HughF

Just realised that where I have easy access to the flow/return in the ceiling void, before the last rads come off, those rads have TRVs on as they are the upstairs bedrooms... If the TRVs shut down the bedroom rads, the flow will stop, the UFH will be drawing on a pipe that has gone cold, as there's no flow. I'll need to try and come off before the drops for the non-TRVd rads...

Ok, gotcha. I’ll need to drain the system down then to add those t’s before the feed to the last rads. I’ve got isolation valves on the flow/return after the last of the rads at the moment, so I could plumb this all up with the rest of the system live, but the installation of the Ts will require a drain down. Any benefit in T’ing into the return leg instead? Might be able to do away with the mixer if I can get a low enough temperature.

I’ve brought the flow and return down from the ceiling void to where my mixer is. So I would put the Ts in the flow line, come off, through the mixer then back again to the flow. Joining the flow and return together after the Ts to complete the circulation. What stops the now joined flow and return acting as a short circuit and my rads all staying cold?

Thanks for the input…. The rads are on from 0600-2300 at the moment, and that might change to 24hrs a day with the weather comp bumped down a bit as we head into winter. I wasn’t intending any zone valves at all, just use a floor sensing stat to switch the pump on/off. It was more the hydraulic separation issue I wanted to get clarified. I’ve already got short circuiting issues through my rads (see my other thread) and didn’t want to exacerbate the issue with a close coupled T arrangement between flow/return. Hence why I assumed it would need some resistance in the separation.

The unimix 3 is one of the few valves that will mix down to 20 degrees or so, it’s a good valve, or so I’ve been told. Plenty of people still say you should have a blending valve with a heat pump, for safety. I know @Nickfromwales is an advocate of this strategy. The situation is what it is, I’ve got rads in the rest of the house sized for 45 flow at -4, and I can’t feed that temperature into the ufh…

Cheap ones from Screwfix, unfortunately….

Ok, something interesting has happened… I’ve put 1.5 degrees on all the weather comp points and it’s sitting here ‘almost’ ticking along at minimum output. That’s encouraging. I’ve got the extra fan coil in the bathroom running now, that’s what’s changed since yesterday. Short cycling seems to have reduced.

Yep, standard blending valve…. But it’s supposed to be a really good one

I’m using an ivar unimix 3, the rolls Royce of blending valves. @Nickfromwalesdo you have anything to add?

Rads are sized for 45 deg at -4, can’t run the ufh at that temp so I need a blending valve/mixing station. Ideally they should, yes…. But we’re dealing with what we’ve got and have to make it work. Or we put rads in the extension and forget about the underfloor, I don’t really want to do that.

Yep, I’ve seen that. Can’t see a way around providing hydraulic separation between the two pumps without it though…. I don’t have any zone valves, just a stat to turn the ufh pump on/off. Rads are on all the time on a time clock with weather compensation.

Caleffi make a manifold that has exactly that, separation at the manifold…. why shouldn’t I put separation at the manifold? Surely it doesn’t matter where it is? And the boiler (ashp actually) is at the bottom of the garden so that’s not particularly practical.

I’m adding a ufh mixer to my rad system. If I use Close Coupled Tees (ccts) just before the input the manifold, do I need to add a lock shield valve in the middle of the t’s so that I don’t make a short circuit and then end up with no flow through my rads? My head says yes….

Yep, I get that, but I’d expect them to be a bit more granular, it’s all the same for 95% of the range, then it’s off…. I upped the bottom end of the pump pwm from 20 to 30, it seems to overshoot it’s temperature setpoint by 5 degrees or so at such a low pump pwm. Give me air2air all day 🤣

Adjusting the lock shield valves on the upstairs rads seems to make zero difference to the delta-t across the rad, so that would suggest that the pump speed is ideal, would it not? I can get a delta-t of 4 when the flow temp ramps up, and the delta-t drops back as the compressor shuts down.

Max speed of 60% and try that? edit: pump min of 20, max of 75…. Seems to be throttling back a bit more. Still need to get balancing and figuring out the flow direction.

The plumber is also my builder mate, who’s doing our extension/kitchen. I don’t really want to lump him with another job at the moment, nothing I can’t take care of (I do plumbing anyway)…. I’ve identified that the rad in the above photo is plumbed correctly (inlet at the top), and I’ve managed to get delta-t 2 ish…. Need to pop the front off the fan coils and set the ball-o-fix valves down on those first I think.

Ill identify the flow/return on each radiator and make a plan for re-piping. I imagine it will be easier to just swap from TBOE to BBOE, that way the flow doesn’t matter?

Moved my rad balancing/delta-t issue to another thread…

All the rads in the system are heating up, even ones further away, it’s just the flow through the rad is high. Downstairs rads have standard valves so I can throttle the flow on the outlet, but my engineering head says the upstairs ones need to be the right way round.

I need to throttle the flow to get the delta-t across the rad up, so I need the lockshield on the outlet, don’t I? This is on a heat pump system, open loop, no buffer. My rads are running at a delta-t of about 1.5 and a thermal camera shows the flow is short-cutting between flow and return across the rad.

I recently installed a new central heating system, bunch of new rads, and three fan coils. How can I balance my rads if the trv is on the outlet of the rad and the lock shield is on the flow? They are tboe with the trv at the top. I have trvs upstairs only (ashp, open loop, no buffer)…

Yep, short circuiting….. I need to get the lockshields set I guess. Rads are plumbed tboe but some of them might have the flow to the top and others to the bottom….. plumbers…. All the rads are currently wide open, balancing is needed.

At the moment we’ve got 5 rads in circuit, and close to a 40m loop of primary pipework (32&28) before the three port. There are two fan coils in circuit at the moment but they’re not emitting as the electrician is messing about with the wiring. One more fan coil to go back on the wall. All the rads are wide open, trvs upstairs only. I’ve yet to connect the ufh mixer but that’s running into 2x 50m loops. I designed for 21 at -4, but the wife isn’t happy with 21 so I’ve bumped the weather comp up 2 degrees on each setpoint. It’s running 40@15, 47@0 for now, as we’ve got reduced emitter output into the house. I am having an issue getting any sort of delta-t across the rads when I try and balance them, they’re all close to 1 degree between flow and return. I’ve got the pump pwm set to auto and the target delta-t is 5. It works sweetly on dhw.

Compressor and fan runs probably 20% duty cycle in a 10 minute period.