Storing heat and …coolth?

Water is an eminently fascinating material. It is a material which is remarkably common, and at the same time, remarkably uncommon in it’s characteristics. It has an extremely high specific heat and enthalpy of fusion, meaning that it can contain a great deal of heat for a given volume, and even more “coolth” when it’s frozen (coolth could be considered inverse heat, as in a block of ice put in a room will absorb considerably more heat as it warms and melts than will a block of iron at the same temperature as it warms up to room temperature). These properties, along with the commonality of water, make it an extremely useful substance for temperature regulation. This effect is already enjoyed by coastal communities, especially ocean coasts, but it can be applied more directly through several new(ish) technologies and techniques.

One of these is known as seasonal thermal energy storage, which consists of passing water through solar water heaters in the summer, and pumping it underground to store until the winter in one well, while water cooled in winter is used to cool in the summer. This technique is most applicable where there exist old mines or other underground spaces that can be filed. The best example of such a system exists in Drakes Landing Alberta, Canada1. This system is primarily aimed at winter heating, since Alberta has a minimal cooling requirement, yet a similar system could be very beneficial to communities in hot summer climates, since traditional cooling techniques requires considerably more energy than does heating.

When cooling is the goal however there are even better ways of storing energy (coolth). As mentioned, water has an extremely high enthalpy of fusion. The amount of energy required to move from 0oC water to 0oC ice is 80% of what it takes to move from 100oC water to 0oC water. This characteristic means that ice provides a much better means of storing cold than merely cooling water to near 0oC. An excellent example of this already being applied is in large buildings, with correspondingly large cooling loads. They use cheaper nighttime energy to make ice, and then use the ice to cool the building during the day2. This process is aided further by the ambient air temperature being lower at night and thus requiring less energy to cool it to below freezing. Nighttime energy often uses more efficient/renewable sources than peak power, making this technology sustainable. Further application could be found anywhere water and naturally freezing temperatures coincide to create reservoirs of cold to be used for refrigeration or climate control.



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