A variation of the standard Thermo Probe, the looped evaporator does not require a constant grade to ensure the return of the condensate to all of the evaporator. By encorporating an accumulator beneath the radiator, the condensate is directed out one side of the loop and returns along with the vapour on the other side of the loop. This ensures that the evaporator walls are constantly being wetted.
The accumulator places a head on the liquid in the evaporator and as heat is picked up around the loop the ratio of liquid to gas changes within the evaporator and the density is reduced. This forces the liquid to travel in only one direction while the evaporators can be flat and undulating.
One advantage of the looped system is that installation is simplified and excavation problems are reduced. This allows longer loop lengths to be used with out requiring deep excavations. Loop lengths up to 200 m are commonly used and loops as long as 600 m have been installed. Typically the evaporators are made of 3/4″ steel pipe.