Jeremy Harris

In this thread I mentioned that boost charging our Sunamp in winter from E7 off peak rate would give a modest saving in electricity cost: https://forum.buildhub.org.uk/topic/7743-sunamp-container-bulging/?do=findComment&comment=138790 Rather than take that thread further off-topic, I've started this one, to try and work through the arguments for changing to E7, and also look at how best to try and optimise our use of PV generated energy. I started from the position of assuming that E7 wouldn't make sense for us, as the increase in standing charge and peak rate unit cost would offset any saving from off peak use. However, it seems that there isn't now much, if any, standing charge penalty for switching to E7, and that, plus some reorganisation of the time of use of our demand, can shift the balance in favour of E7. The first thing I'd say is that working this out in enough detail, so as to be able to see whether or not switching to E7 would make sense, wasn't easy. I drew up a spreadsheet, put in all our 24/7 loads (treatment plant, UV water disinfection, fridge freezer etc), then tried to estimate all the other loads in terms of energy used per 24 hours and whether or not that energy was used in peak or off peak times. I then chucked in the mean daily PV generation for each day of the year and offset that from the peak rate daily usage. More by luck than judgement, I ended up with a total for electricity usage over the year that seems to tally pretty well with reality, as far as I can tell. From this data I've been able to work out how much electricity we would use at peak rate, compared with that which we would use at off peak rate, and concluded that, with a bit of careful demand management, we can get our off peak rate usage to between 40% and 45% of the total, which is comfortably inside the region where E7 makes sense (the break even point for most households seems to be around 35% of total usage being at the off peak rate, it seems). Having done this, I then looked at the impact of charging my electric car, and also at the impact of adding battery storage. This is where things get interesting, as it's dead easy to switch all the car charging to the off peak rate during the 4 to 6 months of the year when the chances of charging from excess PV generation are very low. Even more interesting is that battery storage still looks to make sense, even if that is charged in winter from off peak electricity, rather than excess PV. The main advantage in winter comes from being able to use battery storage to supplement PV generation during the peak rate period, so offsetting import during this time. In turns out that this gives a significant saving, and doesn't need a lot of power, but does need a reasonably large capacity battery. So, based on this, I've asked for our meter to be changed to an E7 one, so we can switch to an E7 tariff. Even without battery storage this makes sense, just by changing some of our winter demand so that it's during the off peak time. It looks like we could save around £200 a year by switching to E7, probably more if I include car charging energy in the sums. At the moment I don't know how much the car charging demand is going to be, as I don't have enough experience to be able to make a reasonable estimate.

The saving is far from just the DHW, now that I have a fully electric car. I've had a go at modelling our year around electricity usage and reckon that around 40% to 45% of it could be at the E7 rate, and that does result in a worthwhile overall saving. This is getting to be a bit off topic, though, so I'll start a new thread, referencing this one.

I've just had a look at the way the Sunamp is performing, with the regular reset procedure every day. Looks pretty good still, in that it still seems to be utilising close to 100% of the available excess PV generation. It seems that the time switch reset makes a significant improvement in the ability of the Sunamp to charge from any available excess PV generation, such that I'd now say that the unit is performing perfectly (albeit with a bit of a bodge to get it this state). Interestingly, it now looks as if we are getting around 1/3rd of our DHW energy requirement met by excess PV generation,even during what's been a pretty dull December, with lower than average PV generation for the month. This bodes well for us being able to get to zero imported energy for DHW by around the end of February, based on the history of our PV generation system since it was first installed. The next stage is to switch to E7 to reduce the cost of the early morning boost charge in winter, but the saving is modest, as even at peak rate it looks as if we're paying only around 30p to 40p/day for DHW in winter, which still seems pretty reasonable to me. Switching to E7 would drop this to around 20p to 25p/day for winter DHW at a guess, so only a saving of around £20 a year or so.

One nice thing about MDPE is that it's rare to get any damage from freezing. On the farm we had decades old alkathene pipe (same stuff as MDPE, just the 1950's trade name for it) running to troughs. This would freeze in cold weather, but I can only once recall any damage, and that was just a loose fitting blowing off from the expansion. One of our outside taps has a length of uninsulated MDPE running up the post to the tap, and that's frozen a good few times now, but as we never want to use that tap in cold weather I can't be bothered to do anything about it, as no harm seems to be done by just letting it freeze. Be nice to find some type of pipe insulation that mice don't like chewing, though. I've noticed that they seem especially fond of any black neoprene foam type insulation for some reason.

I must admit I have thought the same, as the ICF EPS is only 70mm, thick, I believe, which is pretty marginal, even in terms of meeting building regs, I think. A quick estimate, based on 300m thick concrete and two 70mm layers of EPS, seems to suggest the U value of the walls may only be around 0.22 W/m².K, not sure what the floor make up is. I believe basement walls are treated as floors as far as the regs are concerned (not sure about this, I've not checked the most recent regs), so it looks like this build up may just meet the regs, which aren't exactly demanding in terms of thermal performance, plus I believe that just meeting the limiting fabric standards may well not meet the required TFEE/TER.

