Comment Datacenters and DC/AC power (Score 3, Informative) 379
Hi everyone,
I am a datcenter manager that has had the opportunity to not only run but also build a datacenter from pretty much scratch. In my experience I have found that both DC and AC powered equipment both have their places in the environment. Neither system is perfect so by running hybrid you can get the most flexibility.
We recently moved our datacenter form a 10K sq ft facility down to a 1700 ft facility by doing a technology refresh and changing many of our key infrastructure methods. In the new facility I currently have 315 HP blade servers plus another 10-15 traditional rack type servers running. I have the capacity to add up to another 144 blades (assuming they are 1U) before I run out of floor and HVAC capacity. The power delivery method is hybrid. I run DC for the blades which are fed by Emerson Energy's Candeo XL rectifier stacks (originally designed for telco) and AC for everything else. To eliminate a lot of the under floor clutter I use a trough system instead of conduit for the various AC circuits. HVAC is provided by 4 Liebert 22TON units which keep my room at a comfy under floor temp of 66 degrees.
Adequate airflow is critical so we spent a lot of time planning tile placement. The key for proper cooling in this scenario was a high volume of airflow pushing the cooling to about 5.5ft up from the raised floor. This way my cooling isn't being sucked up by just the bottom half of the rack. Low voltage cabling is overhead.
We chose to power the blades DC for two reasons. First was the limited space I had for installing breaker boxes on the walls. The number of AC circuits I had was limited so I pulled fat feeds directly to the Candeo systems. A full rack of HP p-class blades would require 4 x 3phase 208 circuits per rack. My initial installation of blades would have consumed 144 of my 168 circuits leaving next to nothing to power my SAN/Network/Tape Library/etc equipment. The other reason was power supply efficiency. In the conversion of power from AC to DC the efficiency of the power supply must be taken into consideration. It's not just the number of conversions you do but the loss at each. Typical power supplies in servers run about 80% efficient while my Candeo as they are setup gets about 90%. For me this ultimately meant less heat and more available cooling, therefore I could bring in more servers under the existing HVAC.
I prefer a best of class mentality. IMHO there is no best universal solution. For those of you that use traditional rack mounts servers like Dell you can purchase these units with a DC option. I am not sure if HP offers a similar option but they might.
Len
p.s. Someone also made the comment about DC not generating noise in network cabling while AC does. This is not a totally true statement. Anytime you run a current through a conductor you will generate a magnetic field. Put this in parallel to another conductor and you will further induce a mag field (this is why any power runs that have to intersect low-voltage cabling should only intersect at 90 degree angles to avoid inductance). The big difference is the way DC cabling runs. In most DC circuits the feed and return lines run together so the proximity of the out of phase magnetic fields will cancel each other out. Don't believe me? I had this problem when we intially wired these Candeo systems up. The small feeds to the racks and the big mains that connected to the common buss bar were about a foot apart. Because the fields weren't cancelling, we were getting enough noise on the lines that it looked like there was AC leaking through the circuits (6volts p-p in some cases). By simply wire tieing the lines together, the proximity cancelled the fields out and everything was peachy.
I am a datcenter manager that has had the opportunity to not only run but also build a datacenter from pretty much scratch. In my experience I have found that both DC and AC powered equipment both have their places in the environment. Neither system is perfect so by running hybrid you can get the most flexibility.
We recently moved our datacenter form a 10K sq ft facility down to a 1700 ft facility by doing a technology refresh and changing many of our key infrastructure methods. In the new facility I currently have 315 HP blade servers plus another 10-15 traditional rack type servers running. I have the capacity to add up to another 144 blades (assuming they are 1U) before I run out of floor and HVAC capacity. The power delivery method is hybrid. I run DC for the blades which are fed by Emerson Energy's Candeo XL rectifier stacks (originally designed for telco) and AC for everything else. To eliminate a lot of the under floor clutter I use a trough system instead of conduit for the various AC circuits. HVAC is provided by 4 Liebert 22TON units which keep my room at a comfy under floor temp of 66 degrees.
Adequate airflow is critical so we spent a lot of time planning tile placement. The key for proper cooling in this scenario was a high volume of airflow pushing the cooling to about 5.5ft up from the raised floor. This way my cooling isn't being sucked up by just the bottom half of the rack. Low voltage cabling is overhead.
We chose to power the blades DC for two reasons. First was the limited space I had for installing breaker boxes on the walls. The number of AC circuits I had was limited so I pulled fat feeds directly to the Candeo systems. A full rack of HP p-class blades would require 4 x 3phase 208 circuits per rack. My initial installation of blades would have consumed 144 of my 168 circuits leaving next to nothing to power my SAN/Network/Tape Library/etc equipment. The other reason was power supply efficiency. In the conversion of power from AC to DC the efficiency of the power supply must be taken into consideration. It's not just the number of conversions you do but the loss at each. Typical power supplies in servers run about 80% efficient while my Candeo as they are setup gets about 90%. For me this ultimately meant less heat and more available cooling, therefore I could bring in more servers under the existing HVAC.
I prefer a best of class mentality. IMHO there is no best universal solution. For those of you that use traditional rack mounts servers like Dell you can purchase these units with a DC option. I am not sure if HP offers a similar option but they might.
Len
p.s. Someone also made the comment about DC not generating noise in network cabling while AC does. This is not a totally true statement. Anytime you run a current through a conductor you will generate a magnetic field. Put this in parallel to another conductor and you will further induce a mag field (this is why any power runs that have to intersect low-voltage cabling should only intersect at 90 degree angles to avoid inductance). The big difference is the way DC cabling runs. In most DC circuits the feed and return lines run together so the proximity of the out of phase magnetic fields will cancel each other out. Don't believe me? I had this problem when we intially wired these Candeo systems up. The small feeds to the racks and the big mains that connected to the common buss bar were about a foot apart. Because the fields weren't cancelling, we were getting enough noise on the lines that it looked like there was AC leaking through the circuits (6volts p-p in some cases). By simply wire tieing the lines together, the proximity cancelled the fields out and everything was peachy.
