In the first
of two articles about power quality, we outlined the basic elements needed to plan and implement a data center power project.
In this article, we will review some of the important factors to consider when reviewing vendor proposals. You should take the following into account:
Sole Source -- How valuable is it to have a single point of contact for the whole solution, including wiring, installation, maintenance and so on? Is it worth the effort and potential finger-pointing to go with separate vendors versus one group to hold accountable?
Power Conditioning -- Line conditioners are designed to smooth out spikes, sags and remove EMI/RFI and harmonics from the line. Some UPSes (uninterruptible power supply) have line conditioning as an integral subsystem, while others require an external system to be effective.
Part of the site survey should include issues detected. Note, there are many AC power issues to consider beyond voltage, EMI/RFI and harmonics. A search on Google can readily turn up many sources of additional information. Also, hardware vendors sometimes can provide insight as to what their systems can tolerate.
Lightning Strike Suppression -- Some line conditioners can handle a lightning strike without any problem, some marginally so and others not at all. Make sure that your power systems are capable of protecting your electronics. (A small footnote: You may have other lines going into your building that can be affected by lightning and may need protection. The author lost a fairly expensive PBX once due to a lightning-related power surge that came through an unprotected analog phone line port.
Uninterruptible Power Supply (UPS) -- There are two main types of UPSes, differentiated by how they handle power prior to a power loss. There are units that are online all the time -- thus, all power supplied to the data center flows through the UPS first. Due to this filtering, these systems provide conditioned power and there is no switching time associated with converting from "street" power to UPS power.
The second type of UPS is often termed a "standby" unit, as it is offline until the power fails and then there is time associated with switching from street to UPS power. This switching time may only take milliseconds, but there are some devices that are so sensitive that they can crash during that time.
All things being equal, an online UPS is recommended for critical data center power. In sizing the UPS, take into account how long you want to keep the systems up plus how long it takes to do an orderly shutdown. Make sure that policies and procedures reflect this timing element.
Electric Generators -- There are many types of electric generators. There are ones fueled by gasoline, natural gas, propane, and diesel. Your organization should select the fuel based on what will be most available during a crisis in their area. For example, inline natural gas sounds appealing, but can the gas company be depended on? The generator should be sized to meet the data center's need and expected growth.
Keep in mind, however, that a generator does not replace a UPS. When power first fails, the data center needs to run off the UPSes while the generator(s) start and stabilize. Power is run from the generator through the UPSes to garner conditioning benefits and to recharge the batteries in the event of a generator failure, refueling, etc.
Monitoring & Alerting -- The software and hardware needed to generate alerts when street power goes down and the UPSes and generators go online are cheap investments. Look for hardware and software combinations that allow for logging of power data and alerting when certain conditions are met. In remote data centers or in shops that aren't 24x7 staffed, the alert may be the first indicator that there is a problem. Also, be sure that the alerts can be sent via the Internet, phone and/or wireless allowing for increasing levels of fault tolerance.