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Override Node Temperature using EMS

asked 2015-11-03 17:31:52 -0500

To your knowledge, is it possible to override the temperature at a particular node using an EMS program?

I'm using an EMS to calculate duct losses to plenum zones. Once I calculate the losses, I recalculate the air supply temperature (to take into account the losses to the plenum) and use an OtherEquipment object to add a load to the conditioned zone that represent the difference in the air supply temperature. This works but not in the case of a VAV system with reheat. Ideally I would like to instead adding a load using OtherEquipment override the air supply temperature, which would be more correct.

My EDD file only contains Temperature Setpoint Actuators. Am I missing something?

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answered 2015-11-04 03:04:20 -0500

Archmage's avatar

System air nodes created by OutdoorAir:Node (or OutdoorAir:NodeList) input objects do have actuators for setting node conditions. AirTerminal:SingleDuct:UserDefined could be used for this application, but it is fairly advanced and the OtherEquipment approach you have seems simpler.

I am not sure why you say OtherEquipment doesn't work for the VAV. If it is because of varying air flow, put an EMS sensor on the system node mass flow rate and use that in your duct loss model. If it is because you are concerned the reheat coil will actually use less hot water with warmer supply air, I am not sure that is a problem because the reheat coil control will account for heating provided by OtherEquipment. The coil leaving water temperature may be a bit different but that should not really impact boiler energy consumption much.

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You are right, I shouldn't have said that it doesn't work... It's just that it doesn't work the way I'd like it to!

Yes, I was concerned by the fact that the reheat coil would not behave exactly the same way as it does by adding a load to the zone but as you said, the difference, if there is one, would be small. So I'm going to keep my EMS the way it is then. Thanks!

Jeremy's avatar Jeremy  ( 2015-11-04 10:27:52 -0500 )edit

answered 2015-11-03 20:27:36 -0500

updated 2015-11-03 20:30:06 -0500

It is not possible to override the room air temperatures (or other status parameters, such as room air humidity ratio, room CO2 concentrations) at a particular node using an EMS program.

The room air temperatures are included in the heat balance equations, which are ordinary differential equations. In the solver, you need not only the temperature values, but also the derivatives. Most of the system nodes are somehow connected to the room air temperatures. So simply changing the status parameters is not a option in EMS.

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Asked: 2015-11-03 17:31:52 -0500

Seen: 346 times

Last updated: Nov 04 '15