[Equest-users] Baseline vs. Proposed Fan Curves

[Nick Caton]

Hi Bernie,

 

>From your phrasing, I'd caution to avoid a mistake I once made regularly
until corrected: A single value should be determined for the baseline system
fan power (Pfan).  Put another way, Pfan should not be calculated separately
for each fan.  The language in Appendix G preceding the Pfan calculation
method specifies this value accounts for supply, return, relief, and exhaust
fan energies for the system (as they may occur). If you wish to explicitly
model both supply and return fan energies for your baseline system, you can
apportion the Pfan quantity/result between those kW/CFM inputs, but the
resulting sum between the two should not exceed the singular Pfan calculated
for the system.

 

As you touched on, kW/CFM is not the only input affecting fan energy end-use
sums.  How those proposed/baseline fans operate relative to each other for
8760 hours can be a much bigger deal.  It's almost always a worthwhile QC
check to state how both baseline and proposed system fans SHOULD operate
(VAV/CV?  Cycling?  On 24/7? Setback behavior?), then run a couple system
and/or zone hourly reports to track the flow rates simulated and confirm
whether they match your expectations.  There are enough "gotchas" between
the various system types and enough potential for simple human error between
all the involved inputs to potentially trip up even very experienced
eQuest-ers on this front.

 

This advice may already be on your radar, but if I've presented a new
perspective it may help you shape/understand where the reviewer is coming
from in anticipating an overall performance reduction.

 

 



NICK CATON, P.E.
Senior Engineer

 

360 Analytics
9750 3rd Ave NE, Suite 405

Seattle, WA 98115
office:  206.557.4732 ext. 205
 <http://www.360-analytics.com/> www.360-Analytics.com

 

From: Equest-users [mailto:equest-users-bounces at lists.onebuilding.org] On
Behalf Of Bernie Hont
Sent: Tuesday, October 28, 2014 5:38 PM
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] Baseline vs. Proposed Fan Curves

 

I have just revised a baseline and proposed model for LEED submission and
the fan energy savings has changed dramatically as a result. The first
go-round the fan energy savings was 27% between baseline to proposed. The
formulas in G3.1.2.8 and G3.1.2.9 were used incorrectly though in the first
round, so I had to revise the supply and return fan power calculations. The
result is that they both were higher (0.001217556 KW/CFM supply and
0.001049567 KW/CFM return now). The baseline fan curve is the equation from
G3.1.3.15 Method 2.

 

The proposed model fan power matches the actual units purchased, (0.001164
KW/CFM supply and 0.000435 KW/CFM return). This represents a 4.4% reduction
in supply fan power and a 58.6% reduction in return fan power. The fan curve
used for the proposed model is Variable Speed Drive FPLR.

 

There is a huge savings on the return side and a slight savings on the
supply side, so I can visualize how a 60% overall savings between the two
models is feasible, but is the sizing for the return fan under the baseline
scenario accurate? I followed the G3.1.2.8 method of sizing them based on
the supply flow minus the ventilation (or 90%) but the calculations still
come out with a substantially higher return fan power than the proposed
model. This may be perfectly acceptable, but USGBC always put the disclaimer
on the review comment that "the comments are perceived to reduce projected
savings". That would be the case otherwise, but since the fan energy has
changed so dramatically after revising the baseline calculations that the
savings actually increased from 17.99% to 21.77% solely on the fan energy.
Does anyone have experience where, with an explanation of why this occurred,
that USGBC will accept the revised results even though the savings is
actually higher now?

 




Bernie Hont, PE, LEED AP

Girard Engineering, P.C.

7600 Leesburg Pike

West Suite 310

Falls Church. Virginia 22043

703.442.8787 (T)

703.734.3946 (D)

703.356.0169 (F)

 <http://www.girard.com/> www.girard.com

 

 <http://www.linkedin.com/in/berniehont> 

 

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