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While it may seem like a silly obsession, I have been enthralled by the simplistic notion of ice energy storage. I generally subscribe to the KISS principal, and you’d be surprised how often I get in heated debates at work and at conferences about how the best solution is the simplest solution.

The whole idea of freezing ice in the evening when power is cheap and then melting the ice during the day is so simple it is brilliant. It isn’t very different to when one of Sentilla’s founders, Rob Szewczyk, observed that you can compute how much energy any piece of equipment is using (from washing machines to computers) if you know how much work it is doing.

I first heard about ice energy storage about 3 years ago, when an urban legend was circulating through the IT community. A gentleman named Bill Beck had been rumored to store ice in the basement of a Credit Suisse building on Madison Avenue in New York City. First, who would even believe you if you told them you were storing ice in the basement of a Manhattan skyscraper? Second, you’d probably think Mr. Beck was simply crazy — why create vats where ice could be stored simply for cooling data centers (not even the building as a whole!)? Today, Credit Suisse calls these vats “slush tanks”. While no one will confirm the rumors, I’m inclined to believe they do exist.

The most publicized instance of ice energy storage is with the new Bank of America building at One Bryant Park, also in Manhattan. They’re not the only ones, the USGBC estimates that there are thousands of ice energy storage projects in the US. For example, Glendale, California has begun installation of a 53MW ice energy storage project. Here’s the idea: we store ice at night when energy is from wind power (renewable, and thus low carbon impact) using refrigerant that freezes water in a tank. During the day, the same refrigerant flows through the tanks, and due to the higher temperature, melts the ice (which cools the refrigerant) which is then used in the chillers. It is even more of a “win-win”: the air pumped from the ice cooling is actually colder, increasing occupant conform during the summer months.

Why even bother with this “complex” process? The idea is fairly simple (only complicated by the utility companies): if I reduce the total “demand” of the building, then I reduce its energy bill. Commercial and industrial electricity users are charged by both how much they consume (consumption rate) and the maximum demand (demand charging). So if I use 1MW of electricity on average (8.76 million kWh) but my peak demand is 2MW, I get charged for the 8.76 million kWh plus a monthly demand charge for the 2MW (typically charged per kW demand). Why? The electricity company has to provision that amount of power distribution in their substations, so they’re charging for the cost of maintaining the distribution of that much power.

As a result, if you can smooth out your consumption so that there’s less peaks, you can reduce your electricity bill. This is exactly what Bank of America and Credit Suisse are doing. Use more energy at night when the consumption rate is cheaper and demand is lower, then use less electricity during the day when demand is typically higher and consumption rates are higher. Seems brilliant, but what I love about it is that it is simply brilliant.




  1. Heitor (Reply) on Thursday 26, 2010

    That idea is really brilliant! It’s a shame though, that would take SEVERAL years to implement this in business buildings all around the world; specially in developing countries like mine – Brazil – where things take a long time to happen. :(