SimonD

Here we go again. In some ways he's correct. In others he isn't. MIS 3005-D provides a basic procedure that must be followed. The Standard for heat load calculations and the correct method is defined by BS EN1283-1 2017 which is also covered in the CIBSE Domestic Heating Design Guide. Lots of designers and installers falsely believe it's prescriptive, but it isn't, especially where building details are known. The outputs aren't defined by the procedure/standard/methods, but fundamentally by the inputs. Again, this is kind of correct. The changes were implemented in June this year according to the standard BS EN1283-1 2017. This provides two methods of ventilation calculations. one based on actual door blower tests and the other based on a simplified method, which isn't too many miles off the old one. It's also based upon the designer's perspective on the building. The standard also includes infiltration losses based on the building height and exposure. What was his basis for telling you this? Is this installer MCS certified or using an MCS umbrella? What heating qualifications does the installer hold above the basics? I'd really be wanting to use someone who has at the very least done extra training by some recognised provider in hydronics. So in terms of calculated heat loss what are the figures being used for reference for all their design?

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With a flow return 35/30 something like DT50 output of 1985. Have a look and play with the attached spreadsheet. What I've generally found with radiators is that as soon as you get into the 35 and below flow temp and DT5 the sizes start to get quite ridiculous, especially with warmer rooms - e.g. with this one the conversion factor is 0.115 bathroom rad size estimate.ods

Neither! It's a good room-by-room heat loss calculation that must come first which you then use to size the heat source, followed by the emitter design. Then you look at flow rate, velocity and pressure loss through your pipework.

Nice floor then! 😁 What are you planning mean water temp wise v air temp as at 26 you'll need to have a very small DT?

Why as low as 24? Most of my commissioning of wooden floors over ufh say max 27C floor temperature and on gas systems this has sometimes required floor temp sensors.

I'm all on radiators. Hindsight since getting the heat pump tells me UFH would have been a good idea and I could have run much lower flow temp. But isn't that self-build and learning for you? The rads aren't too intrusive thankfully. Quite pleased though as my calculated theoretical flow temp at -3 was 37C.

-6 last night with pump running at 32C flow temp most of the night with a peak of 34C after a defrost cycle. Indoor temp just above 21.5. I actually had 4 defrost cycles between 10pm and 9am.

Thanks. Well spotted. The measurement procedure was changed in the latest CIBSE revision. It used to be full storey height, which was when I created the spreadsheet, now it's just internal measurements, ignoring height of floors. So you're fine. The old process also used to call for adding 1/2 thickness of all partition walls.

You should have a ground floor u-value in the designs somewhere? On ventilation loss, you're fine as you've put it in. Regarding ceilings, what is the build up you have? I assume there's 100mm insulation in there?

Here's a single sheet spreadsheet you can use that covers all the basic heat loss calcs. Should be fairly self-explanatory. I built it using open document format so it runs best in LibreOffice or similar, but excel will be fine even if it then throws up compatibility errors. For the whole room losses you need to calculate all walls, ceilings/roof and floor and then air change rates. If you have a solid ground floor, room temp - 7C for design temp difference should be fine although some regions say 10 is fine. For any part walls, which I assume you may not have, use your target room temp - 10C. For your air change rates, with MVHR, 0.5 is the max you want to go for. Internally, with a well insulated home with MVHR, you can assume no difference in temperture between rooms so those internal walls/ceilings/floors can be set to 0 losses, unless you want to have different temperatures, then you need to input U-Values and temperature differences between those rooms. Have a crack at it and let us know. Heat loss single sheet.ods

True, but you also have to look carefully at the Viessmann outputs as although their performance curves appear to be honest in the reduced output just above 0C, their 8kW is unlikely to perform in this situation so it would probably need to be a 10kW unit going by the rated output as opposed to max output. Someday we might see some consistency around output figures that are also properly localised. Interestingly, I was listening to HVAC education hub's interview with Graham Hendra re his new appointment as an R & D development manager for Haier. He acknowledged that they need different products for different geographical zones due to environmental conditions...so maybe watch this space?

