We have seen many different aspects of data centers and their operational features. Did you ever think what are the factors that decide the efficiency of a data center? How can we make sure that our data center is running in the most cost-effective way, energy efficient and environment friendly? Because the data center is essential to an enterprise’s operation and houses an ever-increasing amount of mission critical equipment, there are several key considerations and challenges when it comes to ensuring reliability and performance. In this article, we will discuss the 4 main factors that determine the efficiency of a data center such as,

• Power Usage Effectiveness(PUE)
• Data Center Infrastructure Efficiency(DCiE)
• Water Usage Effectiveness(WUE)
• Carbon Usage Effectiveness (CUE)

General Note – Data Center Power, Cooling and Efficiency

Energy consumption is a key consideration in the data center, given the cost and increased amount of power required for today’s advanced data center computing. Data center managers are therefore tasked with ensuring efficiency to reduce operational costs, and they often use the Green Grid’s PUE metric to ensure that power coming into the data center is being efficiently used by equipment and not wasted.

Data center cooling also has a significant impact on energy consumption. Preventing the mixing of cold inlet air and hot exhaust air in the data center helps to raise return air temperatures, which improves the efficiency of data center cooling systems and prevents overprovisioning of power-consuming air conditioning units. Preventing the mixing of hot and cold air is also critical to ensuring reliability as hot spots can adversely impact equipment lifetime and reliability.

The use of a hot aisle/cold aisle configuration in the data center is one way that data centers prevent the mixing of hot and cold air. It involves lining up rows of cabinets in a way that cold air intake from data center cooling systems is optimized at the front of the equipment and hot air exhaust from the back of the equipment is optimized to reach the cooling return system. Containment systems can also be used to completely isolate hot and cold aisles from each other where roof panels are used to isolate the cold aisle from the rest of the data center (i.e., cold aisle containment) or vertical panels are used to isolate the hot aisle and return the hot exhaust to the overhead return plenum.

Data center cooling can also be affected by the amount of cabling in pathways. When cabling is congested in underfloor pathways or at the front of the equipment, it can prevent proper movement of cold air to the equipment inlet or hot air from the exhaust. The use of effective cable management and moving high-density cables overhead are strategies deployed to enable proper airflow.

There are many factors that are forcing data centers to become more sustainable and run efficiently in terms of power usage. Business demand, cost and ROI, environmental pressure and security concerns are just a few of the influencing factors. These issues are targeted by governments all across the world and other organizations such as The Green Grid and even the European Union.

Power Usage Effectiveness(PUE)

The most common energy efficiency metric is called Power Usage Effectiveness, widely known as PUE. Power usage effectiveness (PUE) is a metric used to determine the energy efficiency of a data center. PUE is determined by dividing the amount of power entering a data center by the power used to run the computer infrastructure within it. PUE is therefore expressed as a ratio, with overall efficiency improving as the quotient decreases toward 1. PUE is a green computing principle promoted by The Green Grid, a global organization based in the US which aims to develop and promote data center energy efficiency. The Green Grid is a non-profit association of technology providers, end-users, facility architects, utility companies and policy makers. They all work together toward improving the resource efficiency of data centers and information technology all around the world. The Green Grid is famous for creating efficiency metrics, PUE being their biggest hit so far.

How to Determine PUE

Have you ever come across the PUE value of your data center? How efficient is your data center in terms of power efficiency? Now let us understand the ways to detect the PUE of a data center?

1. Take a measurement of energy use at or near the facility’s utility meter. If the data center is in a mixed-use facility or office building, take a measurement only at the meter that is powering the data center. If it is not on a separate utility meter, estimate the amount of power being consumed by the non-data center portion of the building and remove it from the equation.
2. Measure the IT equipment load after power conversion, switching, and conditioning is completed. According to The Green Grid, the most useful measurement point is at the output of the computer room power distribution units (PDUs). This measurement should represent the total power delivered to the server racks in the data center.

Further to simplify this concept,

PUE is determined by using the following formula:

PUE = Total Facility Power/IT Equipment Power

Total Facility Power is the power measured at the utility meter. The IT Equipment Power includes all the actual load of IT equipment such as workstations, servers, storage, switches, printers, and other service delivery equipment.

PUE Example:

Having a facility that uses 100,000 kW of total power of which 80,000 kW is used to power your IT equipment, would generate a PUE of 1.25. The 100,000 kW of total facility power divided by the 80,000 kW of IT power.

