By C.J. Joshlin
From the July 2013 issue of Today’s Facility Manager
With rapidly growing energy demand and expanding requirements in modern electrical distribution systems, there is an increasing call for approaches in coordination, configurability, monitoring, and maintenance that will help facility managers (fms) better control and maintain their electrical distribution systems properly. With complete monitoring activity in place, combined with proactive response initiative, there can be savings of up to 30% on costs of energy consumption and greater assurance that fms are meeting critical codes and standards.
Reduce Consumption, Optimize Costs
Intelligent use of an electrical distribution monitoring system helps to reduce the cost of energy at a facility by cutting energy consumption. Typically in the past, metering has only been cost-effective at the incoming distribution board. This is in part due to installation complexity and space limitations.
By integrating the metering functionality into molded case circuit breakers, the meter can be accommodated in approximately the same amount of space as a standard molded case circuit breaker, and allows fms to have an increased amount of data to leverage for their energy management programs. As a result, fms can monitor their entire system in order to raise awareness of energy consumption, identify cost savings, and ensure system reliability.
New generation molded case circuit breakers help fms combine the capability of electronic trip units, advanced metering, and open protocol communications in a single, modular unit. This allows for:
- the creation of a power monitoring point, which can be used to provide power quality data, energy management data, system capacity information, input to a facility supervisory control and data acquisition (SCADA) system, and preventive maintenance;
- enhanced selective coordination between the protective devices of the system with single-ampere adjustment capabilities in the trip unit;
- capacity for zone-selective interlocking, for reducing arc flash hazard at high energy locations and for coordination of similarly sized protective devices, without reducing system capacity; and
- reduction in the cost of installation by combining in a single package the functionality of a protective device with a meter capable of power quality readings and alarm functionality. This creates savings by reducing cost of equipment, installed equipment size, and installation time.
Power Quality, System Reliability
As dependence on electronic devices increases, electrical systems are becoming more sensitive to disturbances. Placing meters throughout a system can help track many parameters to ensure system reliability, providing a methodology for predicting system reliability and creating a predictive maintenance schedule.
Having the capability to collect power data through molded case circuit breakers can trigger required maintenance in a proactive and timely manner, instead of relying on only routine maintenance. In addition, alarm functions can help identify overloaded equipment before the operation of the protective device. Customizable alarms, which are built into some advanced metering trip units, allow each circuit breaker to be configured to trigger an alarm locally at the equipment or to the SCADA system in a way that is meaningful to that location in the system. This allows quick detection and analysis of potential events before a problem arises, minimizing downtime and maximizing the capacity of the system.
Reducing Power Consumption, Improving Data Center Efficiency
By Clemens Pfeiffer
Data centers waste a substantial amount of energy. This is because they are designed for capacity, performance, and reliability, usually at the expense of efficiency. Fortunately, there are numerous ways facility managers (fms) and IT managers can cooperate to improve overall data center efficiency—sometimes dramatically—without adversely impacting capacity, performance or reliability.
Eliminate Cooling Inefficiencies
In a typical data center only about half of the power available is actually used by IT equipment, with the rest going mostly to cooling. This problem is so significant that the Green Grid created the Power Usage Effectiveness (PUE) rating system to help organizations improve data center energy efficiency. PUE is the ratio of total energy consumed to the energy used by the IT equipment; today’s typical data center achieves a PUE rating of around 2.0. The U.S. EPA has established a target for data centers of a PUE rating between 1.1 and 1.4. Achieving this likely involves a range of initiatives, and some require close cooperation between fms and IT managers.
A common technique for reducing cooling power consumption is to adopt a hot/cold aisle configuration with the cold aisle inlet temperature set to 80.6°F as recommended by ASHRAE. To avoid creating hot spots that could potentially cause an outage, it may be necessary to balance equipment power load, and then calibrate and monitor cold aisle temperature to maximize cooling efficiency and minimize potential problems.
Upgrading an aging computer room air conditioning (CRAC) system should also be considered. Although this may require capital expenditure, the ability to use variable cooling and/or make greater use of outside air will reduce operational costs. For multiple, geographically dispersed data centers, shifting application loads to operate mainly at night (when outside ambient air temperatures are at their lowest) can minimize or eliminate the need for CRAC’s power hungry compressor.
Eliminate Power Distribution Inefficiencies
In most power distribution systems, there are multiple sources of inefficiency. Rightsizing distribution equipment and uninterruptible power supply helps minimize inefficiencies caused by power conversions in a data center. Another source of waste is reactive power, which consumes real energy but produces no real work. Using a controller to keep a data center’s power factor close to unity essentially eliminates the waste.
