[Equest-users] Fan Powered Terminal vs Std VAV Terminal

[Bishop, Bill]

Morteza,
Yes, I agree the DTQS should be modeled as Series PIU terminals.
To your second question, I suggest you DON’T keep everything equal. The central air handler of System 5 has to supply the peak cooling airflow AND the peak heating airflow. In your proposed design, the packaged RTUs need to supply the peak cooling airflow to the zones, and could be controlled with low minimum flows based on the minimum ventilation rates. Then the Series PIU terminals use recirculated zone air to meet the heating loads. (Change the ZONE:INDUCED-AIR-SRC to ZONE-RECIRC.) So you might be able to capture energy savings if you enter specific zone design and minimum airflows for each zone/terminal. I suggest reviewing the help file literature for Powered-Induction Terminals and the many zone airflow keywords including the terminal ZONE-FAN-RATIO, ZONE-FAN-FLOW. The baseline should be modeled with minimum zone flows per Appendix G but the proposed design minimum zone flows (provided by the packaged rooftops) should be different.

Regards,
~Bill

William Bishop, PE, BEMP, BEAP, CEM, LEED AP
Senior Energy Engineer

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From: Paul Riemer <Paul.Riemer at dunhameng.com>
Sent: Wednesday, July 10, 2019 11:13 AM
To: 'Morteza Kasmai' <morteza.kasmai at gmail.com>; Bishop, Bill <bbishop at pathfinder-ea.com>; equest-users at lists.onebuilding.org
Subject: RE: [Equest-users] Fan Powered Terminal vs Std VAV Terminal

Morteza,
When series FPTUs are used throughout a system, the central fans typically have lower static pressure because the FPTUs are doing some of the air pressure work.  You may need to change that as well as changing the terminal units.  I don’t think any of us can say make a universal statement that FPTUs are more or less efficient than plain VAVs.  There are a lot of variables there including climate, fan system power, hours of operation, set back behavior, type and efficiency of the heating source, etc, etc.

Paul Riemer, PE, LEED AP BD+C
Senior Associate / Mechanical
DUNHAM

From: Equest-users [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Morteza Kasmai via Equest-users
Sent: Wednesday, July 10, 2019 9:44 AM
To: Bishop, Bill
Cc: equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>
Subject: Re: [Equest-users] Fan Powered Terminal vs Std VAV Terminal

Hello Bill,
Thank you so much for reviewing the model. Since I am not familiar with energy performance of different terminal boxes was wondering if my selection was correct. The mechanical drawings include diagram bellow for VAV terminal and a schedule titled “Fan Powered Terminal unit Schedule” that marks DTQS as the model of terminal boxes. Manufacturer’s (Titus) literature indicates DTQS as a Digital Series Fan Powered Terminal and very energy efficient.
My first question is if selecting Series PIU is a correct selection for the proposed terminal. If yes, then my second question would be the energy performance of Series PIU terminals vs Std VAV terminals. Keeping everything equal, when I change terminal types from Std VAV to Series PIU the annual energy costs increase, which indicates Std VAV terminal is more energy efficient than Series PIU terminal. Is this correct?

I truly appreciate your help,
Morteza
[image.png]

Morteza Kasmaei
Senior Architect
LEED AP BD+C, GGP








On Wed, Jul 10, 2019 at 9:52 AM Bishop, Bill <bbishop at pathfinder-ea.com<mailto:bbishop at pathfinder-ea.com>> wrote:
Hi Morteza,
I looked at your model and nothing jumps out as far as obvious problems. I can’t tell if you’ve modeled anything incorrectly without reviewing the design (which I’m not volunteering to do).
My question back to you is – what is it about the proposed design that should save energy compared to the baseline?
Regards,
~Bill
From: Equest-users <equest-users-bounces at lists.onebuilding.org<mailto:equest-users-bounces at lists.onebuilding.org>> On Behalf Of Morteza Kasmai via Equest-users
Sent: Tuesday, July 9, 2019 5:07 PM
To: equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>
Subject: [Equest-users] Fan Powered Terminal vs Std VAV Terminal

Dear eQUEST experts,
This is a LEED v4 C&S project modeled with eQUEST 3.65 build 7175 DOE 2.3.
System Type for the Baseline Case is System 5 – Packaged VAV with HW boiler and for the Proposed Model is Gas fired RTUs with Digital Series Fan Powered Terminal (DTQS).
Comparing the annual energy costs of the two models, when I change terminal type of the propose design system to Series PIU the energy costs of the model increases by 12%, which indicates the baseline system is more efficient the design system. Is this correct or there is something wrong with the terminal type selection? INP and PD2 files of the model are attached.

Thank you for your help.
Morteza

Morteza Kasmaei
Senior Architect
LEED AP BD+C, GGP






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