Beelbeebub

The lowest flow temp for a given power output is going to be with the ufh and rads both on together (and balanced) because that is the largest emmiter area. So you could run open loop WC, and just balance the UFH and rad flows to give you the best results. What about the salus autobalancing trv/actuators? They monitor the flow and return and adjust the flow (they sit on standard trv valves or even ufh loop actuators) so the dT is 7c (or maybe 5c, I forget)

Understood, but is the root problem that there are some rooms that cannot be heated without using rads at 45C and UFH at 40C at the same time? What is the.max temp the UFH can stand?

Not scare mongering. *if* the heat exchanger freezes, it's buggered. As you correctly point out, it won't freeze that easily. The only real possibility is a long power cut during a persistent cold snap eg beast from the east (the conditions when the electrical hearing trace won't help) However, in the unlikely event that happens you are onky concerned with draining down the HP. The buried portion prob won't freeze and even if it did it's not that big a disaster. So an AF valve will still provide protection as long as it is positioned to drain out the HP. The rest doesn't matter

If you go with an AF valve below the HP but out of the ground - ideally just as the pipe emerges then it should protect your HP should there be an extended power cut and cold spell. Ultimately if your bit of pipe sticking up from the ground to you AF valve freezes it's not that big a deal. The goal is to stop freeze damage to the heat exchanger in the HP. If that freezes you HP is scrap. Even if the pump inside freezes it's not the end of the world, so all you need is thr freeze valves to be such that the HP drains down. I would argue a single one on the lowest outlet (doesn't matter if flow or return) is enough. The goal is to get a flow of water through the HP so it can't freeze solid. If the valve opens and some water flows out that achives the goal. If enough water flows out to empty the HP, that also achieves the goal.

S I can get this straight in my head. You want to run in 3 conditions 1) Just rads at WC curve suited to rads 2) Just UFH at WC curve suited to UFH 3) Both rads & UFH with HP outputting WC curve for rads You can currently run 1 & 2 no problem, the issue is with 3 where the UFH circuit drops the return temp so much the HP cannot achive the desired rad temp? Is that correct? Assuming it is, I imagine you essentially have 2 choices. During the overlap time you can either run with Rads WC, and (as you suggest) have a lower flow rate through the UFH such that the return flow/temp doesn't drag the bulk flow down and cause the HP problems. The other option is the inverse, run both at the UFH WC temp. The UFH will be fine (obviously) the rads will be a bit cooler and output a bit less but the return temp shouldn't be an issue for the HP. The downside of this is the rad zones will be a little underpowered but this could be compensated for by switching to rads only for periods to "blip" a bit more heat into the zones. The upside is there shouldn't be any plumbing changes.

Thanks all. I'll have a chat with Octopus to see what the best way is. Exporting to the grid would be a nice bonus to help the payback.

Are your rads on separate circuit to your ufh? Ie can you run just rads and just ufh? If so, and your controller has the facility for separate wc curves per zone you should be able to run each set of emitters at the optimum temp. It might be worth working out which emitter is your "worst" ie needs the highest flow temp. It might be that it is just one or two rads are markedly worse. If those were upgraded it might allow a significant drop to a lower temp.

Just a thought. UFH tends to have a fairly high thermal inertia compared to rads (especially if it's in slab). Could you have 2 zones UFH and Rad. Each zone is set for the ideal flow and temp and you just "multiplex" between them say 30min on UFH, 30min on rads. Alternatively, you could flow to the rads all the time and, as needed, drop the flow temp and open up the UFH loops, so your rads will cool a bit (but still put out some heat) for a while whilst your UFH slab heats up.

I think the benefit is from the manufacturer pov. The outdoor unit is a standard aircon unit (manufactured in vast numbers) . It doesn't care if it's connected to a common indoor fan unit or a hydro box that dumps the heat to water. There are some secondary benefits about not freezing outside and typically smaller and easier runs to the outside unit. The downside is the need for refridgerant handling during install.

But in both cases the compressor is often outside. The internal bits of both refrigerant and hydro split only contain standard central heating circulators, diverter valves etc which should be fairly quiet.

Was it a new system? I know some of the older designs had the compressor inside. Which would be noisier, but I was under the impression that all the newer split systems had the compressor outside.

