Computer Room Air Conditioning (CRAC) Monitoring Strategy

Computer Room Air Conditioning (and computer room air conditioners - CRAC's) help keep your data center cool. However, as equipment in your computer room becomes more complex and compact, computer rooms are watching their power draw and heat generation quickly rise. The increase in computer room power consumption, density, and heat generation requires a more exact approach to computer room air conditioning than ever before.

Cooling the computer room used to be a relatively painless affair. When data centers were expending less power and generating less heat per square foot, a technician or administrator could simply offset the heat from equipment with additional CRAC units within the computer room, without much regard for an over-all cooling plan. Simply pumping cold air in the room was enough to bring down the temperature.

Now, however, that proves to be a feeble way to cool your computer room. Hot air is generated by computer room equipment quickly. Simply turning the thermostat down doesn't offer the cooling you need to safeguard your equipment. Cool air must circulate to ensure that heat is displaced.

Keeping the Modern Computer Room Cool

To achieve the air circulation necessary to keep the computer room cool, many technicians are placing racks in hot and cold configurations. They place their computers and racks on raised floors, two tiles apart, with their air intakes facing each other. CRAC units pump cool air through perforated floor tiles between the racks, the computers and racks intake the cool air and exhaust hot air into the opposing, hot aisle. Computer room air conditioning units on the floor then pull in the hot air exhausted into the hot aisles, and release it underneath the floor tiles, completing the cycle. In this way, a series of CRAC units can keep cool air running through the system and help keep a steady airflow through the environment.

It's even become common to take advantage of the space above computers and racks, and make another "hot aisle" of the room's ceiling, where heat normally escapes and hovers. To keep the whole computer room cool, technicians advocate turning the area above racks into a hot air plenum by placing ducts and more CRAC units. Hot air escapes into the plenum to be pushed back into the system, below the floor, where it can be cooled and released back into the system. This works for your computer room by both removing hot air from the data center and, bringing in more hot return-air helps the heat exchangers in the CRAC units produce colder air to pump out to the computer room floor.

Hot cold aisle strategy
A diagram of the hot-cold aisle strategy for computer room air conditioning

Monitoring Devices for Your Modern Computer Room

Of course, monitoring your computer room's air conditioning systems means much more than simply monitoring the CRAC units themselves, because even if they're working, there's no guarantee that the cool air they pump into the environment is making it to your equipment. And since there's no guarantee of homogenized equipment across the computer room, it's likely that you'll have hot and cold spots.

To ensure that your CRAC units are working properly and keeping the computer room cool, you'll have to check airflow both below the floor and above, temperature throughout the room to check for hot and cold spots. Fortunately, there are a number of small devices that can fit in line with your computers and monitor your computer room's environment.


DPS Telecom's TempDefender is specially designed to monitor conditions in your computer room. The small, rack mountable RTU connects to up to 16 analog sensors, to measure the temperature, humidity, air flow, smoke, or any other conditions you may be worried about in your server room. Sensors for the TempDefender are daisy-chainable via RJ-11 connectors, and can be assembled in any configuration, so you can run a set of sensors through your server room without running 16 cables across your computer room, all the way back to your temp defender. You can run sensors from a temp defender to monitor air flow in your hot aisles, temperature in your hot and cold spots, and humidity at the return air space, all from one RTU.

TempDefender in server room
TempDefender monitors your computer room air conditioning systems to ensure the safety of your equipment and optimal operating conditions. Preventing hardware failures and shutdowns due to poor data center conditions keeps costs down

The TempDefender also has 8 dry contact alarms and 3 control relays so you can augment monitoring and control for devices inside your cabinet. Or, mount your temp defender near HVAC equipment and monitor both environment and HVAC equipment for failures.

While the computer room is a delicate environment, you don't want to have to play babysitter to a bunch of computers. When TempDefender measures a threshold alarm for any of the environmental factors it's monitoring, it can send a trap to your master station or email you directly. It also has an easy-to-use web interface, so you can see what's going on in your data center in real time.

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NetGuardian 216: Making Sure CRAC Units Perform at the Equipment Level

Of course, you don't have to monitor your whole data center with one device, or even run sensors throughout the data center. Hot, cold, and humid spots will appear throughout the room naturally both because varying equipment will emit varying amounts of hot air, and because air is simply a hard element to control. You could simply install monitoring devices individually with your cabinets, so you can monitor your each individual cabinet, thereby giving you a good over-all view of the computer room environment. DPS Telecom recommends the NetGuardian 216 device for this sort of application, because it has the both the dry contacts you need to monitor the data center equipment in your cabinets, and four analog inputs you can use to measure the environment inside or just outside your cabinet.

Computer room cooling requires a good plan and a large amount of environmental data, but getting the data you need to maximize cooling in your computer room doesn't have to be hard. The TempDefender and the NetGuardian series remotes are perfectly equipped to handle analog and discrete coverage within the computer room, giving you the information you need to keep your computer room cool.

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