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Thread: HR92 Observations on temperature and control processing

  1. #11
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    @DBMandrake
    Yes, having added a -1C calibration offset, today I have realised that on radiators that are off the difference is 1C unsurprisingly, I have also used a high precision SHT35 thermometer and the HR92 results are with a few percentage points, interestingly I believe the HR92 reports temperature to 0.5C resolution and the only device I've seen on the market that does that is the BOSCH 18B20 sensor, so my guess is it's one of those, either that or software is setting the resolution and a cheap bead thermocouple is being used.

    Are you using hot water overrun in your system, I'm thinking of buying a 3rd BR91 to use that capability as a boiler relay in my Y-Plan system, but I recall you saying you've turned your time to zero? I can see some advantage in allowing the BDR91 to remove boiler demand whilst the pump continues to cycle residual heat through the water circuit.

  2. #12
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    On the contrary, it can and does happen. If you have one radiator flowing and all the rest are off your boiler will be modulating its burner (or cycling on and off) to try to maintain your flow temperature based on the warm water coming back from that one radiator.

    Now what happens if 5 cold radiators open simultaneously ? All that cold water will come rushing back to the return pipe of the boiler and cool the heat exchanger right down - even if the boiler is burning at maximum burn the output flow temperature can't help but drop dramatically, maybe 20 degrees initially, and it could take a good 5-10 minutes for the flow temperature to recover as the 5 additional radiators warm up. In the meantime if the first radiator was still flowing it would be cooled down by this drop in flow temperature.
    I don't disagree with what you're saying here in general and maybe my case is not typical. But I can see the flow and return temperatures of my boiler and I know that regardless of how many radiators I turn on, the boiler is never going to be that slow to react to the return flow difference and have any trouble at all in increasing the flow temperate to compensate. We're talking seconds, not minutes and certainly not 5-10 minutes, where a small amount of water may leave the boiler at a lower than previous temperature, and only a proportion of that is going to make it to the already 'on' radiator, in fact 1/6th of it given your 5 new radiators opening example above.

    What do you call massive ? It is true if you had one radiator running at a low temperature then another zone is scheduled to come on you might see an overshoot of up to about 1 degree initially.
    I have my sons bedroom set to 21c and when other zones were coming on-board it would go to 23.5c. This was happening in other zones too which meant in the current cold weather you start to feel cold once the over-shot temperature started to stabilise.

    I can't actually follow what you're trying to say there...if a room is below temperature it needs to call for heat from the boiler does it not ? Is it a modulating boiler or just an on/off thermostat type. (like mine)
    It's a modulating boiler. What I was trying to say is if I'm only trying to heat one room in my home from 18c to 20.5c this can be done without running the boiler continuously to the point where the temperature is reached and ultimately overshot. I think I'm expecting too much from the technology here.

    If zones are 1.5 degrees or more below their set points the system will call for the boiler to be on 100% - why wouldn't it ? The rooms need to heat up...
    My problem is that the continuous running (100% demand) of the boiler is only stopped once at the set-point (or very near it) but then the set point is always overshot.

    If the return flow is too hot that suggests your pump speed may be set too high. If the boiler can't modulate low enough that suggests it might be oversized for the house... but there is nothing wrong with the boiler cycling of and on when the demand is low, and if its oversized for the house and doesn't have a sufficient modulation range then that's what it will have to do.
    The combi boiler was sized based on two showers running at the same time, whether this means its oversized for the heating demand of the house I do not know?
    My problem with the boiler is that when cycling it does not check whether the return temp has reduced or not. The boiler purely relights after 3 minutes regardless of any temperature. I know this is nothing to do with Evohome. Perhaps its me expecting too much from technology again, but quite why you'd design a boiler with anti-cycling that just relights after 3 minutes regardless, without checking the return temp just seems bizarre to me!


    I have no doubt you are correct on the design of the system, the builder had the plumbers put in a conventional heating system and then the electricians did the Evohome installation after. The boiler supposedly has an integrated bypass, however I have no separate ABV. This means I have 3 towel radiators without HR92's that are 100% open on the system.
    This is part of my frustration with the system that has led me to do a full-reset, I have 3 towel radiators 100% open at all times and the zone(s) in question that require heating, all radiators get too hot to touch almost instantly meaning the flow return to the boiler is very warm causing the cycling. In those instances I think its pointless having a 100% heat demand when clearly we can't get rid of enough heat to at least reduce the cycling.
    Does this mean my radiators are too small as they don't get rid of enough heat? I doubt that as they get the rooms up to temperature from cold in 10-15 mins?
    Or does it mean the boiler is too powerful? But I can't avoid that as a combi boiler is going to be sized based on the DHW requirements?

