How are we heating?

Last updated on January 10th, 2025

In February 2024 we replaced our 31 years old gas based heating system with a modern heat-pump.
See some photographs here.

• Viessmann Vitocal 250-A AWO-M-E-AC 251 .A08
• Viessmann Vitocell 100-E SVWA200L
  • Buffer for heating system water
• Viessmann Vitocell 100-V CVWC250L
  • Buffer for domestic warm water

• 2nd floor via raditors
• 1st floor via raditors
• ground floor via underfloor heating
• basement via raditors

How did it turn out?

The system works pretty well, we are saving ~ 1/2 the monthly costs compared to the gas heating system. Combined with the photovoltaics system this is even much better. Warmwater is also provided by the system at 50°C currently. I integrated some metrics in Grafana and Home Assistant to get an understanding about how the system behaves.
The JAZ (Jahresarbeitszahl) is currently at 4.3, which means we are producing 4.3 times the heat energy out of the electricity consumed by the system.

Winter Strategy

Sure, sun is not shining in winter that much for PV and despite still saving 1/2 the costs of gas we can improve further by utilizing hourly dynamic electricity prices using Tibber. As we have an intelligent Smart Meter, which sends electricity consumption every 15mins to the provider we can plan around hourly prices.
So what I did is setup an automation in Home Assistant which is charging our PV battery when the electricy prices point is at the daily lowest. This way we can use at least 10kWh at really cheap prices (normal would be 32 Cent/kWh, we are charging at 18 Cents). We only have this setup since beginning of October 2024, let's see how this turns out.
If you also want to join Tibber you can use my invite code to get 50 EUR Bonus for the Tibber store.

What I don't like

The system is fine and we stay warm, but some things could be improved.

• Connectivity is only supported via WiFi, despite LAN is right next to it in the basement
• metrics can be fetched via
  • Viessmann Cloud API. very unstable, small dataset
  • external CAN bus locally, requires some effort, see Open3E
• SG-Ready (Smart Grid) only means you can switch between different energy levels via wire. No API, modbus etc. available (yet)

Numbers

We are heating our ~ 130qm home the following way:

• 2nd floor: home office with raditors, 4x/week at 23°C, else 18°C
• 1st floor: 3 rooms, heated with radiators, 22°C
• ground floor: heated with underfloor heating, 23°C

• COP: Ratio of how much thermal energy was produced from the consumed electricity.