JohnMo Posted August 7 Posted August 7 54 minutes ago, SBMS said: 9kW at -4 in total So including DHW if 9kW is correct you need a 10kW Vaillant, but if 9kW is rounded up you could use a 7kW. Your flow temp shouldn't exceed 35, possibly lower and a 7kW puts out 8.8kW.
JamesPa Posted August 8 Posted August 8 8 hours ago, JohnMo said: 10kW Vaillant Which is the 12kW model firmware limited.
Nick Laslett Posted August 8 Posted August 8 (edited) 13 hours ago, SBMS said: What is your current approach to cooling? Nothing special. ASHP with UFH upstairs and downstairs. Solar Control glazing with moderately sized windows. MVHR with attention to air tightness. Small roof overhang of 50cm, which doesn’t do much and needs to be more like a metre. Back in 2019, when I first joined BuildHub, the house overheating issue featured in a lot of discussions. @Jeremy Harris’s ideas were very helpful on this topic. We have an ICF build with insulated slab foundation and insulated poured concrete first floor. The ICF core is 150mm. All this concrete gives the house high decrement delay. A good primer on the topic here. https://www.greenspec.co.uk/building-design/decrement-delay/ We also have the Zehnder Comfopost, but as the MVHR isn’t commissioned, very hard to tell what effect this will have. If it reduces the house temp by 2°, I will be happy with the investment. I worked in the Middle East for 12 years, and have developed an aversion to A/C, so that wasn’t going to work for my build. I didn’t discover Fancoils until too late in the design process. An ICF build lends itself to things like poured concrete stairs, poured concrete first floor, etc. These were very specific design choices that were a prerequisite for our build. Not a fan of timber frame construction and all the associated building movement and high levels of sound transmission. Which requires a lot more skill and attention to mitigate IMHO. The first floor UFH is specifically there for cooling the bedrooms, we have more pipework in this floor than downstairs. SWMBO didn’t want radiators, so that was also a design consideration. Edited August 8 by Nick Laslett 1
SBMS Posted August 8 Author Posted August 8 13 hours ago, JamesPa said: Which is the 12kW model firmware limited. Does the 10kW modulate down to same level as the 12kW? What’s the point in going for the 10kW then??
JamesPa Posted August 8 Posted August 8 (edited) 1 hour ago, SBMS said: Does the 10kW modulate down to same level as the 12kW? What’s the point in going for the 10kW then?? So far as I know yes and none respectively, except for a relatively small price difference. There is detailed data (in Czech) around but I can't find the link currently. PS found it https://community.openenergymonitor.org/t/vaillant-arotherm-owners-thread/21891 Original here https://downloads.vaillant.cz/downloads/projek-n-podklady/kl-06-e2-verze-01-18012023-2564719.pdf The give away for same hardware (many manufacturers play this trick) is same dimensions, same weight and same refrigerant charge. Edited August 8 by JamesPa
JohnMo Posted August 8 Posted August 8 Attached. Page 33 on At 7 degs the 10kW puts out between 7 and 15kW. The 12kW puts out 7 to 18kW At -7 the 10kW puts outs 4 to 9.5kW While the 12kW puts outs 4.5 to 13kW kl-06-e2-verze-01-18012023-2564719.pdf
SBMS Posted August 8 Author Posted August 8 1 hour ago, JohnMo said: Attached. Page 33 on At 7 degs the 10kW puts out between 7 and 15kW. The 12kW puts out 7 to 18kW At -7 the 10kW puts outs 4 to 9.5kW While the 12kW puts outs 4.5 to 13kW kl-06-e2-verze-01-18012023-2564719.pdf 5.83 MB · 1 download Interesting that the 10 modulates lower than the 12 in heat mode (and outputs higher) but in cooling mode the maximum output is identical. (Page 5) makes me think it’s the same hardware but software is range setting in heating mode but allowing the compressor to run full speed in cooling mode. Which actually is a useful thing for me as there is no additional cooling output with the 12kW but the 10kW is possibly better suited for my heat loss requirements 🤷♂️
JohnMo Posted August 8 Posted August 8 6 minutes ago, SBMS said: Interesting that the 10 modulates lower than the 12 in heat mode (and outputs higher) but in cooling mode the maximum output is identical. (Page 5) makes me think it’s the same hardware but software is range setting in heating mode but allowing the compressor to run full speed in cooling mode. Which actually is a useful thing for me as there is no additional cooling output with the 12kW but the 10kW is possibly better suited for my heat loss requirements 🤷♂️ It's good to have facts to allow you to make informed decisions.
