Haha. Yes and no, and I do see your point.
The idea of raw seawater circulating offends me, as well as enjoying the 'challenge' of doing this. It is ostensibly more complicated sure, but it's not involving anything that isn't mainstream and readily available. The relay was £4, the pump £20, the other pump was laying in the garage as was the heat exchanger, so the whole enterprise (?) has cost under £50, and entertained me, as well as giving 'excuses' for congratulatory wine supping/glugging. as my wife questions me about "Another one???!"
I’d be interested to how long the PHE keeps clear as you cannot filter the dissolved solids/ minerals that will drop out, the internal passes between plates are very small as opposed to shell and tube heat exchanger.
Yes indeed, I'm hoping that the gap between plates, will be sufficient for durability and flow.
However, it's easy to monitor, and converting back to raw water is a 1 minute job.
The cooling pump thermal switch operates at 65°C which is (near enough)10% cooler than salt water would crystallize within the heat exchanger.