Jeremy Harris

Just as @Bitpipe says, opening a window doesn't do anything much, and creating a cross-draft by opening windows at either end of the house works, but tends to make rooms that aren't too hot a bit cooler than needed. With the MVHR in active cooling mode (it switched to 100% bypass and passive cooling mode a couple of hours earlier, I think) it tends to preferentially cool the bedrooms, as i've set those up to have a fairly high flow rate. This is ideal for cooling, as cooling the first floor (which doesn't get much direct solar gain) tends to limit the amount of heat that rises from the large entrance hall space, as long as we keep the bedroom doors closed during the day. The other point is that I don't want to have to faff around opening or closing windows, so the house systems are set to regulate the environment without me needing to twiddle with anything. The cooling is set to come on when the upstairs landing reaches 24 deg C, and at first it will try to passively cool by just switching to 100% bypass and feeding cool air from outside into the house at a low flow rate (the normal background ventilation rate) and if the temperature continues to rise the MVHR will automatically increase the fan speed, then turn on the air-to-air heat pump.

As if on cue, today has provided a good illustration of the way a passive house can overheat during spring and autumn, or even winter. Today has been bright and clear, and despite the shading overhang over our south-facing glazing (which does nothing at all at this time of year), despite the fact that our heating hasn't come on at all for the past two days, and despite the fact that we have heat-reflecting film on the outside of our east and south-facing glazing, our house reached well over 24 deg C early this afternoon and the cooling system came on for a couple of hours. The outside air temperature didn't exceed 8 deg C all day, and was around 7 deg C when the cooling system came on. The house is now just under 23 deg C, still a bit warm, but we would have been in for an uncomfortable night if the cooling system hadn't come on for a couple of hours and cooled the bedrooms down to below 20 deg C. We have suffered from the house getting a bit too warm in the spring and autumn, when the sun is low in the sky and penetrates deeply into the house, bypassing the shading, but I can't remember the cooling system having to come on in January before. The saving grace was that our PV system was generating a fair bit of power all day, more than enough to run the air-to-air heat pump that is built in to our MVHR system and which provides comfort air cooling. So. to sum up, I think your design definitely needs some better shading on those large glazed areas that face south, if you are not to suffer the same sort of problems that we've had to deal with. I modelled our house in PHPP, and accepted a small overheating risk, without realising that any overheating risk shown in PHPP can be unacceptable, because of the very long thermal time constant of the house, which is a consequence of having a long decrement delay structure and low heat loss rate.

Today's PV generation exceeding my best guess, at 18.3 kWh for the day. The downside of this was that despite the reflective film on the windows, the big shading overhangs (which do sod all at this time of the year), the relatively cool outside air temperature and the fact that our heating hasn't come on at all for the past two days, the house reached well over 24 deg C this afternoon and the cooling system came on (thankfully powered by the PV generation, so effectively free). The maximum outside air temperature I saw was 8 deg C, and it was down to 7 deg C when the cooling came on. The house is still a bit warm now the cooling is off, at 22.9 deg C, so even though it's expected to be cold overnight I doubt that we'll need heating tomorrow as the fabric of the house will still be holding a lot of heat for the next day or so.

The problem with the investment in battery technology (if it is a problem) is that all the money has gone into producing very light, energy-dense, battery technologies, mostly using the lithium ion exchange mechanism. This is what electric vehicles need, both a high energy density and a high power density. Electric vehicles don't really care too much about cycle life, as with a range of >200 miles per charge only a small number of electric cars will need more than around 1000 cycles before the rest of the car falls to bits from old age (200 miles per cycle and 1000 cycles gives a life of around 200,000 miles, more than most cars will ever need). Either home energy storage (which makes sense in terms of grid efficiency for homes that have renewable generation to spare at peak times) or centralised grid energy storage needs a much longer cycle life to be viable. Batteries will be cycled at least once per day, possibly several times per day for a peak-lopping grid storage system. The types of lithium cell technology that have been getting massive amounts of development funding isn't really the ideal technology for this, as weight and size aren't major issues for fixed storage, neither is peak discharge rate (home storage probably doesn't even need a 1C discharge capacity, unlike electric cars that may well need a peak capability of 10 to 20C). There are a few technologies that make a lot more sense for grid storage, and one of my favourites is the redox flow battery. Cycle life for this type of cell is pretty much infinite, but they do take up a fair volume for a given capacity. Some research is being done, but there just doesn't seem to be the high level of development investment that, say, Tesla have put in with their battery partners, Panasonic/Sanyo. Similarly, the one type of lithium chemistry cell that does have a cycle life of around 10,000 to 20,000 cycles if managed carefully, LiFePO4, has had very little development over the past ten years or so, because it has a relatively poor energy density, and this makes it less well suited to electric vehicles.

