Jeremy Harris

One or two have tried this, using things like a very large central water tank as a seasonal store. On another forum, years ago, a few of us discussed ways of using a large tank filled with a phase change material, as used in the Sunamp (sodium acetate) or something simpler like paraffin wax. Somewhere I've read an article (might have been in an old copy of Passive House magazine) about a house that had a very thick column up the centre, with a helical staircase curved around the outside. This column was a massive, well-insulated, water tank that acted as a seasonal store. Even using water, that can store around 4 times as much heat as concrete for a given mass, it's challenging to make a tank big enough to work as a seasonal store. You should be able to go carbon negative with a bit of PV. Our house came out with an EPC of A107 and a CO2 of -0.9 tonnes/year and we're not PH certified. The thing that made the difference was the 6.25 kWp PV array.

Heat storage isn't proportional to mass, irrespective of the material. The key parameters are specific heat capacity (see here: https://en.wikipedia.org/wiki/Specific_heat_capacity) and thermal conductivity (see here: https://en.wikipedia.org/wiki/Thermal_conductivity) Materials with a high mass do not necessarily store the most heat. For example: Gypsum (plaster/plasterboard) = 1,090 J/kg.K Concrete = 880 J/kg.K Water = 4,182 J/kg.K From the above it's clear that concrete has a significantly lower specific heat than other materials, which pretty much proves that mass is not a good indicator of the ability of a material to store heat.

Will do. The fibre arrived in the post this morning, so I'm going to try and see if I can rig something up later today or tomorrow.

There's nothing to move in there, as there are no moving parts behind a switch. Also, the wires are stiff enough to stay where they are put when folded into the box.

No, definitely not the case. When I was the Lynx IPTL the Chinook IPTL was on the floor below me. The software was definitely supplied with the cabs as a condition of the deal. The price was a lot lower than if the normal practice of buying the arframes and fitting UK spec avionics had been used, and there was a time saving. SF were keen to get the cabs into service ASAP, to meet an urgent operational requirement, so the normal procurement process by DPA Abbeywood was pretty much bypassed. The result was that when the cabs were delivered, Boscombe Down refused (quite rightly, IMHO) to give them a CA Release. The cabs were grounded and locked away in a hangar for years, until someone found the money to retrofit them with Mk 2 cockpits and get them into service. The accident on the Mull of Kintyre was an entirely different aircraft type, the much older HC Mk 1 (converted to HC Mk 2), without the glass cockpit and associated software that caused the problems with the Mk 3 CA Release. The instrument panel on ZD576 was "clockwork", with old-style analogue instruments. Some of the families continued (still do, I think) to hold the view that there was an unknown FADEC problem with the HC Mk 1, but frankly, having seen pretty much everything that went into the FADEC investigation (it was directly related to our own FADEC concerns with the CTS800) I'm very far from convinced that the ZD576 accident was anything other than CFIT as a consequence of pilot error. There was a long chain of mistakes and pressure applied to the crew that led to them flying in conditions that were well below minima for that type.

Yes, I just used Wago 773s tucked into the back of the boxes. Using a deep box just gives a bit more room to work in.

Bit like the pineapple house at the Lost Gardens of Heligan: https://www.heligan.com/explore/news/the-story-of-the-10000-pineapple

I'm convinced there's a bit of subconscious influence at work when it comes to whether or not we feel cool. 21°C indoors when it's dark, grey and wet outside feels too cool. the same temperature indoors when it's bright and sunny feels fine. We've noticed that this effect is far more pronounced in the early evening, for some reason. I guess we must sense the change in light level for the time of day and that somehow recalibrates how we feel temperature.

Me too. I fitted deep back boxes for all the light switches, just to make it easier to fit the loop-in-switch wires and wagos. Twice I've had reason to be thankful for that decision when I've shifted lights around.

Yes, my error. It's their solar thermal system that seems to need maintenance. Last time I fixed it was when the pump controller packed up, before that it was air in the system (might have been the pump controller starting to fail and letting it occasionally overheat, looking back).

I've only bought one Sunamp, I've spent nothing on getting it working, and Sunamp have now sorted out the controller problems, it seems. Our PV system has been faultless, unlike my neighbours solar PV system that I've now repaired twice, and which had been repaired three times prior to that. That's in an eight year period. My neighbours PV system (same age as the solar thermal system) has been as faultless as ours. A read through some of the renewable energy forums quickly shows that solar thermal systems have a lot more maintenance issues than PV systems. Not much use in having an 8 kWp solar thermal system that can only heat hot water, and then sits there doing sod all for several hours a day. At least a PV system can heat the hot water as well as offset the cost of other loads in the house during all the hours of daylight. Even at £2k (which seems very cheap compared to the cost of a Navitron evacuated tube system I costed up a few years ago) that would have bought well over 13,000 kWh of electricity to heat hot water directly with an immersion 13,000 kWh would be around 6 years worth of hot water at peak rate electricity prices, or around 10 years at off peak electricity prices. When I checked solar thermal prices about a year ago they seemed no cheaper than they were when I looked at them around 2012. I've just had a quick look, and a ~2 kWp solar thermal system (30 off, 58mm tubes) system costs about £1.67k, plus delivery, plus installation.

