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Green Building Bible, Fourth Edition
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Heating and cooling: Opentherm options

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    • CommentAuthorSeret
    • CommentTimeAug 27th 2017
     
    Hello folks, long time no see.

    Just about to fit a new Intergas boiler to my extension and I was wondering what people's thoughts were on the best way to make use of Opentherm?

    Currently my nasty old boiler is just on on/off control, with two thermostats dividing the house into upstairs/downstairs and eTRVs preventing individual rooms from cooking. The CH is all one circuit, and that won't be changing.

    I was leaning towards the Honeywell Evohome, but it's frankly bloody expensive and I don't think it makes any sense from a cost/benefit angle. Happy to cough up for the central controller, but £55 per TRV on top is pretty cheeky IMO. IIRC my current ones cost less than £20, although admittedly they don't have the features you'd get in an HR92.

    Worth just biting the bullet and going for the gold-plated Honeywell system, or am I missing a good alternative?
    • CommentAuthortony
    • CommentTimeAug 27th 2017
     
    I have never been a big fan of TRV's but web linked ones could be more interesting.

    I don't like the sound of on / off

    http://readinguk.org/draughtbusters/going-further/heating-control/ Try this and it will save you lots of energy
    • CommentAuthorgravelld
    • CommentTimeAug 27th 2017
     
    Heat Genius is (a bit) cheaper.

    Not sure how Damon's OpenTRV project is going...
    •  
      CommentAuthordjh
    • CommentTimeAug 28th 2017
     
    Posted By: SeretI was wondering what people's thoughts were on the best way to make use of Opentherm?

    Opentherm is anything but. Different manufacturers implement different capabilities so consult your products' manuals and determine what if anything is possible with the kit you have that you actually want to do.
    • CommentAuthorSeret
    • CommentTimeAug 30th 2017 edited
     
    Posted By: tony
    I don't like the sound of on / off


    It's the standard way that room stats work, Tony. The stat either calls for heat or not, and the boiler works at full effort, modulating only due to its own sensors. OpenTherm provides a way of the stat asking the boiler for a specific level of response. So much more nuanced control, quite useful for trimming off any losses from the control side once you've got the building fabric sorted..

    Posted By: gravelld
    Heat Genius is (a bit) cheaper.

    Not sure how Damon's OpenTRV project is going...


    Hmm, just checked out Heat Genius, and from the look of it each room you want to treat as a zone requires both a temp sensor (£35) and an eTRV (£60), which makes it actually come out quite a lot more expensive than Evohome. So cheers for the suggestion, though.

    I looked at OpenTRV a while back but wasn't happy with its feature set. Seems like a very strange beast.

    Posted By: djh
    Different manufacturers implement different capabilities


    Cheers for the heads up, I'll double check, but I'm pretty sure Evohome with the Intergas boilers is a pretty common setup.
    • CommentAuthorgravelld
    • CommentTimeAug 30th 2017
     
    Posted By: SeretHmm, just checked out Heat Genius, and from the look of it each room you want to treat as a zone requires both a temp sensor (£35) and an eTRV (£60), which makes it actually come out quite a lot more expensive than Evohome. So cheers for the suggestion, though.

    You don't *have* to have a temp sensor.

    I'd be interested to know if Evohome's approach, to measuring temperature at the radiator, works. The thermostat is inside the TRV right, so how does it know, in a Craphaus (tm) what the temperature is elsewhere?
    •  
      CommentAuthorDamonHD
    • CommentTimeAug 30th 2017 edited
     
    Posted By: Seret
    Posted By: gravelld
    Not sure how Damon's OpenTRV project is going...


    I looked at OpenTRV a while back but wasn't happy with its feature set. Seems like a very strange beast.


    What didn't you like the look of?

    We have a new "TRV3" due out at the end of the year, that would be a drop-in replacement for your existing TRVs without anything else needed, at a minimum.

    Rgds

    Damon
    • CommentAuthorSeret
    • CommentTimeAug 31st 2017
     
    Posted By: gravelld
    You don't *have* to have a temp sensor.

    I'd be interested to know if Evohome's approach, to measuring temperature at the radiator, works. The thermostat is inside the TRV right, so how does it know, in a Craphaus (tm) what the temperature is elsewhere?


    Ok, but what's the point of the TRV without it? Even old fashioned manual TRVs sense temperature. You can get decent eTRVs for £20 or so and manual ones for less, so unless I'm missing something about Heat Genius it doesn't seem to be good value.

