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Thread: Measuring real time gas consumption

  1. #11
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    Quote Originally Posted by chrisgare View Post
    Again I wouldn't particularly disagree with you but it took me a long time to get to Evohome before it was launched. I turn off my heating at 22:00 and turn it on at 07:00 and now I 15-minute data points I've been doing some calculations to see whether it might be more economical to keep the heating on overnight at a lower temperature to reduce the big blast in the morning.
    It's a common misconception that leaving the heating on "low" over night will use less gas than turning it off followed by a "big blast" to heat it back up again from a lower starting point in the morning, but it's not true.

    Yes its the case that if you let the temperature drop further at night then the heating will have to run longer in the morning to heat it back up, however the extra gas use during the longer warm up period is offset by the reduced gas use earlier in the night when the heating went off earlier.

    More importantly, heat loss through walls is directly proportional to the temperature difference between either side of those walls. If the outdoor temperature is 0 degrees and indoors is 10 degrees, heat loss through the exterior walls is half as much as it would be if it was 20 degrees indoors. The warmer the inside of the house is maintained at night through running the heating, the more total energy is used.

    The longer the heating is off and the lower the inside temperature is allowed to drop during the night the less the total energy use is because the the rate of heat loss is redued during the period of lower inside temperature.

    If you have a conventional (non-condensing) boiler, this is where the buck stops. Lower night time set points (or keeping it right off) uses less total energy without question. A lot less.

    If you have a condensing boiler there is a minor wrinkle to this analysis though, because the efficiency of a condensing boiler starts to drop if the return flow temperature is above 55 degrees. In this case if you have opentherm to control the boiler the Evohome will run the boiler at a reduced flow temperature when rooms are up to temperature and just requiring "maintaining", while during initial heatup it will run the boiler at maximum (user set) flow temperature, which may result in non-condensing operation.

    However in this case any significant set back is still going to cause a significant period of non condensing operating - even if you maintained a night time temperature of 15 degrees and a daytime temperature of 20 degrees, the Evohome would still ask for maximum flow temperature during most of the warm up period from about 15 to 18 degrees.

    So there will be some penalty from a longer period of non-condensing operation of the boiler, but I very much doubt it would make it more efficient than simply turning off the heating at night. Turning it off or setting the lowest possible set point at night will still be a net gain for economy.

    Any non-condensing penalty would also not apply at all at times of the year when you set your flow temperature back.
    Last edited by DBMandrake; 10th October 2016 at 08:54 PM.

  2. #12
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    DBMandrake thanks and useful as usual even though that has been the story for many a year on chat sites like this. I've always believed this to be the case. I've done calculations based on the 'big blast' and 'ticking over' data I now have and theoretically this confirms your view by quite a margin. Of course, these sorts of calculations are very difficult to undertake because of the wide variation of outside temperature during the daily cycle. Several years back I did implement this approach in the mid-winter and I was shocked at how much more gas I used so the experiment did not last long.

    Interestingly though, until I installed Evohome when it was first launched and replaced my 25-year old boiler, I had had the heating on twice a day for for my whole my home-owning life. I now have it on between 7 a.m. and 10 p.m for far less cost. I joined the 21st century and just love the comfort the new boiler and Evohome supply.

    I've upgraded to each new controller model launched sold the old ones on Ebay for good prices so I have not lost that much cash. I needed the last one because I built an extension and needed 12 zones rather eight.

  3. #13
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    Quote Originally Posted by chrisgare View Post
    DBMandrake thanks and useful as usual even though that has been the story for many a year on chat sites like this. I've always believed this to be the case. I've done calculations based on the 'big blast' and 'ticking over' data I now have and theoretically this confirms your view by quite a margin. Of course, these sorts of calculations are very difficult to undertake because of the wide variation of outside temperature during the daily cycle. Several years back I did implement this approach in the mid-winter and I was shocked at how much more gas I used so the experiment did not last long.

    Interestingly though, until I installed Evohome when it was first launched and replaced my 25-year old boiler, I had had the heating on twice a day for for my whole my home-owning life. I now have it on between 7 a.m. and 10 p.m for far less cost. I joined the 21st century and just love the comfort the new boiler and Evohome supply.

