To return a little to the subject and for those who the question of the comparative losses of a circuit in 24V and and 220V interested, we have, with ThierrySan, made a small calculation on the last pages of
this subject.
You can go take a look. Otherwise, for lazy people, the result of the races is as follows: to have losses equivalent in 24V to those of a 1,5mm² circuit in 240V (aproximation to simplify the calculations), 24V wires would be required
14mm in diameter !!!
Now, the question remains posed to know if, on the lengths of wiring of a house not too big (max 30m for a given circuit), these losses are reasonable or not in 24V.
It could also be interesting to compare the losses of a DC low voltage wiring with the losses due to the efficiency of 220V ~ -> 24V- transformers.