richard_scotland

I filled a cavity wall from the top using beads for a similar sized area of internal cavity wall, which in our case was allowing cold loft air down into the wall. I just bought some beads from ebay and lots of PVA glue, mixed the glue up in approx 10:1 water:pva in a watering can, then worked up in layers of beads/PVAmixture, pouring from above The beads flowed very well so I had no worries about voids etc, and I could see with a headtorch that all areas were being filled. If you had two people then you could pour both beads and pva mixture at the same time which would probably work better; I am sure that the PVA mixture in my case didn't quite reach all areas. Its made a big difference for us, so I think would be well worth doing. I knew it was unlikely we would ever drill a hole through the wall and it wasn't connected to other cavities, so I guess I was a bit more relaxed about how well the PVA mix worked, as long as the beads reached all parts of the cavity (you could foam the top?).

Turns out it is a 3-phase 50 kva transformer, which brings the 3PH connection cost down a bit- £3250+VAT, subject to a detailed quote. However, our 3PH supply would be limited to 30 kva to leave enough capacity for the other 3 houses. I'm not sure what this means in practice. They said they would install 3x80A fuses, but we would have to have an agreement to limit total use to around 30 Kva - which they thought would be plenty for almost all domestic situations. Does that roughly equate to 120A? So our options are: upgrade from 60A to 80A single supply for no cost. or pay £4k for a slightly less than full capacity 3PH connection (+ some internal electrical costs) So the question becomes which is best: at the moment we have 12 Kw ASHP 7 Kw car charger Induction hob a dishwasher, washing machine and tumble dryer which are on constantly 4 Kw solar and we frequently hit 11-12Kw import for hour+ periods in the future (next 5 years)? we might want to add: 5 Kw invertor for battery storage More solar (where this thread started!) Sauna or hot-tub (the hot tub mainly for hyrdotherapy for my son). Possible garden annex (with kitchenette, electric shower, electric heating etc) A second electric car (so more frequent use of the charger) I think for all the wish list items we would be better off with 3PH, but perhaps we could do some of them just fine with an 80A single phase and careful use. Anyway, this thread has been helpful to explore options - thanks to all contributors

They actually followed up this morning to ask me to send a photo of the transformer 'just in case our records are incorrect'. With binoculars I can read some of the values on the faceplate on the side and it suggests its 433V and 3-phase, with a 30 kva capacity (not 240V single phase). If its is 3-phase, that should make things a bit cheaper.

I just spoke to the designer and apparently it isn't - its a 50 kVa single phase transformer. They come in 3-phase and single-phase versions and this is a single phase version. They said I could upgrade our supply to 80A for a fairly minimal fee (they are just checking), and that would be good for 23 kVa.

I've had a quick look through last months data and the min voltage recorded (the data is averaged over an hour period) was 223 when I was drawing 12 Kw (car and heat pump at 1am), and the mean voltage over the month was 236 Volts. So no, it stays above the minimum, although there are definitely shorter periods where I am drawing a bigger load (e.g. 15 Kw) but I don't have the voltage data on that

The DNO go back to me with an estimate for 3-phase to the house. Its £4500+VAT. It includes a £1250 design fee (?) for upgrading the transformer to 3-phase, the actual upgrade cost would be covered under SCR. It doesn't include excavations on our land (a 10 m long trench). More than I was expecting, and makes it hard to justify as a route to add more PV or some more batteries. Our existing supply is 60A, so will explore if there is scope to up that to give us a bit more headroom (I seem to remember being told there wasn't, but I will ask again), and see if there are any other options. But even if they gave us 100A, I am not sure there would be much scope for adding batteries to shift some of our load onto cheaper rates, as I feel we are already pushing the limits (its not uncommon for there to be a 15kW load at 3am if the car is charging and the heat pump is doing hot water, or its a a cold night). This house was fairly recently (in the 90s) two cottages, and one cottage still has the old supply in situ, and it was working when we moved here. I don't know if there would be any way of utilising that, without having to pay two sets of standing charges? A very rough calculation would be that if we had a substantial battery (say 20kw) and did all the car charging and DHW heating overnight or at cheaper periods, we could shift maybe 10,000 kWh of our annual load to a cheaper rate, so the bill savings might be in the region of £1300-500 a year. But we might have to spend £10k to be able to do that.

I will get in touch my DNO and see what they say.

This is the pole nearest to the house - it serves 4 properties.

thanks all for the responses and @frankmcs65 for the interesting ideas. Wondering about an alternative approach. The electric pole which is 5 m away from the house has 3 phases to it and a transformer on it. Our single phase supply is limited to 60A (due to size of cable apparently) and the cable goes under the slab to the middle of the house (the house was renovated in the early 90s). The fact we have a 12 kW heat pump, a car charger, induction hob + oven and everything else all on this 60A supply already makes me a bit nervous. We will likely go from one to two EV cars within a year or so, so the charger will get used several nights per week. Is there any merit in seeing how much it might be to have 3 phase installed to a new external meter box? as the pole is so close you hope the cost might not be too terrible... This might mean any new meter works as a smart meter, as its no longer surrounded by thick solid walls, allowing us to access TOU tariffs. From there we could connect up to the existing consumer boards internally? It used to be two cottages, so there are already two consumer boards, they could have a phase each and then the EV charger could be on its own phase? And doing this I would automatically get all the the extra PV export capacity I could want or use. An additional factor is that its reasonably likely we would want to build an accommodation annex in our garden at some point in the next few years - one of our children is disabled and has complex needs so ideally we will like to have additional accommodation for carers or helpers on site. That would be an additional load on our electric supply (heating, hot water, some basic cooking facilities etc) - so this might be another aspect pushing me towards looking into 3PH Obviously how sensible this is depends on how much the 3PH upgrade might be and if any of the above plan actually makes sense!

