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VAV system not meeting setpoints

asked 2017-09-08 02:49:44 -0500

Laurence gravatar image

updated 2017-09-08 08:19:27 -0500

Hi all

I am new to EnergyPlus, I have a VAV system with reheat to perimeter and a couple of internal zones. After running the model we have found there is currently no heating being done by the reheat coils for any of the VAVs connected to the AHUs. This is causing a unmet hours for some zones with AHUs that service perimeter and internal zones. The AHU’s overheat the space and only keep 1 zone at the heating setpoint.

We are able to reduce the unmet hours by effectively turning off the heating ciol at the AHU and letting the reheat coils heat the zones however this is not desirable. We think it might be an issue with the cooling coil setpoint reset type which is currently set to warmest.

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What are the maximum and minimum setpoint temperatures you have on the Setpoint Manager Warmest object? And where have you located the setpoint manager object in the air loop?

mdahlhausen gravatar imagemdahlhausen ( 2017-09-11 16:46:03 -0500 )edit

Hi Matthew, the max = 18C, min = 10C and the setpoint manager is set to at the supply fan of each AHU. The thermostat temperatures for the office that I am modelling is between 21-24C between 07-18. Cheers

Laurence gravatar imageLaurence ( 2017-09-11 19:42:30 -0500 )edit

Those values seem reasonable. Perhaps it is not an issue with air-side. Does the sizing on your VAV terminals appear ok, and you've checked the temperature setpoint and availability schedules on the heating loop that supplies them?

mdahlhausen gravatar imagemdahlhausen ( 2017-09-12 12:32:13 -0500 )edit

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answered 2017-09-16 21:12:37 -0500

You say there is currently no heating being done by the reheat coils and that We are able to reduce the unmet hours by effectively turning off the heating coil at the AHU. So it sounds as if the main air loop heating coil is controlled to a set point temperature that is too high. You also mention the cooling coil set point manager as the cause. Are you controlling the heating and cooling coil with the same set point manager? The main air loop coils can be controlled using the same set point manger but more likely will be controlled using two different set point managers. The mixed air set point manger should additionally be used for draw through systems where the fan is downstream of the coils and you need to account for fan heat.

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Asked: 2017-09-08 02:49:44 -0500

Seen: 111 times

Last updated: Sep 16