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How are modelers getting transcritical compressor capacity coefficients when modeling CO2 transcritical booster systems?

asked 2024-11-25 15:36:15 -0600

slaflamme's avatar

updated 2024-11-25 15:42:23 -0600

I can calculate transcritical compressor capacity and performance at specific points, but I haven't been able to get the 10 capacity coefficients for transcritical compressors operating in transcritical mode for compressors I'm modeling for use in OpenStudio. I reached out to Bitzer and was told they're not yet available. Does anyone have a solution for this?

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Just a remark that openstudio application does not support directly CO2 transcritical systems nor gascoolers and you will need a measure to add them

Petros Dalavouras's avatar Petros Dalavouras  ( 2024-11-29 03:29:36 -0600 )edit

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answered 2024-11-26 04:28:19 -0600

PmP's avatar

updated 2024-11-26 04:36:43 -0600

I understand by your phrasing that you want a way to model an specific CO2 compressor. But first, if any industry standard compressor would be enough for your purposes, there are hundreds of those curves and coefficients already in the EnergyPlus datasets. Here is a link for the gitbhub .idf file but it is present in the "datasets" folder of any EnergyPlus download. I personally used some in simulations and they perform as standards relatively well.

If an specific compressor is needed for you, I suggest two approaches: A hard one and an easier one.

The hard one

You need all of these curves and you said you can get "Capacity and performance and specific points". If that is because you have access to a compressor map software, then you could get the 11ish points needed for each cuve in subcritical and transcritical operation, then use a curvefitting tool to get the exact parameters you need that are in the link to the documentation.

The easy one

Most refrigeration systems do not change the suction (evaporation) temperature, thus for simulation purposes the only dependency of power and capacity is to outside temperature (Which directly correlates to GasCooler pressure and enthalpy). At the same time the COP has the relationship between power and capacity implicit in its value.

This means that you could get a simulation done with any compresor from the dataset and YOUR operating conditions (Superheat, subcooling, evaporation temperature) and then plot COP vs outside temperature. Then compare it with your compressor COP vs Outside temp. and adjust the coefficients manually knowing that you only care about those relating to outside variables, not suction variables.

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Asked: 2024-11-25 15:36:15 -0600

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Last updated: Nov 26