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

Nick Caton ncaton at smithboucher.com
Thu Jan 20 17:33:35 PST 2011


What a pain.  =(

 

Matt:  

If the “coil upsizing factor” for altitude (1.08 in your example below?) is not derived from the site altitude as entered under ‘site properties,’ a much easier solution might be to identify where else the altitude is being from and entering a zero there… The site properties dialog pulls it from the weather file, right?

 

DOE2 / eQuest developers:  

Is there any feasible possibility of adding an option in a future release/patch to turn altitude adjustments on/off?  This might logically be located adjacent to the altitude input in the Site Properties dialog (I’d vote for default = off).

 

~Nick

 

 

 

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: MattDubrovich at Eaton.com [mailto:MattDubrovich at Eaton.com] 
Sent: Thursday, January 20, 2011 6:55 PM
To: cmg750 at gmail.com; Nick Caton
Cc: equest-users at lists.onebuilding.org; ktupper at rmi.org
Subject: RE: [Equest-users] Does eQUEST derate equipment for altitude?

 

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

 

 

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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