Air-to-water heat pump sizing in new construction

Ok, but wasn’t there a risk that he would then also plan too large installation distances? So that a lower VT would no longer be sufficient? Or are the 20° really enough for you?

That’s why I set the specification of max. 30°C flow temperature and 10 cm spacing.

When the objection came up that it might be tight in the bathroom at 24°C, I brought in the 20°C and the construction-side electric heater.

As I said, most general contractors, property developers, and prefabricated house companies have their systems designed for free by their suppliers (e.g., the underfloor heating manufacturer or heat pump manufacturer), and the rule of thumb is usually that it’s okay to have a little more, as long as the place gets warm.

Higher flow temperatures and large spacing mean security for the general contractor that the place will get warm, and at the same time it’s cheaper because they need less material (heating pipes, actuators, smaller manifolds, less installation effort). But your electricity bill goes up because the heat pump doesn’t run as efficiently as it could. Your electricity bill doesn’t interest the general contractor. The main thing is the place gets warm.

You reduce the necessary room temperature to reduce the heating load? If 20 degrees are not enough now, you have a cold house and a heat pump running at 99% max. Better to set the pipe spacing everywhere to 7cm or even 5cm and then throttle the heating system.

It's even easier. Contractually specify the following:

- Room-by-room heating load calculation according to DIN
- 30/27/21 (flow temperature/return temperature/RT) or 30/27/23 in the bathroom
- Heating circuit length set at 80m/circuit ±10%

Then the heating engineer is obligated to meet these parameters. By the way, I would proceed the same way if I were planning a heating system other than a heat pump. Why? Because then I am always on the safe side with political peculiarities and changes.

For me (at least) it’s about a tactic to somehow get the respective heating installer to set a lower flow temperature indirectly and then accordingly design the planning that way. So if he already says that we won’t get under 35° flow temperature, how I can push it with other parameters I give him so that I can still set the flow temperature to 30° afterwards and set my desired temperatures.
So 20° would be too cold for me, for example. It might even be better for me to say, ok just do 35°, but no more than that and I want 23° everywhere?

I can’t agree anything directly contractually with the heating installer. All I can do is communicate wishes (temperature) or special requests (upgrades)...
I’m not sure if I can tell him exactly how to plan. Supposedly he does room-by-room heating load calculations, although I think he lets the manufacturer do them...

The "specification," e.g. max. 10cm VA and in the bathroom 8cm or something similar, simply comes from not wanting to bother with calculations. If you have a correct room-by-room heat load calculation, you can calculate it accordingly. For example, in my "all-purpose room," I definitely don’t need 10cm with a 30-degree flow temperature. Even 15cm was enough there. 10cm with lengths of 70-100m would have meant a few more meters of pipe and probably one more heating circuit. I then told my heating technician to make it a bit tighter in the bathroom. It somewhat depends on how and on which points you can talk to the heating technician. I think that also varies a lot. If, of course, you have one who doesn’t agree to anything and you suspect that not much calculation is done, then it’s better to work with the VA specifications.