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Thread: Extractor fan and/or heat recovery

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    Automated Home Jr Member jcmiguel's Avatar
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    Default 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

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    Moderator Gumby's Avatar
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    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.
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    Automated Home Jr Member jcmiguel's Avatar
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    Default 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

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    Automated Home Jr Member jcmiguel's Avatar
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    Default 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

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    Automated Home Legend chris_j_hunter's Avatar
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    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 ?

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    Automated Home Legend Karam's Avatar
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    Quote 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.

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    Automated Home Legend Paul_B's Avatar
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    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

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    Automated Home Legend Karam's Avatar
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    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.

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    Moderator Gumby's Avatar
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    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.
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    Automated Home Jr Member jcmiguel's Avatar
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    Default dH/dt

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

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