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Green Building Bible, Fourth Edition
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    • CommentAuthortopher
    • CommentTimeSep 5th 2015

    Do you have a link to the study that Evohome uses to claim the 40% saving? I can't find the formal Salford study.

    My existing system has a cylinder thermostat, a Honeywell digital room thermostat that controls the whole house, but has different temperatures for different times. So 17 degrees at night, 19 in the morning and 21 in the evening.

    Another time clock controls the cylinder on times, 1 period morning, one noon, and one in the evening.

    I have TRVs on most radiators, two rooms have skirting board heat, no TRVs. No external temperature measurement.

    With Evohome, I would have control of absolutely everything.

    I guessed at 30% saving, to try and be a bit conservative. What do you think? Too high?
    • CommentAuthorJonG
    • CommentTimeSep 5th 2015
    This is a link to the Salford test topher:


    I don't believe it was Evohome though and haven't seen a trial where Honeywell claim 40%, but with the level of control you already have I would be surprised at 30% to be honest I would say much less than that, especially given that your Vaillant won't get the benefit of the Opentherm potential which can make a good bit of difference.

    Your Honeywell control, depending on its age may well already have TPI and optimum start embedded in it.
    • CommentAuthortopher
    • CommentTimeSep 6th 2015

    Thanks for the link. Very interesting.

    I think you are right, 30% is too high, but I must get some benefit from only heating the part of the house that is being used, not the whole thing as today.

    My Honeywell digital control is old and just puts the temperature up/down at the set time. I dont think it has TPI. However I will get a benefit in comfort from Evohome's TPI and optimum start related to outside temperature.

    This Honeywell website http://getconnected.honeywell.com/en/evohome claims the 40% saving and refers to this bit at the bottom of the page. . . . . .

    * Source Energy Saving Research Unit, Strathclyde University 2013 & TACMA 2013 - Energy savings quoted were calculated using a 3 bedroom, 2 level home, located in the UK, modelling a family of 4 over a typical week’s activity, comparing an evohome smart zoning system, with recommended settings, to a system comprising of a simple timer, single non-programmable room thermostat and no Thermostatic radiator valves. Individual Energy savings gained are dependent upon existing controls, environment and lifestyle.

    So the 40% saving is made by comparing a very basic system with the most sophisticated available. Not surprising really.

    You mentioned Opentherm, I had a quick read, and can see the benefit, but my Valiant has modulated flame control and I can hear the boiler operating at a low setting when the demand is slight, and at full power when the demand is high. Is this not similar to the Opentherm advantages?
    • CommentTimeSep 6th 2015
    Posted By: topherOpentherm

    Opentherm is definitely not open. The only way to know the capabilities (or not!) of any two pieces of equipment connected by an Opentherm connection is to ask the manufacturer(s). Or reverse engineer it, but is that supposed to be illegal now?
    • CommentAuthorJonG
    • CommentTimeSep 6th 2015
    Hi topher, you will save something but your TRV's are limiting heat input too, assuming that they are not fully open.

    The Strathclyde survey started with a property without TRV's so this is a relatively significant difference in upgrade.

    Opentherm improves modulation, by starting the process earlier based on the load indicated by the room thermostat, so as it approaches set point or if the demand occurs when the start point is close to set point but still below it, it modulates the gas valve and controls the flow temperature between pre-determined bands to void overshoot and only consume the smallest amount of gas required to achieve air temperature.

    In comparison your Vaillant starts at full rate and attempt to achieve the flow temeprature set on the manual boiler stat, it will then modulate based on flow and return temperature, but the thermal mass of water will react much slower than air in terms of rate of temperature change.

    This means that if the load (room temp) is close to set point, it may well hit flow temp and potentially switch off before the room stat is satisfied, before then switching back on when the return temp drops, conversely when the load is high and large volumes of cold water are circulating it will then go to full rate and stay at full rate until the return drops or room temp is reached.

    These effects will be influenced by the system design, presence of TRV's, speed of pump, type of building, start and set point temp etc.

    Opentherm seeks to overcome some of the potential issues by effectively simmering the boiler to achieve room temp.
    • CommentAuthorJonG
    • CommentTimeSep 6th 2015
    Sorry meant to also say that this is considered superior to weather compensation because on a cold windless day, heat loss from the property will be lower than on a cold windy day, WC on it's own does not take this into account.

