SEER Rating and Energy Costs - How accurate

[pingable]

for example, my 10 year old Frigiaire has a Seer rating of 10
The split ductless same BTU has a Seer rating of 21.

Does that in the literal sense mean that for every 2 hrs I run the splitless, it would cost me the same as 1 Hr running the older Frigidaire ?

[amd]

Efficiency greatly varies depending on operating conditions, sizing, and quality of installation. If the blower doesn't move enough air, the ductwork leaks into a unconditioned space, or the system isn't charged correctly, you can kiss the high SEER rating goodbye.

SEER ratings should only be used to compare units of the same class. (Ex: 3 ton 13 SEER vs 3 16 SEER split system, everything else being equal)

[pstu]

for example, my 10 year old Frigiaire has a Seer rating of 10
The split ductless same BTU has a Seer rating of 21.

Does that in the literal sense mean that for every 2 hrs I run the splitless, it would cost me the same as 1 Hr running the older Frigidaire ?
I believe you have it exactly right, the SEER number is advertised to homeowners as being in direct proportion to the electricity consumed. I am a homeowner and so not qualified to know many technical aspects of HVAC, but I learn what I can. And this after all is a number directly promoted to homeowners.

AMD's warning about comparing only similar systems, that sounds important and I did not know that. He points out SEER is a laboratory number, and assumes the installation is essentially perfect. Any shortcomings in one's actual installation, such as poor ducts, can piss away much of the savings you think you have gained with high SEER. One of the most repeated statements on this board is that the installation must be high quality or you cannot get quality results, I hope you can get the best installer available in your area.

Best of luck -- Pstu

[gary_g]

SEER is a weighted average of EER's over a fictitious cooling season.

Here are the outdoor temps and the weighted averages associated with each temp to calaculate SEER for a system with a variable speed air handler:

67F (21.4%)
72F (23.1%)
77F (21.6%)
82F (16.1%)
87F (10.4%)
92F (5.2%)
97F (1.8%)
102F (.4%)

Total = 100%

Note that the 2 lowest ambient temps make up almost half of the value of the SEER calculation.

[pstu]

I really appreciate that added info Gary_G. Where I live in S.Texas, we could spend nearly zero time at those lowest ambient temps, for most of the summer. One more example of a nationwide rule that ill fits our region. People have told me that in Texas at least, the EER is a more reliable number to look at. Unfortunately the Trane systems I have are not outstanding at EER the way they are at SEER. Do you agree?

Are you saying with a non-VS air handler, the temperature categories are different? I would not have thought of that.

One more thought: the XL19i specs I see, suggest EER about 30% higher on 1st stage vs. 2nd, a benefit I believe is not reflected in SEER ratings because of the standard test. That is plainly true in the Trane performance data, and is a pleasant surprise because my system as installed has very long runtimes in 1st stage.

Best wishes -- Pstu

[pingable]

Interesting Read Gary...
Let me dig into PDF sheets of systems I am looking at
I wonder if there is different published SEER ratings for a unit that does both heat and cooling.

Makes me wonder how much I should be getting ~CAUGHT UP~ in SEER ratings when comparing units...

[gary_g]

Interesting Read Gary...
Let me dig into PDF sheets of systems I am looking at
I wonder if there is different published SEER ratings for a unit that does both heat and cooling.

Makes me wonder how much I should be getting ~CAUGHT UP~ in SEER ratings when comparing units...

For a heat pump, you should be looking at HSPF also.

My State, Maryland, has more of a heating climate than cooling, so HSPF and heating btu output were very important to me when selecting a heat pump.

[gary_g]

I really appreciate that added info Gary_G. Where I live in S.Texas, we could spend nearly zero time at those lowest ambient temps, for most of the summer. One more example of a nationwide rule that ill fits our region. People have told me that in Texas at least, the EER is a more reliable number to look at, do you agree? Unfortunately the Trane systems I have are not outstanding at EER the way they are at SEER. Do you agree?

Are you saying with a non-VS air handler, the temperature categories are different? I would not have thought of that.

One more thought: the XL19i specs I see, suggest EER about 30% higher on 1st stage vs. 2nd, a benefit I believe is not reflected in SEER ratings because of the standard test. That is plainly true in the Trane performance data, and is a pleasant surprise because my system as installed has very long runtimes in 1st stage.

Best wishes -- Pstu

3 years ago, when I was looking to replace my old heat pump before it failed, HSPF, haeting btu output, and EER were what I was going for. I wasn't interested in a 2-stage condenser (16 SEER) because the heat pump would be used more for heating. I went with a 14 SEER that got 12 EER and 9 HSPF. The 13 SEER had too low of an EER and HSPF for me.

For a fixed speed fan in the air handler, the SEER calc is very different.

There is no weighted average summation of the EER's at various ambient temps.

SEER = EER at 82F ambient multiplied by a few fudge factors.

The SEER calc for a 2-stage compressor with a variable speed air handler is much more complicated than for a single speed compressor, although the same weighted average summation of EER's at the stated ambient temps is used.

The SEER calc for a 2-stage compressor does indeed take the higher 1st stage EER into consideration. That is reason for the higher SEER#. Same applies to variable speed compressor systems.

If you want to read all of the details, download a copy (125 pages) of
AHRI Standard 210/240, Performance Rating of Unitary Air-Conditioning & Air-Source Heat Pump Equipment.

It's heavy on the math, but it gives you a good idea on how these efficiency ratings are calculated.

Take care.

[skippedover]

How the actual SEER rating is calculated is interesting but irrelevant to the question. If any unit operating at a given temperature is rated at 10, then another unit operating at that same temperature and rated 13 is 30% more efficient than the 10-SEER unit. Whether the user sees that 30% over the coarse of a summer depends on how warm or hot the summer is from year 1 to year 2. Or for that matter, from hour 1 to hour 2, etc. In a mini-split system there are no duct leaks and no duct gains or losses. The entire unit is in the treated space. The fact that the mini-split is an inverter/ECM type of motor application compicates the daylights out of establishing a SEER rating but some of them are getting right up there at 26-SEER! But take the same indoor unit and connect it to a 2 or more zone outdoor unit and the SEER ratings are impossible to find. I don't think they've settled on a methodology to determine the rating as yet.

[gary_g]

If any unit operating at a given temperature is rated at 10, then another unit operating at that same temperature and rated 13 is 30% more efficient than the 10-SEER unit.

That would imply that the EER is 30% better.

Take care.

[beenthere]

That would imply that the EER is 30% better.

Take care.

EER is a straight line rating.

A/C's don't have a straight line in their operation for 10 to 15 minutes.
EER is not an accurate method for any A/C with a stat set to 2 or more CPH. Except when the outdoor temp is above 60 or 70% of the systems capacity.