Ewan

Thanks for the insight. A couple regular fans sound good for moving the cooler air around. Got plans for shade that can be easily retrofitted to the west side where needed (fakro rooflight external solar shades are retrofitable, and some generic external window blinds I'm looking into), and a2a can be routed through the loft easily enough. Will see where our hot spots are next summer.

Is this single air handler in the landing a strategy that comes recommended? Some results on google saying don't bother, but I guess if the house is well insulated, and you're blowing air into the bedrooms, roughly, it could make a difference?

How's the upstairs, do you feel the need for any active cooling up there? (or do you have UFH on all levels)

We're in the depths of a deep retrofit and have UFH going in, rads upstairs. ASHP due in a later phase (don't ask 😄), so bit of time to plan cooling. Had been looking at FCUs, but the complexity, lack availability of knowledge etc is off putting. Why would you not use the UFH for cooling, in your hypothetical? The cool air coming down would be enough? ** edit, just realised this was @joth , not yourself ** We're also a bit stuck with west facing solar gain, but currently looking at designing in some external automatic blinds. Multi splits should be minimally disruptive to install upstairs if needed after renovation is done... right... ? @markocosic any chance you could explain the +3kW/-2kW thing for me? not sure what you mean there

Yes does seem like a bit of a weird stipulation. What do you use for cooling? UFH?

interesting, they considering the DHW cycle to be problem even though it can be done in one go at night when cooling is less likely to be used?

So perhaps that's the reason the other NOx filters are so expensive? Although they are seemingly physical filters too, just massive ones. Would be pretty misleading of Zehnder etc to sell filtration units that do not...

Thanks Mike, looks like it will be just the ticket. The 200mm version has the best static pressure performance, looks like it adds about 30Pa at our normal fan speed.. which basically doubles our system Pa but should be within tolerance. The Zehnder unit was about 11Pa, but £4k is just ridiculous. Yes Kelvin, the message re log burner harm does seem to be slow to filter through to people who aren’t actively looking.. though reasonably regular articles in newspapers these days, hopefully awareness will grow.

Sorry for the necro of this old post, but I'm looking for a NOx filtration system that is not in the £1000s.. (Zehnder, Nuaire etc). What was this modular Zehnder system if you can recall? I've only seen their large unit: https://www.zehnder.co.uk/products-and-systems/comfortable-indoor-ventilation/zehnder-filter-housing-nox For which I have been quoted £3850 +VAT . Currently considering the Blauberg CleanBox or the Nuaire supply valves (but they add 8Pa of pressure each), but a modular zehnder in the similar price range would be worth considering if you know the details? How has your Blauberg cleanbox worked out, not too much extra noise in the end?

Seems to be the approach favoured by Heat Geeks, contacted the nearest "Heat Geek Elite". With some instruction, we can probably do that. I think it will take a long time with UFH in the slab, long heat up and cool down times. Hopefully not impracticably long..

Ah I see where you were coming from now. According to heat punk and other heat loss calcs, we should be able to run everything at 35ºc flow without radiators being particularly large, IF we install the EWI. Balancing UFH with rads would be the key then. We'd have plenty of volume then. Thanks for all the input. I appreciate the disclaimer and won't be making any decisions based solely off your remarks. Lost me there.

UFH downstairs rads upstairs. Make much odds?

Samsung Gen 6 could work, although it's a little noisier at 61dB and we're right on the borderline with MCS noise calcs, I'll have to move it along a bit. Eats up our space for other planned uses but could be worth considering. Midea 6kW could be a good shout. Going in search of technical data (mostly turndown) on these now..

Vaillant 5kW (2.2kW turndown) was our preferred choice but is not compatible with Homely. Samsung HTQs start at 8kW, so a possibly a bit big, assuming a 1/3rd turndown of 2.6kW. What other heat pump with modbus for Homely should we be considering?

This was all very interesting and took me a while to read and understand 😄 I also listened to a podcast where the guy who did those tests was interviewed, also quite interesting: https://www.buzzsprout.com/509671/11946910 - they talk about a lot of the things you all mentioned in discussion here. He sounds quite knowledgable (to my untrained ear). Very big on pointing out that Manufacturers docs mostly show buffer tanks in use (in the UK, but not EU versions!), and why they think this is the wrong approach. @JamesPa, from your earlier post you suggested the having UFH and radiators (5 in my case) could be a candidate for mixing to deal with flow rates etc. One installer is suggesting we go direct with no buffer or volumiser, have the UFH & rads on one open circuit, but size the rads down slightly to avoid overheating bedrooms (at my request) and balance the whole system. Does that sound achievable / sensible?

