By Jorge A. Gil, DCEP

1. THE DESIGN PUE CURVE IS ALL ABOUT THE SITE INFRASTRUCTURE LEVEL OF
EFFICIENCY AND IT UTILIZATION.
Every Data Center facility has a Design PUE curve, sometimes implicit, so the owners and operators might not be aware of that. This curve is basically the result of the Data Center’s designed level of energy efficiency as the function of the IT Load utilization. So, the Design PUE value is obtained at 100% of IT Load Utilization. In figure 1, there is an example of a Design PUE curve.

FIGURE 1

Understanding the correlation between the PUE value and IT Load utilization is an important take, since once the Data Center is in the operational stage, there might be very few things to do in order to improve its efficiency, without retrofitting the site. So, trying to improve the IT Load utilization might sound like the logical first step before getting into the Site Infrastructure side. By optimizing the IT Load first, we can look for a better adjustment of the Site Infrastructure optimization later, getting the best possible efficiency scenario.

The IT Room Utilization (ITRU) set of metrics, can effectively be used in assessing the current state of the IT Load utilization and Room occupancy, of any Data Center implemented with Racks (EIA-310-D and/or OCP Racks).

The IT Room Utilization (ITRU) method, is a way to assess the maximum Potential utilization of the IT Load, by
modeling and projecting the consolidation of IT Equipment into fewer Racks, and deactivating the empty Racks and its collateral Site Infrastructure.

The interesting side about the ITRU method is that it helps in projecting improvement scenarios with few input data collected from the Data and Telco Room, producing key information about the current state of the overall Room efficiency and the future potential optimization.

2. HOW CONTROLLING THE IT SPACE CAN IMPROVE THE IT LOAD UTILIZATION
The IT Room Utilization (ITRU) proposes a way to measure the IT Load utilization in a standardized way, as in the equation:
ITRU = Average Used IT Load / Design IT Load
Where the Design IT Load, is obtained by the Summation of Total Rack Capacity (typically in kW) in the Computer/Telco Room. The Average Used IT Load will be the average power consumption by IT Equipment in the Computer/Telco Room.

As IT Equipment are usually arranged in Racks, having a standard way to measure the total Room occupancy with respect to its functional approach (Rack Units), is key in order to be able to improve its efficiency.

Rack Usage Ratio (RUR) is a way to measure the occupancy of the Computer/Telco Room capacity, in terms of the IT Equipment functional space (Rack Units or Open Units). As Site Infrastructure components capacity are directly dependent of the IT Racks power capacity (aka Rack Power Density), the reduction of IT Racks might directly impact Site Infrastructure components. However, the amount of Site Infrastructure equipment to be impacted will depend on the way the Computer Room is designed. Highly modularized Computer Room architectures will be more impacted than less modularized ones. Understanding the relation between the Site Infrastructure Components and the IT Racks, is an important take in order to understand how efficient a Data Center might operate.

In addition to Rack Occupancy (RUR), it’s also important to know what the average Rack Power Density usage is, also according to its functional space (Rack Units or Open Units), and the resulting indicator called Rack Power Ratio (RPR), was designed to address that need.

Rack Power Ratio (RPR), is an important metric, since it allows you to determine:

• A sense of the level of Computer Room potential efficiency range, after consolidating IT Racks at 100%.
• The maximum Potential Utilization at 100% of Rack Occupancy.
  Potential ITRU = RPR x 100%
• RPR>100% means Power overload at Rack Unit Level.
• RPR<=100% means No Power overload at Rack Unit Level, therefore potential to move IT Equipment to other Racks with the same Rack Power Density.

Finally, as RPR and RUR are related to Rack Units, ITRU alternative equation can be used to project potential IT Load
utilization scenarios (ITRU alternative method).

ITRU = RPR * RUR
Summary of ITRU Set of Metrics.

• IT Room Utilization (ITRU): measures the IT Load utilization ratio, as in the Equations:
• Rack Usage Ratio (RUR): measures the Room Occupation ratio, considering Open Units (OCP) or Rack Units
  (EIA-310-D), as in the Equation:
• Where:
  U_USED is the total of units (Rack Units or Open Units) occupied with IT equipment. U_TOTAL is the total of units (Rack Units or Open Units) available for IT Equipment (occupied units + empty units).
• Rack Power Ratio (RPR): measures the average use ratio of Rack Power Density relative to Open Units (OCP) or Rack Units (EIA-310-D) level, as in the Equations:
  

RPR metric and Potential ITRU (Potential IT Load Utilization).
The RPR (Rack Power Ratio), helps in projecting the Potential ITRU improvement, after consolidating the Rack Space.
The RPR will be the maximum theoretical ITRU value (utilization) to be obtained, by consolidating the IT Equipment at
100% of Rack occupancy: Potential ITRU max = RPR x 100%.
However, the real Potential ITRU, for any assessed Data Room can be obtained by the following equation:
POTENTIAL ITRU = RPR * POTENTIAL RUR
The Potential RUR (Rack Usage Ratio), will be obtained after dividing the Total used Rack Units (used by IT
Equipment) by the resulted value of multiplying the Racks Needed by Racks Units per Rack (If RPR<=100%). Projecting the Racks Needed is critical, since it’s the basis for Rack Consolidation. After calculating the Racks Needed, the remaining Racks can be effectively deactivated, potentially impacting the correlated Site Infrastructure. The RPR indicator can also be used to determine if there is overload at Rack Unit level (RPR>100%). In that case, it
helps during the Rack consolidation process by preventing the overload at Rack level (avoiding a safety issue).