SimonD

😁 ESBE make outdoor/indoor regulated mixing valves for multiple zones - the company you've spoken to will know about these. And Viessmann has some weather comp mixing functionality, but whether it is suitable for your needs, I don't yet know as I haven't got that deep into the Viessmann design guide.

I'm familiar with the Heat Geek article and I'm almost sure I've watched a video on the subject. I've also read a number of other sources on the topic, including one of the lead books on hydronic systems design. The fact is that the calculations are incredibly complex to really work this out because it depends so much on the fabric of the building as well as partition wall structure, door open, open plan etc., but it also depends on external factors. The heat geek article sums are a serious simplification of the dynamics involved and they also use the extreme design temp of -3 C and a mean room temperature of 20C which typically represents a fraction of the heating season. But also, doesn't take into consideration solar gain, for example. But also, heating systems almost never function in their set design state, they're by their very nature dynamic If you don't take into consideration things like solar gain and instead design only for the static figures, you risk ending up with overheating, especially during autumn and spring. This is why I think heating system design is always a bit of a compromise. The reality is that you probably don't need as many zones as you have and I'm sure you could rationalise them somewhat and still have the same levels of comfort with improved efficiency. What you could probably also test is a set period of time where you don't zone your heating but keep everything open and see how you experience that. You can take meter readings to see what happens with your consumption.

Don't worry, we're talking about something different. However, the 4 pipe system isn't really designed to have towels radiators on the high temperature hot water circuit and if they were, they would only get heated when the boiler is reheating your hot water cylinder. If you want the freedom to heat the towel radiators at any time, they would need to be on the normal central heating circuit. Th ideal situation depends on the customer's specific needs, not a generic one size fits all solution. What stops you from implementing this is: 1. you both want and need zoning for comfort and due to solar gain. This requires a buffer in your system to reduce short-cycling risks due to the microzoning you have throughout your house. 2. you want a towel radiator circuit with some extra warmth. This would be fed either directly from the boiler, or a pre-heated buffer tank. I'm sorry, but what are you talking about? Delta T 20 is a standard design figure for hydronic systems and it is usually specified by boiler manufacturers although Viessmann has reduced it to 15 degrees, but other high efficiency boilers, like the Ideal vogue Max spec Delta T 20. You comment about Delta T 20 being old hat for high temp boilers is misconceived and certainly not supported by current industry design guidelines. But to get back to the actual issue that arose out of my questions about the installed system and suggested modification. The design of the system however is about how to get enough heat to the right parts of the house at the right time, so it's about moving energy in a way that works for the occupant. In this sense, it is about finding a balance between function and efficiency, not merely optimising efficiency and using arbitrary figures that don't give any indication that they'll work for the required heat load of the house over the heating season. Simply running a system for longer will not sufficiently heat a home if it doesn't supply enough heat energy into the space. Your solution may not do so unless there are high flow rates through the system which may potentially add unecessary resistance and noise to the system - but at the end of the day, neither you nor I know that as the flow rates need to be calculated based on the installed system. This is one of the reasons I'm trying to suggest weather compensation and load compensation because they'll dynamically adapt to the heating loads of the building by increasing flow temperature where necessary while maintaining lower flow rates. It's also one of the reasons that against the consensus on here I supported keeping the zoning in place because @Adsibob has said the heating system works well for their comfort. And that's where the suggestion of a buffer originally came from. As is so often the case, the pipework arrangement and set temperatures has become the distraction whereas the original issue highlighted was control of the system in a way that is consistent with the ops needs, original intent, and the balance of comfort and efficiency. Fundamentally the problem resides with the original system design because the installer has followed the herd by installing UFH when actual real world use and the nature of the house actually indicate that a low thermal mass/inertia system with generous buffer would have been the way to go which may have run at a higher flow and/or mean water temperature, but would have been more efficient overall due to the context.

A big problem with this suggestion is that it doesn't deal with the different Delta Ts of the heating system. You need 20 at the boiler and about 7 across the UFH which means a significantly different flow rates! Just one pump feeding the system is not going to cut it, I'm afraid. And with the mass flow rate calcs, you're very likely to still need a flow temp of around 50C at the boiler for this to actually work. There has got to be some form of mixing in there. @Adsibob may I suggest that with the engineer/s you're speaking to, you focus on the principles of the system, not specific suggested solutions or products? So highlight the solar gain, modulation, efficiency, comfort etc. and of course your budget and if necessary be willing to junk existing controls and set aside your preconceptions etc. (although by the sounds of it, you're rather close to that point anyway - I personally would be outraged at a £3 per month subscription for control functionality that can be gotten more acurately with good system setup and a sensor plugged into the boiler itself). At the end of the day you're only really worried about a system that provides comfort, simple manageability and reliability without much regular input by you.

