Green data center

PUE was invented in 2007, and proposed new guidelines to measure energy use in data centers.

${\displaystyle \mathrm {PUE} ={{\mbox{Total Facility Power}} \over {\mbox{IT Equipment Power}}}}$

This ratio describes how much extra energy a data center needs to maintain IT equipment for every watt delivered to the equipment. The best PUE a data center can have is 1: an ideal situation, with no extra energy use. When PUE was introduced, studies found that the industry-average PUE was between 2.5 and 3. In more recent studies, the average PUE fell to about 1.7 by using this framework. PUE began the shift of the data-center industry towards energy efficiency.[5]

Although PUE is the most-frequently-used metric for data centers to measure energy efficiency, its reliability is still debated;[7][8]

Carbon usage effectiveness (CUE) is another metric used to measure energy usage and sustainability in data centers. It is calculated with the following formula:[9]

${\displaystyle \mathrm {CUE} ={\frac {Total{\rm {{CO_{2}}EmissionsCaused}}}{ITEquipmentPower}}}$

Another way to express this formula is as the product of the carbon dioxide emission factor (CEF) and the PUE, where the CEF is the kg of ${\displaystyle {\ce {CO2}}}$ produced for each kilowatt-hour of electricity:

${\displaystyle \mathrm {CUE} ={\frac {\rm {{CO_{2}}emitted(kg{\rm {{CO_{2}}eq)}}}}{unitofenergy(kWh)}}}$ × ${\displaystyle {\frac {TotalFacilityPower}{ITEquipmentPower}}}$

IBM modular data center

Low-power servers are more energy-efficient than conventional servers in data centers. They use the technology of smartphone computing, which tries to balance performance with energy consumption. The first low-power servers were introduced in 2012 by large IT providers such as Dell and Hewlett-Packard. Used correctly, low-power servers can be much more efficient than conventional servers. They can have a significant impact on data-center efficiency, decreasing power consumption and the operating cost of cooling facilities.[12]

A modular data center is a portable data center which can be placed anywhere data capacity is needed. Compared with traditional data centers, they are designed for rapid deployment, energy efficiency and high density. These ready-made data centers in a box became very popular. The HP EcoPod modular data center supports over 4,000 data centers with a PUE rating of 1.05 in and free-air cooling.[12]

Schematic drawing of server racks with and without cold aisle containment (1) circulating air-cooling device (2) cold aisle (3) server racks (4) warm aisle (5) barrier between cold and warm aisles. Blue lines: flow of cold air; red lines: flow of warm air

Free air cooling systems uses outdoor air instead of traditional data-center computer room air conditioner (CRAC) units.[13] Although outdoor air still needs to be filtered and moisturized, much less energy is required to cool a data center with this method. Outdoor air temperature is an issue here, and the data center's location plays a critical role in this technology.[14]

In this method, the rows of racks are aligned with the backs of the servers facing each other; the aisles are enclosed, to capture the air. In hot aisle containment, the heat produced by the servers is pumped to the cooling units. In cold aisle containment, cold air is pumped to the enclosed aisles. Both containment methods are more effective than traditional cooling technologies, and can help reduce energy consumption (and its impact). Although it may be more difficult to implement, hot aisle containment is more effective than cold aisle containment.[15][16]

Data centers use electric power, releasing more than 98 percent of this electricity as heat. Waste heat can be actively reused, and a data center becomes a closed-loop heating system with no waste. Examples include:

• The IBM Reusing Data Center in Switzerland, where the heat warms a local swimming pool
• In Finland, the Yandex and Academica data centers replacing the heat used by 500-1,000 homes with data-center energy.
• Amazon reused heat from a nearby data center for a biosphere project in Seattle.[17]

Facebook's custom-built data center in Prineville, Oregon

Some humidity is necessary for data centers to work efficiently and prevent damage to devices and servers. Ultrasonic humidification uses ultrasound to create moisture, using 90 percent less energy than conventional methods such as resistance steam humidifiers.[18]

Evaporative cooling reduces heat by the evaporation of water. Two main methods are used: evaporation pads and high-pressure spray systems. With evaporation pads – the more popular method – air is drawn through the pads, making water evaporate and cooling the air. The other technique, high-pressure spray systems, needs a larger area and consumes more energy with pumps. Evaporative cooling is dependent on geographical location and season, because both affect the moisture level of the air. Compared to traditional mechanical cooling systems, evaporative cooling generally uses significantly less electricity.[19]