IanR

Just read a bit of one of the articles you linked to and I believe the point it was making is that the air permeability tests measuring at 50Pa are over-estimating "general" permeability as the pressure difference is "typically" between 3Pa and 6Pa. The article didn't appear to be considering the max energy loss, but rather what the background ventilation rate is, so it would be correct for it not to consider worst case. (But I have not read the whole article.) For your max energy loss calculation to size your heating system to, you should use air permeability at 50Pa (windy day), 30 degree temp delta and ensure there is some head-room for hot water production.

Your energy loss also works out at 15W/m². You've done exceptionally well on a refurb if you've achieved that. 0.43 ACH is very low. Specialist builders (or self-builders), doing a new build with lots of tape and gaskets for all penetrations would be very happy with that level of air tightness. Have you got mechanical ventilation? you need it with that level of air tightness in order to bring fresh air in. If you've done lots of working fixing all the leak paths then I'd go with 3ACH on a refurb, and somewhere between 5 and 10 if you haven't. Better to over-estimate the energy loss, rather than under spec the heating system. Without the UFH you can expect to pay £10K - £12K for the install from a decent MCS installer. With the cost of the UFH on top, it depends on the work and the spec, but the price sounds a little expensive. Have you tried Eco East Anglia? The RHI is to cover the cost of the ASHP & UVC, over and above what gas combi would cost. Are you saying that's unlikely due to you not being able to get it commissioned by 31.03.2021?

Seems low for a refurb. What's you internal floor area? what Air tightness value did you use? and what inside to outside temp delta have you based the calc on? My total energy loss at a 30 degree delta T is just under 15W/m². My U values are Walls 0.12, Roof 0.11, Floor 0.09, Windows and Doors 0.65, no/minimal cold bridging and air tightness is around 0.1m³/m².h@50Pa Edited to add: Actually, that's my calculated energy loss which used an air tightness of around 0.4m³/m².h@50Pa iirc, rather than my actual air tightness.

Ref. https://www.vent-axia.com/file/792933/download?token=6vlpcIyG It also states:

Without an air tightness test there is no knowing even if an MVHR will be effective at heat recovery. Opening a window is likely a better option. Today's Building Regs in England require an air tightness in a new build of better than 10m³/m².h @50Pa. MVHRs are ineffective (for the heat recovery portion) at more than 5m³/m².h @50Pa . At less than 3m³/m².h @50Pa building regs wants centralised mechanical ventilation to ensure sufficient fresh air. It's unlikely a 2012 house, built by a volume builder has achieved better than 3m³/m².h @50Pa, unless a subsequent owner has done lots of work to improve air tightness. If you are feeling it is hot a stuffy up stairs, there could be plenty of air flow, but the fabric of your building has heated up and is rewarming the fresh air as it comes in, giving you the impression there is no air flow. Dormers and rooms in roof are especially prone to this.

Hi Nick, and welcome. All the points you have made are valid. The only one they could argue is the 3rd. While the fixings do not look substantial enough, it hasn't failed (yet). But I wouldn't be happy with it. As per @MJNewton, I'm more concerned that MVHR will not fix your issue, and is not required in your house. Why do you think it is "air tight", have you had an air infiltration test done? Do you know the air tightness figure for the house? When you say uncomfortable, are you referring to excessive heat? Are you a full 2 storey, or do you have rooms/dormers in the roof? If the MVHR was installed to get rid of the excess heat, unfortunately it will have negligible effect during the day when it is hot, and only start to help overnight when the ambient temperature outside drops.

Not for then pumping into homes for heating, as far as I know. It seems to be being considered as part of the energy storage mix for power generation, although co-located with Nuclear and powered by excess Nuclear, when renewables are fulfilling the demand. Whichever way, you can't then consider the excess usage for hydrogen production to be free or low cost, if you're able to make use of more of the renewable energy generated, then it lowers the overall cost of that energy, which is a good thing, but it still requires 6 times more of that energy to heat a house with hydrogen, than it does with a heat pump.

Are you paying the builder in instalments? If the planning you have at present is for an extension, then the builder will need to charge you VAT for that work. He'll only be able to zero rate the invoices once you have Planning Approved for the demolition and rebuild. You won't be able to recover the VAT charged on the invoices from the builder prior to when you have the new Planning is Approved. The HMRC recommendation for a build that changes from an extension to a demolition and rebuild is that all work stops until the new build planning is in place.

I believe that current commercially viable green hydrogen production requires 2 - 2.5 kWh of renewable energy to create 1kWh of hydrogen.

Not if it were the stepping stone that created a secure hydrogen demand for investment into green hydrogen production, that brought about the Unobtanium discovery. But, if we get to 2040, and Unobtanium has still not been discovered, meaning that a home heating system powered by 100% green hydrogen is still requires 6 times more renewable energy than one powered by a heat pump, then we'll have to do in 10 years, what we currently have 28 years to do, or more likely, we'll miss our 2050 commitments.

