Heat pump radiator sizing 50% larger is enough - fact of fiction

[Refrigerologist]

HI guys,I keep seeing and hearing designers and engineers saying that radiators should be 50% oversized for heat pump operation at 50deg C flow temp.Having looked at the manufacturer's data charts for different temperatures I can see this is not true.

Faral radiators would need to be over double the size to give the same output at a 50deg C flow against a flow of 75deg C. I have checked other data catalogues and they are all about the same. After all you cannot get more heat out than the surface area/water content/temperature and flow rate will produce.

I am sure many installations of air to water or water to water heat pumps will not work correctly if the 'mantra of 50% oversized is stuck to rigidly'. This will be true if the insulation values of the building are increased to suit the maximum output of the radiator at the new flow temperature.

In fact Faral quote an output per section of only 41% at a flow temp of 50deg C compared with a flow temp of 75deg C.

Is this why many systems are suffering during cold spells?