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Thread: Will I Install Evohome Again?

  1. #1
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    Default Will I Install Evohome Again?

    So it's goodbye to Evohome/Opentherm, and 19TRVs in 12 Heating Zones: my house sale completes this coming Tuesday. We move into a new build - much smaller - property on Friday which has 3 zones (2 CH and 1 HW) with TRVs on all radiators. The new property has wall and floor insulation; argon-filled DG and an EPC of 87. The heating controls are ESI.

    In amongst the stresses of buying and selling, I have been looking carefully at smart heating options. At the outset, let me say that, even after 4 years of Evohome use, my wife is no great fan of smart heating controls. She knows that if I was no longer around, she would struggle even with a simple HR92 battery change. I have tried, unsuccessfully, to persuade her that SiL will only be 20 miles away so the cavalry is close by.

    Even if she was to agree, I have yet to convince myself that the sums add up. We will be two senior citizens at home for most of the day with the heating on from 7 to 10pm. Close monitoring of my present system (Atag boiler with OT) shows conclusively that maximum efficiency and lowest cost is achieved by letting the system get up to heat, and then letting it run with no controller; App or HR92 fiddling. In my recent exchange with BRE about EPCs and smart heating controls, it is clear that they do not believe that Evohome offers savings greater than those that can be achieved by turning down TRVs in unused rooms. So in a home the shouldn't cost much to heat, the RoI on smart controls does not really stack up. I will only know when I have monitored usage and cost over a Winter period.

    I have enjoyed the 'challenges' of Evohome which at times has been frustrating, and I most certainly have learnt a lot from the knowledgeable posters on this forum: so thank you one and all. So was it all worth it? The answer has to be 'yes'. Over 4 years, a new boiler and Evohome has probably cost me over £4K. We have seen some small savings but not enough to cover the cost of Evohome. That said, I think that a new boiler with 8 1/2 years remaining on the warranty and Evohome was a USP - so, overall, I don't think that I have wasted my money.

    I shall of course continue to monitor the forum.

  2. #2
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    Quote Originally Posted by HenGus View Post
    So it's goodbye to Evohome/Opentherm, and 19TRVs in 12 Heating Zones: my house sale completes this coming Tuesday. We move into a new build - much smaller - property on Friday which has 3 zones (2 CH and 1 HW) with TRVs on all radiators. The new property has wall and floor insulation; argon-filled DG and an EPC of 87. The heating controls are ESI.

    In amongst the stresses of buying and selling, I have been looking carefully at smart heating options. At the outset, let me say that, even after 4 years of Evohome use, my wife is no great fan of smart heating controls. She knows that if I was no longer around, she would struggle even with a simple HR92 battery change. I have tried, unsuccessfully, to persuade her that SiL will only be 20 miles away so the cavalry is close by.

    Even if she was to agree, I have yet to convince myself that the sums add up. We will be two senior citizens at home for most of the day with the heating on from 7 to 10pm. Close monitoring of my present system (Atag boiler with OT) shows conclusively that maximum efficiency and lowest cost is achieved by letting the system get up to heat, and then letting it run with no controller; App or HR92 fiddling. In my recent exchange with BRE about EPCs and smart heating controls, it is clear that they do not believe that Evohome offers savings greater than those that can be achieved by turning down TRVs in unused rooms. So in a home the shouldn't cost much to heat, the RoI on smart controls does not really stack up. I will only know when I have monitored usage and cost over a Winter period.

    I have enjoyed the 'challenges' of Evohome which at times has been frustrating, and I most certainly have learnt a lot from the knowledgeable posters on this forum: so thank you one and all. So was it all worth it? The answer has to be 'yes'. Over 4 years, a new boiler and Evohome has probably cost me over £4K. We have seen some small savings but not enough to cover the cost of Evohome. That said, I think that a new boiler with 8 1/2 years remaining on the warranty and Evohome was a USP - so, overall, I don't think that I have wasted my money.