    Load compensation via the air temp in the room under control reflects more accurately the internal ambient temperature at that point in time and influences the boiler accordingly.

    Evohome will make a difference and also give you a very modular platform that can be upgraded and improved over time and when the boiler dies if you choose an option with Opentherm you can add the OT bridge at that point for about £90.

    We favour Intergas as our boiler of choice at the moment.
    • CommentAuthortopher
    • CommentTimeSep 6th 2015
    Brilliant JonG, many thanks. I have a lot to learn.
    • CommentAuthortopher
    • CommentTimeJan 2nd 2016
    Starting to install the system now. It will be a slow process, as I have some plumbing changes to make. First problem was that the controller would not find my Wi Fi signals. All my other stuff would find them as normal. I even tied to enter them manually. Still no good.

    I have a Sky router with the Wi-Fi turned on (it is normally off), also an Apple Time Capsule which has dual band Wi-Fi. So in frustration, I tried to do it with the controller plugged into the power supply. Worked straight away, found the Sky and Time Capsule signals.

    Checked the manual, no specific instruction to have it powered up.
    • CommentAuthortopher
    • CommentTimeJan 5th 2016
    I have now got a temporary hybrid system. Boiler is still controlled by my old digital thermostat in the hall, but most rads have Honeywell Evohome wireless radiator valves. After one day messing about, it seems to be OK now. My main comments are -

    1. One valve was not getting a signal. Valve and controller were at diagonally opposite points of the house. I moved the controller closer to its final position and it's OK now.

    2. Binding, unbinding and factory reset have to be done frequently on the valves. I now know how to do it. Honeywell could have a much simpler menu system instead of short presses, long presses, and cancellation long presses. Still, I know how to do it now.

    3. If you get error messages as I did from communications problems, the error log gets bigger and bigger. It can not be erased. You have to put the controller on battery power, remove the battery for a few seconds, and re insert. This is a reset, not factory reset. Data is retained, and the system takes ages to re-establish communications.

    4. Honeywell supply an adapter to convert my RA style rad valves (the thing with the pin that is pressed down to control the flow). They can easily be wrongly fitted. After excellent support from the Evohome Shop, I was able to fit them properly. The trick is to open the split fully so that it sits right up against the shoulder.

    In summary I think I made the right decision to start with a hybrid system. If I had done the boiler controls and rad controls at the same time, I think we would have a cold house and me rushing about to fix things late into the night.
    • CommentAuthortopher
    • CommentTimeJan 12th 2016
    A week later, I now have an almost complete Evohome system and I am very pleased with it. The old system is easily re-installable, and will be, when I prepare the electrical wiring for the final system. I plan to have a board with the components needed - 13A switch fuse, boiler control, hot water controller, 12 way junction box with my added indicators. I plan to have indicators to show boiler on, HW on and HW off.

    Good things
    1. Obvious savings that are apparent when you go into a bedroom during the day and find it cool.
    2. Being able to use an iPad anywhere in the house and elsewhere to see and control every detail
    3. Bathrooms cosy with hot towels ready after the morning shower.
    4. Occasional little whirring noises from TRVs confirm that room temperatures are being correctly controlled
    5. 'Open window' feature that shuts down the radiator when the valve detects a sudden drop in temperature. After a bit, normal control is restored.

    Bad things
    1. Documentation is not too helpful, customer installers (me) have to learn by experimentation.
    2. I think boiler efficiency will be reduced, because my older on/off condensing boiler now has long periods just ticking over, keeping a few radiators warm. With the old system, in the morning the whole house has to be heated, giving a longer time with condensing operation.

    Next tasks are to modify the plumbing to have suitable valves for my skirting board heat and one radiator. Then finally to install the new system with a mounting board having all the Evohome boiler control units.
    • CommentAuthorgravelld
    • CommentTimeJan 12th 2016
    How about overrunning the TRVs slightly so the room slightly overheats? Might be condensing more that way.
    • CommentAuthortopher
    • CommentTimeJan 12th 2016

    Thanks, interesting idea, which I think could be developed.

