Heat Output and cooling options

[GuitsBoy]

Im trying to help my old man out with some cooling for his machine shop.

Does anyone know how much heat (ballpark) a typical CNC 5 axis machine puts out? The Machine in question is:

KURAKI KV-1000 CNC Vertical Machining Center
15 HP 50-Taper Spindle, 42” x 24” x 24” Travel, Fanuc 11M Control, unlimited Memory, ATC-32 Tools

Id like to know if standard a standard consumer / home a/c unit will be enough to cool this thing off come summertime.

Thanks,
-Tony

[Geof]

I was wondering this but had never done any calculations. I don't think it is possible to be too accurate because the answer depends on a few assumptions.

15 hp is roughly speaking 15 Kilowatts. Practically all the electrical energy going into the CNC eventually ends up as heat either in hot air from cooling the motors and electronics, hot air from the regen resistor and hot air from hot chips. When coolant is used the heat from the cutting action finishes up in the coolant so it doesn't produce as much heat in the air of the room.

Air conditioners are normally rated in BTU per hour. Kilowatts multiplied by 3413 gives BTU so at maximum power the machine is dissipating a maximum of around 50,000 BTU.

But the CNC is very unlikely to be running at full power all the time. Based on the time recorders on my machines a CNC typically is cutting metal for about 30 or 40% of the cycle time and the cycle time is rarely more than 80% of the work day. So you can make the assumption that the machine is only going to run at maximum power for maybe 32% of the time.

32% of 50,000 is about 16,000 BTU so an air conditioner with this rating per hour should be able to keep up with the heat the machine dissipates. Probably it would be possible to go smaller than this. However, this has to be added to the amount of air conditioning capacity that would be needed even if the CNC machine was not operating so the required capacity could be up around 25,000 to 30,000 BTU per hour or more depending on the size of the shop and the outside temoeratures.

[GuitsBoy]

Originally Posted by Geof I was wondering this but had never done any calculations. I don't think it is possible to be too accurate because the answer depends on a few assumptions. 15 hp is roughly speaking 15 Kilowatts. Practically all the electrical energy going into the CNC eventually ends up as heat either in hot air from cooling the motors and electronics, hot air from the regen resistor and hot air from hot chips. When coolant is used the heat from the cutting action finishes up in the coolant so it doesn't produce as much heat in the air of the room. Air conditioners are normally rated in BTU per hour. Kilowatts multiplied by 3413 gives BTU so at maximum power the machine is dissipating a maximum of around 50,000 BTU. But the CNC is very unlikely to be running at full power all the time. Based on the time recorders on my machines a CNC typically is cutting metal for about 30 or 40% of the cycle time and the cycle time is rarely more than 80% of the work day. So you can make the assumption that the machine is only going to run at maximum power for maybe 32% of the time. 32% of 50,000 is about 16,000 BTU so an air conditioner with this rating per hour should be able to keep up with the heat the machine dissipates. Probably it would be possible to go smaller than this. However, this has to be added to the amount of air conditioning capacity that would be needed even if the CNC machine was not operating so the required capacity could be up around 25,000 to 30,000 BTU per hour or more depending on the size of the shop and the outside temoeratures.

Thank you for this... I had come to similar calculation based on current draw. While I agree that most of the electricity used will be converted to heat, i cant imagine the machines to be 100% thermal efficiency. Also, even if the motor is rated at 15 HP, I cant see it under full load very often. Ill bet its only a fraction of that full 15 hp during the vast majority of the time. Like you said, theres just so many variabled I dont know if calculations are really going to add up correctly. Glad you had posted up though as I had forgotten about downtime between tool changes and swapping parts...

Thanks again!

[Geof]

Possibly one way you can get an estimate of the electrical energy being dissipated in the building is look at the meter. Record the watt hours consumed on a day when the machine is not being and on a day when the machine is being run. The difference is the electrical energy the machine is dumping into the building as heat when it is operating.

[mugabe]

There is a link to efficiency of electrical motor , which of course under load could decrease . the mechanical job of the motor will be converted to heat but not all 100 percent.
http://www.engineeringtoolbox.com/el...ncy-d_655.html