SEER and power consumption

Posted by Mr_Bill on April 10, 2007, 8:07 pm

Perhaps somebody can explain for me how to reconcile air conditioner
SEER specs with current consumption specs.

I am looking at installing a Trane XL19i split system condenser
(compressor).
The spec sheet says to use branch circuit protection of 30A minimum
and 35A maximum. The spec also says to use wire of at least 22A
ampacity. This all seems reasonable so far.

Then the spec sheet says that the "R.L.A." for the compressor is
15.1A,
and the RLA for the fan is 2.8A. So the total RLA is 17.9A.

Now to my confusion. This is a 36kBTU unit rated at 19+SEER.
36000/19 = 1895watts or 8.6amps.

So, when the compressor and fan are running (but not including any
starting
transients) how much current is being drawn?

This is more or less an academic question. I intend to use a 30A
breaker and
8 ga. THWN which is 50A ampacity, but I'd like to know in advance
when
the unit is sitting there running, how many amps will I be drawing?

Grateful for any explanation.

Posted by Joseph Meehan on April 10, 2007, 8:24 pm

Mr_Bill wrote:

> Perhaps somebody can explain for me how to reconcile air conditioner
> SEER specs with current consumption specs.
> I am looking at installing a Trane XL19i split system condenser
> (compressor).
> The spec sheet says to use branch circuit protection of 30A minimum
> and 35A maximum. The spec also says to use wire of at least 22A
> ampacity. This all seems reasonable so far.
> Then the spec sheet says that the "R.L.A." for the compressor is
> 15.1A,
> and the RLA for the fan is 2.8A. So the total RLA is 17.9A.
> Now to my confusion. This is a 36kBTU unit rated at 19+SEER.
> 36000/19 = 1895watts or 8.6amps.
> So, when the compressor and fan are running (but not including any
> starting
> transients) how much current is being drawn?
> This is more or less an academic question. I intend to use a 30A
> breaker and
> 8 ga. THWN which is 50A ampacity, but I'd like to know in advance
> when
> the unit is sitting there running, how many amps will I be drawing?
> Grateful for any explanation.

I don't think you can do what you want as SEER is only for one set of
controls.. Change the test criteria like temperature humidity etc and you
will have different results.

--
Joseph Meehan

Dia 's Muire duit

Posted by udarrell on April 10, 2007, 9:15 pm

Mr_Bill wrote:

>Perhaps somebody can explain for me how to reconcile air conditioner
>SEER specs with current consumption specs.
>I am looking at installing a Trane XL19i split system condenser
>(compressor).
>The spec sheet says to use branch circuit protection of 30A minimum
>and 35A maximum. The spec also says to use wire of at least 22A
>ampacity. This all seems reasonable so far.
>Then the spec sheet says that the "R.L.A." for the compressor is
>15.1A,
>and the RLA for the fan is 2.8A. So the total RLA is 17.9A.
>Now to my confusion. This is a 36kBTU unit rated at 19+SEER.
>36000/19 = 1895watts or 8.6amps.
>So, when the compressor and fan are running (but not including any
>starting transients) how much current is being drawn?
>This is more or less an academic question. I intend to use a 30A
>breaker and 8 ga. THWN which is 50A ampacity, but I'd like to know in advance
>when the unit is sitting there running, how many amps will I be drawing?
>

Get an amprobe, it varies due to load conditions and other factors.

>Grateful for any explanation.
>

There are far too many factors that affect SEER Ratings and energy
consumption to even begin to address here.
If you want to do some reading on some of the factors affecting SEER &
efficiency of operation, here is a link to begin the journey.
http://www.udarrell.com/proper_cfm_btuh_duct_sizing_air_conditioning_systems.html
- udarrell

--
WISDOM PRINCIPLE DIRECTED EMPOWERMENT COMMUNICATIONS -
THE REAL POLITICAL ISSUES and WISDOM BASED PEOPLE EMPOWERMENT
http://www.udarrell.com/
http://www.udarrell.com/my_pages2.htm

Posted by Mr_Bill on April 10, 2007, 10:30 pm

Thanks for the link. Very interesting.

In some sense, this all got started several years ago.
My wife had a friend, and her husband was a commercial
HVAC contractor. He walked me through the correct way
to design ductwork. What a revelation. I replaced all the
ductwork in my house, and not only is the place a lot more
comfortable, but my energy bill went down significantly.

I then started paying attention in other houses, and essentially
all the houses I've seen have improperly designed ductwork.

So, long story short, I became interested in the basic physics
behind HVAC design. Fast forward to today. I'm putting in
an A/C unit, and I just want to connect the dots between the
specs on the branch circuit and the SEER specs. Either
the branch circuit specs are way too conservative (which is fine,
wire is cheap), or the SEER value is meaningless, or somewhere
in between. I was just curious. Nothing is going to change.
I'm still going to run an 8 ga branch circuit with a 30A breaker.
I'm still going to buy the 3 ton condenser unit. I was just curious
what is really going on with the energy conversion. Oh, well.

Posted by Dave Martindale on April 10, 2007, 11:06 pm

>Then the spec sheet says that the "R.L.A." for the compressor is
>15.1A,
>and the RLA for the fan is 2.8A. So the total RLA is 17.9A.

That's probably worst case conditions.

>Now to my confusion. This is a 36kBTU unit rated at 19+SEER.
>36000/19 = 1895watts or 8.6amps.

I expect SEER is based on some kind of expected operating conditions,
not worst case. Also, the compressor and fan motor are likely inductive
loads, so when the unit is drawing 1895 watts the current is larger
than 8.6 A, by a factor of 1 over the power factor.

>So, when the compressor and fan are running (but not including any
>starting
>transients) how much current is being drawn?

Under what conditions?

Dave

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