    I've upgraded to each new controller model launched sold the old ones on Ebay for good prices so I have not lost that much cash. I needed the last one because I built an extension and needed 12 zones rather eight.
    I think that the on/off versus continuously on argument is not as clear cut with Evohome as it is with a conventional programmer, thermostat, manual TRV heating configuration as off can effectively be achieved by turning down the target zone temperatures overnight. In other words, savings can be achieved in a different way. I doubt that many people dash around the house late at night turning down manual TRVs so timed on/off periods make a lot of sense. That said, if forums are to be believed there are many people who leave their CH on continuously and just turn the main thermostat down before going to bed.

  4. #14
    Automated Home Legend paulockenden's Avatar
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    I think to a degree it also depends on the home. The thermal mass, the insulation, etc.

    There's also a comfort element. After an 'off' period a room can be technically up to temp (i.e. air temp is OK), but the floor, furniture, etc. can still feel cold.

  5. #15
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    even if you buy elec and gas, loop is damn sight cheaper than this danish thing. I use loop on both. gas (works well) and electric (tends to over-read on low consumption levels,I believe a known issue with inductive coupling), the website and app both work well.
    once they have your data they will try and get you to switch via their price comparison system but if you just ignore that , make your own switching decision, and are happy for them to have their data which they undoubtedly use for comparison with other users and probably some relationship with energy suppliers, it works great.
    N.B. I have no relationship with loop other than as a user.

  6. #16
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    I also use Loop, but the gas usage isn't instant due to how the optical sensor works, but it's close enough. My only real gripe is that there is no API access or way to get your usage statistics other than use their app, so I can't import it into the same logging as I do my evohome stats. I did email about this, but they just said no

  7. #17
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    Quote Originally Posted by PaulB View Post
    I also use Loop, but the gas usage isn't instant due to how the optical sensor works, but it's close enough. My only real gripe is that there is no API access or way to get your usage statistics other than use their app, so I can't import it into the same logging as I do my evohome stats. I did email about this, but they just said no
    We wouldn't have had an Evohome API, if we simply waited for Honeywell to publish their API. If their app can read the data coming in, you can too. You need to monitor the traffic between the mobile app and the internet and you'll slowly figure out what the app is doing.

  8. #18
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    Quote Originally Posted by PaulB View Post
    I also use Loop, but the gas usage isn't instant due to how the optical sensor works, but it's close enough. My only real gripe is that there is no API access or way to get your usage statistics other than use their app, so I can't import it into the same logging as I do my evohome stats. I did email about this, but they just said no
    There's a Python API - https://github.com/pavoni/pyloopenergy

    I wouldn't be using it for billing purposes, but as a rough and ready elec (10s) + gas (15min) value, it works well

  9. #19
    Automated Home Guru MichaelD's Avatar
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    DBMandrake is absolutely right, I'd just add a couple of thoughts:

    1. Although we might talk about leaving heating on continuously, in most cases, and particularly with EvoHome, the boiler is actually switching off and on throughout the period.

    2. You only pay for the heat you lose, i.e. in a perfectly insulated house you'd get the house warm and it would stay that way, without needed to burn any more fuel. But in the real houses we live in, as DBMandrake has said, we lose heat and that loss is dependant on the heat differential between inside and outside. Letting the house go cold overnight will reduce your overnight losses, then you boiler gets to do a very efficient condensing burn in the morning to get things warm again, its a very efficient way to do it.

  10. #20
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    Quote Originally Posted by jdp80 View Post
    There's a Python API - https://github.com/pavoni/pyloopenergy

    I wouldn't be using it for billing purposes, but as a rough and ready elec (10s) + gas (15min) value, it works well
    Super! I didn't even know this existed...

    I've integrated it now into the rest of my monitoring scripts as an 'always on' service logging data, which is then picked up & passed through to graphite every minute (graphite storage is set to a minimum of 1 minute, so I have to average the electricity consumption from the readings it gets every 10 seconds.) Gas, as mentioned above, is logging at 15 minute intervals.



    The only thing missing now is for the Evohome to actually report when a zone is requesting heat. The hot water active is just showing from the schedule, but again, I'd much rather this display 'real time' heat demand, not just schedule related heat periods regardless of whether it's heating or not.

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