Case Study 1 : Electric Current 23

Case : 

You have been asked to determine the number of servers that can be mounted in a newly installed rack in the data center. The facilities team has already installed the standard 5KVA UPS in the rack in the bottom rack position.

Server Information:

Power requirement per server – 110 volts AC

Current draw per server –3.75 amps per server

UPS Capacity –  5.0 KVA

This paper has been written in research paper format, however contains good info, good references, and good equation formulas for solving, hope this helps.

KVA = Colts * Amperes / 1000


Thank you for acquiring with us, in regards to your server racks, I understand that you want to know the number of servers that can be mounted in your new rack. There are a few key components of knowledge that’s needed to ensure the proper amount of servers for your rack, and to ensure your servers will run efficiently, and effectively. To determine the amount of servers needed, it’s important to know the KVA per server, or Kilowatts volts amperes per server. Based upon the data that was provided to use in regards to server information, and server power, we have provided this information below.

KVA = Volts * Ampere’s / 1000

KVA = 100 * 3.75 / 1000 = 0.375 KVA *per server


With these 0.375 KVA’s per server a rough total estimation of the amount of servers that will be needed with be around 13 per rack. However, this is not a permanent number, there are a number of things to take into consideration when it comes to mounting your servers, that affect your overall power supply, and how long these servers will last as well. “In a recent survey conducted by the Uptime Institute, enterprise data center managers responded that 42% of them expected to run out of power capacity within 12-24 months and another 23% claimed that they would run out of power capacity in 24-60 months,” (42U) that is why it is important to pay attention to energy efficiency and consumption.

A key factor that is important to remember is that although you have a 5.0 KVA UPS the amount of “Real Power” or capacity is yet to be determined without the power factor of your rack. This key information will need to be provided in order to fully evaluate or determine the amount of servers needed. In addition, a primary factor that needs to be addressed is what type of cooling systems you have set in place for your servers, and with knowing this, knowing the type of rack you have is important as well. For example, is your rack fully perforated, meaning does it contain holes, or is your rack fully sealed? Knowing this vital information will help us to determine your cooling system, to then determine the final estimation of servers you will need for your rack. Lastly, what is important to note is space, meaning space of your servers, this will determine the amount of servers per rack, and also it affects the cooling system of your rack. The company HP, who also sells server racks, recommends “HP recommends spacing out high power racks, especially as the powerful ventilation systems impact other racks of equipment. They also recommend an average floor spacing of 24sf/rack and a thermal analysis to position floor vents correctly.” (IXEROPE, 3) However, this is only a recommendation; if you want to find out more information about rack spacing you can do so by contacting the manufacturer of your rack.

Once I have been provided with this vital information I can better answer your question. Also providing us with the power factor of your rack to determine real power is also needed.


IEXUROPE. (unknown). Data Centres. In High Density Rack Configurations and their Associated Cooling Issues. Retrieved Jan 25, 2013, from

42U. (unknown). 42U. In TOP CONSIDERATIONS WHEN BUYING A SERVER RACK. Retrieved Jan 25, 2013, from

ABR Consulting Group. (unknown). Electrical Conversions. In Electrical Unit Conversions. Retrieved Jan 25, 2013, from


Jasmine Shavers







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