# Thread: How calculate power consumption?

1. Web Hosting Master
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## How calculate power consumption?

Hello, could calculate real monthly cost of electricity in a 42U rack (A+B 16 Amp AC @ 230V) with the following equipment.

35 Servers 1U (intel quad-core, 8gb, 2 hd sata, ~160W each)
2 x 24 switches (~110W each)

The price of electricity is 11cent € kWh.

Thanks.

2. Aspiring Evangelist
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You aren't going to be able to run that amount of equipment on 16amps, let alone keeping the supply at a maximum of 80%.

It'll cost you around €450 - €500/mo.

Work out the total wattage, divide it by 1000, times it by 24 hours, times it by 30 days. That'll give you the total KW/mo. Then times the total KW/mo by the price per KW.

So 5600 watt's for the servers and 220 watts for the switches = 5820 watts/hr

5820W/hr, x 24 (hours) = 139680W, x 30 (days) = 4190400W / 1000 (to make KW/mo) = 4190KW/mo

Take the price per KW (€0.11) and times it by total KW/mo (4190KW/mo) = €460

Of course your never going to get a 100% accurate price, but it's a decent guide price.

unless my calculations are wrong, which is likely as it's 2am.

3. Web Hosting Master
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In a little more detail...

Watts = Volts x Amps
so
Taking wattage numbers.
35x160+2x110 = 5820Watts used total
Amps Req = 5820 / 230 = 25.3A lets call it 25A that over the 16A as pointed out above.

Now as for the cost, you simply multiply the total wattage x number of hours in the month and divide by 1000 (1000W = 1KW)

So you actual cost if you get a 25A circuit would be

Hours in month = 24 x 30 (assuming 30 days in month) = 720
Watts used = 25A x 230V = 5750W
Kw used = Watts/1000 = 5750/1000 = 5.75Kw
Kw/h = Kw used x number of hours used = 5.75 x 720 = 4140 Kw/h
Cost = Kw/h's x 11c = 4140 x .11 = 455.4 euro

Dave

4. Web Hosting Master
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I'm a little surprised my provider had estimated a much lower cost.

thanks.

5. Web Hosting Master
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To be honest the power I think the power esitimates you gave look like max power. Most of the time those serves and switches will use less watts than stated so the cost would also be less. Lets say ave watts = 50% max watts the your power bill would be 50% lower as well.

You should pick up a power meter and try one of the serves to get a better estimate.

The following costs about \$25 but is for US 110V but I am sure there is something similar in Europe.

http://www.p3international.com/produ.../P4400-CE.html

6. Junior Guru Wannabe
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Generally, a server of that specification with 80+ efficiency PSUs will use about 0.4A on idle, 0.7A under full load; so about 0.5A typical use (assuming ~120W TDP CPU, 2x RAM, 80%+ PSU). The 24 port switches will on average use about 0.1A each.

35x 0.5A
2x 0.1A
-------
17.7A

17.7A * 240V = 4248W

4248W * 24 hours/day * 28 days / 1000 = 2854 kWh per 4 weeks
2854 kWh * €0.11/kWh = €313.94/4 weeks
€313.94 * 13 / 12 = €340.10 per calendar month - give or take.

But bear in mind, in a DC - you're not just paying for the electricity. You're paying for their UPS, generators, HV circuit, cooling and possibly the PDU itself.

7. Web Hosting Evangelist
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Generally, a server of that specification with 80+ efficiency PSUs will use about 0.4A on idle, 0.7A under full load; so about 0.5A typical use (assuming ~120W TDP CPU, 2x RAM, 80%+ PSU). The 24 port switches will on average use about 0.1A each.
Sorry for the top post, but I had to respond to this. 0.5A at typical use? You're kidding me right? What sort of server is that, P3?

Xeon processors have typical wattage of 60W, HDD each is 30W, add Board, RAM, RAID controller and you can easily get 200W-300W . Divide that up by 110v and total Amps needed will not be less than 2 - 3 Amps. Surge Amps at boot upcan be 1.5 x typical usage amps.

Unless you're building so called "servers" out of desktop grade components, then you'd be at 1 - 2 Amp, but no way with today's Dual and Quad core you'll be getting 0.5 Amp at typical load.

8. Junior Guru Wannabe
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@tamouh

Before flaming, get your facts straight. I quoted @ 240V, not 110V - as per the OP.

My post is based on experience of bench testing and racking ~25 servers of similar specifications to the OP, 1xQC E5620, 3x4GB RAM, 2x2.5" HDD. Using 1x E5620, power is typically 0.5A at 40% load, using 2x E5620's, power is about 0.6A.

No "desktop grade" components in our racks, and not a *single* UP/DP board that consumes anywhere near the figures you have quoted.

In fact, I've just racked this system:

Supermicro X8DTL-iIF
Supermicro 825TQ-R720LPB
2x Intel X5680
6x 4GB DDR3 RAM
4x 2.5" 10K RPM drives

Its typical draw is 1A with BOTH PSU's connected, 1.6A on full load (using Stress Linux) @ 240V.

