(Click on the picture to see it large.)
I inserted the heat exchanger to allow me to add a radiator heating, if the tank is full or cannot be heated, and the panels stil lhave enough energy.
It came handy, however, when I noticed several times when the graviational flow brakes in the solar station did not work 100%, so during some nights, the collectors were heated up by a reverse circulation. Bad Idea!
Now I use the 3-way-valve to cut off the tank from the circulation, which works perfect, but disallows the use for a radiatior. No problem at the moment, as the UVR control does not allow any more parameters for such a task anyway. I must find a way if I ever exchange the control by a more sophisticated, or a control designed and programmed by myself.
Of course we don't like an all-time circulation! What are the alternatives?
Timed switch: not flexible enough, sometimes superfluous, sometimes we need more
Warmth-sensitive switch (electronic control that switches the pump on when warm water was requested for a very short time): bad idea, as nearly all people here in the house tend to forget to turn the tap to "cold" if they need a small amount of water - this would switch the pump on unnecessarily.
Manual switch: this was the way to go. As I don't want to put wires all over our house, we use a remote control and a timed plug socket (FS20 S4A and FS20 ST). About 40 EUR from ELV Elektronik. First we did create one ourselves by using a very cheap remote control door bell (4 EUR), a 555 timer and two relays, but it was unreliable.