ServerTech Blog - Information for the Data Center Equipment Manager

Does an IT Energy Czar make sense for your company?

With power usage being one of the largest operational expenses in a data center, it goes without saying that it also offers the greatest opportunity for savings that directly affects the bottom line. In the end, all the talk about "green" initiatives and increasing energy efficiency distills down to simply saving money. The challenge is bringing together the disparate groups and breaking down organizational barriers so teams can work together. Kenneth Brill, executive director of the Uptime Institute, wrote recently in his weekly column for Forbes about creating an energy czar within a company, breaking down organization barriers and establishing goals.

Wanted: IT Energy Czars
By Kenneth Brill
http://tinyurl.com/klhgvc

Ask the Engineer - Why do STI 60A CDU's have 6 output branches?

Question from Derek <omitted>: I see that your 30A strips have three output branches, but your 60A strips have six branches. Why?

Engineer Reply: The branch circuit protection, as required by the NEC, limits the output branch draw to 20A. If you have only three branches on a North American 208/120V three-phase circuit, you are then limited to roughly 35A maximum on the input lines (20A x 1.732 = 34.64A). So, in order to keep from limiting your 60A circuit to 35A, the optimal thing to do is split those output branches in two. With six branches each protected by 20A fuses or circuit breakers, the entire 60A circuit capacity can be utilized.

NetApp offers 10 tips on making a data center more efficient

This is an interesting article published in Network World where NetApp shares 10 tips they used in their data centers to make them more efficient.

10 ways to make your data center more efficient
By Laura Pickering, NetApp, Network World
http://tinyurl.com/n37bgp

A couple tips worth highlighting are:

• Tip 1. Measure to control
• Tip 10. Constantly monitor and tune

In order to control or reduce power consumption, there must be tools and equipment in place to monitor and to trend energy usage to establish efficiency metrics such as PUE or DCiE from The Green Grid, or some other standard. Depending on how much detail is desired Server Technology offers three approaches to monitoring power.

1. Power drop to the cabinet
   The Smart PDUs measure input current (amp) and provides power (watt) values for monitoring at a the rack level
2. Power monitoring and control
   The Switched PDUs offer the same capabilities as the Smart PDU but with the addition of individual outlet control to power down servers and devices when sitting idle to reduce power consumption
3. Power monitoring at the device-level and control
   For device-level monitoring, the Switched POPS PDU used in conjunction with the Sentry Power Manager (SPM), provides current (amp), power (watt and VA) and power consumption (kW-h) measurements for a detailed understanding of each device's usage. The power control features allow for individual outlet control so users may power down underutilized or dormant devices, while SPM delivers trending and reporting tools to help monitor power usage.

For more information, visit www.servertech.com.

Have you updated your Sentry Smart and Switched PDU firmware recently?

If you have not updated your Switched or Smart PDU firmware to version 6.0g, here are some features you may be missing.

• RADIUS Support
  RADIUS (Remote Authentication Dial-In User Service) is a centralized authentication, authorization, and accounting service.  The Smart and Switched PDU firmware supports the authentication and authorization features of RADIUS. See release notes for details.

• User-defined session timeout periods
  Allows users with administrative access rights to adjust the session timeouts for both the web and command-line interfaces. This is particularly useful when the PDU needs to be accessed frequently throughout the day. The default timeout period is five minutes. Now admins can adjust the timeout period between one and 1440 minutes.

• Input Current Measurement Resolution Update
  For products that previously reported current (amp) in 0.25 A increments, this update increases the resolution to 0.125 A increments. For products that reported in 0.50 A increments, now report in 0.25 A increments. This update provides support for Server Technology's new Digital TRMS input current measurement hardware that provides 0.01 A resolution with better than 2% accuracy.

• Updates SSH Authentication Methods
  Allows admin to individually enable and disable the support SSH authentication methods (password and keyboard-interactive).

