Intuitively I feel that a slower-moving fluid will collect more heat energy as it passes through the panels and therefore be able to deliver more heat energy through the heat exchanger in the hot water tank than cooler, faster flowing fluid would - but is my intuition deceiving me?
What do you think?
The circuit has a pump plus flow limiting valve than can deliver anything between 2 and 15 litres per minute.
Following the installer's visit last week to investigate the reported SYS fault (see the other thread) they set the flow to 5 l/min, which is faster than it was originally.
I've had a funny feeling since that the water wasn't getting as hot as quickly as it used to - we've had a couple of very good days of weather in the interim. Hence the need to think about how to determine whether hot and slow is better than cool and fast.
In the meantime I've reduced the flow to 2 l/min to see if that makes any difference, subjectively. This was the original setting after initial commissioning.
Opinions (plus justification, ideally) very welcome.