air cooled spindle VS water cooled spindle

cnc router mainly use the water cooled spindle and air cooled spindle,which one is better?
 Water cooled spindle, mainly power is 1.5kw,2.2kw 3.2kw 4.5kw 5.5kw 7.5kw , atc water cooled spindle is 2.2kw 3.2kw 5.5kw .  constant torque /constant power  2.2kw 3.2kw 5.5kw for metal material milling.
rotated speed 24000rpm/min

Air cooled spindle power 3.5kw,4.5kw 6kw ,9kw (atc spindle with ISO 30bits,18000-24000RPM ),rotated speed 18000RPM/min.

Comparison:

1. Water-cooled spindle motor as the name implies is to use water cycle to cool the heat generated after high-speed rotation of the spindle, this way the effect will be very good, because the temperature after circulation will not exceed 40 degrees.  Air cooled spindle motor adopts fan to heat, its effect is certainly not as good as water cooling.  

2. Noise.  The water-cooled spindle motor is basically noiseless, but the air-cooled spindle motor is very loud.  

3. Service life.  Because the water-cooled spindle motor should pay attention to maintenance, frequent water change or the use of industrial water cooling machine, so its service life is much longer than the air-cooled spindle motor.  
4. Accuracy.  Axial and radial runout of water-cooled spindle motor are basically below 0.003 mm, which is far less than air-cooled spindle motor (domestic)!  

5. Easy to use.  Because the water-cooled spindle needs a water pump, it needs a bucket to hold water and a water pipe to be connected, especially in the cold winter in the north, it is easier to freeze, and some customers may feel more troublesome;  Air-cooled spindles do not have so many use problems