i will have a look at this. We have an 11Kv line with a transformer on within 10 m of the house and that line only supplies 4 houses, I don't know if this is a sign there is likely to be extra capacity in the system? I guess the other option is to just get a few more panels and run them on the existing inverter.

That sounds like a good idea - are they happy for you to chat to them to see whats possible? Yes thats true, but I guess it would only be for a few months of the year? I wouldn't be adverse to getting batteries, but I think the economics of them is poor when you can't charge them cheaply in winter.

ASHP runs with radiators. I thought E7 was being phased out?

Context We live in one of the sunnier parts of Scotland (east fife). Our overall electric use is high: We have ASHP (uses about 7000 kwh a year for heating and DHW - its an old cottage), 1 electric car (possible we may get another one within 2 years), family of 5 so relatively high overall other domestic usage (washing machine, cooking etc), totals around 14-15000 kwh a year? Zappi car charger. 3.6 kw Grid connected system (Solis 3.6 hybrid invertor), connected to 4 kw of Viridian in-roof solar panels, about 2.5 years old now. Invertor is located in the loft, with access through a standard loft hatch. No batteries. System generates about 3800 kwh a year, we use about 2700 kwh of that generation. We have a smart meter but it does not get signal (located in middle of house), so presently cannot access TOU tariffs, so everything is on standard rates and as much as I’d love to change that, we might be stuck with a non-functioning smart meter. Roof is directly south facing about 45 deg slope, easy access as its single story, mostly unshaded apart from in the depths of winter when it gets a bit of shade from tree branches. Room for around 5 or maybe 6 kw more panels on the roof, all on the same orientation. What’s the best strategy for expanding this system? My gut feeling is better to get more generation than batteries, as the most batteries could save is ~ 1000 kwh a year without TOU tariffs. Whereas we would surely be able to use more extra generation than that. Do we replace our relatively new invertor with a bigger one (e.g. 6 kw connected to 8kw of panels), or simply add another 3.6 kw invertor? Any ideas welcome.

If its fixed then the flow temperature probably too low to keep your house wam for when its cold as it has been this last week - much better (and cheaper) to have it change flow temperature with the weather. This is something easy to set up yourself using the Daikin menu. I can look later at how you do this. We went to town with large radiators (quite a few K3), but we still needed 43 flow temperature this past week, you might need higher still if your radiators are fairly normal sized. Our design temperature was 55 degree flow at -3 outside (do you have this information anywhere?), but in practice we can run it cooler than that and be fine. This suggests to me that the unit is probably powerful enough. As I said ours is 12 kw and is not operating at max output and keeping our 200m2 single story cottage, half of which has no insulation on the walls, to 20deg. Our unit is mostly very quiet and never makes a noise like you describe, so I wonder if something is not correct here. Also, ours does occasionally 'whoosh' as part of a defrost cycle, but we never have to top up pressure and bleed radiators after this - the fact you have to top up the pressure frequently also suggests something is not quite correct with the pipework or system. when its not heating and its below a certain temperature outside ours does cycle the water in the system every 20 mins or so to prevent freezing - does yours do this? 100kw a day also suggests it is using the backup heater a lot. our 12 kw unit has only been using 55-60kwh a day (it sometimes uses the backup heater for a few minutes at the start of a cycle but they soon switch off). When its milder we are using 20-30kwh a day. I would persist in trying to get the installer back to look at the system as it doesn't sound like its working as it should do.

Hi Tog I have the same model of heatpump and it is working OK to heat our 200m2 house (a not particularly well insulated old cottage) to 20 deg, and is using about 55 kwh a day at the moment to do that (producing 160 kwh of heat). We also upgraded our radiators and pipework. 1. what size in kw is your heat pump? we have the 12kw model which seems to be plenty big enough for us and works out at 60W per sq m 2. does it usually reach the 39 degree set point when its not so cold? 3. Our flow temperature is 43-44 degrees at the moment (-5 this morning), so I suspect 39 would be too low anyway at these temperatures, unless your house is very well insulated. Can you try turning the flow temperature up and see if the room temperatures improve? are the radiators warm at all to the touch? are you running weather compensation (flow temperatures vary with outside temperatures) or fixed? 4. we run our system with only a 1 degree setback at night - if yours is set to turn off overnight it might be that room temperatures have dropped too low and its struggling warm things up? You could use the Daikin menu system to go to Information>Sensors On ours this shows you more information about the actual flow temperature and also the flow rate etc which may be helpful. I think there is also a malfunction log in that menu which might be worth a look at.