[Equest-users] How intermittent fan operation works

[Nathan Miller]

Assuming you have another system/method responsible for providing ventilation  to the units, I’d model it more or less the way you have, but I’m not clear from your description that you have all the settings correct for a cycle-on-demand system. In the climate zones I usually model in there would be hours where the fan does not run at all, but that’s obviously highly depending on T-stat settins and ambient conditions.


  1.  Coolin fan schedule should be something that is all-zeros (meaning the system never HAS to run). This essentially means the unit thinks it is in “night/unoccupied” mode all the time.
  2.  Select Cycling fan control, and intermittent operation (looks like you did that)
  3.  Night Cycle Control should be “Cycle On Any”. Since you already told the system it is ALWAYS in night-mode (meaning it’s not forced to run), then fan will remain off until temps in the space drift out of dead-band mode, and then system will turn on fans and condition the space until temps are satisfied, and then shut off agin. With settings above, partial hour fan operation is allowed.

You said you want to know if you can “create schedule to restrict cycle off on sub-hourly”. I’m not clear what you mean. If you want the fan to be prevented from only running for partial hour you can use Continuous instead of Intermittent Indoor Fan Mode.

Nathan Miller, PE, LEED AP BD+C – Mechanical Engineer/Senior Energy Analyst
RUSHING | O 206-285-7100 | C 207-650-3942
www.rushingco.com<http://www.rushingco.com/>

From: Equest-users <equest-users-bounces at lists.onebuilding.org> On Behalf Of Mayank Bhatnagar via Equest-users
Sent: Thursday, April 4, 2019 9:31 AM
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] How intermittent fan operation works

Dear all,

I am working on a residential project in which the indoor units fan is cycling with load. For this, I have modelled as PSZ HP (as designed) and changed indoor fan mode from continuous to intermittent operation. My first question is whether it is correct to model intermittent for system with cycling or should I model different system.

Additionally, as per definition of intermittent operation : The indoor fan operates as in CONTINUOUS, but only for  that fraction of the hour required for space heating or cooling. I want to check how many hours it is cycling as I assumed that the eQUEST is working on hourly timestep. By extracting hourly report of fan cycle ON for continuous and intermittent operation, the hourly profiles are:
[image.png]
From the figure, it appears that fan is running maximum 60% of an hour in intermittent operation whereas 100% in continuous. As it is providing results in sub-hourly basis, is it possible to create schedule to restrict cycle off on sub-hourly?

Thank you.

Regards,
Mayank Bhatnagar


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