I’m thrilled to share my recent DIY project that turned my old Viessmann heat pump into a smart device, all without breaking the bank! 
The Challenge: My heat pump, installed back in 2007, had no data interface, making it impossible to integrate into my smart home setup. With my energy provider offering hourly pricing, I wanted to optimize when the pump runs to save costs.
The Solution: I rigged up a system using temperature sensors, relays, and Home Assistant. Here’s how it works:
- Sensors: I installed two PT500 sensors in each boiler tank to monitor water temperature. These sensors connect to the heat pump’s existing wiring.
- Simulation: By adding resistors to the sensor lines, I can simulate different temperatures. This tricks the heat pump into thinking the water is at a certain temperature, controlling when it turns on or off.
- Automation: I programmed Home Assistant to handle scheduling based on electricity prices. The system now runs during off-peak hours, significantly cutting my energy bills!
Key Tips:
- Calibrate Sensors: Test the resistance of your sensors to ensure accurate temperature readings.
- Safety First: Set maximum temperature limits to prevent overheating.
- Fail-Safe: Configure the relay to default to the original state during power outages.
Results: After two months, the system is running smoothly. I can now control the heat pump from anywhere and it automatically adjusts based on real-time energy prices. Plus, I built a custom dashboard in Home Assistant to monitor everything!
If you’re looking to retrofit older appliances, I highly recommend exploring DIY smart solutions. It’s a bit of work upfront, but the savings and convenience are well worth it! 
Would love to hear if anyone else has done something similar or has tips to improve my setup! 