    I would like to get an ABV fitted, however no flow and return pipework is visible in the house other than directly underneath the boiler. Given that I already have 3 towel radiators already 100% open though, the ABV is going to do nothing with regard to lowering the the return temperature. It may only increase the flow through the boiler which if anything will cause the cycling to happen sooner.

    You mentioned pump speeds, is this something I can easily look at and change myself?
    Last edited by rcopus; 29th November 2016 at 12:12 PM.

  3. #13
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    Quote Originally Posted by g6ejd View Post
    interestingly I believe the HR92 reports temperature to 0.5C resolution and...
    Nope. As you'll see if you ever get an HGI80 the HR92 reports with 0.1 degree resolution.

    It's the controller which applies the coarser granularity, and also biases towards the setpoint.

  4. #14
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    Quote Originally Posted by paulockenden View Post
    Nope. As you'll see if you ever get an HGI80 the HR92 reports with 0.1 degree resolution.

    It's the controller which applies the coarser granularity, and also biases towards the setpoint.
    If you want to get really pedantic the measurement resolution is actually 0.01 degrees!

    In the protocol the temperature reading is a 16 bit signed integer where the decimal temperature is multiplied by 100. So 21.56 degrees = 2156 as a signed 16 bit integer. Negative valves can be represented as well although the handling of negative readings by the Evotouch is somewhat buggy! (Try an HR92 or DTS92 in a freezer and you'll find out...)

    If I look on my domoticz dashboard at the moment I see 41.35 for hot water and 14.14, 16.35, 16.63, 13.9, 15.75 and 8.85 degrees for various rooms. (No I'm not at home shivering, I can access it remotely )

    So it does seem to be finer resolution than 0.1 degrees. That's not to say that the sensor will send an update for very small temperature changes - it almost certainly wont send an update if the reading went from 20.12 to 20.18 for example, and I'm not sure what the minimum temperature change to prompt an update is. But at the time updates are sent the resolution does appear to be two decimal places, and the DTS92 does seem to be very accurate - I see it agreeing with a standalone thermometer within less than 0.1 degrees if they are side by side and left to settle for a while.
    Last edited by DBMandrake; 29th November 2016 at 12:27 PM.

  5. #15
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    Quote Originally Posted by rcopus View Post
    I have my sons bedroom set to 21c and when other zones were coming on-board it would go to 23.5c. This was happening in other zones too which meant in the current cold weather you start to feel cold once the over-shot temperature started to stabilise.
    It is a weakness of the system I'll agree, although I only see overshoots on the order of 1 degree in these circumstances - enough to notice but not to be uncomfortable. The problem is that a zone that has its valve open wide while the boiler duty cycle is low (like a night time bedroom radiator) is unaware of other zones coming on in the house increasing boiler demand to maximum so its not until the room starts to overshoot due to the flow temperature increase that it will react to the rise in room temperature and close its own valve down.

    It would be good if it was forewarned that the flow temperature was about to go up so it could take proactive measures but it doesn't look like the wireless protocol allows this kind of information to be passed back to the HR92's.
    It's a modulating boiler. What I was trying to say is if I'm only trying to heat one room in my home from 18c to 20.5c this can be done without running the boiler continuously to the point where the temperature is reached and ultimately overshot. I think I'm expecting too much from the technology here.
    Well it shouldn't actually run the boiler continuously in these conditions and it shouldn't overshoot either. It's possible that it hasn't had enough "learning" time yet. How long has it been installed ? It actually takes several weeks of regular use with a consistent schedule (not constantly changing the schedule around) for it to adapt to the characteristics of your system and radiators and stop overshooting.

    What should happen is that if you start at 18 degrees and change to 20.5, the boiler demand will be 100% until 19 degrees then will rapidly drop back to a lower demand and at the same time the valve on the radiator will progressively close. It should keep progressively closing and reducing demand as the target is approached and in theory not overshoot.

