Adiabatic cooling by wet media systems in data centers

Evaporative Principle

Dry air has an enormous natural ability to cool itself by exchanging heat with water. Water absorbs a large amount of heat from the air to evaporate. As a result of this exchange between air and water, the temperature of the air decreases. This air cooling process uses much less energy than the traditional cooling processes used by typical air conditioning systems.

A wet media cooler basically uses this principle to cool hot air by forcing it through a large surface area of ​​inorganic panel that is moistened with water (works like a sponge). In this type of cooling, no energy is consumed to evaporate the water. The media itself has an air pressure drop that will represent a small increase in the power consumption of the fans, and a small circulation pump is used to distribute the water through the panels. The total energy consumption resulting from the additional air pressure drop and the water recirculation pump is not significant in the total energy consumption of the data center cooling system.

Where evaporative cooling works

The evaporative cooling effect is directly associated with the air’s ability to absorb water. In other words, it depends on the difference between the dry bulb temperature and the wet bulb temperature. The greater the difference, the greater the cooling effect. Evaporative cooling can significantly reduce, or even sometimes eliminate, compressor cooling equipment in data centers, depending on indoor and outdoor air conditions and the type of cooling solution implemented.

With that said, there are some places in the world that are better suited for the use of evaporative cooling than others. The wet bulb temperature will set the theoretical minimum temperature to which the air can be cooled during the evaporative cooling process, assuming the saturation efficiency of the process is 100%. It is therefore very important to consider the distribution of the outdoor wet bulb temperature around the world to identify the most suitable places for the use of evaporative cooling.

Typically, for data center applications, locations where the wet bulb temperature is> 25°C are considered to have low potential for implementing evaporative cooling solutions.

Data center cooling requirements

ASHRAE Technical Committee 9.9 (TC9.9) issued the 4th edition (2015) of the thermal guidelines for data centers defining cooling requirements.

This new envelope with wider operating ranges supports the introduction of new energy saving technologies such as free cooling (also known as free cooling and / or economizers) and the use of evaporative cooling solutions.

Here is a representation of the different ranges (A1 to A4, both recommended and allowed) with the specifications for air cooling.

Taking advantage of the latest generations of IT and electrical distribution equipment operating at higher and higher temperatures while maintaining high reliability rates, data centers now use higher chilled air drive temperatures, while maintaining the usual ∆T ( supply / return), which in many cases allows the supply air temperature during summer peaks (which in some cases represent a very small percentage of hours / year) to deviate from the recommended values ​​to the values ​​allowed by ASHRAE ( many of the times within range A1).

This enables data centers to implement highly energy efficient cooling solutions, with very low energy use effectiveness figures and, in some cases, allowing the data center to operate without “compressor cooling”.

Energy efficiency

PUE (Power Usage Effectiveness) is a metric that determines energy efficiency in a data center. It is calculated by dividing the total amount of energy supplied to a data center by the energy used to operate the IT infrastructure:

The total energy of the facility includes all the energy of the IT infrastructure plus everything that supports its load, such as the power supply infrastructure (for example, UPS, switches, generators, PDUs, batteries, distribution losses), the infrastructure cooling systems (eg CRAC, AHU, chillers, cooling towers, pumps, etc.) and others.

The consumption of water

WUE (Water Usage Effectiveness) is a metric that determines the use of water in data centers and is expressed in liters / kilowatt-hour (l / kWh):

Annual water use includes all water used to run the data center, such as water used for humidification, to cool the data center (cooling towers, CRAC, or AHU), or to cool electrical power generating equipment.

In the same way as for PUE, cooling represents a significant percentage of total water consumption in data centers, and it is common practice to analyze its partial effectiveness (pWUE).

Advantages of Using Fisair Contact Panel Evaporative Cooling

  • Maximum levels of energy efficiency (annual pPUE) (pPUE anual)
  • The best saturation efficiency on the market
  • The media with the lowest pressure drop on the market
  • Reduced water usage (pWUE), compared to other evaporative cooling solutions
  • Reduced emergency water storage compared to other evaporative cooling solutions
  • Operation with all types of water (without water treatment)
  • There is no risk of water droplets on the inside of the enclosure or on the components (for example, the air-air plate heat exchanger)
  • Allows cooling solutions without the use of a compressor (“mechanical cooling”)
  • Reduced electrical infrastructure
  • Reduced CapEx, OpEx and cost of capital

Product range

FISAIR offers a complete range of evaporative contact panel cooling products:

Small to large-scale data centers: HEF2E for integration in air handling units (AHU)

Features and main advantages:

  • Low energy consumption;
  • Made entirely of AISI304 stainless steel, optionally AISI 316;Media pads evaporative coolers | HEF2E
  • High efficiency / hygienic evaporative panel. Non-flammable and inorganic
  • Glueless assembly, which provides high saturation efficiency, very low pressure drop and a long life cycle;
  • Operation with all types of water, including demineralized water;
  • Silver ions on the surface of the evaporative panel (antibacterial and protection against mold formation);
  • Standard cassettes for easy maintenance;
  • Allows maintenance from the sides or from the front of the unit;
  • Quick and easy assembly in the AHU;
  • Hygienic certificate according to VDI6022.

