[Equest-users] How intermittent fan operation works

[Mayank Bhatnagar]

Dear Nathan,

Thank you for quick response.

The project is a residential building and the ventilation is through the
system. To meet the ventilation requirement with *intermittent* operation
mentioned in *ASHRAE 62.2-2010,* the system need to run atleast 30 minutes
in each hour. From this the question is come for sub-hourly operation.

I am thinking of an approximation which I want to put for expert opinion:
A PVVT system can be modelled with minimum air flow ratio to 50% with
continuous fan to approximate cycling and minimum operation time for
ventilation.  The reduction of low speed based on cooling/ heating load can
be similar to intermittent operation where the system is running for
fractions of an hour (similar pattern as in intermittent operation in my
earlier mail).

Please let me know your thoughts and/ or other work around.

Thank you.

Regards,
Mayank Bhatnagar

On Thu, Apr 4, 2019, 7:29 PM Nathan Miller <nathanm at rushingco.com> wrote:

> 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: 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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