    I shall of course continue to monitor the forum.
    I think the convenience aspect of EvoHome is the main selling point, could I achieve the same level of comfort with standard TRVs? Yes. Do I have enough time to remember and go round altering each valve when required? No. The fact that it allows you to have different set points at different times is the main advantage for me, we have rooms we don't use in a morning in winter but do during the evening, along with rooms that get cooler quicker than others so maintaining a minimum set point is useful. My main thing with EvoHome is that you a better temperature throughout the house in each room, rather than one being boiling and another cold.

    In turn does this save me money, I think it does. Having EvoHome installed since we've moved in it's hard to tell what our running costs would have been without it. However judging off our gas bills i'd say it'd cost us more to run it without the system. Factor in the cost of EvoHome, I think it's at least a good 5 years to get a return on your investment.

    I think even in a new home (Ours in 17 years old so fairly well insulated) with two zones you'll find that it's still hard to maintain a even temperature across the building. Out of interest what is the boiler in the new house?

  3. #3
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    Quote Originally Posted by mtmcgavock View Post
    I think the convenience aspect of EvoHome is the main selling point, could I achieve the same level of comfort with standard TRVs? Yes.
    If by "standard TRV" you mean a conventional mechanical wax pellet TRV then I would say, definitely not, and that you may have rose coloured glasses for your old TRV's.

    A conventional mechanical TRV does not maintain a steady or accurate room temperature, especially under changing conditions anywhere near as well as an HR92 does. And this is independent of scheduling, optimal start or any of those other features.

    Before I installed a complete Evohome system I replaced my living room TRV with a single HR92 in standalone mode - no controller etc, just the HR92 by itself, for nearly 6 months.

    Ostensibly the reason was to check compatibility with my radiator valves before a large outlay but I also wanted to see whether there was an improvement in temperature control that I expected an electronic TRV to have. And sure enough there was. With the mechanical TRV the room was forever too hot or too cold, requiring constant adjustment to maintain a "comfortable" temperature.

    During initial room heat up it was necessary to set the temperature significantly higher - "4" on the dial to get the temperature of the room up in an acceptable amount of time but it then had to be manually turned down to around 2-3 after an hour or so to prevent the room overheating. Every night was a game of fiddle with the TRV to get some sort of comfort. Too hot - turn it down a bit. Too cold, turn it up a bit. Rinse and repeat.

    The HR92 was a revelation - with no scheduling available in standalone mode I just set it to a constant 21C and the room would get quickly up to temperature but then stabilise and stay at a comfortable constant temperature. We could go the whole evening without feeling a need to fiddle with the temperature, and within the same season at least, we left it at the same temperature setting day after day.

    I've discussed at length in other threads why this is so, but in short, it's because it's a full PID (proportional integral differential) controller with self tuning heuristics to adapt to the room thermal response time characteristics as well as the valve body characteristics, compared to a manual TRV which is only a proportional controller, and one which suffers from stiction as well. It's this stiction and the inability to adapt to the room thermal response time that causes the constant temperature cycling of the room you get with manual TRV's.

    Another problem with manual TRV's which is a result of them not having any integral term is that they have offset error. This causes two problems - one is if the amount of heat required to reach the target temperature is greater (colder outside) this requires the pin position on the valve to be higher up, but this means the set point of the room will go down because it is only a proportional controller, which needs a lower temperature for the pin to be higher. An integral controller can cancel offset error.

    This same problem also means that any tiny difference in the pin lengths or characteristics of the valve bodies means that a given number setting on the dial will be a different temperature. So a setting of "3" will be a significantly different temperature in each room of the house, something which irritates me no end in a conventional system, and the reason why conventional TRV's are numbered 1-5 and not in degrees!

    On top of the improvements of temperature control that an HR92 brings you can improve it even further by using a remotely located sensor to eliminate the influence of localised heating from the radiator being beside the sensor - something that you can't do with a mechanical TRV.

    In short, I would never go back to mechanical TRV's in a heating system now. If I decided Evohome wasn't for me anymore after moving house I would look at one of the competing systems with electronic TRV's like Tado. It's not just about scheduling for me, it's about the vastly superior temperature regulation that electronic TRV's can provide - especially when coupled with remote temperature sensors.
    Last edited by DBMandrake; 24th July 2018 at 06:31 AM.