I'm sorry, but you're obviously not talking from any recent experience. Most UP 1U servers use ~0.5A. If you aren't a believer, have a play with this:

http://solutions.dell.com/dellstaron...unch.aspx/ESSA
Last edited by ben_uk; 06-28-2011 at 03:58 PM.

9. Web Hosting Evangelist
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Ok, I've misread the 220v vs 110v. It makes a great difference. 500W Power supply at 110v requires 4.5 Amps circuit while on 220v is only 2.2 Amps.

Since most new servers will use anywhere from 200W - 350W on 220V circuit your calculations are correct.

But put that on 110v and the Amps need will double easily.

I've seen many people claiming 0.5 Amps for servers and I know that number is impossible with newer type of server grade hardware, loaded disks and RAM even with 220v circuit.

The last server you've quoted can not be 1.5 Amps under heavy load even on 220v. The CPU alone is 130 Watts EACH. Each RAM stick is 10 Watts, each drive is 20 Watts , plus your onboard components. Your reading theoretically should be 2Amps+.

How you checking for Amps usage?

10. Junior Guru Wannabe
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@tamouh 0.5A is more than possible, trust me. We've got half racks, populated with 16 servers and 2 access switches coming in at 8A average usage. All chassis are Supermicro, 1xE5620, 3xRAM, 2x10k 2.5" HDD as above.

You are confusing TDP with actual power usage, they are not the same thing. In fact, we tested L5420 vs E5420 and the power consumption was negligible for typical 40% load.

Plus, none of our drives consume 20W,

VelociRaptor 10k - 6W avg.
Seagate Cheetah 15k - 15W avg.
Samsung Spinpoint F3 - 7W avg.

RAM is more like 7W per stick for 1.5V memory.

For measurement we bench test using a Fluke clamp meter with split live cable set-up. When in the rack, we rely on the cumulative output from the APC 7920 PDUs.

In the UK - power is the single biggest cost, we would be mad not to be anal about measuring/spec'ing equipment!

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To get 16 Amps draw able you need 20 Amps provisioned at 80% utilization.

(20 amperes) * 240 volts = 4800 watts

That's dual 20 Amp circuits (A+B) at 230 V at 80% utilization to get you to 16A for the branch.

You generally pay for 1.5 as you get a 50% discount on the B link.

20 * A * (240 volts) * 1.5 = 7200 watts

Your bill will be for 7200 watts or KVA.

Of the 7200, you'll be able to use 80%=

(20 amperes) * 240 volts * 0.8 = 3840 watts

I would say you are under powered in density to the rack to host 35 servers.

(3840 watts) / 35 = 109.714286 watts per server

Instead, at this density you may be only able to power 20 or so servers safely while still leaving overhead for your switches.

20 * 160 watts = 3200 watts

3200 watts + 220 watts=3440 watts

3840 watts-3440 watts= 400 watts

((3840 watts) - (3440 watts)) / (240 volts) = 1.66666667 amperes

That works out to a spare 1.6666667 amps. So maybe you could add a few servers more.

12. Web Hosting Evangelist
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could the 220v be making that much of a difference?

We've setup 1/2 rack colo before with 8 servers and our usage on low-usage is 9 Amps, on medium/high usage is close to 10-12 Amps. These are all supermicro dual-core or quad-core Xeon servers.

The problem most DCs here supply standard 110v, the 220v circuits end up being more expensive.

Originally Posted by ben_uk
@tamouh 0.5A is more than possible, trust me. We've got half racks, populated with 16 servers and 2 access switches coming in at 8A average usage. All chassis are Supermicro, 1xE5620, 3xRAM, 2x10k 2.5" HDD as above.

You are confusing TDP with actual power usage, they are not the same thing. In fact, we tested L5420 vs E5420 and the power consumption was negligible for typical 40% load.

Plus, none of our drives consume 20W,

VelociRaptor 10k - 6W avg.
Seagate Cheetah 15k - 15W avg.
Samsung Spinpoint F3 - 7W avg.

RAM is more like 7W per stick for 1.5V memory.

For measurement we bench test using a Fluke clamp meter with split live cable set-up. When in the rack, we rely on the cumulative output from the APC 7920 PDUs.

In the UK - power is the single biggest cost, we would be mad not to be anal about measuring/spec'ing equipment!

13. Web Hosting Master
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Ben_uk's numbers look reasonable for calculating average drawer for calculating the power bill if you are getting charged by the kWh used.

But don't forget you also need to know the peak draw across the rack so that you don't overdraw power from the circuit. Assuming Ben_uk's numbers are right for peak also (and they again look reasonable to me), I make that (35 x 0.7 +2 x 0.2=) 24.7A (~6kW) total load.
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edit - I see dmst beat me to it!

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You can also call your selected power utility and they will most likely help you and explain what it would cost.

Your major concern is first metering your power properly. If you can't turn off your hardware then clamp meter your breaker at the breaker box. It can be hard to fit the clap around the wire but you just try to find a smaller clamp then. Google "clamp meter"

I simply cut into the wire (with knifes) while it's hot and then clamp on it. (Don't worry I'm good at it and have never messed up.)

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