Data Center Waste Heat Reclaimation

For several years I’ve been interested in PUE<1.0 as a rallying cry for the industry around increased efficiency. From PUE and Total Power Usage Efficiency (tPUE) where I talked about PUE<1.0:

In the Green Grid document [Green Grid Data Center Power Efficiency Metrics: PUE and DCiE], it says that “the PUE can range from 1.0 to infinity” and goes on to say “… a PUE value approaching 1.0 would indicate 100% efficiency (i.e. all power used by IT equipment only). In practice, this is approximately true. But PUEs better than 1.0 is absolutely possible and even a good idea. Let’s use an example to better understand this. I’ll use a 1.2 PUE facility in this case. Some facilities are already exceeding this PUE and there is no controversy on whether its achievable.

Our example 1.2 PUE facility is dissipating 16% of the total facility power in power distribution and cooling. Some of this heat may be in transformers outside the building but we know for sure that all the servers are inside which is to say that at least 83% of the dissipated heat will be inside the shell. Let’s assume that we can recover 30% of this heat and use it for commercial gain. For example, we might use the waste heat to warm crops and allow tomatoes or other high value crops to be grown in climates that would not normally favor them. Or we can use the heat as part of the process to grow algae for bio-diesel. If we can transport this low grade heat and net only 30% of the original value, we can achieve a 0.90 PUE. That is to say if we are only 30% effective at monetizing the low-grade waste heat, we can achieve a better than 1.0 PUE.

Less than 1.0 PUE are possible and I would love to rally the industry around achieving a less than 1.0 PUE. In the database world years ago, we rallied around the achieving 1,000 transactions per second. The High Performance Transactions Systems conference was originally conceived with a goal of achieving these (at the time) incredible result. 1,000 TPS was eclipsed decades ago but HPTS remains a fantastic conference. We need to do the same with PUE and aim to get below 1.0 before 2015. A PUE less than 1.0 is hard but it can and will be done.

So, a PUE of less than 1.0 is totally possible but doing it efficiently and economically has proven elusive so far. The challenge is finding a process that can make use of the very low grade heat produced by data centers and turn it into economic gain. The challenge is producing economic gain from the low grade heat where the economic gain exceeds the combined capital and operational expense of recovering that energy.

In the posting Is Sandia National Lab’s Red Sky Really Able to Deliver a PUE of 1.035?, I pointed to an innovative sewage waste heat reclamation system in Norway: Flush the loo, warm your house. In this system, heat pumps are used to reclaim waste heat from sewage and convert to home heat.

Other possible applications of waste heat are heating green houses to allow the growth of valuable crops in adverse climates. See Vertical Farming for most radical extension of these ideas. Another possible approach is to grow biodiesel from microbes and use the low grade heat as a heat source for the culture. See A Better Biofuel for an example of this approach.

Yesterday, I came across an interesting application of waste heat reclamation from datacenters from Helsingin Energia (Helsinki public energy company).

In this proof of concept datacenter that will come on line next month, they have a conventional datacenter water cooling design but rather than releasing the waste heat to the atmosphere via a cooling tower or related technique, they run it through a heat pump to add heat to a heating loop to heat homes in the Finnish capital. The data center is located in an unused bomb shelter.

In a conversation I had earlier today, the project manager Sipilia Juha said:

We provide facilities for datacenter operators including underground property, electricity and cooling. We can capture almost 100% of the heat that comes out of the datacenter and put it in to the district heating system to heat buildings in Helsinki. Our customers make the detailed planning inside the premises and bring their own IT-equipment.

The cooling costs for the customer from 7€ to 20€ per MWh depending on the size of the center and of the time in the year. We can do it very ecologically and economically.

Computerworld also talked to Juha: Green Data Center Recycles Waste Heat.

I’ve been unable to get the details on the capital cost, the operational costs and the estimated cost recovery time and model used. The facility won’t be live until January so, even with good cost models, they wouldn’t yet be calibrated by real operational experience.

They are aiming for a PUE of around 1.0 and its quite conceivable they will get there:

The energy efficiency of computer halls is quantified by the so-called efficiency factor which expresses the ratio of the total energy consumption and the energy used for actual computing. The efficiency factor of ordinary computer halls is between 1.5 and 2, with the figure for computer halls deemed to be extremely ecoefficient possibly under 1.5. The efficiency factor of Academica’s and Helsingin Energia’s hall is around one, and it is possible to get even below this figure.

The next test is to see if this level of efficiency can be achieved in a economically positively or at least without loss. It’s an interesting project. I’ll continue to watch this and similar proof of concept facilities closely.

A brochure from Helsingin Energia is at: Hel_En_Eco-efficient_computer_hall.pdf (1.93 MB).


James Hamilton



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4 comments on “Data Center Waste Heat Reclaimation
  1. Shawn says:

    Please continue your discussion.
    I am very interested to see equations relating to sub-1 PUE calculations.
    Meta’s ODN Data Center normally has about 1.15 PUE but I’ve seen it as low as 1.08 during testing.
    ADDITIONALLY, it was the first hyper-scale data center in the world to utilize municipal waste heat recovery.
    What’s your method for incorporating this added power utilization?

    • Nice work. 1.12 to 1.15 are pretty good PUE numbers if you can deliver them annualized. On your 1.08, there are always great times of the year so I ignore these and only look at trailing 365 days to factor weather variation out of the metric.

      Generally, to get better than a PUE of 1.0 you need to be recovering sufficient heat energy to more than cover your power distribution and cooling overheads. In your case, you are directly selling the heat energy rather than using it to generate electricity to power the facility so it’s not quite a direct less than PUE 1.0 candidate. However, a reasonable approach is to take what the heat customer is willing to pay for the heat and use that payment to cover a portion of your power budget. Given your current PUE of 1.12 to 1.15, if you could get your heat customer to pay for more than 15% of your total power budget, you would have a better than 1.0 PUE application. And, even if you don’t get quite that large a payment (likely the case), it’ll reduce your PUE closer to 1.0 and it’s good for the environment.

  2. Eas, I did know about the Seattle steam plant. In fact, I live only two blocks away from the plant. Many corporate complex use central heating plants. For example, the Microsoft corporate campus uses central heat over the central part of their facility. If we can get heat reclamation cost effective, there are plenty of places where it can be applied.


  3. Eas says:

    I’m skeptical of biofuels in general. They have high demands for fresh water, and they aren’t a very efficient use of land compared to photovoltaic or thermal solar electricity. Food growing greenhouses may be a better option, as long as they don’t rely on artificial lighting.

    On the heat recovery front, did you know that Seattle has a private steam utility that serves a number of downtown buildings? I’m pretty sure that it was originally a way to make use of waste heat from urban generating stations. I don’t think Seattle is alone among older cities in having that kind of working infrastructure. Perhaps it is something that could be leveraged for heat recovery from urban datacenters. I wonder about the cost and efficiency of heatpumps that could boil water.

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