Yes, you're almost there. 1. You must confirm your calculated room-by room heat loss - this is the foundation of everything. 2. You then take each room's floor area and divide the room's calculated heat loss by the area. This gives you a W/m2 value. 3. You would then normally use this W/m2 value to determine the pipe spacing and output for each room, getting the flow temperature as low as possible Unfortunately, the UFH has already been installed in your ground floor, but you can work around this using both mean water temperature and flow rates through the system. At present, assuming the 3.3kW heat loss is the correct value the UFH system you have had designed and partially installed would output this at a mean water temperature (flow temp+return temp/2) of around 27C - obviously this is just an averaged value as it just divides your heat loss by your total floor area of 158m2. This gives about 21W/m2 that the underfloor heating needs to produce. The advantage you have here is that the spacings are pretty close and this means you have the opportunity to run your heat pump at low flow temperatures.

I agree with @JohnMo. Yes, these are premium models with great reputations, but there are lots you could choose from that could bring you in under the BUS Grant. If the installation is as straight forward as you describe, I think even a Vaillant unit could give you some change out of the grant too.

As I'm using clay paints, which may behave differently to the scrubbable paints, I use the auro plaster primer https://www.auropaint.co.uk/product/plaster-primer-no-301/ It goes on a treat and works far better than mist coat. but as it works with emulsion, it might be fine.

It's much more than for a gas boiler. There's virtually nothing in a gas boiler, even a system boiler - gas valve, fan, heat exchanger, circulation pump and pcb with some wiring. Plus it's far less volume and weight. A heat pump, lets say with the output required for the OP at about 5kW for arguments sake will weigh nearly 3x the boiler and have about 3x the packaged volume. From a manufacturing perspective it's far more complex. But over its lifetime the heat pump will produce much, much less especailly as the grid continues to decarbonise. For example, this article: https://les.mitsubishielectric.co.uk/the-hub/carbon-embodied-operational-and-whole-life-cycle

Nowadays, I rarely just change the motorised head. Even in my short time operating my business, I had a few too many call backs after just changing the head, so I now just do the whole thing as you never know how old the valve is because it is so common for plumbers to just chuck in the motorised head. Looking at the pipework arrangement, you might be lucky and be able to create a no pressure pocket so as to limit the drain down - is the system pressurised or open vented? Totally bemused why someone would need to get in an electrician to wire it in. Even if in doubt and you don't want to go into the wiring centre, it's so easy to buy a 5 way connector, made especially for this purpose so you can cut and strip back the existing cable to the 2-port valve and connect it with the 5 way. Available at any decent plumbers merchant. E.g like this https://www.teslauk.com/product/7831/easyplug-3-or-5-way-wiring-connector

That limits the options to about one. Although the Ideal thermostats are actually black on the face, but unlikely to work for you. What ASHP do you have and do they not have integrated controls? There is a tendency for some European controls to default to on if there is a problem, either with connection or batteries. The Viessmann controls do the same as they say this removes the risk of freezing if there's a control failure. So first I'd suggest the controls supplied by your ASHP manufacturer. Another, although not in black are the EPH CP4 controls as they function without internet connection and you can buy them with or without a wifi hub. The EPH controls can integrate with weather compensation curves etc. but it entirely depends on what you've got. For UFH you've got Heatmiser which it seems pretty much every other UFH supplier uses/copies under white label.

Are any of us when we start out on a self build journey? Thank goodness for BH where we can dispense with worries about our incompetence and ignorance to ask stupid questions and get sensible answers I say ☺️

Spray painting is great, I love it. But you need to mask everything up properly against overspray and spray mist. This takes time. You also need to spend some time with each type of paint you use to get the settings right through watering down the paint to ideal consistency and then the sprayer so you get a nice consistent spray. Both are worth it in my view as it ends up saving a lot of time. I've found my sprayer and paint (clay paint) finishes with a slight texture so no need to go over it with anything.