It's a question of evaluating the real, versus imaginary, risk. If the DHW system is closed, so that disinfected mains pressure water comes in and hot water comes out, with no means for anything to enter the system, then the legionella risk is miniscule, as there's no path for the bacteria to make their way into the system. If the DHW is fed from an open cold water tank, or a water source that has not been disinfected, then there's clearly a significant risk that bacteria may be able to make their way into the DHW system and then multiply. Similarly, if the DHW only has a small volume, such as a thermal store or Sunamp, where the only volume of hot water is in the heat exchanger and pipes, then the risk is also small, as the water will be flushed through often enough to reduce the risk of any bacteria multiplying.

I guessed you may have been a radar person, being where you are. I was OiC of the ranges at DERA Funtington and DERA Fraser during the late 90's, when they were still a part of DERA Above Water Systems at Portsdown.

Early in my career I spent several years modelling the underwater plunge behaviour of air launched torpedoes, to try and predict the 3D underwater trajectory for the short time between water entry and motor start up, so the range of attitudes, depth and velocities in all axes could be predicted (the aim was to inform the guidance control people of the sort of start up conditions they would have to deal with). Back then we were coding in Fortran 77, using an ICL located 200 miles away, that compiled our code (transmitted via a 300 baud teleprinter link) overnight. Each day started by going through the errors flagged in the printouts that had piled up overnight, before trying to fix the code and move on to the next section. The best bit was validating the model, as that meant designing and building a pretty robust sensor and data logger (using 1/2" magnetic tape and missile data recorders) that we fitted inside dummy torpedoes that were released over as wide a range of drop conditions as we could manage. It did mean I got to fly a lot, though, which led to a shift to a career in flight test. To get the highest release speeds, we had to chuck the things out of a Canberra, doing around 400kts at maybe 150ft ASL. Lots of fun...

Depends. A PV system with microinverters may well last well over 25 years, as they don't have the potential issue with electrolytic capacitors ageing. A conventional inverter mounted in a cool location may well last 20 years or more, as electrolytic capacitor life is very temperature dependent. A 50,000 hour life capacitor at 50°C may well have four times that life at 25°C, for example.

We've noticed the same thing over the past few days, as we've had a sustained period of fairly low temperature. Here the outside temperature hasn't risen above 16°C for about four days now, and has been down around 10°C to 12°C overnight. That has pulled the house temperature down slowly, to the point where our UFH came on the night before last (it's set to come on at 21°C). The house climbed back up to about 22°C and is sitting close to that now, some 24 hours or so since the heating last fired up. I find our house takes a couple of days to react to a sustained drop in outside temperature, and then takes half a day to warm up when the heating comes on after having been off for a long time. Ideally I'd like to have the controls linked to the weather forecast (if it was always accurate) so that the heating could come on several hours before a predicted period of sustained cool weather. Not that easy to do, although I believe that @TerryE has been working on doing this, with his home brew control system. If there was a reliable off-the-shelf predictive controller I think I'd seriously consider fitting one, but I'm not sure there is at the moment.

My personal view is that it's best to keep things as simple and reliable as possible, and also to keep the initial capital cost down to as low a level as meets all your requirements. Modelling is great fun (I spent months doing it...), but ultimately there are lots of parameters that are not easy to fully model. For example, solar thermal hot water can only ever deliver useful energy when the temperature of the collector exceeds the temperature of the hot water storage system. This means that solar thermal, despite having a high efficiency, can only usefully heat water once the collector has risen to a high enough temperature, and this depends on both the insolation level and the overnight cold soak temperature, so is not easy to model. What happens in practice is that there is a variable delay in the morning between the sun coming up and the system starting to deliver sensible heat to the hot water system, and that delay is also dependent on the temperature of the hot water storage system at that time (which will vary with pattern of use). By contrast, PV has a lower efficiency, but doesn't care about temperature, if anything it will work more efficiently when the panels are cold first thing in the morning. PV will always transfer sensible heat to the hot water storage system as long as electricity is being generated and fed to the heating element. There is no dependence on either the outside temperature or the temperature of the hot water storage system (as long as the storage system thermostat is calling for heat). In terms of cost, then PV is generally a lot cheaper through life than solar thermal, and is maintenance free. Last time I checked, the installation cost of solar thermal was a lot higher than that for PV, on a Watt-for-Watt comparison basis. There's also the fact that solar thermal is a one trick pony; all your investment can do is heat hot water. A PV system can heat hot water, supply power to the house and export power to the grid.