Nickfromwales Posted August 8 Posted August 8 48 minutes ago, JohnMo said: It's good to have facts to allow you to make informed decisions. Amen. Can they also use some of the stuff I am utterly convinced about or just "feel in my bones" too?
JamesPa Posted August 9 Posted August 9 (edited) 9 hours ago, JohnMo said: It's good to have facts to allow you to make informed decisions. Steady on, that goes head to head with the prevailing trend in politics, or at least politics of a certain kind. Facts may mean you cant justify doing what you want to do or deceive those you need to deceive to remain in power. What we need is the complete absence of facts. Edited August 9 by JamesPa 1
JohnMo Posted August 9 Posted August 9 9 hours ago, Nickfromwales said: Amen. Can they also use some of the stuff I am utterly convinced about or just "feel in my bones" too? Only if a seasoned professional, that isn't a politician. But have the case history to back up them old bones. 1
joth Posted Sunday at 07:33 Posted Sunday at 07:33 On 03/08/2025 at 10:30, -rick- said: 5. @joth wanted the ability to cool the fancoil zone while heating the ufh. Did I? I forget where i might have said that. Certainly, that's not the system i ended up with in my own home; we have a single 2 pipe monoblock
-rick- Posted Sunday at 07:56 Posted Sunday at 07:56 18 minutes ago, joth said: Did I? I forget where i might have said that. Certainly, that's not the system i ended up with in my own home; we have a single 2 pipe monoblock Oh now I'm confused. Am I thinking of someone else? I thought you had a heat gain problem in the bedrooms even during heating season so wanted the ability to cool the bedroom while the downstairs wanted heat. After I read that I looked back at some old threads and thought I read about how to do that you had to install a second zone with a big buffer tank to give the zone enough volume to avoid cycling. Have I misunderstood something?
SimonD Posted Sunday at 09:02 Posted Sunday at 09:02 On 08/08/2025 at 23:07, JohnMo said: It's good to have facts to allow you to make informed decisions. Unfortunately, Vaillant don't really have the data for modulation on the Arotherm plus heatpumps - all you get is an approximate at certain outdoor temperatures. I asked the question just a few days ago when I was at Vaillant for training on the Arotherm plus heatpumps and they went internally to ask the technical design team. Therefore, you can't use any data to accurately design a system according to modulation on these heatpumps. The Vaillant quick guide charts are given at maximum compressor speed only.
JohnMo Posted Sunday at 10:09 Posted Sunday at 10:09 1 hour ago, SimonD said: The Vaillant quick guide charts are given at maximum compressor speed only. Have you looked at the data book I attached above? Me thinks they just don't want to tell you. Here is snippet - all temps full range of compressor speed. All compressor sizes in data book attached above.
SimonD Posted Sunday at 11:58 Posted Sunday at 11:58 1 hour ago, JohnMo said: Have you looked at the data book I attached above? Me thinks they just don't want to tell you. Yes, I've looked at the data book. That's a cynical position, which may be true but they have lost sales to me as a consequence. The problem is that if I'm designing a system where I hold liability to a customer for the design and installation, I can't be relying on a foreign data sheet to assess the suitability of a system for their needs. It may be the case that they're playing a similar game to Tado (in removing Opentherm from controllers in the UK without telling anyone) and providing different specification equipment to the UK market or that they think the UK market isn't sophisticated enough to design systems with modulation in mind - who knows. Generally though, my experience has been that if the information is available, manufacturers have provided the information I ask for. It's anyone's guess why this information isn't readily available from Vaillant in the UK....
JohnMo Posted Sunday at 12:09 Posted Sunday at 12:09 2 minutes ago, SimonD said: It's anyone's guess why this information isn't readily available from Vaillant in the UK Maybe a different set of rules, we have diddly to enforce manufacturer to tell us stuff, maybe other European countries demand a full range of tech data. Vaillant UK information is best part of zero. Almost trust me - we are 'Vaillant'. Even their badging is suspect, choose a 7kW ASHP and it puts 9.4kW at -2. Mitsubishi, not always easy to find, but published, have pretty robust set of data. Quite like there new 8kW with two compressors, one fixed output 2kW and one 6kW inverter driven. Should cover all bases.
