joth

If the overarching goal is to reduce energy use, you're probably better not making any changes to the windows as the winter losses are likely greater than the shoulder season gains, just because of the difference in temperature is that much higher in winter. Instead add some solar (PV or thermal) to capture shoulder season radiation and reduce cost of the internal heating. So I'd say only consider adding glazed doors if they will add aesthetic and utility value as well as solar gain increases. And then as you say it's about maximizing desirable gains Vs reducing undesirable gains and losses: 1/ unwanted winter heat loss All windows leak heat through the frames just as much as the glazing, especially once you're at triple glazed levels Bifolds are a particular issue as having a higher ratio of frame to glass, they also struggle to get such a good seal due to their shape. In terms of energy efficiency the preference order is approximately single door, french door, lift and slide door, fold and slide door, bifold door. So If you're looking for the whole wall of glass/bring the outside in Kevin McCloud moment, I think a big slider or fold and slide doors maybe best choice. Even so, the winter losses will always be higher than a solid insulated wall. 2/ unwanted solar gains The sun is higher in the sky in the summer so many solutions work on the angles, e.g. recessing the glass in the reveal, pulling the eves low over the windows, or install external awning or brise soleil to throw shade over the glass in summer, but in the shoulder season the lower sun can get in under it. Assuming there's a patio out there, a big retractable awning could work well and serve multiple uses. Else there's shutters or smart glass tinting but they have drawbacks (limit size of door, cost). If still undecided a detailed energy survey could help with all this.

The VAT savings on demolish+rebuild make that a surprising economic option - basically the more work you're planning to do all in one go (flooring? electrics? plumbing? kitchens and bathrooms? etc etc), the greater the case we'll be to knock it down and get the whole lot VAT free. And as you say, you'll then get a much better end result for the money.

Yes, it's very likely there is no DPM back then - we're pretty sure our 1960s doesn't. We're planning to remove our entire slab to insulate so following this with interest. Are you planning underfloor heating? This in particular helps from redoing the ground floor insulation

I think CoP could technically go below one if it spends more time on defrost cycle than actually heating, maybe? Otherwise, some idea of not wearing out the expensive heat pump working so hard is the only reason I can imagine. And noise. It would save on some noise.

Surprising there's a whole housing development without any three phase supply nearby. Regardless, if they're all in this same state, it would seem the ideal situation to invest in a shared ground source loop.

If I understand this correctly you've already removed and disposed of the tiles? That is the more dangerous step especially if the tiles broke up while being removed. The bitumen layer that remains will have trace amounts but that should remain encapsulated in the tar and much less likely to get airborne. There are online asbestos testing services you can use, not sure how much use it would be in this instance though. If you're digging out some of the concrete anyway, strongly consider just digging up the whole floor. This will save on dealing with that bitumen and more importantly allow a descent amount of insulation to be laid under the floor, at least 100mm of EPS/XPS generally recommended.

On a sample of 2, Green building store and Enhabit were both very happy to quote for design, supply and commissioning. Neither seemed particularly interested in doing the install work. If you have a radial topology the install is very simple. However looking at you linear layout a trunk and branch might be more efficient. Still not terribly complex to install from what GBS said.

Fwiw I'd first look into doing the install DIY as that's the bulk of the cost and very easy to learn to do, then get in someone experienced to commission it. Green building store recommend this approach (saying DIY install is often better than paying e.g. a builder to do it, as generally the DIYer will take their time and follow the design more accurately) There's certainly an argument for learning to do the commissioning so you can maintain and adjust it if needed in future too, but for for a few hundred pounds I'd prefer to know it was at least initially all running correctly.

The garage would not normally be recommended place for the MVHR as it's outside the thermal envelope: it works more efficiently to have it inside the envelope.

Passivhaus institute, that make the rules of passive house and who's database you linked above.

The NIBE one you link has Heat recovery rate: 79 % What am I missing? Also note, like windows, PHI a different way of calculating effeceiency to everyone else so either just use their numbers or the manufacturer numbers but don't try and compare across them

Wooden, but I think their external grade doors can have metal frames. I do agree with others that a well fitted UK style door shouldn't rattle, but I've seen many that do, and often it seems to develop over time. On the other hand a rebated door had three separate interfacing faces, so feels more robustly solid yet reassuringly "soft close" than a single leaf clattering against the jamb - maybe like closing a high end Mercedes door Vs your old Ford Cortina.

