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nowty wrote: ↑Fri Nov 10, 2023 9:53 am

Mart wrote: ↑Fri Nov 10, 2023 8:03 am
Regarding the 8kWh figure, obviously I haven't seen the reference yet, but that sounds about right for domestic leccy (not total energy, nor for BEV's) at around 3,000kWh pa. I think the UK household average has been steadily falling for over a decade. I recall 3,600kWh, and 3,200kWh as averages, but I'm not sure what the current figure now is.

The latest annual average for leccy recently agreed by OFGEM is 2,700 kWh down from 2,900 kWh.

Or 3,900 kWh down from 4,200 kWh if your on E7 with a split of 58% peak and 42% cheap rate.

For completeness, Gas is 11,500 kWh down from 12,000 kWh.

https://www.ofgem.gov.uk/sites/default/ ... Letter.pdf

Tesla app telling me we have imported 10.6MWh so far in 2023, no gas here either. So, should be happy with that

Mart wrote: ↑Thu Nov 23, 2023 10:32 amAgain, apologies to anyone with or aiming for Passivhaus, I'm honsetly not knocking the idea, just wondering how things may have changed now, as technology improves, so what gives the best bang for your buck, as you chase those harder and harder last savings.

Hope this is fun, and of course the great thing, is that both energy saving, and energy generation, plus heatpumps and batts, are all improving, so it's all good news.

So firstly, remember that no sensible build will ever get on Grand Designs. Part of my brief to the architect was in fact "must not make a good episode of Grand Designs"!
So a drawing of the elevations taken from our planning application is below: looks pretty normal, and if I've done my sums right will be at or very close to Passivhaus Premium. That isn't actually a design requirement, just where the design has taken us.

• Front and rear elevations have most of the glass because we don't want to be overlooking the neighbours. They're SE/NW, with the glazing sized for daylighting not heating.
• Insulation is reassuringly boring - plan is cavity wall brick & block, with 300mm of mineral wool in the cavity and roof. Incremental cost less than £5k compared to building regulations minimum, most of which will probably be cavity ties.
• Windows are 3G - not quite sure what the price premium is over 2G at the moment, but probably not all that much.
• Heating is a small heat pump - design heat load is just under 2kW.
• PV is whatever fits on the NE and SW elevations of the roof (at the sides). Incremental cost of a 12kW system compared to just tiles is under £10, slightly more with a battery.
• Airtightness will either be wet plaster on the interior walls or possibly airtight paint on the outer side of the inner leaf. Incremental cost again ~£5k over building regulations minimum.

Basically if you have a Passivhaus then heat pump + a bit of PV gets it to the Plus standard. Premium is basically down to how much PV you stick on your roof - because I'm close to E/W with a fairly shallow pitch, it turns out that filling up the two side roofs gets pretty close to the 12kW limit for 3-phase G98 limit. Won't be fussed if it doesn't happen, just looked at the roof layout and went "huh" one day...

Paul_F wrote: ↑Fri Nov 24, 2023 12:18 am

Mart wrote: ↑Thu Nov 23, 2023 10:32 amAgain, apologies to anyone with or aiming for Passivhaus, I'm honsetly not knocking the idea, just wondering how things may have changed now, as technology improves, so what gives the best bang for your buck, as you chase those harder and harder last savings.

Hope this is fun, and of course the great thing, is that both energy saving, and energy generation, plus heatpumps and batts, are all improving, so it's all good news.

So firstly, remember that no sensible build will ever get on Grand Designs. Part of my brief to the architect was in fact "must not make a good episode of Grand Designs"!
So a drawing of the elevations taken from our planning application is below: looks pretty normal, and if I've done my sums right will be at or very close to Passivhaus Premium. That isn't actually a design requirement, just where the design has taken us.

• Front and rear elevations have most of the glass because we don't want to be overlooking the neighbours. They're SE/NW, with the glazing sized for daylighting not heating.
• Insulation is reassuringly boring - plan is cavity wall brick & block, with 300mm of mineral wool in the cavity and roof. Incremental cost less than £5k compared to building regulations minimum, most of which will probably be cavity ties.
• Windows are 3G - not quite sure what the price premium is over 2G at the moment, but probably not all that much.
• Heating is a small heat pump - design heat load is just under 2kW.
• PV is whatever fits on the NE and SW elevations of the roof (at the sides). Incremental cost of a 12kW system compared to just tiles is under £10, slightly more with a battery.
• Airtightness will either be wet plaster on the interior walls or possibly airtight paint on the outer side of the inner leaf. Incremental cost again ~£5k over building regulations minimum.