JamesPa Posted Sunday at 13:18 Posted Sunday at 13:18 Imho it's pathetic how little info some manufacturers publish. Vaillant isn't the worst by any means, or at least it wasn't two years ago when I did the bulk of my personal research. Quite why the most complete Vaillant info is on Czech is a mystery, perhaps that is where they are designed even though it's a German company.
JamesPa Posted Sunday at 14:35 Posted Sunday at 14:35 https://professional.vaillant.co.uk/downloads/aproducts/renewables-1/arotherm-plus/arotherm-plus-installer-quick-guide-2848532.pdf Has got a bit more (Vaillant UK) information, but only on maximum outputs for heating and cooling, not minimum.
SimonD Posted Sunday at 16:32 Posted Sunday at 16:32 4 hours ago, JohnMo said: Maybe a different set of rules, we have diddly to enforce manufacturer to tell us stuff, maybe other European countries demand a full range of tech data. Vaillant UK information is best part of zero. Almost trust me - we are 'Vaillant'. Even their badging is suspect, choose a 7kW ASHP and it puts 9.4kW at -2. Mitsubishi, not always easy to find, but published, have pretty robust set of data. Quite like there new 8kW with two compressors, one fixed output 2kW and one 6kW inverter driven. Should cover all bases. I do wonder whether it's to do with rules. It's also more important as their climates are a bit more extreme compared to ours? Who knows. Nibe publishes the data right in the installers manual so it's easy to find.
JamesPa Posted Sunday at 16:48 Posted Sunday at 16:48 (edited) 22 minutes ago, SimonD said: It's also more important as their climates are a bit more extreme compared to ours? That's an interesting debate. In one sense at least ours is one of the worst in Europe. In much of the UK we design for -2 or -3 and have a damp climate, which means that any reduction in output due to defrost really matters. If you are designing for -10 in a drier climate the penalty for defrost is of lesser consequence, arguably of no consequence at all, since it will be occuring most at temperatures higher than the design temperature (where the demand is less). Edited Sunday at 16:55 by JamesPa
JohnMo Posted Sunday at 17:06 Posted Sunday at 17:06 15 minutes ago, JamesPa said: designing for -10 in Or designed for the same condition but 6 miles from the coast. Plenty of defrosting goes on, even at very low temperatures.
SimonD Posted Sunday at 20:03 Posted Sunday at 20:03 3 hours ago, JamesPa said: That's an interesting debate. In one sense at least ours is one of the worst in Europe. In much of the UK we design for -2 or -3 and have a damp climate, which means that any reduction in output due to defrost really matters. If you are designing for -10 in a drier climate the penalty for defrost is of lesser consequence, arguably of no consequence at all, since it will be occuring most at temperatures higher than the design temperature (where the demand is less). That's a very good point. Most manufacturer's don't publish output inclusive of defrosting - Nibe do publish these figures and I think more are on the way due to pressure from installers and customers. Speaking with some other designers it's the fear of defrosting that often drives the addition of a buffer, but again manufacturers are getting to grips with this and will now give better guidance on minimum open volumes without buffer to deal with defrosting - even if it ain't rocket science to figure this out anyway. At least one start is we're seeing better specification of output figures at the relevant design temperatures rather than just at 2/35 or 7/35, for example. E.g. Grant Aerona 290 heat pumps stated output is the actual output at -5/55C so a bit more helpful.
JamesPa Posted Monday at 07:26 Posted Monday at 07:26 14 hours ago, JohnMo said: Or designed for the same condition but 6 miles from the coast. Plenty of defrosting goes on, even at very low temperatures. Indeed. Yet people still ask why the actual output differs from the sticker figure. It's just not a simple question! Mitsubishi (and Samsung htq I think) solve this 'problem' by clamping their outputs, but I can't say I like this practice much.
JohnMo Posted Monday at 08:23 Posted Monday at 08:23 57 minutes ago, JamesPa said: by clamping their outputs Panasonic do this also
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