    Some rooms are very difficult to heat without some overshoot though. It depends on your flow temperature, size of your radiators, heat loss in the room, location of the temperature sensor and so on. I have some rooms that do overshoot a bit and other rooms that rise quickly and effortlessly to the target without overshooting at all. It just depends on the room.
    My problem is that the continuous running (100% demand) of the boiler is only stopped once at the set-point (or very near it) but then the set point is always overshot.
    As I said above, it doesn't sound like it has had time to adapt. It's not normal for it to run at 100% demand until very close to the set point unless the radiator is struggling to reach the set point and it is basically requiring full output to reach the target. My hallway is a bit like that in winter due to an undersized radiator - if I set it to 20 the radiator valve is fully open and boiler duty cycle is high to just make the target. If I drop it to 19 I don't have an issue. A bigger radiator would help too.
    My problem with the boiler is that when cycling it does not check whether the return temp has reduced or not. The boiler purely relights after 3 minutes regardless of any temperature. I know this is nothing to do with Evohome. Perhaps its me expecting too much from technology again, but quite why you'd design a boiler with anti-cycling that just relights after 3 minutes regardless, without checking the return temp just seems bizarre to me!
    Seems bizarre to me too, and bad design. Not knowing the design of that boiler I can't really comment on whether its normal behaviour from it or not but it does seem stupid.
    I have no doubt you are correct on the design of the system, the builder had the plumbers put in a conventional heating system and then the electricians did the Evohome installation after. The boiler supposedly has an integrated bypass, however I have no separate ABV. This means I have 3 towel radiators without HR92's that are 100% open on the system.

    This is part of my frustration with the system that has led me to do a full-reset, I have 3 towel radiators 100% open at all times and the zone(s) in question that require heating, all radiators get too hot to touch almost instantly meaning the flow return to the boiler is very warm causing the cycling. In those instances I think its pointless having a 100% heat demand when clearly we can't get rid of enough heat to at least reduce the cycling.
    Have the lockshield valves on your towel radiators been balanced properly or have they just been left wide open ? If they're just wide open then when there is little demand from other radiators the bulk of the flow is just going to go through your towel radiators with little temperature drop and contribute to a high return flow temperature. Closing them down a little bit might help here.

    I don't have any always on bypass radiators on my system both the bathroom and hallway radiators have HR92's and there is an external automatic bypass valve installed in the system.
    You mentioned pump speeds, is this something I can easily look at and change myself?
    Probably. Most pumps have three fixed speeds and typically get set on high speed even though medium is more often appropriate. Too high a speed will lead to high return flow temperatures even when radiators are open.

    If its fairly new it might be a modulating pump though that varies its speed based on demand. If it is a modulating pump then having some towel rails fully open would tend to cause the pump to run fast all the time as modulating pumps only slow down when they detect flow resistance from closing radiators.
    Last edited by DBMandrake; 29th November 2016 at 12:47 PM.

  6. #16
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    OK thanks, then it must be a thermocouple bead device calibrated via software for linearity as there are no sensors on the market with that resolution, not digital types anyway. Noting resolution is not the same as accuracy.

  7. #17
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    I meant to take a look at the HGI80 code in Domoticz today, because I'm not convinced that the HR92s are reporting with that resolution.

    As this is coming via the API it could be a moving average, for example.

    Where's Dan when you need him - he'd know.

  8. #18
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    Quote Originally Posted by g6ejd View Post
    OK thanks, then it must be a thermocouple bead device calibrated via software for linearity as there are no sensors on the market with that resolution, not digital types anyway. Noting resolution is not the same as accuracy.
    I didn't say the accuracy was 0.01 degrees. Resolution is 0.01 degrees over the Ramses protocol but accuracy is probably more like 0.1 degrees.

    I've tested both of my DTS92's against a weather station system with indoor sensor and the indoor sensor agreed with both DTS92's within 0.1 degrees after they had both had time to settle to a constant room temperature and were placed next to each other. (The weather station readout only goes to 0.1 degrees)

    Actual sensor A/D resolution might be quite a bit coarser than 0.01 though - out of curiosity I exported my Domoticz log for the living room as csv, sorted on temperature then removed duplicates to see what the minimum step size appears to be. This zone uses a DTS92 for the sensor. This is the result:

    Code:
    Temperature
    14.8
    15.02
    15.25
    15.32
    15.39
    15.46
    15.54
    15.69
    15.91
    16.06
    16.13
    16.35
    16.57
    16.8
    17.02
    17.24
    17.46
    17.68
    17.91
    18.12
    18.35
    18.5
    18.57
    18.79
    19.01
    19.23
    19.46
    19.68
    19.9
    20.12
    20.34
    20.49
    20.57
    20.64
    20.71
    20.78
    20.93
    21.01
    21.16
    21.23
    21.38
    21.45
    21.6
    21.67
    21.89
    22.12
    The smallest interval I see there is 0.07 degrees.

