Frost detector for solar heating system - has large heat exchanger fins and small quantity of distilled water which expands on freezing to actuate electrical switch

摘要

The defector monitors the outside temp. and initiates emptying of the system water when there is a danger of this freezing. The detector comprises a small chamber (22) containing water whose heat is exchanged with atmosphere through a series of copper fins (24). One end wall of the chamber is an elastic diaphragm (26) which deforms when the water freezes and expands to close a switch formed by two steel leaf springs (30,32). Alternatively the freezing of the chamber water displaces a mercury column in a U-tube, the mercury closing on electrical switch. In a further modification the change of resistivity between water and ice is used to provide a signal to drain the system. A small and large plate of copper are separated by an insulator containing a small amount of water in a trough bore.