SEER and Fan Energy

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This forum has discussed fan energy before, and since that time I have
grappled with the concept of fan power, specifically how to avoid double
counting fan power since even indoor fans are included in SEER ratings.

I suppose that I should start by confirming that indoor supply and
return fans are included in SEER ratings. I have read the DOE 49 CFR
Pt. 430, Subpt. B, App. M UNIFORM TEST METHOD FOR MEASURING THE ENERGY
CONSUMPTION OF CENTRAL AIR CONDITIONERS AND HEAT PUMPS. It seems clear
in that method that indoor fans are included in the power and energy
calculations. If not, please let me know what I am missing.

OK, if indoor supply and return fans are included in the SEER rating,
then why would we put additional fan energy into our calculations? Does
EQuest, EnergyPro, E+, and all the rest do some math to subtract this
out, and if so, how is that done?

Sorry for the basic question, but I have thought about this a lot and
haven't reached a comfortable solution. At one point I thought that the
SEER calculation did not account for indoor fans, but I now find that to
be wrong.

Your thoughts are appreciated.

--
Robert Wichert P.Eng. LEED AP BD&C

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Robert, I don?t know if I understood your question; If I did this is my
opinion: In some cases Indoor fans are included in SEER (E.g. Rooftop).
Since you are modelling fans and Refrigeration cycle efficiency separately,
you need to subtract this energy from the SEER calculation. On the other
hand, additional fan power is related to the baseline for 90.1, and its
additional fan power your Baseline will use so that certain beneficial
aspects of the proposed design or equipment (eg. Merv 13 filter) are not
excluded from the project because of energy increase.

In *Energypro* you model the rooftop and you have inputs for Cooling

Santiago Velez

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That makes sense, Glenn. So it's a manual adjustment to the EIR. In
Energy Pro, which I use a lot, that can be done by using the
"Compressor/Condenser Power" option and then adding the fan power in
separately, but only for systems over five tons. Smaller systems are
stuck with SEER.

I think the problem I'm facing is that Energy Pro uses SEER for small
systems, not EER/EIR.

Robert Wichert P.Eng. LEED AP BD&C

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If I understand the quandary you are referring to packaged systems where the fan energy is included in the package. In eQUEST - if you select the EER rating (or SEER rating) in the wizard, then its my understanding that the program does this automatically for you. However, if you are using the 90.1 methodology, then you probably want to go beyond the wizard. I developed the attached spreadsheet to parse out the energy by fan and cooling - feel free to use it. I would appreciate feedback from anyone willing to check my math and methodology.

Vikram Sami, LEED AP BD+C

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Thank you very much, Vikram. So far it looks great!

I'll let you know more as I find out more.

Best regards,

Robert Wichert P.Eng. LEED AP BD&C

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Vikram,

I agree with your assessment of the way eQUEST deals with packaged
systems fan energy and cooling efficiency through the wizard. I always
end up using the detailed interface instead though.

Thanks for sending the spreadsheet. I did look at it and made a few
edits that I will describe below. I would also appreciate any feedback
from anyone.

* I edited the lookup table to find the next size up motor hp
based on bhp; this is to find the motor efficiency only

* I used different fan cfm for the example units you listed (400
cfm/ton)

* I changed some of the units of measure to kW instead of Watts
(just personal preference)

* The main change I made was to deal with fan heat. Rated
capacity and efficiency are based on total input power and net cooling
output. So in order to deal with the fan separately we need to subtract
the fan input electricity from the unit electricity input (as was done),
but we also need to subtract the fan heat from the net cooling capacity
to arrive at the gross cooling capacity. The gross EER and EIR are then
calculated with fan input and heat removed. After eQUEST adds the fan
input electricity and fan heat then you end up with the rated efficiency
(if you're at rated conditions). I added columns related to fan heat
and adjusted the EER and EIR equations. You can change Fan Heat Frac.
To zero (as if the fan motor is outside of the unit) to see the impact.

Hopefully this is of help to some.

Best regards,

Michael L. Kingsley, PhD, PE, CPMP, LEED AP

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The testing and calculations for SEER include a small amount of supply air fan heat.

Suggest reviewing AHRI Standard 210/240-2008, particularly Table 11 on page 20 (same as Table 2 in 10 CFR Part 430 which is shown further down in AHRI 210/240-2008 on page 56).

http://www.ahrinet.org/search+standards.aspx

For example, for a 4-ton cooling system the minimum external static pressure for testing is only 0.2 in. H2O. In real systems installed in the field, the external pressure drop due to ductwork, etc. is typically much higher that this test value. That is why its typically best to subtract the fan power and enter "gross" cooling capacity in the software, and then model fan power separately using more reasonable external static pressures than those used for lab testing to support the SEER calculations.

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