[Equest-users] Fan energy fundamentals - Appendix G models

Bishop, Bill wbishop at pathfinder-ea.com
Tue Oct 11 12:26:27 PDT 2011


Paul,

 

The 50.8% difference is Baseline w/default eQUEST VAV curve vs. Baseline
w/ASHRAE 90.1 curve. An hourly report for one of the systems shows it
averages around 0.50 or 0.55 PLR. Using the curve coefficients shown
(below) for the two curves, power at 0.5 PLR is .196 full load power for
the eQUEST curve and 0.373 full load power for the ASHRAE curve. That's
a 90% difference right there.

 

Bill

 

From: Paul Riemer [mailto:Paul.Riemer at dunhameng.com] 
Sent: Tuesday, October 11, 2011 3:06 PM
To: Bishop, Bill; Nick Caton; Dahlstrom, Aaron;
Equest-users at lists.onebuilding.org
Subject: RE: [Equest-users] Fan energy fundamentals - Appendix G models

 

I agree it is not trivial but I am really surprised by that 50.8%
number.  I think the curves are relatively similar at the high end and
most systems rarely spend time on the low end where the curves do differ
considerably.  Is there a big difference in the system volumes,
specifically are the baseline fans bigger in volume and thus always
operating at a lower ratio than the proposed?

 

Generally, I assume that the curve in 90.1 was supposed to represent a
VAV VFD curve and that my VAV VFD fans should not be penalized against
it.  VAV vs. CAV is trickier and brings the temptation to switch your
rationale based on which side your project falls on. 

 

Paul Riemer, PE, LEED AP BD+C 

DUNHAM

 

From: Bishop, Bill [mailto:wbishop at pathfinder-ea.com] 
Sent: Tuesday, October 11, 2011 1:07 PM
To: Nick Caton; Paul Riemer; Dahlstrom, Aaron;
Equest-users at lists.onebuilding.org
Subject: RE: [Equest-users] Fan energy fundamentals - Appendix G models

 

Nick's concern about VAV fan curves is not trivial. I am working on a
LEED model using Baseline System 5 (PVAV). The Baseline fan energy using
the 90.1 G3.1.3.15 VAV FPLR curve is 50.8% more than the fan energy
using the default eQUEST "Variable Speed Drive FPLR" curve. YMMV of
course but that is a big difference. This penalizes the Baseline for my
project - the total electrical use increases 8.9% in the Baseline vs.
only a 4.1% increase in the Proposed model when switching to the same
G3.1.3.15 curve.

 

Bill

 

 

 

From: equest-users-bounces at lists.onebuilding.org
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Nick
Caton
Sent: Tuesday, October 04, 2011 3:30 PM
To: Paul Riemer; Dahlstrom, Aaron; Equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Fan energy fundamentals

 

Paul & others:

 

I just wanted to say off the bat:  the EDR resource Paul linked us looks
to address the heart of my query directly (and thank you so much!), but
it's difficult for me to summarize further right now...


I think I'll need to re-read the appropriate parts of this document a
few times over and arrive at a deeper understanding of actual
methods/sequencing strategies for static pressure reset before I come to
any definite conclusions regarding VAV fan curve.  

 

The query I'm trying to nail down is what assumptions and specific
system behaviors the DOE2 library/default curves and particularly the
prescribed 90.1-2007 baseline curve represent, and from there answer
what's fair game insofar as defining/modifying a different sort of
EIR-FPLR curve for a proposed model.  I have the understanding that the
associated fan energy savings between various approaches are potentially
big and real, but I'm scratching the surface of how to actually model it
to a realistic degree.

 

If anyone has pondered the same topic or is a few strides ahead of me
and wishes to share any thoughts/guidance, please do not hesitate =).

 

~Nick

 

 

 

NICK CATON, P.E.

SENIOR ENGINEER

 

Smith & Boucher Engineers

25501 west valley parkway, suite 200

olathe, ks 66061

direct 913.344.0036

fax 913.345.0617

www.smithboucher.com 

 

From: Paul Riemer [mailto:Paul.Riemer at dunhameng.com] 
Sent: Friday, September 30, 2011 7:21 AM
To: 'Dahlstrom, Aaron'; Nick Caton; Equest-users at lists.onebuilding.org
Subject: RE: [Equest-users] Fan energy fundamentals

 

As for fans I suggest two resources:

Advanced Variable Air Volume VAV System Design Guide
<http://www.energydesignresources.com/media/2651/EDR_DesignGuidelines_VA
V.pdf>  by Energy Design Resources has some good discussion and
suggested fan curves.

 

Reid Hart of PECI did a presentation to BSUG on September 16, 2009 on
fan curves and static pressure reset.    BSUG posted their items,
including this one, to their yahoo group at 
http://tech.groups.yahoo.com/group/BSUG/files/. BSUG has morphed into
BESF and has a new home at 
http://energytrust.org/business/building-energy-simulation/.

