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#### Gary_F

· San Antonio Area
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30 Posts
Discussion Starter · ·
Background: Location south central Texas
Equipment: Rudd Achiever, 12 seer, 4 ton (actual 46.5 btu) age 14 years
air handler located in attic.
Home: aprox. 2350 sq ft. (I have 2 bdrms. closed off, aprox 300 sq ft.) total 2650
Supply: (2) [email protected] [email protected] 12x12 (total of 684 sq in)
Blower: 3/4hp, 2060 [email protected] .5 static (guessing on static)
Outside temp 90F
Subcool 9 to 10 degs.
Condenser delta 20 to 22 deg

I took some temp measurements and ran thru a calculator I found on the web. (http://efficientcomfort.net/jsp/PsychroCoilCalc_Web.jsp)
CFM leaving 2060 (est)
Entering: DB 78, WB 63.5 45%rh
Leaving: DB 61.9, WB 48, 33.6rh

The calculator came up with answer:

Sensible cooling btuhr 36,237
Dehumidifying btuhr 52,167
cfm per ton 682.2
Sensible heat ratio .41

Is this what I can expect. Or is my AC not putting out like it should?

Thanks

Gary
Gruene, Tx.

#### beenthere

· In Loving Memory
Joined
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42,671 Posts
Because you guessed at CFM.

That calculator result is meaningless.

You need to know the actual CFM.

Guessing is worthless.

Plus, there is noway, you can get a total capacity of 7.37 tons from a 4 ton unit.

#### Gary_F

· San Antonio Area
Joined
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30 Posts
Discussion Starter · ·
beenthere,

I used the blower performance data from the mfg.
.7 =1910 .6=1985 .5=2060 .4=2130 .3=2200 .2=2260 .1=2320 (static=cfm)
How does one measure CFM?

Also it appears you added sensible btuhr to dehumidifying btuhr, to come up with 7.37 tons 88.4 btuhr. If you don't mind please explain.
I am just trying to understand so I can talk with tech.

Thanks,

Gary

#### beenthere

· In Loving Memory
Joined
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42,671 Posts
The nominal rating of an A/C, is its combine latent and sensible capacity.
A 4 ton unit would be 4 tons with the sensible and latent added together.

To find your CFM. You either need to measure your actual static pressure. And then look it up on the fan data for your air handler.
And youo must know what speed tap the blower is running on.
Or, use a mini vanemanometer to measure it.

A typical 4 ton unit at 85°F outdoor temp, and 80°F indoor dry bulb 67°F wet bulb(57%RH), will have around will have around 13,000BTUs of sensible capacity at 1600 CFM.
At 1800 CFM, that sensible will drop to 11,000BTUs.

At 2000 plus CFM, it will be much lower yet.

23,343 at 1400CFM
26,082 at 1500CFM
27,820 at 1600CFM
29,599 at 1700CFM
31298 at 1800CFM
34776 at 1900CFM
36,514 at 2000CFM

#### Gary_F

· San Antonio Area
Joined
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30 Posts
Discussion Starter · ·
Thanks,

Will go back to calculator and try again, will use 1400 cfm.
It's fun to play around with the different figures to see what comes up

Regards,

Gary

#### Gary_F

· San Antonio Area
Joined
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30 Posts
Discussion Starter · ·
beenthere said:

"A typical 4 ton unit at 85°F outdoor temp, and 80°F indoor dry bulb 67°F
wet bulb(57%RH), will have around will have around 13,000BTUs of sensible capacity at 1600 CFM.
At 1800 CFM, that sensible will drop to 11,000BTUs.

At 2000 plus CFM, it will be much lower yet.

23,343 at 1400CFM
26,082 at 1500CFM
27,820 at 1600CFM
29,599 at 1700CFM
31298 at 1800CFM
34776 at 1900CFM
36,514 at 2000CFM"

At the time the I was getting the temp data etc, the outside temp was 94f. Blower speed set on high.
Recalculating at 1400 cfm, and the relative humidity inside of house is 44%, (according to my gauge), is 24353btuhr indicative that my unit is putting out like it should.?

Thanks

Gary

#### beenthere

· In Loving Memory
Joined
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42,671 Posts
At 95°F outdoor temp. And an indoor 78°F drybulb with 63°F wetbulb temp(44%RH).

At 1400 CFM, a 4 ton would normally be around 39,900BTUs sensible.

Until you KNOW what your CFM really is.

You will never know what capacity its operating at.

Sort of like guessing how many miles you drove. And then trying to figure out what your MPG is.

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