Page 1 of 3 123 LastLast
Results 1 to 10 of 26

Thread: EvoHome Advice

  1. #1
    Automated Home Jr Member
    Join Date
    Mar 2018
    Posts
    12

    Default EvoHome Advice

    So I've just moved into a new 5 bed house, which is over two floors and has 2 heating zones (S-Plan Plus). The boiler is an OpenTherm boiler (Logic Heat h15) but the existing thermostats and timer (ESi) are not OpenTherm compatible.

    My parents have moved in with us and my mother is home all day, so I thought that per-room zoning would be ideal for us. In the previous house we had a Nest, however when I queried them about multi-zone and OpenTherm compatibility, it looks like they can only do one or the other. My plan is now to use the EvoHome system, having a mix of smart TRVs and standard TRVs.

    Currently there is a bedroom zone (Which includes an en-suite bathroom towel radiators) with its thermostat in the largest bedroom on the second floor and a zone for the rest of the rooms with its thermostat in the ground-floor hallway.


    My plan was to put 6 smart TRVs (HR92) on the following radiators:
    - Radiator in Bed 1 (Our room, largest bedroom on the second floor - There are no other rooms on this floor other than an en-suite)
    - Main radiator in Bed 2 (Parent's room, second largest on the first floor - There is a second small radiator in this room but I was going to leave this with a standard TRV)
    - Radiator in Bed 3 (Office space)
    - Radiator in Bed 4 (Craft room for my mother)
    - Main radiator in lounge (I'll leave the second radiator with a standard TRV)
    - Kitchen (I'll leave the attached dining room radiator with a standard TRV)

    The idea for rooms with more than one radiator is to use a HR92 on the largest radiator to allow the room to call for heat, but leave a standard TRV on the second radiator so that it just assists.

    I was planning on using three relays (BDR91), one for each zone valve. (Including the hot water cylinder's zone valve) I'd also need the cylinder thermostat (ATF500DHW) which I don't believe has a relay output, hence the third zone valve.

    In Bed 1 and 2, I was going to fit a wall-mounted thermostat (T87RF2059) to make adjustment easier.

    The boiler would be controlled via the OpenTherm unit (R8810) - I don't believe it then needs any other signals, specifically the call for heat from the zone valves ?

    Obviously I'd also get the main controller, wall mounted.


    Does this setup sound right ? I don't want to spend this kind of money, only to find that it isn't going to work right for our needs.

    Thanks,
    -Andrew.

  2. #2
    Automated Home Legend paulockenden's Avatar
    Join Date
    Apr 2015
    Location
    South Coast
    Posts
    1,558

    Default

    How many rads do you have? I’d be tempted to fit HR92s on all of them, and dispense with the zone valve BDRs for the two zones (just keep them o0en). But obviously if you have shedloads of radiators that can become expensive.

  3. #3
    Automated Home Legend
    Join Date
    May 2014
    Posts
    988

    Default

    Before going firm on Opentherm, you might like to read some of the posts about Ideal boilers and Evohome/Opentherm. Opentherm is not as universally standard as some people think.

    Moreover, Evohome’s fuzzy logic is not as efficient as it could be. For example, when radiators demand heat first thing in the morning it will increase the boiler temperature to the set flow maximum temperature until all the zones are within the set temperature range. No problem with that. But, if someone plays with an HR92 in a zone later in the day, then Evohome will again demand max temperature flow until the set temperature is reached. To get maximum efficiency - lowest cost - then, in my opinion, it is best to attain and maintain rather than have variable zone temperatures.

    In your situation, a mix of HR92s and standard/electronic TRVs might work. The downside being that when any zone demands heat, then all the standard TRVs will also potentially get heat depending on the TRV setting.

  4. #4
    Automated Home Jr Member
    Join Date
    Mar 2018
    Posts
    12

    Default

    Quote Originally Posted by paulockenden View Post
    How many rads do you have? I’d be tempted to fit HR92s on all of them, and dispense with the zone valve BDRs for the two zones (just keep them o0en). But obviously if you have shedloads of radiators that can become expensive.
    In total I have ten in the main zone and eight in the bedoor zone. Four of these are towel radiators in the bathrooms so they can probably be discounted (two per zone) and three are in the hallways (Main zone) so they can probably also be discounted. Eleven HR92s look to be around £600, so it should work out cheaper to get the two extra BDR91 relays if I can get away with less HR92s.


