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HHW pump running even when boiler is off

asked 2021-04-13 16:06:35 -0500

updated 2021-04-14 19:56:35 -0500

I am running into an issue, in OpenStudio, where the constant speed pump (intermittent control) in my HHW plant runs even when the boiler is not firing. As a result, the pump runs (cycling somewhat unpredictably) throughout the summer months, causing the HHW loop to continuously heat up - I assume due to waste heat from the pump.

I don't fully understand how the controls work by default, but I would assume that if there is a demand for heating at a coil, the pump runs, and then the boiler fires to maintain loop temperature (?). This would mean that something is telling the pump that there is a demand for heating; however, after assessing zone temperature, I can't see why that would be. Is there any basic troubleshooting around this issue (e.g. don't set the controls to intermittent)? Or, as a worst case scenario, is there some way I can force the pump off during summer months using an availability manager?


Hot Water Loop Plot

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answered 2021-04-13 17:13:55 -0500

The availability manager for your HHW plant is specified in the Plantloop object. You can modify the availability managers to turn off the entire plant (including pumps). Alternatively, you can modify the availability managers controlling the airside systems, as I suspect this summer cycling is caused by airside equipment calling for heating during that period.

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Thank you. You're right - it is to do with airside. Looking at it more closely, I see that during summer the pump is only operating overnight (likely when outdoor air temps are too low), but is off, as expected, during the day.

jbatt's avatar jbatt  ( 2021-04-14 08:07:03 -0500 )edit

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Asked: 2021-04-13 16:06:35 -0500

Seen: 166 times

Last updated: Apr 14 '21