PUE- Overview Part 2

PUE - Overview Part 2

PUE has become an important metric for the data centre and almost gained infamy as the panacea of metrics for data centre energy efficiency, but unfortunately it is not as simple as that.

In essence PUE is a simple metric that is unsuited for use as a comparison metric except under specific circumstances. It is suitable to e PUE between data centres and organisations as a means of establishing either technical credibility or marketing benefits that might accrue from showing energy efficiency. However such comparisons have little or no value as the PUE does not take into account any other factors other than ITP and ITEP and each data centre will be constructed differently and have different equipment, software, infrastructure, processes and other factors within it that make it unique.

Here lies the problem with PUE. As it is a raw metric defining power delivered against power consumed it does not account for any specific characteristics of the data centre that should be taken into account when the metric was taken.

Occupancy

For example if a PUE of 2.2 is measured in one data centre (DC1) and at the same time a data centre (DC2) in the same locality measures a PUE of 3 then it could be assumed which is the more efficient data centre. However, the data centres may have completely different configurations, usage or occupancy levels. If DC1 is an older more traditional data centre that is fully occupied and would have difficulty in accommodation expansion, then the 2.2 may be reflective, without planned modifications or change, of its longer term PUE. However DC2 may be only forty percent (40%) utilised and therefore as it increases its occupancy its PUE would therefore improve considerably, potentially close to a PUE of 1.2 at 100% occupancy.

For the measurement of such a complex infrastructure, PUE is a really quite a simple metric. In essence it establishes the relationship between the power supplied to a data centre with the power it consumes. This relationship is then expressed as a simple numeric value and could be used as a guidance factor for understanding how efficiently or inefficiently energy is consumed in the data centre.

Mathematically PUE can be expressed as :

PUE

=

Total Facility Power (TFP) IT Equipment Power (ITEP)

Total Facility Power includes the power consumed by all of the equipment included under the definition all IT Equipment Power, such as, servers, storage, switches, workstations, printers and all of the power used in the power delivery, cooling, air conditioning, UPS. Lighting and other ancillary power consumed in the data centre is also included.

IT Equipment Power includes all IT equipment used in the delivery of an application, such as, servers, storage, switches, workstations, printers and any other service delivery equipment.

PUE is a closely related metric to DCiE and they can be considered as the inverse of each other.

Application of this metric will produce easy to understand ratios about the data centre energy efficiency, for example, a PUE of 2 means that the power used to run the actual IT equipment for delivery of IT services, is fifty percent (50%) of the power consumed by the data centre. Therefore if you need to install a new server requiring 460 watts, then the actual energy draw on the data centre will be 460 * 2 = 920 watts. In this way quick estimates of energy capacity requirements can be made. Used effectively and collected over a long period of time, the PUE will provide a more accurate and useful figure for use in capacity planning of the data centre's IT Equipment.

A more typically observed PUE of 2.2 reflects a more consistent ratio where forty-five percent (45%) of energy consumed actually delivers IT services.

Use the PUE Calculator to work your own PUE calculation.

There are instances appearing where data centres are proclaiming a PUE of closer to a value of 1, which implies that there are low or minimal electrical overheads for ITEP and the data centre is performing at close to peak efficiency. It is likely that PUE's in the range 1.25 and 1.5 will become the more typical value over time and data centres with high levels of resilieince required are likely to be in the region of 1.8+.

Assessor incorporates online software tools and expertise to enable you to monitor the energy consumption and work with key data centre metrics such as PUE and DCiE in your own data centre and IT computer room facilities.