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Thread: How do setbacks work?

  1. #1
    Automated Home Guru MichaelD's Avatar
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    Default How do setbacks work?

    I've just had a new boiler fitted (Worcester Bosch combi), and am taking the opportunity to make the control much more sophisticated. I have an X10 appliance module that takes the place of a room thermostat, so effectively, the boiler is under X10 control (X10 works very reliably here)

    I have internal and external temperature sensors, an Ocelot, HomeSeer, and can write scripts, so all the basics are in place.

    What I don't have is an intelligent user requirement ops:

    How do commercial systems use the external temperature to setback the heating? Surely, if its cold indoors, then it doesn't really matter that its warm outside?

    And why does it feel cold at 18 degrees in winter, but warm enough on a summers evening? And if its midsummer, but a chilly morning, do I want the heating to come on?

  2. #2
    Automated Home Jr Member
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    Default Re: How do setbacks work?

    I have a similar set-up using a modified Z-wave module in place of your x10 module.

    1) Why not leave a room thermostat in series with your X-10 module this way if the house is warm the boiler won't even fire up. Should you automation system fail at least the house won't overheat !

    2) You could use an electronic thermostat that delays the boiler based on room temp Drayton make quite a nice unit that delays the start time by 1 hour if the space is already near setpoint. (you set your timer to enable the heating at least 1 hour before you need it.)

    3) You could use two thermostats with your x10 module on Thermostat 1 would control at 21 deg C with the X10 module off it uses the other thermostat set at 18 deg C. you could take some outside air readings and decide if its summer or winter !

    4) You could use your outside air temp sensor to disable the heating if the Outside air temp is greater than say 18 Deg C

    Just some ideas hope some may be of interest

    Jason

  3. #3
    Automated Home Sr Member n07tv's Avatar
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    Default Re: How do setbacks work?

    The answer to you last question is simply human perception. You can have a nominal 21C inside with a clear blue sky and the sun shining (but cold) outside and you will feel comfortable.

    However if the weather changes outside to sleet and driving winds or snow, it can still be 21C inside but you will think it is colder.

    I did a PhD in HA especialyl intelligent heating and I still can't get the message across to my other half who keeps overriding my system ...

  4. #4
    Moderator toscal's Avatar
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    Default Re: How do setbacks work?

    This is something I have been looking into. Its sometimes called weather compensated heating.
    The idea I had is to set upper and lower limits. For heating to come on at the normal time the temp has to be below 18 but if it gets to 10 the heating would come on an hour early. And then if the temp was at 15 the heating might come on 25 mins early unless it could be seen that the temp was still decreasing. Then there is a similar thing for turning the heating off. If its 18 outside then it gets switched off at the normal time and earlier if its above 18.
    I know some underfloor heating systems use a weather compensation type system to detemine when the heating should come on or not.
    I still haven't got round to actually programming my HA controller yet. Its one of those projects that always seems to be on the back burner.

  5. #5
    Automated Home Sr Member n07tv's Avatar
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    Default Re: How do setbacks work?

    you may want to speak to th guys at IDRATEK (www.idratek.com) a when I spoke to them at UKHA2004 there seemed did this and was very impressive.

  6. #6
    Automated Home Guru MichaelD's Avatar
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    Default Re: How do setbacks work?

    Thanks for the ideas - keep them coming.

    It seems that this sort of thing must have been worked through for commercial buildings, where there is more at stake than a residential property. But no commercial suppliers seem to give away their secrets.

    The factors that I think should play into the 'heating algorithm', in order of importance, are the inside temperature, outside temperature, and weather forecast (sunny/cloudy, and predicted outside temperature)

    All these are available to HomeSeer, I'm just not sure how to connect them together to decide when to turn on the heating.

  7. #7
    Automated Home Lurker
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    Default Re: How do setbacks work?

    I have implemented a very simply setback in my existing cottage. Homeseer checks the outside temperature 30 minutes after Sunrise and if it is above 10c it sets back the temperature to 18c...

    I have a very accurate method for testing the effect of this, my wife. At the moment she doesn't notice when this kicks in.

    This is not the best set of circumstancies though as the Cottage is a simple wooden building with little insulation.

    My understanding of comfort (heat) is that it is a combination of temperature and humidity. The higher the humidity the higher the temperature needs to be to feel as comfortable. There is also the issue of temperature gradient from floor to ceiling as well as horizontally accross a room. Radiators and a drafty building can feel colder at the same measured temperature as a 'non-drafty' house with UFH. This is why a warm 'Summers day' at 18 - 20 can feel better than a 'Winters day' at the same temperatures. Radiant heat (sunshine) also needs to be accounted for...

    I am hoping my new house, with UFH, will operate at slightly lower temperatures than I need in the cottage. I'm not looking to vary the house temperature much during the day / night. I'm not sure this is possible with UFH due to the slow response times associated with heating 30 tonnes of screed... The house is also insulated to a high standard.

    I will be looking at setting back temperatures based on external temperatures rises every morning, mcsTemperature in conjunction with Homeseer is very powerful. I will also monitor windows (approx 40) and external door (7) position. I see no point trying to achieve 21c if the door is open... It would also be interesting to try and use weather forecasts (reliability???) using mcsTemperature and Homeseer again.

    I would be interested in any comments especially if I made any incorrect assumptions...

    Nigel

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