SimonD

Yes, it was some time ago. It also commonly happens on cladding - I went into a panic years ago because my lovely new cedar cladding started developing black splotches on the north face of the house. Now it's a uniform silver. On the south side, the same process is happening but much more slowly.

It's not necessarily mould. You can find that new timber gets black marks after it gets wet as bacteria like to devour the sugars in the wood. Once the sugars are gone, and/or moisture dissappears there will be no further problems and you'll probably find the black softens to grey.

No, I said that the research at present suggests that there shouldn't be a great different between heat demand in different areas for this to work effectively. You asked me what the Heat Geek mantra is and I clarified this, then you try to tell me it's not? 🤔

Room influence from a heat pump controls perspective is where a room thermostat is integrated into the manufacturer's control system to provide input data from the thermostat to influence some or all of the below (depending on how you commision it): - the call for demand (i.e. if room temperature is above set room temperature, there is no call for heat) - the system flow temperature based on an combination of weather compensation, actual room temperature and target room temperature - so the heat pump will modulate where necessary. So if my weather compensation curve is set to operate at a flow temperature of 35C at 0C outdoors but room temperature is nearly satifsfied, the room controller modulates the flow temperature of the heat pump accordingly. On some heat pumps you can set the room co-efficient to change the weighting of the room influence to weather compensation. But you can also use modulating mixers for UFH, for example, that can either be wired into the heat pump manufacturers controls to regulate flow temperature going into a specified zone. You can also buy room/weather compensated mixers (like from ESBE) or even room/weather compensated UFH manifolds if necessary that have their own sensor and controls if absolutely necessary. And of course, not forgetting radiator systems, you can employ simple ways of restricting flow using TRVs. Or if you decide on a more permanent turn down of flow to some areas of the home, you can use self-regulating TRVs where you set for flow rate for a specific output and delta T across the radiator. You could also technically use a mixer to the whole radiator circuit, if needed. The main difference in room influence versus the main stream understanding of the zoning term is that with room influence you are not closing down flow to areas of the heating system, simply balancing flow rates and flow temperature, so you don't experience the problems associated with low system volume when zones are closed down. You tend to do this minimally using 1 or 2 room thermostats with proprietary control, but some manufacturers have begun to supply support for up to 6 in their controls. There's nothing particularly complicated about this in terms of overall system install, it just needs a thoughtful design process that understands the building and what the occupants want/needs. As manufacturers now build these into their control systems, it's also something that is fairly straighforward to adapt, should you need to. As a note: @JohnMo's system is technically a system with room influence as it runs very low flow temperatures where there is only a couple of degrees difference between flow and room temperature, which permits a self-regulating effect on the heating system. This is a behaviour of the system that works independently of the controls and heat pump.

Research suggests differently and I'm more likely to trust a balance of trusted research. And you're not doing that John, so you shouldn't pretend that you are. Not quite, it's more subtle than that. The mantra is to use open-loop managed with pure weather compensation on retrofits and less well insulated homes (including some newbuilds) but in highly insulated and airtight homes use weather compensation together with room influence. The balance between weather compensation and room influence is dependant of specific design elements and context of the house. Come one John, I've already said that open-loop is the preference many times. What I've been saying, yet again, yawn, is that the specific circumstances of the building must be considered and that building in room influence is preferrable when dealing with well built, highly insulated homes, with good air tightness, especially if they experience large inputs of energy outside the heating system. This isn't complicated either. Occupants might also like more control in their bedrooms.... Err, so below you're suggesting what? Not room influence by any chance?

