SimonD

It's looking like you've got multiple things going on with the system and you need a proper design in place that looks at the system as a whole. Best wait for the Vailant person and see what they say.

Not necessarily. There are multiple factors at play: Heat demand Delta T Flow rate Flow velocity Pump rating System control settings At the moment you're trying to test and commission the system at an ambient temperature of about 20C. At this temperature your radiators are not going to be able to dump the heat into the atmosphere, which is why I'm slightly surprised you are seeing a delta T of 5C at full load right now, unless the system is modulating its output and therefore its flow rate. Also, with Vaillant heatpumps, output to dhw is managed according to a measured delta T so Flow rate will vary too.

I think this comes down to product choice at the start. I've recently completed 2 repairs to UFH systems in houses built within the last 10 years. The systems used different manufacturers but in each of those systems one manufacturer had completely withdrawn from UFH and the other had completely redesigned its system and no older parts were available. The industry is partly to blame here, of course You don't use pure weather compensation but also use a room thermostat that provides load compensation. The problem is response time inherent in ufh systems, so you'll always get inertia. I have specifically chosen to use radiators as they provide a more response system. Like you say, when you're busy with work and family and everything else life throws at you, you can't be spending everyday planning for weather and temp changes and tinkering with the system. But this should be dealt with at commissioning stage after which the system shouldn't need touching. My worry is more about long term support from the manufacturers and the inclination now to take everything online and start to charge subscription fees. Once a system is set up and commissioned properly, it should take care of itself.

But you've said you have 2000l/h running dhw. If the primary was the problem, you'd see dhw problems too. So to me it's an indication that you have to investigate the whole index circuit, as suggested earlier.

In room temp. mode on your controls, what is it configured to? Is it Inactive (so weather compensation only), Active or Expanded? If it's on active or expanded your sensocontrol will be influencing output and modulation of the heatpump together with weather compensation. You might try to adjust your weather comp curve to highest as well as any room temp sensors to get the HP cranking up its output as much as you can. 1st you need to go around the whole system to make sure that all valves and actuators are fully open and then make sure that all your radiator valves and any TRVs are also fully open. If you have any TRVs do you also have a bypass valve in the system, or is it just installed fully open loop? Once you know the heatpump is running and all your radiators are getting warm, Now check your flow rate. If your flow rate is still looking low, then go into your installer menu and into the configuration menu and look at Config CH Build Pump and make sure this is set to auto (your installer may have set this to a fixed output because your heat loss is approx 10kW and your current flow rate coincides with 10kW at delta T 5). In auto the Config CH Build Pump will target the max/nominal flow rate, but if it had been adjusted, it won't. Then let us know.

What delta T are you measuring between the flow and return of your heatpump when it is running on CH?

Some are now asking for type F RCDs only. And some want mcb and rcd type b for protection.

Absolutely. I've just completed an installation with a new ashp and when commissioning the thing I found some new stuff within the control software and some behaviour of the system that wasn't covered anywhere in the manuals. So I made my list of questions, called up technical support and in a tone that suggested they though I was an idiot, they told me that what I was asking either wasn't possible or wasn't implemented - but I played with it anyway and my tests show that what they told me was incorrect. It's not the only time tech support have told me the wrong thing even with Gas boilers and controls. I think the nature of this forum is that we're happy to push the boundaries and take some risks whereas the manufacturers have to cover their backs, just as I do with a system installation. You know you have to when you try to explain system flow temperature and they look at the thermostat quizzically telling you that it says 21....not 55

This is what I thought too. And I thought that using cooling could be advantageous to recharge the soil for the next winter. However, it was explained to me that the ground loop system can't take the quantity of heat dumped into it which therefore reduces the hp cooling capacity. Apparently the borehole solution can take the dumped heat. You don't see the same behaviour with ashp of course because it's dumping the heat to the atmosphere and you're limited to the units ability to transfer the heat. This is why you might employ an air battery such as a fan coil unit to assist the gshp to dump heat outside the ground. Tbh, modelling the thermal behaviour of the ground is beyond my knowledge at the moment, so I'm kind of accepting their wisdom in this until I see some evidence to the contrary.

