Posts Tagged ‘UPS’

Can we replace UPSs in our data centers?

Tuesday, April 27th, 2010

It has been common since I entered the data center realm 15 years ago that a data center had Uninterruptible Power Supplies (UPS) feeding all computer equipment or other critical loads. The UPS did two things: 1) kept the power flowing from batteries in the UPSs for a short duration until generators came on, utility power was restored computer equipment could be shut down; and 2) kept voltage and frequency stable for the computer load while the utility (or generator) power fluctuated, known as sags or surges. However, UPSs consume about 5-15% if the power entering them as losses in the units (a.k.a inefficiency). So if IT load equals 1 MW, UPS power will be about 1.1 MWs with the additional 100 kW lost as heat, which then requires additional cooling to keep at the roughly 75F temperature batteries and UPS run best. Here is a photo of some UPS systems:ups

Now, enter 2010. UPSs are still assumed by nearly every data center engineer and operator to be needed or required, yet, power electronics within the computer equipment can ride thru just about any voltage sag or surge a utility would pass on thru their protective equipment. Computer equipment power supplies have been rated for 100-240VAC and 50-60 Hertz for about 10 years now, so a far greater range than an utility will likely every pass on. Furthermore, due to capacitors in the power supplies, these devices can ride thru complete outages of about 15+ cycles, which is roughly 1/4 second. So the UPSs job is really now only to provide ride thru of outages over 1/4 second and until a generator comes on or as needed by the operation.

In many of the data center design charrettes that I have been part of over the last few years, we ask the users what really needs to be on UPS, avoiding the assumption that all computer load must be on UPS. Once we dive into the operations, we always come back with an answer from the data center operators that only a portion of the computer load needs to be on UPS and the rest can go down during a usually irregular utility outage. The reason is that these computers can stop operating for a few hours and not affect the business. Examples might be HR functions, crawlers, back up/long-term data storage, research computers, etc. Computers that might need to be on UPS include sales tools, accounting applications, short-term storage, email, etc. but not every application and function. Think about your own data center operations about what can go down every now and then from a utility outage (usually about once per year for a few hours) and see if you can reduce the total amount of UPS power you require and repurpose that expensive UPS capacity and energy loss to the critical functions.

Some data centers avoid UPSs entirely by putting a small battery on the computer itself, in widely publicized Google’s case, an inexpensive and readily available 9V battery. While this is an excellent idea for those that have custom computer hardware, it is not as easy to implement for most folks buying commodity servers today. Perhaps another idea better for the masses is to locate a capacitor on the computer board or within the server that can ride thru ~20+ seconds until generator(s) can supply load during a utility outage. Capacitor technology of today should make this fairly easy to implement and could be a standard feature on all computer equipment with a minimal added cost, much as the international power supplies did for us 10+ years ago and higher-efficiency power supplies (90+) are today. A great new technology that could make this easy to build on the computer board can be seen here:
http://newscenter.lbl.gov/feature-stories/2010/04/23/micro-supercapacitor/

Using a technology like this we could avoid UPSs entirely in our data centers by having enough ride thru built onto the computer boards, into the hardware, allowing us to save very expensive UPS power capacity, operating and maintenance expenses and space within our data centers for more important functions, compute and storage capacity. My thought for the day. Think about it and you might save some money and energy.