Calculating power consumption and dataroom AC

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Calculating power consumption and dataroom AC

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Hi there,

Trying to figure out my power consumption of servers with respect of installing a new AC unit and potentially adding a battery pack on UPS. By no means do I consider myself an electrician so I would value your input.

I am basing my calculations of this article where in essense the formula is: Equipment BTU = Total wattage for all equipment x 3.5

Q: Is it safe to assume that if a server has dual power supply to double the wattage used?

After digging through some dell docs and random sites I gathered the following info and I am not sure if this is correct assumption:

 

Dual Power Supply  Wattage  Total Wattage
PowerEdge 850 no 345 345
PowerEdge 1550  no 240 240
PowerEdge 1750  yes 320 640
PowerEdge 1750 yes 320 640
PowerEdge 1850 yes 550 1100
PowerEdge 1850 yes 550 1100
PowerEdge 1850 no 550 550
PowerEdge 1950 yes 670 1340
PowerEdge 2850 yes 700 1400
PowerEdge 2900 yes 930 1860
Grand Total Wattage: 9215
Total BTU needed: 32252.5

1 Ton of cooling = 12K BTUs roughly needing a 2.6 Ton AC unit.

Does this sounds right? Your thoughts?

Granted I am not including the room size etc. but I just wanted to make sure that I am calculating the consumption of servers correctly. I have also read that these are just starting numbers and that number of disks in raid and memory sticks in server will draw more power...something as adding 10W per per disk/memory stick...is this true??

Thanks for your time!

Verified Answer
  • No , you need to use the clamp over individual wires, not over a 3 or 4 wire bundle in a cord. Best to find the circuit at the breaker box, remove cover, and clamp on one of the circuit legs off the breaker. I would leave it connect for a day , monitor it for peak power consumption. You will need to get lighting power consumption figured into the total, and heat gain through wall/floor/ceiling/door.

All Replies
  • Doesn't dual power supply equipment only require the power of one supply, so that if one fails, it will keep working normally?

    Now if it's triple power supply, that could be the power of 2 of them, with the ability to only lose one.

  • Exactly ... they are typically for redundancy/failover, not for extra power.  Larger servers with 3-4 power supplies do use 2-3 of them for total power load, with a failover.  Some servers with dual power supplies will actually do load balancing, but not to exceed the wattage of a single power supply - simply to reduce the load on any one unit.

  • But they both are 'live' by simple fact that are powered no? Doesn't that imply they are using some power?Maybe adding 20% of 1 power supply and 100% of the other is fair usage?

    Again, I am no electrical engineer but rather an admin and this is slightly out of my scope...or learning process at least to say.

    Do you think that the formula in the article is good approach to calculating AC power?

    I also read at this article that power consumption might go up depending on # of disks and memory. Is this true?

    ...that disk drives require about 10 watts and each GB of memory requires about 12 watts...

    Thanks guys!

  • With varied equipment you have, the easiest method to get the total wattage use would be to use a clamp on ammeter (preferrably with a peak hold) on each circuit feeding the room, adding all the amperage draws of all the circuits, multiple this by the voltage, giving the total wattage of the room, not an Engineer, but I would add approx 25% to that for expansion/ambient building temperature changes/peak usage times.

     

  • Thanks,

    I am running it all through an APC SmartUPS 3000XL with 2 additional battery packs....would it be an accurate measurement if I just inserted the ammeter between the UPS and wall plug? ...sort of just clamped it on the 1 power cored powering the UPS.

    Thanks a bunch!

     

  • No , you need to use the clamp over individual wires, not over a 3 or 4 wire bundle in a cord. Best to find the circuit at the breaker box, remove cover, and clamp on one of the circuit legs off the breaker. I would leave it connect for a day , monitor it for peak power consumption. You will need to get lighting power consumption figured into the total, and heat gain through wall/floor/ceiling/door.

  • I strongly suggest you leave any current measuring to qualified electricians/electrical engineers. Do not open any service panels since there is exposed wiring capable of providing lethal currents and voltages.

    The safest way is to determine what configuration of your dual power supplies are running in is to find the manual online or contact the service representative. Dual supplies typically are configured to run with only one providing the power or both providing half the power each but never double.  The amount of power the "off' supply is probably less than 10%.

  • Get one of the meters from Megger.  It uses hall effect sensors to allow it to give you a reading while clamping all of the wires in the cable.

  • Agree with engr00 the power at a breaker panel can be dangerous, so get either an electrician or the building engineer to get your readings if your a candidate for the Darwin Awards. Using the info from the manuals will not give you the peak wattage used nor will it give you an accurate average usage of the server room , as a meter which can do both peak and average will. The room may or may not have more then one circuit for all plugs, lighting will also be on a separate circuit form the plugs.

  • Dell has an online tool for capacity planning, www.dell.com/.../config_calculator

    This can work out power and cooling requirements for your estate.

  • p

  • Definitely a lot of free tools.  ESSA AND DCCP.

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