[BLDG-SIM] Energy savings from oprating fan of HVAC system alone

gail gail22 at gmail.com
Fri Jun 15 09:07:22 PDT 2007


It also depends on your overall control sequences for when you intend to
operate the whole system.  We once audited a large government office
building where the building engineers were responding to a governor's order
to reduce energy consumption by keeping the chillers / towers, etc. off in
the morning until the outdoor temperature exceeded a certain temperature
(maybe 80 deg. F).  The resulting energy consumption for the building was
actually higher than the previous energy use.  This was because when the
chillers were turned on, they had to operate at higher lift conditions, and
were therefore operating less efficiently than they otherwise would have.
Meanwhile, the indoor temperatures of the building had been creeping up all
morning (due to outdoor air conditions, interior loads, and fan heat added
to the air stream), so the cooling demand was much higher when the chillers
were turned on than it would have been if the chillers had been turned on
earlier in the morning.  Also, the VSD fans had been operating at 100% all
morning, and continued operating at 100% after the mechanical cooling
systems had been turned on, since a higher volume of air was required to get
the building back to reasonable comfort conditions.  If the mechanical
cooling had been turned on earlier, the fan energy would have been much less
throughout the day.

There's definitely a right application of air-side economizer and night
ventilation controls to limit mechanical cooling (and these are all
modelable within energy simulation tools), but integrated control between
free cooling (air-side economizers / night ventilation w/ thermal mass) and
mechanical cooling systems tends to provide the highest levels of comfort,
and can provide the best levels of efficiency if controlled correctly.

Best Regards,
Gail Stranske
CTG Energetics, Inc.

On 6/15/07, Peterson, John <JPeterson at vanderweil.com> wrote:
>
>  That's too hard to say.  It would depend on the systems used & modeled.
> Most can tell you exactly how much energy a fan is pouring out, and you can
> run a few quick simulations in Carrier's HAP to figure out how much is fan
> vs. chillers & pumps.  BTW, coils don't have an energy use associated with
> them.
>
>
>
> John Peterson, PE, LEED AP
>
> *R.G. Vanderweil Engineers, LLP*
>
> 625 N. Washington Street     Alexandria, VA  22314-1913
>
> Tel: (703) 683-9700
>
> Fax: (703) 683-2480
>
> www.vanderweil.com
>
>
>
>
>  ------------------------------
>
> *From:* BLDG-SIM at gard.com [mailto:BLDG-SIM at gard.com] *On Behalf Of *
> Kofoworola
> *Sent:* Friday, June 15, 2007 1:17 AM
> *To:* BLDG-SIM at gard.com
> *Subject:* [BLDG-SIM] Energy savings from oprating fan of HVAC system
> alone
>
>
>
> what percentage of energy can be saved by running just the fan of an HVAC
> equipment as against when the whole system (fan, cooling coils, chillers,
> AHU) is running?
>
> Thanks
>
> --
> Kofoworola, O.F.
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