Validity of SEER ratings on AC units 1

[wfowfo]

I may not have the right forum here, so apologies in advance. Also for length!

The electric Coop I work for spends a lot of time and effort promoting high efficiency AC units (SEER 14 or better).
On the other hand, my brother-in-law sells AC units for a living and has the opinion that, once you get above a certain SEER rating (ie-12), the SEER values become more a matter of the manufacturers ability to manipulate the criteria involved in establishing the values.

His example: The poverty level of <$8,000/yr. hits 10%. So you re-define the poverty level to <$10,000/yr. Fewer people qualify, therefore the poverty level drops to 8%, and it looks like everything is getting better for everyone.

His point being that the criteria used to develope high SEER values becomes more of a marketing game than pure engineering.

What little I can find on the subject indicates that SEER values are established at some arbitrary temperature difference (a 2 degree differential) and not particularly representative of the units efficiency at more realistic temperature extremes.

Any comments? If the above is true, is there a better method of evaluation? We don't want to promote something at our Coop that costs our members more money, but isn't founded in anything more than a marketing ploy.

 

[MintJulep]

You might have been better off in the HVAC forum.

Your brother-in-law is close to being correct. SEER is determined by testing a unit using the test methods described in ASHRAE Std 116. I don't have a copy handy, but I believe that the standard defines the test method only, not the test conditions.

This means - as your brother says - that the manufacture gets to pick the test conditions that return the highest SEER number for a particular piece of equipment. These test conditions are unlikely to be representative of any real-world installation.

So, to put any real meaning to SEER ratings you need to know the test conditions. Manufacturers typically do not give these out.

I beleive that ASHRAE is in the process of revising std 116 to define a standardized test condition to stop this game.

 

[tombmech]

It may be that DOE references certain ASHRAE Standards, but the essential equipment testing procedures are defined by law by the DOE. If I'm not mistaken, the ASHRAE Std. deals more with the temperature and bin data for estimating year round loads to be used in the DOE SEER calculations.

For the specific equipment testing procedures, this is a good place to start:

http://www.eere.energy.gov/buildings/appliance_standards/residential/central_ac_hp.html

It's pretty rigorously defined as far as the actual procedures, and as mentioned, is law. We may debate the finer points of efficiency ratings and whether mfrs have learned to optimize the results, but the discussion is really moot.

 

[bigTomHanks]

The process/equations used to calculate the SEER value of a system is very complicated and I would suggest that you get the ASHRAE Std. 116 just to see for yourself. The minimum SEER requirement will soon be 13, if it is not already. Companies add thermal expansion valves (TXV's) and more efficient compressors to increase the SEER value to 13(federally required). Other techniques are used as well. The TXV optimizes the evaporator efficiency and switching to a scroll compressor helps efficiency because they are more efficient. So in my opionion, the addition of these components do increase the SEER rating(and cost) of the system and to make the claim that the testing method or conditions are just being manipulated have little merit. Marketing is slick, but when you add technology that is proven to increase efficiency then you should actually get increased efficiency.

 

[tombmech]

I don't think anyone is stating that the testing method is being manipulated, or that the results are false. The manipulation occurs in optimizing for the specific SEER value, when other factors may be just as important in cost and value to the customer.

Improvements in increased efficiency are often accompanied by penalties elsewhere. Those penalties may increase long-term costs by more than the specific energy savings.

So, the more accurate way to frame the discussion may be, "Is a unit with the highest SEER the absolute best purchase at all times?" The answer to that question is not always simple.

 

[wfowfo]

Quote;
"Is a unit with the highest SEER the absolute best purchase at all times?"

Perhaps that is how I should have phrased my question to start with.
For example, I infer that the "82 degree outside, 80 degree inside' test doesn't necessarily reflect real operating perameters. So given a certain SEER derived from this process (no matter how legitimatly) will any given unit with that SEER work equally well at 100 degrees in Houston as it does at 40 degrees in St. Paul? Or will some perform better than others?
If, for a given SEER, the efficiencies do vary between "test" temperatures and "realistic" temperatures, is there a more realistic way for a layman to evaluate the efficiency of a unit for a given environment?

 

[IRstuff]

You're actually asking two different questions. The fundamental question about SEER is similar to that about car MPG, i.e., your mileage may vary.

The first question posed can be answered by asking yourself whether the incremental increase in SEER is justified by the commensurate cost increase. In some absurd cases, the highest SEER comes with a substantially higher cost that may never be recovered, resulting in a less than "best value" purchase.

TTFN

 

[tombmech]

There's an interesting Table below that reduces this info down to a typical 3 ton residential A/C unit. You can compare the estimated energy savings per year in dollars, and use that to compare to the increase cost of a higher-rated SEER unit. In the old days, paybacks were based on 5 years or less. These days, commercial and industrial life-cycle costs are based on 20-30 year time periods. Of course, these calculations also take interest and the time-value of money into consideration.

For a residential unit, 10 years is probably a reasonable life expectation. If the cost difference won't result in a payback of less than half that period, then I wouldn't buy it. Half of that period is reasonable because as mentioned, there's the time value of money (earning interest) and inflation. There are other considerations as well. A unit on the cutting edge of energy efficiency will often have a shorter life, too.

http://www.acdoctor.com/enegry_savers/table.htm

It says the table is " *Based on 2800 annual cooling hours, 3-ton (36,000 BTUH) A/C, and 9 cents per KWH." for reference, the originating page is here:

http://www.acdoctor.com/enegry_savers/air_conditioning_system.htm

 

[wfowfo]

Good table. Thanks!