There's another indicator that something's not quite right with that story.
Automotive AC compressors eat up a lot more than 3HP when they're engaged -
somewhere in the 10-15HP neighborhood. Now, you could spin one with a 3HP
motor, but it would be at a much lower RPM. As the graph showed, the lower
the compressor turns, the less cooling capacity it has.
Let's assume that it takes 12HP to turn this particular compressor at
3000RPM, where it's producing right around 2 tons of cooling (24,000 BTU).
That means the torque component is 21ft.lbs (12HP000x/5252, x!). With a
3HP motor (that's actually capable of putting out 3HP - most electric motors
are in the high-80's to low-90's efficiency rating), it would only be
capable of turning that load at 750RPM (3HP!x/5252, xu0). At 750RPM,
the compressor has about 8,000BTU's of cooling capacity (reference the chart
So, 8000BTU's is your basic bedroom air conditioner. Looking up one of the
popular models, an 8000BTU window AC unit draws 7.5 amps at 115VAC, or about
860 watts. That 3HP motor above is drawing over 2200 watts (1HPt6 watts),
not even factoring in motor efficiency.
Given the cost per kilowatt hour, it's much better to comsume 860 watts per
hour, than 2200 watts per hour.
I have no idea if the guy was telling a story or not. But, I do know when
Dodge introduced the 1994 trucks with 134A systems they bragged that the A/C
system was capable of cooling a 1500 square foot home, FWIW.
While it may be possible, the compressor would require serious HP to spin it
fast enough to accomplish it and even if you could find a motor strong
enough to do it, the power bill would be astronomical.
If at first you don't succeed, you're not cut out for skydiving
"BigIronRam" < firstname.lastname@example.org> wrote in message
Wrong. EER is the efficiency rating of a unit operating at a specific
or constant temperature and constant humidity.
EER = BTU per hour of cooling 95F / watts used at 95F
SEER is the efficiency rating of a unit (**A/C OR heat pump**) over the
SEER = BTU of seasonal cooling / seasonal watt hours used
SEER is a more useful measurement, because the temperature never stays
constant. SEER also includes other factors that effect efficiency, like
cycling and total energy used for indoor/outdoor blower motors, fans, etc.
There is a good explanation here:
The closest analogy I can think of is mpg. If you measure the mpg of a
vehicle in a controlled test, (no A/C, specific number of miles, flat
terrain) you will get a number comparable to EER.
If you measure the mpg over the course of a tank of fuel or a few tanks
of fuel, varied terrain, varied temps (A/C on/off) and varied driving
conditions, you get a number comparable to SEER.
Obviously, the number most people would be interested in is SEER since
none of us are in a constant/controlled temperature and humidity
6 years ago we had a Trane heat pump installed. 19 SEER. Twice a year
maintenance from the installing contractor. No problems at all.
Electric bill is $110.00 a month year round. 10 cents per kilowatt.
Thermostat is set at 78 degrees in the summer and 68 degrees in the
winter. House is more than well insulated. We don't have gas so
everything is electric. 3 years from now, when the 10 years parts and
labor and everything is up, I will renew the service contract again
for 10 years.
Do what you want, but usually those service contracts are a rip off. You
might be better just paying the HVAC company to stop by twice a year for
service and pay what ever his rates are. It really depends on how the
contract is written, and what is, or is not included. If the contract was
written by the local company it is probably ok. If it is through some
national warranty company, my bet is you are paying too much.
I while back I had a customer ask me if they should renew their contract.
They had spent $360 a year for ten years and got two quickie services a year
out of the deal. If they had paid for the service calls they would have
saved well over $2000 over the ten years. Then when the unit did die, the
warranty company would not pay to get the equipment replaced with a
comparable unit. they had one of Trane's best systems, and the company would
only supply the cheapest equipment they could find!
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