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Thread: Outside Air Temperature sensorfor Evohome

  1. #1
    Automated Home Lurker
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    Default Outside Air Temperature sensorfor Evohome

    Hi all,

    Had an Evohome zoned system for several years which works really well. Had one of these Oregon weather stations things to tell us actual OAT- that's just died and wondered whether possible to integrate OAT measurement and display on Honeywell app. Idea is NOT for that sensor to feed in to Evohome calculations, but simply to be standalone OAT reporter. Thought I might be able to use an old HR80 to doi the job by setting up the garden as a separate zone- tried putting HR80 in fridge to test the idea and that worked fine, but when theh put HR80 in freezer to test temps below zero C, seemed that either sensor or app wouldn't report anything below 0.5 deg C and just sat at that level even through freezer about -18 deg C. And whole point of OAT would be to know when temp has dropped to zero and below.

    So would like to call on experience of forum members on how to create an OAT sensor that will link/report to Evohome app. Can't find any commercial device that seems fit for purpose, so could either an HR80 or app itself be pimped to report lower temps and/or any other suggestions for workaround much appreciated. Have been in touch with Honeywell but their response is that Evohome doesn't need OAT sampling- which of course was not the question...all I want to be able to do is know is the temperature in our garden via the Honeywell app from wherever I happen to be.Thx in advance.
    Last edited by Gnasher; 29th December 2020 at 12:44 PM.

  2. #2
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    The HR92 can measure lower than freezing (I've tried it when testing frost protect mode) however doing so you will trigger frost protect mode and likely cause the boiler to come on even if it's not fitted on a radiator, so I don't recommend using a normal zone as a faux outdoor sensor.

    The new WiFi model of controller does not support binding outdoor temperature sensors, so if you have that model you're completely out of luck with displaying a 3rd party outdoor temperature sensor.

    If you have the older non-WiFi model which uses the RFG100 then theoretically it would be possible to impersonate the official Honeywell outdoor sensor and have it display on the status bar but I'm not sure if there is any software which currently does this. A couple of possibilities would be Domoticz or @zxdavb 's evohome_rf script, but I'm not sure if they have that functionality or not.

  3. #3
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    Thx for useful response- HR80 going back in freezer to see whether will go/show lower than 0.5 if I 'cook' it for longer. Could probably live with frost protection being activated, but interested in idea of using 3rd party sensor and script as I do have the older RFG100 setup. Any suggestions for sensors worth experimenting with? Probably a sledgehammer to crack a nut but intrigued to know if I can find a solution. UPDATE ***HR80 definitely doesn't display anything below 0.5 deg C on unit or via app. Next job will be to put an HR92 in the freezer and see what that reports.
    Last edited by Gnasher; 29th December 2020 at 11:09 PM.

  4. #4
    Automated Home Jr Member DerekWilliamsUK's Avatar
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    See link for official HR92 Specification datasheet PDF. If i understand this correctly it may not show below 0c ('Environmental Temperature' from page 2).
    https://heatingcontrols.honeywellhom...eet%5B1%5D.pdf

  5. #5
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    Perhaps if Evohome was made to be compatible with HomeKit, there is nothing preventing that now, then an outside temperature sensor could possibly be configured in HomeKit to feed information back to Evohome. I have Philips Hue sensors and in HomeKit they can be configured to operate other things. It ought to be possible with Evohome. But then there seems to be a lack of desire on the part of Honeywell to bring the product into today’s world.

  6. #6
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    The RFG100 cannot be used to display the external temperature on the V2 controller. The RFG100 was never programmed to transmit or display external temperature, that was a local function. You could pair a local external sensor and have that displayed on the V2 controller. I used to use that, as I had my external sensor from my Hometronic days. Evohome V2 also only used the temperature part of the sensor, not the light sensor. Hometronic used to use both and that's what used to determine when our curtains would operate.
    Domoticz (along with the HGI80) has a function coded in it where, you could display any temperature you wanted on the V2 controller. You could even point an Internet feed to have that displayed.
    All of this has disappeared on the V3 controller. If you want to use your HRxx as a outdoor sensor, make sure you create an Electric Underfloor zone, so that it doesn't fire up frost protection and actually doesn't even create a boiler demand. I still don't know how much below 0C the HRxx's sensor is accurate enough.

    The HR80 apparently uses an NTC 20K, which actually has an operating range of -50C to 130C. So it is possible to measure external temperatures with this. I used to use it to measure my loft temperature, and disconnected the motor etc from it, so that it just had the bare minimum for my needs.

    https://products.ecc.emea.honeywell....-ge51r0319.pdf
    Last edited by bruce_miranda; 30th December 2020 at 04:42 PM.

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