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HVAC Control Logic

asked 2015-09-17 14:25:36 -0600

CY_BH gravatar image

updated 2017-05-17 12:33:56 -0600

is it possible to model a control logic as follows in either OpenStudio or DesignBuilder (I assume it's the same logic since using E+):

  • if outdoor air temp is below 10C, the chiller is shut down;
  • if outdoor air temp is above 10C, the chiller is used to provide 13C chilled water

in DesignBuilder, the "setpoint manager" has only 2 types - "scheduled" or "outdoor air reset" in the water loop. when using "outdoor air reset", only setpoint at outdoor low temp and high temp can be defined. How to achieve the control logic above?

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answered 2015-09-17 14:40:58 -0600

I would take a look at the following post, which provides some general guidance for hydronic loop operation.

Control Strategies for Plant Loops

To accomplish the situation you have described above (in E+), one would use 'PlantEquipmentOperationSchemes' to enable/disable equipment under certain conditions (lockout chiller operation for OA temperatures below 10C in your scenario). I can't speak to DesignBuilder, but OpenStudio 1.8.0 does not expose the E+ operation Scheme 'PlantEquipmentOperation:OutdoorDryBulb' needed to lockout chiller operation based on OA dry bulb.

Once the equipment is enabled, a typical scheduled SetpointManager will establish the temperature setpoints of the active loop (13C in your scenario).

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answered 2015-09-17 16:47:45 -0600

updated 2015-09-17 16:55:59 -0600

I think what you want is a combo of a SetpointManager (tells the equipment what the setpoint should be while it is running) and an Operation Scheme (defines when particular equipment runs).

  1. On the chilled water loop supply outlet node, put a SetpointManager:Scheduled with a 13C temp schedule
  2. Add a `PlantEquipmentOperationOutdoorDryBulb' to the chilled water loop. This object is available in OS 1.8.5 and onward. Because it is not yet available through the GUI, you'll need to add it via a measure.

Here is some code that shows how to do it:

chiller_op_scheme = OpenStudio::Model::PlantEquipmentOperationOutdoorDryBulb.new(model)
chiller_op_scheme.setName('Operate Chiller Above 13C')
chiller_op_scheme.addEquipment(lead_chiller)
chiller_op_scheme.addLoadRange(13.0,[]) # No equipment operates from -50C to 13C
chiller_op_scheme.addLoadRange(70.0,[lead_chiller]) # Chiller operates from 13C to 70
chilled_plant.setPrimaryPlantEquipmentOperationScheme(chiller_op_scheme)
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Asked: 2015-09-17 14:25:36 -0600

Seen: 361 times

Last updated: Sep 17 '15