[Bldg-sim] Fan Power and EER

RobertWichert robert at wichert.org
Tue Dec 13 07:47:57 PST 2011


Back about four years ago:
http://lists.onebuilding.org/pipermail/bldg-sim-onebuilding.org/2007-October/005973.html

There was  a long discussion of COP and EIR and fan power and many 
interesting points were made by many knowledgeable engineers and 
modelers on this list.  I learned a lot from this discussion, but now I 
have started using EnergyPro and the topic has reared its ugly head 
again for me.  If anybody wants to stir the old coals of that 
discussion, or point me to the definitive post on the topic, I'd be 
pleased to hear from you.  Brandon Nichols and Xiaobing Liu were 
especially helpful before.  Gentlemen, if you are still on this list, 
I'd love to hear from you.

Here goes:
EnergyPro asks for fan horsepower for the AC unit.  I have been entering 
the nominal horsepower and getting out-of-compliance results (fan power 
too high).  I have also computed actual horsepower using FLA and 
Voltage, but that doesn't drop it much at all.  When I put FLA x Voltage 
horsepower in, it's still out-of-compliance with CA T-24 CEC.

I reviewed ANSI/AHRI Standard 340/360-2007, which is the EER rating 
standard, and it says:
6.1.3.2 Indoor-Coil Airflow Rate. All Standard Ratings shall be 
determined at an indoor-coil airflow rate
as outlined below. All airflow rates shall be expressed in terms of 
Standard Air.
a. Equipment with indoor fans intended for use with field installed duct 
systems shall be rated at the
indoor-coil airflow rate (not to exceed 37.5 SCFM per 1000 Btu/h [0.06 
m3/s per 1000 W] of rated
capacity) delivered when operating against the minimum external 
resistance specified in Table 5 or at a
lower indoor-coil airflow rate if so specified by the manufacturer.

And then Table 5 says "0.75 in. H2O" for my size unit (25 tons).

So, I conclude from this that if I design the duct work to have NOT MORE 
THAN 0.75 in. H2O pressure drop to the supply register I can omit the 
fan power.  IS THIS CORRECT?

OUTSTANDING QUESTIONS:
1)    Is a rooftop unit "Equipment with indoor fans intended for use 
with field installed duct systems".
2)    If I did design for more than 0.75 in. H2O, how would I compute 
the extra horsepower?
3)    Or is this fan horsepower just for auxiliary fans, not associated 
with the equipment?


Sorry about the deja vu of this, but it's something I have to get a grip 
on today....

Cheers!



-- 
Robert Wichert P.Eng. LEED AP
+1 916 966 9060
FAX +1 916 966 9068







===============================================



More information about the Bldg-sim mailing list