# 90.1 App G Fan Power and EER Calculations

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I'm sure this must have been asked before but I cannot find an answer in the archives - if there is one please point me to it.

I have interpreted the requirements of 90.1, App. G to split the EER of cooling equipment with a supply fan into its components to model the fan energy separately as follows:

1. Say a space has a cooling load of 80,000Btu/h and the system is packaged single zone, EER - 11.2.

2. Calculate airflow for 20?F temperature difference - 3708cfm

3. Calculate fan bhp from Table G3.1.2.9 - 3.49bhp

4. Calculate fan power as per G3.1.2.9 - 2972W

5. Calculate gross input power from load and EER - 7143W

6. Subtract 4 from 5 for compressor/condenser input power - 4171W

7. Convert to EIR - 0.1779

This appears to make sense from reading App. G but ends up with high fan power consumption and low space cooling loads. Am I wrong here?

Thanks,

Steven Burley

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Uday,

My understanding is the EER in the table, in this case 11.2 for packaged AC between 65,000 and 135,000 Btu/h, is the overall efficiency of the equipment, i.e. including the fan power. It seems from what you have written below you say it does not; is that correct?

Regards,

Steven Burley

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Steve,

There are two schools of thought for dealing with fan power in cooling efficiency calcs. The first pulls away the baseline fan power Pfan, as you're describing, and the other instead pulls out a fan energy draw based on ARI testing procedures... 400 CFM/ton --> 365W/1000CFM. I follow the latter these days, but see both as viable.

The two approaches result in similar results when your Pfan calculation doesn't involve a lot of static pressure adders. When it does, the approaches diverge in a fashion that may be either problematic or helpful in a LEED rating sense. Attached discussion sums up things further, includes an outline of an ARI-based approach. You can find more discussions and read into advantages/disadvantages to both approaches in the mailing list archives.

That said, I haven't checked your math or references but the procedure you've roughly outlined sounds alright for a Pfan approach. There are steps in between what you've written for correctly coming up with Pfan, but I take it that's implicit.

~Nick
[cid:489575314 at 22072009-0ABB]

NICK CATON, P.E.

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Nick, Steve, and list,
I think I concur more with Steve. If you use Nick's approach to calculate the cooling EIR by subtracting out ARI rated fan power from the 90.1 EER AND then model the 90.1 fan power limits directly, you will be modeling a packaged unit that does not comply with the package EER.
I could see using other splits of fan and cooling, but a baseline model should comply with both limits.

Paul Riemer, PE, LEED AP BD+C

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Hi Paul!

I maintained the exact same position for a long while, though I thought I was the vocal minority =)! Ultimately, you can argue for/against either approach as having different advantages of 'correctness.' I've heard future addenda or versions of 90.1 may address the conundrum by stipulating something more simplistic than either approach, like a uniform "factor" to come up with compressor/condenser energies from the total consumption.

My final position is both approaches make sense, and for different reasons - modelers should use whichever they feel most comfortable defending should their methodology come into question. My LEED reviewers have to this point taken zero interest in which approach I've used in my calculations, after using both, so I take it this degree of nuance is probably not on their usual checklists. I've switched over to the ARI approach for a few reasons, but not because I feel a Pfan-based approach is 'wrong.'

Best wishes,

~Nick

[cid:489575314 at 22072009-0ABB]

NICK CATON, P.E.

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Nick, Steve and Paul,

I believe that using ARI fan power in EIR calculations is the way to go,
because the efficiency tables in 90.1 Section 6 show the required
performance at ARI conditions (see the last column in each table), not at
the project conditions. Here is the related abstract from 90.1 Section 6:

6.4.1.1 Minimum Equipment Efficiencies?Listed

Equipment?Standard Rating and Operating Conditions.

Equipment shown in Tables 6.8.1A through 6.8.1G shall have

a minimum performance at the specified rating conditions

when tested in accordance with the specified test procedure.

When a packaged system that meets 90.1 efficiency requirements at ARI
conditions is installed in a project where the fan power is higher than in
ARI testing procedure (e.g. projects with more extensive ductwork, air
filters, energy recovery, etc.), it will have a lower actual EER than what?s
listed in Section 6. However, this wouldn?t make the installation
incompliant with mandatory efficiency requirements in 90.1 Section 6. In my
experience, LEED reviewers do comment on EIR calculations if EIR is not what
they expect. However, using Appendix G fan power in baseline EIR
calculations typically results in a more stringent baseline (lower EIR), so
they do not insist on changing it.

