[Equest-users] Supply Fan Power
Bishop, Bill
wbishop at pathfinder-ea.com
Fri May 20 06:50:58 PDT 2011
Michael,
I'm confused by your LEED reviewer's comments. As Patrick mentioned, it
would help to know what the reviewer means by "independent fan systems".
I can think of only two situations where you would need to model
identical fan power in the baseline and proposed models. One is if you
have no heating and/or cooling system in the proposed design, in which
case the proposed system "shall be identical to the system modeled in
the baseline building design" per Table G3.1(10.). Since you mention
that you used the actual fan power in the proposed building, I'm
assuming that heating and cooling systems have been specified for your
proposed design.
The other situation is for process loads. If you have fan power
associated with non-HVAC systems, it should be treated as a process load
and modeled identically between the baseline and proposed designs. An
example of this that has been discussed on this forum previously is
parking garage exhaust.
I rarely model anything but supply fans in the baseline model unless
there are process loads. I see no point in modeling return, exhaust or
relief fans. The fan power calculated in G3.1.2.9 is for the sum of
supply, return, exhaust and relief fans. The baseline systems have to
move the same amount of air regardless of the combination of fan types,
and the fan power is based on, and entered as, kW/cfm, so you will end
up with the same fan energy in the baseline model regardless of how many
fans you model for each baseline system.
I don't know what the reviewer is trying to say with their comment about
system types 1 through 8 and Table G3.1.1A.
Regards,
Bill
From: equest-users-bounces at lists.onebuilding.org
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Nick
Caton
Sent: Friday, May 20, 2011 9:50 AM
To: Patrick J. O'Leary, Jr.; equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Supply Fan Power
Color me concerned... This reviewer may have an argument but I can't
reason it. I think he/she may be leading us off the path regarding what
the baseline fan power calculations apply to...
You've got exhaust fans in a proposed model matching the construction
documents. Sounds okay so far... Going through this line by line:
* I would start with directing the reviewer to the glossary.
The entry for "HVAC system" reads: the equipment, distribution systems,
and terminals that provide, either collectively or individually, the
processes of heating, ventilation, or air conditioning to a building or
portion of a building."
o Clearly, an exhaust fan providing ventilation to a building
independent of other systems is an HVAC system. The reviewer's phrasing
of "..independent fan systems of the HVAC systems" is a
misinterpretation.
o Building on the understanding that an independent exhaust system is
a complete HVAC system, Table G3.1.10.a is as far as you need to go for
support of following the construction documents.
* I'd again reject the reviewers' choice of words: Exhaust fans
are not "independent fans of the HVAC systems."
* Sections G3.1.2.8 and G3.1.2.9 agreeably apply only to
baseline systems. They have no bearing on the topic at hand (what goes
in the proposed model), unless your baseline fan capacities/efficiency
calcs didn't follow the instructions.
* The request to document the independent fan systems' energies
separately is not new. May as well do that after all's said and done.
That's my initial take. Thoughts, anyone?
~Nick
NICK CATON, E.I.T.
PROJECT ENGINEER
Smith & Boucher Engineers
25501 west valley parkway
olathe ks 66061
direct 913 344.0036
fax 913 345.0617
www.smithboucher.com
From: equest-users-bounces at lists.onebuilding.org
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Patrick
J. O'Leary, Jr.
Sent: Friday, May 20, 2011 8:35 AM
To: equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Supply Fan Power
it reads to me that your initial interpretation is what the reviewer is
asking for. on the other hand the question is what is constituting an
"independent" exhaust fan here. if the exhaust fan is part of the
balance of the supply/return/exhaust system it probably should be
modeled as such as it is not really different than having a return fan
installed in the ductwork somewhere and not in a unit itself. per hte
90.1 user's manual (page g-28 in 2004), "System fan electrical power for
supply, return, exhaust and relief fans is calculated based on the
following formula. The power from this formula includes supply, return,
relief, and exhaust fans ..." if the exhaust fan is not part of the
designed system supply/return/exhaust then i would think your initial
interpretation of what the reviewer is asking is correct. whichever
situation applies make sure the response documents the purpose of the
exhaust fans and how 90.1 applies (including section/user manual
references).
On 5/20/11 6:15 AM, M. Shields wrote:
The exact comment is this:
"The fan power spreadsheet for the Baseline and Proposed models indicate
that the fan power of the exhaust fans have not been modeled identically
in each model. All independent fan systems of the HVAC systems in the
actual design must be modeled identically between the Proposed and
Baseline models at actual equipment capacities (fan volume and fan
power) as required by Table G3.1.10 in the Proposed building column,
since the fan design air flow rates and fan power per Sections G3.1.2.8
and G3.1.2.9, respectively, only applies to system types 1 through 8 in
Table G3.1.1A. If appealing this credit, revise the Proposed and
Baseline models so all independent fan systems of the HVAC systems are
modeled identically between the Proposed and Baseline models. In
addition, separate the energy consumption and peak demand energy for
independent fans in Table 1.8.1 and Table 1.8.2 of the template and
provide revised SV-A reports for each model reflecting the changes."
I initially interpreted this to be that for exhaust systems the bhp/kw
needs to be identical in both buildings and based on the specified
equipment from the mechanical designer, however, my supply fan energy
was Ok. After reading the comment and Appendix G I am not unsure if I
also need to specify the fan power to be the same for both models, ie
use table G3.1.2.9 to calculate fan power for both instead of just the
baseline.
From: equest-users-bounces at lists.onebuilding.org [
mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Patrick
J. O'Leary, Jr.
Sent: Friday, May 20, 2011 8:57 AM
To: equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Supply Fan Power
from your wording of "independent" it sounds like you may have an
application where you have a unit in the proposed building that is
required but not provided in the design? or something similar. is this
the case? if a unit is required in the proposed per the requirement all
spaces be heated/cooled (per the definitions) they are required to be
the same as the units in the baseline building. if this is not the case
if you post the exact comment it may shed some light on the subject.
otherwise i would argue the comment is in error - if all of your zones
are served by units in the proposed and you have matching units in the
baseline (regardless of system types) then your approach would be
correct.
On 5/20/11 5:31 AM, M. Shields wrote:
Good Morning All,
I recently received comments back from LEED and one of them was about my
fan power. In the submission I calculated all of my fan power using
G3.1.2.9 for the baseline building, and I used the actual fan power in
the proposed building. The reviewer has commented that all independent
fan systems have to be modeled identically in both the baseline and the
proposed building. The supply fans use very high efficiency motors, and
as such are substantially more efficient than the calculation that
G3.1.2.9 provides. Is there no way to take credit for using high
efficiency supply fans?
Thanks,
____________________________
Michael Shields
Email: mshields at fstrategies.com
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