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Fans consumption too high (OpenStudio)

asked 2014-11-20 15:25:03 -0500

nicolas_hadjip's avatar

updated 2014-11-21 08:46:14 -0500

For some reason the electricity consumption due to the fans in my model is more than 50% of my total electricity consumption. This is really weird since I do not even know where the fans are used. I have not included any fans in my model. The only fan present is in the HVAC system. Any suggestions?

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If you can provide a link to the model it will help us diagnose the problem.

Kyle Benne's avatar Kyle Benne  ( 2014-11-20 15:31:07 -0500 )edit

how can I provide a link? sorry, it is the first time I am using this forum

nicolas_hadjip's avatar nicolas_hadjip  ( 2014-11-20 15:44:35 -0500 )edit

There is not a specific file attachment system provided by the website. If you can provide a Drop Box or similar (gDrive) link that would be easiest.

Kyle Benne's avatar Kyle Benne  ( 2014-11-20 15:50:13 -0500 )edit

ok thanks. Here is the link with my .osm file.

nicolas_hadjip's avatar nicolas_hadjip  ( 2014-11-20 16:01:01 -0500 )edit

Got it. I see this is a large school with many spaces (maybe over 100?), but there are only a handful of zones connected to one giant VAV air system. What is your zoning strategy? You might consider rezoning and break up that huge system to something more realistic first. Or just turn on ideal air loads / zone equipment if you are not at the stage where you want to model the HVAC in more detail.

I was looking to see if maybe you didn't assign any loads, making the fan energy proportionally large, but it appears you have things setup with a default template and there are in fact loads.

Kyle Benne's avatar Kyle Benne  ( 2014-11-20 16:26:36 -0500 )edit

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answered 2014-11-20 21:09:56 -0500

The model has many spaces which are lumped into 4 thermal zones. All 4 zones are served by a single, very large VAV system. This VAV system:

  1. Has no Demand Control Ventilation (DCV)
  2. Has no max OA fraction schedule (to close the OA damper at night)
  3. Has a low fan efficiency (~0.4)

This combination of controls likely means that you are bringing in very high (design day) amounts of Outdoor Air 24/7/365, and you are moving it with a low efficiency fan...resulting in higher than what you'd expect for fan energy. I'd recommend zoning the model into smaller zones and perhaps (unless this is an existing building) splitting the zones onto multiple VAV systems based on their loads.

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thank you very much Andrew, your recommendations solved my problem! appreciated!

nicolas_hadjip's avatar nicolas_hadjip  ( 2014-11-21 05:11:11 -0500 )edit

@nicolas_hadjip, which schedule did you choose for max fraction oa schedule name?

keb's avatar keb  ( 2014-12-30 15:43:43 -0500 )edit

answered 2014-11-20 17:57:18 -0500

Compare your end-use breakdown per area vs AEDG or other similar reference point. Maybe the fans are normal, and the other end-uses are too low?

Or more likely, confirm with that your other end-uses are in the proper range so that you know your are troubleshooting the correct equipment.

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Asked: 2014-11-20 15:25:03 -0500

Seen: 723 times

Last updated: Nov 20 '14