Galvanised conduit may be a real pain to run along that fence, plus it's not easy to pull cables through long runs of the stuff. If it were me I'd just cleat SWA to the fence and perhaps add a batten alongside it to give a bit of added impact and rub protection from stray branches. As to legality, whilst it's true that the wiring regs are only guidance, and not the law, this is a Part P notifiable job (in England and Wales) and failure to comply with building regs may be unlawful.

It's a judgement call as to whether the cable is adequately protected in that individual set of circumstances, as the regs don't clearly define when it's OK to clip a particular type of cable to a wall or fence. My rule of thumb is based on whether something can bash into the cable easily or not. For example, I'd not run a non-mechanically protected cable along a fence or wall where stuff could bash into it, or be leant up against it, but I'd have no problem running a length of NYY-J along a fence or wall at a height where damage was a pretty remote possibility. I'd have no problem with surface mounting SWA in pretty much any situation, except one where it might see severe impact, or regular mechanical contact, when I'd use a length of metal conduit over the exposed area. Areas that bother me are situations like walls at the end of a drive, where a car might accidentally crush a cable, or walls or fences where things like bikes might be leant. On fences I've clipped NYY-J underneath arris rails before now, and pretty much every car charge point that's been professionally installed in recent years will be wired with NYY-J clipped to a house or garage wall. Some may use SWA, but from what I've seen they are the exception, rather than the rule, as it seems that many of the grant-funded installers prefer to use NYY-J (probably because it's quicker to terminate).

My father was completely technically illiterate. He never even learned to drive, and was hopeless with anything practical. My mother was the one that did all the decorating, drove a car (and stripped and repaired it when needed) and fixed stuff like our bikes. My father was incredibly good at mental arithmetic, though, and could do pretty complex sums almost instantly, without needing to write anything down.

Perhaps worth mentioning the correct way to wire a plug? For those who've not wired one, then, looking at the plug with the top off, the brown wire goes to the (line) fuse terminal on the right, the blue wire goes to the left (neutral) pin terminal and the green and yellow wire goes to the top (earth) pin terminal. Only strip the wires back just enough to fit the terminals, and if the flex is thin, then twist it and double it over, making sure no loose strands poke out of the terminal. For enhanced safety, try to make the green and yellow wire slightly longer, so that if the cable grip fails and the cable is tugged, the earth wire will be the last wire to come free. Always make sure that the cable grip is tightly clamped on the outer insulation of the flex, not the individual cores.

I can very clearly remember my mother teaching me to wire a plug when I probably about 8 or 9 years old. "Always remember, "red on the right" and make sure the earth wire is longer than the others". I still think of it whenever I wire a plug up now, nearly 60 years later (and even though the colours are now different).

Yes, no problem with wiring that to a suitably fused plug with a length of flex. A 3 A fuse in the plug would be OK to protect the cable.

You most probably won't have much need for many (if any) maintenance free junctions. There are none in our installation, for example. When I've had to use one in the past I've used a Wagobox and Wagos, as they are cheap and the Wagos are probably the most useful general connector around. This is a Wagobox: https://www.screwfix.com/p/wagobox-junction-box/7355f and this is a typical Wago connector (there are several variations): https://www.screwfix.com/p/4-way-push-wire-connector-773-series-pack-of-100/27374

SWA is usually the easiest solution, as it provides mechanical protection and it's resistant to sunlight, so can just be clipped along a fence or wall without the need for anything other than adequate electrical protection. If you can ensure the run is adequately mechanically protected, then you could use NYY-J, which is very slightly easier to terminate, is rated for permanent outdoor use, but doesn't offer the degree of mechanical protection that SWA gives. You can opt to bury SWA directly, whereas NYY-J is only OK for burial if mechanically protected, so if opting to put this run underground then SWA is the sensible choice. There's not much in it price wise, I think. The important bit is to ensure that the cable and the installations that it supplies are adequately protected against overload and possible earth faults, and that the earthing at the installations is adequate. If this run of cable is quite long then I'd be inclined to look at running the installations in the shed/greenhouse from their own local earth rod and RCD, as TT installations. That avoids having to export the earth from the house supply and is often a safer option if the length of cable is quite long.