    I did overrun the bathroom towel rail for 15 minutes to get hot towels. I could do that for other rooms too.

    Each radio controlled TRV has its individual schedule. Thinking about the morning for example, I want to heat the bedrooms, bathroom, landing, hall and kitchen (ready for making a cup of tea). Rather than having them come on at different times to suit my lazy getting up process, I could have them all come on at once.

    This might mean heating some parts a bit earlier than needed, but would put a bigger load on the boiler.

    I could do a similar thing at night for going to bed.

    I will give it a try, but I don't think I can measure the results. Does anyone know a typical condensing boiler efficiency at start up from cold, compared to efficiency when hot and just maintaining a light heating load - which mine seems to do most of the time.

    Another thing I could change is the predictive start up and shut down. Evohome can be set to "learn" how long a room with its TRV takes to reach set temperature. If Wi Fi connected, it also takes account of predicted outside temperature, sent by Honeywell. At the moment, I have predictive start up turned on, so different TRVs will start at different times depending on radiator sizing vs room volume and room heat loss. If I turned this off, I think they would all start at once.

    To many variables and no way of measuring results.
    • CommentAuthorJonG
    • CommentTimeJan 13th 2016
    I love it, and it is one of those things that you don't realise you need until you have it! Definitely keep the optimum start and optimum stop enabled, it is a key feature of the platform.

    What cyclical rate have you set up, with a condenser it should usually be 3 starts per hour and 5 mins min run time, this should prevent the TPI from screwing too much with the modulation rates in built into a condenser.

    Check your flow and return temps to see if it is condensing and try and reduce the FT as low as possible and balance to suit.
    • CommentAuthorgravelld
    • CommentTimeJan 13th 2016
    When I say overrun, I mean set the TRVs to aim for a slightly higher temperature. When this is achieved, boiler switches off and temp slightly overshoots. You get a more jagged temp curve but might work out better if heat loss isn't too high?
    • CommentAuthortopher
    • CommentTimeJan 13th 2016

    I contacted the boiler maker (Vaillant, premium rate call) about boiler starts per hour, and I understood him to say it didn't matter much as the boiler modulated the flame to suit the heat demand. I will take your advice and set to 3 starts per hour. I will leave optimum start and stop enabled.

    Q1. I have the boiler temperature set to 70 degrees and the hot water to 45. When you say keep the FT as low as possible, how low?

    Q2. I have a little hand gun with a red laser beam that measures temperature. If I put black tape on the pipes, could I use that?

    Q3. I understand that the biggest temperature difference between FT and RT causes the boiler to condense. What values should I use to determine if it is condensing?


    If I set to a slightly higher temperature, it would keep that slightly higher temperature for all the on-time, using more gas. What I could do, is set a higher temperature for say 10 or 20 minutes, then revert to normal, this would put a slightly higher demand on the boiler at start up. I believe with the central controller and the "learning" programme, there would be a critically damped rise, with no overrun.

    I have set a lot of rooms to all come on at the same time in the morning. I have to do a similar thing for the evening start and going to bed events.
    • CommentAuthorgravelld
    • CommentTimeJan 13th 2016
    Ok, I didn't know if there was a "tuning" override you could apply to the TRVs only. Personally I think it's just a bit broken to rely on TRV sensed temperature. What you say should work though, assuming heat loss is not too great?

    It's not just condensed boilers affected by this, it's also oil boilers, because of their non-modulating nature.
    • CommentAuthortopher
    • CommentTimeJan 13th 2016

    I agree. I don't know how well a TRV in the far corner of a big room can control the temperature.

    I have ordered a separate room thermostat which will be linked by radio to the controller which then drives the TRV. It has the advantage of being portable - I can put it in different parts of the room to find the best position. It can also be fixed to a wall. Seems to me a cool idea, the trouble is the more I find out, the more expensive it gets.
    • CommentAuthorJonG
    • CommentTimeJan 13th 2016
    The FT can be set as low as possible whilst still allowing your rooms to reach temp, so the size of the rads relative to the room and its insulation values are the key metrics.

