Boiler Control

The laundry node won't just be a passive note-taker, it will also control the boiler.

Our boiler has a basic programmable timer built in, with a limited number of timing slots (which are cumbersome to change). That should be much easier with a tablet based gui, with schedules uploaded to the jeenode. The boiler provides contacts that are in series with the timer switch (by default bridged), meant for an external thermostat.  It's easy to just add a relay into the circuit, turn the built-in timer to 'always on', and have the node control the on-off times (just in case, I will add a manual switch parallel to the arduino-controlled relay, so that we can always fall back to the build-in control).

We can do more than just provide a better control of the schedules: optimized start up. Instead of pre-programming the startup time of the boiler in the morning, we can sense the external temperature over night, and then delay starting the heating to the last possible moment. The longer the house remains cool over night, the less heat we lose. There' a possible downside to this though: it could increase our consumption. After cold nights, we sometimes find it too cold for our taste in the kitchen - we've under-heated. With optimal startup, the kitchen should always be reasonably warm when we need it, but that might mean coming on earlier than we'd program it to.

Ideally, I'd want to control the temperature setting, but that would require a more invasive change to the boiler. It has a potentiometer for setting the heating circuit temperature. I'd have to either somehow connect a motor to turn the potentiometer, or replace the potentiometer with something like a switched resistor ladder. Varying the temperature throughout the day should improve the efficiency of the boiler, but that's something that may have to wait.

Update I've realized that I can find out something else: the flow through the heating circuit depends only on the state of the thermostats in the house. If most of them are closed, the pump will be able to pump less water. If very little water flows (only through the bathroom), I can consider turning off the heating (at least for a while).