Still not satisfied

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!

 

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5 Responses to Still not satisfied

  1. jwestra says:

    Can’t you set the “measured” temperature with an OpenTherm Gateway?

  2. Nope… only the outside temperature.

  3. Sander says:

    I really like your site! Some cool stuff your doing here 🙂

    I’m quite new to home automation and only have a programming background so I’am missing some electronics knowledge (for the time being that is 😉 So I started with a JeeNode with a RF12B radio attached to it.

    The challenge I now face is that I have a new boiler (an Intergas HReco) which has an internal RF module. So the best (cleanest) way to connect would be to hook up the build-in RF module directly to the RF12B radio on my JeeNode.

    But I assume that will be quite a challenge right? Did you every tried that yourself? As I understand it I would need more insight in the OT v3 protocol description as that one aslo defines the RF part of the protocol used for the build-in RF module. But I cannot seem to find anything newer then the v2.2 version. Do you know someone who could help me get my hand on the v3 version?

    The purpose is that I want my floorheating pump to only run when the CV pump is running, as the HReco is a “doorloop” (no clue how to translate that one 😉 heater. So if my pump keeps running, the CV will keep burning and burning 🙁

    So for now I pulled the plug from the pump as our floorheating is only for the kitchen, so we do not depend on it. Any other thoughts about how to fix this are also welcome, but the RF one seems the coolest solution… But maybe also the hardest 🙂

    Cheers!

    • Hi Sander,

      Thanks, and never mind what background you have – mine (a long time ago, it seems) is industrial automation technology, where you get ‘a bit of everything‘. Still learning!

      And I think you’re facing quite a challenge – OTOH, the thrill of accomplishing something by yourself is the biggest of all…

      I never tried this myself cause my boiler doesn’t do RF and I’ve never seen any OTv3 documentation yet, nor do I know someone that does have OTv3 documentation. I’d like to get my hands on that too.

      What if you could determine whether the CV pump is running or not – wouldn’t that suffice? That shouldn’t be too hard, although it would mean you’ll have to add some kind of sensor for that. You could think of monitoring the voltage applied to the CV pump, or adding a flow meter in the CV piping circuit; or just adding a temperature sensor to measure the boiler flow temperature – just like a pump switch works, like this one does…

      Depending on whether the boiler produces hot water, the floor heating pump will work or not…

      Isn’t that what you’re looking for? OK, you might not think this is a cool solution, but this one is cool by simplicity! 😉

      • Sander says:

        Hi Robert,

        Thanks for your reply, and I was indeed also thinking about a less cool, but more efficient (and more achievable) solution 😉

        I think one simple solution is adding a wire into the 24v pins that control (on/off) the motor. It’s a 230v motor, but it seems to be switched on or off by an additional 24v output.

        I suppose I could hook up a Opto-coupler Plug with the (right resistor) directly to an additional JeeNode mounted inside the CV to monitor if the motor is running or not. And then send that using the RF12B radio to another JeeNode mounted near the floor heating pump.

        The other suggestions (flowsensor or tempsensor) do not work as the water will keep flowing as long as the floor heating pump is running, even is the CV pump is stopped. And the CV will also keep heating the water in that case as it will try to keep the water in the CV at a certain temp so hot water is readily available.

        That is exactly why I’m looking into this 🙂 I actually currently have the pump switch you linked to, but as said that looking at the temp of the water pumped into the system. And that will remain hot as long as water keeps flowing and the CV keeps burning to get hot water pre-heated 🙁

        Intergas has a electronic two-way valve to solve this as well, but that solution is even less cool of course 😉

        Cheers,

        S.

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