How EvaPack™ Works | Armstrong | Americas

The adiabatic process is simple, natural and extremely efficient.

EvaPack™ converts liquid water to water vapor using the adiabatic process. Dry air passes through a corrugated bank of wetted cells media made from non-organic wet fibers. EvaPack™ uses the sensible air heat to evaporate the water, which cools and humidifies the air. The adiabatic process consumes no electricity, making Armstrong’s EvaPack™ the ideal choice for data centers trying to achieve a reduced energy footprint.

EvaPack™ Brochure

Direct Adiabatic Cooling

Using the adiabatic process, outside air is cooled and humidified, then directly injected in the server room.

Indirect Adiabatic Cooling

After warm exhaust air has been cooled using the adiabatic process, it enters a heat recovery exchanger where it is used to cool fresh air. This solution is especially convenient when outside air must be cooled without increasing its humidity.

Adiabatic Process Psychrometric Chart

There are two common psychrometric design processes for evaporative humidification.

Sensible heating: red horizontal lines

Evaporative humidification: blue oblique lines

Heating + humidification (line A-B-C)

Pre-heating + humidification + post heating (line A-D-E-C)

Both processes have humidity ratio (Δx) increase:

from Xin (A) to Xout (C).

The Saturation Efficiency (η) or Cooling Efficiency is expressed in % and corresponds to the ratio between the entering dry bulb temperature and exiting dry bulb temperature over the wet bulb depression:

η = Real cooling/ Ideal cooling = (Tin – Tout ) / (Tin – Twb )


  • Tin is the inlet air dry bulb temperature,
  • Tout is the outlet air dry bulb temperature,
  • Twb is the wet bulb temperature.

For the humidification process B-C: the pad efficiency is smaller, and its thickness is thinner.

For the humidification process D-E: the pad efficiency is higher, and its thickness is bigger.

Typical Configurations

Direct evaporative humidification adds humidity to the supply air.

Heating + Humidification

Pre-heating + Humidification + Post Heating