SimonD

That's a good point. The solar designer wanted to lather the entire roof with panels and I was less keen. Due to the aspect of the house sitting on a hill together with the curve of the roof, we can get away with some of the roof without it being visible. For solar gain, it's definitely the best place for it, but there's a long way to cable to the garage. I've clearly got to have more of a think about it.

Not at all. It's fascinating. This is another of your stunning posts Gus, so thank you for taking the time. I'm going to enjoy digesting it. Ah yes, nobody mentioned that when we started our project, which was supposed to be removing the roof and adding an additional story, as soon as the existing roof with conceprete tiles was removed the walls could just be lifted apart, do I had to rebuild significant portions of it. Yes, like this: 2350D 8 Detail Front Elevation Rev B.pdf Thank you I'm quite relieved to read this. I raised the question during the initial solar design meeting as my experience from the standing seam roof design raised my worries a bit. Haha, yes, will do! No, thank you 🙏

Thanks for this. Really useful to know your experience of North facing panels. I'll check out the modelling. We could do fencing. Would quite give us the surface area of the roof but would be directly south facing and without shading during low winter sun.

I had a friendly solar designer put together a design for me, but when he went out to his usual roofing people he didn't get any joy. Even the electrician he works with that does a lot of solar installs with others hasn't had joy with his contacts. The problem is that I have a roof with 2 curves and it's a standing seam metal roof. The issues are partly: 1. The curvature 2. Calculating wind uplift loads to see if they're an issue I installed the roof and know my clipping distances which is fine so I'm going to ping the manufacturers a question and also get in touch with the se who original did the designs, including wind uplift calcs. The next issue is to deal with the curvature which nobody seems to be able (bothered) to model. And also the issue and cost of scaffolding they want - unfortunately nobody likes my kwikstage scaffolding. If i just went ahead and did this myself, my thoughts are I could use the portion at the top of the roof where it's almost flat together with a flat portion of the roof between the curves. However, I was actually thinking that the easiest solution would be to use the existing garage which has a standard tiled roof. The only problem with this is I've been told there's no point putting solar on a North facing roof (which would be half the installed area). The second is that the south facing roof is quite shaded by the house during the winter months. I'm not so sure this is as much of an issue any more? I really don't know what the current understanding is about shaded and North facing walls for solar and would really like to understand this better. Can someone explain? The advantage of this is that the batteries and infrastructure are going to go in the garage anyway so I think it might be better to have the panels there anyway. Thoughts?

In most systems I work on and commissioning, I find anything between 5 -9 is okay. Start on minimum pump speed and only if necessary up the speed. Don't worry about playing around with it. You can up the pump speed and see what happens and then leave it for a few days to see how it performs. And then if necessary reduce pump speed back to where you are now.

I know that, I've read enough of your posts to know you'd never go near one 😉 Exactly and that was who my question was for. Because this is where design starts: What is the problem and how am I going to solve it? Therefore logic states you need to ask why you want it (and that doesn't mean you, exactly) You don't just follow the level 3 heat pump training and follow up your heat loss and emitter sizing with a blind buffer sizing calc. You need to know what you're doing it for. Yet it's common in the industry to use the term interchangeably, so probably a good thing to clarify this in a terms of reference rather than make assumptions. I should've had my 2nd coffee first 🙄

I've just sat down with mine😀 Oh, you've gone and started Saturday morning by opening up a whole new can of worms here! What side of the bed did you wake up on 😉 So 🤔 My first question to ask is why do you want the buffer? Is it for batch charging/dumping excess heat or is for hydraulic separation, or a mixture of both. Is it perhaps to supplement open system volume. Are we making a distinction between buffer and volumiser? This is more important that I used to think it was because I've now seen manufacturer design strategies and schematics that use a 2 port volumiser which then becomes a buffer/bypass to increase run times when heat demand is lower, all controlled by the native controls, which then releases its stored heat back to the secondary system when needed. This apparently reduces many of the drawbacks of both 4 and 3 port buffers. ChatGPT obviously makes a preferrential decision for a 4 port, but 3-ports are used very commonly, again because they provide advantages. Because I rarely touch buffers, the design strategies and calcs are shelved somewhere in my brain I can't access very easily and don't have the time to dig out my guide to buffer selection somewhere in a pile of dusty papers! I'll revisit when it's at the forefront of my mind and instead go and rip a gas boiler off a wall ☺️ Coffee done...

