Baseline Airflow Autosizing

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I've been trying to look?on the equest interface where we can set the airflow to autosize itself as per LEED baseline requirement.
I don't think we have this option here. Have we?

Thanks in advance.

Reniel

reniel barroso's picture
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Joined: 2011-09-30
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Reniel,

Are you referring to the sizing runs from G3.1.2.2.1? If so, leave the
design cfm on each air-handler blank (see screenshot below) and eQuest
will size the flows based on the sizing option you've specified (Click
on a system, go the Basics tab, and see "Sizing Option").

If you need to size the baseline equipment capacity as per G3.1.2.2,
then multiply the auto-sized flows from the first step, by 1.25 for
heating and 1.15 for cooling and enter the result as the design cfm.

I think you might be able to do the second step directly by specifying a
sizing ratio (see second screenshot), although for whatever reason I
haven't done it this way in the past, so I'd be curious to hear from the
more experience eQuesters what approach they take.

Hope the helps,

Luka Matutinovic, B.A.Sc., LEED(r) AP

Matutinovic, Luka's picture
Joined: 2011-09-30
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Hello everybody

I use the auto-sizing option as Luca described and I trusted that the
when specifying the Sizing Ratio to be 1.15 for cooling and 1.25 for
heating would give me the equipment capacity as required by G3.1.2.2.

I then run the baseline for the first time just to get the supply
airflows (cfm) from the SV-A Report. Then I used this value to find the
fan Brake Horse power from Table G3.1.2.9 and then calculated the Pfan
from the formula G3.1.2.9

Then I find the fraction of fan power per flow Rate in kW/cfm and input
this value with a DT of 19.8 (as per G3.1.2.8)

It seemed to work fine and the USGBC accepted the model. I am really
interested to double-check with other modellers methodology.

But mostly I want to ask the following Question:

Do you use the auto-sizing method for the Proposed building?

You can still input the actual Sizing ratio, DT and kW/cfm of your
design that will determine your energy consumption and thus reflect your
design principles. I will appreciate the feedback of the experienced
users.

Kind Regards,

Christina

Christina Galyfianaki's picture
Joined: 2011-09-30
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Christina,

I always just solve the equation in AHSRAE 90.1 for kW/cfm and input directly into eQuest. The Delta T box you are referring to, is the increase in temperature of the airflow due to motor heat at design conditions I leave default in baseline case(2-4F usually). I always let the program autosize in the baseline case 1.00 for system, 1.15 for cooling and 1.25 for heating. I then look at SV-A reports to get maximum heat extraction rate of the equipment and calculate my dt's (1.08*cfm*dt) which I then adjust airflows for each zone to match the 20F found in ASHRAE 90.1. I have not found a way to directly input design delta T (20F per ASHRAE) of zones to calculate airflow. Maybe someone else can knows a better way and will answer this post. Hope that helps some.

Josh

Joshua D. Wolfe's picture
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Joined: 2011-09-30
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Hi Josua!

Thanks for replying.

Yes you were right that the DT at the fan power and control
specification has to do with the motor heat.

The Delta T of 20 degrees will be the difference between the
Cooling/Heating indoor design temperature (specified at the Zone
Parameters) and the Zone entering Min/Max Supply temperature specified
at the HVAC Systems Parameters. So this is the way to input your DT.
What do other eQuest user say?

What about using auto-sizing on Proposed building, was any project
accepted by the USGBC done this way?

Regards

Christina Galyfianaki

Christina Galyfianaki's picture
Joined: 2011-09-30
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Christina,

My understanding is that the proposed building should not be auto-sized,
rather the actual design capacities should be used, as shown on the
mechanical drawings and equipment schedules. In this way, I believe
ASHRAE 90.1 gives you a credit for "right-sizing" your systems.

I often develop preliminary models to evaluate design decisions and the
information is simply not available, in which case I let eQuest autosize
the proposed systems, often using the same sizing ratios as in the
baseline to give a conservative result.

Cheers,

Luka Matutinovic, B.A.Sc., LEED(r) AP

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Joined: 2011-09-30
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