Keeping It Cool

1. Keeping It Cool Dr. NatheerKhasawneh Rafat A. Dasan

2. This chapter will cover… • The features of a Data Center's environmental control and protection systems—cooling and fire suppression

3. Topics to be covered …

4. Cooling Requirements • The environmental controls within a building that regulate temperatures and air circulation are referred to, collectively, as HVAC—heating, ventilation, and air conditioning. • HVAC infrastructure has three jobs to do in a Data Center: • Keep temperatures low • Keep them constant • Diffuse hot spots created by clusters of equipment • Server environments are typically maintained somewhere between 65 and 75° Fahrenheit (18.3 and 23.9° Celsius) • There's a rule of thumb among electronics manufacturers that for every 18° Fahrenheit (10° Celsius) decrease in temperature doubles a device's reliability

5. Cooling Requirements – Cont. • Chilled Liquid Cooling System : • Air handlers: circulate air within the Data Center, drawing in warm air from the space between the floor and ceiling and discharging cold air into the room's plenum. Air is cooled within the handler by passing over coils containing chilled liquid and then expelled into the Data Center. • Chillers: do the work of keeping the air handler coils cold. They contain three components—an evaporator, compressor, and condenser. The evaporator transforms liquid refrigerant into gas and in the process chills the water that circulates to and from the air handlers. The compressor draws in this gas, changing it into high-pressure, high-temperature vapor that can be condensed easily. The condenser transforms this vapor back into liquid, discharging heat, and then returns the liquid refrigerant back to the evaporator. • Cooling towers: The processes that occur within the chiller generate a significant amount of heat. It is the job of the cooling tower to dispose of this heat and keep the chiller cool. Fans within the cooling tower draw air across a series of filters, which cools the water inside, similar to how the air handler functions.

6. Cooling Requirements – Cont.

7. Cooling Requirements – Cont. • House Air: if you are constructing a very small server environment—say, one with just a few cabinets—it might be possible to cool the room using the same air conditioning infrastructure that cools other spaces within the building. This is known as house air. • Makeup Air: Just as makeup water must be added as part of the chiller process to compensate for water that is lost to evaporation, so too must makeup air be supplied into the Data Center. Makeup air is necessary to prevent the server environment from becoming depressurized. Makeup air is drawn from the outside and should be filtered to prevent contaminants from entering the Data Center.

8. Cooling Requirements – Cont. • Cooling Quantities and Temperature Ranges • A ton of cooling— This term represents the amount of heat involved in melting one ton—2000 pounds—of ice in a 24-hour period. Data Center air handlers generally come in 20- and 30-ton capacities. • BTUs— Cooling units are generally rated in British Thermal Units. This term refers to the amount of heat needed to raise the temperature of 1 pound of water by 1° Fahrenheit (.56° Celsius). One ton of cooling equals 12,000 BTUs. • Watts per square foot—is watts per square foot or watts per square meter depending. This refers to how much energy is used in the Data Center. It is relevant to cooling because energy produces heat. So, when someone says they want 100 watts per square foot of cooling, they are asking for enough cooling to offset that amount of energy usage in that space. One watt equals 3.41 BTUs.

9. Cooling Requirements – Cont. • Redundancy in Your Cooling Infrastructure : • At a minimum, provide at least one more air handler in your server environment than is required to meet its cooling needs • Having a spare chiller and at least one spare air handler provides your Data Center with N+1 cooling coverage • Providing an additional cooling tower with each chiller. • Cooling Distribution and Air Pressure: • The level of air pressure in your Data Center is called its static pressure. This measurement, expressed in inches or centimeters of water column or water gauge, refers to the resistance of air as it is pushed in to the room. Data Centers are typically designed to have a static pressure between .2 and .5 in. wc. (.51 and 1.3 cm. wc.). • To maintain air pressure in the Data Center, properly seal all walls and doors and carefully manage any openings in the plenum—either the raised floor or space above the false ceiling, depending upon your room's design. Fully open perforated floor tiles at cabinet locations that are packed with equipment and close them near locations that aren't. Also cover tile cutouts to prevent air from escaping. • Humidity • Humidity is the amount of water vapor in the air • Adding or removing moisture from the air can be done by way of properly equipped air handlers or through the use of separate humidification units. • Aim for a relative humidity level in the Data Center of somewhere between 45 and 55 percent.

