I spoke with the heating engineer again today. I am feeling increasingly confident and will probably be satisfied.
Laying plan:
He noticeably doesn’t like it that much. He would prefer to do his standard (15cm in living rooms, 7.5cm in bathrooms). Now there are a few more heating circuits than he would have preferred or than the standard the main contractor is paying him for. He is concerned that the many bends at 5cm will damage the screed. In summary, it can be noted that he will make an effort to stick to the laying plan.
The topic of wall heating is no longer a problem for him, as he seems to have come to terms with it.
Additional costs are €4/sqm for the smaller pipe spacing.
Heat pump:
He would prefer to install Daikin, since he knows the devices, has a good connection to sales, and until a few years ago did customer service for them himself. It would have been the 6kW Daikin Altherma 3 R F. The device seems decent. Unfortunately, my wife does not like the outdoor unit at all. He advised me against the black outdoor unit because apparently they just send it to a painter and for him the result is only so-so.
It will probably now be a Viessmann VWL 105/6 A in combination with the Viessmann ventilation system. Although I just noticed that it has a 9.2kW heating capacity? I definitely need to check again if I understood that correctly and insist on at least VWL 75/6 A with 7kW.
Viessmann would be quieter, more economical, and also greener due to the propane filling. Where could the catch be, except for the oversizing with the 105/6? As an end customer, I find the homepages of heat pump manufacturers really terrible. Why can’t you find a technical data sheet for the heat pump right away?
Buffer tank:
In the conversation, he said he would install a 100l buffer tank on the return flow. Then the heat pump could recharge it when the ERR turns off. I immediately pointed out that I wouldn’t need that if I deactivate the ERR in the long term. He immediately agreed and said that would then be pointless. He would only do it as a standard because otherwise the ERR would cause the heat pump to short-cycle extremely, which would be unpleasant for both him and the customer.
Overflow valve:
He will definitely install an overflow valve on top of the heating circuit distributor. He will not be stopped from doing so. He said he has to deliver with ERR and otherwise it would be criminal without it. He said if I turn it off when I deactivate the ERR, it will be corroded in 3 years anyway – so it would end up being the same as if he didn’t install it at all.