Green Notes

SearchDatacenter.com recently had a great article by Bob McFarlane with several handy tips on sizing computer room air conditioners and save on energy. Here are some excerpts:

Sizing a data center air conditioner is not like choosing a refrigerator. Bigger is not necessarily better! Correct sizing is even more critical to effective operation and energy efficiency than right-sizing the uninterruptible power supply (UPS). But with so many factors that determine capacity, it can be a bit tricky.

 

When someone plays with the thermostat at home (not you of course!), the temperature is never right. It gets too hot, then too cold. It’s worse with computer room air conditioners (CRACs). The unit that’s the wrong size can mess up cooling. Wrong settings or improper location will make it even worse.

 

Under-sizing can’t cool effectively — that’s obvious. But over-sizing won’t either. Thankfully, many CRACs will adjust to a range of loads, but there are many that won’t. They all need to be sized realistically, but over-sizing will always result in cooling going on and off too often. It’s called “short cycling,” which is hard on the machine and does a lousy job of maintaining room temperature and humidity. Yes, temperature swings do hurt computing hardware!

Air conditioners have to deal with two kinds of heat. Sensible heat — the kind we can feel — is what our computers give off. Latent heat is what evaporates moisture. Simplistically, dealing with moisture or humidity requires more latent capacity from our air conditioners, which steals from sensible capacity. There’s not much reason to keep a data center above 45% relative humidity (RH), but if you over-cool you’ll pull moisture out of the air (latent cooling) and have to use more energy to re-humidify. The problem is that relative humidity is “relative” to temperature. Warmer air has a lower relative humidity for the same moisture content because it can hold more vapor than cool air. Temperatures in a data center vary widely, so RH depends on where it’s measured, which is why we’re trying to get away from using it. However, RH is still the most common way to determine humidity.

Thankfully, today we can use variable frequency drives (VFDs) to automatically adjust fan speeds for appropriate air flow, controlled by sensors in the room. These can be retro-fit to most existing CRACs, and can save a lot of energy. (A professional computational fluid dynamics, or CFD, analysis is a good idea before buying any expensive air conditioner.)

So Step 1 is to know your real loads. Step 2 is to see if you can get higher temperature return air back to the CRACs. Step 3 is to decide cold air temperature. The American Society of Heating, Refrigeration & Air Conditioning Engineers (ASHRAE) Technical Committee 9.9 has recently increased the temperature envelope, so there’s no need to over-cool the equipment. Step 3 is to set your humidity standard. ASHRAE TC 9.9 now recommends dew point monitoring and control, but existing CRACs may not be able to do that, so you’ll still need to control relative humidity. Then, if possible, pick an air conditioner that can adjust to load and choose a sensible capacity that will operate Day 1 in its midrange. That will give the best stability and control.

Let’s look at three other important issues before we finish: reheat, humidification, and water temperature. If you have more than three or four CRACs, it should not be necessary to put humidifiers on every unit. Moisture diffuses and stabilizes in the room pretty quickly (another reason for dew point sensing). Putting humidifiers on every air conditioner can be counterproductive if one unit humidifies while another de-humidifies. That’s wasted energy for no better result.

Reheat was the norm for years, and it’s the biggest energy waster of all. The CRAC over-cools the air and a heater warms it back up to discharge temperature. In many situations it’s possible to design without reheat, or to use minimal reheat. But it takes a knowledgeable engineer to make that determination and to provide a proper design.

If you’re using chilled-water computer room air handlers, you’ll need to have a knowledgeable engineer involved. Published capacity ratings are based on specific entering water temperature and water temperature rise. Chiller plants today may be designed on higher numbers to improve energy efficiency, but that reduces the effective cooling capacity of the CRAHs.

For the full version of the original article, visit  http://searchdatacenter.techtarget.com/tip/0,289483,sid80_gci1371079,00.html?track=sy185# . Free Registration might be required on the site to view content . To know more about Green Rack Systems and the suite of services we offer in addition to sustainable cooling practices for Data centers, contact us at sales@GreenRackSystems.com .

Financial giant Citi is priding itself on the company’s modern data center infrastructure that is flexible enough to take on a variety of requests from clients.Five years ago, Citi ‘s data center faced a number of challenges lack of capacity, limited flexibility limited and high risk of proximity.

Due to lack of cohesive, global data center strategy Citi  decided to reduce the number of data centers worldwide from 52 to 14 strategic sites, including five constructed from the ground up. As a first step, it implemented a global standard for data center construction and engineering. One of Citi’s latest constructions in Georgetown, received Leadership in Energy and Environmental Design (LEED) Gold certification from the U.S. Green Building Council (USGBC). It was a team effort with the data center team providing the engineering perspective and the corporate real-estate representatives lending the construction expertise to the projects.