10. Layout, Cabinets, and Cooling • The server rows and different types of floor tiles—as well as what types of cabinets you deploy can have a significant effect upon how air circulates and where cooling is directed. • Space:evenly distribute equipment among your server rows, mixing low-profile servers with larger ones and hotter devices with cooler ones. This can help reduce the formation of hot spots. • Positioning Air Handlers: Keep the plenum space immediately in front of the air handlers free of obstructions, so that air circulation is not disrupted.

11. Layout, Cabinets, and Cooling – Cont. • Hot and Cold Aisles: Design DC with heat sources occurring in predictable locations. Cooling can then be more easily directed to deal with them. This is most often done by creating what are called hot and cold aisles. • To do this, arrange the Data Center as follows: • Face consecutive server rows in alternating directions. The front of each row faces the front of another, and the backs of each row face one another. • Place perforated floor tiles in front of each server cabinet location, opening their adjustable dampers so that air flows into this aisle. • Install ducting in the ceiling than begins with a vent above the aisle behind each server row and connects back to the air handler's intake.

12. Layout, Cabinets, and Cooling – Cont. • Cabinet Design: • The most obvious approach to dealing with servers that generate tremendous heat is fans built directly into the cabinets that house them. Cabinet fans can be used to draw cooler room air into a cabinet or to expel warmer cabinet air out, or both. Some cabinets even contain variable flow fans linked to their own temperature sensors—the amount of cooling applied to the servers within the cabinet varies as needed. • Another option is use of open cabinets, that is cabinets without any door, wall, top, or bottom panels. This is a potential plus, although the same lack of doors and panels also means that server exhaust can't be channeled as easily into hot and cold aisles. • Another approach is use of liquid-cooled cabinets. Though their specific operations can vary, these cabinets generally draw server exhaust from the back of the cabinet across a chilled coil or cooling module and then recycle the air back to the front of the servers to cool them.

13. Fire Suppression • Suppression Materials: • Inergen or IG-451— An inert gas composed of nitrogen (52 percent), argon (40 percent), and carbon dioxide (8 percent). Inergen removes oxygen from the air so that combustion can't occur. Inergen is a preferred suppressant in many European countries and is considered to have no environmental risk due to ozone depletion or global warming. • Argonite or IG-55— An inert gas composed of argon (50 percent) and nitrogen (50 percent). Argonite reduces the oxygen content of the air. It is considered to have no environmental risk due to ozone depletion or global warming. • FM-200 and HFC-227— Made by different manufacturers, but both consisting of heptafluoropropane. Used in server environments around the world, particularly in the United States, but prohibited in some European countries due to its potential contribution to global warming. FM-200 and HFC-227 are not considered toxic, but might break down under intense heat and produce hydroflouric acid, which is toxic. • FE13 or HFC-23— Made of trifluromethane and originally developed as a chemical refrigerant, it absorbs heat from a fire until combustion can no longer occur. As with FM-200/HFC-227, this has global warming potential and, though non-toxic itself, can produce toxic hydroflouric acid as a byproduct.

14. Fire Suppression – Cont. • Sprinklers: • Fire sprinklers are a system of pipes designed to discharge water in specific areas where intense heat, presumably from a fire, is detected. Each sprinkler head contains either a liquid-filled glass bulb or a solder link that bursts at a certain temperature, causing water to be released. • There are multiple types of fire sprinkler systems. A so-called wet system keeps pressurized water in the pipes at all times, while a dry system uses compressed air to keep water out of the pipes and behind control valves until a fire condition exists. • Install a dry or pre-action system into your server environment. This reduces the risk of water being accidentally spilled into the room. If a sprinkler pipe in the Data Center is somehow damaged, there is no liquid to spill out of a dry or pre-action system.