The marginal cost of installing weather compensation alongside all the other suggested works is so minor and the long term benefits such that it would be silly not to install it if @Adsibob decides to modify the system. To me it's a bit like suggesting a shiny new efficient boiler but keep the old thermostat - oh, hang on, that's exactly what this suggestion is 😉 Remember, we're here because of the controls in the first place!

This is a really good point. Most, if not all control systems that provide modulation, whether weather comp or load compensation are really best in single zones. I was talking to a technical person at Honeywell who was indicating that as Opentherm is designed as a heating protocol it doesn't really work very well with DHW (e.g. when using Opentherm to manage priority hot water) and it is not optimal when dealing with motorized valves -it doesn't like them that much. When I've spoken to various boiler manufacturers and control manufacturers both the implicit and explicit message is the same. For example, with Worcester Bosch boilers, you can have modulation and pdhw without any zones, or you can have zones without modulation because as soon as you add motorised valves, the design of the control system means that the signal must be converted to 230v so relies on relay to work. I do think there is a mismatch between control manufacturers and boiler manufacturers and I also think that some of the boiler designs are defficient in this regard - they are often limited by silly design implementations/limitations. This makes it extremely difficult to design and install some systems that by their nature might need zoning, but especially when you consider the Building Regs Part L requirement for zoning.

Like others have suggested, don't discount EPS. It's far cheaper than the other options, more installers, probably more resilient than say wood fibre, especially if in a windy area where there is risk of wind driven rain. If using wood fibre and there is dampness at the bottom of the wall, it is possible to use EPS towards the bottom and wood fibre further up. Indeed this is recommended if the EWI falls below about 300mm above ground level. I have EPS along the lower portion of my wood fibre wall for a significant proportion of the house, including the whole plinth.

The European model refers to the combi controller, not 2 channel for s or y plan. See link here: https://uk.shop.tado.com/products/add-on-wireless-receiver-eu-version This model has to be ordered specifically from Tado and is shipped from Germany. I have ordered these for installation. I have done one on a Viessmann combi too. The problem is that this model costs £199 from Germany whereas the combi model you get from a local UK supplier can be as little as £89, but which doesn't have Opentherm compatibility and there's no clarity about this either - although there was an apology from Tado on the Heat Geek website but only after they'd removed the functionality from UK models without telling anyone. Regarding S or Y plan here's a recent thread from the Tado community confirming no modulation: https://community.tado.com/en-gb/discussion/16937/opentherm-with-y-plan-setup Basically combi is fine, lots of threads on the internet about Tado,opentherm and s/y plan and how to get it to work and general conclusion is get something else or go PDHW and weather comp.

Yes, that's certainly an option. I have to admit that I initially incorrectly assumed the huge Grundfos circulator was in part for a large rad circuit.

Given 2 major things: 1, you typical lifestyle and usage of the system, and 2, the solar gain in certain rooms, I will go against the grain here. So briefly, I'd go down the route of 4 pipe priority hot water with weather compensation BUT retain/or install new room based zoning controls to deal with intermittent use and solar gain. The weather compensation deals with heat distribution through the temperature of the system and the zones by controlling flow. To deal with potential low system volume due to closed zones, the buffer would counterbalance this and reduce short-cycling risks. Now this would mean a compromise when it comes to the towels rads temperature, but they could easily be kept warm for good comfort. There is a trend to opt for UFH as the default but I think there are situations where a low thermal inertia system is more appropriate due to occupancy patterns, system use, and building characteristics and I think this is such a situation, but the UFH is alreadsy installed. It's just to do the requirement for zoning and if you have lots of zonesand youuse then, it's better to have a buffer in there.

You'd certainly hope so. Here's a link about controls and ErP from the Worcester website: https://www.worcester-bosch.co.uk/professional/support/troubleshooting/faqs/erp-faqs/how-do-controls-affect-erp

No, I'm saying that every other manufacturer of controls publishes their ErP certification class so as a system designer and installer I can certify the installation properly - with Tado I can't and couldn't without this data and frankly their report supporting efficiency savings they publish on their website is worthless.

