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Thermal Heat Storage – Rock stores.

Updated: Nov 1, 2022

Passive Annual Heat Storage (PAHS) is a way of storing heat from the summer to use in the winter. You could think of it as a heat battery, it stores the heat until it is needed.

This technique of storing heat which has come directly from the sunlight during summertime is already happening all around us. If you think about a wall in the summer, when the sun has been on it for a while, even when it enters the shade, that wall will still be fairly warm due to the thermal heat it has stored. This thermal heat will be released slowly back into the atmosphere. This is the reason that snow doesn’t instantly stick to the ground when it falls, it takes a while for the ground to cool down enough for the snow to stick. The colour of the object which is storing the heat helps to determine how quickly it will discharge that stored heat.

The traditional way to store heat directly from the sun in a domestic setting, utilising this method, is to implement rock stores in your home. Heated air from the summer is mechanically driven to the rock stores, which contain crushed rock.

The heat stored there can be transferred back from the store by one of two methods:

  1. Air can be blown through the store, into the space which needs to be heated.

  2. The store can be thermally coupled to the space and heat is transferred through radiation and conduction.

Although the first option enables some remoteness between the store and the space to be heated, the second method has the advantage of being simple, passive and is generally more popular.

Rock stores have been proven to work reasonably well. Plus they have some very good positive points:

1. Rocks are not toxic and non-flammable 2. Rocks are inexpensive, and can be obtained near enough anywhere. 3. Rocks act both as heat transfer surfaces and storage. 4. The heat transfer between air and a rock bed is good. 5. The heat loss from the pile is low.

Rock stores are a very environmentally friendly, and economical way of keeping your home warm through the winter.

Written by Jade Turney – Building Tectonics Ltd.

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