Separating Fan Energy from EER

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Hi All,

There are strings about this subject in the archives, but they do not fully
answer my questions and I am not able to open some of the key attachments.
Here is my question: Is there a LEED-accepted method for separating out fan
energy from an EER? I am looking for how this can be done without eQUEST
doing some behind-the-scenes calculations/assumptions. There is an equation
that was given in a former string, but I don't know its source or whether it
is an accepted method by the reviewing committee. Again, I am looking to be
able to show how this is done by hand.not how to get eQUEST to do it for me.

Thanks very much for your help,

Christian

Christian Kaltreider, LEED AP

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Joined: 2011-09-30
Reputation: 1

Hi Christian,

USGBC/LEED/90.1 does not officially sanction or require any eQuest-specific procedure (nor any other program), so ultimately it falls on the modelers to know what the heck we're doing and be able to defend it in cases like this.?

As a qualifier, not all efficiency ratings are fan-energy-inclusive.? For those that are, the procedure I follow (using a spreadsheet) is to basically:

1. Using the maximum design capacity, translate the prescribed/scheduled efficiency from SEER/EER to kW input at maximum capacity.? You may have noticed there's more than one SEER equation out there... For seasonal efficiencies (SEER/AFUE), there are various formulae for conversion to steady-state efficiencies (EER/COP) that vary based on what kind of equipment you're dealing with.? You'll also find that certain equipment like heatpumps have multiple equations referenced, as there are multiple white papers published over the decades that attempt to establish a relationship between nominal seasonal efficiency and steady-state efficiency, where each study sampled different equipment from a different period of time.? What does this mean for today's LEED modeler?? There are multiple right answers (provided you know where you're coming from).? To give a more concrete response on this point, here are the equations I have collected and currently use for baseline system seasonal efficiencies (with references):

EER=f(SEER):

[Reference: NREL Building America House Simulation Protocol (Revised), citing Wassmer, M. (2003). A Component-Based Model for Residential Air Conditioner and Heat Pump Energy Calculations.]

(AC) (Baseline Systems #1, #3, #5 & #6):

EERNET = -0.0182*SEER^2 + 1.1088*SEER

(HP-cooling) (Baseline Systems #2 & #4):

EERNET = -0.02*SEER^2 + 1.1268*SEER

COP=f(HSPF):

[Reference: Wassmer, M. (2003). A Component-Based Model for Residential Air Conditioner and Heat Pump Energy Calculations. Masters Thesis, University of Colorado at Boulder.]

(HP-heating) (Baseline Systems #2 & #4):

COPNET = -0.0255*HSPF^2 + 0.6239*HSPF

HIR = f(AFUE):

[Reference: California Energy Commission's 2005 "Nonresidential Alternative Calculation Method (ACM) Approval Manual"]

For single packaged central furnace (baseline system #3):

HIR = (.005163*AFUE+0.4033)^-1

For Boilers where 75 ? AFUE < 80 (Baseline systems #1, #5 ):

HIR = (0.1*AFUE+72.5)^-1*100

For Boilers where 80 ? AFUE < 100 (Baseline systems #1, #5 ):

HIR = (0.875*AFUE+10.5)^-1*100

*Note: The cited references above are freely accessible on the internet, last time I checked.? If anyone has a "better" equation to suggest, (knowing where the equation came from), please share!?

2. For baseline systems, calculate the system fan energy Pfan.? For proposed systems, calculate the actual system fan energy in kW.

3. Using the system fan design airflow(s), enter the calculated fan energy as kW/CFM under airside systems tab.

4. Subtract #2 from the cooling "kW input" in #1 - this is the "other-than-fan energy."? Using the design cooling capacity for the system, turn that into an EIR figure for input in the model.

Those who make the effort to understand what's happening have the right idea.? Relying on others' work and tools without fundamental understanding on occasion is necessary, but it's a slippery slope to be sure.?

Best of luck to you!

~Nick

NICK CATON, P.E.

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Reputation: 805

Nick and Christian,
The 90.1 prescriptive performance values for unitary equipment are based on ARI rated conditions. The 90.1 baseline fan power allowance does not directly align with the fan energy used in the ARI test. The fan energy in the ARI test is based on 365 W/1000 CFM and 400 CFM/12000 Btu/h. I believe you should use your baseline system equipment capacity (Btu/h or KW) to calculate the amount of fan energy to 'extract' from the cooling equipment EER/SEER/COP rather than the 90.1 baseline fan power allowance as indicated below in step 4. If you use the 90.1 baseline fan power allowance, you could be removing a larger fan power value, making the cooling equipment more efficient in the baseline than the tested performance requires.

Also, the ARI tests are based on specific temperature conditions so you may need to adjust for project specific design conditions.

Regards,
Bill

Bill Talbert PE, LEED(r) AP

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Bill,

I agree that the fan power at ARI conditions, and not the Appendix G
baseline fan power (#2 in Nick's email) should be used to calculate EIR.
Using the method that Nick described may create various anomalies, for
example negative baseline EIR in instances where Appendix G baseline fan
power is high due to allowed pressure drop adjustments from Table
6.5.3.1.1B.

Thanks,

Maria

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Bill and Maria, thanks for adding to the discussion!

Maria, my apologies: ?I recall you and I delved deeply into what the ARI standards do and don't explicitly say on this issue, and I feel sorry for forgetting to express this parallel viewpoint.? I believe you and I ultimately agreed to disagree on this particular issue. ?For others' benefit, here is a small excerpt I'd like to share where I think I drew the line as clearly as I can:

To put it another way: I immediately recognize that the approach you're describing, which sticks to 365W/1000CFM on the EIR/HIR calculations while imposing the calculated Pfan separately, is advantageous from a performance rating perspective in that it maintains "realistic" fan-exclusive cooling and heating efficiencies (EIR/HIR), but it also tosses the idea of a "whole system" efficiency (like SEER) representing the total of fan and other energies - a reality your proposed systems are naturally representing if you're working from real-world equipment cutsheets.? I'm all for adopting procedures that boost my modeled performances, but could you reconcile this concern?

Ultimately, it's a question of whether one feels the calculated system fan energies (i.e. Pfan) should or should not be used to ensure the prescribed whole-system efficiency is maintained.? Maintaining the system efficiency while sticking with system fan power as prescribed may result in "unrealistically efficient" heating or cooling.? You must give from one end or the other when you take either approach.

Personally, I am comfortable and content to stick with the approach I've described, as I feel the overall system efficiency is the more explicit mandate.? Simultaneously, ?I do not begrudge anyone for taking an approach to calculate EIR/HIR values using varying fan powers, but I'll also maintain the approach I describe will result in more efficient (if occasionally "unrealistic") baseline performance (to the detriment of the final performance rating). ?If one thing's clear, it's that 90.1 is not clear on this issue =)!?

I would much rather encourage all interested parties to read up on the ARI testing procedures (see attached discussion with links from Maria), consider both sides, and make a personal decision.? The best position is the one you can defend, and I personally see both sides as quite defensible.

~Nick

NICK CATON, P.E.

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