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Thread: New System Install Advice...

  1. #1
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    Default New System Install Advice...

    Evening all,

    First post so go easy on me! Iíve done plenty of reading, and Richard has helped over on EvoHome, but I wanted a bit more information about the bare bones of the system.

    Long story short, we have purchased a 1920ís detached, and it needs a complete re-plumb. To make it a bit more efficient, we are going to install and EvoHome system at the same time. Iím going to be using my usual plumber for the job (Iíve built up a lot of trust in him), but heís not a Honeywell Connected specialist, so we will be working the EvoHome set up between the two of us. Iím a Mechanical Engineer by trade, so reasonably handy Ė Hopefully we will be able to manage it! (Famous last words?)Ö

    To simplify the installation, I am going to install it as a standard EvoHome system first, and then hopefully move to OpenTherm later. This should take out the complication of the OpenTherm set up, so we can concentrate on the zoning etc.

    It will be installed on a system boiler with 14 radiators. Boiler will either be Ideal, ATAG or Valliant (so I can complete the OpenTherm upgrade later). Tank size somewhere around 210-250l. I'm leaning towards the Valliant so I can run a matched cylinder, unless anyone has any other thoughts?

    Intial question is what system layout is best to go for, S, Y or W. From my understanding an S will require some modification to hold open one of the valves later with the switch to OpenTherm? Can Y and W be set to hot water priority? Is getting hot water priority best to do to get quick recharge times for the cylinder?

    I know I am going to need the hot water kit, and I believe a BDR91 to control the valve. I take it that I need a separate BDR91 per valve? Also Honeywells installation guide shows a V4073 valve offset from the T of the system. I thought this was a 3 position valve Ė Is this just schematically shown in the wrong position? Why does the valve move position when the HR92s are added to the radiators?

    Also, I understand that with HR92s there needs to be some kind of bypass for the boiler. Is it better to do this as an uncontrolled radiator, or an automatic bypass valve? If the EvoHome controller is going to be positioned in the hall, could I run the hall rad without a HR92 (i.e. as the bypass) and then rely on the controller to stop the boiler when the temp in the hall is OK?

    Finally, has anyone got any experience of using these on cast iron rads? We are replacing all the radiators in the house at the same time, and am massively torn between cast and columns. The rooms are quite large (lounge is 5w x 5l x 3h) and I know cast rads are supposed to be better for larger rooms. I just wondered how the system copes with the different way they deliver the heat.

    Thanks in advance, and sorry if the questions are a little thick!

  2. #2
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    Quote Originally Posted by kimber.kimber View Post
    It will be installed on a system boiler with 14 radiators. Boiler will either be Ideal, ATAG or Valliant (so I can complete the OpenTherm upgrade later). Tank size somewhere around 210-250l. I'm leaning towards the Valliant so I can run a matched cylinder, unless anyone has any other thoughts?

    Intial question is what system layout is best to go for, S, Y or W. From my understanding an S will require some modification to hold open one of the valves later with the switch to OpenTherm? Can Y and W be set to hot water priority? Is getting hot water priority best to do to get quick recharge times for the cylinder?
    From what I've read Y-plan is not recommended for larger systems, because the maximum achievable flow with both hot water and heating demand at the same time is not as great as an S-Plan system because all the flow must go through the single central port on the mid position valve, (past the ball valve which only has a small gap on either side) whereas with two 2 port valves you have a separate input port for each valve, and the ball valve can move further away from the input.

    Some other reasons S-Plan is probably preferred over Y-plan are that mid position valves are more complicated and not as reliable as 2 port valves and harder to diagnose if they start misbehaving, also you can't tack on additional heating zones like you can when you convert an S-Plan system to S-Plan plus, by basically adding additional heating zone valves. The latter is not so much of an issue with Evohome because you use HR92's to perform per room zoning rather than relying on multiple traditional zone valves, however if you add underfloor heating later you may want to use a zone valve there.

    W plan uses a diverter valve which is a three port valve like a mid position valve, but which doesn't have a mid position - its either all hot water or all heating. Since you're never supplying heating and hot water at the same time you don't have the flow restriction issue that Y-Plan could have.

    W-Plan is OK if you have a modern fast reheat cylinder and you're happy with your radiators not being heated for the entire duration that hot water is being reheated. On my old slow heat cylinder it takes about 25 minutes from cold to heat so W-Plan wouldn't work very well for me. Honeywell has this to say about W-Plan:

    http://www.honeywelluk.com/products/...undial-W-Plan/

    "Because the W Plan is a priority control system, it is recommended that it should not be used when there is likely to be a high hot water demand during the heating season which could lead to the space temperature dropping below comfort level. This situation is likely to occur, for example, in large family dwellings or in poorly insulated properties."