    A condensing boiler generally works off a 20 degree delta, not sure how effective an infrared will be at measuring the temp on the pipes, but the installer menu on the boiler may display them anyway?
    • CommentAuthortopher
    • CommentTimeJan 24th 2016

    Over the recent cold spell, I have learned that with my radiator sizes, I have to run the boiler at 70 or 75 degrees to get the house warm enough. When I have got the installation completed I will try and achieve that 20 degree delta.

    Another matter that may be if interest - the firmware update that corrects bugs and shows radiator override settings on the controller and the app is now available. But you have to request it from Honeywell. I have made the request and will explain how it works here.

    Yet another matter that may be of interest - for some unknown reason the app showed two rooms incorrectly. Both had the wrong name, but the temperature on both was 62 degrees. Honeywell advised me to delete my account on the server, delete the app, reinstall my account on the server and reinstall the app. This was a very tedious process because the server was very slow, but in the end the problem was solved.
    • CommentAuthortopher
    • CommentTimeJan 26th 2016
    The firmware update was installed in the background yesterday. I did not have to do a thing. The noticeable difference is that if you locally change the temperature in a room with radiator valve or thermostat, then it shows on the controller, and can be modified or deleted.

    If you want the update, just send an email to consumersupportuk@honeywell.com
    Tell them your account user name, they may ask for more info.

    Unfortunately it is not on the app. I have asked Honeywell if/when it will be added. It would be really useful, because with the app on an iPad, one can wander about the house making tweaks, its not so easy with the controller.

    Still delighted with it.

    Today I am fitting new valves to skirting board heat and one rad that does not have one. Bit cool in the house now.
    • CommentAuthortopher
    • CommentTimeJan 30th 2016
    Got everything back together and working. Have left the house for a week and set up the 'Away' setting. All rooms go to 13 degrees and HW to off. With the app, I can see the temperatures reducing from the remote location. I see that one room is dropping faster than the others. This is helpful as it encourages me to consider increasing the insulation for that room

    I also see how slowly the hot water temperature is dropping. I am pleased that the HW cylinder has such good insulation.

    One hairy problem just before leaving was loss of communications between the HW relay and the controller. I called the Honeywell customer support (00 44 1344 656 200) and was given excellent help by Ben who talked me through the button pressing sequence to cancel the binding and reset it. I need to spend some time learning the process because I have had a number of communications failures.
    • CommentAuthortopher
    • CommentTimeMay 14th 2017
    Hi, Anyone there? Long time since Jan 2016.

    Today is hot. All rad valves are off, as ambient is well above setting. HW is off on the time switch.

    But the boiler controller is calling for heat. So the boiler is briefly on, and the HW is passing through the bypass.

    I am wasting gas.

    Any advice?
    • CommentAuthortony
    • CommentTimeMay 14th 2017
    What is the room stat setting?

    Sounds like something wrong with the hard wiring to me.

    Check HW stat is working and in contact with cylinder
    • CommentAuthorgravelld
    • CommentTimeMay 15th 2017
    Don't know much about EH but... how are the room temps monitored?

    I know with my HG system which has separate room stats in each room, sometimes the temps of wall and air can lag behind each other, meaning it can sometimes feel cold but the stat thinks its warm, and the other way around, thus a call for heat.

    I think it's the air getting colder quicker in our house, because it leaks like a sieve but the walls are masonry.

    The only workaround I have for this is manual control.
    • CommentTimeMay 15th 2017
    Posted By: topherBut the boiler controller is calling for heat. So the boiler is briefly on, and the HW is passing through the bypass.

    What controls the boiler's demand for heat? If the boiler itself is just measuring the temperature of its water, that would produce the symptoms you see, for example.
    • CommentAuthorgravelld
    • CommentTimeMay 15th 2017
    I think topher meant turn the boiler on/off by "call for heat"... might be wrong though (AFAIK boilers only sense their water temp when they are turned on).
    • CommentAuthortony
    • CommentTimeMay 15th 2017
    Turned on either by the HW, or the heating, or both. But it should not come on when neither are calling for heat.
    • CommentAuthortopher
    • CommentTimeSep 19th 2021
    I dont know if anyone is there. But I have fixed all the problems. My well liked Evohome system is now controlling and ASHP, the gas boiler is gone.

    Unfortunately Evohome is not compatible with ASHP (Daikin) hot water. I have to use the Daikin controls for that. But they seem to be fine.
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