• New Smart Web GUI and other features
  Upgrading the firmware from v5.3x to v6.0x provides the user with a refreshed web GUI. Those that are familiar with the Server Technology Switched PDU interface will find many similarities. Additionally, the Smart v6.0x firmware will provide the ability to poll a supported networked UPS for voltage for a more accurate power (watt) calculation and a watts per area calculation.

To download the latest firmware visit the Server Technology website at www.servertech.com or our FTP site (http://tinyurl.com/ms3zzs).

Data Center Dynamics - Seattle (August 6th)

Server Technology will be exhibiting at the one day Data Center Dynamics show in Seattle, WA on August 6th at the Hilton Bellevue.

Early registration for the show ends on Monday, June 26th.

This conference is formulated around recent updates from the US Environmental Protection Agency, The US Department of Energy, ASHRAEs TC9.9 and The Green Grid.  Changes regarding accreditations, efficiency metrics, reports on growth expectations and consumption predictions have all been considered in the program schedule for this Data Center Dynamics show in Seattle.

Case studies and technical presentations will address the following topics. 

• "Energy stewardship - How to maximize performance per watt in your data center whilst balancing the requirements for availability and agility
• Data center design - The latest construction techniques including adaptive thermal management, modular building platforms, and power architectures
• Automation - How to build command and control toolsets that optimize your IT and facility infrastructure end-to-end
• IT - New perspectives on how cloud computing, virtualization and service orientated architecture will impact your facility
• Managing expansion - How will investments and specifications for data centers be affected by  new demands of content and data as a result of the ever-growing information superhighway?
• Regulation – How will existing and potential tools from LEED v3 through to Carbon Cap and Trade promote the drive towards sustainable eco facilities?"

Find more information including registration and show sponsors online.

Ask the Engineer - How important is it to balance 3-phase loads?

Question from Joseph Jones: I know I'm supposed to balance the loads on my three phase circuits, but I don't know why.

Engineer reply: Balancing loads on a three-phase circuit is often misunderstood. Three-phase balancing is most commonly an issue for motors and generators, in which the voltage (not current) must be balanced to prevent damage. At a facility level, the overall loading of the three phases might be required to be balanced to within a certain tolerance in an effort to keep voltage drops equal for backup generators. For our purposes at the cabinet level, the balancing is not an issue of preventing damage. There are four effects that must be considered as reasons to balance loads on an individual three-phase CDU circuit.

1. Calculation Accuracy: When dealing with a 208V Delta load, power usage can only be accurately calculated using current measurements at the outlets (cross-phase XY, YZ, and XZ). Current measurements of the input phases (X, Y, Z), which is most common, can result in power calculations 15.4% high for worst case imbalance. Though an imbalance where the highest output phase load is 50% higher than the lowest (e.g. XY=8, YZ=8, XZ=12) only causes power calculations to be 0.5% high.
2. Efficiency: When dealing with 208V Delta load, an imbalance of the output loading causes wasted power in the feeder lines. For worst case example, a 9A load on output phase XY will cause 9 amps to flow through each line X and Y. Because the power loss of current flowing through a resistive line is I*I*R, the loss is 162 watts (9*9 for X plus 9*9 for Y) for every ohm of feeder resistance. But, if that 9A load was distributed as three 3A loads between XY, YZ, and XZ, the loss is 81 watts ([3*1.732]squared times 3) for every ohm of feeder resistance.
3. Efficiency: When dealing with 120V or 240V Wye loads, an imbalance causes wasted power in the neutral line. A perfectly balanced three phase Wye circuit will have no current flowing in the neutral line.
4. Density: To fully utilize the available power of a three-phase 120/208V circuit as distributed to output branches at 208V, all output branches (XY, YZ, XZ) must be used. For example, a 30A three-phase circuit is good for maximum of 52A combined output load; but if only the XY branch is used, the circuit will be limited by the branch circuit protection to 20A max.

The end result is that coming anywhere near balanced will effectively negate all four of the effects above.