Basically if you have a Passivhaus then heat pump + a bit of PV gets it to the Plus standard. Premium is basically down to how much PV you stick on your roof - because I'm close to E/W with a fairly shallow pitch, it turns out that filling up the two side roofs gets pretty close to the 12kW limit for 3-phase G98 limit. Won't be fussed if it doesn't happen, just looked at the roof layout and went "huh" one day...

You mean you don’t have to spend £100k on silly-shaped windows?

Stig wrote: ↑Thu Nov 23, 2023 12:07 pm I'd suggest there should be two cost-benefit calculations done when starting such a project, one for money spent now vs. money saved on running costs and another for carbon 'spent' now vs. carbon saved during the life of the building.

I suggest a regular XY graph, with money on the X, CO2 on the Y. The upfront build cost and CO2 give a point on the graph, as do the cumulative totals projected over the next 20 years. So the house( or whatever) ends up with a line on the graph, and you could easily compare one approach versus another - eg heating types or whatever. A picture is worth a thousand words, they say.

Paul_F wrote: ↑Fri Nov 24, 2023 12:18 am

Mart wrote: ↑Thu Nov 23, 2023 10:32 amAgain, apologies to anyone with or aiming for Passivhaus, I'm honsetly not knocking the idea, just wondering how things may have changed now, as technology improves, so what gives the best bang for your buck, as you chase those harder and harder last savings.

Hope this is fun, and of course the great thing, is that both energy saving, and energy generation, plus heatpumps and batts, are all improving, so it's all good news.

So firstly, remember that no sensible build will ever get on Grand Designs. Part of my brief to the architect was in fact "must not make a good episode of Grand Designs"!
So a drawing of the elevations taken from our planning application is below: looks pretty normal, and if I've done my sums right will be at or very close to Passivhaus Premium. That isn't actually a design requirement, just where the design has taken us.

• Front and rear elevations have most of the glass because we don't want to be overlooking the neighbours. They're SE/NW, with the glazing sized for daylighting not heating.
• Insulation is reassuringly boring - plan is cavity wall brick & block, with 300mm of mineral wool in the cavity and roof. Incremental cost less than £5k compared to building regulations minimum, most of which will probably be cavity ties.
• Windows are 3G - not quite sure what the price premium is over 2G at the moment, but probably not all that much.
• Heating is a small heat pump - design heat load is just under 2kW.
• PV is whatever fits on the NE and SW elevations of the roof (at the sides). Incremental cost of a 12kW system compared to just tiles is under £10, slightly more with a battery.
• Airtightness will either be wet plaster on the interior walls or possibly airtight paint on the outer side of the inner leaf. Incremental cost again ~£5k over building regulations minimum.

Basically if you have a Passivhaus then heat pump + a bit of PV gets it to the Plus standard. Premium is basically down to how much PV you stick on your roof - because I'm close to E/W with a fairly shallow pitch, it turns out that filling up the two side roofs gets pretty close to the 12kW limit for 3-phase G98 limit. Won't be fussed if it doesn't happen, just looked at the roof layout and went "huh" one day...

Many thanks Paul, I think that's exactly where I was coming from, and trying (hopefully) desperately not to offend anyone, like yourself, who may be achieving excellent reductions in energy consumption.

I think your 'not a Grand Designs choice' is a great starting point. And from what you've explained, all of the efficiency savings seem to be entirely sensible and economically preferable too. Perhaps a 10-20yr payback financially, but immediate environmental savings?

Just wondering, as I have similar orientations to you, just favouring the E rather than the W with ESE + WNW - Have you specifically chosen to not use the front roof, as you have so much PV already? It's just that an E/W arrangement does drop off far more in the winter. Over the year, the 'loss' is only about 20% v's S facing, but that loss is mostly packed into the already lower winter period. My June v's Dec target is 8:1. Checking PVGIS, if my PV was S facing, it would be about 4:1.

I'm only guessing, but assuming at the extreme, that the side roofs are ~6kW, and perhaps 4kW may look OK on the front, then a 3phase inverter capped to 11kW, would probably see little capping, only on the perfect summer days, and none in winter, which would aid your HP use.

Stinsy wrote: ↑Fri Nov 24, 2023 6:44 amYou mean you don’t have to spend £100k on silly-shaped windows?

I'm trying hard not to catch the attention of the window police until it's too late.

Mart wrote: ↑Fri Nov 24, 2023 8:38 amMany thanks Paul, I think that's exactly where I was coming from, and trying (hopefully) desperately not to offend anyone, like yourself, who may be achieving excellent reductions in energy consumption.

Don't worry about it. Anybody thin-skinned enough to be upset by that is going to get a horrible shock when they start building!

