Smart Heating Control ...

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  • Kevin
    Moderator
    • Jan 2004
    • 558

    Smart Heating Control ...

    Well every time I start to look deeper into Cortex I find more and more sophistication - it certainly is a very different HA application. Enjoying it...

    I've been looking at the heating control and it seems really thorough in some aspects, yet appears, although perhaps I have missed something, to not address more typical opportunities.

    For example I was interested to see support for the outside temp as a modifier for internal setpoints based on the users perception of 'comfortable'. I believe that one of the German car manufacturers found that inside temperatures had to be higher at night than during the day (also when you can see snow) so maybe light level is a consideration too. Certainly very fancy stuff.

    ... Yet at a more fundamental level I can't see any support for optimised start. The aspect of calculating in advance the time to start your heating (at a zoned/room level) such that at your chosen time it just reaches the setpoint temperature. The same for hot water too. This I believe would be a great addition.

    The outside temp obviously has a significant bearing on this as does the current room temperature. I'm not sure though that I see a way of employing the outside temperature sensor to estimates heat loss based on this temperature differential - although maybe it is already included as the objects do seem very sophisticated. Perhaps I just need to explore fuzzy logic more. I guess the loading a radiator applies is dependent on its temperature differential to the room too, perhaps having a temp sensor on the radiator would be a useful sensor input .

    This aspect of the radiator temperature is an interesting one for me as my current system - which I now want to overide with Cortex , lowers the flow temperature by modulating the boiler down to balance the system as setpoint is approached. Unfortunately it can only do this for one room and I would like something similar in several independent rooms . The problem is that if that one room is satisfied and I wish to change another room upwards in temperature the flow temperature has been reduced to make it very slow or even impossible :-( Also I am not sure the aspect of a varying flow temperature would sit well with Cortex and its proportional / PWM control , I guess the key aspect is the radiator temperature. - but I need to play more and see.

    I wonder if Cortex calculates and uses thermal gradients for each room ?

    Anyone else exploring this route ?

    Kevin
    Last edited by Kevin; 16 March 2008, 09:40 PM.
  • chris_j_hunter
    Automated Home Legend
    • Dec 2007
    • 1713

    #2
    my car has automatic air-conditioning, and I usually set it it 19degC in the morning, go to-work, and +21degC in the evening, goinmg home ... ie: what's comfortable varies also with time of day !

    smart temperature control - through which the HA achieves comfortable temperatures at the times they're wanted, rather than just coming-on & going-off at chosen times - could perhaps be automatically learned ... ie: Cortex might perhaps be able to determine building time-constants by itself, over the course of a few days ... IIRC, some German heating controllers do this sort of thing ...

    'wonder if the weather forecast should be an input, too ??
    Our self-build - going further with HA...

    Comment

    • Paul_B
      Automated Home Legend
      • Jul 2006
      • 608

      #3
      You can get weather compensation units for some heating systems. I am not sure if this is built into the HVAC modules of Cortex.

      Comment

      • Gumby
        Moderator
        • May 2004
        • 437

        #4
        There's a bunch of features in HVAC to make use of outside temperature, including a transfer function where you can program exactly how much the demand temp should be modified -/+ for every value of outside temp between -10 and +40 and the option to use booster heat source if outside temp is below a programmable threshold. Similarly for cooling control.

        Those are the user-exposed ones, I will await Karam to comment on how the built-in algorithms utilise external temps for optimising control effect.
        ----------------------
        www.gumbrell.com

        Comment

        • Karam
          Automated Home Legend
          • Mar 2005
          • 863

          #5
          In a sense you have touched on some our long standing deliberations on the subject of 'optimisation'. Cortex does indeed provide a means for adjusting setpoint based on external conditions, and of course dealing with different setpoints for different times of the day is already done by the fact that you can shape your setpoint profiles on a 24/7 basis, but these measures mainly deal with the comfort factor and other not so obvious physical realities. For example adjusting the set point due to external conditions may seem theoretically absurd since after all if the sytem controls tightly then why would the occupant feel any different irrespective of outside conditions?

          But the fact of the matter is that many other factors affect perceived comfort - some psychological some physical. The physical ones for example include the fact that temparature gradients exist within a room and are more pronounced when the internal/external differential is greater. Similarly draughts of colder air have a similar effect but more on the vertical gradient. Another important factor is relative humidity. Most 'comfort' indices include this as a parameter and indeed we know of some IDRATEK installations where humidity is actively controlled as well as temperature. Many psychological factors as well of course.

          As for 'optimisation', I use the quotes deliberately since you have to be clear on what it is you are trying to optimise. If you try and optimise comfort you are very likely not to optimise energy efficiency. Similarly you may seek to optimise regulation (how closely the temperature follows the setpoint when this is level) but this may not optimise the life of your plumbing nor even energy efficiency.

          As an example, 'early start' optimisation (by which I mean advancing the heat switch on time depending on conditions) may try to get the temperature to the desired value at the required time but may not necessarily be better from an energy consumption point of view. The reason is one of the 'human factor'. You may feel good and comfortable that your house is at 21C at 8am no matter what the conditions, but on the other hand without the optimised start you may have tolerated it only getting to 21C by 8:30am in winter months.

          As far as I know most optimisation schemes seek to optimise reaching a setpoint at a given time - based on the older style concept of timed heating controls (ie. that you switch the heating off for example overnight). So in effect the idea is that you advance the switch on time relative to that which the user has specified. The amount of advance can be based on some suitable measure eg. external temperature or simply deduced indirectly from internal heating characteristics (eg. how long did it take to get to this setpoint yesterday, or to rise by n degrees after last switch on). Using external temperature can make the adaption mechanism forward looking.

          If you want to go the whole hog or refine the adaption you can start creating parametric models and then try and deduce the parameters from input/output data. But it is a balance of how good your data is, how good your models are, and how worthwhile the return might be.

          Cortex advanced controllers feature does provide a means for using fuzzy logic or parametric controllers eg. PID or higher order. This is mainly to address the regulation optimisation aspect - but of course you need capable plumbing or electric heating to actually be able to do this properly (ie. ability to go beyond slow on/off heating either through PWM or some other means). And then you have parameters to select ... (we have stopped short so far of providing a self tuning mechanism)

          We have not yet introduced a 'time advance' type of optimisation in Cortex. To a large extent the timerless paradigm with gently profiled setpoint curves means that you barely notice any difference in the 'setpoint attainment' objective come winter or summer, but this is just addressing the 'comfort optimsation' i.e it hides an element of cumulative energy inefficiency which no doubt will be our next task to address ;-)

          Comment

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