Modulating OpenTherm Thermostat behavior

A few days ago i was cleaning up my office and found a cable with a 1-Wire DS1820 Temperature sensor connected to it. I completely forgot about that… before we got our new Remeha central heating, i had this sensor connected to the pipe through which the hot water flows to the radiators.

I added a second DS1820 to the cable, plugged the cable back into the HA7Net, connected the sensors to the pipes for incoming and outgoing water and started logging the temperatures to the database. Of course, this was a good opportunity to make a new chart with the ASP.NET Charting Control. I haven’t done much with this control yet, so this would be a good exercise.  The result of this exercise has already been embedded in my website.

With a Oregon Scientific temperature sensor placed on top of the thermostat that’s in the livingroom, i can also monitor the temperature near the thermostat very closely.  It would be nice to see what the heating is doing in relation to the temperature in the livingroom. Here it is:

Heating Temperatures

The Oregon sensor and thermostat sensor don’t always agree on the right temperature; most of the time the Oregon displays a value that’s 0.1 lower then that of the thermostat. That explains the average of 20.9 degrees in the upper chart. With the thermostat having a constant setpoint of 21 degrees (Celsius)  you can say it does a good job.

The temperature of the water that warms up our house, is much lower than i remember when we had an ‘on/off’ heating. Now the outgoing temperature barely comes above 45 degrees anymore. Looking at the behavior of the incoming and outgoing temperatures of the heating, you can see that the heating is still switched on and off quite a lot of times. Apparently it’s not cold enough yet to keep the heating burning for longer periods at it’s lowest energy level. Over dimensioned heating? 🙂 . I wonder what this will look like in the middle of the winter; the periods that the heating is constantly burning should get longer then.

Now all i have to do is add a flow-meter in the heating water circuit and i can calculate the amount of energy that is effectively pumped into our house…

To monitor the heating in a more convenient way, I’m going to create an extra page on my website soon with all the real-time details.

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