Last week I wrote about interesting stuff that UNH is doing in space, but there’s something interesting on the ground in Durham, as well. A big something. Big and cold.

Admittedly, it doesn’t sound all that interesting. It’s just a giant water storage tank that has arisen in the middle of campus over the past year. 

But it intrigued me because it doesn’t actually store water even though it stores water – it really stores energy, making it part of the huge transition happening to the electric grid. 

I learned the details about the system from a talk given by Adam Kohler, executive director of Energy and Utilities at UNH, at last week’s Energy Symposium in Concord. 

UNH has long used water to cool 11 of its main campus buildings. The water is cooled by big industrial chillers that use a lot of electricity. When the school decided to build the Spaulding Life Science Center, they knew they needed more cooling capacity. The obvious move was to build another chiller but UNH has been trying to be efficient in both energy use and spending, so they wondered if they couldn’t take better advantage of the current system.

Electricity, as you know, is hard to store, which is why we have a system that can generate exactly as much electricity as is needed at any given time. This requires having enough power plants to meet the maximum demand known as peak load – usually mid-summer afternoons when AC is blaring everywhere – even though some of that power production isn’t needed much of the time.

That is inefficient and expensive. The solution is to store some of the electricity we generate when demand is low – overnight or weekends – so it can be used when demand is high, reducing the number of power plants needed to meet peak load. This need for storage is why so many batteries are being installed these days.

But chemical batteries aren’t the only way to store electricity. The Durham water storage tank does it indirectly: It takes energy from electricity, stores it in the form of water temperature, then releases the heat to displace future electricity needs.

In other words, it’s just a great big battery.

As Kohler explained it, even in mid-summer there are hours when the chillers generate more cool water than the buildings need, such as overnight. These periods also tend to be when electricity is cheapest.

UNH will run the chillers on cheap electricity at night or on weekends and fill what’s known as the TES, or thermal energy storage tank. When temperatures rise the following day the cool water can be discharged, reducing the amount of work that the chillers have to do when electricity is expensive. This is a closed-loop system, reusing the same water over and over.

“We have effectively doubled the capacity of the chiller plant without adding generation,” Kohler said.

An extra financial benefit: This helps UNH avoid demand charges, an extra fee that electric utilities charge following moments of very high usage. Demand charges can be a huge extra cost, increasing the benefit if you can “trim the peak” of your power usage.

All that is straightforward enough but even so building the thing took more than seven years, even though construction only lasted eight months. The idea was first formally recommended back in 2017 in an analysis by Jaclyn Kinson, a fellow at the UNH Energy Office.

The long delay was partly due to COVID and then the resulting inflation and partly due to size. The tank holds 1.4 million gallons of water, equivalent to two Olympic swimming pools.

There are also technical issues. The system is more complicated than standard water storage because you have to make sure that the water doesn’t mix as you add it. You want stratification, when layers of water exist at different temperatures, to get the biggest benefit. Ideally, he said, there’s a 12-degree Fahrenheit difference between where water comes in after going through the cooling system and when it discharges.

Another thorny issue was placement. The tank was going to be tucked away on a parcel further away from the center of campus but that added six figures to the cost due to the need for underground piping, which is always a joy to build in the Granite State.

Instead, the tank is prominently placed alongside the chillers, which are near Philbrook Dining Hall and passed daily by thousands of hungry students. That raised the questions of aesthetics, something that Kohler, a mechanical engineer, admitted isn’t usually prominent in his planning.

Is it less visually disruptive to be tall and skinny or short and squat? (Short and squat won out.) And what about the exterior? Kohler showed slides of some handsome design possibilities that were put aside for cost reasons; the tank now has panels with various shades of blue, the color of water, and while it’s nice enough it won’t be a highlight on architectural tours of campus.

Total budget for the project was $10 million, about a quarter of which was covered by the Inflation Reduction Act, a far-thinking piece of federal legislation that is likely to be gutted by the privatization fanatics in the Trump Administration. The payback period – the number of years it will take UNH to save $10 million in electricity cost – is uncertain at the moment, since there’s not a lot of cooling done in the winter so actual data isn’t being collected. You also have to factor in the money that UNH avoided by not having to build another chiller.

In the big picture, this is exactly what the grid needs: More intelligent use of existing electricity generation rather than building expensive towers and wires and substations and power plants. Whether it comes via energy efficiency, battery storage or a great big tank of water isn’t important, as long as it happens.