Option 1 ? the user?s manuals are a bit more clear, and specify that the its
is the supply cfm that should be used to calculate the fan power. This fan
power includes supply, return and exhaust.

Section G3.1.2.8 says "if return or relief fans are specified in the
proposed design, the baseline design shall also be modeled with fans
serving the same function and sized for the baseline system supply fan
air quantity less then minimum outdoor air, or 90% of the supply fan air
quantity, whichever is larger."

This would lead me to believe that you need to specifically model
return/exhaust/relief fans the same as supply fans and not group
everything together. Section G3.1.2.9 is written poorly because it
calls out "supply CFM," but should be applicable to all types of fans.

Comments?

Sam Mason

Sam,

Option 1 is the correct way to model. It is painful for a lab building, yes. Designs are often 50-100% higher in horsepower than what is allowable per Appendix G. It's very important to help the design team understand this and emphasize the importance of finding ways to reduce the fan bhp.

Paul Erickson

Mike,
Option 1 does seem to be the correct way to model. However, for a few
lab buildings following this method, the fans used almost twice as much
energy in the proposed model as the baseline, so option 2 was used.
Also, if you bunch all of the fan energy into the supply, would it be
possible to model 24/7 constant volume supply or exhaust (fume hoods or
clean rooms) on the same system?

Sam Mason

George and Sam,
I may just misunderstand what you are saying, but I suspect you may not
be reaching a correct conclusion. Whether the fans are modeled
separately or together, the baseline fan power allowance covers all the
fans in the system (I divide this among the various fans based on the
proposed system fan power ratios of supply to return, etc).

As Bill Talbert mentioned earlier in this thread, look at Addendum ac to
90.1-2004. Specifically read through the definitions of "fan system bhp"
or "fan system motor nameplate hp" therein which should clarify that the
hp allowance values are for "all fans that are required to operate at
design conditions to supply air from the heating or cooling source to
the conditioned spaces and return it to the source or exhaust it to the
outdoors".

I hope this helps to clarify things.

Kind Regards,

Molly Curtz, P.E.

Sam,
Addendum ac includes an exception for fans exhausting air from fume
hoods (6.5.3.1.1 exception c). A LEED CIR submitted on 6/15/2007, ruled
on 8/13/2007 allows use of the Addendum ac fan power calculation
approach, including the fume hood exemption. Does this help for your
application?

Kind Regards,

Molly Curtz, P.E.

I would submit (without knowing anything about the project, of course)
that `There is no way to meet code' simply isn't true. Perhaps no way to
meet it economically - which rests on the definition of `economical'.

There are many strategies that can be employed to reduce system pressure
drop, even in demanding lab situations. Duct sizing, control losses
(selection of the pressurization control valves in the supply/exhaust),
coils, filter and system effects, fan efficiencies, duct run
(distributed systems), etc. There is no one silver bullet but a lot of
little things add up quickly.

We often see the same results - as-designed fan power in excess of App G
calculations but when you look into it, it's because the designer uses
the same approaches they've been using for the last ten years. If you
want efficient systems, you have to put more effort into the design, and
probably more money into the construction.

I'm sure I'll upset a few designers saying this, but complaining that
you can't meet code is a cop out.

This is a very interesting discussion, and I believe I'll agree with Mark.
An overall summary of my position is that I find it interesting that folks
are saying the code is still difficult to meet, because the code (90.1) was
recently significantly overhauled to provide more allowance for lab systems.

I would say that 400 HP for 80KCFM, or 5 BHP/KCFM is quite a bit of fan
power, either under the older 2004 standard or the newer 2007 standard.

For comparison purposes, in the original ASHRAE 90.1-2004 standard, the base
allowance was 1.2 BHP/KCFM & 1.1 BHP/KCFM for constant volume systems (< 20 KCFM & >= 20 KCFM), and allowances of 1.7 BHP/KCFM and 1.5 BHP/KCFM for
variable volume systems (< 20 KCFM & >= 20 KCFM ).