There just seems to be some bizarre obfuscating circle going on here John, 1. You are running a very low temperature UFH system that also utilises a specifically designed slab arrangement. 2. You have spent countless hours/days/months/years tinkering with your system to get it working right for you. 3. You are using 1 anecdotal example, which is your own, to base a general conclusion that is being suggested as suitable for all and everyone. 4. You have some very particular views on indoor temperatures such as your view on bedroom temperatures for example. Your system, because it utilises the self-balancing effect, actually manages to self-regulate independently of the controls in your system - that is what these systems are known for. But, it requires a significant amount of pre-planning and integrated design, and if being applied in a retrofit situation, a hugely costly upgrade process. Your graphs therefore don't reflect the nature of the heapump and it's controls but this thermodynamic behaviour which is independent of it, but nevertheless impacts the behaviour of the system as a whole. This is a great solution if you have the low heat loads required and all areas of the house have similar heat demand (e.g. there's no area where there is a significantly higher demand), as a basis to allow it to work. These are highly significant caveats to what you are proposing and I believe people reading posts on this forum need to be aware of this and that there are so many other factors involved, such as floor coverings etc. I'm not saying anywhere that your approach is wrong, I'm suggesting that other approaches may be more suitable for other people considering designing their own system, and whether you accept this or not, is neither here nor there as it's something that good designers and installers of systems are utilising more and more from their vast experience of putting these system in.

Just to add - yes, but if the weather compensation is calling for heat and the heatpump sees an increase in return temperature, it will increase the flow temperature to maintain target Dt, which is one reason why a buffer, for example is less efficient when there's too much distortion. Just seeing an increase in return temperature is not enough - the heat pump needs additional feedback. This is another reason why room influence is useful in circumstances where there is additional heat input into rooms. Hence your description of the heat pump modulating down when it sees a higher return temperature, is not necessarily, nor universally, correct. It depends on controls.

Can you explain what you mean by this?

Yes, if there are significant heating inputs that are not measured by weather compensation alone, and/or if the occupant want some control in rooms such as bedroom. In our house, for example, we can have the triple glazing on the north face still covered in ice while the upstairs has already been heated to 23C by the sun. In this instance, even if the MW-AT delta T is such that the radiators then don't theoretically add heat into that space, it seems a bit silly not to modulate the heatpump using room temp feedback as the home heat load has reduced. In ours this is easily by 50%. The idea around room influence is that an internal thermostat provides input to the heatpump to modulate. This can also be achieved using TRVs on radiators without modulating the heatpump, or with electronic mixers. Most manufacturers will provide 1 or 2 of these room stats but companies like Stiebel Eltron can build a system with up to 6 and it also provides the ability to weight system control input between weather compensation and room. Nobody here is saying that a heatpump installed with open loop and weather compensation isn't the simplest solution. It's just that get a heating system to work for its occupants may NOT be that simple, especially in highly insulated homes. Room influence does not make the system more complex. It can infact make it simpler for both the occupant and the installer. Room influence does not necessarily shut down flow and therefore reduce system open volume, except for at the extremes. Zoning, using relay type controls is a different matter as this does reduced system open volume and therefore the system becomes more complex. For me the issue here is the understanding of controls, what they, do and how they work, and then when to implement them - but that's a headache for the whole industry right now which is still learning. But most good decent installers will go for open loop with some room influence baked into the system in current designs.

Unfortunately you can't do that. You must be MCS registered and be a verified BUS installer. Your 1st option must surely be to go back to the installer and instructs them to sort the application - again? I'm a bit bemused why they haven't just said they'd do that and instead argue with you - perhaps they're one of these companies in trouble who don't really know what they're doing?

Okay, quite rightly, you're very pissed off! And yes, it's cearly down to the installer - their responsibility and their probelm. What was the other partly reason?

The company should handle this. You should have received an email from OFGEM granting permission for them to deal with it. Installers will often ask for the relevant information, particularly self-build, before this so it can be provided to OFGEM for any assessment. Did this happen? When they say they haven't received the grant, why hasn't it been granted? OFGEM will usually ask for any additional information reuiqred, so they must be able to tell you. There is some small print that if a grant isn't accepted, the installer can come to the homeowner for the outstanding sums, but I'd expect a decent installer will communicate with you to tell you what exactly is going on. You could contact OFGEM but you will need your application ID which you should have received when you provided consent for the installer. Tel: 0330 053 2006

