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  #1   Report Post  
Robert11
 
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Default Air Conditioner Running Costs ?

Hello:

Have moved into a 30 yr old house that has central air conditioning.
Condenser is outside, and evaporator is part of the gas, forced hot air
furnace.

Very curious about what it might cost to run the A/C.

Realize there are a zillion caveats involved, but would like to come up with
a
very approximate number. Data from previous owner is unavailable.

Tried looking up A/C Cost Calculators on the web, but couldn't find anything
appropriate. All seemed to want to know house insullation characteristics,
etc.

So:

The unit is a 3 Ton
Installed in early 1984 (assume SEER of 9. Is this reasonable ?)
Cost of electric is 12 cents per KW Hr.

If the unit is running continuously, what would the cost be per hour ?

Questions, and thoughts:

a. is it simply a matter of converting 3 tons to BTU/HR (=36,000 BTU/HR),
and
converting this to KW HR (not sure how to) ?

b. Does the SEER rating, house characteristics, etc. come into play at all,
if one assumes continuous operation ?

Seems to me, and I really don't know for sure, that the Tons of A/C being
put out, and the electrical cost rate are really all one needs ? Is this
so ?

Thanks,
Bob


  #2   Report Post  
Travis Jordan
 
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Default

Robert11 wrote:
Very curious about what it might cost to run the A/C.


The unit is a 3 Ton
Installed in early 1984 (assume SEER of 9. Is this reasonable ?)
Cost of electric is 12 cents per KW Hr.

If the unit is running continuously, what would the cost be per hour ?


Unless it was a "high efficiency" system, 9 SEER sounds a little high
for mid-80's. 8.0 would be more likely, and even that is probably
degraded by the wear and tear on the compressor valves, etc. In any
case at 8.0 SEER, 3T (36K BTU) is 36,000/8 or 4.5KW/h. That should be
close enough to give you an idea of operating costs.

HTH.



  #3   Report Post  
borgunit
 
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Default

An ac calculator..

http://www.nppd.com/My_Home/Services...calculator.asp

  #4   Report Post  
Robert11
 
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Default

Hi Travis:

Thanks for help; appreciate it.

On clarification, please, regarding the units:

Should, perhaps, the 4.5 KW/h you derived be 4.5 KW-h ?

Thanks,
Bob

--------------
"Travis Jordan" wrote in message
...
Robert11 wrote:
Very curious about what it might cost to run the A/C.


The unit is a 3 Ton
Installed in early 1984 (assume SEER of 9. Is this reasonable ?)
Cost of electric is 12 cents per KW Hr.

If the unit is running continuously, what would the cost be per hour ?


Unless it was a "high efficiency" system, 9 SEER sounds a little high
for mid-80's. 8.0 would be more likely, and even that is probably
degraded by the wear and tear on the compressor valves, etc. In any
case at 8.0 SEER, 3T (36K BTU) is 36,000/8 or 4.5KW/h. That should be
close enough to give you an idea of operating costs.

HTH.





  #5   Report Post  
udarrell
 
Posts: n/a
Default

The best way to know what it will cost is to run it during a couple of hot
days and then project the run-time over the number of estimated days you
will be using it.
If you are in a high humidity area, the run-time will be a lot longer until
all the latent moisture is removed from the interior materials in your home.
Also, " high rates of air infiltration will cost you plenty "in a high
humidity climate" &/or hot climate." Check the insulation, windows, etc.
Electric power companies will sometimes do a heatload and recommend measures
to reduce A/C operating costs, (Contact your Power Co., and ask!). Do what
you can before you run the old power guzzler!

Considering the amp draw of that old unit and the indoor blower, --you do
NOT want continuous operation even during the daytime! Do everything you can
to reduce the heatload and increase the efficient operation of the system.
(That is usually, a lot!) (Read, Study, and Learn all you can, it can pay
big dividends.)

Before you ever use the system, it would be wise to brush up on a number of
things that can have a large impact on the amount of run time to cool and
dehumidify your home.
The ductwork and especially the Return Air system needs checking. You would
be wise to call the best tech in your area to check everything out, but
first learn what all needs to be thoroughly checked and asked him/her how
they check those things! Read and study and apply what you learn to save on
operating costs.
- udarrell - Darrell
--
Air-Conditioning Manufacturing Companies - Adding Marketing Values to A/C
Equipment
http://www.udarrell.com/aircondition...companies.html
===============================================
"Robert11" wrote in message
...
Hello:

Have moved into a 30 yr old house that has central air conditioning.
Condenser is outside, and evaporator is part of the gas, forced hot air
furnace.

Very curious about what it might cost to run the A/C.

Realize there are a zillion caveats involved, but would like to come up

with
a
very approximate number. Data from previous owner is unavailable.

Tried looking up A/C Cost Calculators on the web, but couldn't find

anything
appropriate. All seemed to want to know house insulation characteristics,
etc.

So:

The unit is a 3 Ton
Installed in early 1984 (assume SEER of 9. Is this reasonable ?)
Cost of electric is 12 cents per KW Hr.

If the unit is running continuously, what would the cost be per hour ?

Questions, and thoughts:

a. is it simply a matter of converting 3 tons to BTU/HR (=36,000 BTU/HR),
and
converting this to KW HR (not sure how to) ?

b. Does the SEER rating, house characteristics, etc. come into play at

all,
if one assumes continuous operation ?

Seems to me, and I really don't know for sure, that the Tons of A/C being
put out, and the electrical cost rate are really all one needs ? Is this
so ?

Thanks,
Bob






  #6   Report Post  
 
Posts: n/a
Default

Travis Jordan wrote:

...at 8.0 SEER, 3T (36K BTU) is 36,000/8 or 4.5KW/h.


