seer rating doesn't match power draw

SEER ratings are done at specific Dry bulb & Wet bulb temps for both the exterior and interior. Interior Temps: 80 F Dy bulb, 67 F Wet Bulb Exterior TEmps: 82 F dry bulb, 65 F Wet bulb

High SEER system see can see a faster degradation in efficiency than lower SEER systems as it gets hot outside. ASHRAE recommended a better system for testing efficiency, where a perforance range is calculated over a range of indoor and outdoor conidtions. So far, the Feds have ignored this advice. As a result, using the SEER rating to estimate what your operating costs will be, will not give you an answer close to what you really get!

snipped-for-privacy@hotmail.com wrote:

I should also mention that the quality of power coming into your home will affect the efficiency. During the summer, the voltage going into your home could drop as much as 5%, raising the amp draw. Also, if there are a lot of inductive (motors) or capacitive (flourescent lights) on the grid you draw power from, the power factor could be off. Since simple amp meters don't read power factor, you may not be measuring what the true power draw of your A/C system is.

snipped-for-privacy@hotmail.com wrote:

This is moot, since household kWh meters only charge for real power.

Nick

The S in SEER stands for "Seasonal". Most of the run time during the cooling season occurs at lower ambients, i.e. when the compressor draw will typically run half or less than half of the RLA. You also need to figure in power factor, which will improve your numbers. HTH.

hvacrmedic

I am looking afor a new central AC. I live in Florida so efficiency is important. I looked at Tranes, and found that the 4 1/2 ton unit I looked at was rated at a 14 SEER, yet the specs stated it drew 27.5 amps for the compressor, an amp or so for the compressor fan, and 7 amps for the air handler blower (full speed). Now 4 1/2 tons is 54000 BTU's per hour, and the power draw is (27.5+1+7)amps X 220V, or 7800 watts. This would seem to me to give a SEER of 6.9. This is less than half of the stated SEER of 14. Can anyone explain this? I looked at the ARI website and this seems to be the case for every manufacturer. If I buy a buy a 14 SEER 54000 BTU/hour AC, I would expect it to draw

As I recall SEER ratings are given based no actual test under specific conditions. The amps listed are generally the highest amps expected, and an AC will not draw the same amps under all conditions.

Right, it's about true power, of which amps are required to compute. IOW, it is indeed about amps, but in ways that you apparently don't understand.

hvacrmedic

You are wrong to assume that amps are indirectly proportional to SEER.

What I mean.....

I notice that increasing the size of the evaporator will increase the SEER. The figures from several evaluations show that a 3 ton compressor connected to 5 ton evaporator is a couple of points higher in SEER that when matched.

Using controls that let the inside fan continue blowing after the compressor shuts down also increases the SEER.

In other words, it's not all about the amps.

On the current draw side:

John

How does a bigger coil reduce the amps?

Reduces load for starters.

Amps mean nothing of great importance here..you can have a 16SEER unit pulling 50 amps and its still 16SEER.

Bottom line, for every watt used, how many BTUs are being removed?

You might enjoy learning the difference between power and energy :-)

Nick

Carolina Breeze HVAC wrote on 7/30/2005 7:24 AM:

Exactly.

Elaborating on this answer, for lights, power is watts times amps. This is still true *instantaneously* for everything, but for motors the current and voltage or not in phase. These means that part of each cycle voltage and current are of the same sign, resulting in positive power consumption, just like lights.

But for the rest of the cycle,they are of opposite sign, so that the power is negative. In other words, the motor is actually returning power to the power company for this portion of the cycle.

You only care about the average power consumed over an entire cycle, which for a motor running at full speed is considerably less than the rms current times rms voltage.

And you might enjoy learning what ASHRAE says about SEER.. :-)

No flame, just back at ya.

You also know that your contractor must make over 150 measurements to make sure you have the SEER you bought, right? SEER for all intents, is marketing in this example. You DO normally get a higher quality unit with the higher SEERs, but with most, once you leave the 14SEER realm, and go into the 14+ you have over engineered equipment, that while it IS of higher than 10 SEER quality, it also is more expensive to replace, or work on. If you want the best of both worlds, might I suggest GeoThermal, altho, expect to pay out the nose for your initial installation, and you DO have to make repairs to it every so often, but with the right installer, and the right equipment, you can achieve SEER values that are sky high compared to a conventional air to air unit.

The 27.5 amps were stated by the Trane distributor to be running amps, not the peak amps on the housing. Perhaps he misspoke. The 7 amps on the blower was peak, though. The blower moter is ¾ hp 240V, and runs at close to peak most of the cycle, even though it's variable speed. I ignored power factor to keep things simple, and used 220V rather than

That's correct: The SEER is calculated to include the phase shifts etc. introduced by the loads, which is why direct calculations such as the OP used won't wash. In addition, nameplates & labelling isn't always accurate. It's often stated to be even higher than the actual draw, just to account for the possible variations in the production of multiple units. So they use a max number on the plates and for the saftey agencies. Plate numbers are only for sizing wiring to the unit. If it has a SEER rating, and a safety label (UL, CSA, CE, et al), which is a requirement, then the numbers are correct.

HTH

Pop