BLOG: Power Perspectives

[#1]

Would you like to save 5% per year on your data center energy bill?

Energy efficient servers, virtualization, cloud computing - these are all burning platforms in the green data center discussion. I am not going to talk about these.

However, I do want to bring up a fundamental topic that could have a significant impact on your energy bill – power distribution. Re-thinking site design, as well as considering your many options for power distribution equipment (transformers, switchgear, panel boards and UPS) can yield real energy savings.

Green design philosophies and mission critical facility designs often have conflicting goals. Green designs look to operate equipment at peak efficiency ranges, often near 100% of the equipment rating. Mission critical designs focus on 24/7/365 availability.

To achieve high levels of availability, design engineers are using redundant components... N+1, N+2 and 2N are not uncommon. In a 2N design, power distribution equipment operates at loads of 50% (or less) of the equipment nameplate rating, which may decrease the equipment efficiency. Take a typical double conversion UPS. At rated load, the UPS will operate at 92%-95% efficiency, but at half load the efficiency of the UPS could be as low as 85%.

There are several benefits to a green power distribution design, including:

• Increased equipment utilization, operating at higher efficiencies
• New efficiencies gained through atypical technologies
• Reduced energy usage
• Decreased carbon footprint

There are also associated challenges – above and beyond traditional designs:

• Gaining acceptance to utilize (or even consider) newer, high efficiency technologies that are not normally applied in mission critical applications
• Designs become more complex to achieve the same level of reliability

If you decide the green path is the right direction for your facility, I’ll offer a few simple steps to help guide the process. By taking a little extra time on the front end, you’re more likely to end up with the best (and most cost-effective) solution.

Considerations when developing a new mission critical design:

1. Define and understand your loads. Make sure you know the average and peak power consumption – not just the nameplate rating.
2. Once the loads are defined, determine how critical each one is. Does the load truly require uninterruptible power, or can a momentary power outage be tolerated? What about outages of up to 30 seconds?
3. Develop initial designs, with special attention to the selection of each and every “cog in the wheel” to drive incremental improvements in efficiency. For example, you may consider using a high-efficiency flywheel UPS as part of your power system.
4. Once equipment has been selected, work with the equipment suppliers to determine if additional efficiency gains can be achieved.

What other challenges do you face? What else can be done to promote green designs? Please post your comments below.

Message Edited by doziece on 06-29-2009 04:51 PM

[#2]

Several years ago, long before "Green" was th focus, I worked on refurbishing a system that was powered by Caterpillar genertors.  It was totally off-grid, supplying all its own power 24/7/365.  The goal was primarily to improve reliability (reduce frequency of outages), not energy savings.  The first step, as you so astutely point out, was to "define and understand...(the)...loads".  This facility had been running for something like 40 years since originally designed, and I can guarantee you that none of the loads looked anything like the original design load.  After determining the actual requirements, we essentially redesigned the system by changing the generator voltage from 240 V to 480 V (originally, the 240 V was stepped up to 2400 for transmission over about 1/4 mile distance), and resizing the distribution cable and stepdown transformers.  We did not modify the generating facility at all, other than change the generator voltage.  When we were finished, Surprise!  Cost of generation had dropped by 30%!  That decline in cost was essentially fuel savings resulting from a more efficient distribution system...

[#3]

I ran across an interesting article in the Data Center Journal the other day.  The article contains some very good points to consider when designing a system, specifically in terms of the correct level of redundancy:

- A 2N system is easier to maintain, where a N+1 system may not allow for complete equipment isolation for maintenance

- A 2N system is fault tolerant, where an N+1 system typically has a single point where failure can take down the system.

- A 2N system may be less expensive (and complex) than an N+1 system, particularly if it is designed into the facility up front.

I agree with Partick - a 2N system has many benefits to the customer in terms of reliability and maintainability.  However, on the cost side, there are additional increases to the total owning and operating cost that you need to be aware of:

- More equipment = more maintenance.  While the maintenance process can be simplified with the ability to completely de-energize equipment, you now have twice the equipment to maintain. 

- As I mention above, operating equipment at less than 50% load will decrease the efficiency, and result in increased utility costs.

- Additional ancillary equipment may be required to support the added redundancy.  In the case of a UPS, you may need to increase the size of the HVAC system to properly cool the additional equipment. 

So what is the right level of redundancy?  It really comes down to is understanding the customer requirements.  How critical are the loads? Can down time be tolerated?  What is the cost of down time?  Once the answer to these questions are understood, a reliable system that meets the customer needs can be designed. 

For the full article: 

 http://datacenterjournal.com/index.php?option=com_content&task=view&id=3170&Itemid=43