Originally posted by Jemster
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I figured that if a room gets up to temperature 30 minutes early, surely the HR92s sense this and close off the radiator to just a trickle, so it's not like the heating is going to be full-on for that half an hour extra. I didn't want to introduce the extra variability of the optimal start until I got the usage reduced and the system set right (takes a while to tweak at 9 zones to a point where we're all happy).
However the correct way to look at the situation is that heat loss from a house is proportional to the temperature differential between the inside and outside. The higher the temperature differential the more heat loss, the more heat loss, the more heat the boiler has to produce to maintain equilibrium of the inside temperatures and maintain the set points.
Therefore the more time you spend with a higher temperature differential (higher set point) the more overall gas consumption. So if a room falls back to 15C naturally over night on a particular night and you want it to be up to 20C at 6am, if it gets to that temperature at 5am instead of 6am that's a whole extra hour where you have the additional heat loss of the higher internal temperature, thus more gas usage. So shaving off any unnecessary lead time should save gas.
Got to say I also felt a little bit out-of-control until I got Domoticz up and running a couple of nights ago. Now I can see the temperature history, even if not the actual boiler demand. I turned on optimal start last night. It will be interesting to see how much it alters the usage (haha I'm guessing not at all, still be 15 units ) but EvoHome turning on the bedroom heating at 4:45 for a 6:30 wake-up this morning was a little excessive. A bit of adjustment is definitely required as that's 1hr 15m more than I'd previously been using to get a little heat to get up to.
Regarding the bedroom, was it actually up to the set point too soon though ? If it was, it should adjust its start time by about 15 minutes per day (assuming prevailing room/weather conditions are similar) until it hits the target. If it's a long way out like say an hour, that can take several days to adapt. I'd give optimal start at least a week to learn the characteristics of your rooms before giving up on it, and compare your daily graphs to see if it is making an adjustment on the start time.
Of course, in my constant battle, the weather keeps getting colder. Makes it hard to tell if I'm making a difference by tweaking or not. So far, from Domoticz, I've identified the overnight 15 degrees wasn't low enough to stop the heating kicking in at 3am for some rooms. I've corrected that one. Similarly in the late mornings it was also running pretty much pointlessly. I can also see one bedroom that's unable to reach its set-point, new radiator required and some insulation I think. Hopefully in the next week I'll get the usage down.
It's amazing such data isn't readily available direct from the controller. I don't know how anybody could possibly work these things out in any other way on anything other than the simplest installation. Many thanks to all who've helped me out here!
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