Mart wrote: ↑Fri Nov 24, 2023 8:38 amI think your 'not a Grand Designs choice' is a great starting point. And from what you've explained, all of the efficiency savings seem to be entirely sensible and economically preferable too. Perhaps a 10-20yr payback financially, but immediate environmental savings?

Umm... environmental is a bit unclear because it's a demolish/rebuild of a 1930s bungalow (with no foundations) and a botched 1970s extension on the back. Any new build has an embedded carbon issue, but this one also has an avoided embedded carbon issue (needs major work to get up to decent comfort standards - solid walls and 70s windows). Overall I'm thinking about 10 years financially .vs. building regulations minimum, or 0 years against buying somewhere equivalent.

Mart wrote: ↑Fri Nov 24, 2023 8:38 amJust wondering, as I have similar orientations to you, just favouring the E rather than the W with ESE + WNW - Have you specifically chosen to not use the front roof, as you have so much PV already? It's just that an E/W arrangement does drop off far more in the winter. Over the year, the 'loss' is only about 20% v's S facing, but that loss is mostly packed into the already lower winter period. My June v's Dec target is 8:1. Checking PVGIS, if my PV was S facing, it would be about 4:1.

As drawn it's 7 kW SW facing and 6 kW NE facing, for a total of just over 10 MWh/yr. Moving the NE facing to SE would increase the specific power output (≈660 => ≈920 kWh/kWp) but there's quite a bit less room and as a result total generation is about the same. Given that the panels themselves cost about £50/m2 which is about the same as concrete roof tiles and having more than two MPPT points adds a lot to the cost of the inverter, it really all comes out in the wash.
Avoiding use of the front roof is primarily a pragmatic planning consideration, with a nod to kerb appeal. First attempt at planning was turned down for not fitting in with the street, this is the free 2nd go and we've tried to dial back a bit so they haven't got any real room to object. Expecting it to pass this time from the feedback we've had.

Mart wrote: ↑Fri Nov 24, 2023 8:38 amI'm only guessing, but assuming at the extreme, that the side roofs are ~6kW, and perhaps 4kW may look OK on the front, then a 3phase inverter capped to 11kW, would probably see little capping, only on the perfect summer days, and none in winter, which would aid your HP use.

At a pinch there is room for 10kW on the SW face and 6.5kW on the NE face, giving ≈13.5 MWh/year of generation. Worst month per PVGIS is December, and that still generates ≈10 kWh/day on average. Cost of parts including battery less cost of roof tiles is about £12k, VAT-free because it's a new-build and a relatively cheap install because electricians and scaffolding will already be in place.

Mart wrote: ↑Fri Nov 24, 2023 8:38 am Just wondering, as I have similar orientations to you, just favouring the E rather than the W with ESE + WNW - Have you specifically chosen to not use the front roof, as you have so much PV already? It's just that an E/W arrangement does drop off far more in the winter. Over the year, the 'loss' is only about 20% v's S facing, but that loss is mostly packed into the already lower winter period. My June v's Dec target is 8:1. Checking PVGIS, if my PV was S facing, it would be about 4:1.

I'm guessing you guys are further south than Northumberland? My PV is East / West, but the June to December is more like 14:1!!

Thanks again Paul. Really interesting, and for me, helps to get my head around, what Ken correctly identified, when I was lost for the words, as a 'cost benefits analysis'.

Not about the money, but I love the economics side, as it can completely undermine/topple any arguments against going greener, even for those that don't care about the environment/AGW.

So you identified 2 x £5k cost increases. Add on a bit for the 3G, and then I'm gonna bump it more, just to play worst case, so +£15k. [Edit, just to say, you hit the nail on the head with 'v's building standards minimum', that's exactly what I'm interested in.]

I appreciate the PV is a wash, but it doesn't seem to be being deployed at a high enough level for most new builds, which saddens me. But that PV will reduce running costs. Plus the savings from the efficiency expenditure, and perhaps a slightly lower cost for the heatpump and heating install, due to the lower needs?

But sticking with a pessimistic £15k extra, your 10yr figure looks solid, assuming £1.5k per year energy savings, incl BEV fuel savings and export payments. In fact, may be a bit better than that. It really seems like we've moved forward a long way since 2010(ish) when I started to take a serious interest in all this 'stuff'.

10yrs ..... kinda silly not to do it really.

I'm figuring that my particular costs will be a bit more than that - I forgot MVHR (which is an air quality AND energy improvement), and there will be some additional costs from having fewer builders willing to quote. Say +10% on build costs at the moment, dropping to +5% if it was deployed en-masse.