The most important function of a data center’s cooling system is to maintain the proper environmental conditions suitable for IT equipment operation.
To achieve this, it is required to remove heat produced by IT equipment and transfer that heat to a heat sink. In most data centers, the cooling system has to operate continuously and reliably. Different data center tiers require different levels of cooling and redundancy to the cooling capacity.
Operating a data center is energy intensive, and often the cooling system uses as much (or more) energy as the computers it supports. However with a well-designed and operated cooling system, it is possible that the cooling system will use a fraction of the energy used by the IT equipment. The ratio of power to cooling in the data center is known as the PUE (Power Usage Effectiveness).
In this article we will examine some of the most commonly used data center cooling technologies, and a few new approaches.
Calibrated Vectored Cooling (CVC)
This cooling technology is designed specifically for high-density servers such as modular systems and containerized data centers.
The airflow’s path is optimized through the IT equipment. This increases the density of the circuit boards per server chassis and utilizes fewer fans. This results in improved efficiency of cooling and lower costs.
Chilled Water System
This technology is most commonly used in mid-to-large-sized data centers.
The air in the data center is brought in by air handlers, known in the data centers as Computer Room Air Handlers (CRAH), and chilled water (supplied by a chiller plant in the facility) is used to cool the air temperature. The diagram below shows a typical chilled water system for a data center.
This is a newer cooling technology, and can be very energy efficient in certain climates with low outside temperatures. Facebook have built one of their large data centers in the Arctic Circle to take advantage of this.
This system uses the outside atmosphere to introduce cooler air into the data center. The cold air is brought in through filters, rather than continually cooling the same (recirculated) air as with traditional HVAC systems.
Cold Aisle/Hot Aisle Design
This is a data center rack layout, which is using alternating rows of “cold aisles” and “hot aisles.”
In front of the racks there are cold air outlets for the servers to draw in air, then the hot aisles will take out the heat from the back of the servers. The air conditioning unit’s intake vents will take the hot air from the “hot aisles” to be chilled, then the cooled air vented into the “cold aisles”.
The empty server racks are filled by blanking panels, to prevent overheating and reduce the amount of wasted cold air.
Computer Room Air Conditioner (CRAC)
This is one of the oldest technologies used for cooling, thus not energy efficient but the CRAC equipment is usually inexpensive.
The CRAC units are very similar to conventional air conditioners: they are powered by a compressor that draws the air across a refrigerant-filled cooling unit. CRACs are used in conjunction with a raised floor. The raised floor’s benefit is to deliver the cold air directly where it will be needed.
The cold air from a CRAC pressurizes the space below the raised floor. The perforated tiles provide an outlet for the cold air to leave the plenum and enter the main space in front of server intakes. After passing through the server rack, the heated air is then returned to the CRAC to be cooled. However, usually this will result in also mixing with some cold air, reducing the efficiency. Often the CRAC unit’s return air temperature is the set thermostat point used to control the cooling system’s operation, and this can lead to high temperature differences between the bottom- and top of the server racks. Most commonly the CRAC unit’s fans are running at a constant speed, and the CRAC has a humidifier within the unit that will produce steam.
Because of the cooling efficiency issues, CRACs should be used only with low-density IT equipment.
Computer Room Air Handler (CRAH)
In data center applications, this cooling technology’s method is similar to the CRAC, but the CRAH are more efficient when used in locations with colder climates because they function by chilling the outside air.
The CRAH unit functions as part of a larger cooling system involving a chilled water plant (or chiller) located in the facility. The chilled water flows through a cooling coil inside the CRAH unit, which then uses modulating fans to draw air through filters from outside the facility.
This technology is traditionally used in conjunction with the older CRAC and CRAH cooling systems.
The data center floor is lifted on a frame above the building’s concrete slab floor. This raised space between the two is used for running water-cooling pipes or providing the pressurized airflow for cooling.
