Heat pump for KfW55 house 148 sqm

Monovalent heat pumps are often far superior to split systems, only the German manufacturers missed this

Are you confusing monovalent operation/design of a heat pump with the difference between monoblock and split heat pumps?

Thank you for the suggestions.
I am currently trying to read up on and understand a few things.
So that I can then make a decision.

1. Heating load
I assume that the heating load calculation from the MEP office, which we have on hand, is correct.
(With the data known to the MEP planner up to that point)
Standard heating load: 5115 W
Norm heating load: 6233 W (includes a pre-heating surcharge of 1118 W on the standard heating load)

2. Improvement of the building fabric
Our heating load is probably somewhat lower, since we, for example, upgraded the front door from double glazing to triple glazing. In the MEP planning, a U-value of 1.5 was assumed for the door, this was before the upgrade. Now the two fixed glazed side panels have a Ug value of 0.6 (glass) and the front door panel 0.8 (Ug).
Then we want to additionally insulate the topmost floor ceiling. Towards the unheated attic (used for storage), we have laid or plan to lay 10 cm of mineral wool WLG 0.35 on top of the existing floor ceiling (plasterboard, vapor barrier, 20 cm mineral wool WLG 0.35, spruce beams). The material is ordered. According to Ubakus, the U-value will go down from 0.194 to 0.132. The heating load calculation assumes a U-value of 0.210. That probably includes thermal bridges. The attic stairs are also still included. Nevertheless, in the future, it will be less than 0.210.

[IMG alt="Bildschirmfoto 2022-12-11 um 11.49.44.png"]https://www.hausbau-forum.de/data/attachments/76/76182-e9d40a7d676d49270c27df85da07d2ae.jpg[/IMG]

3. Design of the underfloor heating
We can no longer change anything about the pipes. The pipes are laid, the screed is in.
We do not know how long the individual heating circuits are. The laying distances are very clear. 15 cm, somewhat less in the bathrooms.

Heating circuits:
Ground floor
1 guest WC
1 utility room
1 hallway
1 guest room
3 for open plan kitchen, dining, living

Upper floor
1 bathroom
1 corridor
1 bedroom
1 study
1 child’s room
1 hobby room

WC and bathroom each have an electric auxiliary heater

4. Refrigerant lines
The outdoor and indoor units of the heat pump are not planned wall to wall. (due to acoustic and floor plan reasons)
From the utility room, refrigerant lines run in the screed through the bathroom to the exterior wall. That is maybe a total of 6 m refrigerant lines, considering the height differences in the wall and at the indoor unit.

For this reason, a monoblock system is probably no longer possible, right?

5. Ventilation
We do not have one, windows open and cross ventilation.

6. Planned heat pump
The planned heat pump seems to be designed for monovalent operation, and somehow the MEP planner arrives at 11 kW with the "Heating Solutions Navigator."

[IMG alt="Heizen.png"]https://www.hausbau-forum.de/data/attachments/76/76183-6d34e9489a63f5085cfa6ae15de41c38.jpg[/IMG]

[IMG alt="Heizen-Loesung.png"]https://www.hausbau-forum.de/data/attachments/76/76184-7f5a4fe835de9e9061d67ca1c7f86c24.jpg[/IMG]
From the 5.1 kW, he arrives here at 7.48 (however that may be) as required heating capacity. (Well, hot water still has to be added to the heating load)
Then at 8.31 kW as the heating capacity of the heat pump at -8.6°C as min ambient (whatever that means)
and then goes to the next available heat pump size with 11 kW at Daikin.

Here again the comparison via an online tool which was recommended:

[IMG alt="Bildschirmfoto 2022-12-11 um 12.48.42.png"]https://www.hausbau-forum.de/data/attachments/76/76186-0b6121745680be44dba7b2f2be0471bd.jpg[/IMG]

I only found the transmission heat transfer coefficient in the building energy law planning.
Building envelope area and heated gross volume taken from the MEP planning.
22°C is a very cozy temperature for us.

6. Decision?
I am not a professional, but I would think that a 6 kW system would serve us well.
We can no longer optimize anything on the heating circuits, so a 4 kW system might be too tight.
The Daikin has a 180 l hot water tank.
We are 3 people, if we calculate 1 kW hot water load instead of 400 W, since the tank is a bit small, we end up at just under 5 kW.