Thanks,

Maria

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I received a comment back from a recent LEED submission. The reviewer required
that I calculate pfan per G3.1.2.9. I didn't argue since this increased my
baseline energy consumption and increased my proposed savings.

Paul Diglio, CEM, CBCP

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Paul,

I think we are all in agreement that Pfan must be calculated as described in G3.1.2.9 when modeling the baseline fans. This discussion is about extracting the fan energy from the rated EER when modeling system efficiency (EIR) to satisfy G3.1.2.1 quoted below:

G3.1.2.1 Equipment Efficiencies. All HVAC equipment

in the baseline building design shall be modeled at the minimum

with Section 6.4.Where efficiency ratings, such as EER

and COP, include fan energy, the descriptor shall be broken

down into its components so that supply fan energy can be

modeled separately.

G3.1.2.1 refers to efficiency requirements in Section 6.4, which in turn refers to efficiency at the rating conditions and not the project?s design conditions (see 6.4.1.1 included in my earlier email below). If the efficiency requirements in 6.4 were for the design conditions, then I would agree that Pfan should have been used to convert from EER to EIR.

Maria

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Maria:

Yes, I agree. I use the supply fan power at the design static from the
manufacturer's data sheet for the proposed model. I then re-calculate the unit
EER without the supply fan power, which raises the EER and lowers the EIR.

Perhaps I am misunderstanding the thread. It seems that some people are
talking about the baseline because they reference Section 6. So it appears
that some simulators are using the ARI fan rating instead of using G3.1.2.9 to
calculate pfan for the baseline? It doesn't appear to be any wiggle room in
G3.1.2.9 as it states:

"G3.1.2.9 Supply Fan Power. System fan electrical power
for supply, return, exhaust, and relief (excluding power to fanpowered
VAV boxes) shall be calculated using the following
formulas:"

Is this your understanding of the thread? I am a bit confused.

Regards,

Paul Diglio, CEM, CBCP

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Maria/Pauls:

My reading is everyone is talking about the same topic: Whether fan energies removed to determine cooling EIR should be the value calculated for Pfan or an independent value determined via ARI testing protocol. Paul is taking the position Pfan is better because using that maintains the implicit ?whole system efficiency? requirement, and Maria is taking the position the ARI procedure is better because doing otherwise can/will result in cooling efficiencies (cooling EIR) that are entirely arbitrary and non-representative of the testing conditions.

Having played for both teams over time, I?m sitting on the sidelines saying you?re both correct.

I don?t think anyone is suggesting using anything other than the calculated Pfan for baseline fan energies.

~Nick

[cid:489575314 at 22072009-0ABB]

NICK CATON, P.E.

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Paul,

Here is the way I look at it. EER describes combined performance of the refrigeration system and fan at some given conditions. To isolate refrigeration system efficiency as required in G3.1.2.1, we need to take out the fan energy at the conditions for which EER is given. Since Section 6.4 gives EER at the ARI rating conditions, we need to use fan power at the ARI rating conditions in the EIR calculations. The same logic is followed by eQUEST Wizard, and is described in the eQUEST EER to EIR Conversion document that was shared on the forum many times before.

Once EIR is calculated, the next step is to model the fan power explicitly as required by G3.1.2.9. To get there, I use G3.1.2.9 to calculate total W/CFM for the baseline fan system, and then enter it into eQUEST allocating it between supply, return, etc. eQUEST Wizard similarly allows you to specify the actual fan power for the project via pressure drop in the ductwork and fan motor efficiency. I apply the same logic to the proposed design. To calculate proposed EIR, I use the fan power at the conditions for which EER is given, and then model fan power based on the fan system specified for the project.

Thanks,

Maria

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Maria has brought me closer to the testing protocol side (thanks Maria) but I am still struggling a bit with it. The AHRI standards do not regulate cfm/ton or W/cfm directly , they bound cfm/ton and require a minimum external static value that varies by system size. Hence the assumptions that I am tempted to scrutinize especially when 90.1 Ap G requires a 20F DT and some equipment has DC/EC motors.

(Rhetorical questions: What am I looking at when my custom AHU selection shows an EER value? For the baseline should I always start with the electric resistance/no heat EER value because the difference between the EER values is mostly due to the added static of the heating coil?)

Lake is too muddy today, should have never gotten in?back to the dock.

Paul Riemer, PE, LEED AP BD+C

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