    Personally I think S-Plan using two 2 port valves is the best arrangement because it is the most flexible - by default you get independent switching of heating and hot water as demanded, however you could choose to implement W-Plan style hot water priority with a simple wiring change. Or if you decide later you don't need a heating zone valve you can effectively wire it out of circuit by wiring it to the pump power feed instead of a relay. Any configuration is possible with just wiring changes once you have those two 2 port zone valves.

    It doesn't have any problems with adding any extra zones later like underfloor heating, doesn't have the flow restrictions of Y-Plan, and in theory should be more reliable and easier to diagnose/repair that Y-Plan.

    One difference though is that S-Plan always requires an automatic bypass valve as under some conditions both valves can close at once leaving nowhere for the flow to go, whereas in Y and W plan there is always at least one port open. (Although technically you still need an automatic bypass valve on those too if you don't have a bypass radiator - whereas on S-Plan you always need an automatic bypass even if you have a bypass radiator, as that bypass radiator can get isolated)

    I know I am going to need the hot water kit, and I believe a BDR91 to control the valve. I take it that I need a separate BDR91 per valve? Also Honeywells installation guide shows a V4073 valve offset from the T of the system. I thought this was a 3 position valve – Is this just schematically shown in the wrong position? Why does the valve move position when the HR92s are added to the radiators?
    Without seeing the exact diagram you're referring to that's hard to answer (can you find the diagram online ?) but regarding a heating zone valve, if you have one it will TPI modulate the zone valve based on heat demand, as well as the individual HR92's adjusting their valve opening. It is debatable whether this is the best way of doing it or not and I've just been through the exercise of modifying my S-Plan wiring to avoid this, as discussed in this thread, which you might find interesting reading:

    http://www.automatedhome.co.uk/vbull...ll=1#post30338

    The above circuit only applies if you go for a three relay configuration using a separate boiler relay, if you just do a standard two relay configuration (where each relay powers a zone valve and its up to the zone valve switches to fire the boiler) then you have no choice but to let the heating zone valve be TPI modulated so that the boiler is in turn TPI modulated.
    Also, I understand that with HR92s there needs to be some kind of bypass for the boiler. Is it better to do this as an uncontrolled radiator, or an automatic bypass valve?
    As above if you go S-Plan then you need an automatic bypass valve no matter what, and generally its good to have one because it regulates the differential pressure across the radiators when the number of open radiators changes. Without one even if you have a bypass radiator the pressure differential will change a lot so by the time only one or two radiators are open the pressure will be high and those remaining radiators will be noisy. An automatic bypass valve is just an adjustable pressure relief valve between pump output and return to the boiler, this sets a cap on the pressure differential when there are only one or two radiators flowing, but closes to avoid any "wasted" flow when there is a higher demand from more radiators.

    Personally I think another reason to prefer an ABV over a bypass radiator is that a bypass radiator is wasteful. It will get hot no matter which other rooms are calling for heat even if the room the bypass radiator is in is already too hot. In winter you might be OK with this but in spring and autumn you may find that rooms gets uncomfortably hot when you try to use the heating somewhere else.

    My original system used the hallway radiator as a bypass radiator and also located the main thermostat there, when I installed Evohome I changed the valve body on that radiator so I could fit a TRV head, added an HR92 and had an automatic bypass valve fitted - my summer gas use is now only 50% of what it used to be and apart from zoning in general I put quite a bit of that down to not having any bypass radiator cranking out heat when it is not needed. (For example when I'm just trying to warm the bathroom in summer and not any other room, now that hallway radiator won't be cranking away just because I'm drying towels in the bathroom!)
    If the EvoHome controller is going to be positioned in the hall, could I run the hall rad without a HR92 (i.e. as the bypass) and then rely on the controller to stop the boiler when the temp in the hall is OK?
    There's a bit of debate in other threads about this at the moment but I've been told by people that should know including Richard that you can't do this. Having the evotouch as a sensor with an uncontrolled radiator and able to call for heat can't be done in a multi-zone configuration. I also have the evotouch as the temperature sensor for the hallway on the wall mount but I have an HR92 on the hallway radiator as well for it to control.
    Last edited by DBMandrake; 24th January 2017 at 09:46 PM.

  3. #3
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    Just realised I haven't replied to this to say thank you! Response really helped me plan the system, and helped me realise I had read the Honeywell diagram wrong!

    Going to start a new thread on the install. Want to check a few things are right...