Standard series:

From 570 mm x 350 mm (425 m3 / h to 2.5 m / s) to 2975 mm x 2400 mm (55,000 m3 / h to 2.5 m / s) in one piece, and up to 6150 mm x 4800 mm in modular assembly (220,000 m3 / h to 2.5 m / s).

Large-scale data centers: HEF2E for air handling units (AHU)


Direct Free-Cooling

 Example of direct free cooling with evaporative cooling by contact panel from FISAIR

Location London Madrid
Heat load 125 kW 125 kW
Supply air temperature 26 26
∆T 12 12
Cooling modes
Free-Cooling 8582 h/a (98%) 7324 h/a (84%)
Evaporative (HEF2E)* 178 h/a (2%) 1436 h/a (16%)
Compressor 0 h/a (0%) 0 h/a (0%)

* using the FISAR HEF2E evaporative system with the following details: frontal air velocity 2.0 m / s; impulsion RH <80%

HEF2E performance under extreme annual design conditions a = 20 years
Madrid 41 25,3
London 35,8 22,6

Indirect Free-Cooling


Indirect Free Cooling Example with FISAIR Contact Panel Evaporative Cooling

Location London Sydney Tokyo
Heat Load 125 kW 125 kW 125 kW
Supply air temperature 26 26 26
∆T 12 12 12
Cooling modes
Free-Cooling 8276 h/a (94%) 6505 h/a (74%) 5984 h/a (68%)
Evaporative (HEF2E)* 484 h/a (6%) 2255 h/a (26%) 2776 h/a (32%)
Compressor 0 h/a (0%) 4 h/a (0,1%) 1484 h/a (17%)

* using the FISAR HEF2E evaporative system with the following details: frontal air velocity 2.0 m / s; Air-to-air plate recuperator efficiency = 75% @ 1: 1 air flow ratio

Small-scale data centers: online conduit – HEF3-CAD

Features and main benefits:evaporative air cooler | Contact panel evaporative humidifiers | Fisair

For direct water pipeline applications.

  • 6 standard sizes with airflows up to 3,700 m3 / h without droplet carry-over.
  • Optimal performance with minimal operating costs.
  • Easy installation and maintenance.
  • High increase in heat recovery efficiency in the return air.
  • AISI-304 stainless steel, in the basin and structure.
  • Complete emptying of the tray.
  • Easy to disassemble for cleaning and maintenance purposes.
  • Accessible on all faces.

Small to Large Scale Data Centers: Fluid Chillers / Dry-Coolers / Chillers: – HEF7

Evaporative cooling sections composed of:Cellular panel evaporative coolers | Fisair's Photos adiabatic cooling system

  • The adiabatic cooling system has a high efficiency organic or inorganic evaporative panel in a stainless steel frame.
  • Pump unit (tank, level switch, motor-valves and flow regulator)
  • Control panel (IP-55 protection, protections, luminous screen and status indicator).
  • Optional: communication with BMS and water conductivity control to minimize consumption.

Application references

Among the outstanding references is the Telefónica Alcala Data Center (Alcalá de Henares, Madrid, Spain)

Certification: TIER IV Gold

Annual PUE: <1.3

Supplied product: FISAIR HEF2E evaporative coolers for AHUs.

The incorporation of FISAIR’s HEF2E evaporative coolers in the air handling units allowed Telefónica’s data processing center to operate without the need for mechanical cooling for 92% of the time throughout the year, only using free-cooling and / or evaporative cooling, thus contributing to achieve the TIER IV Gold certification from the Uptime Institute, with an annual PUE (Power Usage Effectiveness) between 1.2 and 1.3.

Installation type: Chillers + AHUs with direct evaporative cooling (DFC)

No. of UTAs: 36

Use of free-cooling (outside air) and / or evaporative cooling: 8,460 h / year (92%)

Use of mechanical cooling (compressor): 300 h / year (8%)

    Other outstanding references:

    • HP 
    • Oracle 
    • Telefónica (Movistar) 
    • BBVA 
    • Maphre 
    • Popular Bank
    • Data4 (Milan and Paris)

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