 

Paul Riemer, PE, LEED AP BD+C 

DUNHAM

 

From: equest-users-bounces at lists.onebuilding.org
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of
Dahlstrom, Aaron
Sent: Friday, September 30, 2011 12:03 AM
To: Nick Caton; Equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Fan energy fundamentals

 

Nick - 

 

We're in the midst of asking the same questions about the
Pump-Power-fFlow equations.

 

I imagine in both types of flow networks there may some fixed pressure
drops that won't be reduced:

1)      Min static pressure across flow control devices (VAV boxes,
water control valves)

2)      Static pressure in critical branches that may not be at reduced
flow, even though the overall flow network is at reduced flow

3)      In staged plants, static pressure across individual
constant-volume plant components (eg in our case, chiller 1 of 6 always
has 12 psig, regardless of whether it is the only chiller on or not)

 

With this mixture of fixed and variable pressure drops, I imagine
multiple different power-versus-flow curves for the same building,
depending on the physical location of the prime movers and the
intervening pinch points / critical flow networks. 20000 cfm out of a
peak 30000 cfm fan probably looks different in terms of power depending
whether the majority is headed to west zones from an east mechanical
room 400 ft away or headed to east zones just a few feet away.

 

Probably the most accurate method would be explicitly defining the flow
network and calculating these pressure drops dynamically (if the modeler
had the time to do that explicitly, or software cool enough (BIM?) to do
it automatically). Anyone familiar enough with Energy Plus to know if
that's a feature?

 

I guess no answers here, just more questions ...

 

Aaron Dahlstrom , PE, LEED(r) AP

In Posse - A subsidiary of AKF| 1500 Walnut Street, Suite 1414,
Philadelphia, PA 19102 

d: 215-282-6753| m: 267-507-5470| In Posse: 215-282-6800| AKF:
215-735-7290

e: ADahlstrom at in-posse.com | in posse web: www.in-posse.com
<http://www.in-posse.com/>  | akf web: www.akfgroup.com
<http://www.akfgroup.com/> 

 

 

 

From: equest-users-bounces at lists.onebuilding.org
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Nick
Caton
Sent: Thursday, September 29, 2011 12:08 PM
To: Equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Fan energy fundamentals

 

Bill Bishop suggested a good clarification that I want to take on.  I've
edited my language below (highlighted) to clarify the question I'm
trying to pose.  

 

~Nick

 

From: equest-users-bounces at lists.onebuilding.org 
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Nick
Caton
Sent: Thursday, September 29, 2011 10:32 AM
To: Equest-users at lists.onebuilding.org
Subject: [Equest-users] Fan energy fundamentals

 

Hi everyone!

 

A recent discussion with a mechanical mentor brought up a question I'd
like to share with the list...  If anyone has a partial or complete
response I think we'd all benefit and appreciate it if you'd share your
thoughts!

 

For a given duct distribution system, you've got a certain static drop.
At full flow, your supply fan also has to deal with a certain velocity
pressure drop due to friction with the duct distribution.  If you reduce
the supply airflow rate, you also lower the velocity and therefore the
velocity pressure drops for the given duct distribution.  The net result
is system supply fan has a lower total pressure drop to overcome, and so
should operate more efficiently.

 

Does anyone know:  Whether we choose "variable speed" fan control, use
the FAN-EIR-FPLR curve generated by the wizards, or use the VSD curve
defined in 90.1 appendix G... are we simultaneously accounting for the
efficiency gains due to lowered velocity pressure drop in addition to
the drop in fan energy from lower RPMs?  If this is not accounted for
inside/outside the fan curves, is there a direct way to define that or
logically work it into the curves?

 

If it helps anyone answer, I can illustrate from recent checks that the
wizard-generated FAN-EIR-FPLR curve has a "Nike Swoosh" shape with an
inflection around the 20% mark.  This shape best matches the (limited)
data I've seen for "real world" VSD input measurements.  Here's a
screenshot:

 

 

 

The following illustrates the 90.1-2007 VAV curve we're made to use for
baseline systems 5-8 (I haven't checked to see if this still applies to
2010).  It does not have the same "inflection point" as zero is
approached.  I think it's based on the fan law power equation or
something similar that doesn't account for motor/VSD losses:

 

 

 

The help files illustrate a different, third shape for "variable speed"
control different from both of the above...

 

 

 

Seeing these side-by-side raises another question for me regarding
90.1-2007 intent/practice... not specific to eQuest... but I've already
spent too much of my time today writing this out!  Another day =)...

 

Thanks in advance for anyone joining in the discussion!

 

~Nick

 



 

NICK CATON, P.E.

SENIOR ENGINEER

 

Smith & Boucher Engineers

25501 west valley parkway, suite 200

olathe, ks 66061

direct 913.344.0036

fax 913.345.0617

www.smithboucher.com 

 


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