The boiler is essentially dumb and slow to respond. It measures just flow temperature so by the time the return temperature has reached the point at which flow temperature increases the heat is already in the system, so there's always going to be some intertia. It's not sensible from a design perspective to make the system respond too rapidly as that affects operating efficiencies and can cause various unwanted attempted control oscillations within the system. The real issue here is that the focus at the moment is only on the boiler and not your controls together with your boiler. At present, even though they might call it a smart thermostat, it's actually pretty dumb because the Hive only provides relay control of your heating. To get this boiler modulating properly in relation to room temperature or outside temperature you need some decent controls that actually modulate the boiler - so either weather compensation, or if you want load compensation, something like the Worcester Easy Control which uses EMC Bus to communicate with the boiler. You can use Opentherm to do modulation, but only with a third party translation kit that you need to get from Europe. Get yourself some proper controls and the boiler will behave much better and can be refined from there.

You have a UFH system that appears to be based upon flow/return temps of 45/40 with a total output of 8.3kW versus your heat loss of 3.3kW. Your heat pump supplier is then suggesting a flow temperature of 35C which would overheat your house with the current UFH design with a 5kW heat pump and you have selected a 300l dhw cylinder. You don't seem to have been informed if this 5kW output of the heat pump is at design outdoor temperatures, or the implications of the large cylinder and heat up times with the current proposed heat pump. And then not to mention the proposal for a buffer and secondary pumps. For the actual UFH output there does need to be a calculation based on proposed floor coverings as they have such a large impact on the system output - one of the two companies should have had this discussion with you. I'm also curious about the figures given in the UFH design tables. For example, your dining room says the ouput is 660w with 150mm spacings and a length of 92m and flow rate of 1.9l/m and your entrance hall/wc has exactly the same output but with almost half the loop length at 57m and exactly the same flow rate. I would expect to see some variation in flow rate and/or output with loops that are so different in length but have the same spacing.

If that's the case, then your output from the UFH needs to be around 21W/m2 assuming the 158m2 area is floor area. Very roughly, in screed UFH would output this at a mean water temperature of around 27C or a flow temperature of just under 30C at outdoor design temperature - this would vary depending on actual buildup and floor coverings, like if you decided to have carpets and wood floor etc. Do you know if any of the designs took into consideration the floor coverings you have? And do you know whether you have an in screed ufh throughout the house on both GF and FF? If does look like you have a situation where the design doesn't quite hang together based on the information we have. With your DHW, as @Nickfromwales and @JohnMo have pointed out, your heat up times with the chosen cylnder could be quite long depending on usage and this is something you need to discuss with the designer/installer to get the system sized correctly to work for you.

Of course. The index circuit is the part of the heating circuit that has the greatest pressure loss. So each meter of pipework, each fitting, like elbows, and for each valve the water in the heating system flows through there is a loss of pressure due to resistance. If you start at the outlet of the primary circulating pump of the system, often now inside the heat pump itself, you will have an available head pressure (usually specified by the manufacturer where they often provide graphs for how this changes according to flow rates) and this is what is gradually lost as the water travels through the system. The index circuit is just the total length of pipework that has the greatest resistance. Once this is known, you know whether the pump for the main circuit produces enough pressure to supply the heating circuit at the required maximum flow rate. This is what should primarily tell you if you need hydraulic separation and secondary pumps. The total resistance of the circuit is done by calculating the total heat load that is carried though each section of pipe from the heat pump to the end of the circuit along with using pipe diameter and resultance resistance of the pipe together with fittings. This should be done with every heat pump design. Yes, these are useful. There are already some discrepancies here. Earlier you said the design temperature of the system was a flow of 35C but the data re the ufh loops says the design temperature is 45/40. The tables each state the output of each manifold, being 4kW and 4.3K which is obviously more than the 5kW unit. I don't know the Samsung units so don't have the technical specs but you need to know what the heat pump is capable of outputting at your outdoor design temperature, which should be given in your design from the heat pump supplier. The tables suggest, I assume, that each manifold has less than 25kPa pressure drop across the manifold flow and returns whcih equates to about 2.5 meters head, but nothing more specific. However this can be calculated more specifically as the relevant data is there in the tables. What is the estimated heat loss calculated for your house?

No, not your fault at all. The ASHP supplier should be doing at least a basic calculation of the index circuit of the UFH as that will help them to design the ASHP system properly. But I assume from what you say that the people who installed the UFH have installed just the UFH manifolds without mixers and pumps on the manifold? Yes, absolutely. The simpler the better, but for a 3 bed house, there should be no need for any hydraulic separation or additional pumps with a system that runs low flow temps straight into the UFH.