Power is expensive in the Caribbean so data center efficiency is all the more important. Modern Power and Cooling Technology Limited successfully designed and implemented a cold aisle containment solution at the state of the art tier 3 Digicel Collocation Facility at Caymans using Polargy’s Aisle Containment System with the one of a kind “drop away” panel. A few classic site conditions were columns down the aisles, uneven aisle ends, and a single sided aisle. What is most impressive is that the design was done locally by Modern Power and they installed the system with no difficulties.
This cold aisle containment project enjoyed pure simplicity.
The site, near Denver, was purpose built so Xcel Energy could just take a before and after meter reading for the entire building. The IT load did not really change over the course of the project, so the reduction was attributed to the shutting off of 39 CRAC units out of 70 units running. This reduction was measured at 435kW, or about 11kW per CRAC unit. These CRAC units were the old AirFlow brand and the per unit reduction was higher than anticipated but we double checked the meter readings and verified the constant IT load (via the UPS) to confirm the numbers.
Old Airflow CRAC Badge
The containment was a combination of cold aisle containment, under floor partitions, and CRAC unit extensions. PUE before was 2.0, after it was 1.8.
Polargy helped calculate the ROI. The project’s net costs were $400K ($569K less $169K). The 435kW savings yielded $225K annually (power rate is about 6 cents per kWh). This results in a project payback period of 1.6 years.
Vanderbilt contributed to the AFCOM event with a tour of its latest energy savings efforts in its Nashville data center. The university installed Polargy’s Cold Aisle Containment System on one of its newly installed aisles. 73 people toured through the site and experienced the containment system as shown below.
Our friend Jeff showing how the sliding door works:
Taking a peak inside the contained cold aisle. The site has a glass brick wall which is illuminating the wall above the CRAC unit, a neat look.
Jay (now at Twitter) presented Pixar’s results from Polargy’s Cold Aisle Containment installation. This is a simple and compelling story on containment’s ease of implementation and rapid ROI.
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
Existing data centers protected with FM200 or other clean agent systems can be a challenge to contain because the cost of adding or moving nozzles is very high. One alternative has been the use of electronic fuse links that trigger off the FM200 system. Though the links are pricey (about $250 each) and need testing, it is a workable solution that can still offer an ROI that meets project goals.
Electronic Fuse Links
The electronic links pictured above where installed on a hot aisle containment system pictured below. The site has a ceiling with two levels and the FM200 nozzles are installed in the lower section of the ceiling. The curtains were installed with a gap above them to allow some air movement (so not total isolation) in order to assure that air flow to the existing smoke detectors were not obstructed.
Hot Aisle Containment
These links have an electronic trigger off a signal from the FM200 system as well as a thermally activated mechanism. The wiring requirements are similar to those for smoke detectors and is through conduit that you can see in the above picture. The other wires are tethers to stop the fall of the curtain after it drops about two feet to clear the FM200 nozzles.
A customer did a burn test on Polargy’s PolarDAM Air Dam Foam and posted it on Youtube. Of course, we were happy to see that the foam performs as specified and is self extinguishing.
Interestingly, I visited another customer who had put a few pieces of our air dam foam in an environmental test chamber to see how well it withstands high temperatures and varying temperatures. I had no idea that they were doing this until my visit. We examined the sample pieces and could see no indication of the foam decaying. I was surprised to learn he had this test running for the past three months.
Today I talked to a facilities engineer for a lab data center. They have already added strip curtain doors to the ends of the cold aisles and the top of the aisle remains uncapped. Next, they plan to install VFDs and put temperature sensors at the rack tops in the cold aisle. They plan to drive the VFD’s off the temperature at the top of the cold aisle.
This is an interesting approach because it seems to assure that the air flow is sufficient to the cold zone. And, with an open top, it is especially important to assure sufficient cold air into the aisle. Without that, or in an under-supply situation, the aisle would take hot exhaust air from over the tops of the racks.
