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Thread: Evohome S plus with add-ons query

  1. #1
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    Question Evohome S plus with add-ons query

    I am hoping to use an evotouch programmer to control the system I’m in the process of setting up which is basically an S plan plus with a few add-ons. I believe I know what I need, but I’d really appreciate it if someone who knows more than I do about these things could just confirm that I’ve got this right. I have a Worchester combi boiler (Geenstar 40CDi) that is being used only as a system boiler, an unvented indirect dhw cylinder with its own stat, a hot water underfloor heating system with three zones that, unfortunately is controlled by another system altogether (OJ Electronics), and three hw radiator zones. I’d like to use the evotouch to control the three radiator zones and the dhw, but I’d also like to use it to control the timing of two other things: a circulation pump for the dhw (to circulate it through the system which I have set up with returns so that I can get hot water close to the taps at times of high usage) and the night set back function on the ufh system.
    I believe that I need the following to do this: 1 evotouch controller, 2 DT92E room stats, 1 CS92 cylinder stat, 6 BDR91 receivers: three receivers to control the three zone valves for the three rad zones, one to control the dhw valve, one to control the dhw circulation pump, and one to control the nsb on the ufh system. Then there will be a wiring centre that will turn on the boiler and hot water pump whenever there’s a demand for heat or hw for the cylinder. Does this sound right?
    Now here are my questions:
    1. the cylinder has its own stat: can I use this or should I just disconnect it and use the CS92? I assume there’s no way to get the cylinder’s stat to communicate with the evotouch through a bdr91, but I suppose I could just wire it directly to the boiler with its own time switch. This would save me the price of the CS92, but it would cost a time switch and in addition the firing for dhw wouldn’t be modulated by the evotouch’s TPI system. So I might as well go with the CS92, right?
    2 . Can I use the evotouch to act basically as a time switch through bdr91 receivers to switch on and off the dhw circulation pump (that will circulate the actual dhw up to the taps) and the nsb on the ufh? The OJ electronics people say nsb can be controlled by a ‘time switch or a programmer’ in the Product Sheet for the EMR temp controller at their website: http://www.ojelectronics.com/Hydroni...ller-4704.aspx ) Am I right in thinking I can just assign a zone to the circulation pump and the nsb and programme the evotouch to turn these two things on and off at the set times?

    Any comments very welcome. Many thanks in advance.

  2. #2

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    There are no time-only channels on an Evo controller so you cannot control your bronze pump or night setback using this system. It is a feature that has been regularly requested from Honeywell since Evo launched, but as yet there is no mention of an update to allow this. The hot water control using the CS92A is a UK-only modification to the system and is not offered elsewhere in Europe, and Honeywell have made no provision for control of a hot water secondary pump as part of this update.

    You could replace the existing UFH controls in their entirety to get control from Evo - the Manifold Controller will offer improved accuracy and efficiency from its self-learning time-proportional control of each zone (where the manifold actuators are pulsed at part loads to match the heat input to the floor with the heat losses), and provided the manifold uses 230v thermal actuators them it is an easy change.

    Do not be tempted to disconnect your existing cylinder thermostat when adding new controls, it is usually a combined control and high limit vice that is part of the safety features for the cylinder. You can wire the BRD91 in series with the existing stat (with the stat set to maximum so that Evo is in control) and your only challenge is to work out how to fit the CS92A to your cylinder.
    Sensible Heat
    SensibleHeat.co.uk

  3. #3
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    This is a great help, thanks. I realise now that I’ve basically asked questions you have already answered elsewhere – my apologies for being slow on the up-take here. I really appreciate all your suggestions, and particularly the warning about the cylinder stat.

    But I was thinking that maybe I could trick the evo into effectively using one channel for time-only control (to act as a wireless time switch) by binding a dummy stat for that ‘zone’ and setting its schedule so the evo asks for 40C when I want the bdr91 to say ‘on’ and 0C when I want it off. It’s pretty idiotic, but could it work? Thanks again.

  4. #4

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    You can only use temperature channels in the way you describe if you do not intend to uses a BR91 as a boiler relay registered to the Evo controller, if you do then your pseudo-time zones will also fire up the Boiler Relay every time they operate too which is not what you would want to happen.
    Sensible Heat
    SensibleHeat.co.uk

  5. #5
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    Many thanks for all the help. I'm afraid I have a few more questions about unconventional evo configurations I hope someone can help me with. Any thoughts really appreciated.

    1. As for above: I have an S plus system with three hw radiator zones controlled by zone valves plus a dhw zone valve. So I will have four bdr91's each controlling a zone valve. I can easily wire them so that each one turns on the boiler and pump whenever it opens its valve. Then I wouldn't need an additional bdr91 to use solely as boiler relay. Is there any advantage to having a separate bdr91 bound to the boiler channel? Would it fire more efficiently or would it simply save me some wiring of all the bdr's? (Btw, I assume evo uses TPI control: is there no provision for leaving the valve(s) and pump running a bit longer than the boiler in the TPI protocol, or do boiler, valve and pump always come on and off together?)

    2. If I do hard wire in all the bdr's without a separate boiler relay, and I do set up some dummy zones for time-only control in the way suggested above without wiring these bdr's to the boiler or pump, will there be problems in the way the evo controller calculates the most efficient way to fire the boiler? For instance, say one of the dummy zones is 'on': the controller will assume the boiler if firing (but it isn't), so it may throw caution to the wind and open and close other zone valves without coordinating them? Not a big problem, right?

    3. Here's the big one. Again, I have three zones plumbed in, controlled with zone valves. I'd like to know if it will be possible to split one of the zones into two using HR80’s but a single BDR91 controlling the zone valve. To simplify things say I have one zone controlled by one zone valve, with a bedroom, a study and a bathroom each with a radiator. It’s plumbed as one zone, but I want to be able to heat either the bedroom and the bathroom or the study and the bathroom as separate zones with separate schedules. (Having the bathroom on both zones is just an extra but I don’t see how it will affect the set-up.) Can I put a HR80 on the radiators in the bedroom and the study and set up two zones on the Evotouch such that the BDR91 controlling the relevant zone valve is bound to both zones? (The two HR80 actuators would also be bound – one to each zone.) Will there be conflict at the level of the orders sent to the BDR? In other words: A) will the Evotouch accept to bind the same BDR as zone actuator (not boiler control) to two different zones? And if so, B) when one of the two zones wants to open but the other doesn’t (or when one wants to close but the other wants to stay open, etc.), will conflicting demands be sent to the BDR or will the ‘open’ command prevail? Is it possible to find out what the actual commands are? Because I suppose the question is this: assuming I can bind the same bdr91 to two zones, and assuming evo controls the bdr91 by sending discreet 'open' and 'close' commands, there will be a problem if zone one and two are open and then zone one closes while zone two wants to stay open, because the 'close' command will close the zone valve for both zones. But if the schedules are set up to make sure that we always close both then open one, that should work, no?
    (Having said all this, I realise that I could always plumb in two zone valves in parallel for that physical zone, with two BDR91's, one for each effective zone: then this set-up should certainly work I think. Even if it's kind of mad.)

    Maybe this is asking too much. Honeywell just told me none of this is possible, but without any specifics. Thanks again for any thoughts!

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