For me a large part of the "solid" feel of a door is how well it sits in the frame (jamb) when closed and the mechanism of closing. I noticed this visiting Switzerland, Austria & Germany last year and realized it was because of the rebated door design and rubber seal / baffle that all the doors use there. As well as a much more satisfying action on closing and opening, there's absolutely no "rattle" to the doors when closed which made me seek this style out for our renovation as we have a trainline nearby which mostly don't notice except around 4am there's a heavy goods train of some sort that can rattle the current lightweight doors. This is about the only supplier I found in UK for European doors, happily not too far from us https://www.doors4uk.co.uk/what-is-a-european-style-door-with-frame-and-architrave As you see there they sell the benefits of reducing drafts and energy saving -- not so relevant if the whole house is well insulated and draft-proofed (not to mention building regs + MVHR require 1cm gaps under the door anyway), but it's mostly for that well engineered rattle resistant sold feel I'm going for them.

How are you controlling the circulation pump? At the very least this should be on a timer so it just runs for a couple minutes in every 20 . Ideally you can trigger this based on motion sensors near the rooms it supplies - but that's OTT if you don't already have the motion sensors. Reducing the UVC supply temp will help reduce the loss & overheating, although you then might need increase the circulation pump freq a little bit more often to compensate.

@AliG ah without an export meter it'd be very tricky to do any useful measurement unless you can remove all the other load (e.g. trip all breakers briefly). Btw 3x inverters could be ab expensive way to do this, one 3-phase inverter is less than the price of 2 single phase inverters, in the quotes we got The A1140 is the one I pasted a link to install manual for upthread. Useful to know that they're used by some suppliers, can I ask which co. installed it for you? although there's about 8 different ways they can be configured so it depends on the specifics of the install. Indeed, I spoke to new connections team at two suppliers yesterday and they were both hesitant to make any statements about how a 3phase meter gets installed other than say it's a specialist job, takes longer, costs more, and they often have to go back and fix it when they discover it's been configured wrong or running backwards or whatever. The smaller supplier actually recommended going with a Big 6 supplier to have it installed, then switch to then after it's in. None has any timeline for availability of SMETS2 polyphase meters, but at least when they do eventually become available the metering is well defined in Part C of the spec: it will indeed sum usage across phases prior to metering so no penalty for exporting on 2 phases while importing on a third. Also speaking to DNO they are totally fine with installing 3ph to the cutout and actually said they don't care one jot how we load the phases - we could entirely not use 1 or 2 or them, that's regularly what they see with London houses split into flats.

Great! Do you already have the immersion heater? (Or, a standard kettle) and is the system already commissioned? If so you can answer this question for both of us by waiting until a sunny day (>3kW generation), and turning on the 3kW single-phase source, and seeing if your import meter increases or decreases. You'd need to run it for >20mins to see 1kWh of usage. I presume you also have an export meter? In which case it'd be equally useful to know how much that increases by.

This page also confirms via experimentation that existing (non-smart) 3ph meters only charge the net import, in fact explaining it in terms of the 1Wh bucket the same as a single phase meter uses to smooth over import/export fluctuations https://openenergymonitor.org/forum-archive/node/1613.html I.e. each phase contributes into a single shared by bucket I'm going to assume the statement upthread that phases are metered independently only applies to commercial users (which will potentially also be liable to kVA and phase balancing metering too)

Politically it'd be very tough to impose kVA metering on domestic 3ph users as part of the already widely disliked smart meter upgrade. And by the same token why not do single phase users too? Also I think there's a large risk of unintended consequences here: the world you describe of penalties for anyone using 3ph in a non-perfectly balanced way will force everyone to stay on (or request a downgrade to) single phase. If the goal is balancing demand as the energy market electrifies, they'd be better off doing everything to encourage 3ph installs in homes even if only the occasional appliance (e.g. the heat pump) would use it at first. Anyway, back to my previous question - do you have any source for information on how 3 phase smart meter will work, or is it educated guesses? Thanks.

Indeed - I'm not questioning how a 3 phase inverter works, the question is how a 3 phase smart meter works. If the meters will actually sum the phase power usage prior to metering, then it doesn't make any difference if you feed generation into 1, 2 or all 3 phases, or in what balance: in all cases generation will be automatically optimized to reduce to domestic consumption prior to contributing to export. This is the point the SMA video most clearly makes. It'd be useful to know country that's aimed at, but regardless -- if that's the metering mode that inverter manufacturer’s are all designing for then there will be a good deal of pressure on SEG 3ph metering to accommodate it.

