Thermal energy storage has often seemed an attractive technology application for data centers – providing a sure-fire way to cut energy costs while delivering redundancy for cooling that isn’t found in most facilities.
Here’s how the case would play out:
You’ve got a data center with a totally predictable day-to-day cooling load, so install a thermal energy storage system sized to the four- or six-hour peak rate period from my utility. (There is a big advantage to having this predictable load; TES systems for offices often fail in execution because control systems are unable to accurately predict loads.)
Make ice or chilled water at night, when electric rates are lowest and when your chiller plant is most efficient due to lower ambient temperatures. Then draw on the thermal bank during peak periods, avoiding peak energy and demand costs.
The redundancy play is that you can provide backup generator power only for pumps and fans, assuming that you’ll have some storage on hand to meet your cooling needs, at least for the duration of a power failure.
The economic model would yield pretty good results for this design: you’ve got to pay for storage, probably an up-rated chiller plant, and controls; in return you get solid, predictable cost savings every summer weekday and probably winter one as well, and some redundancy you didn’t have before that can lower your need for power backup.
So what’s not to like?
In a retrofit scenario, this might all make sense, with the caveat of finding space for the chilled water storage tank or ice bank. (Space limitations could be the leading killer of TES retrofit projects.) You may already have sunk the costs of backup generation for your chiller plant, but the economics may still work out.
But here’s the real rub: the leading data center designs of today don’t use chilled water at all, they rely instead on air-side economizers supplemented with evaporative cooling. No need for TES in these designs, and no need for backup power for cooling beyond supplying the fans.
It’s a much more efficient and elegant solution, and leads me to believe that TES for data centers is an unlikely application.