    Quote Originally Posted by HenGus View Post
    Before going firm on Opentherm, you might like to read some of the posts about Ideal boilers and Evohome/Opentherm. Opentherm is not as universally standard as some people think.

    Moreover, Evohome’s fuzzy logic is not as efficient as it could be. For example, when radiators demand heat first thing in the morning it will increase the boiler temperature to the set flow maximum temperature until all the zones are within the set temperature range. No problem with that. But, if someone plays with an HR92 in a zone later in the day, then Evohome will again demand max temperature flow until the set temperature is reached. To get maximum efficiency - lowest cost - then, in my opinion, it is best to attain and maintain rather than have variable zone temperatures.

    In your situation, a mix of HR92s and standard/electronic TRVs might work. The downside being that when any zone demands heat, then all the standard TRVs will also potentially get heat depending on the TRV setting.
    Thanks for the heads up regarding OpenTherm, I'll have a read into that.

    In terms of usage I was planning on scheduling temperatures with the intention that they would not need to be manually overridden, very much how it was when I had a Nest. Will the EvoHome manage scheduled changes better than ad-hoc changes or would it again demand the maximum flow temperature ?


    I've always read that modern boilers are most efficient when the return temperature is below a certain value. How true is this ? If it's true then the thermostat shouldn't really need to set the temperature and it should be set by monitoring the temperature of the return pipe instead. (Which could be done entirely from within the boiler) I've noticed that the Ideal h15 just goes to its set temperature each time without an OpenTherm input, so it's clearly not doing this but I've it leaves me wondering why.

  5. #5
    Automated Home Legend
    Join Date
    May 2014
    Posts
    988

    Default

    Quote Originally Posted by yngndrw View Post
    In total I have ten in the main zone and eight in the bedoor zone. Four of these are towel radiators in the bathrooms so they can probably be discounted (two per zone) and three are in the hallways (Main zone) so they can probably also be discounted. Eleven HR92s look to be around £600, so it should work out cheaper to get the two extra BDR91 relays if I can get away with less HR92s.



    Thanks for the heads up regarding OpenTherm, I'll have a read into that.

    In terms of usage I was planning on scheduling temperatures with the intention that they would not need to be manually overridden, very much how it was when I had a Nest. Will the EvoHome manage scheduled changes better than ad-hoc changes or would it again demand the maximum flow temperature ?


    I've always read that modern boilers are most efficient when the return temperature is below a certain value. How true is this ? If it's true then the thermostat shouldn't really need to set the temperature and it should be set by monitoring the temperature of the return pipe instead. (Which could be done entirely from within the boiler) I've noticed that the Ideal h15 just goes to its set temperature each time without an OpenTherm input, so it's clearly not doing this but I've it leaves me wondering why.
    Rather than answer your thread point by point, I will describe my system. I have had Evohome installed now for nearly 4 years. I live in a 5 bed/19 radiator house which is divided into 12 zones. All the radiators have HR92s fitted to them. The boiler (an ATag is24) is protected by an automatic bypass valve. HW temperature control is via the Evohome HW kit connected in series with the unvented stat in the HW cylinder and controlled by a single BDR91. CH is via the Evohome controller connected to the boiler via an Opentherm Bridge. The system is configured for HW priority. The boiler parameters are set to a maximum temperature profile of 70C (TMax Set).

