Air compressors operate in a wide range of environments. In addition to general ambient conditions, altitude is a key factor. As altitude increases, atmospheric pressure drops, air density decreases, and oxygen content declines. These changes have a systematic impact on compressor performance, and the effects become more significant at higher elevations.

1. Relationship Between High Altitude and Compressors

1. Higher compression ratio
   The higher the altitude, the thinner the air and the lower the absolute pressure. This means the compressor must operate at a higher compression ratio.
2. Reduced cooling efficiency
   At higher altitudes, cooling performance declines, and the temperature difference between the motor operating temperature and ambient temperature increases. Lower air pressure also reduces fan performance, further weakening heat dissipation.
3. Higher oil–air ratio
   As altitude increases, the oil-to-air ratio in the system becomes higher.

Because air is thinner at high elevations, motor cooling is impaired. As atmospheric pressure drops, fan pressure also decreases, resulting in poorer heat dissipation. Under standard rated conditions, a standard motor can operate at altitudes up to 1,000 meters. When ambient temperatures reach or exceed 40°C, Table 1 can be used as a guideline for selecting standard motors.

It should also be noted that for certain types of compressors, motor performance degradation at high altitude may be much greater than the auxiliary power required by the compressor itself.

Permissible Motor Load Percentage by Altitude

Altitude (m)	<30°C	30–40°C	45°C	50°C	55°C	60°C
1000	107%	100%	96%	92%	87%	82%
1500	104%	97%	93%	89%	84%	79%
2000	100%	94%	90%	86%	82%	77%
2500	96%	90%	86%	83%	78%	74%
3000	92%	86%	82%	79%	75%	70%
3500	88%	82%	79%	75%	71%	67%
4000	82%	77%	74%	71%	67%	63%

2. Reduction in Air Delivery

The rated air delivery shown on a compressor nameplate is based on standard atmospheric conditions (0 m altitude).

Decrease in flow rate for every 1,000 m increase in altitude

Compressor Type	Free Air Delivery Loss (%)	Mass Flow or Standard Flow Loss (%)
Single-stage oil-free screw compressor	0.3	11
Two-stage oil-free screw compressor	0.2	11
Single-stage oil-injected screw compressor	0.5	12
Single-stage piston compressor	5	17
Two-stage piston compressor	2	13
Multi-stage centrifugal compressor	0.4	12

This table is based on project experience and field data summarized by the Elang team, assuming a working pressure of 7 bar and constant temperature.

Note: The compressor’s maximum compression ratio must not be exceeded.