markocosic

No; but it should be a fair term in a consumer contract. If they are using the MCS accreditation of the heat pump installation in order to claim carbon reduction credits that reduce their scope three emissions footprint...then this should be explicit and result in a discounted interest rate. It could help subsidise energy efficiency etc. Else; yes; they ought to be prevented for doing this in much the same way as they should be prevented from allowing lodgers etc. But MCS are the darlings of government who give them the warm, fuzzy, fictional figures to report on their spreadsheets...

Heat pumps have little choice in this respect. Their only meaningful output variable is compressor frequency. There's a sweetspot for this to maximise performance at a given source/sink temperature. There are also min/max limits. (with the sweetspot often near the minimum but not quite) You need to pull heat away at the rate the compressor is pumping it. Dropping flowrates through the plate just forces up the dT until you trip out on high temperature/pressure. You want to be running flow as quickly as you can through the plate before (a) it has to operate above the sweet spot output to maintain a minimum dT (usually 3C or so;. tunable on some units in DHW mode) or (b) the pumping power increase exceeds the COP benefit of a lower dT. (could happen I guess, if primary runs in a retrofit scenario are large?) Thermosyphon is going to be insufficient to generate the turbulent flow in the HX needed for efficient heat transfer. On the space heating plates in district heating schemes we have issues at low space heating outputs where the flow through the exchangers is so low that it stratifies and transfer is at high DT rather than being turbulent over the whole plate

You can mitigate this by finding a competent installer willing to use non default insulation and ventilation requirements. The latest wheeze by the self serving pigs at the MCS trough, however, is persuading mortgage companies to start asking for MCS certifications for heat pumps. Almost like they're planning for new reasons to exist after their role as the sole pathway to government gravy ends...

Nope. You're too optimistic in the cost of gas. 😉 Multiply the gas unit rate by 1.25 (80% boiler efficiency), so base price is actually 9.4p/kWh for gas. Then add the standing charge in that you would avoid buying sacking off the gas supply (say £100 divide by 10,000 kWh for 1p/kWh) And you're at 3:1 or a sCOP of 3 for cost neutrality.

The negative is more "the people who usually base designs on an Ecodan" - it's rarer to see one installed correctly / installed alongside a heating system / heating controls that allow it to operate correctly than it is other brands. Loads with 4-pipe buffers and elevated heat pump flow temperatures for a given system flow temperature. Loads with zoned UFH systems with air thermostats that ensure short cycling etc. There are some good ones but more often than not the installs are nasty. e.g. on heatpumpmonitor: - The top ecodan listing is space heat only (no hot water use that reduced the COP) into an underfloor heated old building. So it's sitting there pretty much all year (not just in the cold season) chucking in heat at the lowest possible temperature. A passive house will have a shorter space heating season and lots more hot water use. - The second one looks good but you'll not that it uses solar thermal for DHW so is again not particularly representative Compare with say the Telford/Banbury/Oxford projects that are R290 Vaillant units actually providing DHW and running basic weather comp into rads or UFH etc. Or look at "which are in the top 20" and "which are in the bottom 20" I think illustrates the "hmmm...the person doing the design likes Mitsi...they're more likely to be useless than useful based on the real world results observed..." Your space heat loads will be "who cares" for a passive house. Small and a very short season. You do want to ensure that the heat pump can actually run long cycles though; which isn't a certainty if you're introducing zoning and effectively "decoupling" the heat pump from the thermal mass of the slab. Your hot water loads will be more important. My understanding is that the published sCOPs don't include hot water generation. The performance of the units in (low temp) space heating mode will mask their performance at higher temperatures during hot water production that, in the real world, is more important to you with a passive house.

Shower probably 8-10L/min? It's the bath fill that'd be nice to have not take an age. And both to not make a noise. I'll put an ear to some fittings I think.

Would you sleeve through joists at all?

Thanks @JohnMo MLCP book of words suggests pressure drop is ~0.3 bar for 20/min at 10m; say 0.4 bar allowing for fittings that make the effective length more like 13m You don't think the flow will be audible then? I have 15 mm PEX (similar ID to 16 mm MLCP) to a bath filler in the other house l, which is both noisy and annoyingly low flow rate; so wanted to sanity check. It's also going through a combi and what is probably a lower flow fixture with naff mains pressure (incoming main 1/2" copper with a meter cut into it) The volume difference is meh for a shower IMO. Warming the pipe/valve/shower head takes the time; not purging the pipework. More critical for the handbasin/kitchen tap though.

Fair points. Perhaps PV or PVT as a shade over terrace would have been an better use of that high rise roof space. Keeps the rain off the air source heat pumps to be used for heating/cooling the place. Walkway around them for servicing and viewing? Not trendy enough for architects/planners/funders though!

Perhaps worse? Zero benefits whatsoever since they were shut down due to vibrations/sound in the penthouses.