    I do most of my HW re-heating from 0530am. Evohome demands 90C to re-heat the cylinder but this is limited to a maximum flow temperature of 70C by the boiler settings. This does not happen with all boilers ( problem 1). CH comes on under Optimum Start conditions so from about 6.45 onwards various HR92s are whirring as the CH comes on in a particular zone. Unlike some other controls, Evohome will demand a flow temperature of 70C until all the zones are within their set temperature range (problem 2 if you are just adjusting a single zone). The boiler tries to maintain a 20C differential between flow and return but it rarely does so. Once zones reach their set temperatures, then my boiler drops back firmly into the condensing mode (having fallen from its max output of 24kWs down to 5kWs). Yesterday, when I checked the boiler, it had a flow temperature of 47C and a return temperature of 42C. More often than not, the pump was just running and the boiler had no flame. In sum, condensing does matter which is why fiddling with the HR92s is not to be recommended. I have the zones that I use set at 20C with the rest of the house at 13C from 0630 through until 22.00.

    I attach a couple of graphs which show my gas usage (yesterday) and the efficiency associated with a low flow return temperature. To make the point about not fiddling with the HR92s, the usage spike at the end of the day is associated with one zone heating our main bedroom from 15 to 19C just before we go to bed. This adjustment is set in the Evohome schedule.
    Attached Images Attached Images

  6. #6
    Automated Home Legend paulockenden's Avatar
    Join Date
    Apr 2015
    Location
    South Coast
    Posts
    1,558

    Default

    Quote Originally Posted by yngndrw View Post
    In total I have ten in the main zone and eight in the bedoor zone. Four of these are towel radiators in the bathrooms so they can probably be discounted (two per zone) and three are in the hallways (Main zone) so they can probably also be discounted. Eleven HR92s look to be around £600, so it should work out cheaper to get the two extra BDR91 relays if I can get away with less HR92s.
    Can't help thinking that only fitting HR92s on half of your rads is a bit like driving in icy/wet conditions with two bald tyres on your car. You're going to struggle to get the level of control and (particularly) comfort that Evohome can provide.

    Other might disagree though!

    P.

  7. #7
    Automated Home Legend
    Join Date
    May 2014
    Posts
    988

    Default

    Quote Originally Posted by paulockenden View Post
    Can't help thinking that only fitting HR92s on half of your rads is a bit like driving in icy/wet conditions with two bald tyres on your car. You're going to struggle to get the level of control and (particularly) comfort that Evohome can provide.

    Other might disagree though!

    P.
    i don't think that it is a question of disagreeing. i think that the decision has to be based on cost and how people use their rooms. For example, I have one room that is rarely used even when the whole family descends on us. Knowing what i know now, i would probably fit a Pegler Terrier i-temp at £18.

  8. #8
    Automated Home Jr Member
    Join Date
    Mar 2018
    Posts
    12

    Default

    Quote Originally Posted by HenGus View Post
    Rather than answer your thread point by point, I will describe my system. I have had Evohome installed now for nearly 4 years. I live in a 5 bed/19 radiator house which is divided into 12 zones. All the radiators have HR92s fitted to them. The boiler (an ATag is24) is protected by an automatic bypass valve. HW temperature control is via the Evohome HW kit connected in series with the unvented stat in the HW cylinder and controlled by a single BDR91. CH is via the Evohome controller connected to the boiler via an Opentherm Bridge. The system is configured for HW priority. The boiler parameters are set to a maximum temperature profile of 70C (TMax Set).

    I do most of my HW re-heating from 0530am. Evohome demands 90C to re-heat the cylinder but this is limited to a maximum flow temperature of 70C by the boiler settings. This does not happen with all boilers ( problem 1). CH comes on under Optimum Start conditions so from about 6.45 onwards various HR92s are whirring as the CH comes on in a particular zone. Unlike some other controls, Evohome will demand a flow temperature of 70C until all the zones are within their set temperature range (problem 2 if you are just adjusting a single zone). The boiler tries to maintain a 20C differential between flow and return but it rarely does so. Once zones reach their set temperatures, then my boiler drops back firmly into the condensing mode (having fallen from its max output of 24kWs down to 5kWs). Yesterday, when I checked the boiler, it had a flow temperature of 47C and a return temperature of 42C. More often than not, the pump was just running and the boiler had no flame. In sum, condensing does matter which is why fiddling with the HR92s is not to be recommended. I have the zones that I use set at 20C with the rest of the house at 13C from 0630 through until 22.00.

