Data Center Temperatures and the News

I use a variety of ways to track the news these days and few use traditional paper publications.  I mostly use web-based and, yes, cloud computing applications to manage the inflow of news. These primarily consist of Google Reader, Google alerts, Twitter, and email newsletters. I bring this up for two reasons:

#1. Because unlike physical magazines or journals I don’t actually own any of this content I read.  It’s all stored somewhere else, in various data centers around the world, waiting for me to access it.

#2. It’s a great example of how web-based tools can increase the efficiency of my life, and even decrease my energy footprint.

This latter point is important, because it’s what a lot of us people interested in data center efficiency stress all the time: we don’t want people to stop using data centers and the tools they provide, we just want data centers to follow best practices and minimize their energy footprint while providing the same level of service.

As an example of my news review practices, I just skimmed the titles of probably over a hundred articles in a pretty short time (~30 minutes). Of the few articles I actually skimmed or read, I found this interesting blog post on the data center temperature debate. This is not a blog I follow, or an issue I follow particularly closely, but after scouring my many news sources this is the article that caught my eye enough to post about.  It does a good job of explaining the issues around data center temperature setpoints and the arguments of whether they result in energy savings.  The bottom line, as usual, is that energy savings will likely depend on your specific situation – if it allows you to cool more with outside air it’ll likely help, if it just causes your server fans to kick into higher gear it might not.

I’m not going to take one side or the other on this issue, but what I think is interesting is this: for years, engineers have overdesigned everything. Structures are built with a factor of safety of many times the needed strength; capacities are built out well over requirements just in case more is needed later or something goes wrong; and, yes, data centers are kept much colder than they need to be just to be safe. In some cases these decisions are based more on superstition than sound engineering. One of the things computers and servers have given us is the ability to dial in and optimize some of these design points through computer aided design, advanced monitoring, automated controls, etc.

Here’s where it all comes together:  these new tools should allow a savvy data center operator to dial in the correct cooling level across the data center and not have to significantly overdesign the cooling system or setpoints.  Good monitoring should identify problems quickly or even before they occur.  Good controls should alter settings to compensate for potential problems.  The two together should be tuned to optimize efficiency and decrease costs.  I’d be willing to bet that for the majority of data centers there can be significant energy savings by increasing temperatures, but you need to use these tools to address potential hotspots and to determine if that increase should be 1 degree, 2 degrees or 10 degrees.  Too much or too little and there may not be savings, or worse, there could be an increase in energy use.

So, in summary, we continue to keep using computers and data centers to increase efficiencies across all aspects of the economy, and, of course, use these techniques on data centers to slow the energy growth of these tools themselves.

Now, if I could just get the Economist to forward my magazine subscription to my new address.  How could this possibly take 3 weeks in this day and age? Maybe that will be the subject of another post. No matter, I’ll just read it online…

“Energy Savings” versus “Demand Reduction”

A funny thing in the efficiency and utility segment is the constant confusion between power and energy, or between kilowatts and kilowatt-hours. Even among engineers who clearly know the difference, it’s interesting that people are still constantly confusing the two, or at least use them interchangeably in situations where you really can’t.  A sure way to insult an energy engineer is to say they “can’t tell a kW from a kWh.

Technically, power (kW) is an instantaneous measure of the rate in which you’re using energy, while energy is a cumulative measure of how much of a resource you’re using.  Confused?!

Another way to think of it is that our resources, such as coal or natural gas, store a certain amount of energy. The power you draw dictates the rate at which you are using this energy.  If you draw more power you’ll use up your coal more quickly.  If you use less power your coal will last longer.  Obviously using less power is a good thing because your resources will last longer.

Turns out this distinction between power and energy is very important in the utility industry, and therefore effects how they run their conservation programs.  As residential customers, most people are used to being charged by the kWh, a measure of cumulative energy used.  A residential utility meter therefore measures the cumulative kWh you use in a given month, which is what the utility charges you for.

One of the chief goals of conservation programs is to reduce the peak power draw (kW) on the system, and not necessarily the overall energy used.  The peak demand is what dictates how many power plants need to be running to service a population.  Utilities that are trying to delay the construction of new power plants will look to reduce the peak power demand from their customers.  For this reason, large energy users (such as commercial and industrial customers) will pay not only for the energy usage, but also for their peak demand usage.  This gives a clear pricing signal to the customer to reduce peak demand.

A lot of utility energy efficiency programs will focus on reducing demand and will pay incentives based on reductions in peak kW – not kWh savings.  Austin Energy and Southern California Edison are two examples I’ve found of utilities that base some incentives on kW reduction.  Often this reduction needs to happen during times of peak demand to be eligible for incentives. Typically peak demand occurs in the middle of the afternoon on a hot summer day when everyone is running the AC. In contrast, here in the Pacific Northwest almost no one has AC but most people have electric heat, so demand peaks on cold winter days.

To illustrate this concept, here’s a peak load curve on a natural gas plant I found at natgas.info.

This topic came to mind as I’ve been preparing my materials for my talk at AFCOM, where I will be summarizing data center utility incentives to data center managers and IT professionals. I’m seeking different ways to explain these concepts in simplified terms so that industry members can understand the utilities’ motivation in running conservation programs.

This whole concept reminded me of a neat article I read a while back about an Arizona data center taking advantage of time-of-use pricing.  The data center has installed a system that makes ice at night and uses that ice during the day to cool the data center.  While systems like this don’t necessarily produce energy savings, they create a significant amount of peak demand reduction by shifting that demand to off peak hours (this approach is often referred to as “load shifting”).  The local utility (Arizona Public Service Co.) charges only 2¢ per kWh for off peak energy and 13¢ per kWh for on peak energy.  In this way, the company can save 11¢ per kWh (or 85%) on their energy costs by shifting the demand to off-peak hours (this is probably not quite true since there are likely some loses associated with the load shifting but you get the point).

One of the attractive things about the “smart grid” or “smart meters” is the ability for utilities to offer different prices based on time of use to residential customers so that consumers can reduce their individual peak demand.  This would help further flatten the load profile, reduce the number of power plants needed to service the population and help make electricity production more efficient.

I’m sure that I, like others, will continue to interchange the words energy and power when talking about conservation, but it’s often important to recognize that difference when identifying opportunities to increase efficiency in the system.