Froma slightly nerdy perspective, I have yet to find an Erp certificate for the Tado controllers. Erp of controllers is important because their functionality determines the overall energy efficiency of the boiler over 89% - therefore if you're installing a brand new system and need to provide 94% efficiency you haven't got the info, you can't actually provide that guarantee whereas with other controllers I've got the certificate to back up the install.

@Adsibob can you describe the zone setup you have in more detail please? I'm particularly interested in the UFH setup and zoning, where this is and how you manage the spaces with UFH, but also the radiator circuits. I haven't kept up with your retrofit but generally speaking, I'm guessing you have brick walls with added insulation (where? IWI, EWI cavity?), upgraded floor insulation and roof insulation. What I'd like to understand is the level of heat loss in relation to the thermal mass of the building. (Yes, I've used dreaded thermal mass, and in terms of figures, thermal mass = Building element volume x Volumetric Heat Capacity). Also, which rooms experience significant solar gain and how are those rooms generally used? Your stove will also play a role here as you don't want that interfering too much with heating through the rest of the house, as you've mentioned. What I'm getting at here is that I don't always think that whole house weather compensation is the right answer for everyone and every house. With well planned zoning, you can get good results. The problem is the control of this, especially with a mixture of UFH and radiators because they'll behave so differently, particularly where you've got thick coverings. But in terms of controls, I do think that using load compensating combined with weather compensating controls can be used to good effect for improved efficiencies in a zoned situation. In this instance we need to figure out the best way to approach this, and as you've mentioned, whether it it is more efficient than the existing Tado arrangement without modulation. In terms of the difference between load compensation and weather compensation, it is just a different approach to ensuring the heat input to the house matches its heat loss. With weather compensation, it uses outdoor temp (and sometimes other inputs) matched to a curve a closely matched to corresponding heat loss of the house.With load compensation, it does this by measuring actual reference room temperature to target temperature and the better load compensating controls will learn how the room responds to heat input/loss over to time to control heat output of the boiler. As I've been thinking about your system and earlier comments about the low loss header, I wonder whether your installer confused the use of low loss header versus a buffer. Their functions can be the same but from a control perspective, they are different. If you're running a system with lots of zoning, then you use a buffer, not a low loss header and the low loss header can't replace it, because its function is different. So my thoughts are drawn to thinking about whether a buffer can be installed in place of the LLH together with a 4 pipe system for DHW and then turn down your flow temperature on the the boiler. Then, only if necessary look at replacing the tado which I'm guessing has lots of smart TRVs installed through your house too? Just a strawman though at the mo.

Now he's not going to sleep for a week 😁

After saying all of that, I've spoken to technical support and found out the Worcester diverter kit I need for the above job actually converts the boiler to a 4 pipe system.

Yes, to become an installer all you need is a Gas Safe certificate, or if employed ACS qualification. None of this training covers efficiency in systems and only recently has low temperature system design and wiring controls been included, but at a basic level for sizing boilers only. It's on the installer to train themselves as few of the bigger companies invest the money. But then there is the issue of the marketplace. If I quote for a boiler to be properly sized, set up and controlled, it will cost more than the installer who chucks it in over a few hours and runs off to the next job, all booked online through one of those fixed price cheapo websites that are cropping up everywhere. I was contacted by one of them offering me a fixed rate of £900 for install of boiler and the installation of 9 radiators all while I have to provide vanof minimum age, equipment, insurance etc. - yeah, right! But then you also get those that charge a fortune to install a complex system that doesn't work at all, just like this one I've got to go and sort out. You can't see it in the photo but the installer has put in 3 pumps on one flow pipe from the LLH all teed off a 22mm pipe. Heating is on constantly but relay only and no timers for anything, plus none of the rads work as they should while both boilers merrily cycle away. Oh, and it's all in a garage with no pipe lagging anywhere - the garage is toasty! And @Adsibob thinks he's got problems..😉