Am I thinking correctly here, or am I missing something?

Thanks to you all.

A well-designed heat pump and underfloor heating system do not need a stratified storage tank. The heat pump should go directly into the underfloor heating. The high volume flows of a heat pump are not always conducive to the trouble-free operation of a stratified storage tank. ERRs must of course be dismantled then.

How this is connected, and whether we open the ERRs and adjust the volume flows directly, we want to see when everything is installed. We keep that in mind. At least the hallway and vestibule do not have any ERRs in our case, for whatever reason, so we have to regulate the volume flow directly at the HKV anyway.

Refrigerant line line correction factor

Is a line correction factor for the refrigerant lines perhaps still needed for split systems?
After all, they are not as short as possible in our case.
Is this relevant for about 6m of refrigerant line?

, I am talking about modern monovalent systems, here a floor heating system is not sufficient in terms of volume, as confirmed by the manufacturers.
(Daikin, Panasonic, Lambda, ...) Hot water of course via a fresh water station.

monovalent refers to the heat source, here one, therefore the bivalence point is also not relevant in our latitudes.

the pipe lengths should be included for each room in the building services calculation, that’s why it’s called room heating load. That means the heating load such as for the floor heating and the hydraulic balancing are determined for each room. U-values of interior walls, interior space assemblies, ...

For a KfW55 building, a ventilation system is mandatory, as well as the blower door test and hydraulic balancing.
The U-values cannot be as bad for KfW55 heat saving as you stated.

Well, I don’t know, maybe I just don’t understand you, but some things you write I cannot follow.

What kind of volume is supposedly not sufficient for a monovalent system? You make it sound as if there are heat pumps that by manufacturer definition are monovalent and others that are not.
I know what monovalent means. It’s just that you write it at least in a way that is misleading to me.
Whether a system is monovalent or not does not depend on whether it’s a monoblock or a split system. You threw in the latter term.
The difference between monovalent and bivalent is whether there is one or two heat sources, which you already wrote. Of course, in our latitudes you can find a sufficiently sized heat pump that covers the heating load fully even in colder regions. The question is whether that always makes sense. You can see it in this case here. If the heating load calculation includes five times a safety margin, then the heating load is higher.
Now you can of course simply say I’ll take the bigger heat pump. That’s exactly what happened here. One could also say you design bivalent, in that at a certain temperature, e.g. -10 degrees, the heat pump on paper no longer provides the heating capacity that the heating engineer calculated in the heating load calculation. For this case the heat pump has a fallback solution on board.
The heating element. In practice, it probably never turns on. For the reasons mentioned. If it does, then maybe about three days every four years or so. That doesn’t really affect much.
By the way, one should not confuse monovalent and bivalent with the problem that the heat pump does not work at certain sub-zero temperatures. That might have been true in the past. I still know those stories. They persist in people’s minds to this day. When we were planning, some people said to me: yes, but if it gets colder than -10 degrees all heat pumps stop working. Today that is obviously no longer the case. However, usually the maximum heating capacity decreases as temperatures drop. There are characteristic curves and values for that.
Concrete example: I have an IDM ILM 2-7. According to common understanding it would provide 7 kW heating capacity. It actually does, even more, but never mind. Below -8 degrees it slowly decreases, so that at our design temperature only about 5.8 kW capacity is available (I don’t recall exactly). The heating engineer calculated something close to 7 kW (including one or two safety margins). According to classical logic, the next larger heat pump should have been chosen. That would have been the ILM 4-13. Another heating engineer would have installed that size (another manufacturer was offered but the size was the same). On paper, our heating engineer designed bivalent. And from about -9 degrees practically factored the heating element as support.
We have now been living in the house for over two years. It got colder than that. The heating element never ran. It was never really cold.

And to come back to : I don’t know why you make such claims. And what monovalent has to do with which volume.
There are different hydraulic schemes. IDM for example also has some with direct heating circuits (and is not the only manufacturer doing so). You don’t necessarily need a buffer tank. Of course you have to plan properly. Either without ERR or with enough non-reduced circuits.

A fresh water station is great, we have one too, but a “naturally” is a subjective opinion. It’s not necessary.
Likewise, I wasn’t aware that for KFW55 a ventilation system is mandatory. Sure, it makes it easier to achieve but it was possible without. Has that been changed?