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Thread: Some Help Please With Multiple Zone Valves On Evohome

  1. #1
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    Default Some Help Please With Multiple Zone Valves On Evohome

    I'm just sourcing the bits for my domestic system and have already got the EvoHome starter kit with 4 x TRV controllers. There is going to be a thermal store for DHW and heating, which will demand heat from the boiler and pretty much look after itself to keep at tempearture. Solar PV will be warming the store via 3 x 3kW immersion heaters whenever the sun shines.

    DHW will be direct from the store via a plate heat exchanger at mains pressure with no need for any control. So all the EvoHome system has to do is demand heat from the store, control the circulation pump and open/close any valves. It's a big system all piped in 28mm because of the distances from end to end.

    In total I have 16 radiators, not all of which can be fitted with a TRV (long story) plus some other emitters that can only be controlled by 2 way valves for which I plan to use several V4073H (28mm). The thermal store also has a separate loop for UFCH, delivering water at a lower temperature and so not needing a mixing valve and to do this it will have it's own pump.

    I want to control the system, using EvoHome as follows:

    • About 8-10 rads with TRVs under EvoHome control, as normal with HR92s.
    • The remainder of the emitters grouped as conventional "zones" with three 2-port 28mm valves. These "zones" to be time controlled only with no need for any thermostatic control. All the EvoHome has to do is open or close the 2-port valves at the required time (or not at all if in holiday mode).
    • The UFCH controlled with a Honeywell HCC80R (if necessary), but it will need to activate the dedicated pump, not the main circulation pump.

    My question is, how can I control these 3 or more zone valves and preferably have some indication of whether they are set for open or closed? I know I can use a BD91 to control one zone and just pretend it's controlling a hot water cylinder on an S-Plan, but how can I deal with several of them?

    If I can control the UFCH without needing the HCC80R but just another 2-port valve, a metering manifold and a wireless thermostat that would be the icing on the cake.

    It goes without saying that I want to do this all on a single controller/display.

    Any ideas?

    By the way, I failed to get any help from Honeywell when I rang other than "read the installation instructions" and my heating engineer booked us a visit by the local area technical guy/rep who failed to turn up after we'd both waited for hom for 2 hours. No apology, no rearrangement. I e-maled with no reply

    Cheers.
    Last edited by Chunky; 17th April 2018 at 08:22 AM. Reason: typo

  2. #2
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    Hiya,

    you can use BD91 to control any number of the zones (up to the max of 12).
    The BD91 can be added as a few types of zone (note you'll need a separate thermostat to get the zone temp):
    - Electrical underfloor - it just switches electrically
    - Zone valve - it switches electrically (to operate the valve) AND requests heat from the boiler

    For any of your zones use the second option, this'll then mean they'll pull for heat from the boiler. You say you don't want thermostatic control in some of your zones, how come? Surely it's better to keep them regulated rather than full heat continuously?

    I'm about to get UFH (CH based) in my kitchen and this will also be done using a BD91 rather than the very very expensive HCC80R - this is because the UFH kit I'm going to buy (from these guys www.theunderfloorheatingcompany.co.uk) already has a mixer and pump, so all the BD91 needs to do is know when to request heat from teh boiler, the UFH kit then does the mixing.

    Hope that helps

    thx

  3. #3
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    Quote Originally Posted by Chunky View Post
    [*]The remainder of the emitters grouped as conventional "zones" with three 2-port 28mm valves. These "zones" to be time controlled only with no need for any thermostatic control. All the EvoHome has to do is open or close the 2-port valves at the required time (or not at all if in holiday mode).
    This will be awkward.

    Evohome doesn't have a concept of a heating zone only being scheduled "on" or "off", only of a set point schedule and current measured temperature. Why do you not not need any temperature control in these zones ? What is measuring and controlling their temperature when they are "on" ?

    If you have a zone with one or more radiators with no TRV which are instead controlled by their own specific zone valve, the normal approach would be to add a wall mounted sensor in that zone (DTS92, YT87RF or the Evohome itself if it happens to be wall mounted in the zone) and configure a "zone valve" heating zone type for it.

    Bind the temperature sensor and the BDR91 controlled zone valve to that heating zone and configure a temperature schedule just like any zone controlled by HR92's. It will also separately call for heat from the boiler and/or a global system "heating" zone valve, if you have one installed.

    One thing to keep in mind is that "zone valve" zones perform TPI modulation of the zone valve to regulate the temperature of the zone precisely. This means that when the zone temperature is +/- 1.5 degrees from its set point the zone valve will open and close periodically every 10 minutes (by default) for a proportional amount of time, in the same way that a BDR91 controlling your main heating zone valve or boiler would.
    Last edited by DBMandrake; 17th April 2018 at 11:27 AM.

  4. #4
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    Quote Originally Posted by DBMandrake View Post
    One thing to keep in mind is that "zone valve" zones perform TPI modulation of the zone valve to regulate the temperature of the zone precisely. This means that when the zone temperature is +/- 1.5 degrees from its set point the zone valve will open and close periodically every 10 minutes (by default) for a proportional amount of time, in the same way that a BDR91 controlling your main heating zone valve or boiler would.
    That's wise advice from DBMandrake. I have zone valves only controlling my system (i.e. no HR92s) and these are all 28mm motor open/motor close valves. I have set Evohome to 3 cycles / hour (instead of the default 6 / hour) giving 20 minute cycle periods. While the zone is within the +/- 1.5oC band its valve will open and close in each 20 minute period (i.e. six operations per hour - it would have been 12 with the default setting). My valves take 60 seconds to open or close so that still means that they are moving for 10% of the time. So far, none of mine has worn out but I do worry that this TPI cycling is not good for their longevity.

