Data Center Power: Calculating Total Power Requirement


It is now much is easy to install systems of data center power since people have adopted scalable pay as you grow UPS architectures. It allows a manager of a data center to simply add modules as the data center’s needs grow. Nevertheless, in a larger facility, it is easy to lose focus of electrical future needs of a data center or room. Determining the energy usage of a data center requires a full grasp of the electricity amount needed by the UPS system, cooling system and the crucial IT loads. Even though these elements may vary considerably in power requirements, once you determine the power usage of the IT loads, you can estimate these requirements by using simple rules. Besides estimating the electrical service size, these elements can be used to estimate the capacity of the power output of a power generator, in case one is needed in the data center.

Needs Assessment

Any plans to improve the environment and capabilities of the data environment regardless of the scale or size must start by carrying out a needs assessment. A needs assessment is carried out to essentially establish the needs availability of the business applications the IT equipment processes. If a business process is not time sensitive, or is driven by batch process may show that air conditioning and power for the load has an ‘N’ configuration without interior redundancies to boost availability. But for sites that are more time sensitive, a degree of redundancy in major component systems may be required and they may have a configuration topology of ‘N + 1’. Every major system element will have a piece of equipment that is redundant in order that if there is failure of one of the units the system’s function would still be maintained for the IT critical load.

The most crucial applications of data centers that require total availability would have a topology of 2N and the crucial systems would be totally redundant. If one crucial system had a failure, another would take charge of maintaining operational loads. This would also make possible a degree of parallel maintainability whereby you could carry out maintenance on one system while the other supplies the loads. Regardless of the actual design of the UPS configuration, you must address the key issue of providing sufficient energy usage to the crucial load and keep it cool, which remains the same. If you underestimate the capacity required, it may cause power disruption in the future when you are required to increase capacity. On the other hand, over estimating could lead to excessive cost of initial installation and higher expense of ongoing maintenance.

Determining the Needed Capacity of Electrical Power

Most data centers are normally part of a larger building system. There are proper steps for determining the data center power electrical capacity. When calculating the requirements of power capacity, it is vital to know the difference between the peak power and the steady power. In crucial components installation such as chillers and air conditioning or where there is sharing of standby generators to provide loads beyond the data center, you may require a consulting engineer for a more complex and complete analysis of the sizing of the system requirements.

The figure bellow illustrates a common breakdown of the way the electrical capacity divides among various loads that are in a data center. The breakdown assumes a data center of 465M2 that is in an initial steady state of 50kW critical load and a future steady state of 50kW load. It is assumed the cooling system is direct expansion DX and 480 volts AC of utility voltage.


50% – DX cooling system

36% – Critical loads

11% – UPS ineffiency / battery charging

3% – Lighting

Critical Loads

In developing a fully fledged data center from a single sized environment rack, proper planning starts by determining the critical load size that must be protected and served. The critical load is made up of all the hardware components of IT that comprise the IT business architecture which include routers, servers, computers, telecommunications equipment, storage devices and so on, as well as the fire and security and monitoring systems that provide their protection. This process starts with a list of all these devices, the rating of their name plate power, their requirements of voltage and whether the devices are single phase or of three phase. You must adjust the information of the nameplate in order to reflect the real anticipated load. Studies from reputable firms of consulting engineers indicate that in most IT devices the rating of the nameplate is way higher than the actual operating cost by at least 33 percent. The US regulatory body, the National Electrical Code, and most other regulatory bodies throughout the world have recognized this fact and therefore permit planners of electrical systems to calculate for anticipated loads the nameplate data by a factor of diversity, in anticipation that not all devices are operating at full load all the time. You may alternatively use an advanced calculator for sizing. Such calculators gather data of power consumption from a broad range of manufacturers and carry out specifications of various configurations of equipment.

Sizing the Electrical Power System

There are two numbers that will help in the size estimation of the electrical system that in turn powers the environment of the data center. This is the total cooling load and the total critical load. Generally, there must be a large enough electrical supply to the sum of the two numbers and the related lighting loads of the data center. The steady state consumption of power of the loads in a data center establishes the consumption of power in order to determine the electrical costs. Nevertheless, you cannot size the generator power and electrical service sources which provide power to the data center to the steady state values. You must size these sources to the peak consumption of power of the loads and any over sizing or de-rating margins required by standard practices of engineering.


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