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Baseline G3.1.2.9: A term (pressure)

asked 2018-05-09 10:59:02 -0500

Gio's avatar

updated 2018-05-09 10:59:40 -0500

Hi, I'm modelling a Baseline building.

"A" is defined as the sum of each applicable pressure drop from table multiplied for the design air flow in liters per seconds.

My question is: should I consider the baseline or the proposed flow rate?

In my example I have 1000 L/s for proposed and 2000 L/s for baseline and: "Fully ducted retun and/or exaust air system"(125Pa)+"Return and/or exhaust airflow control devices"(125Pa)+"Filtration Credits MERV15"(225Pa): the total is 475 Pa.

Is the "A" term 1000x475/650000 = 0.73 kW or 2000x475/650000 = 1.46 kW?

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answered 2018-05-10 03:00:50 -0500

Marco Furlani's avatar

"A" may be second rule. Proposed pressure may follow design data. Baseline may follow tab of pressure drop adjustment with its airflow sizing and calibration of total fan efficiency due to satisfy the compliance with fan power allowance with formula for constant or variable volume. Fan power allowance refer to the sum of power of all fans (supply-return-exhaust as applicable).

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I thought it was the first. Here is why: if I have a design (proposed) with fan coil units and an air loop that is dedicated only to ventilation, baseline air flows are much higher than proposed ones (baseline air flows have also to meet the cooling load). On the other hand your explanation makes absolutely sense (and is much more convenient in terms of energy) because no mention is made to the proposed design. Have you ever had trouble with the referee when applying the baseline air flow rate?

Gio's avatar Gio  ( 2018-05-10 03:20:32 -0500 )edit

No trouble for air flow directly. Usually baseline airflow sizing is done with EnergyPlus Autosize with attention in setting the same Outdoor Air and availability schedule as in proposed and/or per ASHRAE 62.1 minimum OA (also baseline usually need night cycling). After first run in autosize you obtain the airflow and then you can better calibrate the fan total efficiency in compliance with fan power allowance.

Marco Furlani's avatar Marco Furlani  ( 2018-05-10 03:44:06 -0500 )edit

Yes I use exactly the same workflow as yours. My question was just about the air flow rate to use when calculating the A term.

Gio's avatar Gio  ( 2018-05-10 03:49:21 -0500 )edit

Ok, now I understand the issue. You will take credit between pressure adjustment of devices (proposed vs baseline). For each pressure drop adjustment claimed, input the design airflow rate, CFMD, through each applicable device. I suggest to show this excel at the end of sheet Air-Side HVAC this link:

Marco Furlani's avatar Marco Furlani  ( 2018-05-10 04:01:32 -0500 )edit

The issue came exactly from that file. I don't know if to use the baseline or proposed air flow in the rows from 38 to 65 in the sheet Air-Side HVAC

Gio's avatar Gio  ( 2018-05-10 04:08:03 -0500 )edit

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Asked: 2018-05-09 10:59:02 -0500

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Last updated: May 10 '18