Heating with ice

Key Takeaways

Thermal storage, where ice is made at night using off-peak electricity and used to cool buildings during the day, is a cost-effective and efficient way to reduce the electrical demand on the grid.
-> Thermal storage is suitable for buildings in different climates and sizes, with smaller applications possible for places of worship or buildings with peak loads on specific days.
-> Considering energy storage early in the design process can lead to more sustainable and efficient buildings.
-> Building operators may require training to understand the concept of thermal storage and operate the associated equipment effectively.

Speakers

Q&A

Whitney Smith: As an industry, we’re really looking for transformative technologies that can help us decarbonize at scale. Can you explain thermal storage technology to us?

Mark MacCracken: Essentially, thermal storage is when you make a lot of ice at night using inexpensive off-peak electricity, and then during the day, you use that ice to cool the building. This dramatically reduces the electrical demand on the grid, and it saves building owners money because electricity is much more expensive during the day than it is at night time.

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Ellen Honigstock: Using ice to heat sounds counterintuitive. How do you explain it to clients?

Mark MacCracken: It is counterintuitive to think that you can store heat in ice, but in reality it’s actually not that. The heat is stored in cold water and when you change that water to ice, it changes from a liquid phase to a solid phase. In order to do that, you have to remove a lot of heat from that water. This phase change happens really close to where we need it for storing heat or storing energy.

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Ellen Honigstock: Is this technology climate dependent? Does it work because of the climate that we’re in?

Mark MacCracken: Buildings are heated and cooled all over the country. The further north you go, the more heating dominant they are. The further south you go, the more cooling dominant they are. In either case, energy is needed. With heat pumps, we take the heat out of the water, make ice, and we pump that heat up to a usable temperature level to put back in the building. We’re able to save yesterday’s waste heat for tomorrow’s heating, and that’s the beauty of what thermal storage is.

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Ellen Honigstock: As buildings continue to electrify, we’ll be seeing more use cases for energy storage. How does this type of thermal storage compare with other types of energy storage?

Mark MacCracken: There are many different types of energy storage. There’s potential energy; hydro uses potential energy. You take water and you pump water up a mountain and you make a lake. During the day, when you need the energy back, you let the water come back down. The problem with pumped hydro is it’s only about 70% cycle efficient and we don’t all have mountains near cities where we can pump this water.

There are electric batteries, like the ones in our pockets. If you just take an electric battery, like a lithium ion battery, and put it on the outside of the building, that doesn’t make a whole lot of sense. It’s not legal in New York because of safety concerns.

You want electric batteries for electric loads and thermal storage for the thermal loads, either heating or cooling.

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Whitney Smith: Thinking about the building operator’s perspective–what does the controls system look like for the technology and how does it work? What training, if any, would the operators of these buildings need to be able to transition to working with this type of equipment?

Mark MacCracken: The biggest part of it is to get people to think that there’s heat in cold water. We’ve got lots of jobs where people are well-educated on doing the cool storage part of it, and they are very familiar with chillers. Chillers are big heat pumps and we’re going to operate these chillers in the winter time and take heat out of water to make ice just like the summertime.

The training is needed here because now we’re not going to pipe it to a cooling tower, we’re going to pipe it to the coils in the building. Our company is developing controls to kind of do it all, but there’s going to be education.

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Whitney Smith: Can you talk a little bit about the level of efficiency that this system can bring to a building?

Mark MacCracken: First, let me demystify heat pumps. Heat pumps don’t make heat. They use energy to move heat from one temperature level to a higher temperature level. You put one unit of heat in, and move four or five units of energy up. That is the reason that these things can be 300% efficient, 400% efficient, 500% efficient, because they’re not making the heat. They’re using heat to move heat.

If you’re comparing it to fossil fuels, it may be 90% on a good day. We’re talking 300% efficiency with a heat pump, so there’s big gains there.