Fan power accounting for a DOAS system with DCV

asked 2017-11-29 09:25:49 -0500

kbk78
591 ●1 ●8

updated 2017-11-30 11:38:37 -0500

It appears that DOAS system with DCV acts as a constant volume system and when the outdoor air is reduced the remaining air is just returned. The issue with this is that the fan energy remains constant when in reality you want it to reduce in response to reduced outside air requirement.

This question may be related to similar question but it does not solve the problem: https://unmethours.com/question/22140...

Also, this question suggests using a dual duct system. Would there be an additional energy penalties for using a dual duct system. Is there a better way of doing this:
https://unmethours.com/question/375/m...

Optionally, Is there a work around solution to properly account for the fan energy savings.

answered 2017-12-04 13:38:56 -0500

Annie Marston
4297 ●4 ●31 http://www.resustain.com

The work around I can think of is modelling the DOAS with a variable volume fan and putting a schedule into the fan object that represents the reduction in OA at each hour for the year. You could take this information from the model already run with the DCV. I am not sure but it might just work if you had the DCV with a DOAS system with a variable volume fan

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Thanks for your advice. Here is what appears to be working right:

Use VAV fan system for the DOAS.
Specify the demand control ventilation type as zone sum.
Use VAV no reheat for the zone terminal.
Specify the design specification outdoor object name in the zone terminal to activate control on outdoor air flow.
In the DesignSpecification:outdoorAir specify the occupancy schedule for the OA fraction schedule name.

The fan power does seem to follow the outdoor air in the hourly report with this.

kbk78 ( 2017-12-15 09:33:35 -0500 )edit

I’m sorry but I'm still confused about the same question. My doas outdoor air mass flow is a constant whole year as well as the doas fan power. I wonder if there any other trick to set the doas work with the indoor air demand? (I have already followed your suggest step) Thanks!

shellyhong ( 2018-10-21 08:23:34 -0500 )edit

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Fan power accounting for a DOAS system with DCV