Another source of waste involves the configuration of the automatic transfer switch (ATS). While deploying the ATS between the grid and the generator is common practice, an AC (alternate current) or DC (direct current) distribution bus is far more efficient, and just as effective during a power outage. The bus configuration can also integrate other power sources, including any on-site fuel cells and solar/wind energy, and enable generator maintenance cycles to be put to better use.
When constructing a new data center, another option is to use only DC for IT equipment. According to research from Lawrence Berkeley National Laboratory, the efficiency gains have both a direct and indirect effect owing to fewer power conversions and less heat generation, respectively. Test results reveal about 10% savings in energy for the entire data center compared to even the most efficient AC configurations.
Minimize Server Underutilization
For IT equipment, the most significant savings are normally found in what is the biggest source of waste in most data centers: poor server utilization. A first step is to consolidate and virtualize servers, which can increase overall utilization from the typical 10% for dedicated servers to between 20% and 30%. Overall utilization rates of 50%+ can be achieved with a dynamic management system. A related advantage of consolidating and virtualizing servers is the potential to reclaim rack space and stranded power.
Even with the use of energy efficient, virtualized servers, power continues to be wasted during periods of low application demand. By matching available server capacity in the virtualized cluster to the actual application load in real time, total server consumption can be reduced by up to 50%. The steps involved in resizing clusters and/or de/reactivating servers are normally automated using runbooks, different versions of which can be created for use on a predetermined schedule and/or for dynamic response to changing loads. Utilization rates for the active servers as high as 70% or 80% are possible with such dynamic load management, making this an efficient way to support variable application loads.
The energy efficiency of individual servers is also important, of course, and the most efficient are not necessarily the ones with the most efficient power supply. A better measure of efficiency is the number of transactions per second per Watt (TPS/Watt). To assess a server’s TPS/Watt performance accurately, Underwriters Laboratories created the UL2640 standard that uses the PAR4 Efficiency Rating system. UL2640 enables managers to compare the transactional efficiency of legacy servers with newer ones, and newer models of servers with one another. Indeed, a best practice is to assess transactional energy efficiency of servers during every hardware refresh cycle and whenever adding capacity.
At a minimum, all aspects of monitoring and managing data center infrastructure should be consistent and pervasive across the facilities and IT teams. Effort is required to achieve the requisite holistic view, but the resulting savings easily justify the investment.
Pfeiffer is the CTO of Power Assure and is a 25 year veteran of the software industry, where he has held leadership roles in process modeling and automation, software architecture and database design, and data center management and optimization technologies.
Tracking harmonic information is also an option that can help fms determine if it is acceptable to install a specific type of unit at a designated location or to determine if corrective measures need to first take place.
Proper system coordination is one of the most important aspects of protection in complex electrical distribution systems. For fms, selective coordination helps protect the facility and equipment if there is a fault, while still isolating the loss of power in the case of a trip to the smallest area of the system possible while maintaining power to the unaffected area of the system. Fms can achieve this level of protection by replacing standard thermal magnetic circuit breakers (which make it difficult to achieve optimum selectivity) with circuit breakers equipped with electric trip units (a phase fault at any point along that branch of the system will trip the appropriate protective device ensuring unaffected areas remain in service).
Options for coordination are also a critical consideration and can offer a wide range of potential settings for long-time, short-time, instantaneous, and ground-fault values. In addition, some trip units also have an optional zone-selective interlocking function, where smaller circuit breakers are equipped with an output that allows them to send a restraining signal to an upstream protective device when a fault is detected. When the upstream device receives the signal, it initiates a change in the trip characteristics of that device. This keeps stress on the equipment at a minimum, while still maintaining selective coordination and optimally protecting the electrical distribution system.
Benefits Of Modern Electrical Distribution Systems
Combining the many functions of electronic trip units, including advanced power quality metering, zone-selective interlocking, and alarming options, allows fms to save space, installation time, maintenance, and even procurement efforts. Increased metering capabilities provide an effective way to monitor each power distribution point of the system, making it possible to know where capacity exists in the system as new loads are added. This can potentially eliminate the need to purchase new distribution equipment, which can have a significant impact on potential future expansion costs.
Molded case circuit breakers with trip units can give fms the power to protect, monitor, and analyze their electrical distribution systems at every main and branch circuit, and take control of energy use. These units provide the ability to coordinate system protection, monitor energy consumption, and effectively execute preventive maintenance programs resulting in a cost effective solution.
Joshlin is a staff power system engineer at Schneider Electric. She works out of St Louis, providing a range of consulting engineering services, including system inspections, power quality analysis, short circuit, coordination and arc flash studies, and harmonic studies. She is a professionally licensed engineer in Kansas, Missouri, Nebraska, Iowa, and Tennessee.