  4. #4
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    Quote Originally Posted by kimber.kimber View Post
    Also, I understand that with HR92s there needs to be some kind of bypass for the boiler. Is it better to do this as an uncontrolled radiator, or an automatic bypass valve? If the EvoHome controller is going to be positioned in the hall, could I run the hall rad without a HR92 (i.e. as the bypass) and then rely on the controller to stop the boiler when the temp in the hall is OK?
    As DBMandrake has said, the system does not like this configuration. You have to bind a temperature sensor and at least one actuator on each zone. However, it is possible to cheat a bit. I have the bathroom as the bypass zone, and fitted a thermostat to bring the bathroom on if it got too cold. I ended up with an additional BDR91 relay bound as the actuator. The BDR91 has a mains connection to power it, but no connection to its relay contacts. This allows the bathroom thermostat to work in the same way you suggest your hall could.

    Regards,

    Alan.

  5. #5
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    Just to add my own experience to this thread. If you go for an Atag then I would go for Opentherm at the same time. Set up is nothing more than 2 low voltage wires to the boiler and the selection of boiler relay, and Opentherm in the controller. I have a 5 bed 19 radiator house with a modified 's' plan. All the rads have HR92s. The heating motorised valve has been replaced with an open in line valve, which closes when the HW BDR demands hot water heating. There are two ABVs (boiler and airing cupboard) and two expansion vessels (boiler and airing cupboard) in the circuit. This set up accords with Atag's recommendations for a system boiler with its Atag ONE controller.

  6. #6
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    I have zones where I use a HR80 or the controller itself as a thermostat sensor but with no actuator. So if temperature sensing is all you need then you don't need an actuator bound. However if you want to fire the boiler as well then you need a dummy actuator or just use a HR92 in the room but don't install it!

  7. #7
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    Hi,

    I know this an old thread, but if you went ahead with the HR92's on Cast or column rads can you let me know how they look?
    I'm planning on putting in new cast iron rads in a 1914 build house and we're not sure if the white HR92s will look out of place when on a old style radiator that won't be painted white.
    I have just seen that 'Genius Hub' can provide coloured TRVs but from what I've been reading I prefer the Honeywell system.

  8. #8
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    Quote Originally Posted by gtuser View Post
    Hi,

    I know this an old thread, but if you went ahead with the HR92's on Cast or column rads can you let me know how they look?
    I'm planning on putting in new cast iron rads in a 1914 build house and we're not sure if the white HR92s will look out of place when on a old style radiator that won't be painted white.
    I have just seen that 'Genius Hub' can provide coloured TRVs but from what I've been reading I prefer the Honeywell system.
    TBH they are a bit of a barnacle outcrop! but no more than a normal TRV. This was a major concern for me originally (I like things looking good), but honestly a year after the install, we are used to them. Sure they could look better, but there are plenty more things to worry about, and the £6/day saving we are now getting in winter makes me feel a lot better about it! I have thought about having them wrapped or similar, but I'm not bothering for now.

    We've got an Instagram account for the refurb, and it has got a couple of images. On the tall skirting boards they get kind of lost. It also depends on how big the rad is, as to how dominant a feature they are!

    https://www.instagram.com/p/BZxlhicn...dhouse_ourhome

    https://www.instagram.com/p/BY_dCVTn...dhouse_ourhome

    Hope this helps...

  9. #9
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    Quote Originally Posted by kimber.kimber View Post
    TBH they are a bit of a barnacle outcrop! but no more than a normal TRV. This was a major concern for me originally (I like things looking good), but honestly a year after the install, we are used to them. Sure they could look better, but there are plenty more things to worry about, and the £6/day saving we are now getting in winter makes me feel a lot better about it! I have thought about having them wrapped or similar, but I'm not bothering for now.

    We've got an Instagram account for the refurb, and it has got a couple of images. On the tall skirting boards they get kind of lost. It also depends on how big the rad is, as to how dominant a feature they are!

    https://www.instagram.com/p/BZxlhicn...dhouse_ourhome

    https://www.instagram.com/p/BY_dCVTn...dhouse_ourhome

    Hope this helps...
    Bit confused, why would you use straight valves like that? Surely a normal or corner TRV would have been much more aesthetically pleasing.....

  10. #10
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    Quote Originally Posted by mtmcgavock View Post
    Bit confused, why would you use straight valves like that? Surely a normal or corner TRV would have been much more aesthetically pleasing.....
    You absolutely right on the corner TRV. Would have been much better. However when I was doing the installation I couldnít find corner valves, in chrome, at the right price, from a good manufacturer (and knowing they would suit the TRV head). All of the valves are Honeywell Valencia.

    Itís only the downstairs that is like this, as we have solid subfloors. Upstairs are STD angled valves, going under the floorboards.

    There will be a little rework to the system now we are in, so if anyone can point me in the right direction, feel free!

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