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Advice on new Smart Central Heating and UFH system

Discussion in 'Plumbing and Central Heating' started by gchd, 30 Sep 2021.

  1. gchd

    gchd

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    Hi All,



    I am getting a new Central heating system installed and looking for advice on the best design. The heating system will consist of the following components:
    1. System Boiler.
    2. Megaflo.
    3. 2 Zone Underfloor heating.
    4. 15 Radiators.
    I have narrowed it to the Heatmiser Neo stat system or Honeywell Evohome, however open to suggestions.
    As a minimum I am looking at 6 heating zones as below:
    1. Two underfloor heating zones.
    2. Two Upstairs zones, 1 for Bathrooms/ensuites and 1 for bedrooms.
    3. Two Ground floor zones, 1 for Living Area /study and 1 for Bathrooms.
    If I go with a Heatmiser system, then both UFH and central heating will be connected to Manifold and it will be a 6 Zone star circuit. I think in each central heating star circuit there will be a ring circuit. I will then be able to control each zone using a Neostat-v2 Thermostat.

    If I go with the Honeywell Evohome then I think it will be a traditional ring system for central heating (may be divided into 2 zones for downstairs and upstairs) and manifold for UFH. I can then use the Honeywell smart TRV’s to control each radiator.

    Now with Heatmiser, I think there will be increased meterage of pipes (I am using copper ) and I am fixed to 6 zones. I can go full star circuit and put each radiator in its zone but then it will be a substantial increase in meterage of pipes. However, it will be a modern system and also the cost of the Heatmiser system itself is not as high.

    With Honeywell there is no increased meterage of pipes, Cost of Honeywell Evohome is Higher than the Heatmiser but gives the option to put each radiator in its zone. i.e. I can have more granular control of the heating system. With Evohome I can start small and then increase the smart TRV’s as I learn and start using the system.

    Now I am not a heating expert or plumber. I have just gone through several articles to gather this knowledge. I will appreciate some advice from the veterans of this field.
     
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  3. muggles

    muggles

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    If you want a system which is going to be efficient, there are three very important things you need to do...

    1. Do a full heat loss calculation for the property. www.heat-engineer.com is the best calculator I've come across. Do the £12 room by room one and it'll also give you the outputs you need for your radiators. This will allow a boiler to be selected which is appropriate for your property

    2. Size the radiators for low flow temperatures. The outputs given in the catalogue are based on high flow temperatures and a conversion factor needs to be applied to get the outputs for low temp

    3. Use a control system which can vary the flow temperature according to varying heat loss and demand, such as an OpenTherm based system (you'll need a compatible boiler). That rules out the Heatmiser unfortunately.

    Evohome and similar smart TRV systems are all or nothing. You can't have some rads with smart TRVs and some not, as every time a room with a smart TRV calls for heat all the ones without smart TRVs will come on as well.
     
  4. gchd

    gchd

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    Thanks @muggles , very helpful. I have done the free survey on heat-engineer.com, to understand the concept.

    Below are the calculations :

    Total Heat Loss 13.26 kW
    Main Building 9.51 kW
    Extension 3.75 kW

    Total Energy Demand 47580.71 kWh
    Hot Water 17829.64 kWh
    Heating 29751.07 kWh

    Average W/m2 50.98 W/m²
    Main Building 59.42 W/m²
    Extension 37.48 W/m²

    How do I interpret them for boiler size, Do I need a 47kw Boiler?:eek:
     
  5. muggles

    muggles

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    No, you need a 13kW boiler (although you won't find anything exactly that size). Don't confuse power (kw) with energy (kwh). Best to do the paid survey to get a truly accurate picture, but given your desire to have individual control of each radiator I'd suggest something like the Viessmann 200w 19kW as a good option for you.
     
  6. gchd

    gchd

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    Great , even though we are replacing the whole central heating ( as house is under full refurbishment and extension ) , I wanted to keep my existing boiler ( Worcester Greenstar 24Ri ) as it was installed only 2 year back.
     
  7. muggles

    muggles

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    Up to you, but the issue with the 24Ri is that its minimum output is 7.4kW. You need a maximum of 13.2kW when it's -3°C outside and all your radiators are turned on. When it's a more normal average 9°C outside you'll only need 6.6kW to power all of your radiators, which is lower than the minimum output of your boiler. This will cause cycling which will reduce efficency, and increase wear & tear and running costs. Add smart TRVs into the mix so only half your rads are on and suddenly your boiler at its absolute minimum output will be producing almost three times the power that the system can absorb.

    That was the point of recommending the Viessmann for your proposed setup - it'll modulate down to a minimum output of 1.7kW which will be much more suitable and ensure it remains efficient for the majority of the heating season, even if half the radiators are turned off.

    The Greenstar also isn't compatible with any kind of energy saving load compensating controls such as OpenTherm, and can't do priority hot water which is another feature that can massively boost efficiency in heating systems.

    Up to you of course, but it seems to me to be a shame to go to all the trouble of upgrading to a fancy modern energy efficient system, only to bolt a boiler to it which isn't suitable for the majority of the year and isn't compatible with energy saving controls either
     
    Last edited: 1 Oct 2021
  8. gchd

    gchd

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    Hi @muggles, Thanks for sharing all the knowledge. I searched earlier and figured that WB Boilers do not support Opentherm. So Boiler upgrade is on the cards but at a later stage. I am trying to get the things right which will be difficult to upgrade at a later stage - e.g pipework. I am hoping that Boiler can be simply upgraded later without much issue and it leaves me with a budget to spend on things that I do not have ( e.g megaflo or evohome ) and are new investments.
     
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