Quick answer: Altitude doesn't change the basic rule: condensation happens when a surface reaches the dew point of the air touching it. It does change the numbers. At lower pressure, the same temperature and RH hold more water per kilogram of dry air, and a fan moving the same volume moves less air mass (about 25 % less at 2,000 m). High sites also have big day–night temperature swings and cold, clear nights, which pull enclosure surfaces below the dew point. Use local pressure in moisture calculations, read fan and dehumidifier data at site density, and check the electrical equipment's own altitude limits separately.
Quick answer
- Dew point and RH: unaffected by pressure for given T and vapour pressure.
- Humidity ratio: higher at altitude for the same T and RH; air density lower.
- Fans: same m³/h, less kg/h; check curves at site density.
What changes with altitude
| Altitude | Pressure (approx.) | x at 25 °C / 60 % RH | Air density at 25 °C |
|---|---|---|---|
| Sea level | 101.3 kPa | 11.9 g/kg | 1.18 kg/m³ |
| 2,000 m | 79.5 kPa | 15.2 g/kg | 0.93 kg/m³ |
| 3,000 m | 70.1 kPa | 17.3 g/kg | 0.82 kg/m³ |
| 4,000 m | 61.6 kPa | 19.8 g/kg | 0.72 kg/m³ |
(Standard atmosphere pressure; calculated humidity ratio and density.) The dew point of 25 °C / 60 % air is about 16.7 °C at every altitude.
Use the correct moisture basis
- Use local, coincident temperature, RH and pressure.
- In moisture-load calculations, multiply dry-air mass flow by the humidity-ratio difference, both at site pressure.
- State whether a quoted m³/h is at actual or standard conditions.
See the BESS container sizing method and psychrometric calculation.
Read fan curves at site conditions
Fan curves depend on air density and speed (AMCA explains how to read fan curves with their conditions: AMCA, Straightening out fan curves). At altitude a fan delivers similar volume but less mass. Heat transfer and moisture removal that depend on air mass fall with it. Ask the supplier for performance at site density.
High-altitude climate risks
| Risk | Why |
|---|---|
| Large day–night swings | Clear skies; surfaces cool quickly at night |
| Cold nights with humid daytime air | Moisture entered by day condenses at night |
| Snow and freezing | Drains and outlets freeze; see condensate drainage |
| Strong solar heating | Large thermal breathing; seal degradation from UV |
Related: condensate drainage.
Four separate questions for a proposal
| Question | Evidence |
|---|---|
| What conditions can cause condensation here? | Local air data and surface temperatures |
| What airflow will the installation deliver at site density? | Fan curve and system operating point |
| What water removal does the dehumidifier achieve at site conditions? | Supplier data at the operating condition |
| Is the electrical equipment rated for the altitude? | Product documentation; many electrical product standards assume up to 2,000 m unless stated |
Our energy storage dehumidifiers can be reviewed against site altitude and climate data.
FAQ
Frequently asked questions
Does altitude increase condensation risk?
Not directly; but large temperature swings and cold nights at high sites often do.
Does a dehumidifier work at high altitude?
Yes, but airflow mass and capacity at the site condition differ from sea-level ratings; ask for site-condition performance.
Why is humidity ratio higher at altitude?
Lower total pressure means each kilogram of dry air carries the same vapour pressure with less air, so g/kg rises.
Sources
- ASHRAE Handbook—Fundamentals, Psychrometrics.
- AMCA, Straightening out fan curves.
