Kevin Dawson

Thanks all, some good (and sometimes spirited) input and opinions on here. For sure everyone's needs and approaches to their heating systems will be different to different degrees (no pun intended) but the value of forums like these is the diversity of the Q&A that offers those different perspectives from which we can all learn - so keep it up. Anyway, the original question remains - anyone here with a certified PassivHaus from an MBC timber frame who'd be willing to compare some notes?

Technically yes but the (small) heat pump in the Compact 9 is primarily there to manage domestic hot water production (integral 180l tank) with some residual ability to manage air temperature up or down as appropriate and in an ideal world should be all we need. However, given the heat load and TFA the modelling showed we'd also need either the Air 9 ASHP or the LG and the LG gave us a bit more flexibility with its indoor heating/cooling ducts.

Good to know - and if needed, with the UFH zones we've laid in we'll be able to warm the entrance hall/stairwell and en suites for some extra warmth whilst still leaving the bedrooms off. Fingers crossed.

We're not fitting the Nilan Air 9 ASHP at this time - the Compact P provides 180litre DHW and MVHR, the LG (MU3R19.U22) provides heating & cooling as necessary (5.3kW with a spec'd COP of 5.0). We have multi-zone UFH pipes screened into the GF slab but will suck it and see initially before deciding whether to fire them up as this is the bedroom floor (living space is upstairs). Watch this space as they say.

We're committed and en route down this road/rabbbit warren and would love to be able to sanity check the journey with anyone who's either been there, done that or is already on the same road. For reference - approx 200sqm TFA (circa 20m x 7m externally), two storey (upside down), MBC Passive TF with insulated slab, exterior to be vertically clad in larch (aside from the bottom 50cm which will be stone walling). Nilan Compact PXL MVHR with LG ASHP. Location Somerset. Thank in advance.

We're about to start breaking ground on a Passivhaus Low Energy 200sqm two-storey MBC timber frame house build and the architect has asked if there's a fire hydrant within 100m of the site. No, nearest hydrant is over 300m away although there are 4 other (old, stone built) houses on the same farm/immediate vicinity to our plot who are all on mains water (as far as we know) but we have a borehole - 200+ metres of mains water piping across several farmers' fields or 300m up the track was too big a deal. Hadn't planned on any sort of mass water storage for fire purposes (guessing that'd be a very large hole - and no, our plans do not include a swimming pool) or any sort of sprinkler/mist suppression system (do I understand that Wales now mandates these?) There's nothing in the planning consent about fire mitigation and we're about 40m fro the nearest other building. Are we walking into a bunch of mandated but unplanned cost here or is this a discussion with our (non-local planning) BC officer about all the "should have" text in the Merged Approved Docs? Thanks in advance.

@JonDoe am just pressing the button on a Compact P XL for our newbuild and would also like to know how you integrated it with HA (the Nilan guys closed down that discussion when I asked if it was available/planned). Thanks in advance.

Another data point - for our basically 200m2 liveable area MBC two-storey Passive house and UHF-piped & screeded slab - with a couple of extras like a 3m roof extension over a balcony, a full OSB cover for the planned standing seam roof (from others) and their external masonry footing - comes in at almost exactly £200k of which £50k is for the window/door set, all erected/fitted and airtight to less than 0.6ACH. Hopefully going up just before Xmas '24. So £1k per square meter. If anyone out there has a certified MBC house I'd be interested to compare notes........?

We have the same limit in the UK but our sample was "only" 6x the limit as compared to over 45x for our aluminium. The only other issue was a 1.8x ammonia level, everything else was ok.

No, design isn't nailed at all. The borehole company sent the first (independant) lab report direct to their usual company to put together a "proposal" for the filtration/treatment plant for us and what came back was a (very unexpected) £13k plus VAT list of bits including a week's labour to install and commission it all. We asked a couple of other treatment system providers to cast an eye over the lab report and the shopping list of bit and whilst they basically agreed the list wasn't too far away from they might propose they both instantly said "that aluminium level says the well wasn't properly flushed before the sample was taken" so hence we're now leaving it pumping out for a couple of weeks to confirm the sustainable rate we can drsw from it and hopefully get a more representative sample to retest.

1243ug/L - not as far off-base as the aluminium numbers but (assuming the next sample is as high) will need addressing.

Aluminium in the initial sample was at 9243 ug/L 😱 - consensus was that it wasn't flushed well enough before the sample was taken so we're going back round again right now.

Agreed, I was just roughing the math to see how much I could credibly draw out being having to leave it to rest. Right now it seems as though it'll sustain at least 120litres/hour for 12 hours without stopping because it's been drained. Now we can check whether and/or how much it drops over consecutive days or whether that's sustainable (at least for the current conditions down there).

