Using a air to water heat pump for heating is causing condensing water on the outside unit. The units thus needs regular defrosting and resulting water needs to be handled somehow to avoid covering the unit totally inside an ice cube. In my case there is a drip tray under the outside unit and the water is then flowing to a rain sever. The drip tray is equipped with a self adjusting heating cable. Since I wasn’t happy to have that heating cable powered on all the time, I added a bit of a logic to control it.
I wrote in the previous post, I’m already reading operational values from the heat pump. That data contains also values for outside temperature and status if the defrost cycle is going on. I’m feeding this data to Siemens Logo logic that controls the power for the heating cable. Integration is based on a Nodered (with node-red-contrib-s7) flow that writes values from heat pump to the Logo and also reads status from the logic and archives that the database.
The logic has
- Off state
- On state
- Auto state – where heating cable is powered on for every defrost cycle for a preset time in addition to the actual defrost cycle. There is also some failover logic in case if the input values fail to change for too long period.
- Status indicators (text & background colors) and counters for operating hours