    Using the motor open / motor close valves gives you limit switches at the end of the open and close strokes that let you rig up indicator lights to show when each valve is fully open or fully shut, which is fun to watch if nothing else.
    Last edited by Edinburgh2000; 17th April 2018 at 06:16 PM. Reason: Added comment

  5. #5
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    Okay, thanks for those inputs. To explain my circumstances a in a ittle more detail.......

    1. One "zone" without temperature control is going to be for towel rails, which will always be on during daylight hours (unless we are out) and the only temperature control will be by the manual hand valves. It also includes an en-suite bathroom with pipework embedded in a tiled shelf to keep folded towels warm. Again, no thermostat, just a flow control on a hand valve to roughly tune the temperature. Also, there is some circulation pipework running through an airing cupboard/drying room.
    2. I have some radiators which are not amenable to being fitted with TRVs due to design and placement. As I said originally, long story.
    3. We live in a bungalow with living at one end and bedrooms at the other. I'm keen not to have any circulation in the living part of the house at night time because it's just throwing away energy - even if I have some HR92s on some rads in this area, I don't want circuation through the other rads when the HR92s in the "bedroom wing" call for heat. If I can isolate the "living wing" with a 2 port valve then it's the easiest and cheapest way to acheive what I need.
    4. Forget about any connection to the boiler, the heat store will manage all that and I've no need to worry about boiler cycling or optimising the condensing fucntion.

    I guess what I'm asking is can I have multiple BD91s in the system, each controlled on a time basis by the touchpad controller? I'm envisaging that they will each control a 2 port valve, which in turn will activate the circulation pump when fully open in the usual S-plan fashion.

    It seems simple in principle to me, but I wonder if EvoHome can manage it?

    I hope I've explained it well enough but if not, please shout up and I'll knock up a diagram.

  6. #6
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    You will still need a temperature sensor for each zone controlled by a bdr, even for the non trv ( none zone valve?) bathroom zone. In the later case simply set the sensor to the lowest value Temp that you want . That way most of the time the towel radiator will be on ( and most possibly the bathroom zone will be warmer than the sensor ) by virtue of other heating elements calling for heat and if not it will call for its own heat. You can even use a (cheaper) HR92 as a sensor and simply place it uninstalled on a shelf but a wall mounted one would obviously be neater.

  7. #7
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    Quote Originally Posted by Chunky View Post
    I guess what I'm asking is can I have multiple BD91s in the system, each controlled on a time basis by the touchpad controller? I'm envisaging that they will each control a 2 port valve, which in turn will activate the circulation pump when fully open in the usual S-plan fashion.

    It seems simple in principle to me, but I wonder if EvoHome can manage it?
    Yes. Evohome can control a BDR91 for each zone, if that is what you want. I have four BDR91s, controlling my DHW and three zone valves (one per floor). Here is the wiring diagram. Each node (a coloured text box on the diagram) is a terminal in the wiring centre.

    v26e.jpg

  8. #8
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    You can have a bdr to switch ch flow to each zone, BUT you need a temperature sensor for each zone . Evohome requires this . Hence if you want to switch based on time schedule only you will need to set the sensors high in order to ensure heat is called for according to the schedule.

    I still do not understand why anyone would want a zone controlled by schedule only without a temperature limit. ( except in the non trv bathroom)

  9. #9
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    Quote Originally Posted by Edinburgh2000 View Post
    Yes. Evohome can control a BDR91 for each zone, if that is what you want. I have four BDR91s, controlling my DHW and three zone valves (one per floor). Here is the wiring diagram. Each node (a coloured text box on the diagram) is a terminal in the wiring centre.

    v26e.jpg
    Many thanks for that. I'll have to give it a good looking at to understand it all, probably with a glass of red in my hand. But I think it's exactly what I was thinking about.

    With the BDR91 do I have to go to the hassle of using a wireless thermostat or can I just put a cheapo wired one in the system?

  10. #10
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    Quote Originally Posted by rvb99 View Post
    I still do not understand why anyone would want a zone controlled by schedule only without a temperature limit. ( except in the non trv bathroom)
    Okay, look at it like this. Hold your hands out in front of you.

    In your left hand you have five different rooms, some of them have TRVs with HR92s, some have normal TRvs, but your thumb is not amenable to that sort of control so will be hot while ever there is warm blood circuating. We'll call these rooms "living rooms".

    In your right hand you have pretty much the same arrangement, but we'll call these "bedrooms".

    So whenever one of the HR92s in the "bedrooms" in your right hand demands heat during the night, not only will all the "bedrooms" get warm but also the "living rooms" in your right hand which have normal TRVs or nothing at all. Also, about 2/3 of the pipework will be radiating heat unnecessarily. Your right hand with the "bedrooms" is warm but also so are some of the fingers of your left hand with the "living" rooms and all of your left arm.

    If I can control 2-port zone valves just on a timed basis I can put one on your left wrist and one on your right wrist. Therefore, I cut off the blood supply to the "living" rooms at night. I have no need to worry about boiler controls or pump over runs or any other such complexity because I will have a 500 litre thermal store looking after all of that stuff.

    My actual situation is a bit more complicated than this arrangement, but you've only got two arms to visualise with and I didn't want to put radiators on your toes or other extremities.

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