Thanks for raising the cost issue, as one of my concerns with our set up is that the air pump is a constant power demand, which pushes up the house base load. I've been looking at battery storage for some time, and the added cost of a "no electrical power needed" treatment plant, over the cost of the system we have (around £2k, plus about another £1k in installation cost - just a single round hole around 2m wide and 2m deep) is something worth factoring in to the investment in battery storage, when it comes to the saving in running cost (small as it is).

I like the idea of having a basement, and would have built on if it wasn't for the practical issues surrounding our plot (as it was we had to remove over 900 tonnes of soil just to get it level). Getting enough insulation around a basement seems key, though, especially as we wanted to achieve a passive house performance level, which would have meant at least 300mm of EPS around the outside of the walls and under the floor. Our main problem was the EA, though, who declared that we couldn't have any habitable rooms with a finished floor level lower than about 1.5m above the level of the lane.

I don't know how you do it. My sister in law was a social worker in inner London for years, and I'm pretty sure I couldn't do that job, especially given the major failure of successive governments to understand the true impact of some of their policies.

I'm hoping to clear the final snag list and then start booking holidays...

Any WRAS approved pipe lube works OK. Most are just a water-soluble gel that contains glycerin and thickened with methyl cellulose (pretty much identical in composition to KY Jelly...).

Some countries routinely build cast-in-situ concrete floors and roof structures, along with walls. I recall seeing houses in Spain and Cyprus being made like this, and it's not a lot different to using ICF in principle. The biggest problem here might be finding a builder to do it, as other than for commercial builds I suspect that cast-in-situ floor or roof structures won't be something many will be familiar with.

You can't normally terminate 25mm² SWA at the case of most domestic CUs, as usually there isn't enough room. What I did was terminate the 25mm² three core SWA that runs to the CU in the house to a galvanised adaptable box, then ran 25mm² tails from there to the CU as normal.

Wilo seem to be slightly quieter than Grundfos, based on our experience, although both are pretty quiet. We have a Grundfos pump on the UFH manifold and a Wilo on the DHW preheat PHE circuit and the Wilo is definitely quieter, so much so that I've had to fit a light to show that the flow switch has turned the pump on, as I can't hear it running.

If you get the flow switch I used to circulate water through our PHE, then you can wire it direct to the pump, as it has a built in triac that can switch 3 amps: https://cpc.farnell.com/gentech-international/fs-01/flow-switch-noryl-ac/dp/SN36161

External insulaion, EPS or XPS, will do the job OK. The SIPs thread is on this forum somewhere, IIRC, or may possibly have been on the now defunct Ebuild forum. I seem to remember we had some input from a chap from Kingspan, who started off not realising there was a potential problem and ended up agreeing that there was a possible risk that could be mitigated with an insulation upstand.

It's essential that some form of condensation risk assessment is done, something that is even more important now that insulation levels are significantly better than in times gone by. One consequence of improved insulation is that the sole plate will be colder, as less heat will be lost from the house. It was assumed at one time that including a vapour control layer on the warm side of the build up would eliminate the sole plate condensation risk, but this may well not be the case in the sort of variable weather we have. Water vapour can move into the structure from outside when humidity levels are high, and with luck will move back out again as humidity levels outside drop. The problem arises when the temperature of the sole plate drops below dew point for any water vapour that has migrated inwards. Because it takes, relatively, a lot of energy to turn liquid water back into vapour, and because the sole plate may well be being cooled by the ground beneath to the point where it doesn't get warm enough to drive the water out, there is a risk that it may end up wet for long enough to cause problems. The mitigation measures that can be used include improving the insulation level of the foundation that the frame rests on, by using some form of insulated blockwork, or adding an insulating upstand to try and keep the wall/floor junction a bit warmer. The key thing here is that the issue is a dynamic one, that isn't normally modelled in a standard steady state condensation risk analysis. There's a thread here about the specific issue this presents to a SIPs build, but much of the content in that is equally applicable to timber frame construction where there is no external insulation around the wall/floor junction.

My view is that if you don't have mains gas, and really need high temperature DHW, then the best option may well be a Daikin hybrid ASHP/LPG combi. They have a good reputation for reliability, and use only a modest amount of LPG, as they use the ASHP to preheat to round 45 deg C or so, then boost this up to 55 to 65 deg C with the small LPG combi. I'm not convinced that any of the CO2 ASHPs are a mature enough product to invest in yet.