Thats's a given 🙂 Ok but doesn't that then mean that if I want say 150litres for a bath then my accumulator and its HW equivalent in my MVHR will be pretty much spent and as can only pump say 2 litres/min average out of the borehole am I not creating a problem? Obviously I can pump a lot more water out of the borehole but only until its immediate capacity is exhausted - thinking aloud here - I believe it's a 20cm diameter hole that was drilled so every 3cm would contain about 1 litre, 33 litres/metre, 330litres for every 10m of borehole so actually maybe not a problem after all? Guessing the borehole pump is triggered off the pressure drop in the accumulator in this model? How do I best size the accumulator? I was just envisaging pumping through the filters until I had say 1000 litres of clean water in a tank and topping that up once the water level had dropped (to say 500 litres) but was missing the means of pressurising the supply into the house. Thanks again

Thanks @JohnMo - I think what I'm needing is some sort of basic diagram showing how this would all work - the borehole pump is ok as is a black box saying "filter//treatment here" but how the various other pump(s) and storage tank(s)/accumulator(s) work together to replace what we've previously just enjoyed as a mains stopcock that sprays water at pressure every time we open a tap. I believe that the new version of BS5422 is what we'll (theoretically) be held against by building control so have to plan on insulating both the hot and cold radial runs from the manifolds to each outlet. To your power cut point we'll have PV and some battery storage so expect to protect the water pumping with that as a priority. Thanks again.

@Alan Ambrose strange isn't it, buy a plot with great views and then not have any windows - what are we thinking? What is the J Harris spreadsheet? Interested to try it out and yes, will see if I can get a copy of the PHPP one.

Good questions @IanR Windows are Rationel triple-glazed Auraplus (haven't considered coating options but will check). Brise soleil was added (to the mostly glazed face that is now mainly north facing after we rotated the house clockwise 25 degrees to improve the view and reduce the solar impact) but there is still a fair amount of glass on the "western" face (about 17m2 - about 20% of the wall area) and slightly less on the eastern face. To @garrymartin's points - good catch, yes 14W/m2, the house is upside down in as much as the living/dining/kitchen are all upstairs and open plan and yes that is a vaulted space to the ridge along with the stairwell. According to the architect the total GFA is 108m2 upstairs and 98 down. Site layout including the orientation attached for reference. Note also that the left hand end also has a 3m roof overhang covering an upstairs balcony and downstairs patio) which obviously shades that end and its two sets of 4m glazed doors. @Russdl the PHPP consultant is a certified PH designer within the architectural practice and there is an external/independant certifier reviewing the model for certification purposes so hoping that between them it should be reasonably representative.

The floorplan is a simple 20m by 6m rectangular "barn" and whilst the final PHPP is still being worked on and reviewed by the certifier the initial modelling showed a significant likelihood of overheating so we reoriented the long axis more northwards and debated various shading options but the design issues were a projected heat demand of 24kWh/(m2a) versus a limit of 15 for Classic certification and a projected heat load of 14kW/m2 (versus a limit of 10). So it looks like it'll be certified PHI Low Energy rather than Classic.

Some questions for the hive mind if I may........ For context we're doing a 200m2 two-storey newbuild with 3 ensuites downstairs and kitchen and shower room upstairs (ignoring the odd utility room/workshop taps and washing machines etc) which is about 300m from any mains water supply so had a 75m borehole sunk in the hope that we will be able to get sufficient volume and quality of water. Initial flow rate looks to be around 120 litres/hour in the steady state (still testing) so not massive but as there's only normally two of us I don't think that's a dealbreaker. Lab testing of the first sample showed (amongst other things) very high aluminium levels that several companies simply said "not flushed properly/sufficiently" so we're currently leaving it pumping 12 hours/day and then resting overnight to let it settle (and check the volume extracted is consistently viable) before we retest it in a few weeks. The borehole surfaces in what will be the end bay of a garage so plenty of enclosed (but unheated) space for pumps/filters as needed but at that point my questions start.... The house will be some 25/30m away down a slight gradient so expecting to bury a 32mm MDPE pipe (yes/no?) to get water into the house from the garage where I'm envisaging a 1200litre potable water tank (yes/no?) which would be topped back up overnight on the output of whatever filtering/processing we end up with but how and where do I generate enough pressure to ensure my taps/showers etc all work satisfactorily? Our DHW will be coming from a Nilan Compact P XL which has an integral 180litre ASHP heated tank and the plan is to fit a pair of hot and cold manifolds in the same plant room (in the house) with direct pipe runs to each outlet. Am thinking to have 10mm insulated pipe runs for all the basins/toilets and utility feeds (yes/no?) with insulated 15mm pipe runs for the showers and bath (yes/no?). Will 13mm Armaflex suffice over those or should I go thicker - or change to Kingspan Kooltherm phenolic (except they don't appear to do that for 10mm pipes meaning I'd just have 15mm everywhere)? BS5422:2023 looks like it'd be happy but aren't the condensation protection calculations/table still work in progress? Biggest concern I have is having adequate water pressure without the mains supply - don't need to be showering under a dribble or waiting an hour for a bath to fill. Be gentle please, thanks in advance.

My bad - playing a bit fast and loose with the terminology. It's the MBC Passive Wall structure sitting on their Passivhaus certified slab - we've just gotten a bit lazy describing it to friends.

Repeated visits to the NSBRC in Swindon ended up with us deciding MBC’s offering worked for us.

Hi - starting work on a long term ambition here - self-managing a greenfield passivhaus build (SIPS panels over an insulated raft, timber clad and standing seam roof), aiming for certified low energy (PHPP model says we can't meet Classic levels). Have done several house refits and improvements/extensions over the years but this is a in different league so hoping to be able to pick some collective wisdom from the forums here.