That sounds like an extraordinary deal given those units retail north of £5k!

Also should add that if you are getting a particular room too hot using the single zone UFH, you can just turn the flow down to that room to reduce the output. Effectively your flow temp is driven by the worst loop in your house.

Yes, 100%. Though it does make sense to zone for the older non-WC gas boiler systems. But now, with WC and especially with HPs, don't zone - or onky have the absolute minimum. The physical hardware (manifold etc) is identical just with fewer components.

It is fairly standard to design ufh as zoned per room.. It sort of comes for free with the physical components - all the pipes come back to a manifold. The good news is that it's trivial to "dezone" the system. You just remove the zone actuators (or never install them). You can then adjust the relative flows through each loop to account for the different demands per room. My old ufh was originally zoned per room but I ditched that abiut 5 years ago for the entire house being one zone controlled by a single thermostat. It was actually better and more stable than the individual zones.

How far from the road is your plot? A mini concrete pump can sit on the road and push you concrete quite some distance. One visit for the foundations, then another for the floor slab.

Where does the internal noise come from in split systems? I know there were some systems that had the compressor inside and all that was outside was the heat exchanger and fan. But do modern ones do that? I thought they kept all the gubbins outside and all that was inside was a plate heat exchanger, a pump, maybe an expansion vessel and a diverter valve?

A reasonable point. But the skillset to install. A2A (basically fgas certification) would also be encouraged by subsidising a2a. The skillset to install any HP (vs gas boilers) is basically in the specification. There isn't anything in installing a HP that a gas safe engineer can't already do. The only tricky bits are getting the system design and sizing right in the first place. With a2a the issue is fgas - and there are good reasons for not letting any old sod loose given the higher gwp of the gasses. R290 gets around that issue but does introduce the flammability issue - but that isn't significantly different from gas safe issues.

On a side note, the regs exclude any HP over. 45kw total including shared ground loop systems. This would seem to be an issue for. The Kensa "shoebox" systems or any other shared ground loop systems that might be very useful for blocks of flats etc.

It would get very technical, how do you define delivery? You could argue the heat is *transported* from point of production to the end point by a vapour but *delivered* as a condensing liquid. The bulk of the energy is delivered as the heat of condensation with a minority delivered by sensible heat of the vapour or liquid phases. But the biggest stumbling block is the general lack of DHW provision. Milliband is talking about removing this restriction. Which might pave the way.

I've poked around to try and see where the prohibition on A2A might be. I haven't found it yet, except that the new system must provide all the heating and hot water and no hybrid systems are allowed. There are very few A2A systems that can also provide hot water. I believe daikin do one, but I haven't actually seen it in this country and I don't think it has any mcs certification. So maybe it would be as simple as allowing hybrid systems. Again, I think allowing A2A would see a significant up tick in installs as it would be cheaper and hence might be entirely covered by the grant. It is also potentially less disruptive for some properties. There would be an issue with skills as we don't traditionally have many A2A fitters in the UK. That said, if we coukd get our arses into gear around r290 and the manufacturers could produce r290 multi splits, I don't expect there would be much conversion from a gas safe engineer to an r290 safe engineer. There aren't any actual skill sets that are different the main criterion is being responsible and diligent when it comes to ensuring the gas lines are secure.

Generally liquids are nearly incompressible whilst gasses can be compressed.

Technically speaking the heat in an A2A heatpump is delivered as a hot gas (vapour) that is condensed into a liquid at the point of heat delivery (the room unit heat exchanger coil). So it is a tricky question if the delivery is via gas or liquid. I'm not sure the legal system is capable of dealing with the finer points of thermodynamics

Yes, I am. Suggesting that a. Change in the rules to allow A2A heating without any DHW provision (ie leave DHW as is) to get some sort of grant would increace uptake of Heatpumps and subsequently reduce co2 emissions.

I do think that revisiting the position on A2A and (related) the requirement the HP is the sole heating and DHW source is worthwhile. Fitting an A2A system is typically cheaper and can be fitted leaving the existing system intact. This gives the user the safety net that they will never be worse off in cost or performance than their existing system (because they can just use the existing system).