[Bldg-sim] VAV Operation Question

[Jim Dirkes]

Jacob,
The key here is that in order for one zone to get cooled at night, its fan
must operate.  The fan serves ALL of the zones, however, so ALL zones get
air (and cooling and heating)
Most VAV systems require a non-zero minimum airflow to maintain proper
outdoor air ventilation and maintain that scheme / minimum at all times -
even at night.
It's possible to control VAV boxes for zero minimum airflow in unoccupied
periods, but it would be unusual.
In most cases, the fan itself must also have a minimum airflow for stable
operation and to prevent variable speed drive overheating ... but that's
another problem....

On Mon, Dec 15, 2014 at 7:28 PM, Jacob Dunn <jdunn at eskewdumezripple.com>
wrote:
>
>  Hello all –
>
>
>
> Full disclosure I’m an architecture intern, but I had a general question
> about how VAV systems are controlled.
>
>
>
> If you have one central VAV system with a boiler and a chiller, and lets
> say its serving 10 zones.  At night with the proper night cycle control,
> during unoccupied hours if only one of those zones floats above the setback
> and calls for cooling – do all of the vav terminals come on as well? Or
> does the entire system energize and deliver cold air just to that one VAV
> terminal?
>
>
>
> The reason I ask, is that I’m modeling a large school with a VAV system in
> EnergyPlus.  When cycling at night, it looks like all of the terminals come
> on, even if they don’t need the cooling.
>
>
>
> If anyone can elaborate on how EnergyPlus (or other modeling programs)
> controls this aspect of VAV night cycling, and also how it works in the
> real world, that would be much appreciated.
>
>
>
> Cheers,
>
>
>
> *Jacob Dunn LEED AP BD+C*
>
>  *ESKEW+DUMEZ+RIPPLE, APC*
>
> 2014 AIA National Architecture Firm Award
>
>
>
> 365 Canal Street Suite 3150
>
> New Orleans LA 70130
>
> 504.561.8686
>
> *eskewdumezripple.com <http://www.eskewdumezripple.com/>*
>
>
>
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-- 



James V Dirkes II, PE, BEMP, LEED AP
The Building Performance Team <http://www.buildingperformanceteam.com>
1631 Acacia Drive, Grand Rapids, MI 49504
(M) 616 450 8653

If I decide to act with strength and honor in some instances, but not
always, I have made my integrity optional.  It's all or nothing.
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