Extractor fan and/or heat recovery

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  • jcmiguel
    Automated Home Jr Member
    • Apr 2008
    • 38

    Extractor fan and/or heat recovery

    I just installed an whole house extractor with 3 speeds. Any suggestion for the object to control it? The wiring is 230v with first speed at live and additional second and third speeds connected to live. I would like to use one of my QRI for it. Thanks
  • Gumby
    Moderator
    • May 2004
    • 437

    #2
    I have a similar fan, in my case it's an input fan that pressurises the house slightly and has 4 speeds and a master on/off. I also have a 2 speed fan ventilating my Node-0 which is perhaps more similar to your example.

    In both cases I used a set of on/off load objects on a QRI, one for each speed. There are various ways that you can set up the controls, the simplest is (assuming temp thresholds) to put in three temp thresholds and add the required on/off actions in each one to set the on/off loads to get the desired speed.

    Another way is to set up a macro for each speed with the required switch config as a series of actions and then you can just start the macro if your speed control originates from more than one object - this is really a convenience factor.

    You do need to be careful if your fan does not operate 24/7, since temp thresholds are actioned on a crossing, so the temp transition may be missed if it is outside the fan operating time - Vivian is aware of this so there may be some enhancements to Cortex at some point.

    I have also used a general logic function to define a temperature range inside which the fan will operate.

    It also depends on the exact control wiring of your fan, you might be able to treat speed1 as a master on/off which makes it simpler to ignore threshold crossings being missed.
    ----------------------
    www.gumbrell.com

    Comment

    • jcmiguel
      Automated Home Jr Member
      • Apr 2008
      • 38

      #3
      Extractor fan

      Thanks for your promptly answer Gumby. I am using the simple on/off load to check if everything is fine. Major concern is humidity since Cortex control temperature well and in scotland a heat wave does not ask for fans . So I am just controlling the extractors for ocupancy of loos as well as humidity threshold.
      I will go into the macro approach later as I gather the data from the fans an loos. Thanks again

      Comment

      • jcmiguel
        Automated Home Jr Member
        • Apr 2008
        • 38

        #4
        Humidity

        Now a more technical question. I am a bit lost here. Considering that my major concern is humidity condensation, which should be my best trigger for the extractors? Relative humidity, dew point or dH/dt? I am guessing it is the last but I would like a technical answer explaining what each one measure. Any engineers around to help? Karam or Viv? Thanks

        Comment

        • chris_j_hunter
          Automated Home Legend
          • Dec 2007
          • 1713

          #5
          interesting question ... wonder if presence could be used (perhaps using two or more PIRs, to maybe allow detection of intent) and/or pressure-mats and/or water flow ?
          Our self-build - going further with HA...

          Comment

          • Karam
            Automated Home Legend
            • Mar 2005
            • 863

            #6
            Originally posted by jcmiguel View Post
            Now a more technical question. I am a bit lost here. Considering that my major concern is humidity condensation, which should be my best trigger for the extractors? Relative humidity, dew point or dH/dt? I am guessing it is the last but I would like a technical answer explaining what each one measure. Any engineers around to help? Karam or Viv? Thanks
            Well RH tells you something about the relative saturation of the air irrespective of the temperature - ie. something about its dryness. Absolute humidity tells you how much actual water is in the air eg. mg/litre but this doesn't in itself tell you anything about the air's capacity to take on more water (you can think of as how quickly can it take up your sweat) since that depends on temperature. Hence RH tends to be more useful for comfort assessment

            Dewpoint is the calculated temperature at which the present air would reach 100% RH. However you have to bear in mind that condensation in non 100% RH air occurs on surfaces cooler than the air eg. walls.

            If the fans are to be triggered purely on humidity then perhaps its best to start them based on a suitably large +ve change in RH, but you can also have a fallback of triggering on unusually high RH value. Turning off might be a bit trickier - could be done based on going below an acceptable RH value or could just be time period based after the trigger. The problem is that the RH of the air will naturally vary from day to day and to a lesser extent from hour to hour. However inside a house the variations (not accounting for direct sources of humidity) tend to be slow in general.