    Measuring room temp at the radiator is an issue common to all TRVs, not just Evohome. In practice I don't find it's an issue. My current setup already uses the temp detected at the eTRVs to cut off heating once a room is warm and that works fine. The only difference would be that the Honeywell TRVs could also call for heat, but at that point the rad is probably cold anyway so it should be accurate enough I reckon.

    I don't want to sound like I'm preaching for Evohome though. I came hear specifically looking for something else, because I think Evohome is overpriced too. £55 for each TRV is taking the piss.

    Posted By: DamonHD
    What didn't you like the look of?


    I'm not convinced that room occupancy detected by lighting level will deliver what I want or suit my family's behaviour patterns or expectations. I want to control by time and zone.
    • CommentAuthorgravelld
    • CommentTimeAug 31st 2017 edited
     
    Posted By: Seret
    Ok, but what's the point of the TRV without it? Even old fashioned manual TRVs sense temperature. You can get decent eTRVs for £20 or so and manual ones for less, so unless I'm missing something about Heat Genius it doesn't seem to be good value.

    Well it's definitely more accurate. If there's not a room one, it uses the whole house thermostat, or you can link the TRV to another room to be turned on/off by that.

    Posted By: Seret
    I don't want to sound like I'm preaching for Evohome though. I came hear specifically looking for something else, because I think Evohome is overpriced too. £55 for each TRV is taking the piss.

    Yeah, agree. Would've loved to have something I could've implemented myself. But that was three years ago, there's still nothing around, so I'm glad I did it then (HG was also cheaper back then, didn't realise prices had gone up this much).
    • CommentAuthorSeret
    • CommentTimeAug 31st 2017 edited
     
    Posted By: gravelld
    Well it's definitely more accurate. If there's not a room one, it uses the whole house thermostat, or you can link the TRV to another room to be turned on/off by that.


    How sure are you about that? Having done a bit more research it sounds a bit like their TRV actually does have temp sensing in it, but it's not clear if it reports that to the central brain. The room sensor is more flexible about positioning, and includes occupancy sensing that feeds back to build up a profile of behaviour ("footprint mode").

    The actual info is buried a bit on their site, but Google can dig it out: https://www.heatgenius.co.uk/how-it-works/advanced/

    One plus for me is that Heat Genius integrates with electric UFH and Evohome doesn't.
    • CommentAuthorgravelld
    • CommentTimeAug 31st 2017
     
    Posted By: Seret
    How sure are you about that? Having done a bit more research it sounds a bit like their TRV actually [i]does[/i] have temp sensing in it, it's just that the room sensor is more flexible about positioning, and includes occupancy sensing that feeds back to the central brain to build up a profile of behaviour ("footprint mode").

    That's the standard TRV working. Yes, they still have thermostats like other TRVs, but that temperature is not fed back to the server and it isn't used for boiler interlock.

    It can actually cause some annoying balancing issues between the two - sometimes the TRV thinks its hotter than it is, and shuts down the rad without achieving the target temp. Therefore they introduced an offset to allow it to overheat, which works well.

    That's also why I think TRV temps can be different to room temps.
    • CommentAuthorSeret
    • CommentTimeAug 31st 2017
     
    Posted By: gravelldthat temperature is not fed back to the server and it isn't used for boiler interlock.


    Right, that's not very useful then.

    My current setup does basically that with £20 eTRVs and a basic 7-day progammable stat. Seems like you really need the room sensors to get any real benefit for your money, and at that point Evohome becomes cheaper.
    • CommentAuthorgravelld
    • CommentTimeAug 31st 2017
     
    ... but any linked room or the whole house thermostat CAN turn the boiler off.

    I managed a number of bedrooms without the sensors for one winter. There are little workarounds you can do; so long as another radiator is demanding, it's less of an issue. I eventually bought sensors just because I couldn't be bothered thinking about it anymore.

    Which "eTRVs" do you have? When I was looking I couldn't find any that did interlock.
    • CommentAuthorSeret
    • CommentTimeAug 31st 2017
     
    Posted By: gravelld
    Which "eTRVs" do you have? When I was looking I couldn't find any that did interlock.


    Mine don't do interlock either, they just shut down the room they're in. Pretty bog standard EQ-3 ones. I use one stat upstairs and one downstairs to control the boiler, so I really only have two zones at the mo.
    • CommentAuthorgravelld
    • CommentTimeAug 31st 2017
     
    So HG, AIUI, is basically an application on a Raspberry Pi controlling the rebadged devices (e.g. TRVs are Danfoss) via Z-Wave.

    In principle I don't think there's anything to stop you building something yourself. I chose not to because I've got loads of other jobs in my house and with kids on the way (at the time of purchase) I just didn't have the time.

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