TCO – Power and Cooling – The Secret Cost

Blog Post created by rugby01 on Jan 22, 2016
  • I’ve been doing Total Cost of Ownership (TCO) worksheet for 20 years now.  The basic TCO in the early days was how much does the current solution cost versus the new solution.  Must companies come in with the same song and dance, upgrade today and we save you money. Over time the TCO guideline has grown, but still some of you are missing some cost.

Way back when I started working with computers it was all about features and TCO was not a topic. In the 90s, the conversation turned to space savings when the old DEC VAX 11/780 could be replaced by a single 2U MicroVax server. The following years we seen you could replace an entire racks of disk with 2x the storage and the cost per square foot came into play.  Sometime after that the CPUs started to multiply cores like and ameba being split and cost per compute cycle was created. Today’s big buzz in TCO is cost per Inputs/Outputs per Second (IOPS). The item most people have is, “What is the cost to power and cool the darn thing?”.

When I complete my TCO worksheet these days I have tons of questions for customers. The number one question that most companies don’t know is cost of power and their Power Usage Effectiveness (PUE).

PUE is the ratio of total amount of energy used by a computer data center facility to the energy delivered to computing equipment. PUE was developed by a consortium called The Green Grid. PUE is the inverse of data center infrastructure efficiency (DCIE) (thanks Wikipedia).

The cost of power is a huge expense for most companies and they just ignore it.  Your power cost could be from $.065 a kWh to $1.50 per kWh.  The PUE comes into effect when you have to cool the air around your environment. The PUE for the average Data Center is around 2, and that means of every kWh used, you need another kWh to cool it.  If you in an old building and haven’t upgraded your HVAC strategy, you could be blowing money across your floor.  Google says there Data Centers run at a 1.1 PUE (90% efficient).  At a 1.1 PUE you only need 10% the power for HVAC.

Great engineers have come up with simple ways to enable cooling and heating facilities. I have seen data centers go into warehouses with 40 foot ceilings and simply put vents into the roof to let the raising heat out the holes. The theory being heat raises and just let it go.  That was such a brilliant change, and cheap to deploy. All we did was stop cooling hot air.


So what does the cost of power mean to you?  Let’s take a standard rack in Oregon ( and 10 racks consuming 10kV.

PUE        kV Gear                kV Facility            Cost Per Year (.0726 per kWh)

2.0          10           10           $12,720

1.5          10           5              $9,540

1.1          10           1              $6,996

2.0          1000       1000         $1,271,952

1.5          1000       500         $953,964

1.1          1000       100         $699,574

Just a single rack you could be wasting $5,724 per rack. Say you have a small data center with 4 racks, you might be wasting $22,896 per year on power.

What can you do to lower that cost?  Two things, you can buy gear that runs on less power and thus also reducing the cooling cost. Upgrade that building to use air better. I know in several states they have programs around reducing data center power consumption and will pay up to 60% the cost.   These funds can be used for HVAC, Disk Storage, and Compute that you could lower your consumption and PUE.

So next time you’re talking with your CFO, ask the question, what do we pay for power? What if I could decrease that by 45%?

We have seen cases where installing a NImble Array reduced power and cooling 10X. Do you have any stories around the TCO savings?