    I attach a couple of graphs which show my gas usage (yesterday) and the efficiency associated with a low flow return temperature. To make the point about not fiddling with the HR92s, the usage spike at the end of the day is associated with one zone heating our main bedroom from 15 to 19C just before we go to bed. This adjustment is set in the Evohome schedule.
    Thank you, that's really helpful. As long as I don't have too many schedule changes or I batch them together so that they happen at the same time, I think I should be fine.

    Regarding problem one, does this mean that with my Ideal boiler the flow temperature would be controlled entirely via the EvoHome and would not be subject to the setting on the boiler itself ? I had a search but I couldn't find much information on OpenTherm compatibility problems. (Or I didn't understand them when I found them)



    Quote Originally Posted by paulockenden View Post
    Can't help thinking that only fitting HR92s on half of your rads is a bit like driving in icy/wet conditions with two bald tyres on your car. You're going to struggle to get the level of control and (particularly) comfort that Evohome can provide.

    Other might disagree though!

    P.
    Quote Originally Posted by HenGus View Post
    i don't think that it is a question of disagreeing. i think that the decision has to be based on cost and how people use their rooms. For example, I have one room that is rarely used even when the whole family descends on us. Knowing what i know now, i would probably fit a Pegler Terrier i-temp at £18.
    I think it will certainly work for some of my radiators, in hallways for example, but I think I'll have to have a think about exactly how I want to control it and decide based upon that. I suppose it's not too much of a hardship to add more at a later date if it becomes a problem.

    I have just realised that the ground floor hallway radiator does not have a TRV on it currently as that's where one of the thermostats is currently located so I'm going to have to drain the system and replace the valve body, so that's annoying. (I've already gotten the plumbers to fit a TRV to the upstairs radiator while they had the system drained, but forgot about the second one.)

    So lots of thinking to do before I make a decision, thank you both.

  9. #9
    Automated Home Legend
    Join Date
    May 2014
    Posts
    988

    Default

    Quote Originally Posted by yngndrw View Post

    Regarding problem one, does this mean that with my Ideal boiler the flow temperature would be controlled entirely via the EvoHome and would not be subject to the setting on the boiler itself ? I had a search but I couldn't find much information on OpenTherm compatibility problems. (Or I didn't understand them when I found them)
    I cannot answer that question. On my ATag, the CH manual temperature is made inoperative by the Opentherm Bridge. On the Atag, Evohome and the boiler work together to calculate what is known as the TSet Calculated flow temperature which obviously varies with Evohome demand. As I write, the boiler has a TSet Calculated Flow Temperature of 45C with a lower return temperature so I don't see the lack of manual CH control being an issue for me. On Valliant boilers, I understand that there is still manual CH temperature control. The 'problem' is that some of the parts of the Opentherm protocol are non-mandatory. Boiler manufacturers tend to configure their boilers for their own controls. For example, Atag has the Atag One controller.


    http://www.automatedhome.co.uk/vbull...th-Ideal-Vogue

    In truth, the real problem is that UK boiler support technical teams are not that familiar with Opentherm, and if mentioned to most installers they just run a mile. (The same can be said for Evohome: they just want an install and forget type control system.)

  10. #10
    Automated Home Jr Member
    Join Date
    Mar 2018
    Posts
    12

    Default

    I found the same thing with Nest and OpenTherm, I called their technical support line to ask some OpenTherm questions and nobody had an answer even when they asked around. I think it's one of those things that I'll just have to take the plunge and give it a go. I might start off with just a basic system (No HR92s) and then add to it as I learn how it works.


    One question that I have around the installation of the hot water kit is that earlier you mentioned that you have the EvoHome HW kit in series with the existing cylinder stat. My unvented cylinder is a ThermaQ Evocyl 210 which has a stat pocket going into the cylinder. There's an ESi cylinder stat mounted directly in front of the pocket with presumably its sensors going directly inside.

    The ESi documentation suggests that there's two thermostats inside, an adjustable one and a separate 80C limit thermostat with a manual reset inside - Does the EvoTherm HW kit not fully replace both of these or do I need to find a replacement for the limit thermostat to go with it ?

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •