Monthly Archives: May 2011

PUE Certification

I recently took the step of reporting our PUE figures to the Green Grid for visbility purposes.  This now means we can add the subscript codes “L2, MD” to our PUE so that others will know how we have measured and how accurately.  The following description (courtesy of the GG) explains what the mnemonics mean:

PUE Category 0

This is a demand based calculation representing the peak load during a 12-month measurement period. IT power is represented by the demand (kW) reading of the UPS system output (or sum
of outputs if more than one UPS system is installed)  as measured during peak IT equipment utilization. Total data center power is measured at the data center boundary (e.g. point of electric
feed for Mixed-Use Data Centers  or utility meters for Dedicated Data Centers) and is typically reported as demand kW. As this is a snapshot measurement, the true impact of fluctuating IT or
mechanical loads can be missed. However consistent measurement can still provide valuable data that can assist in managing energy efficiency.  PUE category 0 may only be used for allelectric data centers i.e. it cannot be used for data centers that also use other types of energy (e.g. natural gas, district chilled water, etc.).
PUE Category 1
This is a consumption based calculation. The IT load is represented by a 12-month total kWh reading of the UPS system output (or sum of outputs if more than one UPS system is installed).
This is a cumulative measurement and requires the use of kWh consumption meters at all measurement points.  The total energy  must include all fuel types that enter  the data center
boundary (electricity, natural gas, chilled water, etc).  In a Dedicated Data Center building, this will include all energy captured on utility bills; for a Mixed-Use Data Center, all the same fuels
must be sub-metered if they cross into the data center boundary.  Annual reading should reflect 12 consecutive months of energy data.  This measurement method captures the impact of
fluctuating IT and cooling loads and therefore provides a more accurate overall performance picture than PUE Category 0.
PUE Category 2
This is a consumption based calculation. The IT load is represented by a 12-month total kWh reading taken at the output of the PDU’s supporting IT loads (or sum of outputs if more than one
PDU is installed). This is a cumulative measurement and requires the use of kWh consumption meters at all measurement points. The total energy is determined in the same way as Category 1.
This measurement method provides additional accuracy of the IT load reading by removing the impact of losses associated with PDU transformers and static switches.
PUE Category 3
This is a consumption based calculation. The IT load is represented by a 12 month total kWh reading taken at the point of connection of the IT devices to the electrical system. This is a
cumulative measurement and requires the use of kWh consumption meters at all measurement points. The total energy is determined in the same way as Category 1.  This measurement method
provides the highest level of accuracy for measurement of the IT load reading by removing all impact of losses associated with electrical distribution components and non-IT related devices,
e.g., rack mounted fans, etc.
The “M”, “D” or “Y” after the Category num,ber gives the frequency with which the measurements are taken (i.e. Monthly, Daily or Yearly).