Large data centers can be big power users because of the racks and racks of computer servers in them and the critical air conditioning and ventilation equipment required for cooling. However, when a data center can improve its overall energy efficiency, it not only reduces operating costs but also the requirements for its emergency standby power system, which can in turn make it affordable to size the system for full 2N redundancy. That’s what Vantage Data Centers did at its new data center campus in Santa Clara, CA, using novel energy-saving techniques and emergency standby generator sets from Tognum brand MTU Onsite Energy. For Vantage’s 73,000-square foot (sq ft) expansion facility called V2, the company specified six 3,000-kilowatt (kW) MTU Onsite Energy generator sets that provide a total of 18 megawatts (MW) of standby power for the facility’s 9-MW load.

Energy efficiency is central to Vantage Data Centers’ business model. According to Greg Ness, chief marketing officer, Vantage Data Centers, the company “develops highly efficient and customizable data centers that significantly reduce IT infrastructure, cooling costs, and carbon emissions so customers can substantially reduce their total cost of operations.” While the company’s customers include leading players in social networking, social commerce, online social gaming, cloud storage, and video game development, the V2 facility has been leased to a single tenant.


The heart of Vantage’s energy-saving design is the facility’s cooling system. Ness said that the V2 facility incorporates an energy-efficient penthouse cooling design that uses filtered outside air flowing down on the racks of servers. By also lowering the static pressure inside the building, the velocity of the cooling air is reduced, cutting year-round power consumption by a significant amount.

Vantage’s V2 facility, with a PUE of 1.12, is finding that operational efficiencies also have significant implications for sizing the emergency standby power system: The lower the overall energy needs are, the more redundancy can be built into an emergency standby power system. The result is much higher redundancy and reliability for no more investment—a critical factor for data centers that need to maintain near 100 percent uptime.

Vantage selected emergency standby generator sets from MTU Onsite Energy for the V2 data center based on performance, according to Steve Homan of Valley Power Systems, the local MTU Onsite Energy distributor that supplied the generator sets.

“MTU Onsite Energy generator sets were selected based on superior load acceptance and transient performance—the ability of these generator sets to be hit with a full load and then quickly recover voltage and frequency,” said Homan. “One of the reasons for this performance advantage was that we found that the open protocol design of our generator control systems worked well with the paralleling switch gear that Vantage had selected.”


The six 3,000-kW generator sets are located outdoors in individual weather-tight enclosures with sound attenuation. Each generator set features an MTU 20V 4000 generator-drive engine with approximately 20 percent more cylinder displacement than other engines of similar horsepower.

“The greater displacement supplies more reserve torque and is one of the reasons the MTU Onsite Energy generators can absorb full load in one step and recover quickly,” said Homan. “The greater displacement also reduces fuel consumption and reduces stress on the engine’s internal parts, improving reliability and longevity.” Each generator set is also equipped with dual starter motors and dual best batteries for additional starting reliability.

“We initially deployed these six standby generator sets for V2, but we plan on having a total of ten generator sets when the building is complete,” said Jennifer Fraser, director of design construction for Vantage Data Centers. “The facility is designed for growth, and the self-contained generator sets are located outdoors so we can incrementally increase the number of generators more easily.” To comply with local environmental ordinances, the generator enclosures are sound attenuated to a maximum 73 decibels (dBA). The sound-attenuated enclosures feature acoustic foam, vibration isolation, and baffles in the cooling air intakes to dampen the noise. The generator sets meet all the current EPA emissions standards for emergency standby generators sets, but each generator-drive engine is also outfitted with a regenerating diesel particulate filter (DPF) to capture any soot in the exhaust in order to comply with California’s strict air quality rules regarding particulate matter (PM) emissions.


The International Organization for Standardization (ISO) defines how to measure and rate many quality and performance parameters for emergency standby generator sets. All major generator set manufacturers utilize this standard to communicate their generator set ratings to their customers. In particular, ISO 8528-1 describes how to establish generator set ratings, measure performance, and evaluate engines, alternators, controls, and switch gear.

