[TRNSYS-users] doubt on solar thermal collectors

[DONAZZAN FRANCESCO MARIA]

Dear all,
I have a doubt on the functioning of the solar thermal collectors (types 1,
71 and 73). I run the SDHW example of TRNSYS 16.01.0003.
At the beginning of the day the radiation start to increase. The pump is
not working yet and the temperature inside the collector (the output
temperature) increase too. When the temperature is high enough the controller
turns ON the pump and immediately (in a time step!) the temperature decrease
to a value that it had reached as if the pump would have been ALWAYS ON.
Then the controller switch OFF the pump and the temperature increase again to
a value that it had reached as if the pump would have been ALWAYS OFF. The
temperature increasing rate in this step can be higher than 20 degrees per
second!! I think this is not correct, it has no physical meaning.
Is there a way to solve these problems? Or a way to ignore it or rielaborate 
the final results?
Thanks
Francesco