Air-side and water-side economizers in the data center

What are air- and water-side economizers, how are they used for data center cooling, and why are they crucial to data center energy savings? IBM distinguished scientist and former ASHRAE chairman Roger Schmidt explains the pros and cons of air-side and water-side economizers and discusses why he thinks one type of economizer is the better option.

Read the full transcript from this video below:  

Air-side and water-side economizers in the data center

Mark Fontecchio:  Hi, I'm Mark Fontecchio.  I'm a news writer at  And with me today is Roger Schmidt.  He is a distinguished scientist at IBM.  And he's also the former Chairman of Technical Committee 9.9 at the American Society for Heating, Refrigeration and Air Conditioning Engineers.  So called ASHRAE.  And that committee focuses on data centers.

Today we're going to talk a little about economizers, both air-side and water-side economizers.  So, Roger, could you start by just talking a little bit about outside air cooling or air-side economizing.

Roger Schmidt:  Okay.  So, typically, what data centers want to do when they talk about air-side economizers is really bring in outside air.  And basically letting it exhaust into the data center to cool the servers below the ASHRAE spec.  And the ASHRAE spec right now goes up to recommended at 81 degrees F, 27 C.

So how do you do that?  Basically for high, and again, high-flow rates are needed in data centers.  So you need a huge amount of airflow that comes into the data center if you do 100 % air economization.  So it's a large, large opening basically to bring it in.  You have to do the proper filtration.  Pre-filters.  Filters downstream.  Humidification you may have to do.  Dehumidification.  Depending on what the humidity requirements are, again, per the ASHRAE spec.  So that's the basic what you do.  That's air- side economizer.  And I'll mention one other one which is the water-side economizer, which basically separates the outside air from the inside air. So you have that buffer zone where you don't bring the outside contamination in.  So that does allow you a buffer but it does reduce the efficiency somewhat.  Because you've got a heat exchanger in there.  But it still gives you very good efficiency numbers.

Mark Fontecchio:  Now could you talk a little bit about the potential benefits of both air-side and water-side economizers?

Roger Schmidt:  So, again, from either air-side or water-side economizers, the big advantage if you can use that, and let's say you can it all year round, one of those two methods. You don't need chillers then.  Chillers are a big major component of the energy in a data center.  So if you can get rid of them, that's a huge expense that you can get rid of.  Both from an energy standpoint and just capital expense.

But let's say you can't do it all year round.  Even that is a big advantage by using air-side or water-side economizers from an energy standpoint. Because you can turn those chillers off part-time.  And when the outside air is cold enough and you can maintain that inlet temperature to the racks within the ASHRAE spec, then you can save a lot of energy by basically bringing in outside air.  Either through a liquid air heat exchanger or just bringing outside air in.

So from an energy aspect, everybody understand this is a big thing for data centers.  And I'll say the main reason why we opened up the ASHRAE spec was for this exact reason.  How do we save energy?  And we can do that by growing that recommended envelope for the ASHRAE spec.  Which we did.

Mark Fontecchio:  And now what are the concerns with air-side economizers?

Roger Schmidt:  There are really four major issues, I think.  And we can just name them all.  So temperature is one.  Temperature fluctuations.  Humidity fluctuations.  Particulates from outside.  And then the gasses.  Those four major things.  Because that's what you grab from outside.  Right?

Particulates, I don't think anybody has a problem with that.  We know how to filter that.  You've just got to put the proper filtration in and you'll grab all the stuff before it gets in the data center.  Temperature, I think you can pretty much control that.  You've just got to put the proper controls in.  That can be a little tricky but I think that can be handled. Humidity sometimes can be more of a problem.  But people do that and it can be done.

I would say the major one, if I were to prioritize, I think the gasses is the major one.  And let me just describe that a little bit.  We have, obviously, a number of clients around the world.  And different locations around the world have different pollution levels.  And some of the contaminants that will really damage electronic equipment, the sulfur compounds, ammonia, chlorine, bromine.  Any of those type of compounds.  If you get them into data centers they will damage electronic components.  And you'll have fails.  Guaranteed.  If it's a high enough level.

And there are levels that we want to get out and educate clients about. What levels are acceptable.  And there are ways to measure this now.  And we're trying to get the word out.  And we're trying to get this into some ASHRAE guidelines, if you will.

So two things you want to measure on gasses contamination, are the corrosion rate on silver and the corrosion rate on copper.  And there are low coupons you can put out in data centers and measure this over time. And so if you get roughly 300 angstrom of corrosion on silver or copper over 30 days, you probably have a problem.  So that's kind of simple to do.  Right?  Put it out in the  data center to see if there's a problem.

Now that does the normal air contamination that might come into the data center.  It doesn't look at those spikes that may happen with clouds of gasses or fires or dust storms that come very intermittently, from maybe natural disasters or maybe not so natural disasters.  Like volcanoes. We've had trouble in regions where volcanoes have the high sulfur content that spikes up.  That ends up damaging equipment.

So there areeveral problems here that really be addressed.  The more steady state can be measured with coupons.  The conditions where there are spikes, I think sensor technology has to be looked at.  And whether we can detect those on a real-time basis to basically close off the dampers has to be looked at.  And then when you close off the dampers, obviously, you have to turn those chillers on immediately.  So there's a chiller ramp-up time.

So these are some real concerns, I think.  Again, I'll say gasses is number one.  Maybe humidity might be two.  And then particulate and temperature are the third and fourth ones that are probably more controllable.

Mark Fontecchio:  For the gaseous contamination, is there any way to treat or filter that air in the same way that you treat it or filter it for particulates or humidity?

Roger Schmidt:  Great question.  And I think there are chemical filtration media out there now that can be used.  They're called deep-end filtration.  That will take care of a lot of the bad contaminants that are out there.  And those are things that are being looked at for different data centers in the world that will clean up that air.  Absolutely.  There is a cost associated with it as you can expect.  Because these are major filtration systems that you have to put in place.  Again, you're filtering a major volume of air going into the data center if you're talking about air-side economizers. As you can imagine.  Hundreds of thousands of [??] CFM.  So how do you filter that air in a deep-end filter? That takes a lot of media.  A lot of media to filter that.

But yes, there are solutions and these are things that  have to be put in place for those regions of the world that are having this problem.  China and India are perfect examples.  With all the coal plants and the pollution that ends up in the air, you really have to look at this.

Mark Fontecchio:  And finally, with all that said, it seems like you're leaning towards water-side economizing over air-side economizing.

Roger Schmidt:  Well, I do only because the reliability aspects and how some clients may not apply the right technologies in place for doing air-side economizers.  And again, we're talking about in some cases hundreds of millions of dollars of equipment in a data center that could be damaged if somebody doesn't do the right thing on protecting that equipment with the right filtration.  I think the risks are too high.  So myself, even though there's a little decrease in the overall efficiency on water-side economizers versus air, I think you've eliminated basically a lot of the risk by doing that.  And you still get big energy efficiency gains. Personally, I recommend the water-side.  I think air-side has some work to be done.  Or maybe education to be done.

Mark Fontecchio:  Well, thank you, Roger, for joining us.  And thank you for listening to our videocast.



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