.... How close do your calculations actually come to the real consumption?
In my opinion, very close, after climate adjustment ~ +/- 15%. A higher resolution is hardly possible with reasonable effort.
.... Have you ever calculated a system in advance and recalculated after a few years whether it was actually the right decision?
The calculation is done in advance, the actual condition is evaluated afterwards.
Not just one, but several systems in my region. Among others, my own building, which is virtually "bugged" inside and outside with sensors; the more accurately the input parameters are recorded, the better the final result.
.... With the "botched practical systems" you are always wiser than the planner because you know the actual figures.
If there was any planning for the botched systems, it would be very helpful for me and the builders. However, most of the time there is absolutely -
nothing! No heating load calculation, no measurement protocol of the controlled residential ventilation, no heating surface dimensioning, no pipe hydraulics... etc.
An absolute vacuum, and this is exactly where the problem lies.
.... Do you see what information the builder gave the planner back then and what price increases were factored in?
Usually not, only in exceptional cases. The rule is the general contractor / general planner project!
Counter-question: Does your provider ask you what room temperatures you want in the living room, hallway, utility room, kitchen, etc.? Probably not; nevertheless, he offers you house A with a heating system xy at price Z. How is that possible?
.... Or I become more heat-loving with age and the average temperature is then a few degrees warmer than originally planned. How do you want to factor that in?
Higher room temperature => higher demand => higher consumption costs!
For moderately to well-insulated buildings => noticeable influence
For very well-insulated buildings => minor influence
For heat pumps => minor influence
For conventional heat generators => noticeable influence
For mild outdoor climate => minor influence
For cold climate => noticeable influence
Now you can create a matrix for yourself
.... Provided the heating does not run through the night during extreme cold, after switching off the heating around 9:00 p.m., the temperature drops so quickly that I have to heat higher beforehand than I actually need.
Simple answer, heat lowered! "Preheating" makes no energetic sense! The ideal heating provides just as much energy as the building
currently loses. Most conventional heat generators in existing buildings are miles away from this. They cannot modulate but usually only switch On/Off! Hence also the sometimes considerable losses.
....I cannot say already now what average temperature I have.
If you don’t know what you want, you must live with the consequences.
Not knowing what you yourself want/expect means guessing with an uncertain and sometimes costly outcome
regards