  4. #4
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    That post #3 above should go in the list of 'really useful' posts on this forum which should be in a sticky place for reference by newcomers. Many thanks DBM.

  5. #5
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    Quote Originally Posted by DBMandrake View Post
    If by "standard TRV" you mean a conventional mechanical wax pellet TRV then I would say, definitely not, and that you may have rose coloured glasses for your old TRV's.

    A conventional mechanical TRV does not maintain a steady or accurate room temperature, especially under changing conditions anywhere near as well as an HR92 does. And this is independent of scheduling, optimal start or any of those other features.

    Before I installed a complete Evohome system I replaced my living room TRV with a single HR92 in standalone mode - no controller etc, just the HR92 by itself, for nearly 6 months.

    Ostensibly the reason was to check compatibility with my radiator valves before a large outlay but I also wanted to see whether there was an improvement in temperature control that I expected an electronic TRV to have. And sure enough there was. With the mechanical TRV the room was forever too hot or too cold, requiring constant adjustment to maintain a "comfortable" temperature.

    During initial room heat up it was necessary to set the temperature significantly higher - "4" on the dial to get the temperature of the room up in an acceptable amount of time but it then had to be manually turned down to around 2-3 after an hour or so to prevent the room overheating. Every night was a game of fiddle with the TRV to get some sort of comfort. Too hot - turn it down a bit. Too cold, turn it up a bit. Rinse and repeat.

    The HR92 was a revelation - with no scheduling available in standalone mode I just set it to a constant 21C and the room would get quickly up to temperature but then stabilise and stay at a comfortable constant temperature. We could go the whole evening without feeling a need to fiddle with the temperature, and within the same season at least, we left it at the same temperature setting day after day.

    I've discussed at length in other threads why this is so, but in short, it's because it's a full PID (proportional integral differential) controller with self tuning heuristics to adapt to the room thermal response time characteristics as well as the valve body characteristics, compared to a manual TRV which is only a proportional controller, and one which suffers from stiction as well. It's this stiction and the inability to adapt to the room thermal response time that causes the constant temperature cycling of the room you get with manual TRV's.

    Another problem with manual TRV's which is a result of them not having any integral term is that they have offset error. This causes two problems - one is if the amount of heat required to reach the target temperature is greater (colder outside) this requires the pin position on the valve to be higher up, but this means the set point of the room will go down because it is only a proportional controller, which needs a lower temperature for the pin to be higher. An integral controller can cancel offset error.

    This same problem also means that any tiny difference in the pin lengths or characteristics of the valve bodies means that a given number setting on the dial will be a different temperature. So a setting of "3" will be a significantly different temperature in each room of the house, something which irritates me no end in a conventional system, and the reason why conventional TRV's are numbered 1-5 and not in degrees!

    On top of the improvements of temperature control that an HR92 brings you can improve it even further by using a remotely located sensor to eliminate the influence of localised heating from the radiator being beside the sensor - something that you can't do with a mechanical TRV.

    In short, I would never go back to mechanical TRV's in a heating system now. If I decided Evohome wasn't for me anymore after moving house I would look at one of the competing systems with electronic TRV's like Tado. It's not just about scheduling for me, it's about the vastly superior temperature regulation that electronic TRV's can provide - especially when coupled with remote temperature sensors.
    No I was referring to liquid TRVs. Who has the wax versions these days? Whilst I agree with you to a point, the Liquid ones work relatively well. I have two Liquid TRVs on a towel rail circuit that switch on and off when they should (to the degree actually) and a TRV on a garage radiator that’s on whenever there is a heat demand.

    The liquid ones are never going to be as accurate as a digital TRV, especially if you have a remote sensor but on the whole I think they work well enough. The ones we fit anyway seem too.

    I think you’ll find that you’d be able to regulated the heat quite well in a new house if you’re just going to leave the heating on all day, the issue you’ll have is will the programmable stat turn off before the rooms have hit their desired temperature...