PUE is determined on a scale from 1 to 4, 1 being very efficient and 4 very inefficient. According to the Uptime Institute, the typical data center has an average PUE of 2.5. This means that for every 2.5 watts in at the utility meter, only one watt is delivered out to the IT load. Uptime estimates most facilities could achieve 1.6 PUE using the most efficient equipment and best practices.

Data Center Infrastructure Efficiency (DCiE)

Data Center Infrastructure Efficiency, more commonly known as DCIE, is another popular metric used to benchmark the energy efficiency of a data center. It is used by many data centers throughout the world.

The most obvious difference between PUE and DCIE is that it is expressed as a percentage rather than a number. The higher the percentage the more efficient the data center. Data center infrastructure efficiency(DCIE) is the reciprocal of PUE and is expressed as a percentage that improves as it approaches 100%.

How to Determine DCiE 

1. Take a measurement of energy use at or near the facility utility’s meter. If the data center is in a mixed-use facility or office building, take a measurement only at the meter that is powering the data center. If the data center is not on a separate utility meter, estimate the amount of power being consumed by the non-data center portion of the building and remove it from the equation.
2. Measure the IT equipment load, which should be measured after power conversion, switching and conditioning is completed. According to The Green Grid, the most likely measurement point would be at the output of the computer room power distribution units (PDUs). This measurement should represent the total power delivered to the server racks in the data center.

DCIE is the reciprocal of Power Usage Efficiency (PUE). PUE is defined as the total facility power divided by the IT equipment power. That means that DCiE  = 1/PUE.

Further to simplify this concept,

DCIE can be worked out by using the following formula:

DCIE = IT Equipment Power/Total Facility Power x 100%

IT Equipment Power and Total Facility Power principles explained above apply to DCIE too.

Here’s a quick example that will help you understand how to work out your data center energy efficiency by using the two metrics explained above:

Total Facility Power = 320 kW

IT Equipment Power = 160 kW

PUE = 320/160 = 2

DCIE = 160/320 x 100% = 50%

You can now calculate your data center’s electrical efficiency and then use the spectrum below to determine whether or not you need to improve it.

Not everyone is going to be able to achieve the impressive efficiency levels of a Google, Yahoo, or Microsoft (all have PUE’s of 1.15 to 1.21), but most data centers can make substantial efficiency improvements. The following chart showing data detailed by the EPA and presented by the Green Grid can help give you some ideas of achievable goals. After calculating your current PUE/DCiE, we recommend you set a realistic team efficiency improvement objective, use our calculator to determine the potential savings of achieving that improved level, and keeping in mind the environmental and goodwill benefits, weigh the savings against the costs of your efficiency efforts.

Having any difficulties to calculate this your PUE and DCiE? Don’t worry, we have got many of the online calculators that can be used. Have a look at one from 42u.com.

When we say that we can save a lot of money and carbon emission by reducing PUE, How Much Can Your Organization Save by Being More Energy Efficient in Your Data Center? Here is a calculator for that also which will help you to plan accordingly.

Water Usage Effectiveness(WUE)

For years in data center circles, we’ve been talking about Power Usage Effectiveness or PUE. Largely lost in the discussion, however, is another factor that has taken on increased importance as data centers rely on economizer modes of cooling: Water Usage Effectiveness or WUE. Water usage effectiveness(WUE) is a metric developed by The Green Grid to help data centers measure how much water a facility uses for cooling and other building needs. Both PUE and WUE are measures of data center sustainability developed by the Green Grid.

According to The Green Grid, a water use metric allows a data center manager to understand the effect water consumption has on the local electric grid. By using WUE in conjunction with power usage effectiveness and carbon usage effectiveness metrics, an organization can reduce energy use and, in effect, reduce the amount of water and electrical power needed to run the data center efficiently.

How to Determine WUE

But for starters what is WUE? Most people are familiar with PUE, the total power consumed by the data center divided by the power consumed by the IT gear within the data center. WUE is a similar metric that divides total site annual water consumption by IT power.

To calculate simple WUE, a data center manager divides the annual site water usage in liters by the IT Equipment Power usage in kilowatt-hours (Kwh). Water usage includes water used for cooling, regulating humidity and producing electricity on-site. IT equipment energy includes any power drawn by hardware used in the day-to-day functioning of the data center.

