SimonD

This is where your difference lies as a glycol solution has less heat capacity than water (at 100% it's about 2500 J/kg K). Also, don't forget you'll need to add extra pumping resistance as a consequence of this.

Domestic Heating Design Guide I think you're slightly low on your figures. My calculation at Delta T 5 and 12kW equates to 0.67 kg/s mass flow rate which is about 40.20 l/m and 16l/m if your assumption of 40% distribution to the cylinder works out. So you're looking at a higher flow rate that you expected, I think. Formula taken from Domestic Heating Design Guide.

Maybe I've missed something but this calculation doesn't seem to include how much heat you're moving through the system, which is what you need to determine the flow rate in your heating system. What Delta T are you assuming? At what temperature are you heating your cylinders to? Your system currently works because I'd assume that your oil boiler was commissioned to work at a 70C flow with 50C return - so as an approximate difference, at Delta T 20 and a flow rate of 0.9m/s you'll move about 11kW in water, if you're running a heat pump at 7C Delta T this will move about 4kW. With glycol this will be less as you'll only move about 3,600J/kg K with 20% glycol content. Max velocity is usually considered to be 1.5m/s but more ideally around 1.

This is what they look like as used for fixing all the joists to the steels. No possibility of removing and then replacing the bolt as the whole fixing is the structural element. Thanks both, you've put me onto Rivnuts as an alternativ option but I'm struggling to find structural data for the rivnuts used for wider sections. This is something I briefly considered but followed the guidance of the SE and suggested fixings. I may just review this as an option. It's 3 meters drop so yes, I need to ensure it's robust enough. Currently the only option I know I can use is Interclamp/Kee Clamps tube clamp arrangements and depending on post diameter, I can install them up to 2m centres. Essentially what I want to do is come up with a design we like and then pass it by the SE as a final nod.

Thanks, yes makes sense. The bridge is made of steel box sections so bolts need to be hollo type which causes a bit of a headache. The longest I can find are max total fixing depth of 86mm so notching would be a must, plus they're so big, 33mm diameter hole is required through the posts. If I use Cedar, then stainless ones are over £100 a piece so 2k in total just for these ☹️ If I had my workshop, which is all in storage, I'd fabricate some brackets, which I think may be the only option but prices I've received to make them up also seem a bit ridiculous, but maybe I'm just tight? 😉

Yeah, me too - with some soft wet clay in parts that caved in without the digger being even close!

Well, I only have a little one 🙄 But of course it's how you use it that counts, isn't it?

Totally!

Or maybe it's been lying in the ditch for two weeks since?

(Expletive deleted) you're brave!

SW3.1 is the Dipswitch to enable 2 zones at equal flow temps IIRC. It needs to be set to on.

If you check the voltage at the top two wires where the terminals are label L & N on the FTC6, which is TB2, what do you get? You should see mains voltage there. Across S2 & S3 below you should see a variable DC voltage around about 20VDC.

So that looks very wrong! It looks like your LR from the UH8 is going to neutral on your FTC control board. I'm surprised there isn't a blown fuse somewhere. Have you checked the voltage you're getting at the Heat enable LS and then LR when it's calling for heat? Have you checked what wires are connected to your TBI.1 & TBI.2 terminal blocks? (bottom horizontal row of the FTC6)

Have you got a photo?

Have you got the correct fittings and jaw combo? Those connections look terrible, I wouldn't want them anywhere near an installation. Maybe better to hire a press fit kit, or even buy and then sell on? £1500 quid now is cheap compared to potentially fixing failed fittings later on down the road.

Sometimes it's not the one who's done the work. I've got so much criticism and scalding for redoing work that seems fine to others' eyes, not that I'm claiming to be a master builder by any stretch of the imagination, just want what I do to be right. But back on topic: Would a single T & G plywood subfloor replacement not suffice for replacement? That's what I would settle for if I didn't have the space for additional 6mm.

Try if you can to trace that cable back to the FTC6. I think these should go into TBI as that's where the inputs go, but these also depend on the DIP swtich settings. Although dealing with an earlier version, here is a thread I found that could be very helpful to read and it's about the same connections. I would also look at all your setting as even on weather comp. zones flow temps can be set to 60C I believe.

The Heamiser UH8 is a pretty dumb relay wiring centre so I would have a look at the wiring to the heat pump from the UH8 as per the following: Heat Enable This is the main call for heat for the system, there are 3 connections; LS = Live Supply E = Earth LR = Live Return Electrically this is a volt free switch, whatever supply is placed on the LS connection, is fed to the LR connection when there is a call for heat. Then check the wiring at the FTC6 controller. I wonder whether the 60C output is meant for DHW and the wiring centre is calling for that when it should be heating CH?

I would go with 6mm plywood, which is the normal spec for prepping floor for Vinyl, this even goes if laying on chipboard - usually recommended to be screwed down at 150mm x 150mm squares and 100mm centres along the edges. As for adhesive, she could just order some spray vinyl adhesive like this random link: https://www.best4flooring.co.uk/vinyl-spray-adhesive. Bostik also sell tubs of vinyl floor adhesive that might be a bit cheaper. Last time I paid for an installer to do a vinyl floor for me he even filled and sanded over the screws and joins between plywood sheets and achieved a very good finish.

Just approach a local timber merchant as they will almost always have machinery to both cut and machine profiles to your needs.

Here is a nice video showing and describing it very well. The towel rads could be run from the header next to the Esbe mixers.

😁 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.