Nibe is one manufacturer who makes a distinction between active and passive cooling - they have what they call a 2 pipe system for passive and a 4-pipe system for active. It's the active system that has the expensive add on kit where iirc the passive one is marginal. I can't remember if you can access the schematics openly or whether you've got to be Nibe Pro to access them, but it's all available. Nibe is one manufacturer who doesn't seem to shrug their shoulders regarding cooling but is careful to advise on proper system design.

In Europe there are a few companies selling wet ceiling units where ufh is impractical, and for walls. Apparently the ceiling units work even better than ufh, but I haven't had the opportunity to find out in person yet.

I think you pretty much hit the nail on the head with your post here. The discussion I was having re the gshp was also together with another installer and what came to light was a fundamental misunderstanding about the meaning of cooling such it meant aircon and would work like aircon. This manufacturer had 2 options - 1 the simple passive approach not too dissimilar to what you describe albeit with some caveats (e.g. still a bore hole and not really considering the dynamic behaviour of ground temperature after a winter heating cycle in a loop etc.) and variations, and 2 the active version, which is more of an attempt to move in the direction of aircon like cooling. The other manufacturer of ashp, the first person I discussed it with dismissed it under the same assumptions due to only being able to achieve a room temp drop of about 3-4C in the particular circumstances, but that drop can make a huge difference to the comfort of the indoor space. I still think it should all fundamentally go back to the fabric first approach and use primary resources at design and build stage (just like the BH mantra on insulation and airtightness) to implement passive cooling strategies which are then supplemented by a passive heatpump 'mild tempering' of indoor temperatures. In the industry, customers are asking more and more about cooling, so it's going to be a growing issue, potentially with lots of disappointment and difficulties like in the OP.

From the perspective of using heating circuits for cooling with heatpumps, both air source and ground source, it seems to be on trend at the moment and I have to admit I was sucked into this. I know its popular here on BH, but over the last few months however, I've had conversations with 3 heatpump manufacturer's, all pumps of which can do cooling. Two of them just said they don't recommend it even with fan coils and ufh and with the third, the complexity of getting it to work even with ground source required so much additional plant and complexity, it was ridiculous - e.g. borehole min 150m deep not ground loop and additional air batteries together with a hydronic design utilising a volumiser and the dhw cylinder to dump excess heat. And then there are the controls, some of which already require subscriptions for users and professionals. God knows what this would all be like after 10-15 years. This one was a very clever design, but might as well go home and get a multi- split unit for the short periods it's really going to be used! Long term I think its better to focus on passive cooling designs of the house and only then add minimal additional active measures.

You haven't been on buildhub to know that there is always OP scope creep. Has to be. Whether it's relevant or not it has to happen just in case and because it might just be relevant to someone else reading the thread at some point in the future. It does drive some people a bit crazy but wouldn't be buildhub without it 😁

Couldn't agree more. I had to do a lot of careful prep work prior to installing our ewi. I had to rebuild most of the underfloor vents as there were big gaps allowing air movement into the cavity. And also lots of carefully sealing along the wall plates at the top of the walls as well as round all other penetrations. Unfortunately like all retrofit approaches, care and detail needed and it's never a straightforward as you might think. The other disadvantage as I have recently found is then fixing anything to the ewi - it's a right pia. And then don't let ignorant contractors loose on any later where they have to touch, drill through or fix to the ewi without full supervision! I just had one here recently who said they just use standard wall plugs. I said no you don’t! Ever seen the results of a mindless sds drill going through ewi from the inside and what happens to the mesh and thin coat render??? Don't get me wrong, EWI is great, but it does have its drawbacks on some things.

I see very few problems, only perished bladders, not the cylinders themselves.

Yup, got that one covered. I'd set the blending valve to 50C when I commissioned the TS, but it's a good call for others that decide to change any DHW storage temp!

Loctite 55 is your friend here. Much better for people like me who are too impatient or lack the concentration to count all the way up to 16, and always get the PTFE spool round the wrong way. I used it for all me rad installs nowadays. https://www.henkel-adhesives.com/uk/en/product/thread-sealants/loctite_550.html

Don't start taking your boiler apart for this. Technically you need to be Gas Safe registered as the casing forms part of the flue system by creating the room seal which is an essential safety part of the boiler. With the casing off the boiler is no longer room sealed. Draining the boiler from this point is only for when you are completing repairs on the boiler. Also, this boiler has lots of plastic fixings and these can break, which could make putting the case back on and fixing it properly difficult. Look for your drain cock on the radiator pipework instead!