WUE = Annual Water Usage(L)/ IT Equipment Power (kWh)

Water usage by a data center (or any commercial building) is a complex subject. Not only is water used on-premise, but the electric power generation usually involves significant water consumption by the utility as well. Thus, increasing water consumption at the data center could reduce total water consumption by driving down the electricity needed. Think about a multi-megawatt data center which can easily use tens of thousands of gallons every day. Reduction of water usage is certainly a desirable goal for data centers deploying evaporative (or adiabatic) cooling for both sustainability and local regulatory reasons.

Carbon Usage Effectiveness (CUE)

Carbon usage effectiveness (CUE) is a metric for measuring the carbon gas a data center emits on a daily basis. The metric was developed by the non-profit consortium, The Green Grid. The rising cost of energy, in addition to environmental concerns, has inspired organizations to seek ways to lower their greenhouse gas (GHG) emissions and carbon gas emissions in particular. In addition to helping an organization make informed decisions about changes that affect global warming, knowing the carbon usage effectiveness metric can help an organization qualify for green computing financial incentives in some industries.

Because PUE has proven to be an effective industry tool for measuring infrastructure energy efficiency, The Green Grid believes that it is extremely important for the industry to promote efficiencies in other dimensions to maximize operational efficiency and reduce negative impacts on resources and the environment. The impact of operational carbon usage is emerging as extremely important in the design, location, and operation of current and future data centers. When used in combination with the power usage effectiveness (PUE) metric, data center operators can quickly assess the sustainability of their data centers, compare the results, and determine if any energy efficiency and/or sustainability improvements need to be made.

How to Determine CUE

Unlike PUE, CUE has dimensions while PUE is unit-less; its value is energy divided by energy. Another important difference is the range of values. PUE has an ideal value of 1.0, implying that all energy used at the site goes to the IT equipment, and there is no theoretical upper boundary for PUE. CUE has an ideal value of 0.0, indicating that no carbon use is associated with the data center’s operations. Like PUE, CUE has no theoretical upper boundary.

For data centers that obtain their entire power source from the energy grid and generate no local CO2, CUE is defined as follows:

CUE = Total CO2 emissions caused by the Total Data Center Energy/ IT Equipment Energy(IT Equipment Power)

In Equation above, ―Total Data Center Energy is the same value as the numerator of the PUE metric. The numerator in this CUE metric is the total carbon emissions caused by the use of the energy in the PUE metric. The units of the CUE metric are kilograms of carbon dioxide (kgCO2eq) per kilowatt-hour (kWh).

Total CO2 Emissions – This component includes CO2 emissions from local and energy grid-based energy sources. Ideally, the CO2 emissions will be determined for the actual mix of energy delivered to the site (e.g., the electricity may have been generated from varying CO2-intensive plants—coal or gas generate more CO2 than hydro or wind. The mix also must include other energy sources such as natural gas, diesel fuel, etc.). The total CO2 emissions value will include all GHGs, such as CO2 and methane (CH4). All emissions will need to be converted to ―CO2 equivalents. As recommended with PUE, this value is the annual total emissions.

The ‘Total CO2 Emissions’ are measured in kilograms of carbon dioxide (kgCO2eq) per kilowatt-hour (kWh) and ‘Total Data Center Energy’ is the amount of power used as measured at the utility meter. If your data center is running completely on power-grid electricity, the region-wise government data will give you the numbers. To get the IT Equipment Energy quantity, add up the entire load associated with the IT equipment such as storage, network equipment, switches, monitors, workstations used to control the data center. Exclude the cooling and lighting equipment. The answer from this basic division is a number that you can compare with the numbers of other data centers and see how you compare.

An alternative way to calculate CUE is by multiplying the data center’s annual PUE by the Carbon Emissions Factor(CEF) for the region as determined by the EPA.

CUE = CEF x PUE

This could also be represented as:

CUE = (CO2 Emitted(kgCO2 eq)/Unit of energy(kWh)) x (Total data center energy/IT equipment energy)

If you would like to understand more about this concept, don’t forget to read through this article and this video.

With Carbon Usage Effectiveness (CUE) and Power Usage Effectiveness (PUE), it is a big thrust in the arm for IT organizations to better understand and improve the sustainability and energy efficiency of their existing data centers. This will help organizations to make smarter decisions on new data center deployments.

Knowledge Credits: Datacenterknowledge.com, thegrid.com

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