This article analyzes the operation of the nonpressurized thermal solar systems  in relation with their concurrent directed ones;  the normal systems with "forced circulation".

In this first part we see endured as the systems to emptying taking advantage us of the introduced animation work flash on the right.

In sun absence the systemthe fluid carrier (normal water ) stay all in calorifier .

If the temperature in the panels knows them for effect of the sun and exceeds of a sure DT the temperature of calorifier, the pumps leave in order to concur the filling of the circuit.

In this particular conditions the simultaneous action of 2 pumps in order to gain the prevalence due to the height that must catch up the water.

After a sure time chosen to fill up the system and depend to the length of the circuit to fill up, the second pump exausts its scope and stop.

In fact when the circuit bacame fill , it  the same one behaves like a closed circuit and the circulationcab be maintained also from one single pump.

The heat comes gradually transferred in calorifier where it is stratified for effect of the particular constructive cure of the same one and comes put through of the inserted heat excange for this purpose.
Us they can be coils adapted to heat the sanitary warm water and coils adapted for integration of the heating. 

If the sun does not shine or the system does not need any heat, the feed pump turns off and the complete content of the solar system drains into the calorifier.

There is no need to add anti-freezing additives as the collector is completely empty during non-action .

The air enters in the circuit through an appropriate small hole place to the inside of calorifier in the tube of the solar sent one and the circuit is emptied.