[Equest-users] Does eQUEST derate equipment for altitude?

Carol Gardner cmg750 at gmail.com
Thu Jan 20 12:21:59 PST 2011


Nick/Kendra,

The altitude factor effects the supply air and the outside air. The write up
below suggests that one calculate both supply and outside air at sea level
and then apply the altitude factor to it. In real life, however, the design
engineer is calculating and specifying supply and outside air cfm that is
already adjusted for the altitude and the altitude factor should simply be
set at 1.0 in eQUEST.

The excerpts below discuss the areas of eQUEST impacted by the altitude
factor:

Note: the quantities in this report (SV-A) have been adjusted for
altitudeeven though DOE-2 requires that any flows you enter in SYSTEMS
be at sea
level.

1.    SUPPLY FLOW
is the calculated or user-specified supply flow for each zone.  Only if you
have specified a value for the ASSIGNED-FLOW keyword in the ZONE command
will the value here correspond to your input. The ZONE keywords
AIR-CHANGES/HR and FLOW/AREA will be accepted by SYSTEMS only if they are
consistent with the user-supplied HEATING-CAPACITY and COOLING-CAPACITY and
are equivalent to a flow larger than that of the exhaust from or the
ventilation to the zone. The ALTITUDE FACTOR will be applied.

5.    OUTSIDE AIR FLOW
reflects the user-specified outside air quantity entered at the zone level.
If OUTSIDE-AIR-FLOW is specified, its value is multiplied by the ALTITUDE
FACTOR and reported here.  Otherwise the reported value is the maximum of
the flow-equivalent values of OA-CHANGES and OA-FLOW/PER, multiplied
by ALTITUDE
FACTOR.  For the actual amount of outside air delivered to the zone for
central systems, see OUTSIDE AIR RATIO above.


On Thu, Jan 20, 2011 at 10:49 AM, Nick Caton <ncaton at smithboucher.com>wrote:

>  Kenda,
>
>
>
> I’m curious as to whether you received any responses to the query below.
>
>
>
> I have incorporated a practice of manually setting the site altitude in my
> eQuest models to “0,” because (1) as designers we do not specify equipment
> with CFM’s at sea level, it is already “corrected” for altitude in this
> sense, and (2) those who review models tend to miss the significance of the
> altitude factor in the SV-A reports and complain of incorrectly entered
> airflow rates.
>
>
>
> I don’t know if this constitutes a “best practice,” but I know it is common
> to a number of the regular contributors to these lists besides myself.  As
> it stands, current standards (90.1-2007) don’t have us “de-rate” or
> otherwise adjust required minimum SEER/EER values for altitude… so inversely
> it seem appropriate to remove the altitude variable when modeling for a
> performance rating… thoughts?
>
>
>
> ~Nick
>
> [image: cid:489575314 at 22072009-0ABB]**
>
> * *
>
> *NICK CATON, E.I.T.***
>
> PROJECT ENGINEER
>
> Smith & Boucher Engineers
>
> 25501 west valley parkway
>
> olathe ks 66061
>
> direct 913 344.0036
>
> fax 913 345.0617
>
> www.smithboucher.com* *
>
>
>
> *From:* equest-users-bounces at lists.onebuilding.org [mailto:
> equest-users-bounces at lists.onebuilding.org] *On Behalf Of *Kendra Tupper
> *Sent:* Thursday, September 02, 2010 1:53 PM
> *To:* equest-users at lists.onebuilding.org
> *Subject:* [Equest-users] Does eQUEST derate equipment for altitude?
>
>
>
> All,
>
>
>
> I'm trying to get clarification on exactly how eQUEST handles the altitude
> above sea level that is entered in Site Parameters. My understanding is this
> affects the airflow sizing calculations for cfm, but does not change the
> hourly air density for all calculations. If that is correct, then the
> altitude only corrects the cfms at the zone and system level, but does not
> derate equipment efficiencies. So, if you were to enter the altitude above
> sea level, you should then enter your airflows at sea level, but enter all
> equipment efficiencies at the derated conditions for that altitude.
>
>
>
> Is that correct?
>
>
>
> Kendra Tupper, PE, LEED AP
> Senior Consultant
> Built Environment Team
>
> Rocky Mountain Institute  |  T  303-567-8641 |  F  303-245-7213  |
> www.rmi.org
>
> _______________________________________________
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>
>


-- 
Carol Gardner PE
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