I've been working through the sums on the viability of home battery storage for a fair time now, watching the price of batteries and their associated equipment reduce and looking very closely at the combination of peak to off-peak rate grid supplied electricity and our self-generation capability. Right now batteries are just at the point where they start to make sense. I'm not expecting to recover my whole investment over the lifetime of the battery system (although I think I may well, if the price ratio between peak rate and off-peak rate electricity increases, as I think it will) but am happy to pay a premium both to have an essential services back up supply from the battery pack and also to have the convenience of not having to bother to time the use of appliances to coincide with either a sunny day or the off-peak rate. Already our usage figures since switching to E7 show that nearly 2/3rds of our electricity use is at the off-peak rate. With a battery storage system I'm pretty sure I can get to the point where we have barely any peak rate usage at all, even in the middle of winter. I'll post more on my plans once I've firmed up the details, but I expect to be investing in battery storage soon (and no, it most definitely won't be a Tesla Powerwall, for a host of reasons). My installation will also be DIY, as I already have the signed off circuits in place, two terminated and protected runs of SWA that were put in with the house installation, in anticipation of putting a battery storage shed (a metal one, for safety) in the space between the house and the big retaining wall. These are currently terminated in an IP65 box on the retaining wall that has nothing connected to it, and I'll just move this box so that it's inside the metal shed, something I can do without needing to disconnect the cables, as they already come up through what will be the shed base.

Right now our Sunamp was fully charged to its maximum capacity of ~9 kWH by about 11:00 this morning and we've been exporting well over 3 Kw for the last hour or so, so it looks as if today will be probably our best generation day since early December, probably be around 12 kWh, maybe more, which is well above average for this time of year. I've been sitting here watching the monitor, knowing that my car is now fully charged, the Sunamp is fully charged (after me having to do the usual daily reset to make the damned thing work) and we're still exporting at a fair old rate. Definitely need some batteries to be able to better use all the energy we generate!

This isn't where I bought mine from, but they stock the same type of washer-replacement flow restrictors in a range of different flow rates: https://www.aqva.co.uk/Taps/TapAccessories/FlowRestrictors

Completely off topic: My first ever flight in any aeroplane was a T21 Sedbergh, an air experience flight when I was in the ATC, at RAF Halton in 1965.

Depends on how much water you wish to draw off in one go, with no break for the accumulator to recharge. Also worth noting that an accumulator holds less than half its rated capacity, usually around 40 to 45% of the capacity is water, the rest is the air pressurising the bladder. If you have a 10 minute shower at 10 litres per minute, then a break that's long enough to allow the accumulator to recharge before the next one, then a 300 litre capacity accumulator might be OK. That will be able to supply around 120 to 140 litres of water at a near-constant 2 bar (if that's the peak inlet pressure), so would run a 10 litre per minute shower for ten minutes with some spare capacity. If you need to draw off more water in one go than this, then go to the next accumulator size up, a 500 litre one, which will give you a usable capacity of around 200 to 230 litres before needing to recharge, but this will take longer to recharge. Well worth doing some pressure and flow rate checks before deciding what to do though, so you have an understanding as to what your supply actually does through the day. Fitting a peak-reading pressure gauge (or an ordinary one fitted with a non-return valve and means of bleeding it off between measurements) is a good start, as that will tell you what the peak pressure is. If you get one of the gauges with a peak reading needle it's easy to just reset that several times through the day to get an idea as to how the supply pressure fluctuates. Also worth measuring the actual flow rate with a stop watch and 10 litre bucket from a wide open tap. That should give you a feel for how long an accumulator may need to recharge.

FWIW, we have a 6.25 kWp array, facing slightly west of south, inclined at 45 deg. I can count the days on one hand where we've generated more than about 3 kWp at any time, and the total generation so far since the beginning of December is about 200 kWh, so around 4.2 kWh/day, although there have been lots of days when we've generated next to nothing, which is pretty normal for this time of the year.

