Design of underfloor heating for KFW 55 house with ventilation system

Hello,

Thank you again for the feedback. I now have an appointment with GU and Heizi together. The GU suggested that. We will go through everything again there. There is still some leeway with the pipe lengths below, and we could manage in most rooms without additional heating circuits. Upstairs it's actually tight to aim for the 100 m. But I'll wait first to see what comes out of it.

Due to this thread, I also went into a discussion with my general contractor again. Statement regarding the interpretation of the supply temperature under 35C: “This moves you outside the design standard... The basic setting is based on the generally valid specifications.”

Which standard actually specifies the values for the calculation?
Is the standard referred to perhaps already outdated, but they just don’t want to give any ground and therefore strictly adhere to it?

I think we will have little success now in planning the system for 30 degrees, but we have to see with the given system whether we can still reach a comfortable temperature if we simply throttle the supply temperature ourselves afterwards. That is the “curse of the general contractor” at this point.

That’s correct. With a general contractor, you often don’t get a sensible plan. Here, seems to be somewhat better positioned because at least there is a willingness to have a conversation. If you can’t get a calculated plan that makes sense, then you have to try to create the conditions somehow anyway to later run the heating more efficiently. So pack as much as possible into the most critical room, usually the bathroom (installation spacing 5cm, as large areas as possible, possibly adding a heating circuit distributor) and reduce it in the other rooms. Try to discuss with the heating installer what extra effort it would take to lay 5cm in the bathroom despite the plan and 10cm in the living rooms.

Maybe just play a bit tough against the general contractors. Present recommendations from the heat pump manufacturers (no one writes 40 degrees anymore), announce an expert and say that you will check the spacing exactly. To the heating installer, maybe mention that you will check the temperatures very precisely and that he might have to come back 2-3 more times. Laying a bit closer together is hardly any extra effort, especially if it can save you rework. Maybe this will help.

Due to this thread, I also went into discussion with my building contractor again. Statement regarding the design of the flow temperature below 35°C: "This means you are outside the design standard... The basic setting is based on the generally valid specifications."

Which standard specifies the values for the calculation?

This is relatively easy to answer. There is no standard that limits a flow temperature to 35 degrees. The design of the heating system is carried out according to DIN EN specifications. You have to orient yourself accordingly and comply with them. And if you want underfloor heating with a continuous 5cm installation spacing, that can lead to a design-compliant maximum flow temperature of maybe 27 degrees. Completely legitimate. But it’s a nice excuse, as customers generally don’t ask further ;-)

The flow temperature is also just a means to an end. DIN EN 12831 describes in detail, over about 100 pages, how the heat load calculation must be carried out. This includes standard temperatures such as the standard outdoor temperature and room temperatures depending on usage. These are even minimum temperatures. But this does not mean, firstly, that they represent an absolute target (if someone wants it warmer, they can agree on that), and secondly, it only describes the heat load. How this heat load is generated is then a matter of design. You simply need heating surface that must have a certain temperature to meet the heat load. If you want to go down with the temperature, the surface area must go up. So I would innocently place the question of the standard that prescribes a minimum flow temperature in the design on the general contractor. Unfortunately, in practice, it doesn't make a difference if the heating installer is not willing to negotiate. My story was that he then completely gave up and I was able to find my own.

For me, 40 degrees is calculated, the basement also has underfloor heating

What else comes to mind and also caused confusion for me: wrong outside temperature was used in the calculation (-14 degrees instead of -11 degrees) and the wrong flooring (parquet instead of vinyl). This doesn’t improve the heating, but it could be a reason for the large deviation from today’s appropriate standard. Maybe your "40 degrees" is actually a "37 degrees" according to the current standard. Still not ideal.