ᐅ New Construction with Heat Pump – Experiences?

Hello everyone,

We have built a solid single-family house, 150 sqm (1600 sq ft) plus basement. We have a Viessmann Vitocal 200-S heat pump (with cooling function as well) and a 300-liter (80-gallon) hot water storage tank. Unfortunately, the heating installer set up the system and did not adjust any parameters for domestic hot water production or heating—they just left the settings as they were.

This is my first single-family house; I have always lived in apartment buildings with central heating before.

I have studied and read a lot, and I have now set everything as follows:

Room target temperature: 20°C (68°F)
Heating time schedule: 0–24 hours, no nighttime temperature setback
Domestic hot water target temperature 1: 6–8 a.m. at 42°C (108°F)
Domestic hot water target temperature 2: 5–7 p.m. at 50°C (122°F) (shower/bath time with children)
Hot water circulation pump: 5–7 p.m., cycle 5/25 (the pump used to run 0–24 hours with a 5/25 cycle, resulting in very high electricity consumption)
Slope (heating curve): 0.1
Level (offset): -1K
Manufacturer default settings were slope 0.5 and level 5K

Now the problem:

At night, the house naturally cools down, but I expect the system to regulate the temperature, for example:

Last night, I had 22°C (72°F) in the living room, and this morning at 5:30 a.m. it was 20.9°C (70°F). Is this behavior related to the heating curve? Unfortunately, I have not yet received any instruction from the heating installer (we moved in in August). I know there is a specific procedure to adjust the heating curve, but I have not done it yet.

Thank you very much,
Marco

MarcoGT schrieb:

I know there is a specific procedure to adjust the heating curve, but unfortunately I haven’t done that yet.

You haven’t? Then what is this:

MarcoGT schrieb:

Slope: 0.1
Offset: -1K
The factory settings were slope 0.5 and offset 5K

Do you understand what slope means in your case and how it might relate to the outdoor temperature?

Yes, I have experimented and understood how it works.
Yes, I understand the connections.

MarcoGT schrieb:

Last night I had 22°C (72°F) in the living room, this morning at 5:30 I had 20.9°C (70°F);

Then it's settled. If the relationships between the heating curve and outdoor temperature are known, we have no problem.

Yes, I would say we have a problem. I have understood the basic concepts, but there are still some things that aren’t 100% clear.
Last night, I tried to optimize the heating curve, and the weather fits perfectly because it is -8°C (18°F) outside.

- All thermostatic radiator valves fully open in living room, guest WC, upstairs bathroom, kitchen
- At the desired temperature in the three bedrooms

I set the slope to 0.1 and the offset to 1K and achieved the following temperatures:

- Living room/kitchen: 21°C (70°F)
- Upstairs bathroom: 19°C (66°F)
- Guest WC: 20°C (68°F)
- Bedrooms (all three): 18.7°C (65.7°F)

The temperatures were measured with a simple wall thermometer, so they may not be 100% accurate.

I think the water flow is not sufficient; the heating technician simply set all valves to 1.5 l/h (0.4 US gal/h), which I find odd—this can’t be right. He will come back on Friday, but I want to understand the problem first so I can ask the right questions.

For now, I’m supposed to leave the heating curve unchanged for a few days and observe how the temperatures behave. If they drop and the system doesn’t regulate itself, then the heating curve is set incorrectly, right?

Thanks!

Heat pumps respond slowly.
At night, it gets colder faster than the heat pump can reheat.
In my case, this means 21.5°C (70.7°F) in the morning to 23°C (73.4°F) in the evening with a setpoint of 23°C (73.4°F).
I am quite comfortable with this.
If the temperature is not reached at all, I can adjust the heating curve upwards in parallel.
In our case, one heating loop was out of order for 5 days. After the issue was fixed, it took 2 days for the room to reach its 23°C (73.4°F) again. Heat pumps simply need their time.

Best regards