Then, you could add to the base BHP/KCFM number with some credits. However,
some folks noted that the credits were not sufficient to account for real lab
HVAC systems. Therefore, the folks with the Labs21 program
(www.labs21century.gov) figured out what could be appropriate and published a
draft modeling guideline to modify Appendix G of ASHRAE 90.1-2004
specifically for labs. This document (ashrae_appg_draft_508.pdf) is
available at www.labs21century.gov/pdf . This is a great document for energy
modelers to better understand the demanding requirements of laboratory
systems from a fan energy standpoint. The document basically said, among
other things, that conventional commercial AHU's are designed for ~ 5" of
total static (4" supply, 1" exhaust) while a more realistic value for lab
AHU's is 9.15 inches (5.79" supply, 3.36" exhaust). Appendix A of the
document covers very well the assumptions going into those numbers. I would
say that based on lab systems we have designed, the 9.15 inches is a
realistic number for establishing a baseline fan power value.

The document from Labs21 recommends an allowance of 2.2 BHP/KCFM & 2.0
BHP/KCFM for constant volume systems ( < 20 KCFM & >= 20 KCFM ), and an
allowance of 3.1 BHP/KCFM and 2.8 BHP/KCFM for variable volume systems ( < 20 KCFM & >= 20 KCFM).

I don't know for sure (since I have no affiliation with the Labs21 program)
but suspect that the Labs21 guideline helped to form the basis for a bunch of
changes that eventually made their way into the 2007 version of the ASHRAE
90.1 standard, regarding the fan power limitation and fan power limitation
pressure drop adjustment. The fan power limitation calculations in the 2007
version have pretty much been completely overhauled as compared to the 2004
version. That's a good thing (though I would argue more work needs to be
done for the smaller PSZ systems, more to follow below).

That being said, if you use the 80 KCFM and assume the 9.5 inch total
pressure credit, you get 288 BHP (as Sam mentions) using the new formulas in
table 6.5.3.1.1B of 90.1-2007. This amounts to 3.6 BHP/KCFM. Therefore,
what made it into the final 2007 standard seems to be even higher than what
the Labs21 folks recommended in their draft paper.

I guess my overall question, to anybody who read down this far :) , is
whether people think the new 90.1-2007 fan power limitations are sufficient
to cover labs. It seems like they should be to me, but would love to get
feedback from any designers out there.

Switching gears a bit, I think where more work needs to be done to the 90.1
standard regarding fan power is the fan power calculation/limitation for the
smaller PSZ-AC & PSZ-HP systems (Appendix G, table G3.1.1A & 1B). Why is
this important --> because these system types are used for the baseline
buildings in a lot of LEED projects, and the equations used for estimating
the fan power (watts) actually go the other direction and dramatically
overestimate the fan power requirements, which in my opinion which results in
questionable fan energy savings. This happened with the 90.1-2004 standard
and doesn't appear to be corrected in the 2007 version. I'll provide an
example, let's say you have a 3 ton unit @ standard conditions, or 400
CFM/ton (of which I happen to have at my house). The ARI SEER rating
standards would assume 365 watts/1000 CFM, or 438 watts total. Using the
equations in Appendix G of 90.1-2007 ( 1200 X 0.00094*0.746/0.80), assuming
80% motor efficiency (approximate for small single phase motor), you come up
with 1026 watts, which is very interesting. Curiosity got the best of me and
so I put my Fluke 39 power meter on the circuit and actually measured the fan
power --> I get approximately 550 watts. The ARI assumption may be too low,
but the Appendix G assumption seems way too high. If we are using the
Appendix G fan power values for small systems on our projects, this appears
to show that our projects are saving lots and lots of fan power. But, that's
really not true because all we are doing is comparing our proposed design fan
power to a really bad baseline, one that is greatly exaggerated in the first
place. That's crazy, and in my opinion diminishes the validity of the
savings calcs because it shows savings on paper, but not real savings. If
people want to get serious about energy savings, I think we need a baseline
that holds us to a higher standard. Similar to the lab systems, we need
realistic baseline fan power values for small systems, except heading the
other direction (i.e. decreasing). If this can be changed, savings will be
more difficult to obtain, but they will be more real and therefore valid.

I've been wanting to bring this up to the 90.1 committee at ASHRAE. Haven't
found the time yet, but will.

Any thoughts on this topic would be appreciated as well.

Appreciate any additional feedback, and sorry for the really long email.

Regards,

James A.? Hess, PE, CEM