    Here is the bathroom, which uses the HR92 as the sensor. There are so many more discrete values from the HR92 that I've only posted a narrow slice of the temperature range as the full data from 10 degrees to 25 degrees included 561 discrete values!

    Code:
    15
    15.02
    15.03
    15.04
    15.08
    15.09
    15.1
    15.11
    15.12
    15.14
    15.17
    15.18
    15.2
    15.22
    15.23
    15.24
    15.28
    15.29
    15.3
    15.31
    15.36
    15.38
    15.39
    15.41
    15.43
    15.44
    15.46
    15.47
    15.48
    15.49
    15.5
    15.52
    15.53
    15.54
    15.55
    15.56
    15.57
    15.59
    15.61
    15.62
    15.65
    15.66
    15.67
    15.68
    15.69
    15.7
    15.74
    15.77
    15.79
    15.8
    15.81
    15.82
    15.83
    15.84
    15.85
    15.86
    15.88
    15.89
    15.92
    15.94
    15.95
    15.96
    15.97
    15.99
    16
    16.01
    The smallest interval I see is 0.01 degrees.

    Here is the Evotouch's built in temperature sensor from the hallway zone:

    Code:
    15.02
    15.03
    15.04
    15.11
    15.12
    15.13
    15.16
    15.2
    15.22
    15.25
    15.31
    15.32
    15.34
    15.35
    15.39
    15.4
    15.43
    15.44
    15.45
    15.47
    15.53
    15.54
    15.59
    15.62
    15.63
    15.66
    15.69
    15.72
    15.73
    15.75
    15.76
    15.78
    15.82
    15.84
    15.85
    15.9
    15.91
    15.94
    15.95
    15.97
    16
    Resolution seems similar to the HR92.

    My conclusions are:

    1) The Ramses protocol supports sending temperatures to 0.01 degree resolution over the air. I've seen this reported elsewhere by those who reverse engineered the protocol and the above seems to confirm it.

    2) The A/D resolution of the DTS92 appears to be about 0.07 degrees as no two readings are closer together than this.

    3) The A/D resolution of the HR92 is much greater and appears to be at least 0.01 degrees. Not surprising when the DTS92 came out many years before the HR92.

    4) The A/D resolution of the Evotouch sensor is similar to the HR92.

    4) Accuracy of the DTS92 seems to be at least 0.1 degrees.

    5) Accuracy of the HR92 I'm not sure of - I haven't done critical comparisons like I have of the DTS92 but in more casual testing it appears to be at least as good as 0.5 degrees (when the radiator is cold of course) and I have no reason to believe its not as good as the DTS92. (But in real world use the DTS92 will be much more accurate since its measurement location in the room is far superior)

    6) Accuracy of the Evotouch built in sensor is poor without calibration - I find I have to set it to -1.0 degrees to match a DTS92 - this is probably due to the internal heating from the CPU/display backlight/battery charging etc. Once calibrated it seems good though as long as you leave it on the stand/wall mount and don't handle it.

    Pity that temperature readings shown by the controller and V2 Web API/phone apps are biased 0.5 degrees towards the set point then rounded to the nearest 0.5 degrees. Full resolution without biasing can be obtained with an HGI80 or using the V1 Web API.
    Last edited by DBMandrake; 29th November 2016 at 09:13 PM.

  9. #19
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    Quote Originally Posted by paulockenden View Post
    I meant to take a look at the HGI80 code in Domoticz today, because I'm not convinced that the HR92s are reporting with that resolution.

    As this is coming via the API it could be a moving average, for example.

    Where's Dan when you need him - he'd know.
    You use Domoticz with an HGI80 - try what I did using the HGI80 instead of the Web API. Export a zone with a particular sensor type as CSV, in Excel sort on the temperature column then remove duplicates based on the temperature column to get data similar to mine.

    If we see the same 0.07 resolution from a DTS92 but 0.01 from an HR92 we know that the V1 Web API data is probably not smoothed/averaged/tampered with.
    Last edited by DBMandrake; 29th November 2016 at 09:27 PM.

  10. #20
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    With the HGI80 the reported resolution (in the CSV exports) is 0.1, both in the traffic from the HR92s to the controller, and also the setpoint data going the other way.

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