Too many times when we design data centers, we monitor power consumption at the device only. This could be from a storage array or a server in many cases. Sometimes we may also check in on the power distribution units (PDUs) that may be in use within a rack as well. But do we look closely enough at our uninterruptable power supplies (UPSs)? Chances are, we may find efficiency there if we have to be constantly mindful of data center power consumption. Recently I read a blog by Troy Miller that got me thinking about this very topic.

The logic here is that if the UPS unit is very efficient, it is possible that the “overhead” associated with the power protection can be reduced. That may be that extra few percent of improvement needed in the power- (and space-) constrained data centers of today.

Now, to set the record straight, all UPS devices are not created equal. There are three main types: VFD (line interactive), VI (standby) and VFI (online double conversion). These types were enumerated recently by APC, leaders in the UPS space. There is a certain amount of competitive tension going around about this topic, and the fact that all devices are not created equal is important.

The VFI type is preferred by many as AC power is received, charges the battery as DC, and then the battery power is converted to AC for the devices to consume. In this way, there is no interruption if there is a power loss because the second stage is untouched from the battery.

In fact, some electronic devices in the data center may require a certain type, such as the VFI. In my experience (albeit quite a while ago), I had a telecom system that required that type of power conversion. The system provided voicemail for my office and for some reason, it was sensitive enough to detect normal power fluctuations if a regular UPS (VFD type) switched from AC to battery. Other sensitive systems may require power conditioning, which I have experience with as well. In fact, I’ve even put power conditioning in front of a UPS unit. That gives very clean and reliable power, yet it requires a high power overhead to do it.

The takeaway is to know the devices in your data center, big or small. It also may be worth implementing high efficiency UPS devices that do VFD for one range of equipment and another group that does VFI for the most critical areas. You can get an additional power efficiency via the UPS if you need it.