I did pretty much the whole design, plans, planning permission, building control submission etc myself, having had no previous experience of it at all, other than a bit of DIY over the years. I found it a steep learning curve, but as I was time rich and cash poor I didn't mind spending a lot of time getting to grips with everything, although this was helped by there being a year of enforced delay between having our offer for our plot accepted and actually exchanging contracts, because of some legal issues that the vendor needed to resolve. The one advantage I had was being reasonably competent at producing drawings, and being familiar with using CAD (which itself is a steep learning curve if you've not used it before). The one professional service I had was a topographical survey, which provided me with the base model from which I could produce pretty much every drawing. This cost around £400, IIRC, and the survey company provided me with an electronic copy of the file that I could just load into AutoCAD and work with straight away. The hardest bit of the whole process I found was getting the design to look right. Drawing up houses in CAD is easy, but not being an architect, or having any experience of architectural design, meant I struggled a lot to get a design that actually looked OK, as well as having all the functionality we wanted.

I've never seen the learning behaviour, but according to the manual it must have done it when I originally wired it up for the very first time. It doesn't do this every time it's powered up, though, as it seems to have a supercapacitor inside to allow the calibration to be remembered for a fair time. There is a procedure for getting it to recalibrate, which involves powering it on for 20 seconds, then powering it off again within one minute, then powering it on again, when it will go into the calibration mode. Mine's powered off except when there's a call for heat, and it opens up and starts to regulate within about 30 seconds at the most, until it has settled to its initial opening point. I've not seen the 2 minute turn on time that is given in the manual, and suspect that may be for the worst case condition As the manifold starts to heat up it will occasionally motor the valve for a few seconds as it readjusts, but that's all. When powered off the internal spring just winds the valve back to being closed again. Mine is screwed tight down on to the head, and isn't at all loose. The manual for them is here: https://www.salus-controls.eu/media/product/docs/thb23030-qb-we-v003-compressed.pdf

The simple answer is that they don't have any learning period as such, they just work to maintain a set temperature differential between the two sensors (they don't care which way around the sensors are fitted, either). The flashing LED means the motor is operating to open or close the valve a bit, so they will periodically do this as they motor the valve in order to maintain the temperature differential. The actual temperature differential they try to achieve depends on the flow temperature, so if it's below about 30 deg C (IIRC) it tries to maintain a 4 deg C differential, above 30 deg C and I believe it tries to maintain a 7 deg C differential.

Yes, that's what we have. OSB3 sarking boards, then 50 x 25 counterbattens nailed through along the line of the rafters, then non-tenting membrane laid over the counterbattens, then 50 x 25 slate battens nailed to the counterbattens over the membrane. It makes for a very solid roof, and because we have very deep (400mm) rafters, hung from a ridge beam, with no purlins, it also adds a lot of cross bracing and stiffness to the whole roof structure.

It's very much a regional thing. Sarking boards were always used with slate in Scotland, and it's become standard practice there to use sarking on any roof now. Our new-build bungalow in Scotland had a tiled roof, bit still had plywood sarking. I really like the idea of sarking boards, for a few reasons. They stiffen up the roof structure a fair bit, help to prevent wind-wash through the membrane and also reduce rain noise a bit. In addition they make life easier for the roofers, as there is a solid roof under their feet and they aren't reliant on just the strength of the battens when working up there.

Just the one. IIRC the result was 0.43 ACH @ 50 Pa, so massively under the Part L1A maximum allowable. This included some known air leaks at the door locks (easily fixed with the injection of some very thick, aerosol-applied, motorcycle chain lube) and leaks at two doors where the hinges and catches needed some adjustment (again, easily fixed, although a bit fiddly to do in the case of our French windows). I'm certain our airtightness is now better than when the house was air tested, but whether this makes any measurable difference to performance is debatable. I'm inclined to think that once you get down to below 0.6 ACH variations from changes in the wind speed outside impacting on the MVHR are probably a greater influence. I found that when balancing the MVHR there was a pretty wide degree of variability in flow rate as the wind gusted outside, presumably due to local small dynamic pressure differences between the external intake and exhaust. Not worth worrying about, but it was clear that this variation probably swamped any variation from air leakage.

