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Modulate Flow Through Water-cooled VRF Condenser Inlet

asked 2015-07-13 16:34:11 -0600

pflaumingo's avatar

updated 2015-07-26 18:03:32 -0600

It looks like in EnergyPlus for water-cooled VRF that if there is a load on the AirConditioner:VariableRefrigerantFlow object then the water flow rate through the condenser inlet will be the full design flow rate. I understand that this is traditionally how most VRF systems work, however manufacturers (I know LG does this) are starting to modulate flow through the VRF condenser inlet. This allows for the pumps to turn down and the higher return water temperature from lower flow gets passed on as greater load on the cooling tower. Can anyone confirm that the EnergyPlus water-cooled VRF module will demand full flow for any load? If not, could you please correct me?

Moreover, if this is the case, does anyone have any decent ideas for how to model VRF condensing units that modulate flow through the condenser?

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The first part of this question has been confirmed on the EnergyPlus_Support Yahoo group and can be found here.

The second part of this question has yet to be answered, but I will keep it updated if I get anymore information from anywhere.

pflaumingo's avatar pflaumingo  ( 2015-07-14 17:19:15 -0600 )edit

I feel like your comment deserves to be an answer, even if it links to an offsite source. What do you think? Would you consider promoting to an answer?

Kyle Benne's avatar Kyle Benne  ( 2015-07-14 21:03:18 -0600 )edit

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answered 2015-07-15 10:17:03 -0600

Archmage's avatar

Yes, unfortunately constant flow requests on the condenser side is a widespread issue in many EnegyPlus component models, beyond just VRF.

The Pump:VariableSpeed object does have an optional input field for a Pump Flow Rate Schedule Name. The way plant works, the component will request its design flow rate but if plant cannot actually supply that flow rate then it will only get what it can get. So as a workaround, you could throttle what the pump can actually provide so that the VRF unit will be starved of flow and not get what it is requesting. You could either post process an initial run and use schedule file to control the pump by scheduling, or set up an EMS program to actuate that schedule during the run.

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Asked: 2015-07-13 16:34:11 -0600

Seen: 279 times

Last updated: Jul 15 '15