I think the main strand in the op is that @Post and beam asked the installer for 2 zones and 35c flow temp and didn't receive it. It's not @Post and beam' s fault, it's that of the system designer and installer because @Post and beam doesn't seem to know what he got. The designer and installer whether the same person or different people should have fully explained the plan so he knew what he was actually getting. (E.g. from a flow temp perspective, I can fully understand why you would choose 40C v 35C because the rad size difference there is significant). Unfortunately it is very common for designers and installers to do what they think/want to do with or without a customer's understanding. But then there are also too many idiots in the game that barely have half the required understanding and as a result cause these kinds of issues! (I know this very well as I've just had to explain manufacturer's installation requirements and MCS installation standards to a company operating an MCS umbrella scheme and didn't know what they were talking about!) All of this should have been conveyed by the installer in advance - discussed in depth with the op and confirmed a mutual understanding. As it wasn't they should be on the doorstep ready to get the system working properly!

Not necessarily. The heat outputs curves of radiators versus ufh are different - rads are calculated to the power of 1.3 and ufh to either 1 or 1.1 so it depends on multiple design factors and the thermal properties of the building, including the balance of area between rads and ufh. Because this differential may often result in different flow rates, especially at higher mean water to air temperature differences, a mixer is used to offset this by adjusting flow temperatures to each zone.

I did ask...

As @JohnMo suggests it's down to flow temps and latent heat when condensing. 1:5 modulation ratio ain't that good. Better go with a Viessmann if modulation is important to you. Personally I'd also lean to a system boiler unless you've got particular system issues that make it impractical.

I seriously suggest you ask (instruct them in no uncertain terms) your installer to install one of these as it provides weather compensation across different zones. As standard tmv & pump arrangement won't do that and will essentially have relay control. https://professional.vaillant.co.uk/for-installers/products/vaillant-mixing-module-vdm-69824.html Given your installer doesn't appear to understand open loop, even if they think they do, you might want to suggest they contact Vaillant to get the schematic for this system and make proper adjustments.

But they have them on the wall in their training centres and sell single and dual valve insulated esbe kit. The schematics and wiring diagrams are available. 3 mixers are supported by vr71 connectors r7 through r12 But as you say, not many seem to rtfm, or pay attention during their training, if they've been to it at all? And you're unlikely to get this from many of the big installers I suppose? It's weird they don't make it more obvious.. Grant on the other hand provide an installation kit for the aerona 290 that includes an electronic mixer for combined ufh & radiator circuits and the schematics and wiring diagrams are 1 of the standard one in the manual. What a comparison...

Have you not received a design from the installer? You probably have got the weather comp curve set too high and should have been told by your installer that it takes a while to set the system up properly. Has the installer arranged follow up visits to balance the system when it gets colder? What we really need to know is what mean water to air temperature difference the radiators have been specified to. That way we can tell if there needs to be a flow temperature differential between the radiators and ufh. In 2025, a 2 zone system with rads and ufh needs to have an electronic mixer to properly deal with weather and load compensation within the heatpump and both the zones.

Don't hold your breath there are still schematics abound for HP systems for micro zoning with thermostats in every room. Vaillant have a few that include 3rd party controls too. According to the powers at be, this is what customers want... so the brainwashing continues. I wonder whether Heat Geek zero disrupt cheap version includes keeping any micro zoned systems or whether they'll propose chucking it all in the bin? Personally, I'm counting my blessings I don't have to deal with 3rd party controls any more...

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.