High Tech Getting Too Hot? High Density Environments Require A Different Cooling Approach

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1 High Tech Getting Too Hot? High Density Environments Require A Different Cooling Approach Proper airfl ow and thermal management are the most critical aspects of designing and operating your data center, ensuring uptime of applications, consistent IT equipment performance and effi cient operations. In the past, data center managers would over supply a room with cold air to address small hot spots and perceived requirements for cooling the data center. Typical rack densities averaged 3 5 kw, thus the cooling requirements were moderate. Very few data center managers were pushing the envelope on operational effi ciencies. They were smoothing over the imperfections. Increased Density New technological advancements such as virtualization and cloud computing are increasing power rack density requirements, which are now reaching kw. High density applications are reaching 25 30kW, effectively driving the utilization of any server from 10% to 70 80% and even 90%. As a result, the requirements for power density and airfl ow are doubling or even tripling. It can often be the same server, but there is increased utilization. In the short term data centers have extra compute capacity, but now the servers deployed need higher power and more airfl ow. Increasing densities make it less appealing to simply solve the problem by overcooling. The major problem with over cooling is the cost associated with it. Providing more cool air to the room requires the fans on air handlers to run faster, requiring more power ASHRAE Thermal Guidelines for Data Processing Environments, 2ed., Fig 1.1 Power A general rule of thumb is that you can lower cooling power consumption by 1 to 2% for every degree you raise your air temperature. For example, If you raise your data center supply temperature from F, you can save approximately 20% in HVAC operating costs. By avoiding overcooling, you decrease power consumption and lower your operating costs. Another key principle is to tune the airfl ow by adjusting the HVAC fan speeds which result in energy effi ciency savings. For example, lowering airfl ow by 20% results in a 50% energy savings on the fan motors. This is because the power to run a fan is proportional to the cube of its speed. Advisory Services

2 A few years ago, 50 watts-per-square foot was the typical data center power requirement. Now, 150 watts-persquare foot is the minimum, and a number of facilities are being designed for 250 and 300 watts. This doubling of power density over time causes an exponential increase in heat generated in the data center. Instead of continuing with the overcooling approach, the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) 2011 Thermal Guidelines recommends optimizing the data center to operate at a higher temperatures. As a rule of thumb HVAC systems are generally more effi cient when the difference between the cold air supplied and the warmer air returned is maximized. The key in optimizing either an aging data center or a new data center is to optimize the thermal environment for maximum energy savings by applying the ASHRAE 2011 Thermal Guidelines. This is often done through simulation of the thermal environment before changes are implemented to determine the most optimized scenario that can achieve maximum energy savings. Basics of Thermal Efficiency The real issue for cooling servers and switches is delivering the right air temperature to the inlet for every piece of equipment and effectively removing the hot air. The fi rst step is to implement industry standards and best practices at the room level and cabinet level. Room Level: 1. Implement Hot Aisle-Cold Aisle configuration. Make sure all the inlets are lined up on one side and the exhaust sides of the cabinet are on the opposite side of the row. 2. Ensure perforated tiles are only in the cold aisle. Many times people working in the hot aisle will install a perforated tile to be cool, but not replace the tile when they are done working in the area. Any tiles not placed in front of the equipment they are cooling lowers the amount of cold air to other perforated tiles and this wasted air can unbalance the data center and result in lower overall energy effi ciency. 3. Perforated tiles must be tuned to the equipment. Putting perforated tiles down the entire cold aisle is a blanket strategy and may result in either oversupplying air to low density cabinets or undersupplying air to high density cabinets. Tuning the perforated tile airfl ow to match the equipment in the cabinet maintains uniform airfl ow and results in maximum energy effi ciency. 2

3 4. Align CRAC/CRAH units with the hot aisle. The optimum confi guration is to align the CRAC/CRAH with the hot aisle to evenly pressurize the raised fl oor. When a CRAC/CRAH is aligned with the cold aisle, the air rushes past the fi rst few perforated tiles, resulting in insuffi cient airfl ow that can cause hot spots. 5. Ensure the raised floor is the proper height for airflow. A low raised fl oor height provides signifi cantly less air volume and the result of putting higher percentage perforated tiles will likely unbalance the airfl ow to other tiles since the air volume based on the raised fl oor height is limited. A higher raised fl oor provides more air volume to work with to balance the room and supply adequate airfl ow to higher density cabinets. 6. Make sure you have good cable management practices. Congested cables in front of IT inlets or at the IT exhausts results in starved airfl ow or elevated temperatures. This can result in an increase in IT equipment fan speeds to cool equipment and this increase in fan speeds will lower energy effi ciency. Cabinet Level 1. Use blanking panels. The possibility exists within the cabinet for hot exhaust air to be recycled into the equipment air intake. This recycling of hot exhaust air into the equipment air intake is mainly caused when hot exhaust air returns above or below the equipment and back into the inlets of the equipment. This situation is a cause of equipment overheating in data centers. The installation of blanking panels will help minimize this recirculation by closing off open rack units, thereby eliminating recirculation and preventing bypass airfl ow from going through the equipment. 2. Seal raised floor cable cutouts with air sealing grommets. Appropriate raised floor height and under floor cable management best practices are needed for sufficient airflow. Hot Air Recirculation Several open raised fl oor cable cutouts can leak as much air as an entire perforated tile. An unwelcome side effect of unsealed cable cutouts is hot air recirculation over the top of the cabinet causing hot spots at the front of the IT equipment. Another effect is lost air, known as bypass airfl ow, that contributes to lower energy effi ciency since the air is not being used to cool the IT equipment. Air sealing grommets create an effective, airtight seal to eliminate cool air bypass and hot air recirculation. 3

