FT Data Center – The Plague of High Velocity Airflow
FT Data Centers tackles the issue of high velocity airflow – a plague upon many well-meaning data center operators.
FT Data Center. Drew here. A few years ago I went into a client’s data center because they were having airflow problems on this one row of server racks. I took one look at their setup and I told them it was obvious why they were having airflow problems, gave them the answer and then they didn’t hire me because the fix was so easy. What was the problem? Well, it was an easy mistake for them to make because, for a lot of people the answer is counter intuitive. See, their vented floor tiles were too close to the nearest CRAC unit. I actually took a piece of paper and put it over top of the vented tile and it was sucked down toward the floor. So the question is, why? Well, to answer that we’re going to do a quick little demonstration.
Here we have two ping pong balls suspended from the ceiling about a half inch apart. I’m going to take this straw.
And blow high velocity air between these two. Those of you already familiar with fluid dynamics know the answer, but most people intuit something else. So here we go.
When I blow between the balls, they collide.
See, the balls actually collide together because the air between them was moving at a high velocity. High velocity air has less pressure.
The pressure on the outside of the balls is greater to the pressure on the inside and that differential pushes the balls to collide with each other.
Back to the fish tank, I’ve set up with the floor tile with a piece of paper on it right next to the CRAC.
Back at our data center. The velocity of the air close to the CRAC unit caused that negative pressure we talked about earlier. Let’s see this in practice. I’m going to energize our fish tank server and our fish tank CRAC unit. Then I’m going to put this piece of paper over the nearest vented tile to the CRAC. Let’s see how that looks.
Drew turns on the energy and suddenly the air starts moving. It’s very loud. Drew takes the piece of paper and puts it over the vented floor tile. It gets sucked down toward the ground.
See? This is why design guides tend to tell you not to put the CRAC units at the end of the cold aisles. If you do have this particular problem, you could either relocate some server racks or you could install underfloor baffles which would redirect the air and allow for the proper airflow. Or you could decrease the fan speed of that CRAC unit or you could… Well, you could do a lot of things. The point is that once you’ve identified the problem it becomes a million times easier to come up with a solution. Thanks for watching. Until next time, stay centered.