I did the calculation twice, once for my system (negative number) and once to make sure I was doing it right with numbers that were already worked up. For the second example I quoted, that should have resulted in a positive number, but didn't! This is the example: Or: (4-2)*10/(2*4.2)-100 = -97.619047619 It should have resulted in 42L, which makes me think I'm doing MY calculation wrong also, especially as my numbers do not match the ones Vilks got for my system. If anyone can point out what the heck is going on here, I'd be very grateful.

Ah yes I did see that re balancing. That would leave a lot more volume in the system. Can get more thermostats if needed? Was planning on using weather comp. Problem is that I got a negative number on the calculation they used as an example that did require a buffer! (i.e. shouldn't have given a negative number) I must be doing it wrong? I also can't get the same results as @Vilks Maths failing me 😅

Thanks for doing the heavy lifting for me, that's really useful. I can't make that formulae work at all, (2-1)*10/(2*4.2)-69 = -67.8095238095 ... which sounds good as a negative number means no buffer? But I also can't get the example to work where they did need a buffer: (4-2)*10/(2*4.2)-100 = -97.619047619 Confused. Where am I going wrong? Are Pmin and Dmin in kW? Perhaps it's OK then, 69L is the volume of the UFH which can just be on one zone. Office and upstairs bathroom rads could also be left TRV-less. Questions Do you need Trvs on the radiators? - Fear is that upstairs will become too hot during heating season, so TRVs will be employed in the bedrooms. Could you balance the system instead? - Not sure, the heat loss in the biggest room seems very large compared to the bedrooms. I am not very knowledgable about balancing. Do you need more than one thermostat? - probably not!

going to show my ignorance here, but are you talking about the black cylinder? We easily have space for that sort of thing. I was thinking of buffers in the 70-100l range that would be problematic. what’s dynamic bypass? 27 degrees shouldn’t be exceeded for what reason, flooring?

we’re going quite far, but remains to be seen how it works in reality! Aiming for enerphit levels but not too precious about it. I’d had it in my mind that volumiser = good as no extra pumps, not large (short on space), no distortion etc. Buffers I though the opposite. Heatpump UFH manifolds don’t need to have pumps on do they? At least the one robbens have specced doesn’t. simple as possible while working well is the aim 😅 if we needed we can probably find space something smallish.

Because of the minimum heat demand / minimum output mismatch or another reason? Installer’s initial thoughts were that volumiser would be enough and give better efficiency while saving space, but he’s not done any calcs yet admittedly. thanks, these could be just the ticket if we need one, I’m still hoping we do not.

OK. Just like balancing rads with the lock shields 👍🏼

That’s a very useful calculation. I’ll look into this. Looks like we should be fine with most of the UFH zoned in one. Perhaps the smallest rooms on their own zone. Many thanks 👍🏼

Every chance I'm overthinking this / don't know enough 😅 Is that the same as cycling or is this a different kind of "pause"? Interesting, maybe we could squeeze one in, it's pretty tight. Though I have read there are other disadvantages to them, but if we do need one... Re the retrofit: 150mm EPS EWI & brick walls for 0.22u 400mm Loft insulation with airtightness membrane and eaves detailing 0.11u 200mm solid floor replacement 0.4u with thermal bridges (internal walls still reach the ground) All new kitchens and bathrooms with penetrations taped All joist penetrations taped All new TGU windows & doors installed airtight 1.0u MVHR 20w/m3 likely the very best case, probably end up with some performance gap. Not really sure what to expect, but that's what the calcs come out with at 0.2 ACH. Or 4000w / 27w/m2 at 0.5 ACH. Minimum flow rate on the Vaillant specs. Nothing about minimum output at all otherwise Thanks! This is reassuring Wouldn't the runtime be determined by the return temp? I thought if the UFH rooms are up to temp and return flow goes below 5 DT, then it'll start cycling if already at its lowest output? Concern is that this would happen to us frequently at 10-15º if the lowest output was actually 2.3kW (again may be massively overthinking this!) Volume needed in the system I had thought was for defrosts etc. We will have 69l in the UFH (rads upstairs probably TRV limited), will design it so available volume is always above the volume needed for defrosts.

In the absence of any specs from Vaillant, I've tried to calculate Vaillant 5kW (and 3kW) heatpumps minimum output. Looks like they can only modulate down to 2.3kW: 400l/hr ➗3600 = 0.111 L/sec x (4.2 SCH x 5 DT) = 2.33kw - is this accurate? Our calculated heat demand for our retrofit (best case) is 3000w (20w/m2 * 150m2) at -2.5º. Suspect it will be somewhat higher but not sure how much. This means that at anything between 10º - 15º outside temp our heat demand could be between 1500w - 1000w. We don't want a buffer tank, not enough space. Is this mismatch in minimum output vs heat demand going to be a problem? Some cycling is to be expected, but would this be excessive?