Caleb Tennis Air/Water Economizers – What’s in it for me?

October 19, 2010 by · Leave a Comment 

One of the hot trends in data centers, well, at least in data center marketing, is economization.  Newer constructed data centers like to tout energy efficiency, saying they’re green in certain areas, they’re energy efficiency in others, etc.  One thing heard frequently is the use of air side economization and how it has a substantial impact on the data center’s electrical bottom line.

Let’s look at exactly what that means to both the data center owner, and the data center customer.

Obviously, one of the fundamental aspects of any data center operation is the cooling of the IT equipment.  This is typically done with CRAC (computer room air conditioner) units.

Air conditioners aren’t magical.  Really, they aren’t cooling devices at all – they’re heat removal devices.  They absorb heat and displace that energy somewhere else.  Compressor based units absorb it into a refrigerant that gets sent outside – just like the unit that cools your house.  Many data centers use chilled water units, which put the heat into a chilled water loop – heating up that water – which gets sent back to a chiller to be cooled down again.  Regardless of which way it is used, fundamentally the heat gets rejected outdoors of the data center to the outside world.

Moving this heat isn’t free.  Electrical energy is spent on the motors, pumps, fans and other parts to shuffle the heat around.  The less energy spent for moving the same amount of heat, the more efficient overall the process is.  This translates into a lower bill for the data center operator.

Air side economization helps in this regard.  The way it works is that during the months of the year where the outdoor temperature is cold, outdoor air is brought directly into the CRAC unit and shuffled into the data center.  This warmer return air is then sent back outside.  In a nutshell, we’re basically “opening the windows” and letting the cold outdoor air cool off the data center.  While it’s not quite this crude, it is certainly a very energy efficient way of accomplishing the task!

However, the devil is in the details.  One of the selling points of data centers is that the environment conditions are usually tightly controlled – temperature, humidity, and filtered air.  Outdoor air contains pollutants.  Outdoor air during cold winter months often has very little humidity. And, to get the volumes of outdoor air necessary to cool the data center, large openings to the outside have to be put into the walls of the facility.

So, while air side economization is a great marketing tool, it’s not necessarily the best decision for everybody.  Data Cave uses a different approach, water side economization.  Our CRAC units reject their heat into a chilled water loop, as noted above.  This chilled water loop heats up, and returns to a chiller, which uses power to chill the water again – moving the heat into a secondary water loop, which is sent outside to cooling towers.  This is a very common approach, used in facilities all around the world – not just data centers.

Water chiller, common in many data centers

But, again, the devil is in the details.  Because we send water outside, we can take advantage of the cold winter months to chill the water down to very cold temperatures.  When the temperatures are right, we can actually shut off the chiller completely, and use the outdoor temperature to do all of the “chilling” required.  We benefit exactly the same as air side economization, but we pass the heat via a water loop instead of directly via air.  This brings no external contaminants into the data center, has no impact on the humidity of the data center, and doesn’t require any additional specialized penetrations into the building to support.

We think water side economization is the way to go.

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