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.

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

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_b...syste ms.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

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.

"Mr_Bill" writes:

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

Dave -

Thanks for the reply.

I would have thought that the load that the compressor presents
to the compressor motor is more or less constant. If so,
then the power factor, whatever it might be, is also constant,
and is factored into the SEER.

I agree that the SEER rating is based on some set of operating
conditions, and that in the real world the efficiencies might
go down (for example, if it is really hot then the compressor
radiator becomes less efficient). I would think, however, that
the BTU would go down, and the electrical power consumption
would remain constant. But, obviously this is more complex
than it seems at first glance.

Anyway, thanks for the reply.

On 10 Apr 2007 20:59:56 -0700, "Mr_Bill" wrote:

Dave -

Thanks for the reply.

I would have thought that the load that the compressor presents
to the compressor motor is more or less constant.

I would think that the outside temperature is to the desired inside
temperature, or the closer the inside temperature is to the desired
temperature, the less the refrigerant would be warmed in the
evaporator. So the less effort it would take to compress it at the
next stage.

This is sort of the corollary to, You don't get something for nothing.

You also don't usually have to expend effort for nothing. If you get
so much cooling for so much effort, you can usually get half as much
cooing for somewhat more than half as much effort.

If so,
then the power factor, whatever it might be, is also constant,
and is factored into the SEER.

I agree that the SEER rating is based on some set of operating
conditions, and that in the real world the efficiencies might
go down (for example, if it is really hot then the compressor
radiator becomes less efficient). I would think, however, that
the BTU would go down, and the electrical power consumption
would remain constant.

I dson't think the electric would stay constant. Same reason as
above.

But, obviously this is more complex
than it seems at first glance.

Anyway, thanks for the reply.

"Mr_Bill" writes:

I would have thought that the load that the compressor presents
to the compressor motor is more or less constant. If so,
then the power factor, whatever it might be, is also constant,
and is factored into the SEER.

Ok. But my point was that you were dividing watts by volts and
expecting to get amps as a result. That only works for resistive loads,
where current and voltage are in phase, and VA is equal to watts.
But for inductive (or capacitive) loads, there's a phase shift between
current and voltage, and watts and VA are not equal.

I agree that the SEER rating is based on some set of operating
conditions, and that in the real world the efficiencies might
go down (for example, if it is really hot then the compressor
radiator becomes less efficient). I would think, however, that
the BTU would go down, and the electrical power consumption
would remain constant. But, obviously this is more complex
than it seems at first glance.

Yeah, it's got to be more complex than that. For example, suppose your
house is quite hot, or the evaporator is small for the house. Then the
expansion valve will let all of the liquid refrigerant available into
the evaporator, and there will be lots of gas returning to the
compressor. This will raise low side pressure, the compressor will take
more mass of gas into the cyclinder for each stroke. This requires more
shaft horsepower from the motor, which will draw more current.

On the other hand, if your house is already cool, the expansion valve
will throttle the refrigerant, the compressor has less gas to pump, and
motor current will go down. You're getting fewer BTU/hr of cooling, but
using less electricity doing it. Overall efficiency could be higher or
lower.

Or suppose outside temperatures are unusually hot. The condensor runs
hot, the compressor discharge pressure goes up, and again it takes more
shaft power from the motor to run the compressor. More power to provide
the same number of BTU/hr cooling when condenser air is hotter than
normal.

Dave

"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.
"


Am I the only one that sees a problem with the above?

On Apr 11, 5:18 am, wrote:
"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.
"

Am I the only one that sees a problem with the above?

Actually, this thought occurred to me right off the bat.

I can assure you that the factory spec says 22A ampacity,
30A min breaker, 35A max breaker.

In any case, I am using 50A ampacity (8 ga) wire, and a 30A breaker.

Mr_Bill wrote:

On Apr 11, 5:18 am, wrote:


"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.
Am I the only one that sees a problem with the above? (NO)


The conductors you use should always exceed the ampacity of the breakers
that are protecting them!
The purpose of the breaker or fuse is to prevent exceeding the ampacity
rating of the conductors!

Actually, this thought occurred to me right off the bat.

I can assure you that the factory spec says 22A ampacity,
30A min breaker, 35A max breaker.


If the conductor rating is 22-amps then I would want a 20A or less
breaker on it.
Run at least 35A rated conductors, then use a 30A breaker.
The breaker must be sized no larger in amp size than the ampacity rating
of a conductor
after de-ration calculations have been performed to find the maximum
ampacity of that conductor.

In any case, I am using 50A ampacity (8 ga) wire, and a 30A breaker.


Since when does the Electrical Code allow the ampacity capacity rating
of the wire to be lower than the breaker that is supposed to protect it
from exceeding its conductor amp ratings!

The ampacity of the conductors should always be greater than the breaker
rating that is protecting it from exceeding its amp rating.

-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

Doesn't it use a lot more current to start running the compressor? So
you'd need a higher amperage circuit breaker to cover the few second
surge when starting?

SEER is an average when running, not based on peak draw for a few
seconds.

Shaun Eli
www.BrainChampagne.com
Clever Comedy for Smart Minds (sm)
www.IvyLeagueComedy.com
The Smartest You'll Ever Laugh (sm)

In any case, I am using 50A ampacity (8 ga) wire, and a 30A breaker.

Since when does the Electrical Code allow the ampacity capacity rating
of the wire to be lower than the breaker that is supposed to protect it
from exceeding its conductor amp ratings!

The ampacity of the conductors should always be greater than the breaker
rating that is protecting it from exceeding its amp rating.

-udarrell


If he does what he stated above, the wire will have a greater capacity
than
the breaker.