Efficiency of ducted split system vs packaged system (AC only)

[shaunco]

I am trying to decipher the efficiency of a ducted split system versus a packaged (central) system. For the sake of this discussion, assume both systems have the exact same amount of ducting, and thus this is strictly about unit efficiency. Take for example, the two following configurations:

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Split:
Carrier 24ANA130A0030 + FE5ANB004
Based on the 24ANA1 Product Data sheet, this combo outputs 800/800 CFM, has 20,800 - 26,600 capacity, and is 21 SEER/15 EER.

24ANA124 FLA=13.9A at 208/230V
FE5ANB004 FLA=6.8A at 208/230V

So, the combined full load amps is [highlight]20.7A[/highlight] for a 2.5 TON system


Packaged:
Carrier 50XL-A30-30
Based on the 50XL Product Data sheet, this unit outputs 1000/700 CFM, has 21,400 - 28,600 capacity, and is 15 SEER/11.6 EER.

50XL-A30-30 FLA=19.3A at 208/230V

So, the total full load amps is [highlight]19.3A[/highlight] for a 2.5 TON system

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The questions are:

1. How can the packaged unit have a higher cooling capacity and CFM, but yet have a lower SEER and EER rating?
2. Is SEER and EER that useless?
3. Is there some loophole in the SEER / EER ratings that allows manufacturers to state SEER numbers for just the condenser (without the fan) ... and thus split units can have higher ratings? ... this doesn't seem to be since Carrier lists SEER ratings for the combination of both parts of a split systems.
4. Is this a marketing ploy to get people to buy two units from Carrier instead of one? I can't find pricing online for any Carrier units, but I would guess that the split system is more expensive.

What am I missing here?

 

[shaunco]

Sorry, for question #1 I meant to ask:
1. How can the packaged unit have a higher cooling capacity and CFM [highlight]using 1.4A (322 watts) less power[/highlight], but yet have a lower SEER and EER rating?

 

[walz]

Both Package Unit as well as the ducted split units are comprised of these three things which consume electrical energy.

1. The compressor
2. The Condensor Fan
3. The Evaporator Fan

It is these three things in both whose individual configuration and efficiency counts first. which off-course determines the SEER and EER rating as a whole.

There are different types of fans, because of configuration and their type one may consume more energy and produce less flow and other may consume less energy and produce more flow. Similary there are types of compressors. Some are efficient more than other (in the sense they consume lesser energy)

So i do recommend lets study each of these three components one by one in the two - the package and the ducted split

 

[marcoh]

The amps may also be the full load current for each component and may not actually draw that much.

Everything else being the same, a package unit should be lightly be more efficent as it has less refrigeration pipe length.

 

[walz]

The conditions which shaunco is assuming will not have much difference in the refiregerant piping lengths. He has mentioned the ducting length for both to be the same. In actual its not, Ducting of Ducted split is much less than a package unit. But he is assuming for both of these units to have same ducting.
This assumption can only be possible if both condensing and evaporating unit of ducted split unit are kept at same location / floor. and thus the refrigerant piping shall be almost also same as of package.

 

[shaunco]

For the ducting and refrigerant piping, I'm really comparing a packaged system on the roof of a 1 story house vs a split system with the compressor and Condenser/outdoor fan on the roof with the evaporator and air mover mounted in the attic, directly below the Condenser. So, it reality the packaged unit will likely have 18-24" of extra ducting and the split system will likely have 18-24" of extra refrigerant piping. If both of these were new, tightly sealed, and nicely insulated... there really shouldn't be any difference between the two.

As for comparing individual specs (all for "units without electric heat" ... that is, AC only):

--------------------------------
Split
Product Data:

http://www.docs.hvacpartners.com/idc/groups/public/documents/techlit/24ana1-3pd.pdf

http://www.docs.hvacpartners.com/idc/groups/public/documents/techlit/fe4a-07pd.pdf

Compressor: LRA=52.0, RLA=10.3
Condenser Fan: FLA=1.1
(outdoor MCA=13.9)
Evaporator Fan: FLA=6.6
(indoor MCA=8.5)

Packaged
Product Data:

http://www.docs.hvacpartners.com/idc/groups/public/documents/techlit/50xp-05pd.pdf

(It looks like I messed up previously and took numbers from the -24 unit, not the -30... so, the -30 uses 0.3A more than the 2.5T split system ... is that enough to justify +6 SEER?)

Compressor: LRA=73.0, RLA=15.9
Condenser Fan: FLA=0.8
Evaporator Fan: FLA=4.3
(unit MCA=23.6)
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It does seem that the compressor in the split system is considerably more efficient, but both fans in the split system are less efficient. It seems odd that Carrier wouldn't use the super efficient compressor from the 24ANA split units in their packaged unit.

Are there other specs in those sheets that are worth comparing?

Also, I should mention that my selection of Carrier was arbitrary, as I didn't want this to be an "in general" conversation... but, I see similar data in Rheem and Lennox units.

 

[walz]

Other Specs are the heat exchanger efficiency of condensor and evaporator in both split and package. thats what make the cooling capacity.

 

[MintJulep]

The FLA rating on the nameplate will not be the same as the amps drawn at the "rating" condition.

FLA is used to size breakers and wiring.