How much fan power is included in the EER / SEER ratings for packaged
systems, and split systems? I want to make sure I'm not double-counting
fan energy.
My understanding (from very unofficial sources found while googling) is
that when units are tested per ARI 210/240 (or 340/360), they are tested
with a clean filter and minimal ductwork (total static of around 0.3").
Thus, you would need to back this minimal amount of energy from the EER,
and then add the actual fan energy.
If you simply use the rated EER with no adjustment, and set your supply
fan energy to zero, (as was recommended in the archives), then you will
significantly underestimate your fan energy.
So, is anyone familiar with the ARI 210/240 or 340/360 tests, and know
how much fan energy is included in these tests? Also, is the included
fan energy different for packaged units vs. split systems?
I still have never seen a reliable method of converting a code-listed
unitary performance value to condensing section EIR.
Based on my past work evaluating installed energy efficiency measures where
savings were based on installing high efficiency custom built RTUs rather
than code-compliant unitary RTUs, most savings arise from reduced internal
pressure drops and improved fan efficiencies. The downfall of the analyses
that I reviewed, if you are wondering, is an approach that can be summarized
as follows:
Annual ton-hrs * 12 ? (Base Avg Unitary EER - Proposed Avg Unitary EER)
It seems that many off-the-shelf RTUs have fan efficiencies that hover
around 55% while custom units have fan efficiencies that are around 65%.
Custom units tend to have larger coils with lower pressure drops.
Simply knowing the external static pressure during standard testing
conditions is not going to get you to a performance value for the condensing
unit if you do not also know the specific internal pressure drops or fan
efficiency.
What to assume for the generic code case fan power? For what it is worth,
my rule of thumb is to knock ~0.20 kW/ton off the unitary EER rating.
Here is my favorite, from the archives.
http://lists.onebuilding.org/htdig.cgi/bldg-sim-onebuilding.org/2007-October/005987.html
Robert P. Wichert, P.Eng.
My understanding (from very unofficial sources found while googling) is
that when units are tested per ARI 210/240 (or 340/360), they are tested
with a clean filter and minimal ductwork (total static of around 0.3").
Thus, you would need to back this minimal amount of energy from the EER,
and then add the actual fan energy.
If you simply use the rated EER with no adjustment, and set your supply
fan energy to zero, (as was recommended in the archives), then you will
significantly underestimate your fan energy.
So, is anyone familiar with the ARI 210/240 or 340/360 tests, and know
how much fan energy is included in these tests? Also, is the included
fan energy different for packaged units vs. split systems?
Thanks,
Jim
Actually I wold expect the ARI testing to be done with 0.5" of static,
which is normally the "rated" static anyway.
I don't see any need to call this "significantly underestimating" the
energy use. If you design to 0.5" of static, you're good to go.
Robert P. Wichert, P.Eng.
The Standard is available on the AHRI Web site at
http://ari.org/Content/FindaStandard_218.aspx?Listing_PK=143
All fan energy must be included and that is calculated using a minimum
external static pressure that varies with capacity (See Table 5)
James V. Dirkes II, P.E., LEED AP
This is perfect, thanks! I also downloaded the 210-240 standard.
Thanks James.
Robert P. Wichert, P.Eng.
I've been wanting to download and review those standards for a while.
I appreciate the link.
Thanks!
Regards,
James Hess, PE, CEM
Thanks for the link, James.
I still have never seen a reliable method of converting a code-listed
unitary performance value to condensing section EIR.
Based on my past work evaluating installed energy efficiency measures where
savings were based on installing high efficiency custom built RTUs rather
than code-compliant unitary RTUs, most savings arise from reduced internal
pressure drops and improved fan efficiencies. The downfall of the analyses
that I reviewed, if you are wondering, is an approach that can be summarized
as follows:
Annual ton-hrs * 12 ? (Base Avg Unitary EER - Proposed Avg Unitary EER)
It seems that many off-the-shelf RTUs have fan efficiencies that hover
around 55% while custom units have fan efficiencies that are around 65%.
Custom units tend to have larger coils with lower pressure drops.
Simply knowing the external static pressure during standard testing
conditions is not going to get you to a performance value for the condensing
unit if you do not also know the specific internal pressure drops or fan
efficiency.
What to assume for the generic code case fan power? For what it is worth,
my rule of thumb is to knock ~0.20 kW/ton off the unitary EER rating.
Eric