calibrate it. thank you in advance!

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answered 2020-06-26 08:51:44 -0500

updated 2020-06-26 08:52:19 -0500

@Yi Zhang is correct that the COP you set in DesignBuilder is only used to calculate electricity use resulting from meeting the cooling loads. However, the COP that you set in DesignBuilder should appear in the generated EnergyPlus model. The District Cooling object that meets cooling loads doesn't have an input field for COP or efficiency, that is actually set in the District Cooling COP input field of the Environmental Impact Factors object. That is the COP parameter you should define in jEPlus to represent cooling system efficiency.

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Hi Aaron, thanks for the correction!

Yi Zhang gravatar imageYi Zhang ( 2020-06-26 14:23:45 -0500 )edit

Hi, thanks a lot. I did what you said. Although I'm not sure if I did it right but it solved my problem. Since the cooling electricity is zero I decided to calculate it manually in the results but still couldn't find the COP in the reports. I found that within the "Site to Source Energy Conversion Factors" table, the "District Cooling" factor multiplied by the COP gives the "Electricity" factor. I don't know where the "District Cooling" factor comes from, it's nowhere in idf but I'm able to do the calibration anyway and that's not my problem right now. :) Thanks again!

SJB gravatar imageSJB ( 2020-06-27 02:47:22 -0500 )edit

Because you are using simple HVAC in DesignBuilder, that will use the Ideal loads air system in EnergyPlus and all cooling energy use will only be measured as "District Cooling". If you want to have cooling energy use measured as "Electric" by EnergyPlus, you will need to use detailed HVAC in DesignBuilder instead.

Aaron Boranian gravatar imageAaron Boranian ( 2020-06-28 11:28:00 -0500 )edit

The "Site to Source Energy Conversion Factors" table of the Annual Building Utility Performance Summary shows how much energy is used at the source (utility power plant, e.g.) in order to consume that resource at the site (electricity used by building, e.g.). The Electric factor should be independent of District Cooling COP, since it applies to all components that use electricity (HVAC, lighting, receptacles, etc.).

Aaron Boranian gravatar imageAaron Boranian ( 2020-06-28 11:31:51 -0500 )edit

answered 2020-06-26 06:47:44 -0500

Yi Zhang gravatar image

updated 2020-06-26 14:27:35 -0500

If you are using simple HVAC in DesignBuilder, the COP value is just a conversion factor DB uses in its own post-processing to calculate electricity use from district cooling result of the ideal-loads system. It is not used anywhere in the generated EnergyPlus model.

Since it doesn't affect the model in any way, it doesn't really make sense to have it as a parameter in jEPlus. -- See Aaron's answer

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hi, thank you for your help. it seems that DB works exactly as you said

SJB gravatar imageSJB ( 2020-06-27 02:30:28 -0500 )edit

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Asked: 2020-06-24 02:00:31 -0500

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Last updated: Jun 26