# Thread: One ton equal One HP?

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I'm working in a Copeland compressor, model CF12K6E-TF5, and want to know how many horse power of capacity is, the name plate don't say anithing about it.

Accord with Copeland handbook, compressor nominal capacity in this case is 12000 (I assume are BTU's). If this is correct, compressor capacity would be One ton.

But, what is the relationship between BTU's and horse power?. A friend says that when a compressor capacity is specified just in BTU's, the relation is one to one, that mean one ton equal one HP, is that correct?.

Thanks.

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## there are..

...two ways to measure HP,mechanically(work) or electrically(watts)

1000w (1 kw)= 1.34 hp

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The capacity of a compressor is not a fixed number such as one hp per ton. The capacity varies depending upon the suction pressure and discharge pressure.

As the suction pressure decreases or the high side pressure increases, the capacity drops. Raising the suction pressure and lowering the discharge pressure increases the capacity for the same hp compressor.

It so happens that a typical air conditioning compressor with a one hp motor will provide one ton of cooling capacity at "normal" air conditioning operating pressures. This is an approximate "rule of thumb" conversion. If the high side pressure is abnormally high or the system is operating on a hot day, the one hp compressor will provide less than one ton of cooling. If the suction pressure is abnormally low the same one hp compressor will again operate at a lower capacity.

A low temperature system operating with the required lower suction pressure necessary to achieve the lower suction temperature will require 2, 3, 4, or even 5 hp to obtain one ton of cooling capacity.

This is all related to the changing volumetric efficiency of the compressor. Volumetric efficiency is another topic and an interesting one at that.

Norm

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Compressors do not have their capacity listed on them because the actual capacity will depend upon the pressures. Each compressor model has a chart or graph published by the compressor manufacturer where you can find the actual operating capacity of the compressor if you know the suction and discharge pressures. The charts usually provide the actual power consumption for different operating pressures as well.

Norm

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According to that over-hyped text book,
1btu/h=.000393hp.
Therefore a one ton compressor requires 4.7hp.

(12000 x .000393 = 4.716hp)

But which is "nominal",the btu/h or the hp?

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Originally posted by jacob perkins
According to that over-hyped text book,
1btu/h=.000393hp.
Therefore a one ton compressor requires 4.7hp.

(12000 x .000393 = 4.716hp)

But which is "nominal",the btu/h or the hp?
Jacob, this is totally untrue. Reread my previous posts on this thread. There is no fixed relationship between hp and btuh!

Norm

7. Guys that do strictly A/C refer to compressors in tonnage...."it was a 5 ton compressor"

reefer guys...being the more intelligent breed...refer to compressor size in horsepower...."it was a 20HP compressor"

A/C guys know nothing about the relationship between HP and tonnage and evap temp

There...how's that for opening up a can of worms?

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the CS12 has a btuh range of 3330 to 25700
pretty wide huh ?
depending on refrig, application, suction, condensing
all compressors will have varying btuh curves

the primary factor in compressor design is
bore, stroke and cfh, not horsepower

what A/C guys call a 5 ton compressor is also
used in as 2 ton cooler, 7-1/2 ton A/C,etc.
get the idea

if you want to relate btuh to hp then relagate
yourself to the status as parts changer

note: all current 5 ton A/C units do not have a
5 ton compressor (4 or 4-1/2 usually used)

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Most of the time if you compare HP to tons of refrigeration
You would have to look at the btu capacity on a +45F evap. (common A/C evap temp)
For example:
F3AD-A201 Copeland 2HP condensing unit R22 has a BTU capacity of 23,600 @ +45F evap temp. (right at 2 tons)But on a +25F evap it will only handle 16,200 btu. So it can be relative but not always.
Just another way of looking at things.

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Thermodynamically the HP required can be calced by:

Mass flow(lbs/hr)x heat of compression (btu/lb) x 2545 btu-hr/HP. All of this at a given set of specific conditions.

To get total hp, you would have to account for friction inside the compressor, which isn't something that can be calculated.

Add the thermodynamic Hp required to the friction requirements and thats the total.

It is interesting to only calculate the thermodynamic work required for a given refrigerant and set of conditions, and then compare it to the same refrigerant operating at different conditions. You will see that as conditions change, the HP required also changes; it isn't a constant number.

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"hvacmd2002" change your screen name before implying that a/c guys don't know about hp/tonnage relationship, or the basic lack there of. there is no direct relationship it is as Norm says.

disclaimer; yes it is a joke, no i was not trying to imply that you did'nt know the difference.

[Edited by hvac3901 on 04-27-2005 at 02:03 PM]

12. Originally posted by hvacmd2002
Guys that do strictly A/C refer to compressors in tonnage...."it was a 5 ton compressor"

reefer guys...being the more intelligent breed...refer to compressor size in horsepower...."it was a 20HP compressor"

A/C guys know nothing about the relationship between HP and tonnage and evap temp

There...how's that for opening up a can of worms?
And heat transfer professionals think that this type of irrational, generalized reference to HVAC vs. Refrigeration is silly.

Heat transfer professionals refer to the compressor by make, model, serial, capacity at a given evap temp, and, often CFM, kW, EER and Mass Flow.

13. Originally posted by condenseddave
[
Heat transfer professionals refer to the compressor by make, model, serial, capacity at a given evap temp, and, often CFM, kW, EER and Mass Flow.

[/B]
Wait. So, if I'm working on a rack, and point to compressor 2, I have to tell you all THAT? Or can I just call it the 10HP?

Heat transfer professional. I've never heard that term before. Is there a secret handshake that goes with that?

But seriously, have you ever heard an A/C guy refer to a compressor in anything but tons? Now I'm sure that the A/C guys in here are a cut above. But ask 10 guys at the supply house about tons and HP and evap temp. 9 won't have a clue.

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