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Thread: Rads & UFH with zoned pipes

  1. #1
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    Default Rads & UFH with zoned pipes

    Hi,

    Last year we had an extension built which included 3 UFH zones. The existing part of the house is traditional rads.

    The setup is:
    BDR91 boiler control (Worcester combi)
    HR92s on rads
    HCC80r controlling actuators on the manifold for the UFH zones

    Evohome is set up with each radiator and UFH zone as their own zone, which we can control individually. This is great, and what we were aiming for.

    After the winter and getting used to the setup, we found we generally don't have the radiators on much, and the UFH zones tick over, keeping themselves at whatever temp we've set.

    What is wrong with our setup is that all the heating is on a single pipe circuit. This means that each time the UFH calls for a bit of heat, the radiator pipes in the house fill up with very hot water, which is unused because none of the radiators are on. Firstly this is annoying because they creak like anything as they expand and contract in the middle of the night. Secondly this is inefficient as we only want to heat the UFH.

    I realise what was missed out during our install was a zone value to separate the rads from the UFH. Ideally what we want is for some logic/control in the Evohome system to say "if any of the radiator zones are on then open a zone value, otherwise have it closed".

    However, I've contacted Honeywell to ask how we could achieve this and they've basically said we can't! If we attached a second BDR91 to the system to control a zone valve then we would lose control of the individual radiators. Which we don't want.

    I have two horrible ideas, but any further thoughts would be most welcome.

    1. Put a manual zone valve in the rad circuit. During most of the year we would leave this closed so CH water only flows round the UFH pipes, being more efficient. During the depth of winter we open the manual value to bring the radiators into play. This option is rubbish - we would have to remember to turn the manual valve on and off, and would have no ability to turn any radiators on remotely/scheduled if the manual value wasn't open. It would also mean that when the valve is open, if only the UFH wants heat then hot water would still circulate round the radiator cicruit, wasting energy and making the pipes creak.

    2. Setup a new 'Radiators' zone on Evohome which would be an Electric Heating zone (so that it doesn't fire up the boiler) with a second BDR91 to open and close a motorised zone value on the radiator circuit. I think we'd also need another thermostat. Most of the time this new zone would be set to some very low temperature, meaning the zone value was closed. If we then want the radiators to run we would edit the schedule or override for that radiator in Evohome, AND set the new 'Radiators' zone to some high temperature, causing Evohome to open the zone value and allowing CH water to flow to the rads. This is pretty horrible, but it's the best I can come up with for now.

    Can anyone suggest a better approach please?

  2. #2
    Automated Home Ninja
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    If the radiators are all shut down, water can't flow in the pipes unless there's a bypass somewhere.

  3. #3
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    Quote Originally Posted by dty View Post
    If the radiators are all shut down, water can't flow in the pipes unless there's a bypass somewhere.
    That was my initial thought on reading the query. But clearly the hot water is flowing through the pipes to get to the zone that has called for heat. These pipes may be under floor boards, behind the skirting but they will expand and contract. However, I don’t have the noise issue and often only want heat in one room upstairs. Perhaps it could be the actual layout of the piping?

    There will be an electrician amongst us who may be able to advise that what may help is an electrically controlled valve that is controlled via a connection direct to a BDR91! I could be quite wrong with that thought, but....
    Last edited by G4RHL; 23rd March 2019 at 05:55 AM.

  4. #4
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    Perhaps, but then neither of the proposed solutions would work. If a zone valve would work, the rad and UFH pipework must be separate. And if they are separate but the rad pipes are still getting hot, then there is a bypass (deliberate or accidental) on the rad pipework. Given the UFH is in an extension, I’d say the the bypass is there on purpose to protect the pump in the original installation and trying to shut down that branch would be a bad idea.

    In summary, we need to know more details about the layout of the pipework to answer the question.

  5. #5
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    Thanks for your help all.

    I have since spoken to the plumber who originally installed the plumbing for the extension. His view is that putting in a zone valve is overkill and counterproductive. Blocking the flow to the rads would create a small circuit for the UFH which would cause cycling of the boiler and increase wear and tear on it.

    Given that the rad pipes heating up only radiates spare heat inside the house, which is not a complete waste, and that the cost of parts and labour is pretty high just to save a few pence per day on fuel (as well as the boiler cycling issue) I've decided it's not really worth pursuing the zone valve.

    Instead, at the weekend I've pulled up the floorboards in the main bedroom and added hair-felt where the pipes touch the joists to try to tackle the noise. This has reduced the noise somewhat, but there are still some creaks. Unfortunately there are two 90 degree corners in the pipe where they feed the rad in that room that are jammed into a really tight notch in a joist, so there's no room for any felt without removing the pipework, which means draining the system and cutting the pipe out to create access to the notch and then reattaching the pipe (or routing it differently around the joist) - which is not a job for me. This approach isn't simple for the landing either, where we have glued down tongue and groove wood flooring, so access to the pipework to add the felt would mean breaking the floor open, not just popping up boards.

    I've also tried to reduce the impact of noise by adjusting the Evohome schedule a bit so it's not heating up at night (when the noise is more of a problem), but from what I understand it's more efficient to try to keep UFH ticking over at a consistent temperature than to let it cool and then try to heat it up again in the morning.

    As a note, regarding Evohome and the zone valve, my understanding is still that there's nothing in the control logic that could open a zone valve, probably via a BDR91, when any one or more of a set of Evohome zones (i.e. the rads with HR92s) requests heat. That multiplexing logic simply doesn't exist in Evohome. So even without the cost of more hardware and labour, there is no way to control that zone valve.

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