Phase change. Latent heat. Energy efficiency. And how ice can be used to heat up our homes.
1-Minute NomNom
Cold day? How about using some ice to heat up the house?
WhaaaaAaaaaattt??! Yes you heard right, but first a little bit about ice and temperature.
Ice is usually used to cool things down. For example, we might use ice cubes to make a cold drink (ice-cold drinks anyone?). We even find ways to make that perfect ice cube that does not melt as quickly so that our drinks can stay cold longer (find out how in the 1-Minute NomNom “It became clear that the ice cube thought it was cool to let off some gas“).
One big reason ice cools is because of the latent heat, which is the the amount of heat energy that is needed to melt (or boil) a substance. When the ice melts to liquid water — a process known as a phase change as it changes from the solid state to liquid state — heat energy is absorbed without any change in temperature. 
Ice cubes can thus absorb a lot of heat energy from our drinks without the temperature rising. Our drinks are kept ice-cold as a result. The effect of latent effect becomes apparent when we use ice cubes at 0°C versus cooling our drinks by pouring in water at 0°C . Or keeping our bottles of drinks in an ice bucket instead of a bucket of cold water.
Ice Heaters
But this latent heat phenomenon can – amazingly – be also used to heat houses up. We just need to reverse the process. When liquid water freezes into solid ice, latent heat is released (the opposite of ice melting). This latent heat can then be captured and pumped into the heating system of our homes.
HUF HAUS UK Show House – http://www.huf-haus.com/en/england/london/new-uk-show-house.html
That is precisely what a German builder, Huf Haus, and its partner, Viessmann, did. They installed an underground ice storage tank under a house. When the weather turns cold, they freeze the water in the storage tank and the latent heat released is harvested as heat output that is sufficient to warm up a typical bedroom-size area.
That is not all. When the weather turns hot, they reverse the process: the ice is melted by drawing heating from the house, thus cooling the house down. The ice turns to water, which can be frozen again when we need heat in the colder months.
As a result, the system is both energy efficient system and renewable as it is just really repeating the cycles of freezing and melting over the four seasons. And it’s all thanks to latent heat.
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![By Community College Consortium for Bioscience Credentials (Own work) [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons](https://commons.wikimedia.org/wiki/File:Heating-Curve.png){kind=link}