In older data centers power and networking cables may also be run in this space. The latest trend in new built facilities is to route these cables overhead in cable trays.
Critical Cooling Load
This is a measurement terminology; it represents the total usable cooling capacity on the data center floor, commonly expressed in Watts of power, for the purposes of cooling servers.
Direct-to-Chip Cooling (Liquid Cooling)
This cooling technology uses liquid fed through small pipes, to deliver the coolant flow directly to a cold plate sitting on top of a server’s chips (mainly CPUs). The extracted heat is then fed into a chilled-water loop and carried away to a facility’s chiller plant for cooling.
Because this system is cooling the chips and processors directly, it’s one of the most effective forms of computer cooling.
This is also a new innovative liquid cooling solution, where the computer hardware is submerged into a non-conductive, non-flammable dielectric fluid.
Because the fluid will conduct heat much more efficiently than air, this cooling system is highly energy efficient and offers great cooling performance.
This technology manages the cooling performance by exposing hot air to water, which will make the water to evaporate and this draws the heat out of the air. The water can be introduced either by using a misting system or some wet material such as a filter or mat.
This system requires a great deal of water for cooling, but it is also highly energy efficient as it doesn’t use CRAC or CRAH units.
With this technology, external cooling towers are often used to facilitate the evaporation and transfer the excess heat to the outside atmosphere from the data center.
Data Center Monitoring Systems
To help monitor your data center’s cooling, AKCP has multiple sensors available.
In addition to the Airflow Sensor which can detect the presence or absence of the air flow, you can use our Cabinet Analysis Sensors to help you get a visual representation of each rack in your data center, the temperatures, differential pressures and the flow of air.
Airflow and Thermal Mapping for IT Cabinets
The Cabinet Analysis Sensor (CAS) features a cabinet thermal map for detecting hot spots and a differential pressure sensor for analysis of the air flow. You can monitor up to 16 cabinets from a single IP address with the sensorProbeX+ base units. A Wireless Cabinet Analysis Sensor is also available using our Wireless Tunnel™ Technology (see details below).
Differential Temperature (△T) and Thermal Maps
The cabinet thermal maps consist of 2 strings of 3x Temperature and 1x Humidity sensor. With these sensors you can monitor the temperature at the front and rear of the cabinet, top, middle and bottom. The △T value, front to rear temperature differential is calculated and displayed with animated arrows in AKCPro Server cabinet rack map views.
Differential Pressure (△D)
There should always be a positive pressure at the front of the cabinet, to ensure that air from hot and cold aisles are not mixing. As the air travels from areas of high pressure to low pressure, it is imperative for efficient cooling to check that there is higher pressure at the front of the cabinet and lower pressure at the rear.
Rack Maps and Containment Views
With an L-DCIM or PC with AKCPro Server installed, dedicated rack maps displaying Cabinet Analysis Sensor data can be configured to give you a visual representation of each rack in your data center. If you are running a hot/cold aisle containment, then containment views can also be configured to give a sectional view of your racks and containment aisles.
Wireless Cabinet Analysis Sensor – All In One Wireless Cabinet Sensor
The Wireless Cabinet Analysis Sensor (W-CAS) has the same features as the wired Cabinet Analysis Sensor (CAS): cabinet thermal map for detecting hot spots, differential pressure sensor for analysis of airflow and 2x dry contact inputs for door security sensors. Powered by USB, or 4x AA rechargeable batteries and using AKCP Wireless Wall Penetrating Technology, the data is collected and sent to one of our wireless sensor gateways.
I/O dry contact inputs can be used to monitor the front and rear doors of the cabinet, or alternatively alarm outputs from UPS or other rack mounted equipment.
In this article we have examined the most commonly used data center cooling technologies, and a few new approaches such as free cooling and immersion systems.
It is necessary to maintain the proper environmental conditions suitable for IT equipment operation in a data center, and choosing the correct cooling solution is a very important decision when building the facility.