20% hydrogen can be run into standard boilers without any changes. Green hydrogen at 20% blended gives about a 7% reduction in CO2 due to the lower calorific value of Hydrogen. The Gas industry is lobbying the government hard to get Hydrogen as an option for heating homes, without it the gas network asset they own has no value. Blended grey Hydrogen is being pushed as a stepping stone to, blended blue hydrogen (made from gas but with CCUS), and on to 100% green hydrogen (produced from electrolysis using renewables). The lobbyists are pushing hard for a door to be left open for Hydrogen "ready" boilers. A recent unofficial press briefing is suggesting they've got their way. My view is this is a disaster for Net Zero by 2050 if they have. Blue hydrogen is being mis-sold and over-promised by the gas industry. The process releases more climate change gasses than burning natural gas directly, when you include the fugitive methane released. Heating your home with green Hydrogen would require 6 times more renewable energy than heating it with a HP. We will struggle to build the amount of renewables required to achieve Net Zero by 2050, without needing 6 times more of them for the heat in buildings part of the equation. (Unless the Unobtainium catalyst is discovered mentioned by @SteamyTea) Green Hydrogen is definitely needed, to replace the 70,000,000 tonnes of grey hydrogen current produced plus de-carbonising the industries that are hard to electrify. Unless there is a breakthrough in green hydrogen research that significantly reduces that amount of energy it takes to produce it, its going to struggle to replace the existing uses for hydrogen, let a lone find new uses. If a door is left open for hydrogen ready boilers, in the hope of a research breakthrough, there's going to be a very low take up of ASHPs in the existing housing stock, and ASHPs are the only current clean technology that can get close to the the day-to-day running costs of a gas boiler.

Ah, yes, the original Z purlins. While most were replaced, I had to keep the Z purlins to keep the original structure standing. Going through the PHPP process, It didn't feel like the single story was a negative (but I agree it is), you just keep tweaking different aspects until you get all the requirements in the box. I've not had to go for an excessively thick insulation to achieve the targets. The hardest "negative" to mitigate was the amount of glass I went with, and no opportunity (due to planning) to build in fixed shading. This was an over-heating issue, resolved with external blinds and tinting on the roof lights.

I suspect you're right, certainly from 2025. HP installs will drop with selfbuids if they don't offer some incentive from 2022, the Regs change isn't sufficient to force HP installs from 2022. Current RHI isn't intended for new builds, but self builds are allowed. Maybe the new grant will be the same from 2022-2025.

It's a converted Cow-shed. 465m² foot-print. All habitable space on the ground floor, due to planning, but a 6.5m ridge, so +200m² of height restricted "storage" on the 1st floor. Cullen Timber Design can send a full cutting list to JJ I-Joists, and send a set of Assembly drawing for you to put together. But Touchwood did a half-and-half. Difficult cuts to measure cut by JJ I-Joists, and then several loads of 13m joists that they cut on site. Sole and Eaves plates were all pre-cut and had a 3mm deep slot cut for every upright beam position into. Once Touchwood got the sole-plates laid out and fixed, all the uprights just got placed in with barely any measuring. Accuracy was first class. Window openings were within a couple of mm. My Warcell areas were 196.6m² of 300mm thick & 416.4m² of 350mm thick. 26 bales in total, installed by Payne Insulation (Norfolk) for just under £15K. They were grumbling at Warmcell's pricing going up and up back in 2017, and were talking about a cheaper alternative from the Czech Republic, that was pretty much the same product. Not sure which beam you are referring to. On which Picture?

No pipes run in the insulation. I couldn't avoid a service void in one room ceiling and external wall to get some pipes to some taps. I've got wall hung WC frames on a couple of external walls, but just put them in a false wall.

I'll have a look for pictures. Cellulose was blown in through 100mm holes in the PB, which is a down-side as they all need to be but back in. Yep, wiring through the webs of the I-Joists and down the lengths of then. Very easy for penetrating the outside (airtight) sheathing and gasketting all the holes to seal.. Edited to add: Here's the only image I have of cabling into the insulated area...not much good. But some more general ones of the frame

Roof is same build up as walls. I just have 350mm I-Joists in the Roof, where as 300mm in the walls. This is where PHPP comes in to it's own, and shows you where to spend your money. Single storey Buidings, with their proportionately larger roof area, benefit from more insulation on the roof, and PHPP gives you the sweet spot. Yes, racking is to stop lozenging of the structure. Most timber frames would have an OSB layer for this, but the DHF allows you to avoid it. You do need a breather membrane on the DHF to protect the structure. I have standing seam on the roof, so it's battened 50x50 for ventilation and then 18mm OSB deck, another breather membrane and standing seam on top. For the walls I have a mixture of horizontal and vertical timber cladding, so either just battened, or battened and counter battened. The foil back plaster board takes care of the vapour barrier, so no separate membrane needed. The build-up can easily shift a bit of moisture so you don't need to be too anal over penetrations in the PB for switches and plugs etc. - electrics can run in the insulation, it just plumbing you'd need to run a service void for. I'm not familiar with hemcrete, I'd assume it has a good decrement delay ie. +12hrs, but you should check. Blown cellulose really does, so makes the build up perform better keeping a more stable internal temperature. If you've not got a masonry skin, it's really important to have an insulation with a long decrement delay.

