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Thread: Added Y87RF to external wall -- possible to compensate down by a couple of degrees?

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    Default Added Y87RF to external wall -- possible to compensate down by a couple of degrees?

    Hi folks,

    I added a Y87RF to the master bedroom which has two radiators because it was always below temperature (based on a separate thermometer I have in the room). I assumed that having the Y87RF on the opposite side of the room would even things out nicely, and it made a massive difference. Too massive. The room is now almost 2 degrees above the temperature that the Y87RF sees, and I think the reason is because I mounted it on an outside wall. Using an infrared laser thermometer thingie, I measure 2 full degrees C difference between the external wall and the internal wall it is adjacent to, 20 cms away (the Y87RF is mounted in the corner). So... is there a way of saying "please add 2 degrees to the temperature that this Y87RF thinks it is"? If that's not possible, my two options are:

    1) Move the Y87RF (leaving some holes behind) to the inside wall
    2) Adjust the whole schedule of the room down by 2 degrees -- very confusing, and even more if my wife needs to fiddle with the Y87RF

    Thanks!

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    As far as I know the Y87RF and DTS92 don't allow any "calibration" adjustment like the HR92's or built in sensor in the Evotouch.

    So your only realistic option is to move the sensor. To be honest I would never recommend mounting the sensor on an external wall - for exactly the reason you have discovered - the wall itself can be a couple of degrees colder than the rest of the room or the interior walls, causing the real room temperature to go above the set point as the sensor tries to compensate.

    I tried the DTS92 in my living room on 3 different walls in several locations when I first got it (temporarily held in place) to find where it worked best, and the outside wall, even away from the bay windows and radiators was a big no no.

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    Thanks for the reply. That's quite annoying. Oh well... ruined a perfectly nice wall.

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    Quote Originally Posted by rotor View Post
    Thanks for the reply. That's quite annoying. Oh well... ruined a perfectly nice wall.
    NO Hold On DTS92E definitely has a hidden menu where you can set an offset so it may be possible with Y87RF

    https://www.manualslib.com/manual/81...h.html?page=13

    Worst Case you could Replace Y87 with a DTS92e and Sell Y87RF screw holes will line up as both stats have same mounting template
    Last edited by mylesm; 30th January 2018 at 04:23 PM.

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    Are you sure the temperature offset applies when bound to an Evohome ?

    A lot of the parameters you can configure in the menus of a DTS92 when bound directly to a BDR91 are disabled and unreachable when you bind to an Evohome.

    I can check mine tonight if you like to see if the setting is still available ?

    To be honest I'd still move the stat, because while it might be a 2 degree offset needed now, as the weather warms up the required offset will change. Better to get it somewhere in the room where it will sense the true room temperature correctly then you won't need any offset and won't need a different offset at different times of the year...
    Last edited by DBMandrake; 30th January 2018 at 04:28 PM.

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    Quote Originally Posted by DBMandrake View Post
    Are you sure the temperature offset applies when bound to an Evohome ?

    A lot of the parameters you can configure in the menus of a DTS92 when bound directly to a BDR91 are disabled and unreachable when you bind to an Evohome.

    I can check mine tonight if you like to see if the setting is still available ?

    To be honest I'd still move the stat, because while it might be a 2 degree offset needed now, as the weather warms up the required offset will change. Better to get it somewhere in the room where it will sense the true room temperature correctly then you won't need any offset and won't need a different offset at different times of the year...
    Yes I think the DTS can be offset Even in EVO I did it before when setting up some but its a while ago so worth Checking

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    Quote Originally Posted by DBMandrake View Post
    Are you sure the temperature offset applies when bound to an Evohome ?

    A lot of the parameters you can configure in the menus of a DTS92 when bound directly to a BDR91 are disabled and unreachable when you bind to an Evohome.

    I can check mine tonight if you like to see if the setting is still available ?

    To be honest I'd still move the stat, because while it might be a 2 degree offset needed now, as the weather warms up the required offset will change. Better to get it somewhere in the room where it will sense the true room temperature correctly then you won't need any offset and won't need a different offset at different times of the year...
    Thanks, you're absolutely right about that (in summer the offset would be even possibly in the opposite direction). It goes to show how subtle a lot of this stuff is -- a couple of degrees makes a *huge* difference!

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    Quote Originally Posted by rotor View Post
    Thanks, you're absolutely right about that (in summer the offset would be even possibly in the opposite direction). It goes to show how subtle a lot of this stuff is -- a couple of degrees makes a *huge* difference!
    Finding a good location for a wall thermostat for best control year round is actually quite challenging, which is why I mounted mine with double sided tape trying several locations before settling on one. There are a lot of conflicting criteria including:

    * Not too close to a window (especially not under one) and at least 1.5 metres from any radiator
    * Not too close to any other heat sources like TV/AV cabinet etc
    * Not on an outside wall (that limits you to two walls in many rooms)
    * The right height off the floor (since the temperature is lower closer to the floor and higher closer to the ceiling) 1.2 metres seems to be recommended probably because it is half the height of a typical 2.4 metre ceiling (although our ceilings are 2.8 metres...) and at a convenient operating height for controls
    * Not somewhere where sun could shine directly onto the thermostat - figuring out exactly what parts of the walls don't get sun at any time of year or time of day is not as easy as it looks especially if you have large bay windows or deciduous trees outside the window...
    * Preferably somewhere near where the room occupants are - for example behind a sofa is a good place if it meets other criteria.
    * Not close to a door.