  6. #6
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    Had I not received a box of 16 HR80s as a gift. I would never have gotten into CM Zone, Hometronic and now Evohome. But I still struggle to recommend anything other than Evohome to anyone.

  7. #7
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    Quote Originally Posted by mtmcgavock View Post
    No I was referring to liquid TRVs. Who has the wax versions these days?
    Interesting perspectives both sides, but the notion wax based heads are rarities is wrong, they still dominate the market from the likes of Danfoss and Honeywell etc, and in areas such as here, sourcing bi-directional valves let alone liquid sensors is a nightmare thanks to distributor cartels restricting product availability.

    10c -
    The gas bill here was halved (max 100 euro/month) by adding insulation to an already insulated modern house, and it paid for itself handsomely over the first winter season even on existing wax TRVs with -20 outside. Having observed the upper floor rooms dipping a bit over the worst of the winter (and spotting a sticky valve), a remote TRV system seemed an ideal solution whilst replacing the system anti-freeze for proper inhibitor, and changing radiator valves to bi-directionals (current TRVs jut into the rooms and some one-way valves are fitted on the return complete with hammering).

    Having looked at most of the "Smart" systems on the market, the conclusion was that although remote valve positioners are certainly the future, it is not yet a cost-effective proposal for retrofit in modern insulated homes with existing combi boilers, single point heating control and TRVs, unless tight temperature control is an imperative.
    Whereas Evohome is probably the most well matured of the current crop of "Smart" heating systems the investment cost is pretty hefty, although granted that for new builds or older/larger properties with problematic zones, Evohome et al may make sense.

    Most of the alternatives seem to use Evohome more as a pricing benchmark than a performance/quality standard, all with their own particular glitches and foibles, communications errors and reliance on server connections being the most common. Fetching a local forecast, geofencing, zone presence detection/temperature monitoring, or window open detection are not exactly rocket science these days, but branded peripherals bound to systems are a common business strategy.

    It makes sense for me to swap valves and change heads to liquid types, but I can't see a "Smart" system coming here until costs tumble significantly or a variant can be bodged, which currently looks a long way off...

  8. #8
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    HenGus

    Good luck with your move, and thank-you for your contributions to this forum, which have been of great help to me.

    Glad to read that you will continue to monitor the forum..

    NJSS

    NJSS

  9. #9
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    Quote Originally Posted by mtmcgavock View Post
    No I was referring to liquid TRVs. Who has the wax versions these days? Whilst I agree with you to a point, the Liquid ones work relatively well.
    Judging by the wax that leaked out of two of my manual TRV's that failed, which were only installed 3 years ago (a year before Evohome) wax is still commonly used.

    The wax is a liquid at room temperature - not all waxes are solid at room temperature, so a "liquid one" is still probably going to be wax.
    I have two Liquid TRVs on a towel rail circuit that switch on and off when they should (to the degree actually) and a TRV on a garage radiator that’s on whenever there is a heat demand.
    A towel rail is hardly a demanding application for a TRV - who cares if the temperature is plus or minus a couple of degrees in a bathroom ? Or a garage for that matter ?

    That's different to trying to precisely control the temperature in a living room or bedroom.
    The liquid ones are never going to be as accurate as a digital TRV, especially if you have a remote sensor but on the whole I think they work well enough. The ones we fit anyway seem too.

    I think you’ll find that you’d be able to regulated the heat quite well in a new house if you’re just going to leave the heating on all day, the issue you’ll have is will the programmable stat turn off before the rooms have hit their desired temperature...
    Well I had a conventional thermostat and TRV's for a year in this house before I had Evohome, and the difference in quality of temperature regulation is night and day between the two systems. I would not go back to mechanical TRV's for any reason now. Just my opinion.

  10. #10
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    I'm with Simon (dbmandrake) on this. But I think it's not just the TRVs. Old-fashioned TRVs will usually be combined with an on-off wall stat (possibly even mechanical) which will be +/- 2 degrees at best. This just exacerbates the problems inherent in the TRV.

    It's that fact that boiler demand is driven from the eTRV (or zone sensor) in Evohome that brings all of this together and increases the comfort levels.

    P.

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