15. Fire Suppression – Cont. • Manual Controls: Although sprinklers are activated only by intense heat, gaseous fire suppression systems typically include manual controls as well. These controls consist of two push-buttons—one button resets the automatic countdown-to-activation that occurs as fire suppressant is prepared to discharge, and the other button bypasses the countdown and triggers an immediate discharge. The automatic countdown typically lasts 30 seconds. • Design Details: Whatever combination of fire suppression infrastructure you install in your Data Center, coordinate the design with the installer to make sure that the system not only provides coverage throughout the entire server environment but also strategically places fire suppression infrastructure components.

16. Fire Suppression – Cont. • Air Sampling and Smoke Detection • The most effective detection systems are those that continuously sample the air. In these devices, air is drawn from the target area—in this case the server environment—by pipes, to a central unit that scans the sample with a xenon lamp. • Be aware that these air sampling systems are much more sensitive that conventional smoke detectors—by a factor of 1000 according to some manufacturers. Due to this high sensitivity, adopt the following practices for your server environment to avoid false alarms: • Prohibit cardboard and other sources of dirt within the Data Center. Although air sampling systems include filters designed to screen out dirt particles, they are not infallible. • Prohibit smoking or the use of soldering equipment in the Data Center, or in close proximity to it. • Shut off the air sampling system whenever major construction is performed in the Data Center, or in close proximity. If a lab is being built in a space adjacent to the Data Center, for instance, it is possible for particles to be blown or tracked in to the room.

17. Fire Suppression – Cont. • Fire Alarms: Regional fire and building codes are likely to spell out the proper deployment of fire alarms at your building site, including within your Data Center. In addition to those requirements, make sure that fire-related audio alarms are loud enough to be heard in the Data Center. • In addition to room-wide fire suppression systems, install portable fire extinguishers throughout the Data Center. • There are five classes of fire extinguishers—each is intended to quench a different type of fire: • Class A is for basic fires involving wood or paper. • Class B is for fires involving inflammable liquids such as gasoline or oil. • Class C is for electrical fires. • Class D is for inflammable metals. • Class K is for cooking oil and grease fires. • Suppression materials used by these extinguishers include: • Water (Class A) • Chemical foam (Class A and B) • Carbon dioxide (Class B and C) • Dry foam (Class B and C) • Dry powder (Class D) • Wet chemical (Class K) • Dry chemical (multipurpose) • Class C fire extinguishers are most appropriate for use in a Data Center.

18. Common Problems • Perforated tiles are indiscriminately left open or closed: • Despite the importance of floor tiles to cooling a Data Center, little thought is usually given to these tiles after a contractor first installs the raised floor system. Their adjustable plates are simply left in the position in which they arrive at the site. This can defeat the design of the Data Center's cooling infrastructure. • Chilled water pipes are inadequately insulated

19. Summary • A chilled liquid system is most commonly used to provide Data Center cooling. Air handlers circulate air in the server environment. An external chiller keeps the coils cold by changing refrigerant to gas, and then returns the vapor back to liquid so that the process can be repeated. A cooling tower uses similar evaporation cooling to then keep the chiller cool, replacing any evaporated water by way of a municipal water supply. • Provide redundancy within your cooling system by installing at least one spare air handler to provide full cooling coverage during maintenance or a unit failure and a second chiller and cooling tower to avoid having a single point of failure. • Maintain air pressure in the Data Center so that the cooling infrastructure functions properly and efficiently. • Control the relative humidity within your Data Center to prevent corrosion from too much moisture in the air or static from too little. • Enclosed cabinets containing fans, open cabinets that enable server exhaust to escape, and liquid-cooled cabinets can all be used to improve spot cooling in the Data Center. • Install a comprehensive fire suppression system in your Data Center to protect against fire. • Equip the Data Center with an air sampling system to detect combustion as early as possible.