A two pipe boiler can of course be set up to do this and you can still gain the benefits from PDHW. The problem with 2 pipe is that many boilers don't provide the functionality to output two difference temperatures as it's all based on CH flow temp. I just installed a Vokera for a customer which seem to be flying off the shelf because the company isn't affected by the CHMM and this boiler had single wire switched live only, not even modulation capability, but the customer just wanted a cheap boiler. Those that do have separate temperature capability, like many Worcester's need an additional diverter valve assembly to be installed into the boiler -not a great issue but most installers just don't bother - and then you need specific manufacturer controls. Likewise with Ideal, there is a switched live you can use for PDHW but Ideal will say that this can only be used if weather comp has been connected, although I do use it for PDHW installs and it does actually work. The Ideal Halo Heat & System controller is set up for priority hot water as is the Honeywell Evohome control that uses opentherm to increase flow temps. This, I think highlights the problem - it becomes quite messy unless the boiler manufacturer specifically supports and promotes the solution. The difference with the Viessmann 4 pipe system is that you do away with the need to install separate diverter valves and pump (except for a cut-out 2 port valve to the cylinder on some unvented cylinders). You can also use the boiler expansion vessel & prv for the unvented cylinder. Controls also get wired directly into the boiler such as the cylinder temp sensor so you can in many cases get away without having to use a wiring centre at all. It all works in an integrated way and less time to install. Control wise, you can simly use weather compensation or if load compensation if preferred, you can use Viessmann Vicare which, because the system boilers have wifi installed, you connect straight to the boiler. But if I want to, I can still use any other controller I want and still have the means to get priority hot water, even if the controller itself doesn't support it.

You need to use the manufacturer's flue for the relevant boiler. There's no getting around this. The flues nowadays are mostly 100mm with 125mm options in some cases where necessary. It is no major issue to install a vertical flue through a pitched roof so you'll either need to decide on the boiler now, or just get the roof done and then fit flue later when more appropriate.

No daft question, but yes, it pretty much is. The internal pump does both duties using an internal diverter that you'd see on a combi. I reckon it's the same hydraulic unit as used on a combi minus the plate heat exchanger and uprated pipe size for the DHW flow and return. The normal intake of fresh water becomes the return from the cylinder. All using the system water.

So just to go back to my original conclusion that you're in the Tado sphere and may as well just stay there without changing anything and you specifically asked me to suggest a different controller for your hot water. I'm not trying to steer you down that road due to the upheaval required to do so. My statements were more to explain that your system is not doing what you think it is doing, nor probably what you meant for your system to do when you employed your installer. You thought you had priority hot water and you thought your boiler/controls combo would modulate the boiler that you'd chosen for its ability to modulate and the installation you have does not appear to do either of those. You currently have a fairly traditional system which is either a Y or S plan depending on which motorised valve you have installed, with the additional of a low loss header. This means that the flow temperature of the boiler going into your heating system has to run at a minimum temperature required to heat your DHW to sufficient set temperature and it will do so at all times regardless of the heat demand of the house. So if your hot water is set to 50C the flow needs to be at least about 8C higher, ideally more. At present, your boiler will only modulate in order to keep the flow temperature at that fixed temp. You can obviously get your system running as efficiently as you can by balancing it to mostly be in condensing mode. It's difficult to find reliable data to provide specific figures on the savings, but what we do know is that with either load compensation or weather compensation based modulation provides savings in the region of about 10-16%. With the use of PDHW it's going to be a bit more because you can benefit from the efficiency advantages of lower flow temp & the boiler condensing at lower temps for space heating. But then this also depends on usage patterns and correct system setup. If you are going to undertake further work, then to get the best out of the system you should also install modulating controls, that are either load compensating, weather compensating, or both. I'd probably also ditch the low loss header at the same time. I'm also wondering whether you have some comeback on your installer depending on the nature of the contract and what this specified, bearing in mind that doing all the above mentioned stuff is not really a complex high cost design process.

Yes, it's a 2 pipe install. For PDHW the two pipes between the outer flow and returns and gas pipe would be used to supply the DHW. So it is possible to modify your existing installation, but not without some work. I can't quite make out all the pipework in your photos, but you'd need to run pipes from these boiler connections straight to your hot water cylinder and this can bypass your low loss header pipework completely. You'd then modify the existing pipework that currently goes through the motorised valves to your water cylinder and just cap it off. Wiring wise, you could still use your existing cylinder stat, but wire in a Viessmann cylinder demand terminal box which converts the 230v call from the cylinder to low voltage to go into your boiler to run the 4 pipe PDHW. That way you can still control the schedule from your Tado app. Otherwise, you could rewire to hot water control using the low voltage DHW cylinder temperature sensor. That should, in theory, work...

Do you know if your boiler has been installed with the 4 pipe system or 2 pipe system? Take a pic of boiler and pipework below maybe?

It is totally relevant because it reduces the load on the boiler as well as bringing operating (flow) temperatures down to improve running efficiency. It's also likely to extend running times of the boiler.