[Bldg-sim] Appendix G Fan Power

[James Hess]

This is good discussion on this topic.  I appreciate everyone's responses, and I'll a bit more to the fire :)

My overall thinking is that I don't think breaking up the fan power adds any "significant" value to the overall process.  Yes, it obviously does make a difference but with limited time, resources, and (more importantly) available fees (in my experience most clients want to pay very little for LEED energy modeling)  the question we should be asking --> is this of significant importance that justifies us spending time on it?   And the part about GBCI putting together review teams that enforce compliance with 90.1, that's great.  I am 100% for that.  But splitting up the baseline fan power isn't actually a requirement of 90.1 Appendix G so I do not know what they are enforcing here --> their own opinion of how we should be doing the modeling.  If they want to see the fan power split up, they need to lobby ASHRAE to get Appendix G changed so that we have more appropriate fan baseline numbers that are broken into components.  I think that would be the best approach.

I think we've agreed that splitting up the baseline fan energy into components does not make a difference with regards to overall fan energy consumption.  Now whether the fan energy is dumped in the supply or return, the fan energy still has to be removed by the cooling system or outside air via economizers?  I don't see how splitting up the fan energy makes a difference with regards to cooling energy consumption.  I would say that's true for most applications.  For lab applications, I can see how there may be a difference because the lab exhaust fans could be significant.  For the vast majority of applications, exhaust fans are fractional horsepower motors (i.e. << 1 HP), therefore very insignificant.

Regarding what I was saying earlier about Appendix G and overestimating fan power, this was for the small packaged single zone or split DX systems (i.e. system 3 & 4), which are probably the baseline systems on the majority of LEED projects in the US, hence the significance (may change somewhat now that the requirement for PVAV has shifted from 75000 SF to 25000 SF).  The fan power equations in Appendix G used to overshoot power for the smaller systems, but undershoot for the more intense systems like labs.  Now, the changes in 2007 version better account for labs, but the problem on the low end has not been fixed (could be in the works).  This is because the equations assume 3" to 5" pressure drop while small systems have pressure drops on the order of 1" to 1.25".  The example I use is my house --> a 3 ton/1200 CFM unit.  Per the equations in Appendix G, my system is estimated to use ~ 946 watts of fan power.  When I put my Fluke 39 meter on it and actually measure the power --> 550 watts, or 42% less.  I believe that ARI SEER calcs would assume ~ 365 watts/KCFM or 438 watts total  (I wonder if they are assuming the power based on the heating airflow because interestingly, my fan does use 440 watts in heating mode).  When we do a LEED project and assume PSZ systems for each zone (i.e. proposed design is VAV for example), we show ridiculous amounts of fan energy savings, which are really fake because the fan energy for real PSZ systems would be much less than the Appendix G equations show.

If we want a real challenge in exceeding 90.1 for energy savings --> let's get Appendix G changed to reflect more appropriate fan energy benchmarks for the smaller PSZ systems.  This could make a significant difference on LEED projects because meeting LEED requirements will be much tougher to meet.  I have personally seen projects that would not meet the LEED minimum 14% savings requirement were it not for the combination of artificially high baseline fan energy values along with a very generous allowance of exterior/site lighting power.  These changes could be of significant value to our profession and make our calculated savings numbers more legitimate.  That's the kind of stuff I think GBCI and our profession should focus on (versus worrying about breaking baseline fan energy numbers into components).

That's my two cents.

Have a great 4th weekend everyone.

Regards,



JAH

James A.  Hess, PE, CEM
Energy Engineer
TME, Inc.
Little Rock, AR
ph   501-666-6776
cell  501-351-4667
jhess at tmecorp.com<mailto:email at tmecorp.com>

From: Michael Tillou [mailto:michael.tillou at gmail.com]
Sent: Thursday, July 02, 2009 4:52 PM
To: Zeng, Ming
Cc: James Hess; Gregg Liddick; Bldg-Sim
Subject: Re: [Bldg-sim] Appendix G Fan Power


The Fan Power Allowance in ASHRAE 90.1 is based on "good" engineering practice.  I have attached a .pdf showing the System Pressure Drops used in determining the allowances for both the VAV fan system and the CV fan system.  The fan efficiency assumed in both cases is 65% and air velocity is assumed to be 400 fpm through the coils and filters.  Filter pressure drop assumes dirty filters.  The standard allows additional credits for systems with heat recovery, high performance filtration, lower design supply air temperatures and the use of relief fans vs return fans.

