After monitoring the temperatures in our house for a week with the new external sensor attached to the room thermostat, I’ve seen improvements and some things I didn’t expect.
The good thing is that the temperatures upstairs went up with approx. 2°C in the rooms upstairs, much closer to what they should be. What worried me was that the temperature in the living-room still got too high sometimes – the floor heating just produced too much heat under certain circumstances.
And the fact that the door between living-room and hallway being open for about 10 cm. still had a lot of influence on the external thermostat sensor in the hallway is something I didn’t expect – I’ll have to do something about that. Keeping that door closed is not a real option – our 3 cats (and hence the rest of the family) wouldn’t like that…
So what are the plans for next week?
Capping the floor heating
It sounds like a good idea to ‘cap’ the floor heating – why should I keep the floor heating pump running when the temperature in the living-room is equal to or higher than the temperature setpoint over there? I can’t think of any reason why I should, so I created a time-triggered event that periodically checks the measured temperature in the living-room, compares it to the room setpoint and shuts down the pump if the temperature is OK.
Creating my own reference temperature
Although the idea of an external temperature sensor already improved things a lot, I’m still not satisfied. What I’d really like to do is ‘feed’ the thermostat with a self-made reference temperature, i.e. a temperature value other than just the temperature of the living-room, hallway or any other individual location in our house. That self-made reference should somehow reflect ‘the need for heat’ throughout the whole house, no matter where that need comes from: living, office, bathroom, bedrooms – wherever.
The first one is simple; an appliance module is all that’s needed. The second one needs some more work, namely:
1. How to calculate this reference temperature
Should it be a value calculated based on an accumulation of all errors (measured temperature minus setpoint) of the rooms involved? Or the average error? Should a temperature error in the living-room have a bigger impact than the temperature error in the bathroom? And how about automatic ‘room exclusion’ (as in excluding rooms with a door or window open) from the calculated reference temperature?
2. How to make the thermostats’ external sensor contact ‘sense’ this temperature?
The external sensor is ‘just’ an NTC, a sensor with a resistance that varies with the temperature. Is there a way to simulate an NTC with hardware & code? With a digital potentiometer perhaps? But will this digital potentiometer be accurate enough, provide enough resolution and will I be able to mimic the nonlinear R/T characteristic of the NTC well enough?
A lot of questions, new things to learn, explore and try out; which is just what I like to do most!