4 Lower Hot Air Ceiling Cold Aisle Hot Aisle Cold Bypass Air (Waste) CFM s Lost Through Unsealed Cutouts 90,000 80,000 70,000 60,000 50,000 40,000 30,000 20,000 10,000 Annual Utility Cost CFM s Lost $30,000 $25,000 $20,000 $15,000 $10,000 $5,000 Annual Utility Cost of Wasted CFM s Raised Floor Space Unsealed Cutout Space Number of Cutouts The Cost of Unsealed Cable Cutouts (assumes 4.5in. x 6.5in. cutout spaces) Side-to-Side Airfl ow Equipment IT equipment, such as switches, with side-to-side airfl ow causes hot spots within the cabinet even though cool air is being supplied from the cold aisle. This leads to a false sense of security that the IT equipment is being cooled when in fact the IT equipment is breathing in its own hot exhaust air. This leads to high inlet temperatures that are often above the ASHRAE Thermal Guidelines and can lead to heating up equipment in the same cabinet as well as adjacent cabinets. Instead of drawing in cold aisle temperature air, the switch inlet is now drawing in air that has been pre-heated by 30 or even 40 degrees F, depending on how hard the switch is loaded. To combat this, you need to provide segregation between the inlet and exhaust airfl ow by using an inlet duct system. The inlet duct takes the air from the cold aisle and clearly directs the air to the inlet of the switch. You should also install blanking panels and other equipment to seal off the front of the cabinet from the rear so that the exhaust can only go out from the back of the cabinet. The duct combined with blanking panels fully segregates the air that is coming into the switch inlet from the hotter air that is being exhausted. By doing this, the switch runs at a lower temperature, allowing the fan to run at a lower speed using less energy. This improves your energy effi ciency, and it helps increase the reliability of the switch because electronics have a longer life when operated at lower temperatures. 4 In-Cabinet Recirculation Front of Cabinet Inlet Duct

5 Cable Management With switches, if you do not follow proper cable management practices you can block airfl ow. In the case of large switches using a copper application, there can be 100 square inches of blockage, completely preventing the cold air from reaching your switch inlet. If the cables have been run to the right, the airfl ow path from the cold aisle to the switch inlet can be completely sealed off resulting in inadequate airfl ow. High-Power Density Solutions For high power densities, where greater isolation of hot/cold air and reduction in recirculation is needed, there are a few approaches: Active Cooling with a row or rack-based architecture Passive Cooling Much has been written on active cooling solutions, but there are benefi ts of passive cooling solutions as well. Two passive containment solutions exist to further isolate hot and cold air and achieve energy cost savings: Hot Air Containment and Cold Air Containment. To isolate hot air, a vertical exhaust system can be employed To isolate cold air, a cold aisle containment system can be deployed Without containment, 33% of the air from the cold aisle escapes and doesn t reach the inlets of the IT equipment. In addition an unwelcome side effect of a non contained aisle is that hot air can be draw around the end of the rows and over the top of cabinets resulting in hot spots in the cold aisle. Supplying more cold air will not solve this problem. Cold aisle containment can reduce the airfl ow to the cold aisle by 20 to 30%, which will lead to greater energy effi ciency. 5

6 Vertical Exhaust System Recirculation of exhaust air can be prevented by using hot air containment such as a Vertical Exhaust Duct (VED), which uses solid rear doors to trap exhaust air and a chimney in the top of the cabinet to exhaust air to the ceiling return plenum. The energy effi ciency benefi t is that warmer air reaching the return translates into higher energy effi ciency of the cooling equipment. In addition the containment of the hot air prevents recirculation, unwanted hot spots in the data center and enables higher cabinet equipment densities. Cold Aisle Containment Cold aisle containment not only separates the hot air from the cold air, but it also can reduce the airfl ow requirements to the cold aisle by 20 to 30%. This reduction of air can lead to extending the life of your existing data center and result in cost savings by reducing the fan speeds of your cooling equipment. Enclosing the cold aisle with cold aisle containment, also eliminates air mixing and enables uniform cold air to be delivered to the IT equipment inlets, resulting in a more energy effi cient system. What Passive Solution Is Appropriate for Your Data Center? Both systems achieve the same result: they separate the hot and cold air. It is the separation that allows you to take advantage of HVAC savings. In doing so, you can now supply less air to your data center, lowering fan energy usage. Since there is no bypass of the cold air getting to the HVAC system, the air that is getting to the HVAC system is hotter. Most air conditioners actually run more effi ciently with higher return air temperatures. Of the two passive cooling systems, which one is the best for your data center? Based on Panduit research studies and client deployments, we have found that both hot aisle containment and cold aisle containment provide similar operating expense savings. The appropriate choice is based on your data center and a variety of factors (see chart on page 8). 6