Damp won't rise up blocks stacked on wet ground to any significant degree, but as @PeterW says, they are best left stacked on their pallets to keep them clean, anyway. The mechanism involved for getting moisture to rise is capillary action, and at most you might get damp to rise up a few mm above ground level. Also, blocks are made using concrete with a pore blocking additive to stop any tendency for water to rise through them when they are sat on a wet surface, not just to stop so called "rising damp" (which is largely mythical, anyway) but primarily to stop them sucking the water out of mortar.

They are Chinese, non-inverter controlled, pretty basic units. They have been re-sold in the UK by a couple of companies, and are OK if you can manage with a unit that is "all or nothing", in that they don't modulate and are either full on or off, so they tend to have a fairly high starting current. Spares may or may not be available, depends very much on whether the UK importer has arranged a spares supply.

If you are OK with having bedrooms at the same temperature as the living rooms, then that's fine, but we have found we prefer the bedrooms to be a few degrees cooler. We have no heating at all in the bedrooms, so they end up at a temperature of around 18 to 19 deg C, when the living rooms beneath may be at 21.5 to 22 deg C. Our bathrooms have heated towel rails and that seems fine for us.

If you generate a lot more over the course of a year than you consume, then battery storage is only a partial solution, as during the summer the chances are that you'd still be exporting a fair bit to the grid. At the moment, our total generation since the PV was fitted is around 3.3 MWh and our total consumption from the same time is around 0.9 MWh, although the latter figure will increase a bit now that I have a car with a larger battery capacity. Where battery storage does seem to offer a really useful benefit is if you're on E7, or similar, and can charge the battery up in winter at the cheap rate. This then helps to offset the relatively low PV generation in winter. I'm still doing the sums to see just how all the various options add up, but the combination of E7, reasonably high PV generation plus battery storage looks like it would be worthwhile. The aim is to try to eliminate grid import during the peak rate all year around, or get as close as possible to that.

If you fit an Elster A100C (about £30) you can very easily just fit an IR receiver over the IrDA transmit port on the front and read out all the internal registers into the device of your choosing. The neat thing about the Elster is that it continuously transmits serial data from this port, and you can read both import and export energy from this at any time, along with a fair bit of other data. There's a guide giving the data format here: https://www.rotwang.co.uk/projects/meter.html I have one fitted in our incoming supply and can read import and export data and log it to the house monitoring system.

The problem seems to be that, although "smart" meters can measure export (as can many existing ordinary digital meters) none seem to be certified to do this, and there are no plans to enable them to do this, AFAIK. The pressure to implement "smart" metering is coming from the suppliers, who want to be able to introduce 30 minute tariff changes on the fly, to remove the risk they currently have when they buy wholesale energy on a 30 minute variable tariff and have to try and predict ahead what the mean wholesale price will be, over something like a year, when setting their retail tariffs. One reason some smaller suppliers have gone to the wall seems to be that they either weren't good at predicting the wholesale price that they would have to buy in at, so set their retail tariffs too low, or that they haven't had a big enough capital buffer to allow them to ride the peaks and troughs of the market. There are a big swings in the wholesale price, from zero up to a price not far off the retail price at times, so although it tends to average out to around 5p/kWh or thereabouts over the long term, it can be very volatile in the short term. The export payment that exists at the moment, which is separate from the Feed In Tariff subsidy, is around the mean long term wholesale energy price; IIRC I think it's currently just over 5p/kWh. I can't see any good reason why export payments shouldn't continue when the FiT subsidy stops, as it isn't a subsidy, just a legitimate payment to small-scale generators. Before the FiT came along small-scale generators were paid for the energy they provided to the grid, so there is a precedent for this from before the subsidy system was introduced. A properly certified export meter costs around £20 or so (they retail for around £30) and would be very little hassle to install (an hour's work, at the most, I'd have thought), for those who wish to be paid for the actual energy they export, rather than the deemed 50% of generation that is assumed under the FiT regime. I'd happily pay, say, £100 for an export meter to be fitted, and then be paid the wholesale price for any energy we export. Seems fair and reasonable to me, as I know we export more than 50% over the course of a year, so the meter would pay for itself pretty quickly.

The table is the electrochemical series, that gives the potential difference between different metals. A large PD means a high risk of corrosion, so ideally the metals in contact with each other shouldn't be too far apart, but using something like chromate paste will mitigate the corrosion risk to a fair degree. Cadmium -0.403 V Zinc -0.7618 V Aluminium -1.662 V Iron -0.447 V Galvanised steel will be closer to the potential of aluminium, so slightly better than cad plated steel.

I played around with several ways of controlling the temperature of our house, and settled on a pretty simple system, with a +/- 0.1 deg C hysteresis thermostat that turns the heat pump on and opens the UFH. The UFH pump runs all day, whenever the timer turns the system on, and does work to even out the temperature in the slab well. I personally don't see the need for anything more complex than this, as it seems to control the house temperature very well.