Adding UFH to an existing Evohome system

[andymcculloch]

Hello all,

I'm after some info on how to add UFH to an existing heating system controlled by Evohome. The existing system is straight out of the Honeywell manual - literally - see the diagram below. I re-plumbed the system last year, and used it as a guide for the pipework and controls. I have a single pipework 'zone' with HR92s on all rads (10 in total), and a single 2 port valve to control flow to the hot water cylinder. The boiler is a WB Greenstar 24Ri. I recall having a 'discussion' with the plumber who came to move the boiler and commission the system. He'd not used Evohome previously, and struggled with the differences to a 'normal' system - no pipework zoning, no motorised valves to control flow to the rads etc. Obviously it works perfectly, but he didn't believe it would at the time.

I'm now about to start an extension project, and wish to add UFH to the newly refurbished portion of the house. The new area will be a single large open plan Kitchen/living/dining room - approx 58m sq. I was planning on having this as a single zone, as it's a single space - unless there's a good reason not to.

I can foresee a similar discussion with the builder/plumber when it comes to connecting the UFH into the existing pipework and controls. So I'm after some details of what I need, and how it will connect in to the existing system - pipework and wiring diagrams ideally. I terms of a shopping list, I *think* I need:

• HCC80R
  Remote Zone sensor - HCF82, HCW82 or T87RF2033
  Pipework Manifold, pump, mixing valve
  Actuators

However, I'm unsure if I need another BDR91 and zone valve. The Evotouch controller will call for heat via the existing boiler relay, and from my understanding that should be enough. The HCC80R operates the manifold pump. The mixing valve takes water from the boiler flow and return, mixing it to the correct temp, and the actuators deliver hot water through each circuit within the zone according to the individual return temp on that circuit. So I don't *think* another BDR91 and zone valve is required.

Any advice or corrections gratefully received.

Andy

[rvb99]

When we added a UFH system it was recommended to add a zone valve to the ufh supply feeds. However, I used the HCC80R pump take off to control the motorised zone valve. The valve (in my case honeywell V4043H1080) also has a floating relay. This relay can in turn be used to control the ufh mixing pump. E.g you could set the system so that the HCC80R controls the zone valve via its pump output, and the zone valve in turn (via its relay) operates the ufh mixing pump.

However, to be honest, I'm not sure what additional benefit the zone valve brings other than kill the hotwater feed to the ufh unit more quickly, than just relying on the manifold actuators to close off the hotwater feeds.

[SymzTux]

How did you get on Andy? I'm just going through exactly the same scenario, whereby I have an UFH manifold with 4 circuits but they all ultimately are part of one zone. I have bought the underfloor heating controller, but it looks like I could keep the manifold open (not use actuators) and actually have a BDR91 bound to that zone as a zone valve which would then open a zone valve and activate the pump. What did you do? Did you only have 1 zone of UFH?

Simon

[skwerl]

Very timely for me as I'm about to expand my home and add 7 UFH zones. I was wondering about the need for a zone valve and read a post somewhere that excessive pressure can force the UFH zone valves open, leading to over temperature. Not sure how true this is and, with a bypass valve on the boiler, this shouldn't happen so it looks like belt and braces. Wiring the valve to the HCC80R and then using the valve relay to trigger the UFH pump seems like the ideal option and is how a traditional heating system would work; albeit with the pump being fed by the boiler/controller but triggered via the zone valve orange wire going live on open

[eddiejl]

Hi. I have just added a two zone UFH system to a multi-zone radiator setup. I used an HCC80R, a separate zone valve for the UFH (plus of course a typical manifold, mixing valve and pump), and a couple of remote sensors for the two UFH zones. The HCC80 controls the zone valve and the zone valve turns on the mixing pump. No need to turn on the boiler because the main evohome controller turns on the boiler when there is ANY demand for space heating, rads or UFH (mine does this via the BDR1 to the zone valve for the rads, which thence starts the boiler). The only side effect is that if the UFH requires heat, the rad zone valve opens even if there is no demand from the rads. This isn't much of a problem for me as usually there is at least one rad open when UFH is required. All works well for me.
I hope this helps.

[skwerl]

but then if none of your HR92s are open your rad loop won't run anyway, even if the rad zone valve is open.
You should actually set your rad zone valve to manually open, if all of your rads have HR92s on them.

[eddiejl]

The rads are all normally in parallel (two pipe system), so the hot water will just run round the pipework but not into the rads.
The system wouldn't work if the rads were all in series.