More over/undershoot queries (HR92s and HomeAssistant)

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GP41
Posts: 3
Joined: Tue Sep 08, 2020 6:13 pm

More over/undershoot queries (HR92s and HomeAssistant)

Post by GP41 »

EDIT: Not sure the images are working so I've attached a screenshot showing
WC: tiny room, maybe oversized radiator and affected by Utility temps
Main bedroom - furthest away and slow to reach temp
Hall - cycling?
E bedroom - OK?
Landing - OK and heated by Hall below
Spare room - heavily cycling

I've had Evohome installed for just over a year now and apart from needing an occasional HR92 reset it's been brilliant. Reading some of Richard Burrows (@RichMWPHS) tweets and blogs and with a growing interest in efficiency improvements, I started to tweak the system. I was looking for ways to better understand how it was performing, particularly as some rads were struggling to get evenly hot. I am keen to better balance the system, minimise flow temp at boiler and understand how rooms affect each other. I setup HomeAssistant which provides useful logging and graphs to visualise the system activity. In some cases, rooms behave well, such as the Dining Room:
Image

But in other cases, I see over/undershoots. In the spare room, where we just keep ticking over at a low temp, we see this castellated effect in the graphs:
Image

Could this be because it is a room over a cold garage? Or is it a side effect of trying to maintain a low temp in there? Or is the radiator oversized? Because it is a spare room, I don't have concerns about comfort levels for occupants but I am concerned this apparent cycling could be inefficient.

We've also started to see this in the hall. Is it a coincidence I'm seeing this after I reduced flow temp and adjusted some rads' fully-open lockshield valves to decrease flow in radiators close to the boiler, in an attempt to improve performance of those furthest away. Or is it due to the nature of the shape of hallways with open staircases?
Image

Presumably, the gradient of "warm-up" should be fairly consistent and where there is a dramatic difference between rooms, with some struggling to get to target, that suggests some balancing is needed - is that right?

Finally, I've seen in other posts that people have been logging the valve status (System Summary percentages in the base display?) which I think could be really helpful. It would be great to know how that info is accessed. I saw that, with HR92s, ideally the system should be operating near to 100% with lower flow temps, so it would be great to be able to monitor that alongside other data, instead of having to use the base unit display for that.

Any advice very much appreciated.
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lloyd
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Joined: Wed Sep 30, 2020 6:06 pm

Re: More over/undershoot queries (HR92s and HomeAssistant)

Post by lloyd »

If you want to investigate further, you probably want to be looking at an integration such as evohome_cc (https://github.com/zxdavb/evohome_cc and https://github.com/zxdavb/evohome_cc/wiki/1.-Overview). With the appropriate hardware, you can listen in on the RAMSES-2 traffic, and graph things such as demand, and when the boiler is being asked for heat.

And if you have OpenTherm (which I don't) it will give insight into that too.
eg
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GP41
Posts: 3
Joined: Tue Sep 08, 2020 6:13 pm

Re: More over/undershoot queries (HR92s and HomeAssistant)

Post by GP41 »

Yikes, that's getting complicated now. I thought I did well to set the RaspberryPi up to achieve what I did :-).

Did you have any thoughts on my other questions about the state of the graphs that I have been able to produce??

Thanks
lloyd
Posts: 37
Joined: Wed Sep 30, 2020 6:06 pm

Re: More over/undershoot queries (HR92s and HomeAssistant)

Post by lloyd »

Not sure I can directly answer your questions. But a few points/thoughts.
  • What do we think good control really looks like. In your spare room it looks like you are getting plus or minus half a degree. Is that good or bad? (And I'm not suggesting anything either way - genuine question to the forum in general.)
  • I get very good control on rooms that I keep at 15C during the day, so I don't think that is an issue.
  • I presume that you have optimised start enabled. I'm sure I have some rooms that take longer to heat up than others, but I don't worry about it - optimised start takes care of this very well.
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Richard
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Re: More over/undershoot queries (HR92s and HomeAssistant)

Post by Richard »

lloyd wrote:Not sure I can directly answer your questions. But a few points/thoughts.
  • What do we think good control really looks like. In your spare room it looks like you are getting plus or minus half a degree. Is that good or bad? (And I'm not suggesting anything either way - genuine question to the forum in general.)
  • I get very good control on rooms that I keep at 15C during the day, so I don't think that is an issue.
  • I presume that you have optimised start enabled. I'm sure I have some rooms that take longer to heat up than others, but I don't worry about it - optimised start takes care of this very well.
My thoughts are...

What are your expectations of good control? 0.5C of setpoint is very good control imho.
In a room with an oversized radiator, the best a control can do is guess and then put the brakes on.
A house should have radiators each individually sized to the exact heat loss of the room.
If you have a combi boiler, maybe reduce flow temperature rather than put too much heat in and then have the HR91/HR92 have to put the brakes on. System/heat only boilers can't be reduced any lower than 70C as you have hot water to accommodate safely. Load or Weather Compensation with priority hot water can help here if it is an option on your boiler.
Home: 2012 Built Oak & Timber Frame Home (EPC Score 95 - A Rated)
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