One problem we have seen with curtains on cold aisles is the flapping or drawing in of the curtains due to the airflow through the adjacent perforated tiles. Sometimes people call this the “dancing curtain problem.” The Bernoulli effect (air plane wing effect) of lower pressure on the side of the higher air velocity causes this. This flapping can push the curtains close to the server intakes and then the suction of the intakes can suck the curtains onto them, blocking and essentially starving the servers. We caught this blocking three times before we adopted a policy of avoiding curtains on cold aisles.

After examining this and having the good fortune of a customer doing some testing we concluded that flapping curtains are not a fuction of air balance in the contained zone. Rather, it is a function of turbulence caused by the airflow through the nearby tiles. So, even if one has an oversupply of air, the curtains just don’t push out gently as one might expect.

We tried adding weights to the curtains to prevent their movement, but this only resulted in heavy flying objects banging into the servers. Ultimately, we added two solid panels to the sides of the strip door. By the time we did this, the cost was about the same as a sliding door like the one pictured below.

Sliding Door Preferred Over Curtains for CAC

The design approaches to combat the flapping curtains include:

• Hot aisle containment – there is no air flow from the floor
• Sliding doors – they don’t move
• Solid floor tiles at ends of rows – no nearby air movement
• Extended containment perimeter – basically place doors away from aisle end in some manner