Greenbuilding Archive for August 2002

-- -- Chris Van der Vyver
Earth Design
340 King St. East, Kingston, Ontario,
K7L 3B6, Canada
Tel: (613) 536 5252  Fax: (613) 536 5554




5. Eutectic Salt Chamber
    Potentially the most efficient heating system of the six is the eutectic
salt chamber. The salt being used is sodium sulfate deca-hydrate (NaSO4 €
H2O -- Glauber's salt).  At the right is a curve representing the energy
stored as a function of temperature of a substance as it transitions from
solid to liquid (phase-change). For example, it takes 80 calories to melt
one gram of ice. In reverse, one gram (1 cc) of water gives off 80 calories
as it turns to ice; this is called the heat of fusion. This heat of fusion
principle is often used to save orchard blossoms from freezing if the
temperature drops below freezing in the Spring by sprinkling them with
water. As the water freezes, it gives off this heat of fusion and saves the
blossoms. Thermal storage using water is not nearly so efficient, as water
only stores one calory per gram per degree centigrade. Glauber's salt has
the nice property that it melts at 90o F and has about 83 calories per gram.
It does not take a lot of salt to heat several rooms. The salt in the
chamber is stored in black tubes to pull in the day-time sun so that the
salt melts. At night as the salt freezes at 90o F, the air is heated around
the tubes like a radiator, which then rises, and like the solarium forces
air through the floor joist -- dropping down in the cooler rooms needing
heat with return air going through ducting under the floors.


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