I came across a scenario that I feel using below approach advised by Hevacomp to add hot water cylinder to CWS would almost double the real CWS incoming supply/or booster set.
The attached approach ignores the diversity occurs at the point of sanitary fittings, which would only allow a fixed flow rate of the combined hot and cold water supply. By adding a continuous flow, the pipework will see the peak hot water demand as a single outlet constantly satisfied. I would think the correct way to add hot water cylinder feed by CWS, is to add max flow rate and 0 loading units (screen shot as below). That way, the pipework would be property size and flow rate would be accurately estimated.