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

[MattDubrovich at Eaton.com]

Unfortunately I think it might be more complicated than that; I wish it
wasn't.  I have an old printout of an eQuest/DOE2 document called
"Sizing Air-Side HVAC Systems" which steps through the calculation.  I
haven't been able to figure out where I printed it from (help file?,
dictionary? engineers manual?).  

 

My take is that eQuest sizes coils based on sea level airflow.  At the
end of the calculation it simply multiples the needed sea level airflow
by the altitude factor to account for altitude effects.  Per Carol's
email, eQuest assumes any user entered flows are at sea level.  This is
frustrating because plans usually show airflows at site altitude, not
sea level.  We've tried Nick's work-around which is to change the
altitude to 0 and enter airflows per the drawings.  This works on the
airflow side but not the coil side.  The coils are sized using the
entered airflow x 1.08 so eQuest creates coils that are larger than what
you actually have.  

 

What seems to be more correct is to keep the altitude specified and
divide every airflow you enter into the model by the altitude factor.
If you're in Denver and want to model a 10,000 CFM fan, enter
10,000/1.21 into the supply CFM input.  eQuest takes that number and
multiplies it by 1.21.  Every input with a "CFM" must be adjusted
including exhaust, CFM/SF, etc.  

 

Matt Dubrovich, PE, CEM, BEMP 
Energy Solutions Group



 

From: equest-users-bounces at lists.onebuilding.org
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Carol
Gardner
Sent: Thursday, January 20, 2011 1:22 PM
To: Nick Caton
Cc: equest-users at lists.onebuilding.org; Kendra Tupper
Subject: Re: [Equest-users] Does eQUEST derate equipment for altitude?

 

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
altitude even 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

 
cid:489575314 at 22072009-0ABB<https://mail.google.com/mail/html/compose/st
atic_files/blank_quirks.html?ui=2&ik=367e06555b&view=att&th=12da4c2bcd69
7d9b&attid=0.0.1&disp=emb&zw> 

 

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 <http://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 <http://www.rmi.org/> 


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-- 
Carol Gardner PE

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