No, 47°C to 67°C is way too low. The buildings are not actually circulating boiling water, but not too far either:
> Typically, heating systems in Europe use water flowing through pipes and emitters (radiators) heated to high temperatures (70-90°C). [0]
The radiators are often designed for these temperatures. Supplying with lower heat will not work without replacing the radiators and/or renovating for better energy efficiency.
And heat pumps, AFAIK, can't supply 70-90°C. Thus my original question of what is the current plan to solve this problem.
So, firstly yes, exactly, even in the 19th century they aren't using boiling water, it's just needlessly expensive to make. 90°C seems unnecessarily hot to me (as you can see, by the time I was born it wasn't being used to heat homes) but it isn't boiling.
And yes, some older buildings will need refurbishment, these building often pre-date electric light so that's happened before. The 1970s house example starts with a 70°C flow, but with a combination of insulation and replacing radiators they get to 41°C flow which is a much cheaper 318K in real numbers.
The thing is making 90°C water was expensive and unnecessary even when gas boilers start being commonplace, the manufacturer will tell you that you should turn it down until it's heating the home as slow as you can tolerate. That got more true as the boilers got more efficient, because the efficiency is from recovering more heat energy from burning methane and you do that at lower flow temperatures, the heat pumps are just more of the same. Notice how those diagrams show gradually reducing flow temperatures over the years, in the 1930s recovered heat from an industrial district at 90°C is plausible, but the gas boiler manufacturer fifty years ago will go white when you say you need 90°C -- he's going to suggest 70°C, and his successors will keep bargaining you down because the efficiency numbers are better as flow temperature reduces and while "instant heat" feels good in the moment, the bills for the gas you're burning will not.
We can pump these temperatures but they don't make economic sense. Unlike low outside air temperatures this is just economics. The low outside air temperatures mean you need to defrost the pump, which if it got cold enough might literally become impossible, but if you want to pay far, far more money to heat water to 90°C that would be technically possible, it's just silly, like burning $50 bills to keep warm - use singles they're 50x cheaper.
> Typically, heating systems in Europe use water flowing through pipes and emitters (radiators) heated to high temperatures (70-90°C). [0]
The radiators are often designed for these temperatures. Supplying with lower heat will not work without replacing the radiators and/or renovating for better energy efficiency.
And heat pumps, AFAIK, can't supply 70-90°C. Thus my original question of what is the current plan to solve this problem.
[0] https://www.ifeu.de/fileadmin/uploads/Publikationen/Energie/...