I have a run of 8-10 m from an UVC to a bath filler / shower mixer. No fittings en route as planned. Given free choice would you use 16 mm or 20 mm MLCP? We are thinking this unit for BOTH bath fill and shower: https://www.hansgrohe.com/articledetail-ecostat-bath-thermostat-1001-cl-for-exposed-installation-13201000 https://online.depo-diy.lt/product/181956 (easy to service / swap) I have a choice of 16 mm or 20 mm MLCP (the brackets come equipped for either / or) https://online.depo-diy.lt/product/23810 https://online.depo-diy.lt/product/23812 Notional flowrate of fixture 20L/min @ 3 bar bath filling or 16L/minute showering. (presumably that's the valve not the handset though) Will 16 mm be an appreciable restriction / will it make an appreciable noise at those flowrates? Or asked another way is there any reason not to use the 20 mm? Where it's running through studs / battens would you sleeve it / wrap it / foam it to reduce noise or just pop it through a hole slightly larger than the pipe itself? Supply pressure is fine. (borehole pump maintains 3 bar up to 40L/minute on a 32 mm MDPE incomer)

Useful to know @JohnMo Return temperature based compensation perhaps? (shove the water in hot enough that it comes back at X degC / poor man's slab temperature sensor)

With a slab temperature controlled by a weather-compensated / load-compensated heat pump? (avoiding all those room stats and the associated zone valves)

Mmmhmmm They're using an ecodan too. So not the most performance oriented outfit. https://heatpumpmonitor.org/ Or ecological outfit (it's an fgas unit and not even a particularly low gwp fgas) I'd ask for a 2nd opinion. Most of those ecodans appear to get sold into use cases where the Mitsubishi rep has done all the homework) badly) for some eco grant funding application etc. It wouldn't be the first choice unit of building a passive house where performance and low modulation etc are important.

And your MVHR or exhaust air heat pump will pickup the excess heat and dump it into your incoming air or the DHW respectively; so meh?

Bare tiles vs women's feet. Bare tiles at <25C feel cold barefoot. (some heat pumps have a "enable minimum return temp" setting for summer use that keeps the floor heating circuit at 25C for this purpose) Wood on the other hand feels fine. So do rugs. Rugs on wood even more so.

Primary side @Nickfromwales Pump through the DHW coil then then space heating circuit. (with all other zones off)

I'm grappling with similar. You can't run a heat pump at tiny load. It will need to either dump a shedload into a thick slab then shut down or you'll need to use a volumiser/buffer type setup to allow (a) a high enough minimum flowrate for the unit to operate and (b) sufficient active system volume for it not to short cycle. Burn and coast into a slab is only viable on the ground floor. First floor needs something else. Run the math on how much heat the heat pump will lose (in the case of an outdoor mounted unit), the volumiser/buffer will lose, all the spaghetti from heat pump to/from the buffer will lose, and all the pipework from the buffer to the UFH zone will lose...vs the actual heat delivered into the floor...and I doubt you'll beat a temperature-controlled direct electric setup for a small bathroom. Especially if you then need to take that heat out of the rest of the house with active cooling! There's some argument for using the DHW cylinder as a buffer for the heat pump. You have one anyway. You could run water through the DHW cylinder coil to pinch some heat into the UFH, and allow the heat pump to reheat the DHW in the usual way. That avoids you having a dedicated buffer. I think @Radian toyed with similar. It's less sketchy than using a DHW recirculation loop through a potable rates brass/stainless towel rail for heating bathrooms... I think I'm going to do that AND fit an electric mat / sensor (given the stuff all cost of it now) before laying the floor. Then I'll probably use a wooden floor finish (on top of a suspended wooden floor), in what is otherwise a warm building, and never ever use the UFH. (that's what happened in the house in Cambridge - if you do wood rather than tile you don't need the underfloor heat) So yeah. What @Nickfromwales says. As usual. But perhaps do some head scratching about how you would suck heat out of the DHW tank for running the wet UFH (and the towel rail) in the summer. The COP isn't amazing when heating DHW to 50C but it's better than 1.

Hi, I put this to one side of a while but I'll need a solution before say Christmas. Did you do my homework in the interim by any chance? 🙂

Brass inserts for brass fittings on mdpe?

A brass BSP>mdpe adapter perhaps? With some loctite 55 wound hard into the existing BSP fitting? Plastic BSP fittings will creep if wound tight anyhow.

The fixed windows are ok. Small openers are ok. The French windows are only viable after heel/toe AND and gluing in the glazing. The handles were mismatched by ~4 mm too. The low thresholds are absolutely horrific. Never again. Compare with a cheap rehau frame (e.g. euro 70/total 70) let alone a vaguely decent on (e.g. synergo) and it's absolute night and day. Fine for the odd small window in a house you don't much care about. I wouldn't buy again though.

Not built like this before. Thinking out loud though: Treated sole plate. Sip /sole plate starts at structural floor level. Insulation and floor screed raise raise floor level (fill in between SIPs) and eliminate sole plate thermal bridge. Airtight the poly under the screed to the walls. Done? Airtightness avoids drawing in loads of moisture from outside during heating season. The sole plate dries to outside via ventilated rainscreen. Just like the rest of the sip. And indeed the floor insulation. Where would you need marmox? Useful on door openings perhaps. Can't see it being useful elsewhere. Lifting the sole plate will surely make more of a bridge (1*45 mm through wall) than the OSB otherwise would (1*11 mm down through floor insulation) especially once that sole playe has been fastened down? For rot I would worry more about joints between sip panels and especially those at roof level where stack effect will try to drive moisture through the gaps in a far more concentrated way than you might otherwise get with a stick build. Top layer of roof sandwich then turns to Weetabix.

Ah! I'm about to move the A2A upstairs in Cambridge and chuck in an A2W for rads and DHW downstairs (plus rads upstairs because there; but mainly for downstairs) Will be a single head to upstairs landing though (open the doors during the day to cool); and would like to think I might get around to trying wet ceiling/wall heating downstairs (easier to retrofit as a plasterboard layer under a ceiling / onto a partition wall than it would be to wet UFH; and with higher output per m2 at a given flow temperature; albeit not as comfortable as UFH) Not too dissimilar in conclusion. 🙂

Or build for a smaller heat loss / larger solar gain and use +3 kW / -2 kW for everything?