[bldg-sim] air-side economizer...increase in heating load???

[John Aulbach]

Hi Paul:

I am willing to bet you are using a multizone type of
HVAC unit. I was told by a wise old engineer, and
verified by DOE2 that heating does indeed go up in
reality for this type of system.

Understand that the economizer for this type of system
throws the cool outsider air where heating and cooling
coils are acting simultaneously, with the damper being
the particular zone modulator.

When you add 100% OSA, zones calling for cooling are
satisfied and little heating is used. But those zones
calling for heating, will find the entire airflow to
that zone now needing heating, not just a hot deck.

Thus, the heating energy goes up.

Guys and gals, check my logic on this one, please..

--- Paul Erickson <perickson at aeieng.com> wrote:

> 
> Greetings,
>  
> Has anyone out there experienced a situation where
> DOE-2 predicted an increase in heating energy
> consumption when using the air-side economizer?  I
> was using the OA Temperature as the control (set at
> 65F, and I tried min temp at both 52 and 55, where
> 55 was also my cold deck supply temp).
>  
> I saw an expected decrease in cooling energy
> consumed, but there was an increase in heating and a
> small increase in fan energy.  I am modeling a
> building in Appleton, WI.  However, I made a simple
> base model as well to see if the problem was my
> original model.  For Appleton, Albuquerque, and
> Boulder (I only looked at 3), all three locations
> showed this increase in heating energy and decrease
> in cooling for the simple building.
>  
> Does anyone know if the RA damper modulates when the
> economizer is used, or does it fully close and thus
> provide 100% OA to the supply duct?
>  
> Any thoughts would be much appreciated.  THanks in
> advance.
> 
> Regards,
> 
> Paul
> 
> 
> 
>
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