The 100,000-square-foot Georgetown data center delivers 75 watts per square foot of power, expandable to 100W/square foot. Citi has divided the data center into four equally sized rooms. This setup reduces the amount of cabling needed and allows Citi to group technologies by room based on cooling requirements. Compared with the previous newly constructed data center, the Georgetown site uses 800 kilowatts less power for the same footprint, for a 30% reduction in energy costs, the company reports. Virtualization increased server density and led to 30% to 35% reduction in the number of physical servers. Citi was also able to put a cap on Power consumption for technology . According to Computer World , in the 2002 to 2007 timeframe, Citi’s data center power consumption grew by 10% to 12% per year but now thanks to virtualization, Citi has been flat on consumption year over year. Other major Citi projects that have received LEED certification include data centers in Singapore, Frankfurt, Texas, two Citi office parks in the Dallas-Fort Worth area and a 15-story skyscraper in the New York City Borough of Queens.

Projects looking for LEED certification have to meet certain prerequisites and specific performance standards to gain credits. According to the credits won, you will be certified, Silver, Gold or Platinum. The standards prescribe options for site development, water savings, energy efficiency, materials selection and indoor environmental quality. LEED-certified buildings must also adhere to benchmarks set by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) promoting reduction in energy consumption. Data centers certified by the LEED Green Building Rating System need not necessarily be owned by huge corporations with attached office space. Innovative design, responsible building practices and expert energy management consultation provided by a green consultation firm like Green Rack Systems can help you achieve your green goals.

In December 2008, a survey of Emerson Network Power and Liebert data center users found that respondents planned to double the power densities in their data centers.The Data Center Users Group (The DCUG is a group of approximately 2,000 influential data centers, IT and facility managers founded by Emerson Network Power in 2003. ) surveyed about 150 data center managers focusing on data center efficiency. Energy efficiency was one of the top three concerns for nearly half (47%) of survey respondents, showing a remarkable increase compared to previous years.

Some of the other findings were:
• 61% were cutting their budget due to economic conditions, and 35% were delaying capital projects. Even so more than 75 percent of survey respondents are still planning for changes to take place within their facilities.
• 46% said adequate monitoring was a top three concern.
• The average kW per rack has increased from 6 to 7.4 over the past three years, a more than 20% jump.
• Data center managers have improved efficiency through airflow improvements such as blanking panels and hot-aisle cold-aisle containment and by using variable cooling that responds to need rather than going full blast all the time.
• The top concern of data center managers was heat density.
• Data center managers were unwilling to compromise availability for efficiency. Data center managers will be taking into account corporate initiatives to improve energy usage throughout the data center; yet, this initiative is challenged by the understanding that availability remains the top priority.
• When budgets permit, more than half (52 percent) of respondents indicated future facilities would be designed to support densities of between 10 kW and 20 kW per rack – significantly higher than the 7.4 kW average supported by current facilities. Some of the reasons they cited for moving to higher density data centers was to save facility space, support blade servers and reduce energy costs.
• Energy usage strategy was still missing. Even though one in four respondents had completed an analysis of the efficiency of their data center equipment thereby exhibiting high awareness, only 28 percent of survey respondents had a documented strategy to reduce energy usage.
• Amid the deployment of new technologies and subsequent maintenance of the data center infrastructure, almost half of the respondents indicated that the complexity of their cooling, monitoring and power systems is increasing.
• More than half (55 percent) of the survey respondents turned to power and cooling assessments to help with complexities in the data center. Through these assessments, 74 percent evaluated cooling reliability, 54 percent energy consumption and 51 percent expansion plans.

The results of the survey are extremely encouraging in terms of the awareness and knowledge exhibited by IT managers to adopt energy efficient strategies, identify problem areas and show promising initiative to increase efficiency. But the results also clearly indicate that majority of the facilities are found lacking in terms of having a methodical, clear cut plan to implement changes. The problem might of course be budget cuts. It might also be lack of enough personnel to manage and monitor the renovations. As the results show, data centers might need a little extra help to grasp the mounting complexities due to increasingly sophisticated computing to attack cooling and power problems. That is precisely why a professional consultation and a little outside help will come in handy to help assess, plan and execute precise measures to maximize energy efficiency. Contact us at Green Rack Systems for improving data center control, analysis and overall efficient management, especially in the area of energy management, and expert guidance tailored to your Data center’s functionality, goal and budget.