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Going Green with Data Center Heat Recovery - Yes, It's an Option

Data center heat recovery is an attractive option for data center owners of all sizes because it transforms the data center from an energy consumer into an energy producer. 

Data center customers today care about energy efficiency and minimizing the environmental impact of their data center operations.  There are various ways to maximize the efficiency of a data center design with efficient cooling technologies, economizer strategies (i.e. “free cooling”), high voltage power distribution, and much more.  However, some customers are looking to go beyond efficient design practices inside their data center and inquire about the ability of reusing data center waste heat for other purposes in their facility.

It is no secret that data centers generate a lot of heat, but whether or not data center heat recovery is a viable option depends upon your load and the financial investment you are willing to make in a heat recovery technology.  For large data centers with IT loads above 1 megawatt, the economics and Return on Investment (ROI) of a heat recovery system become more attractive.  In Seattle, Amazon’s high-rise “Denny Triangle” project recently made news for a partnership they have with the neighboring Westin Building Exchange, a 400,000 square foot telecom hub occupied 70% by data center space.  Heat coming from the 34-story Westin Building Exchange will be used to warm just over 4 million square feet of development on Amazon’s four-block campus, saving 80 million kilowatt-hours over 20 years, or about 4 million kilowatt-hours a year.  In an impressive collaborative between Amazon, Clise Properties, and Seattle, warm-water pipes carrying heat from the data center go into a heat exchanger as big as a refrigerator.  The water travels inside the exchanger along stainless-steel plates, which transfer the heat to cooler water that is making a separate trip under Sixth Avenue from Amazon’s Denny Triangle campus.

Data Center Heat Recovery

Intel’s data center in Israel is an example of a single-tenant heat recovery system; they used heat recovery chillers to capture data center waste heat and reuse it to heat the building in the winter and provide hot water for kitchen and bathroom use.  Intel’s data center had 1.3 megawatts of IT load and found an ROI on their heat recovery system of approximately 1.7 months.

Recycling Heat in the Data Center

Diagram of Intel’s Heat Recovery System.  Source: Intel

For smaller data centers, heat recovery is an option but the ROI may not be as attractive as those found with larger companies like Amazon and Intel.  The capital cost of adding heat recovery equipment (chillers, heat exchangers, heat pumps, etc) and the additional real estate required to do so often pushes the ROI on these investments beyond 5 years. This may seem like a short timeframe given that a data center asset is typically built for a 20-30 year lifecycle, but many owners evaluate the added cost of data center heat recovery like they would any energy efficiency project.  An additional challenge is that smaller data centers may not produce enough heat to support an entire building and thus standard boilers or air handling equipment used for building heat will still be required.

For smaller data centers interested in heat recovery, an option to consider is to reuse exhaust heat to ‘preheat’ the water in your building HVAC loop.  In doing so, you can reduce the amount of work your building’s boiler will have to perform in order to heat the cool return water to a temperature required for building heating.  Reducing the amount of work the boiler has to do also reduces the amount of fuel the system will consume.  Washington State University’s data center is an example of a smaller data center that utilizes this strategy.

Heat recovery is an attractive option for data center owners because it transforms the data center from being an energy consumer into being an energy producer.  There are a number of options available to utilize heat recovery in your data center, but all require careful up-front planning and cost analysis to ensure they can be utilized as a successful component of your data center project.