ISO-8528-1 sets a maximum 24-hour average load factor capability of 70 percent for both standby- and prime-rated generator sets, unless a higher average is agreed to by the engine manufacturer. This means that a 3,000-kW generator set meeting this standard must be able to provide an average of 2,100 kW per hour over a 24-hour period. In emergency standby applications, this means that the average load factor that can be sustained by most generator sets over an extended outage of 24 hours or more cannot exceed 70 percent of the nameplate standby rating, a factor that affects generator set sizing.

In contrast, the generator sets installed to backup Vantage’s V2 building are rated to an 85 percent average load factor. That means the 3,000-kW generator sets can deliver a 24-hour average of 2,550 kW each—a difference of 450 kW per unit. For an application such as Vantage, which involves multiple generator sets, this higher average-load-factor capability can reduce the number of generator sets needed to supply the load, especially during extended outages.


For most facilities with properly designed emergency standby power systems, the possibility of exceeding a power system’s 24-hour average load factor limitation is remote. This is because most commercial facilities have variable load profiles that reduce the likelihood a power system’s 24-hour average load factor limitation will be exceeded, even during an extended outage. Many facilities also have noncritical loads that can be taken offline during extended outages to reduce the average load factor on the standby system, if necessary.

However, data facilities often have large, less varied loads that can severely stress standby power systems during an extended power outage unless steps are taken during system design to accommodate the potential for a higher average load factor. In data centers, the computer servers and HVAC equipment create high electrical loads that can vary little over time.

As a result of these large, steady electrical loads, the load profile in a data center application is likely to have less variability, in turn putting a more constant demand on the standby power system. Less load variability results in a higher average load factor that will require either: 1) specifying a system with larger or more generator sets capable of a 70 percent load factor; or 2) specifying generator sets capable of higher than a 70 percent load factor.


Like most mission-critical data centers, the V2 facility has redundancies in its power supply to prevent loss of data or service during utility outages. Configured to the Uptime Institute’s Tier IV topology, the V2 standby system is what the Institute recommends for mission-critical data center applications with the greatest need for power availability. With 2N redundancy in utility feeds, standby generators, and UPS systems, such a system is expected to deliver annual availability of approximately 99.99 percent.

According to Fraser, the facility has utility feeds from two different substations in addition to static UPS systems and emergency standby generators. In the event that one utility feed fails, the second feed would automatically take over and supply the facility. If both utility feeds fail, the UPS system would supply power to the servers while all six generators start, reach rated voltage and frequency, parallel with each other, and take over the load. All six generators would remain online for the duration of the utility outage. With the 2N design, in the unlikely event that one or more of the generators did not start, there would still be enough standby power to supply the load. The generators are fed enough fuel for approximately 24 hours of operation before resupply is necessary.

Southern California is also earthquake country, and all of the enclosures and the generator sets have been seismically certified by an independent testing laboratory to withstand an earthquake.

“All of Vantage Data Centers’ projects are designed to the International Building Code seismic standard and carry a critical facility importance factor of I=1.5,” said Fraser. Facilities that carry an I=1.5 rating have life-safety or mission critical issues that require emergency standby generator sets that can survive an earthquake and still operate normally.

The generator sets for building V2 were among the largest generator sets to ever undergo shake-table testing to certify them to the IBC seismic standards. Weighing in at approximately 60,000 pounds, the generator was subjected to random seismic accelerations in three axes to simulate an earthquake during certification tests performed by VMC Group of Bloomingdale, NJ.


The V2 emergency standby power system went through a rigorous commissioning process to make sure all the components performed as designed. During this process, the generator sets are connected to a load bank to simulate the building load and a utility power interruption. It is especially important during this test to verify that the various controls and microprocessors on the generator sets, the transfer switches, and the paralleling switch gear communicate reliably.

According to Homan, “The commissioning went so well that Vantage and their onsite engineer said it was one of the best commissioning tests they had ever witnessed.”

The design approach used by Vantage Data Centers is a model for energy efficiency, as well as power reliability and resulting business continuity. Through innovative design of building and mechanical systems, plus careful integration of emergency standby power systems, Vantage will be able to supply the growing data center needs in their region at the highest level of reliability.