Also, addendum ac of ASHRAE 90.1-2004 modified the fan power calculation methodology allowing an expanded list of allowances that better suits a wider range of building types including hospitals and lab buildings.  Those changes are incorporated into Standard 90.1-2007.

I think that Michael Williamson gave the best reason yet why it is important to split the baseline fan power among the supply, return and exhaust fan components.  Like many others I distribute baseline fan hp using the same ratios as the proposed design even though the baseline system configurations may be slightly different.

Finally, three cheers to GBCI for putting review teams together that will actually do a decent job of ensuring compliance with Standard 90.1 rather than just taking the design teams word for it.  Maybe folks will begin to realize that exceeding 90.1-2004 by 20-30% is actually a challenge and building designs will begin to reflect the changes necessary to meet that challenge.

Regards,

Mike

Michael Tillou, PE
Associate Vice President
Energy Services
Cannon Design



On Thu, Jul 2, 2009 at 12:51 PM, Zeng, Ming <mzeng at leoadaly.com<mailto:mzeng at leoadaly.com>> wrote:

Hi James,

I actually feel the baseline model fan energy is too small.  Baseline model fan usually gives 0.00078KW/cfm.  For proposed fans, typically it is 0.00016-0.00018 KW/cfm/in static.  With cooling coil at 1 inch, mid life filter at 1.5 (30% and 85%), energy wheel at 0.8, external static of 1.8 inch, you will get .00081 KW/CFM.  And the return fan and general exhaust fans haven't been included yet.



Do you typically have less pressure drop than listed for the system?  Shall we use the clean filter or midlife filter for pressure calc?



Ming Zeng, PE, LEED® Accredited Professional

Mechanical Engineer



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From: bldg-sim-bounces at lists.onebuilding.org<mailto:bldg-sim-bounces at lists.onebuilding.org> [mailto:bldg-sim-bounces at lists.onebuilding.org<mailto:bldg-sim-bounces at lists.onebuilding.org>] On Behalf Of James Hess
Sent: Thursday, July 02, 2009 10:43 AM
To: Gregg Liddick; Bldg-Sim

Subject: Re: [Bldg-sim] Appendix G Fan Power



Gregg,



I appreciate the response.



I see what they are trying to do; I just don't think it needs to be done.  The total fan energy consumption (supply, return, exhaust) is the same for comparison purposes to the proposed design model.



On many projects, the baseline system is different than the proposed --> packaged single zone systems versus packaged VAV RTU, for example.  Therefore, there would not be any return fans on the packaged single zone systems to allocate fan energy to.  I don't know if anyone is looking at this to that level of detail.  Another separate issue is that the Appendix G fan energy equation way over estimates the fan energy associated with real packaged single zone systems, but I've posted previously on that issue and won't bore anyone with those details.



I guess the bottom line is that if GBCI absolutely insists that the baseline fan energy be broken into components, we'll come up with some kind of percentage allocation, similar to what you have done, as applied to the total baseline fan energy consumption for the sole purpose of filling out the template.



Thanks! :)



Regards,





JAH



James A.  Hess, PE, CEM

Energy Engineer

TME, Inc.

Little Rock, AR

ph   501-666-6776

cell  501-351-4667

jhess at tmecorp.com<mailto:email at tmecorp.com>



From: Gregg Liddick [mailto:gliddick at theepstengroup.com<mailto:gliddick at theepstengroup.com>]
Sent: Thursday, July 02, 2009 9:35 AM
To: James Hess; Bldg-Sim
Subject: RE: [Bldg-sim] Appendix G Fan Power



Hi James,



As far as I'm concerned the main point of having project teams break the fan energy down into components is to ensure that the baseline fan power derived from the fan supply volume using Table G3.1.2.9 is not all attributed to supply fans if exhaust fans, return fans, etc. exist.



Regarding the breakdown, as far as I know you're correct in that there is no guidance on that and what I do is take the percentages based on total fan power from the proposed case and apply it to the baseline case (e.g. 70% supply, 20% return, 10% exhaust).





Best Regards,



Gregg Liddick, EIT, LEED® AP



The Epsten Group, Inc.

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Fax: 404-577-1739

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From: bldg-sim-bounces at lists.onebuilding.org<mailto:bldg-sim-bounces at lists.onebuilding.org> [mailto:bldg-sim-bounces at lists.onebuilding.org<mailto:bldg-sim-bounces at lists.onebuilding.org>] On Behalf Of James Hess
Sent: Thursday, July 02, 2009 10:28 AM
To: Bldg-Sim
Subject: Re: [Bldg-sim] Appendix G Fan Power



We got a review comment on a recent LEED project asking us to break down the baseline HVAC power into components even though there is no direction, or requirement, from 90.1-2004 to do so.