The problem with that is that it tends to result in a greater variation of flow from one outlet when another is turned on. I had a pressure reducing valve fitted when we had the original thermal store, and found things were much more even when I took that out, when I fitted the first Sunamp (which didn't need the pressure reducer). Fitting restrictors in the tap fittings also has the advantage of lessening the interaction between outlets even more, not that this effect is very noticeable with a manifold distribution system, but every little helps. We've found that the ceramic insert taps, in particular, are a lot easier to control than before I fitted the flow restrictors, but it's perhaps worth noting that our water pressure is reasonably good; it's always between 2.5 bar and 3.5 bar.

Yes, or missing the strap altogether!

I've probably had three or four hand staple guns and all have had their problems, from being very fussy about the type of staples used to just randomly jamming and being awkward to clear out. A while ago I bought a cheap (around £40) air stapler and it's never once misfired or jammed, so I'd say go for one of those if you have access to compressed air. By the same token I have an air nail gun, and that has never jammed either, unlike the Paslode guns the guys who put our cladding up were using, which seemed to need pretty regularly cleaning in order to keep them working reliably. Mind you, I'm a big fan of air tools anyway, so may be biased.

If you need to drive a nail precisely into a hole, say in a strap or joist hangar, then you need a positive placement nailer, as they they do what their name suggests, put the nail exactly where it's needed. An ordinary first fix nailer isn't very accurate; it will put the nail in more or less where you want it, but can be a few mm out as there is no guide as to where the nail is actually going to go.

Spot on. I just fitted restrictor washers in the tap connectors, dead easy to do as they just replace the rubber or fibre washer that's in them as standard. Cheap too, and makes some taps a lot more comfortable to use, with less splashing. We had a building inspector who insisted on them being fitted, which I thought was a pain, but the only ones I've since removed are those on the shower and bath, as all the others reduced splashing and made the taps easier to use.

Both the same thing. All lithium chemistry cells are lithium ion, and all use a polymer electrolyte/separator, so the terms are interchangeable. The difference is all to do with the electrode chemistry, with LiCoO2 being lithium cobalt oxide, LiFePO4 being lithium iron phosphate and LiCoNiAl02 being lithium cobalt nickel aluminium oxide. There are other variations, too, like LiNiMnCoO2, lithium nickel manganese cobalt oxide, LiMn2O4 and LiMn2O3, both lithium manganese oxide and a few others.

This is the first part of the reply from our Building control Area Manager after I sent in the Air Test Certificate and EPC: This was followed by a request asking me if I'd provide a couple of hours on site to chat to some building inspectors, planning officers etc about how we'd gone about building a house that was so much better than the requirements in Part L1A...

I believe that the "throughput" is measured as equivalent charge/discharge cycle capacity, in kWh/day. Batteries are still, to a large extent, cycle life limited, with even the very best dropping capacity after a few thousand charge/discharge cycles. It's quite possible with a home battery system to have several charge/discharge cycles per day, if the house has a big PV system, and uses off-peak charging as well, so 1000 cycles per year seems possible under a fairly extreme use pattern. That's a fair bit more than most electric cars, that probably rarely go over around 300 cycles per year (judging from a month of ownership I'd say my electric car usage will be well under 100 charge/discharge cycles per year). i can understand Tesla being concerned about this, as the battery chemistry they use is inherently less capable of tolerating a large number of charge/discharge cycles than some other battery chemistries. For example, the Pylontech home batteries use LiFePO4 cells, that have more than double the cycle life of the LiCoNiAlO2 cells used by Tesla, but have a lower energy density and so are less well suited to high power electric vehicle use (FWIW my electric motor cycle originally used LiFe PO4 cells, I changed to using LiCoO2 cells and got more than 5 times the max discharge current and double the range from a pack 2/3rds the size, albeit with increased fire risk). For home storage I'm in no doubt at all that LiFePO4 cells offer far and away the best long term prospect out of all the lithium chemistries currently available. They are bigger and heavier for a given capacity and maximum discharge rate, but that doesn't really matter too much in a home storage application, where weight isn't really a critical issue.

Sod all to do with making one, just about knowing how they work so that one that does heating and cooling can be chosen. Not rocket science, just a matter of reading the specs and understanding that the manufacturers of ASHPs often hide the fact that they will cool just as well as they heat, perhaps because to be eligible for the RHI the cooling functionality has to be hidden, even though it's always there for a heating ASHP.