Video: 60Amp 1U-wide 208V Switched PDU Demo

Andy Szeto, Product Manager, walks you through the CW-24V 60Amp 3-Phase 208V 1U-wide Switched CDU. 

http://www.youtube.com/watch?v=SL4YdUZvkCc

Highlights of the video/CDU include:

• 60A, 3-Phase, 208V
• 1U-Wide/ 1.75" (44mm) Wide
• 21.6kW Solution
• Control Outlet State Via Web or Serial Interface
• Group Outlets as well as turn them: On, Off, or Reboot
• 3 Central LEDs
• Top Cord Entry for Overhead Busways
• 3-Phase Load Balancing
• Invert LEDs via Web GUI
• 21.6kW at 60A 3-phase/ 18kW at 50A 3-phase
• 6 Branch Circuits (3 C13 and 1 C19 per branch)
• Circuit Breakers
• Master and Expansion Unit controlled from a single IP Address
• Optional Temperature and Humidity Probe (2)
• Accessories: Sentry Power Manager (SPM)

Ask the Engineer - What do the 3-phase LED meters indicate?

Question from Jim <omitted>: On the 3-phase CDUs, there are three LED meters on the unit. I assume one per phase. How do those meters map to the outlets? There are three banks of 8 outlets. Is each bank connected to one meter?

Engineer reply:

The three meters are on the input circuits. That is, the X, Y, and Z lines/phases. The outlets are on phase-to-phase circuit branches. That is, XY, YZ, and XZ to get 208V. So a load on the topmost outlet will draw from both the X and Y lines. For example, if you have a single 10A load applied at the topmost outlet (phase XY) drawing at 208V, you will see 10A reading on the X meter and on the Y meter. Now, if you apply a second 10A load, this time to the branch identified by YZ, you will see 10A on the X meter, 17A on the Y meter, and 10A on the Z meter. This is a consequence of the source voltage of XY being 120 degrees off phase of the voltage of YZ. The benefit of seeing the load of the input circuits is that you readily know when you are approaching the ratings of your breakered circuits.

Ask the Engineer - Can I safely convert C13 to C19 outlets?

Question from Jerry Davis: I am installing blade systems with C20 inlets, but have existing PDU strips with only C13 outlets. Is it okay to use conversion cables to feed the chassis?

Engineer reply: In most cases for blade systems, you will be safe. The IEC 60320 C20 inlet is rated for continuous 16A (max 20A), and the C13 outlet is rated for continuous 12A (max 15A). This equates to 208V system power ratings of 3328W for a C19 outlet and 2496W for a C13 outlet. Blade systems often contain power supplies that are rated for maximum output on the order of 2500W, but consider that even a 90% efficient power supply will then draw 2778W at its input. This exceeds the continuous usage rating of the C13 outlet. So, we can see that it is required that the blade chassis itself have C20 inlets; however, it is rarely the case that a blade chassis is loaded to that level.

The end result is that actual draw of the blade system power supplies must be determined to answer your question sufficiently, though it is rare to find a combination of blades that will exceed the C13 outlet rating. Also, consider that when running redundantly, the outlets will only be loaded halfway and that it is allowable to run at the maximum rating of the connections for as much as three hours.

Ask the Engineer - When should I consider using 3-phase circuits?

Question from Rick Beales: We're planning a new build-out. We have always just used 208V/30A circuits, but our new cabinet plans require up to 7kW. What are the trade-offs between just adding a second pair of single-phase circuits to our standard plans and going to 3-phase circuits for new builds?

Engineer reply: As you point out, the main reason to provide 3-phase power is to increase the amount of power available. A single phase 208-volt power run requires three conductors, two "hot" lines and a ground; and can provide a continuous power of 5.0kW for a 30-amp circuit. A three-phase 208-volt power run requires four conductors, three "hot" lines and a ground; and can provide a continuous power of 8.6kW. So, by increasing the number of conductors by 33% (from 3 to 4), power delivered increases by 73%. Being that your 7kW requirement is still below the 8.6kW rating of the 3-phase circuit, you are most likely to find after a full cost analysis that the single (redundant) pair of 3-phase circuits will be much less expensive than two pairs of single-phase circuits.