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Thread: Evohome Zoning Landing/Hallway

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    Automated Home Jr Member WiteWulf's Avatar
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    Default Evohome Zoning Landing/Hallway

    Morning all, quick question re. zoning and installing radiator valves (HR92s in this case):

    I've got my evohome system set up for all rooms in the house but the entrance/hallway and first floor landing are currently on "dumb" TRVs set quite low. I'd like to have more control over the temperature in these areas but am unsure how best to go about it. As this is a relatively large (vertically) open space with a radiator on the ground floor (in the hallway) and another on the first floor (landing), without any doors inbetween, should I put HR92s on both rads and put them in the same zone or separate zones? The hallway rad is obviously going to spend quite a bit of time heating the landing as it's heat rises up the stairs, but if they're in separate zones at least the landing will stop calling for heat once it reaches it's setpoint.

    Any advice/opinion gratefully accepted...

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    I have HR92s on the 3 radiators in my hall/stairs/landing and I use the inbuilt sensor in the EvoTouch to control these HR92s as a single zone. My controller is wall-mounted in the Hallway. No issues as far as I can tell.

    The problem with using dumb TRVs is that the zone will always be ON whenever another zone demands heat.

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    I have one large Rad downstairs and 2 smaller ones upstairs.
    All 3 have HR92s on them, with upstairs(2) being a separate zone from downstairs(1).

    Initially I had it all as one zone but upstairs was getting too hot as it was thinking the whole zone wasn't up to temperature. It never would be as heat rises away from the downstairs portion.

    Now in 2 zones upstairs rarely calls for heat but when it does, it helps build a 'wall' of heat to prevent downstairs from sending too much up the stair well.
    Which allows downstairs to heat up quicker, with the lower temperature differential between the 2 zones. Otherwise downstairs would just pump heat up and it would get too warm on the 1st floor.
    So yes get some HR92s on and make it 2 zones.

    As a test before spending money, make 2 seldom used rooms dumb again and try using existing HR92s.

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    Automated Home Jr Member WiteWulf's Avatar
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    Thanks for the advice guys. I talked to the installer who came out to fix some issues I'd been having with the rest of the evohome system today and he suggested the same, although to be careful to leave enough "open" radiators on the system as Worcester Bosch recommend a minimum demand of 10% of the boiler output. Just having the towel radiator in the bathroom probably wouldn't be enough for our 30kW boiler so I'm a little torn as to what to do now. The boiler's a modulating model, though, so I guess it ought to be okay at a lower power output.

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    Quote Originally Posted by WiteWulf View Post
    Thanks for the advice guys. I talked to the installer who came out to fix some issues I'd been having with the rest of the evohome system today and he suggested the same, although to be careful to leave enough "open" radiators on the system as Worcester Bosch recommend a minimum demand of 10% of the boiler output. Just having the towel radiator in the bathroom probably wouldn't be enough for our 30kW boiler so I'm a little torn as to what to do now. The boiler's a modulating model, though, so I guess it ought to be okay at a lower power output.
    Pump bypass?

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    Quote Originally Posted by WiteWulf View Post
    Thanks for the advice guys. I talked to the installer who came out to fix some issues I'd been having with the rest of the evohome system today and he suggested the same, although to be careful to leave enough "open" radiators on the system as Worcester Bosch recommend a minimum demand of 10% of the boiler output. Just having the towel radiator in the bathroom probably wouldn't be enough for our 30kW boiler so I'm a little torn as to what to do now. The boiler's a modulating model, though, so I guess it ought to be okay at a lower power output.
    If the towel radiator is always on. Then I'd think that as an HR92 would actually fire the boiler then the open HR92 equipped radiator would bring demand up to 10% or greater.

    If a house already has TRVs in it, then there has always been the chance when the timer comes on, demand was below 10% anyway.

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    Quote Originally Posted by WiteWulf View Post
    Morning all, quick question re. zoning and installing radiator valves (HR92s in this case):

    I've got my evohome system set up for all rooms in the house but the entrance/hallway and first floor landing are currently on "dumb" TRVs set quite low. I'd like to have more control over the temperature in these areas but am unsure how best to go about it. As this is a relatively large (vertically) open space with a radiator on the ground floor (in the hallway) and another on the first floor (landing), without any doors inbetween, should I put HR92s on both rads and put them in the same zone or separate zones? The hallway rad is obviously going to spend quite a bit of time heating the landing as it's heat rises up the stairs, but if they're in separate zones at least the landing will stop calling for heat once it reaches it's setpoint.

    Any advice/opinion gratefully accepted...
    I would suggest that you try configuring all the radiators in your hallway/landing space as a "multi-room" zone.

    If you use a single temperature sensor for the zone, (single room zone mode, using one of the HR92's as the sensor or a remote sensor such as the evotouch or DTS92) for multiple radiators in a large vertical space I think you'd tend to find that it will be hotter at the top than the bottom due to heat rising from the lower radiator... If you measure the temperature at the bottom then the top will be hotter than the indicated/set temperature, while if you measure it at the top the bottom will be colder than the indicated/set temperature.

