1) Well the heaters on radiators is also shit, right?
For air- PACs, there are two phenomena which combine when it is cold:
The efficiency drops while the temperature to be supplied by the radiators should increase. The conclusion is obvious.
Otherwise, failing to be ecological (due to electricity production), water-water heat pumps are economical to operate. As for investment, it is something else. Some people are satisfied with it, others not. Difficult to generalize.
but in renovation putting a heated floor is not ideal ... but there are LV radiators ...
Yes I have been talking about it for a while and we must not dream, the majority of homes are in this case and nobody is going to invest in LV on an existing installation unless simply increasing the number of radiators. It's not win .
People who ask me for information on solar (I am far from being a specialist because I do not have an installation), are generally in the same case as me (described above)
I speak to them about isolation at first and then I go to practical experience:
Reduce the temperature of the water circulating in the radiators to the extreme (40 ° or better 30 °). If we manage to maintain a constant temperature despite the cold outside, this is a good sign
Otherwise, isolate, further isolate. Remember to cut the thermal bridge at the base of the exterior walls by digging a deepest possible trench (basically frost-free) because old dwellings (but also modern ones) have a cold floor because of this.
The design of a solar installation, there it is serious and indeed, the secret is the buffer. For the moment I have not found the optimal solution but I am looking before going any further.
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