    In our living room I was able to find a spot that satisfied all criteria except for the not close to a door one, which I had to compromise on.

    My evaluation process was both to compare the sensed temperature with a standalone sensor in the room, but also to determine whether the same set point felt equally comfortable in different conditions like day vs night, cold weather vs warmer weather. If you find the ideal spot for the sensor in theory you shouldn't need to change the set point based on time of day or weather, and that seems to be the case in our living room which is scheduled for 20.5 and seems pretty much spot on for comfort regardless of outdoor conditions. Whether it's 10 degrees outside or -3 and snowing we wouldn't know if the blinds were closed!

    That was certainly not the case with the HR92 as sensor, let alone the original mechanical TRV it replaced. Both had to be manually turned up in colder weather to compensate.
    Last edited by DBMandrake; 31st January 2018 at 12:04 PM.

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    I always think the best position for a room stat is as close as possible to where you normally sit.

    The DT92 comes with a stand, which gives you ever more options (coffee table, etc.) compared to the round stat. Although, it has to be said, it isn't exactly pretty.

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    Quote Originally Posted by paulockenden View Post
    I always think the best position for a room stat is as close as possible to where you normally sit.

    The DT92 comes with a stand, which gives you ever more options (coffee table, etc.) compared to the round stat. Although, it has to be said, it isn't exactly pretty.
    I sort of agree with you, but I also don't.

    Yes, having the thermostat in the part of the room where the occupants are is a good idea, especially if there is any sort of temperature gradient across the room such as an open plan kitchen/living room layout or a permanently open hallway entrance that is sapping heat away.

    On the other hand, if you move the sensor around from one place to another for a given fixed set point the actual temperature that you get in the room is going to vary greatly based on where you position the sensor. I did actually try the DTS92 on its stand in various places in the room for a few weeks and decided I didn't like the fact that the room temperature attained changed so much based on placement of the sensor in the room. (Which is the point of my previous post really) Coffee tables etc are more likely to end up with direct sunlight shining on them too.

    And now that we have a nearly two year old the thought of having the DTS92 on a stand where he can reach it doesn't bear thinking about... Not so much because I'm afraid it will be broken, but more that it will end up on the floor, under the couch, in a toy box, or in another room altogether and no longer serve it's purpose, causing the room temperature to end up either extremely low or high due to the false sensor reading until it can be found and re-instated!

    There is one last reason to prefer wall mounting over table top mounting IMHO, and this fits into something you have said before about the "fabric of the room" taking time to warm up. If the sensor is free standing on a coffee table it is only measuring the ambient air temperature.

    As you've pointed out in other threads when a room initially warms up, when the air temperature first gets to the set point the room may still feel a bit cold and take time to feel comfortable. This is because the air temperature is at the target but the walls are still cold - especially if you have thick, solid interior walls as we do. (Plaster over brick) So the air temperature might have reached 20 but the walls are still 17 degrees! Easily confirmed with an IR temperature gun. It's not just air temperature we feel, we also feel the IR radiation from the walls (or lack of it) on our skin and the two together give our sense of comfort.

    However if you mount the DTS92 on the wall, the close proximity of the wall means that the temperature it senses is biased strongly towards the surface temperature of the wall, as the wall controls the temperature of the back panel of the sensor. So in the scenario that the air is 20C and the wall is still only at 17C the sensor probably reads about 18C, whereas if it was on a table stand it would read 20C. Because it only reads 18C it keeps heating the room trying to reach 20C.

    The air temperature may temporarily go slightly over the target set point (as judged by a free standing thermometer) while the walls are warming up but after a while it will settle in a situation where both walls and air are at the desired set point. (At least the wall the sensor is on) Then the room will feel comfortable. Because it takes the wall temperature into account it won't falsely indicate that the room is up to temperature when really only the air is warm and the room is still cold, and it will get the walls up to temperature quicker than sensing the temperature of the air alone as it will keep heating at a faster rate until the walls near the set point.

    The fact that mounting the sensor on an exterior wall - which in rotor's case is about 2C lower than an interior wall can cause it to heat the room to 2C higher than the set point (as measured elsewhere) shows just how strong the wall proximity effect is on a wall mounted thermostat. Most people believe they measure only air temperature but it's simply not true when wall mounted!

    So I agree that it's preferable to have the sensor near where the occupants are, but I think it should still be on a suitable piece of wall if you want consistent results for a given set point.
    Last edited by DBMandrake; 31st January 2018 at 12:29 PM.

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