    Either way you could end up with quite a big temperature gradient from the ground floor to the top floor. In these standard modes all the radiators in the zone are controlled in unison from the single temperature reading from one temperature sensor, which can't account for this vertical temperature gradient. (Even between the floor and ceiling of a single room there can be quite a temperature gradient)

    However if you configure the HR92's in your hallway/landing as a "multi-room zone" what you end up with is a single zone control/scheduling wise that can only be set to one temperature at a time, however each HR92 in that multi-room zone measures its own temperature independently of the others using its internal sensor and adjusts its own radiator independently of the other HR92's in the zone to try to reach that target. (Only the measured temperature of the first HR92 is reported on the controller though)

    This way any natural tendency of the heat to rise would be automatically sensed by the top floor HR92 causing it to close down its radiator to bring the top floor temperature back down to the same temperature as the ground floor. After a while it would reach an equilibrium where the top floor radiator was putting out less heat than the bottom floor radiator (perhaps not very much heat at all) as the ground floor radiator would heat both the ground floor and partially heat the top floor, while the top floor one would only heat the top floor.

    Note: I haven't tried this as I live in a bungalow, but it should work...

    You could also just make the two radiators independent zones, and always schedule them to the same temperatures as each other but that wastes one of your 12 available zones, complicates programming and control, and gives the user the impression that you can completely independently control them when you can't really as they are in the same "room" so will always interact. Having one zone where both radiators try to keep their part of the vertical space at the same temperature makes more sense and is simpler to control.

    Quote Originally Posted by WiteWulf View Post
    Thanks for the advice guys. I talked to the installer who came out to fix some issues I'd been having with the rest of the evohome system today and he suggested the same, although to be careful to leave enough "open" radiators on the system as Worcester Bosch recommend a minimum demand of 10% of the boiler output. Just having the towel radiator in the bathroom probably wouldn't be enough for our 30kW boiler so I'm a little torn as to what to do now. The boiler's a modulating model, though, so I guess it ought to be okay at a lower power output.
    Make sure they installed an automatic bypass valve and set it correctly and you should be fine. Depending on your system configuration its somewhat mandatory to have an ABV with an Evohome system, without it you would need a bypass radiator which kind of defeats the purpose of fully zoned control where you can get heat in one room without causing a bypass radiator elsewhere to heat up as well.

    I have a pretty old boiler but before I installed Evohome I had a plumber install an ABV while doing some other work... when I later installed Evohome myself I was able to convert the old hallway radiator (previously with no TRV and in the room with the original wall stat) to being HR92 controlled and thus eliminate the bypass radiator. Being able to turn on an individual room in the house without that damn hallway radiator going full blast when not wanted is one of the things I like the most about my system now...

    By the way when demand is low Evohome automatically modulates the boiler - either by directly dropping the flow temperature (if you use OpenTherm) or by duty cycle / TPI modulation if you use the boiler relay.

    If only a single room was demanding a small amount of heat, instead of running the boiler at full blast with the radiator valve only slightly open, what it does is modulates the boiler (drops the flow temperature down low with Opentherm, or runs the boiler relay at a low duty cycle, which also drops the flow temperature) and then opens the radiator valve wider to compensate, allowing a decent amount of flow and allowing the boiler to still operate in condensing mode.
    Last edited by DBMandrake; 21st April 2016 at 07:09 PM.

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    Automated Home Jr Member WiteWulf's Avatar
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    Thanks DBMandrake, super informative reply. I've bought another HR92 (Plumbing Supermarket on Amazon were doing them for 58.99 with free delivery) and have the landing and hallway set as separate zones. I'll see if I can figure out how to set them as a multi-room zone as that sounds the best route.

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    Multi-room zone is just a parameter in the zone configuration.

    If you already have both HR92's bound to two separate zones, first delete one of the zones (and unbind that HR92 through it's own interface) then bind that unbound HR92 to the still existing zone as an additional actuator. Initially it will be an additional actuator in single room mode.

    Then go into Zone configuration->(zone name)->Parameters and change Single/multi room zone to Multiple. Only the "first" bound HR92 in the zone will report its temperature back to the controller, although both will show their own measured temperatures on the HR92 display if you use Room Temp 1 in the HR92 config.

    If the HR92 reporting its temperature back to the controller is not the one you want I think you can change it without rebinding everything from scratch simply by going to Zone configuration->(zone name)->Temperature Sensor->Remote Sensor and then bind when prompted the HR92 of the pair that you want to report its temperature back to the controller. Either way both HR92's will follow the set point schedule for that zone but otherwise work independently of each other.

    I think you can manually override just one HR92 or the other by turning the dial on the HR92's when in multi-room mode, but at the next set point change (whether scheduled or from the controller panel or phone app) they will be brought back into line with each other again.
    Last edited by DBMandrake; 21st April 2016 at 09:41 PM.

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