ᐅ Design of Underfloor Heating for a KfW 55 Energy-Efficient House with a Ventilation System

Hello,

Thank you again for the feedback. I have now scheduled a meeting with the general contractor and the heating engineer together. This was suggested by the general contractor. We will review everything again there. There is still some flexibility regarding the pipe lengths downstairs, and we could manage in most rooms without additional heating circuits. Upstairs, it will actually be tight to aim for the 100 m (330 feet).
But for now, I will wait and see what comes out of it.

Because of this thread, I discussed the matter again with my general contractor (GC). The statement regarding the design of the supply temperature below 35°C (95°F) was: “That means you are operating outside the design standard… The basic setting is based on the generally accepted guidelines.”

Which standard actually specifies the values for the calculation?
Is it possible that the standard being referenced is already outdated, but they strictly adhere to it to avoid any liability or criticism?

I think we are unlikely to succeed in redesigning the system now for 30°C (86°F) supply temperature, so we will have to see if the given system can still provide a comfortable room temperature if we simply reduce the supply temperature ourselves afterwards. This is the “curse of the GC” in this situation.

That’s correct. With a general contractor, you often don’t get a meaningful plan. In this case, @dream2023 seems to be in a slightly better position because at least there is a willingness to communicate. If you can’t get a properly calculated plan that makes sense, you have to try to create the conditions to make the heating run more efficiently later on. So, put as much as possible into the most critical room, usually the bathroom (pipe spacing 5cm (2 inches), as large areas as possible, and possibly a manifold), and then reduce it in the other rooms. Try to discuss with the heating installer what extra effort it would take to install 5cm (2 inches) spacing in the bathroom despite the plan, and 10cm (4 inches) spacing in the living areas.

Compared to general contractors, maybe try to be a bit more assertive. Present recommendations from the heat pump manufacturers (none of them recommend 40 degrees anymore), announce that you will have an expert check everything and that you will verify the spacing precisely. With the heating installer, you might hint that you will monitor temperatures very closely and that they may have to come back 2 or 3 more times if needed. Installing pipes with closer spacing is hardly more work, especially if it can save rework later. Maybe that will help.

Allthewayup schrieb:

Because of this thread, I went back to discuss with my general contractor as well. Their statement regarding the design of the supply temperature below 35°C (95°F) was: "This moves outside the design standard… The basic setting is based on the generally accepted guidelines."

Which standard specifies the values for the calculation?

That is fairly straightforward to answer. There is no standard that limits the supply temperature to 35°C (95°F). The heating system design follows DIN EN standards, which must be observed and adhered to. And if you want an underfloor heating system with a consistent 5cm (2 inches) pipe spacing, the design could very well result in a maximum supply temperature of around 27°C (81°F). Completely legitimate. It’s just a convenient excuse, since customers usually don’t ask further then ;-)

The flow temperature is just a means to an end. The DIN EN 12831 standard describes in detail, over about 100 pages, how the heat load calculation must be carried out.

This also includes standard temperatures such as the standard outdoor temperature and room temperatures depending on usage. These are even minimum temperatures. However, this does not mean, first of all, that they represent an absolute requirement (if someone wants it warmer, they can of course agree on that), and secondly, it only describes the heat load.

How this heat load is delivered is then a matter of design. You need a heating surface that must have a certain temperature to meet the heat load. If you want to lower the temperature, the surface area must increase.

So, I would innocently put the question of a norm that requires a minimum flow temperature in the design to the general contractor.

Unfortunately, in practice, it makes no difference if the heating engineer is not willing to negotiate.

My story was that he then completely backed out, and I had to find another one myself.

HoisleBauer22 schrieb:

My calculation is based on 40°C (104°F), and the basement also has underfloor heating.

Something else that comes to mind and caused some confusion for me: in our case, the calculation was based on the wrong outside temperature (-14°C (7°F) instead of -11°C (12°F)) and the wrong floor covering (parquet instead of vinyl). This doesn’t improve the heating performance, but it could explain the significant deviation from the currently recommended standard. Perhaps your "40°C (104°F)" is actually a "37°C (99°F)" according to the current norm. Still not ideal, though.