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Water-Cooled VRF Priority

asked 2019-02-04 17:39:21 -0600

avril14 gravatar image

I managed to set up a water-cooled VRF system in Open Studio, but I'm having a problem with the equipment priority order. The system has a DOAS which should be providing 65F OA at all times, and all additional heating and cooling should be coming from the VRF system. The VRF is using a ground source condenser loop.

The problem is that right now the DOAS is trying to provide all the heating. I tried to reorder the systems, but since the VRF system isn't a plant loop I can't give it priority. Does anyone know if there's a way around this? IDF file here. Thank you!

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answered 2019-02-05 11:39:08 -0600

For each zone, make sure that the VRF terminal units are listed as the top priority in the zone ZoneHVAC:EquipmentList object.

By default, OpenStudio sets priority in the order that the systems are added. Check to make sure that the VRF terminal units are listed as the first piece of zone HVAC equipment in your zone above the DOAS diffuser.

I'm not sure if there is a way you can change the priority in the app directly other than removing and re-adding equipment, but you can open the .osm in a text editor and manually swap the hash ids:

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The equipment is in the right order but it's still using the DOAS first. I think because of the order of the plant loops. I had to create separate loops for DOAS heating and DOAS cooling connected to the GSHP loop with water-to-water heat pump objects. I put the GSHP loop first in the Plant Equipment List, but since the VRF system isn't actually a plant loop, I can't figure out how to force it to operate before the DOAS loops. It's possible I'm way off track, but that seems like what's happening. I hope that makes sense, I can't add a screenshot to a comment.

avril14 gravatar imageavril14 ( 2019-02-06 11:50:06 -0600 )edit

The order of the plant equipment shouldn't impact the order of zone equipment. It's likely there is some reason your VRF system isn't meeting the load, and the remaining load is being met by the DOAS. Check your zone design sizing information for the zone and VRF terminal units.

mdahlhausen gravatar imagemdahlhausen ( 2019-02-06 12:07:14 -0600 )edit

I tried testing a few things and it seems like you're right. Thank you! Now I'll just have to figure out what's wrong with my VRF...

avril14 gravatar imageavril14 ( 2019-02-06 13:27:04 -0600 )edit

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Asked: 2019-02-04 17:39:21 -0600

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Last updated: Feb 05