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Condenser loop temperatures out of deadband

asked 2015-04-17 13:37:31 -0500

pflaumingo gravatar image

How would you force a strict temperature deadband on a CWLoop in EnergyPlus? I have a dualsetpoint manager on the outlet of the supply of my CWloop, a boiler to handle the heating load and a cooling tower for the cooling load, however it only maintains the upper temperature limit when there is a load on the building. When there is no load the temperature drifts upwards as can be seen in the image - the peaks are occurring outside of operating hours when there is no cooling load being demanded. The cooling towers are able to bring the loop down to the desired temperature (26.7C), but this is just a simplified 5 zone WSHP model and I have a much larger project where the temperature of the loop is allowed to get too hot when there is no load and the cooling towers can no longer bring it back to the desired temperature.

image description

Is it something to do with the plantloop availability? my operation scheme or my setpoint managers?

I'm also not sure what is adding the load to the loop so if anyone has any insight here that would be very helpful. Is it to do with delayed heat rejection from the WSHPs condensing to the CW loop when there is no cooling demand in the building?

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Did you try PlantEquipmentOperation:ComponentSetpoint plant operation scheme? What is the pump control type continuous or intermittent?

Chandan Sharma gravatar image Chandan Sharma  ( 2015-04-17 21:05:15 -0500 )edit

@Chandan Sharma, I have used the ComponentSetpoint plant operation scheme as well as specifying a scheme for the heating load to be controlled by the boiler and cooling load by the cooling tower but I still get the same result. It only returns to the set point when there is a cooling demand from the equipment on the demand side of the loop. Like I said, it's fine for a simplified model but I have a building with a large condenser loop and in the summer when the loop is starting off hot and there is a large cooling startup load in the morning then the equipment can't meet the set point.

pflaumingo gravatar image pflaumingo  ( 2015-04-18 14:29:02 -0500 )edit

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answered 2015-04-18 10:36:28 -0500

Did you check there was flow in your loop or over your cooling tower at the times when the temperature was high, often there is no actual flow.

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Yup, that's part of my issue. My supply side equipment stops running as soon as there is no cooling load on the demand side. I tried putting a dummy cooling load of 1W 24 hours of the day using the load profile object and that fixes the problem, but it is only a short term solution and I can't figure out why the loop is allowed to get so hot when there is no load on the building.

pflaumingo gravatar image pflaumingo  ( 2015-04-18 14:31:15 -0500 )edit

@Annie Marston, you were right. My pumps were allowed to turn down to 0 flow and looking through the engineering reference, using the dual deadband will only see a load provided that the mass flow rate (mdot) is greater than 0. I adjusted my minimum flow and it worked fine. Thanks!

pflaumingo gravatar image pflaumingo  ( 2015-04-18 16:43:21 -0500 )edit

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Asked: 2015-04-17 13:37:31 -0500

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Last updated: Apr 18 '15