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Getting The Measure Of Power Monitoring

William DarbyUsing electrical power efficiently is fundamental to any business looking to reduce energy costs, improve operational efficiency, and meeting sustainability goals. Will Darby, managing director of metering, controls and automation specialist Carlo Gavazzi UK, highlights an innovative solution to measuring power consumption in a data centre.

Energy is one of the most, if not the most, significant cost in running a data centre. There are numerous ways in which a data centre operator can have an impact on power consumption but without a baseline measurement it is difficult to know which initiatives are having the greatest impact. The old adage: you cannot manage what you cannot monitor, is as true for data centres as it is for any other power-consuming business, perhaps more so given the huge amounts of electrical power many of these facilities consume.

The challenge of monitoring power is made harder by almost every data centre having a different power requirement depending on the number of servers in the data hall (and server loadings), the external environmental conditions, the internal environmental conditions that have to be maintained and the efficiency and run-times of the cooling plant.

The only way to run a properly energy-optimised data centre is to have a robust energy monitoring platform covering all the strategic elements of the power system. By combining power monitoring with a robust environmental monitoring strategy, will allow operators to fine tune the data centre to run at its optimal level, maximising its energy efficiency.

Power Usage Effectiveness (PUE) is the industry metric used to determine a data centre’s energy efficiency. An energy efficient data centre would probably have a PUE less than 1.3, or perhaps even less than 1.2 when located in a cool climate where outside air can be used to provide free cooling.

To determine a data centre’s PUE an operator will need to know the total power consumption of the data centre - both IT and non-IT loads such as cooling and lighting loads and the total IT load.

Total power can be easily obtained from the meter at the main power panel, where the electrical incomer enters the facility.

Operators will also need to know the total power consumed by the IT. There is a direct relationship between kilowatts of electricity consumed by the servers, the corresponding kilowatts of heat given off by the servers and the amount of cooling that needs to be delivered to the data hall.

The power-consuming servers are located in server racks, typically up to 48 servers per rack. These racks are positioned in rows to facilitate maintenance access and cooling. A Power Distribution Unit (PDU) distributes the electric power to the racks of computers, Power monitoring of the IT can be undertaken at PDU level with one meter serving each rack.

A data centre can include 100 to 200 distribution panels, which can make traditional metering solutions expensive and time-consuming to install. However, the innovative WM50 branch circuit monitoring system from Carlo Gavazzi was developed specifically for use in data centres after Carlo Gavazzi’s research showed a traditional PDU metering system would take up too much valuable space and require a significant amount of time to install.

Carlo Gavazzi meterThe WM50 is a complete solution for both new and retrofit data centre and critical load applications. While the base unit monitors the mains supply, its two branch buses link up to eight 12-channel split-core current transformer (CT) blocks. The system can therefore be scaled according to specific needs up to 96 branch circuits in any combination of three-phase and single-phase loads or two-phase and single phase loads. This approach reduces installation time by up to 75% when compared to existing solutions and affords a similar saving during commissioning.

System configuration is extremely fast and intuitive: following the graphical suggestions of the proprietary software or app, different topological panel configurations can be easily made. The unit’s display includes: Voltage, Amperage, Power Factor, active energy (kWh), reactive energy (kvah), harmonics analysis. All data collected by the WM50 can be transmitted to the BMS or data centre monitoring system via either Modbus RTU or Modbus TCP/IP protocols.

Using the WM50 to monitor energy consumed by the IT, an operator can calculate a data centre’s PUE by dividing the total electrical energy consumed by the total IT load.

In addition to enabling an operator to calculate the operating efficiency of a data centre, monitoring power at PDU level will also give the operator a detailed, granular overview of IT power loads. This will help in ensuring loads are distributed evenly across the facility, which is why many data centres rely on PDU monitoring to improve efficiency and uptime.

Monitoring the power consumed at rack level using the WM50 will also allow a data centre manager to determine if the facility’s original assumptions for power allocations make sense under actual operation. Quite often, power is allocated to IT equipment on the basis of nameplate ratings which are conservatively high. This means more power, which may be required elsewhere in the facility, is going to an IT equipment rack than will actually be consumed.

The cost of energy can quickly consume a significant proportion of a data centre’s operating overheads. Using a power monitoring solution can help managers as they strive to maintain 24/7 availability and drive up operational efficiency. By choosing flexible, adaptable, accurate and highly functional device such as Carlo Gavazzi’s WM50, data centre managers can respond to the ever-changing power distribution requirements of a critical facility.


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