2. Water Heating - indirect system.
In the illustration at right, two
new components have been added to convert what was a 'direct'
system to an 'indirect' system. The calorifier is a coil of copper
tube inside the hot water storage tank, and the new feed/expansion
tank keeps the calorifier (and also the boiler in the stove)
filled with water.
now have two completely separate circuits, known technically
as 'primary' and 'secondary.' The 'primary' is the closed heating
circuit containing a trapped volume of water topped up as necessary
by the feed/expansion tank. The 'secondary' supplies the hot-water
is essential to adopt an indirect system when central heating
is planned since panel radiators are made of mild steel and are
subject to corrosion. In a direct system, rust particles would
appear in the hot tap water. An indirect system eliminates this
problem and also allows the water circulating through the primary
circuit to be dosed with anti-rust and anti-freeze compounds.
With this in place we can also now fabricate the boiler itself
in mild steel. The cost-saving over copper or stainless is substantial
particularly on the much larger size of boiler needed to drive