I've been researching more into this, and now wonder how you know this - I guess it's based on observing existing (non-smart) 3 phase meters? For metering export, the long term answer will be up to whatever Smart meters will measure. But for all I can find no one yet will supply a 3-phase smart meter, so it's hard to have any empirical evidence how they will meter simultaneous import+export. I'm starting to convince myself that smart meters might sum the phases before figuring a net import/export measure of usage, based on sources of varying provenance e.g.: 1/ "ted" at the end of this thread 2/ This australian(?) presenter from a German inverter manufacturer (SMA) 3/ This australian supplier 4/ The best guess of the tech support guy at my solar supplier (GB sol, via email) The nearest I've found to a technical manual on the subject is for the Honeywell Elster A1140. But page 13 got serious about metering of inductive vs capacitive loads, power factors and mismatched phases, at which point I figure that's for commercial rather than domestic usage anyway; and certainly not UK "smart" meter. The only supplier offering smart export tariff today is Octopus, and they don't yet support it for 3 phase. Putting it all another way: the Smart export guarantee hasn't yet started, 3 phase smart meters don't yet exist, so between the two it looks like second-order case of "anyone's guess". Fair?

I didn't know / think of requesting "as much export as allowed". Our G99 was completed by the solar supplier and they've just approved the exact system designed (8kW) and not 1W more. The real pain is the approval is only valid for 90days, the lead time on manufacturing and supplying the exact dimension panels is longer than that! And we're months away from being able to measure up to place the order. Hence my now looking into 3phase as a less bureaucratic plan B. @JSHarris do you now have a battery storage or still in the planning stages? Is it AC or DC coupled? (To the existing invertor?) It's interesting it needs to be figured into the total export allowance. That's another good future proofing reason to go with 3ph. I'm actually wondering if a future 3ph battery storage could be used to optimize phases. Charge from or feed into each phase independently to minimize thr export on each one, via a shared DC battery store, dynamically rebalancing them. In lieu of that, ASHP, plant room (immersion element(s), washing machine), and perhaps the ovens and induction hob, would be candidates to shift to different phases. Ideally the ASHP could be 3ph but we only need 7kW so totally overkill.

So if fitting 3-phase inverter (and possibly batteries in future), presumably then the goal is to always split demand as evenly as possible across phases? For summer cooling, this could almost become a reason to use a 3ph ASHP on its own. I was hoping the balance of phases would be summed prior to metering, as stated here https://www.solarquotes.com.au/blog/3-phase-solar-what-you-need-to-know-about-connecting-solar-to-your-3-phase-supply/ (that's in Australia, but it was the only reference I could find) Hmmm.

Answering my own question! First. it turns out the cost estimate (with on site survey) was much faster than a G99 request. MUCH faster. Like, 3 days vs 12 weeks. Costs for moving existing vs new : a) moving existing single phase supply by 4 meters: aprx £1100 b) installing a new 3ph supply from the street (17m) and disconnecting the the old: £3900 Most of the costs in (b) is the fact they're digging up public carriageway (pavement only) so need permits, H&S, road signing, 3 crews, etc. Other interestingly tidbits: - we actually have a substation immediately on the boundary behind our house. The surveyor's plans didn't show how it was connected to the main supply out front so he ignored that for costing - the existing mains head could be moved to an "indoor" location because it's already indoors, and it's a renovation. For a rebuild, or for a brand new supply, the "new rules" kick in and the head+meter need to be outside the house. I now have to decide if the future proofing benefits of a 3ph supply justify that hefty upfront cost. (It also de-risks some other parts of the build, namely moving supplies around inside and solar connection, but the cost is too high for derisking alone). The fact we're going all-electric house does push us in favour of doing this. And enabling a 22kW car charger could be useful option in the future too.

Try this thread There's a few others on specific makes in the ASHP topic too https://forum.buildhub.org.uk/forum/119-air-source-heat-pumps-ashp/

It'll always be possible to charge from a single phase, it'll just never be as fast. If you only make one car trip per day or want to charge from self generated solar the option of a faster charge is probably not much interest anyway. The cost of upgrading a new install to it could be negligible, or could be considerable depending whether the nearest supply cable is 3 phase or not.