7 Room Height The VED chimney system performs much better and is easier to install in a tall data center where there is ample space from fl oor to ceiling. The space must fi t the chimney and the chimney must be able to deliver the air to the return plenum and have a path for the air to return to the inlet. If you have a data center that follows the typical hot aisle-cold aisle confi guration and you require a more random confi guration, the separation that the chimney provides can allow that confi guration to occur. The chimney eliminates a hot aisle; the entire room becomes a common pool of cold air. For shorter rooms, where there is limited fl oor-to-ceiling height, cold aisle containment can be used. Cold Aisle Containment also works well if you have applications that use very large volumes of air. In general, cold aisle containment is a large system, so there is more space to pump the air into containment and no restrictions on the exhaust side. Space is plentiful for the hot air coming out of the active equipment to get back to the HVAC system. These are just a couple of examples of the variables (see chart on page 8) that will determine what system will work best in your data center. Engage an expert who will look at all the variables and understand what system will work the best for your data center long term. Common Sense There are many common sense best practices to deploy in the data center to improve thermal performance and airfl ow management. These include: The use of blanking panels in the racks Proper perforated tile placement Sealing cable entry and exit points Separating the hot air from the cold air supply, which will help ensure the IT equipment is taking in the proper cold air, maximizing its performance and improving thermal effi ciency If you are still experiencing thermal issues after following these best practices, Panduit Advisory Services specializes in solutions for thermal issues in the data center and is qualifi ed in HVAC, thermal management and data center cooling, and energy consumption. Contact us at AdvisoryServices@panduit.com. 7

8 Selection Criteria for the Thermal System that Bests Fits Your Data Center Criteria Standard Hot-Cold Aisle Confi guration Hot Aisle Containment (Vertical Exhaust Ducts) Cold Aisle Containment Return Airfl ow Path Does not require any special provisioning for the return of hot exhaust air. It requires either a high ceiling with tall chimneys or a drop ceiling for return airfl ow path. Similar to HA/CA, it does not require any special provisioning for the return of hot exhaust air. Water Cooled vs. Refrigeration based Cooling System Compatible with refrigeration and chilled water-based systems because of the low return air temperatures. Refrigeration based systems may not be compatible with very high return air temperatures that could be produced. Refrigeration based systems may not be compatible with very high return air temperatures that could be produced. Economizers Compatible Increased hours of economizer utilization due to high return air temperatures. Increased hours of economizer utilization due to high return air temperatures. Cooling System Failure Tolerance Hot aisle air will be quickly drawn to the cold aisle. The average room temperature factors into the time for critical alarms in IT equipment. Provides large mass of cold air in case of cooling system airfl ow failure. Provides relatively small thermal mass in case of cooling system airfl ow failure. Room Height Requires suffi cient height for raised fl oor or overhead supply ducting. Needs high ceiling for chimney and allowance for return plenum or hot air stratifi cation. Requires suffi cient height for raised fl oor or overhead supply ducting. Comfort The hot aisle is relatively warm due to mixing of cold and hot air. The entire room is within a few degrees of the supply air temperature (assuming VED is on all cabinets). All areas outside the cold aisle are typically at a very high temperature, which may not be an acceptable working condition. Retrofi tting/ Brownfi eld Fire Suppression Lighting Minimal challenges, but limited thermal density. Depending on local codes, fewer sprinkler heads may be needed than for VEDs or cold aisle containment (CAC). Regular room lighting system is suffi cient. May be challenging to fi t VED into existing overhead pathways (power, structured cable, etc.). Addition of drop ceiling may be required. Depending on local codes, sprinkler heads may be needed in both the hot and cold aisles. Chimneys will prevent light from traveling between aisles. Lighting fi xtures are likely needed in both the hot and cold aisles. Can be built on existing raised fl oors with minimal changes. Depending on local codes, both fi re detection devices and sprinkler heads might need to penetrate each containment system. Containment solutions may block light provided by overhead fi xtures. Transparent roof sections or internal light fi xtures may be required. Lighting fi xtures are likely needed over each aisle. Panduit Corp. Worldwide Headquarters Tinley Park, IL AdvisoryServices@panduit.com US and Canada: Europe, Middle East and Africa: Latin America: Asia Pacific: CPAT03--WW-ENG