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Vaillant weather compensation with 2 zone HW?

Discussion in 'Plumbing and Central Heating' started by RoyMacDonald, 11 Jun 2013.

  1. RoyMacDonald

    RoyMacDonald

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    My house has a HW cylinders at each end and I want to fit a Vaillant system boiler with full weather compensation but the control centres they do don't have connections for two lots of HW sensors and motorised valves.

    Any one know how to do it?

    Thanks
     
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  3. JoeMar

    JoeMar

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    i maybe wrong here but why would you use weather comp on your DHW? surely that will cause you issues...especially in summer?
     
  4. ALEC1

    ALEC1

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    you can't.. teutonic logic says its point less to heat two cylinders as it doubles the standing losses of them...best to stick to one cylinder with a well insulated recirculation loop on a timer to reflect demand.

    that said, if you dispense with the vr 10, and use the cylinder thermostats a competent technician could organise the two cylinders..you would loose a bit of functionality of the controller though
     
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  5. RoyMacDonald

    RoyMacDonald

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    The two HW cylinders are already installed. I think because the bathrooms are about 20 meters apart.

    It has a non condensing boiler and it's that I want to change. I used the Vaillant with weather compensation in my last house and I really liked it.

    I started using weather compensation about 1992 so it seems a bit retrograde to install one without.

    I'd need listed building consent to change the existing plumbing layout as it would involve making changes to the fabric of the building.
     
  6. Agile

    Agile

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    Nothing that difficult for a competent person but he will probably haver to make up a small circuit housed in a Tupperware box.

    Weather comp is only used for heating.

    The system has to be made HW priority and when heating hot water the weather comp sensor is switched out of circuit and replaced by a potentiometer set to provide about 70 C for cylinder heating.

    Tony
     
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  8. Onetap

    Onetap

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    I'd suggest; wire it generally as Fig 5.3 (Connection with two 2-port valves) in the VR65 installation instructions, with two exceptions.

    The 2 cylinder thermostats are wired just to a 2-port zone valve, adjacent to each cylinder. On a hot water demand, the thermostat contacts close, the valve motors open and the end-limit micro-switch (otherwise not used) closes when the valve is fully open. You'll have three 2-port valves (2 HW, 1 CH).

    It is then simply a matter of wiring the two end-limit switches in parallel and connecting back to the VR 65 so that either end-limit switch closing will make the 'CYL' contacts (acting as would the single cylinder thermostat in the diagram) and the HW generation sequence starts.

    The DHW zone valve connections in the VR65 are not used (edit; this is wrong, see post below) ; they could be used, but you'd have to ensure they could operate 2 zone valves or drive the valves through a relay. If you don't use them, you won't be able to use the HW time switching in the VRC weather compensation controller.

    As stated above, you lose the cylinder temperature indication and the cylinder pasteurisation options by not using the NTC temperature sensor, but that would require a major bit of artificing..

    The heating goes off whilst the HW demand is on, so having two cylinders may make this impractical, especially if the house insulation is poor (so that room temperature drops rapidly) or if they're old cylinders (with low heat transfer areas and/or limescale fouling, so taking a long time to heat up).

    Didn't Vaillant suggest something like this?
     
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  9. RoyMacDonald

    RoyMacDonald

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    Thanks.

    The HW cylinders already have a 2 port each on them, also a pressure vessel each and thermostat. I've just been up with a torch, looked around the back, and the tanks are Range Tribune with Range 2 port valve and thermostat wired into a small box on the wall that also says Range.

    According to the heating engineer who rang them up Vaillant said it couldn't be done.

    On my previous install the engineer (different one) didn't use the NTC anyway.

    Just to add the building was converted to a dwelling in 2004 and has very good insulation. (Haven't needed any heating since March) The tanks also are from the same date. Not sure why a non condensing boiler was used.
     
  10. Onetap

    Onetap

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    Two other things.

    I looked at the VR65 manual, it will only operate two 2-port valves or one 3-port valve, so you'd need to use the DHW contacts in the VR65 to operate a relay capable of switching the power supply to the two DHW 2-port zone valves.

    Secondly, there is a mistake in my previous post and you should use the VR65 DHW contacts, as described above. If you didn't ( as my first post had suggested), then a DHW zone valve could open whilst the heating was on, allowing the weather compensated heating to cool the cylinder, if the heating were running at say 45 degC. You need to use the DHW contacts in the VR65 to disable the zone valves during the heating cycle.
     
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  11. RoyMacDonald

    RoyMacDonald

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    Thanks again.

    One thing, the Range Tribune over the kitchen has a Honeywell wiring centre with 4 cables connected plus a Honeywell two port valve. The other one has all Range controls and wiring centre. I’m wondering how many wires go back to the main Honeywell wiring centre by the boiler. Range may have more info on how their cylinders are connected up as they cater for multiple cylinder install of almost any number so may have worked out how to connect to a conventional wiring centre.

    Anyone done a Range Tribune multiple tank install?
     
  12. RoyMacDonald

    RoyMacDonald

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    Can you recommend a suitable relay?

    I tried to follow Vaillant tech dept solution and use their commercial weather compensation system but that didn't work because it had to use the cylinder temperature probes that came with the commercial system and there was absolutely no way to connect them without disconnecting the safety cut out temperature probes on the Tribunes.

    So we had to return the commercial system and use a Honeywell programmable room thermostat but that control is proving highly unsatisfactory due to the nature of the building.
     
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