Hehe, well, the TS is staying in the shed for a while, just in case. And if necessary I'll have to put Octopus intelligent go to full use.. 🙂

I had to give it a go. My heat loss is apparently over 10kW and I need a 12kW heatpump. I'm just putting in a 6.5kW unit and I know my heat loss is less than 5kW. It's going to be fun to tot up my job and compare it to their estimate once I'm done. Yes, it's another company jumping on the AI bandwagon. Just seems to me like they're playing tech scale-up pressured by the exit sign for a number of investors..... e.g. 'we've been working on this for a whole year' just smacks of rolling it out for some testing in the real world like most app developer do nowadays.

Yeah, that's pretty much how I'm using it, but with the difference that I've lowered my storage temp so that cylinder temp at the sensor level is at 60C with a 4 degree hysterisis, and this gives me an indicated temperature of 70-75C 1 third the way down from the top of the cylinder. When I tried to have the water stored like a proper TS, the boiler would just run for far too long on reheat. I'll be able to tell you how this compares to a heatpump install with UVC sized to MCS specs with a storage temp of 50C very shortly as I'm just installing our heatpump at the moment. So we'll go from 19kW input into the TS to a max 6.5kW input to the heatpump cylinder. I've already warned my wife that it might be a bit different going forwards and we'll have to experiment with the DHW strategy...

I have to say I think this is just one of those very weird threads we get here on Buildhub where sense seems to be thrown out of the window. If it were a heating question, everyone would be posting to say you have to start off with a heat loss calc. Or the very least some design drawings to provide a starting point, but the basic questions about DHW design are completely missing on this one. We don't know anything about pressure/flow rates to the house - regardless of size of main, what are typical static and dynamic pressures where the op is planning to build. Second is whether the requirements for infinite hot water is even really what the op wants or actually needs (I've been here too and the questions were resolved through careful whole system design taking into account flow volume restrictions we have got until I can dig a trench and re-lay our mains supply to the road at least). I realised I didn't need infinite hot water. The assumptions we often make about both hot water and heating lead to over-sizing, which I think is what is going on here. e.g. So first we need to ask more fundamental questions about use and behaviour (and also how transient that behaviour might be and not make long term costly decisions about a temporary, short term problem). And then look at the variety of ways to deal with those, which probably don't need to involve chucking in the biggest pieces of kit that we can find. Again and again I find the mention of flow regulators and system pipework sizing missing in hot water management discussion. For example, plenty of calculations about delivery of hot water at certain temperatures at certain flow rates, e.g. 30lpm, bit this misses that a lot, if not all drench showers, for example, provide about 16lpm. But it's very easy to buy models that have interchangeable flow regulators that massively enhance perceived availability of hot water but actually massively reduce hot water use. I too have teenagers who disappear into the shower with their bluetooth speakers, put on a rave and appear what seems to be like a few days later. Not once have I ever run out of hot water or had a complaint by someone we haven't got sufficient hot water. All we've got is 19kW going into a 210l thermal store.

We're at the tail end of a project not a million miles different from yours. All our advisers said keep existing building as it would be easier to get planning, so we did. When we demolished the bits that wold be replaced the whole thing turned out to be much worse than we thought, but were too far in then to change direction - even the BCO said on a visit he thought we should stop work and re-apply for new permission, but then Covid hit and we had to carry on as we were. If I had the option on an old bungalow again, I'd most definitely demolish & re-build. Too many headaches with constantly chasing around defects of a crap old building to make real sense regardless of the VAT tbh!

Robbins Timber in Bristol are excellent for just about any timber. Not the cheapest. Don't go by their website price list which is buried on the site, call them and explain quantities to get a good price. They used to do free delivery for me, but with your distance this may not be feasible for them. If you're casting your net this wide, then also speak to Sydenham Plywood (used to be Avon Plywood) based in Keynsham near Bristol.