[Equest-users] Supply airflow sizing

Bishop, Bill bbishop at pathfinder-ea.com
Mon Jun 11 13:04:21 PDT 2012


Erik,

You can download the DOE-2 Engineers Manual here:
"DOE-2.1A Engineers Manual (theory and algorithms of calculation for the original DOE-2 program - out-of-date but most of the concepts are still used in DOE-2.2 - LOADS calculation is very similar, air-side HVAC is similar but improved, water-side HVAC is completely new but has some similar approaches):"
http://doe2.com/download/DOE-21E/DOE-2EngineersManualVersion2.1A.pdf

Where are you getting the loads from? If it is from DOE-2 LOADS reports, I don't believe any of them account for ventilation, only infiltration. You have a large ventilation load.

Be sure to use 1.08, not 1.8, in your handcalc equation.

You could share your model files with the forum, and/or compare your results to the actual design if it exists.

Regards,
Bill

-----Original Message-----
From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Turner, Erik
Sent: Monday, June 11, 2012 3:16 PM
To: equest-users at lists.onebuilding.org
Cc: SEA Admin1
Subject: [Equest-users] Supply airflow sizing

Is there a place in the documentation that details how eQuest calculates
supply airflows? I'm modeling a VAVS system, and it seems the
MIN-SUPPLY-T for cooling and MAX-SUPPLY-T for heating are used to arrive
at cooling and heating CFMs, and the larger of the two is applied as the
airflow to that space (plus OSA I'd imagine).

I have a space that has a cooling load of 108kBTUh and a heating load of
-36kBTUh. I've done a handcalc (Q=1.8*cfm*deltaT) to arrive at the
following:


Cooling: (supply at 55, space temp at 75) -->3000cfm
Heating: (supply at 95, space temp at 72) -->870 cfm

OSA requirement is 4200cfm.

By hand, I calculate a value of around 7200cfm. However the value listed
as supply flow in the SV-A is 71225cfm, about an order of magnitude
larger than what my hand calc suggests.

Am I thinking about something incorrectly here, or can anyone point me
in the direction to find documentation on how eQuest calculates airflows
so I can try and troubleshoot the inputs that would affect the answer? 

Thanks,
Erik




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