            Comment

            • Paul_B
              Automated Home Legend
              • Jul 2006
              • 608

              #7
              Is it possible with Cortex to use two humidity sensors? For example one in a bedroom and the other in the ensuite and measure the differential? For example RH differential rising about 5% then fan comes on, then falling below 10% fan goes off?

              Paul

              Comment

              • Karam
                Automated Home Legend
                • Mar 2005
                • 863

                #8
                Yes I think this might be easier than trying to capture a reference RH value before a significant change (in one sensor). But either way I don't think there is a way to do these at present without say scripting or API, so I think would require the creation of a specific behaviour function.

                Comment

                • Gumby
                  Moderator
                  • May 2004
                  • 437

                  #9
                  Seems like a generalised math function analogous to general logic object that can operate on value inputs and produce a value output would be nice. Could use it for other things as well.

                  Then either add a thresholding object, or allow thresholds on the output of the math function to get triggers.
                  ----------------------
                  www.gumbrell.com

                  Comment

                  • jcmiguel
                    Automated Home Jr Member
                    • Apr 2008
                    • 38

                    #10
                    dH/dt

                    Ok, I am starting to understand the complexity of the task but could someone explain what dH/dt measures? Thanks

                    Comment

                    • Paul_B
                      Automated Home Legend
                      • Jul 2006
                      • 608

                      #11
                      I'm making an educated guess that dH/dT is relative humidity? The dH being change in absolute humidity. This nbeing a better measurement of comfort level for humans

                      Paul

                      Comment

                      • chris_j_hunter
                        Automated Home Legend
                        • Dec 2007
                        • 1713

                        #12
                        measuring rate of change (of humidity, in this case, so dH/dt) would usually be a way of getting earlier warning of the rise of something (humidity, here) ... ie: the change would be noticed sooner - which would probably useful to get the fan going asap, and so minimise the rise ... measuring d2H/dt2 would give even more sensitivity, but need more accurate sensors, so probably not worth it ! That's as I understand things, anyway !

                        Chris
                        Last edited by chris_j_hunter; 25 June 2009, 12:43 PM.
                        Our self-build - going further with HA...

                        Comment

                        • Gumby
                          Moderator
                          • May 2004
                          • 437

                          #13
                          dH/dt is the rate of change of relative humidity (based on the labelling in the graph in Cortex).
                          ----------------------
                          www.gumbrell.com

                          Comment

                          • Gumby
                            Moderator
                            • May 2004
                            • 437

                            #14
                            I've attached 3 Cortex plots of RH, dh/dt and Dewpoint from the same period of time for comparison.
                            Attached Files
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                            www.gumbrell.com

                            Comment

                            • Gumby
                              Moderator
                              • May 2004
                              • 437

                              #15
                              I have an interest in humidity control due to historical problems with damp that I believe are down to condensation on/in cold solid (ie no cavity) stone walls during winter - despite all the nonsense of injected damp-proofing etc.

                              I don't have whole house extraction but I do have a dehumidifier in the coldest place and a PIV (passive input ventilation) fan that can move air from the loft (preheated from solar gain in winter) into the house.

                              At the moment I control the PIV fan within a temperature range, so that it doesn't blow hot air into the house when the loft is very hot and doesn't blow air in when it's really cold. The speed is stepped up as available air is warmer.

                              I control the dehumidifier based on RH in the room it is in.

                              So far it seems to have controlled damp issues very well through this winter.

                              A more intricate control scheme that attempts to manage the dew point to be above the temperature of the walls might be possible, but I'm not sure that it's worth it - especially since I couldn't find much actual research on the behaviour of water in solid stone walls.
                              ----------------------
                              www.gumbrell.com

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