That's just kW, vs "KW/h," ie 4.5 kW of power, vs 9 kWh of energy if
it runs 2 hours, but 8.0 may be the best case...

I actually measured 92 cfm of 45.3 F airflow cooled from 63.3 yesterday
with 537 watts and calculated 1802 Btu/h of cooling with a 0.98 COP, vs the
9.7SEER/3.412 = 2.84 I expected from the $98 Haier window AC box. I'll
measure the heating COP today, and the $69 "10.2 SEER" Daiwoo... Room ACs
are tested according to DOE 10 CFR 430 Subpart B, Appendix F, at 26.7C [80 F]
db/19.4C wb indoors and 35C [95 F] db/23.9 C wb outdoors. I suppose they are
designed to meet those conditions vs my 63 F room temp and hot fin airflow
restriction. This could heat water in summertime, but it doesn't seem likely
to work all year in a basement, which may kill the water heating economics,
where I live. More basement humidity might help, eg a damp basement floor.
We might dampen the basement floor in wintertime and let it dry in summertime.
We only need AC for 1-2 weeks/year.

A 50 F wet basement floor has Pw = e^(17.863-9621/(50+460)) = 0.367 "Hg, vs
Pa = e^(17.863-9621/(40+460)) = 0.252" Hg near a 40 F AC fin, so a 1000 ft^2
basement might provide 100x1000(Pw-Pa) = 11.5K Btu/h of latent heat, according
to one ASHRAE swimming pool formula, with a 100x0.252/0.367 = 69% basement RH.

I started measuring airflow by moving the Testo stick across a 2"x12" slot
in a cardboard box that collected the cool air, but the readings bounced
around a lot, even with no change in position, with 2:1 differences within
the slot. Next I tried a $400 Dwyer thermo-anemometer, which won't read as
low as the Testo but has more damping. Then I foil-taped a 12"x4" to 6" round
right-angle register boot to the cool outlet and added 5' of 6" pipe, which
reduced the airflow swirling a lot, while warming it a little. There was some
condensation on the outside of the pipe and more inside the AC, which ran out
when I tipped it later. Counting that would improved the COP (as would
disconnecting the fan motor.)

Nick

  #7   Report Post  
Travis Jordan
 
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Default

Robert11 wrote:
Should, perhaps, the 4.5 KW/h you derived be 4.5 KW-h ?


I should have said 4.5 kWh.


  #8   Report Post  
 
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Default

Travis Jordan wrote:

Robert11 wrote:
Should, perhaps, the 4.5 KW/h you derived be 4.5 KW-h ?


I should have said 4.5 kWh.


No. Just 4.5 kW.

Nick

  #10   Report Post  
JimL
 
Posts: n/a
Default


About $15.00 day running blower and compressor and fans full time.

That adds about $450 bucks to your monthly bill.





On Thu, 28 Apr 2005 08:26:13 -0400, "Robert11"
wrote:

Hello:

Have moved into a 30 yr old house that has central air conditioning.
Condenser is outside, and evaporator is part of the gas, forced hot air
furnace.

Very curious about what it might cost to run the A/C.

Realize there are a zillion caveats involved, but would like to come up with
a
very approximate number. Data from previous owner is unavailable.

Tried looking up A/C Cost Calculators on the web, but couldn't find anything
appropriate. All seemed to want to know house insullation characteristics,
etc.

So:

The unit is a 3 Ton
Installed in early 1984 (assume SEER of 9. Is this reasonable ?)
Cost of electric is 12 cents per KW Hr.

If the unit is running continuously, what would the cost be per hour ?

Questions, and thoughts:

a. is it simply a matter of converting 3 tons to BTU/HR (=36,000 BTU/HR),
and
converting this to KW HR (not sure how to) ?

b. Does the SEER rating, house characteristics, etc. come into play at all,
if one assumes continuous operation ?

Seems to me, and I really don't know for sure, that the Tons of A/C being
put out, and the electrical cost rate are really all one needs ? Is this
so ?

Thanks,
Bob




  #11   Report Post  
Edwin Pawlowski
 
Posts: n/a
Default


"JimL" wrote in message
...

About $15.00 day running blower and compressor and fans full time.

That adds about $450 bucks to your monthly bill.



Properly sized, there should be some cycling. Heat load during hte sunny
part of the day if different than night time.


  #12   Report Post  
Abby Normal
 
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Default

Use EER not SEER

  #13   Report Post  
udarrell
 
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Default

"Abby Normal" wrote in message
oups.com...
Use EER not SEER


I didn't find the initial post.
Explain so the readers will understand the reasoning that supports' your
claim.

On split systems and even packaged systems the EER and/or SEER do not mean
they will deliver their ratings. That depends on around a dozen other
factors that have to be right or the units may not deliver anywhere near
their ratings, including their BTU/hr ratings.
- udarrell - Darrell
--
Air-Conditioning Manufacturing Companies - Adding Marketing Values to A/C
Equipment
http://www.udarrell.com/air-conditio...l_readout.html
http://www.udarrell.com/aircondition...companies.html


  #14   Report Post  
Abby Normal
 
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Default

The poster I quoted was dividing SEER by 3.412 to get COP.

  #15   Report Post  
Dr. Hardcrab
 
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Default


"Abby Normal" wrote

The poster I quoted was dividing SEER by 3.412 to get COP.


I just dial 911 to get a COP......

;-]




  #16   Report Post  
John P@ Bengi
 
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Default

Call 911. Make a cop come

"Dr. Hardcrab" wrote in message
news:lNdee.1489$Vu.1483@trnddc07...

"Abby Normal" wrote

The poster I quoted was dividing SEER by 3.412 to get COP.


I just dial 911 to get a COP......

;-]




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