Hi William, welcome! To give you a few names, to help with your research, I have an I-Joist frame from Touchwood Homes. I hope Touchwood are still running, but I notice their website is down. They do have a FB Page, although that's not seen any recent activity. Touchwood specialise in PassivHaus timber structures. I've noticed one of the brothers, Reuben, has started up a new venture. Mango Projects. They look to be advising on PH builds as well as designing and installing MVHR systems and other services. Reuben appears to have Dr. Rod Williams, of Williams Energy Design, working with him at Mango Projects. Rod is, amongst other things, a 1st class PHPP designer and would be able to help and advise the most appropriate layout of your site, as well as getting into the detail design to deliver the best possible performance, for a budget. Rod did my PHPP design. https://mango-projects.co.uk/2020/05/28/who-are-mango-projects-ltd/ Touchwood's timber frames were/are designed and engineered by Cullen Timber Design. They'll design any type of timber structure you want, but, with Touchwood, they have developed a very simple, high performing build process, and are very used to designing out cold bridging etc. for PassivHaus builds. http://www.cullentimberdesign.com/ With Touchwood Homes erecting the Cullen Timber Design frame, and filled with blown cellulose fibre insulation, they guaranteed better that 0.2 ACH air tightness, and often achieved better than 0.1 ACH, as they did with mine. And all without an air-tight membrane, just foil backed plaster board, on to the I-Joists and externally sheathed in T&G Egger DHF sheathing board (with a few construction tricks to ensure air tightness). The DHF board is the air tight layer as well as the racking strength, so no need to OSB internally, unless you want a service void. I used Advanced Foundation Technology (AFT) for my EPS insulated raft. AFT have done a number of rafts to suit Touchwood's I-Joist structure, and have a very simple solution for eliminating any cold bridging. As well as engineering the foundation, Olof at AFT will also come to your site and help you install it, incl. UFH, if you supply a couple of labourers https://www.advancedfoundationtechnologylimited.co.uk/

The EPC also also states your properties heat/energy loss calcs, but they are done in a different piece of software, so should directly effect these calcs. Air tightness is measured at a 50Pa pressure difference, between inside and outside the house. This way of measuring is common across Building Regs, EPC, SAP calcs. They don't state their AC/h figures are @ 50Pa, but I'd assume that they are. I guess their software could calculate energy losses with air tightness at a lower pressure difference, but it's unlikely. Building Regs, EPC and SAP calcs actually use a different unit to AC/h (Air Changes per hour). m³/m².h @ 50Pa is typically used. AC/h is measuring how many times an hour the entire volume of air is exchanged in the property, and the other is measuring how many cubic meters of air, for every square meter of the thermal envelope (ground floor, external walls, top floor ceiling) are exchanged every hour. By coincidence AC/h figures are generally quite similar to m³/m².h figures, for normally proportioned houses. Maybe 1 AC/h = 1.25 m³/m².h in average terms (although this will vary from house to house). Max Air Infiltration to meet Building Regs for a new build is 10m³/m².h, A well built (mass produced) new build will be around 5m³/m².h Older properties will be much, much worse. If you drop below 3m³/m².h, building regs expects you to have whole house mechanical ventilation, to ensure enough fresh air is entering the house Putting 1 AC/h, the equivalent to 1.25 or 1.5 m³/m².h for your property is under-estimating the energy losses due air infiltration, I believe.

It doesn't sound good. They should have used around 10 AC/h for your air tightness, and -3° is not low enough for worst case energy loss calcs. I'd ask them to take you through their calcs. Maybe they'll have an explanation.

18°C Design Temp seems a little low to me, did you give them this as your target internal temp? It would be good to know what outside temp this was done for. Are you very air tight? The Air changes per hour ranging 1.0 - 3.0 is low for a "normal" house. The 5021.29 kW figure is the Total energy loss (assuming all rooms are shown on the sheet), at whatever outside temps they've allowed for. So you need 5kW of energy from your heating system to maintain the Design Temp. A 6kW ASHP doesn't provide much headroom for hot water production, nor raising the temp if you've let the temp drop. If they've used a very low outside temp, say -10°C, then maybe this would cover the lack of headroom. But, with the low design temp, low AC/h, and lack of headroom, at first sight the heat pump looks a little undersized. Edited to add: Do you historic data for how much Gas/Oil/LPG you used to use annually?

You may be surprised, roughly £8,400 from RHI over 7 years. From https://renewable-heat-calculator.service.gov.uk/StartCalculation.aspx Just make sure you change the default SPF (SCOP). I've set it to 4.2, which is easily achievable. A higher grant is available if you choose an ASHP with a higher SCOP.

You are probably right. What's your annual space heating energy demand, off your SAP? I did say "most" cases. But the lower the demand, the less you get with RHI.

But this is a reduction in grant available for heat pumps. RHI offers more in most cases, and significantly more. I believe the new grant may well not be available for new builds either - certainly after 2025, and quite possibly from April 2022. Legislation is being used to tackle new builds.

The Passive House Planning Package. Energy loss/gain calculator for PH Design