Computer Room Evaporative Cooling

I recently came across a nice data center cooling design by Alan Beresford of EcoCooling Ltd. In this approach, EcoCooling replaces the CRAC units with a combined air mover, damper assembly, and evaporative cooler. I’ve been interested by evaporative coolers and their application to data center cooling for years and they are becoming more common in modern data center deployments (e.g. Data Center Efficiency Summit).

An evaporative cooler is a simple device that cools air through taking water through a state change from fluid to vapor. They are incredibly cheap to run and particularly efficient in locals with lower humidity. Evaporative coolers can allow the power intensive process-based cooling to be shut off for large parts of the year. And, when combined with favorable climates or increased data center temperatures can entirely replace air conditioning systems. See Chillerlesss Datacenter at 95F, for a deeper discussion see Costs of Higher Temperature Data Centers, and for a discussion on server design impacts: Next Point of Server Differentiation: Efficiency at Very High Temperature.

In the EcoCooling solution, they take air from the hot aisle and release it outside the building. Air from outside the building is passed through an evaporative cooler and then delivered to the cold aisle. For days too cold outside for direct delivery to the datacenter, outside air is mixed with exhaust air to achieve the desired inlet temperature.

This is a nice clean approach to substantially reducing air conditioning hours. For more information see: Energy Efficient Data Center Cooling or the EcoCooling web site:


James Hamilton



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9 comments on “Computer Room Evaporative Cooling
  1. Dave says:

    Great article Alan. I think innovations like the ones you outline here are fantastic improvements on the technologies currently used in the industry. I would like to offer a question though: For the large parts of the year (at cooler ambient temperatures) that you mentioned, there is a considerable temperature difference between the IT equipment and the ambient air. Wouldn’t it be interesting if there was a technology that exploited that difference to generate power rather than consume power (air handling and fans)?

    • Yes Dave, that is the data center equivalent to the “holy grail.” Rather than pay to remove heat, use the energy productively to either generate power or do something else useful. This is how PUEs of less than 1.0 are possible. Ideas with merit range from running heat pumps and attempting to directly harness the energy through to to delivering the low grade heat for economic gain in district heating systems or in support of agriculture. District heating has been deployed in production and is reported to be working well so progress is being made.

  2. Thanks for passing on your experience Alan. You are pushing 2 boundaries where I see big gains possible: 1) required filtration for air-side economization, and 2) the climates where 100% air-side economization with evaporation cooling can be applied.


  3. I am finding that we can use the evaporative cooling 100% of the time in Northern Europe. It is all about what the wet bulb temperature of the local air is. A good source of free weather data is www wunderground com

    The installation shown has secondary filtration but this is rare for us. The evaporative cooling pads filter out all that is required. Our oldest installation is 3 years old now with this very low level of filtration. I currently do not put this equipment where there are a lot of vehicle exhaust fumes.

    Just commissioned a system in Manchester UK for a 500kW data centre and immediately got a PUE of ~1.18 all with conventional equipment.

  4. Larry asked "When you refer to locals with lower there a threshold you are referring to?"

    I didn’t have any specific threshold in mind. My observation was the more general, Singapore is hard and Phoenix is easy.


  5. Larry Millholland says:

    When you refer to locals with lower there a threshold you are referring to?

  6. Exactly as Rick says Gordon. Just use filtration. There is considerable debate in the industry in how aggressive the filtration needs to be. Some argue that they need to keep anything but small micron particles out and change their filters more frequently. Others argue that you only need to keep birds and small animals out of the facility. Either way, changing filters is remarkably cheap.

    Rick, if permissible, I would love to visit your facility since you are Seattle area. Let me know if that can be done:


  7. Rick Gideon says:

    We’re using evaporative cooling right here in Seattle to cool our data center when conditions require it. We use outside air approximately 90% of the year and reject most of our hot air outside, recovering some of it to temper the incoming air. Similar to the system described above.

    @Gordon – Using filters are sufficient to remove contaminants from the incoming air stream, however if conditions require that we go to cooling tower (like when the generators are running)then the outside air inlet shuts down.

  8. Gordon Laderoute says:

    How do you address the contaminant, dust, hydrocarbon issue. Cleaning the air before re-introducing it into the data center.

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