Ewan

Thanks both! We're in a recent retrofit (to a bit beyond modern building regs I believe) and were aiming for all open zone HP. We've ran one winter on our gas boiler at 30deg and it was fine downstairs (may have over provisioned the UFH downstairs by about double), but a little cool up. Maybe need to upsize one or two rads for that approach. I was considering A2W with a seperate circuit for really cold water along side the usual rads and UFH, fully insulated to two locations. The open plan room with lots of glass (though this room is massively over provisioned with UFH so perhaps that would cool well enough) and the landing upstairs. Fairly easy runs for new pipework. Is that possible or too complex to have different circuits / temps? Some questions: Do fancoils actually cool much with 14 deg air? There are ones that sit on walls in place of radiators aren't there. Can the Octopus Daikins be pressed into cooling easy enough, with Home Assistant or similar does anyone know? How's the noise and drainage from the FCUs in bedrooms? just put a pipe through the wall to drain or not bother if keeping above dew point? Easy option would be to get an AC units in the hot spots and a2w for DHW and other rooms. But would have to get the a2w installed first as would not be PD with 2 a2a external units already installed (I suspect will need 3 inc a2w).

@puntloos what did you go for in the end? currently have the same quandry.

Sounds great! a smarter mixer than a TRV style one would certainly make a difference here.

Just to clarify, you've sacrificed Weather Comp control of your UFH floor temp as the mixer is always set at 28deg?

1600m of pipe, accidentally mis-sold to me off the back of their incorrect calcs. 11 loops. Makes me think that knocking a few loops off would help with the pump too. I'll keep mixing in mind then when it comes to it, thanks.

I was concerned about short cycling too, but that not coming back on at all due to DT is now also a worry! The initial plan was to open loop the whole house and run both rads and UFH at the same temp, no hydraulic separation, no buffer (we're short on space. perhaps a volumiser, but I've got 200l in the UFH alone so not sure), full system volume available for defrosts, which a mixing valve would interfere with. Admittedly, this plan has not been gone over yet by an actual installer. I've got a heat geek lined up for that a bit later in the year, and this was what they suggested an approach could look like (pending them going over the install choices I've made so far!) In theory yes but then according to the heat loss those rooms are under powered.

Can you balance away over provision of 140-170% on 10 out of 11 loops though? Heating engineer on twitter said I may "strangle the flow" with that much restriction.

Can’t go lower than 35deg without changing all the upstairs rads which I sized for 35. I figure best I can do is if I close off 3 of the 6 loops in the open plan room, and 1 of the 3 in the lounge.. even then it looks like 35 deg will see us down to -10 DOT I guess that’s not such a bad problem to have 😄

I've got a Wunda 16mm UFH kit installed at 100m pipe centres in Screed after Wunda told me it would put out 45W/m2 with my floor covering at 35 deg flow for 20 deg air temp. On later enquiry it turns out the sales assistant used the wrong info, they mistook the thermal conductivity of my 7mm SPC LVT flooring @ 0.151W/m-K to be thermal resistance, when it actually works out to 0.05 m2K/W. Turns out it will actually put out 70.3W/m2, which would have caused me to say "no thank you, I'll take 150mm PCs instead" (house is well insulated). So I'm now down a bunch of cash and have a system that is way overpowered for our ASHP design temp due to their error. I'll likely have to turn off half of the loops completely (any problems with that?). I put the floorplan into Loopcad out of interest, but can't for the life of me get anywhere near their figures; it gives 50W/m2 for the same parameters. Wunda say they use the CIBSE Underfloor heating design and installation guide for outputs, fair enough. Which is closer to reality??

Or if your panels on one string are on different aspects, which is actually shade too I guess! That would give one string with 3/4 panels on, and one with 10/11 panels over 2 aspects, and 2 or 3 optimisers on the smaller east facing roof. Seems like the simplest configuration.. Not tried PVGIS, will have a look at that.

Yes that's the thinking Doug. ASHP in the future, maybe bump the battery up to 15kWh at that point too. Induction hob going in, but previous to that our annual usage was 4600kWh. Struggling with the configuration aspect more than anything. Think it boils down to these distinct options: 13/15 panels (if they fit) and Tigo on all 13/15 panels and Solar Edge (pricey) 10 panels and just one or two Tigos.

I’ve been thinking that the batteries would be the star of the show! Keep the excess generation for later, and also charge up on cheap night rates in winter. can see the value in keeping the system costs down though. Perhaps the most simple one is the answer, no West aspect and less optimisers (just on the East face perhaps). no divert yet, although maybe with the future heat pump. Although could just run the pump rather than divert to immersion.

Finding it hard to chose between Solar Edge, Tigo Optimisers or EnPhase + AC coupled batteries. Can anyone advise based on our layout? We won't get much shading apart from maybe the dormer. I've had Solar Edge quoted, and EnPhase as an option, although this would require an AC coupled battery, which I understand you lose out on battery capacity as it needs to be inverted 3 times to use stored Solar energy, (or just twice from the grid, but that's the same with DC coupled I think). Not sure what to go for. Also not sure I need Tigos on every panel (extra failure points?). Option A told me that 3 elevations means all need optimisers, while Option C have suggested only 2, and those are optional. Quotes so far in detail: Option A suggested 13 panels (one less on the East and West) - Tigos on every panel + 5kW Lux inverter (works with Octopus, a plus) with ~10kWh Pylon tech batteries (I like as it's expandable) - £12.2k Option B suggested 15 panels as shown below £12.5k, but currently a 3kW Sunsynk inverter & batteries of unknown type, TBC Option C has run up a few quotes for me, including only 13 panels (but suggested against the rear ones as they're slightly north inclined) - only suggested Tigo optimisers on the East facing elevation due to the dormer = - Solis 3.6kW Inverter (doesn't work with Octopus?) & 9.2kWh Pylon tech - £12.7k (only 2 Tigos) - Givenergy 3kW inverter and 9.5kWh battery £13.5k - Solar Edge - £16.5k - EnPhase & GivEnergy 6kW / 13.5kWh AIO £16k Any thoughts? it's all a bit overwhelming! (this is Option B's suggestion)

I think the Tado thermostats are +/-0.1 degrees, from what I’ve read on their forum anyway. I already have a few of these so will give it a try. Screed is planned to be 70mm. Current idea is to use Bosch sense ii weather comp (this has the option of room influence), & tado as smart relay set a bit higher than desired temp. Boiler only modulates to 7.2kW and heat loss is 4.5kW at DOT so it will cycle a bit. ALso considering Salus ABAs to deal with intermittent heat imbalance from solar gain.. could always be a future option if this turned out to be an issue. Would they be a way to tackle that?

Anyone seen the new Salus THB Ultra ABAs available in the UK yet? Seem's they've done away with calibration need. https://saluscontrols.com/gb/introducing-the-ultra-thb-auto-balancing-actuator/