The MCS rules require any supply and install company to provide a quote minus the BUS grant so you can see that it has been given. The supply & install company, or their umbrella scheme will apply for the grant on your behalf. You'll get a message from OFGEM when they apply where you give consent for the application. As has already been mentioned. If you purchase supply only, you have to pay VAT for all materials and then you'll have to pay VAT on labour because it's not part of a supply and install under the MCS scheme. Best thing to do is find installers local to you, and even try the larger ones like Octopus, Aira, Heat Geek and get some prices - on Heat Geek's site you can get an estimate straight away to give you an idea of costs. Get some quotes and then you can look at the costs and compare. If you can find an umbrella scheme happy to do the MCS side of things for you, you'll most likely be paying something like £1000 plus VAT for the MCS/design stuff, plus another £400 or so for commissioning too. They will usually supply all the heatpump kit from their supplier at their markups, so again best to go out and get price comparisons. With some of these services, you won't see change from your BUS grant and you'll have to complete the installation yourself and probably pay for all required emitters on top.

Lets back up a bit - yes, the OP is about designing a simple UFH, which you can do with both gas and heat pumps and you can make them both efficient. Radiators are relevant because they need to be there in the design library because UFH may not always be the best option for the given situation, whether you like that or not. The reality is that every house is different, it has its own climate context and it has its own users, all of which play into the design of the heating system. I designed my first system just a little before you, which was for my own house. I designed it with UFH in mind and then changed to radiators for several reasons. Mine is currently on gas and will be a heatpump in the next month or so. I also chose not to go down the route of pure weather compensation, but have actually implemented 2 main zones with room influence using Opentherm. My system has actually been extremely efficient and has this year, for example, used about 5000kWh less than estimated at design and that's even with a thermal store on PDHW sitting at 75C at the top for dhw. It's still a simple system and needs some changes, but this is quite good. Without blowing my own trumpet, I found I had a knack for heating systems and now run my own business doing them. And one area I've made quite a lot of money from is fixing UFH systems to run efficiently, especially with gas boilers - so I have a little knowledge about how they work and don't work. One of the things you don't seem to be aware of is that room compensation in controls can apply just as much to UFH as it can to radiator systems. Many heatpump manufacturers provide built in room compensation within their controls, including Grant, Vaillant, Stiebel Eltron, to just name a few. This is because it works well in unison with weather compensation which can and does have some limitations. The room compensation provides, as I said, additional real-time data for the heatpump to modulate output. This isn't to say that your solution isn't valid - I've already acknowledge I understand what you've done and why. It's just that this isn't about being a one trick pony, but acknowledging that there are other solutions out there. Your experience with your gas system is unfortunate and a reality for many, but that doesn't meant to say that you can't design and implement a gas system with ufh that functions well and is efficient and can be simple. Same goes for heatpumps, of course! Even in your case, there is a limit to how much self-regulation there is in the system and how flexible it is because as you say, the response times of UFH particularly when sitting in a big slab, are pretty atronomical.

I know this is a debate between you and @Nickfromwales but I feel compelled to jump in on this because I think you are mistaken. System control is the biggest headache in heating systems. It's something I have struggled with in my place because of surprising and significant solar gains, even with triple glazing. It's the main reason I opted for radiators rather than ufh. I know you have settled for a system that runs low flow temperatures and you have balanced your system to take advantage of the self-regulating effect of those low temperatures, but there are so many other factors that play into whether a heating system actually delivers the heat to the right place and the right time in the house to prevent both over heating and under heating. I have always been a fan of using room influence together with weather compensation because it adds additional and necessary feedback into the system and this is especially important when you have highly insulated buildings because basic activities such as cooking can have such a dramatic effect on internal temperatures. Not to mention the issue of solar gain already mentioned. Thankfully manufacturers are awake to this with newer systems providing the options in both design and operation to commission the systems with pure weather compensation and/or room influence to allow better tuning together with better tunability in defining the weather comp curves. In my designs, and especially after completing all the heat geek training etc. I always design systems with the capacity to have room influence, especially within bedrooms and areas subject to heat input. Now, the problem with many room influence solutions on the market is the tendency for this to be relay rather than modulating, especially in underfloor heating systems. I believe that the way to go is through moderating the flow rates so you still, at least theoretically, maintain decent open volume and more subtle temperature control. But this is a difficult balance to find. Like @Nickfromwales, I'm also doing this commercially, so I have to cover my backside, especially because I'm taking design responsibility. It is very different if you have both the time, knowledge and resources to spend countless hours tinkering.