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eQuest DOAS Supply temperature as function of outside air

asked 2014-09-22 12:36:45 -0500

updated 2017-05-17 12:43:41 -0500

I'm modeling a DOAS system in eQuest, and the HVAC control sequence basically calls for delivering 55°F in cooling mode and 70°F in heating mode. The heating/cooling mode is dictated by outside air temperature. This is basically in order to deliver "temperature-neutral" air to the subsystems (and a few corridors with simple ventilation grilles) that are only going to handle the thermal load of the space, and not the outside air load (handled by DOAS).

In E+ it's a pretty simple task, but here I've been struggling on how to properly do this in eQuest.

Right now I've got a PSZ system with a control zone beeing a "dummy zone" for which I've assigned a cooling schedule at constant 55°F and a heating schedule at constant 70°F. But the hourly output indicates that it's basically always providing roughly 62.5°F, so the average of my cooling and heating setpoints.

I've tried multiple ways, and read through the archives of the different mailing lists, but I didn't find a working answer.

Basically, is there a way to model either of these two scenarios in eQuest for a DOAS system? (aside from manually creating an annual schedule that would turn heating or cooling off.)

Midpoint controller: Midpoint controller

Hysteresis controller: Hysteresis controller

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answered 2014-09-23 09:53:47 -0500

adam's avatar

Have you tried using the Reset schedule? I believe you will need to switch to a packaged VAV for this to work. If you want to model a constant speed fan you can use the fan control option to for the VAV to Constant Volume.

For the SAT reset:

  1. Airside parameters screen -->Cooling Tab --> "Cool Control" = Reset.
  2. Use the library to find a default reset schedule from the "starting points" family. (should be called "Schedule RESET-TEMP")
  3. Open and edit the schedule
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I've tried using the reset schedule indeed (it was one of the first things I tried to do). You need to move away from a PSZ to do that, which I wasn't feeling comfortable with, having seen that this is the system commonly used for a DOAS. I've tried to switch to PMZ with reset and then PVAVS with reset, but this isn't working, the results are clearly wrong (I'm not getting the temperature I should, and the total heating consumption is wrong also). Have you had success modeling a DOAS using this method?

Julien Marrec's avatar Julien Marrec  ( 2014-09-23 11:00:14 -0500 )edit

@adam, I figured it out. You have everything right. PVAVS is fine. Cool control to reset, then build a reset schedule. For heating, it is critical to have "HEAT-SET-T" to be 70°F though (and have a heat source obviously). Set SYSTEM:MIN-OUTSIDE-AIR to 1 to be 100% OA and MIN-FLOW-RATIO to 1 to model constant speed. It'd be great to include those points in your answer, maybe a couple of screenshots (I would post a detailed answer myself but you deserve the karma points...)

Julien Marrec's avatar Julien Marrec  ( 2014-10-03 04:26:42 -0500 )edit

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Asked: 2014-09-22 12:36:45 -0500

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Last updated: Sep 24 '14