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Condenser Loop - Pump:VariableSpeed always running

asked 2018-11-06 15:25:14 -0500

Abarker gravatar image

updated 2018-11-06 20:17:34 -0500

Hi everyone,

I've seen similar questions asked here but haven't found the answer to what I'm looking for.

Why would a variable speed pump run constantly throughout the year on a condenser loop, regardless of the load? I'm in a heating dominated climate so would expect condenser loop pump energy to be 0 in the winter.
Looking at monthly reports, the chiller, variable speed chilled water pump, and cooling tower all show this trend (varying with load, with much less or no energy in heating monthd), yet the condenser pump maintains the same flow throughout the year.

Pump control type is 'intermittent' Chiller flow mode is 'not modulated' Cooling tower is variable speed The design water flow rate of the cooling tower and its respective pump are hard sized and very similar to each other.

Any insights are appreciated.

For the record, eQuest does the same thing and I have always been bothered by it as I know this is not how this system operates in reality.

Thanks in advance,

Adam

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A quick review of the source code for Chiller:Electric:EIR shows that the condenser water flow rate is set to the max value whenever the chiller is operating. The chiller flow mode only impacts the evaporator flow rate. I don't see any explicit mention in the Input Output Reference or the Engineering Reference stating that the condenser flow rate will be constant. I don't know why.

MJWitte gravatar imageMJWitte ( 2018-11-07 20:25:59 -0500 )edit

Thank you for looking into it. It seems to go beyond that, with the condenser pump running at full flow rate even when the chiller is not operating (though, it is available at all times), e.g. throughout the winter.

Abarker gravatar imageAbarker ( 2018-11-15 15:01:44 -0500 )edit

If you'd like to share your idf, I'll use it to post an issue. Either link it here, or send to the helpdesk at energyplus-support@gard.com (please reference this unmethours post).

MJWitte gravatar imageMJWitte ( 2018-11-16 16:39:27 -0500 )edit

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answered 2018-12-26 16:56:33 -0500

Looking at the hourly output for the chiller and the pumps, the condenser pump only runs when the chiller operates, which does happen throughout the year. The chiller (Chiller:Electric:EIR) condenser flow rate is the full flow rate whenever the chiller operates, regardless of load.

I have posted new issue 7111 to fix this or add a new option if there is a reason to keep this mode (variable evaporator flow with constant condenser flow).

Reference helpdesk ticket 13133.

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Asked: 2018-11-06 15:25:14 -0500

Seen: 94 times

Last updated: Dec 26 '18