Can someone please help me understand why this would be necessary?



LEED guidelines say we have to model per Appendix G, but Appendix G doesn't say we have to do this.



I do not think it is necessary to do this as the baseline total fan energy consumption numbers would still be the same.



The equation in Appendix G is meant to give a total allowance (for each system) for supply, return, and exhaust fans. It doesn't matter if we break the allowance down into components or not as the total fan energy consumption remains the same. Therefore, there is no value in doing this.



If we did break the fan energy numbers into components, how would we do that given that there is no direction from ASHRAE or LEED on how to do this?



Thoughts?



Regards,



James A. Hess, PE, CEM

Energy Engineer

TME, Inc.

On Jul 2, 2009, at 8:41 AM, "Jeremy Poling" <jpoling at epsteinglobal.com<mailto:jpoling at epsteinglobal.com>> wrote:

This issue will start to become a problem for anyone running energy models for LEED projects - reviewers on the new review teams are asking to see the total fan power for the baseline broken into individual components and reported as such in the template for Energy and Atmosphere Credit 1.  The 90.1-2004 User's Manual is also silent on the issue; however it raises another issue.  In the example (Example G-J on page G-28) the calculations use total building supply CFM for an 80,000SF medical office building.  Since the baseline is System 5 in that example and there would be multiple zones for the baseline, it appears that the equation should be used for the whole building only and not individual systems.  Is this how you are applying the formulas?  The user's manual notes that fan powered VAV boxes are NOT included in the total fan power number as calculated from G3.1.2.9.



Jeremy R. Poling, LEED AP
Senior Sustainability Analyst
Strategic Services

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From: bldg-sim-bounces at lists.onebuilding.org<mailto:bldg-sim-bounces at lists.onebuilding.org> [mailto:bldg-sim-bounces at lists.onebuilding.org<mailto:bldg-sim-bounces at lists.onebuilding.org>] On Behalf Of Ellen Franconi
Sent: Thursday, July 02, 2009 7:37 AM
To: Vikram Sami; Bldg-Sim; Michael I Rosenberg
Subject: Re: [Bldg-sim] Appendix G Fan Power



At my firm, we proportion the baseline total fan power determined as an aggregated W/CFM based on  the hp assigned to the fan motors (supply, return, exhaust) in the design documents. Of course this assumes that your baseline and your proposed design have a one-to-one fan correspondence.

Ellen





Ellen Franconi, Ph.D., LEED AP
Senior Energy Analyst
Architectural Energy Corporation
2540 Frontier Avenue
Boulder, CO 80301
tel. 303-444-4149
fax 303-444-4303
efranconi at archenergy.com<mailto:efranconi at archenergy.com>
http://www.archenergy.com/


>>> "Rosenberg, Michael I" <michael.rosenberg at pnl.gov<mailto:michael.rosenberg at pnl.gov>> 7/1/2009 4:48 PM >>>

You have calculated the kW/cfm correctly according to the 2004 version of Appendix G. The allowance actually goes up a little in 2007, for your case. As for the second part of your question, no you do not apply the same kW/cfm to the exhaust fan. The calculated allowed fan power the total allowed power for all fans that are part of the system, including the exhaust fan. The cfm component is based on the supply fan cfm only. Unfortunately, Appendix G gives no direction on how to divide the allowed fan power up among the various fans in the system.



Mike



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From: bldg-sim-bounces at lists.onebuilding.org<mailto:bldg-sim-bounces at lists.onebuilding.org> [mailto:bldg-sim-bounces at lists.onebuilding.org<mailto:bldg-sim-bounces at lists.onebuilding.org>] On Behalf Of Vikram Sami
Sent: Wednesday, July 01, 2009 3:03 PM
To: Bldg-Sim
Subject: [Bldg-sim] Appendix G Fan Power



G3.1.2.9 Gives you a formula for calculating system fan electrical power for supply, return, exhaust and relief. Lets sat I have a zone with a PSZ-HP that has a supply volume of 1500 cfm. Using this formula along with table G3.1.2.9 I get a fan horse power of 1.29 and kW of 1.17. This equates to 0.00078 kW/cfm - which seems really high.



The second part to my question is assuming I have 500cfm of exhaust in this zone, do I apply the same kW/cfm to the exhaust fans as well as the return fans? It seems that the lower the fan volume the more inefficient the Appendix G values get from these tables.



Any guidance would be much appreciated.



Vikram Sami, LEED AP
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