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Thread: Honeywell CM Zone - basic questions

  1. #81
    Automated Home Jr Member
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    Quote Originally Posted by SensibleHeatUK View Post
    You don't set a differential temperature as it is not doing basic thermostatic control. The Honeywell system uses fuzzy logic algorithms used are self-tuning so the system will learn the thermal characteristics for each zone (measuring the rates of change of temperature and adjusting the on-off cycling of the manifold controller outputs or modulating the HR80 valve position) thereby minimising the temperature cycling around setpoint usually to around plus/minus half a degree. This can take a good few days before the accuracy starts to improve and only operates when the measured temperature is within around 1 degree of setpoint. If your rooms are always too warm then you may need to think about upping the setpoint for a day or two to get within the range for the self-tuning to operate and improve the control response.

    We also found that the self-tuning precess in the manifold controller was a little too conservative for the UK climate so now have special firmware from Honeywell that is a bit more aggressive when re-tuning the control loops with the self-tuning working over a slightly larger temperature range.
    How does this fuzzy logic perform with a modern weather compensating condensing boiler? It is my understanding that the flow temperature varies all the time so unless the logic in the valve knows what the flow temperature is going to be I don't see how it can achieve what you are saying.

    Separately is there likely to be a firmware update to hometronic to allow DT92E to be used?

  2. #82

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    Applying stand-alone weather compensation to a building that has a separate self-learning system room-side control system is not recommended because the room-side controls have no influence over what the boiler is doing to the flow temperature, and more importantly the boiler does not know how and when to modify the weather compensation to take account of room demand - you don't want the boiler operating in weather compensating mode during the initial room warm up as it simply extends the time to reach setpoint. It is possible with Hometronic to get a percentage demand from the Hometronic Manager and Manifold Controllers that can be used to provide an analogue heat demand signal, but most boilers with integrated controls do not have the ability to be controlled this way.

    With modern houses being well insulated and more air tight then weather compensation is not so much of benefit as the internal room temperature response lags much further behind the outside temperature. Also the controls are improving, with systems such as Hometronic and Evo providing fully zoned room-side controls meaning the room temperatures and rates of change are being measured in each room independently. Nowadays it would be more appropriate to use a boiler with fully modulating burner and OpenTherm control - this means that the room controls are then passing a percentage demand to the boiler and so it can dynamically adjust its burner accordingly to meet this instantaneous demand, and OpenTherm is an industry standard for compatibility amongst boiler and controls manufacturers. This way the control of the boiler is driven by the room demand (or set to maximum for hot water demand for example), and the valves do not need any direct feedback from the boiler. However although OpenTherm has been around for a while it is still not very common in the UK and not widely promoted here.

    Regarding the DT92E, there is no word from Honeywell that they intend to update Hometronic to be compatible with it or the other Evo devices (BRD91, CS92A etc).
    Sensible Heat
    SensibleHeat.co.uk

  3. #83
    Automated Home Jr Member
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    Thanks for your explanation. I think I am talking about a fully modulating boiler but perhaps I misunderstand the algorithm that is used or used the phrase "weather compensation" incorrectly. I didn't mean the old fashioned simple curve of external temp versus flow temp, but thought that condensing boilers varied the flow temperature to try and achieve condensing as much as possible.

    Since most boilers don't seem to get an analogue demand signal, I was assuming that they estimate the demand by calculating the current output from the drop in flow to return temperature, and the rate of change in that differential as a way of seeing if more is being demanded. Presumably they only increase the flow temperature beyond condensing point if the demand seems to be high.

    It is interesting that you note Hometronic can send an analogue demand signal by opentherm. Does the algorithm know if you have a condensing boiler to try and keep that below a certain level? I realise this would be at the expense of response times.

    We are currently thinking of a 46kw Vaillant Ecotec boiler to replace an old conventional boiler. I think Vaillant have their own eBus standard but don't know if that is opentherm compatible or if an interface exists. Perhaps we should look for an equivalent opentherm boiler.

    Actually I can't find any opentherm compatible boilers without going to manufacturers I have never heard of.
    Last edited by fourtears; 30th October 2012 at 08:05 AM.

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