economizer (controller:outdoorair) operation based on cooling signal from thermostat

[JanghyunJK]

Issue overview

• I always thought economizers operate only when the zone is in (or thermostat is calling) cooling mode. Below is one of the economizer manual found from the web.

• and lately I have noticed that that might not be the case for EP's economizer (controller:outdoorair).
• Maybe I need to know the reason why it was implemented in that way.
• But also would like to know if this could be a potential fix to the EP.

Details

• I've been working on modeling stock of buildings (ComStock) that reflect some realistic variability.

• One of the variabilities is overnight operation and we have buildings (=models) that ventilates 24/7.

  • so fan can run overnight
  • ventilation can happen overnight as well

• for a system without economizer, the above case only introduces minimum OA requirement overnight. so, basically OA damper is fixed to minimum position as shown below.

• but when we add an economizer to this same model, then economizer basically opens up OA (because OAT can be cold at night in many regions) even though zones are not calling for any cooling.

• the behavior that we want to see eventually after adding an economizer is to let economizer introduce (1) minimum OA when no cooling is called overnight but (2) do economizing when cooling is called overnight.

Checklist

Add to this list or remove from it as applicable. This is a simple templated set of guidelines.

• [X] Defect file added: link to a zip file including two idfs (with and without issue) and one weather file
• [ ] Ticket added to Pivotal for defect (development team task)
• [ ] Pull request created (the pull request will have additional tasks related to reviewing changes that fix this defect)

[rraustad]

@JanghyunJK in EP the economizer operates to minimize the need for cooling whether or not the cooling coil is on. The economizer is disabled at the point where heating is required. To allow economizer only when the cooling coil is active would hold the zone temperature near the cooling set point temperature. EP allows the zone temperature to float down to the zone heating set point temperature when possible further avoiding cooling operation. If there are economizers available that disable economizer operation when the cooling coil is off then that may be an area for improvement.

[mjwitte]

@JanghyunJK Please share an idf file that shows this. Economizer operation is controlled with a setpoint manager on the mixed air node. If this is a single zone system, it may be possible to achieve this control using available inputs.

[JanghyunJK]

@rraustad thanks for the prompt reply. The first image I attached above is a specsheet/manual from Honeywell's Jade economizer. I believe the table is showing the controls that you mentioned. For example, one of the signals that enables economizing is the thermostat cooling signal (Y1-I, Y2-I). If these are off then the damper is either in min position (occupied mode) or closed (unoccupied mode).

@mjwitte I added a link to my box in the above post. Let me know if you can't see those files! again, thanks for the prompt reply!

[JanghyunJK]

it may be possible to achieve this control using available inputs.

@mjwitte I'd actually love to know what kind of options I have for this!!!