Originally posted by Stevedh
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I had to drop down load scaling from full to partial because I was completely unable to get the bathroom radiator to turn the boiler on if it was the only active zone. (100% heat demand from the zone, 5% heat demand to the boiler - less than the minimum 11% threshold before the boiler will fire!)
Partial load scaling helped quite a bit as it reduced the amount of scaling (but still gave enough scaling to minimise overshoots - the main purpose of load scaling) however I still sometimes struggle to get any heat from my bathroom radiator if it is the only active zone. Typically it will only generate about 20% heat demand to the boiler for 100% from the zone.
This will eventually heat up the radiator but it takes about half an hour, and doesn't get fully hot, versus the "towels nice and hot in a few minutes" that I would like to see. Like you I have had to explain to my other half why the radiator she turned on 20 minutes ago is still cold, and have had to manually turn off load scaling to work around it in a couple of occasions.
As I mentioned to Andy further up the thread the load scaling needs some kind of limit to how far it will scale the heat demand. Scaling a 100% heat demand down to 5% when it takes a minimum of 11% to even fire the boiler at all is just rediculous.
I don't care what the underlying rationale or logic is, any non technical user who turns up their bathroom to 25C with an ambient reported temperature of 20C and 30 minutes later still has a cold radiator and boiler not firing is going to think their system is malfunctioning. End of story.
Load scaling is a good idea but the heuristically learnt scaling factor needs to have a limit of about 4 to 1, eg 100% demand scaled down no lower than 25%, otherwise I think I will ultimately have to disable it. Minimising overshoots is not worth having radiators simply fail to heat up when they should.
Originally posted by frankmalia
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