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The firework instruction phrase "light the blue touch paper and retire to a safe distance" comes to mind. It's been a real baptism of fire, however our builder says it's the worst time and it should settle down now. All in all it's been a productive week and almost all work has moved us forward. The digger arrived to dig out the raft area at 8am as requested and work got under way. We had muck lorries scheduled for Tuesday and it quickly became apparent that we did not have enough space on site to build a significant spoil heap. After a bit of phoning around found a local company who could supply vehicles. Our builder had asked us to take care of paying for the muck lorries which was fine by us, getting the lorry company to accept that it should be a zero rated VAT service was more difficult. Contacted HMRC and had a discussion and they were adamant that it should be zero rated and that if VAT was charged I could not reclaim it as it would have been at the wrong rate... Managed to resolve the problem in the end. Now we had lorries arriving and clearing the soil we were able to make real progress. Tuesday the rainwater harvesting tank arrived, we knew it was big and boy was it big! The tank needed to get dug in just 2.5M deep and 4M long, a very big hole. Fortunately the ground conditions were good and a nice clean hole was achieved without the need to grade the sides. By Wednesday we were ready for site setting out. An interesting activity and an example of technology being used because it's there rather than essential. Making sure the house position is millimetre perfect seems a bit over the top when string and triangulation would get it positioned within 10mm. Where it really does help is positioning services and getting drainage levels set. A second visit on Thursday had all the levels set and perimeters marked, by the time the guy left the site I had changed my opinion and consider it money well spent. More and more lorries to take muck away, the tally now sits at twelve loads and we are mostly done thank goodness as at £240 a 12 ton load for the clay it was making a bit of a whole in the budget, a quick calculation of the volumes validated the figures, so it really should not have been a surprise. In hindsight I'm surprised our builder didn't ask me to organise in more lories in the first place. If I do this again I'll order the lorries in advance rather than madly phoning round for spare capacity so that work can continue. The foul water pump arrived on Wednesday, having the levels all sorted from the site setting out I was able to cut the input to the tank, so it's all ready to get dropped into a hole once it's been dug and a concrete base is in place. The next task was to get all the drainage runs under the raft in place. With the raft due Monday and the builder having to go to another job on Friday to supervise another ICF concrete pour we were running out of time. Hopefully resolved the problem by getting a crew in on Saturday to get the drainage done. Stone for the raft substrate should star arriving first thing Monday, so fingers crossed we should have the raft ready for concrete which is booked for Thursday...we shall see.

It's really about having a high heat capacity internal structure, and a low thermal conductivity outer envelope, plus having an outer envelope that has a high enough decrement delay as to largely damp out the impact of diurnal external temperature variation.

It's a matter of definitions, really. Unless a house is actually sequestering carbon (making coal in the cellar or something) it can't really have a negative CO₂ emission rate, all it can do is produce energy which results in other people emitting less carbon. In the (not so) long run [¹] we need to get pretty close to zero emissions in total. When that happens any energy exports from the house will no longer be negative emissions as they'll only be displacing zero-carbon energy production at another place or time. That might well be a good thing to do but it'll not be negative CO₂ emissions. Suppose you have a house which doesn't export any energy at all but imports a small amount of electricity, say 1000 kWh evenly spread throughout the year so causing (going by my recent SSE bill which indicates above-average emissions per kWh) 300 kg of CO₂ emissions. If all the 25 million houses in the UK did that total household emissions would be 7.5 Mt. The house next door imports 3000 kWh during the winter but exports 4000 kWh in the summer so it's “net negative”. Still, if all the houses did that there'd be total emissions of 22.5 Mt during the winter (or a huge investment needed in technology (electricity -> gas, perhaps) to save the spare energy from the summer for use the next winter which will result not insignificant emissions in itself). So, yes, this “negative emissions” scenario does result in greater emissions. [¹] A lot less than the lifetime of houses we're building now.

I’m going to buy some popcorn ???

There's only one question that needs to be asked and answered about this, and that is, if "thermal mass" is real, then what are the units used to measure it? What would be a "good" value for "thermal mass", and what would be a poor value? Heat capacity can be measured, and has defined units, see here: https://en.wikipedia.org/wiki/Heat_capacity Thermal conductivity can also be measured, and has defined units, see here: https://en.wikipedia.org/wiki/Thermal_conductivity Decrement delay and the decrement factor are a useful measures of the interaction of heat capacity and thermal conductivity, in the context of the materials from which a house is constructed, and they can also be measured and defined: http://www.greenspec.co.uk/building-design/decrement-delay/ The thermal time constant of the inside of a building can also be measured, and has units: https://en.wikipedia.org/wiki/Time_constant#Thermal_time_constant I've yet to discover any units that can be used to describe "thermal mass", and frankly if it cannot be measured, then it isn't a real physical property, just a loose and ill-defined term to try to describe the complex interaction between heat capacity and thermal conductivity in the context of house building and the way that might relate to its thermal time constant. There is a Wikipedia entry (under review) https://en.wikipedia.org/wiki/Thermal_mass that attempts to describe "thermal mass", but it is flawed is several ways, not least the fact that it tries to tie the heat capacity of a structure to its mass, which is a poor way of trying to describe something, as mass is generally a poor indicator of the heat capacity of any material. For example, plaster has a heat capacity of around 1.09 J.g-1.K-1, yet concrete only has a heat capacity of 0.88 J.g-1.K-1, so a given mass of concrete will store less heat energy at a given temperature than plaster. Going even further, water has a heat capacity of around 4.18 J.g-1.K-1,so will store about 4.75 times as much heat energy as concrete for a given mass. Clearly, trying to use mass as a measure of the ability of a structure to store heat is not really valid, as there are very large variations in the heat capacity of a given mass, depending on the material that that mass consists of.

That's it, draw a bead on @Onoff! Leave me alone. I'm not well and feeling sorry for myself. Don't even have the strength for a witty retort! Christ knows where this came from, been going downhill all week. At first I thought it was the silicone fumes but I could have just as easily caught something on the Tube.

Or in @Onoff‘s world scraping the new silicone out ?

Do you know any of the local fire service, they will blast it for you.

If you get I-------- windows your frame will have done all its moving before they have finished the install!

If someone wants to define some units to measure it and get the Système International (d'unités) to accept those units, so that they have international acceptance, like those for heat capacity, thermal conductivity, etc, then I can't see a problem, other than the fact that the term "mass" is misleading. We already have all the units we need to define the comfort level of a house (and this is about perceived comfort, not energy conservation, no one considers "thermal mass" to be a measure of efficiency, AFAIK), perhaps the one most people might relate to is the thermal time constant, which is roughly how long it takes for the temperature inside the house to change when there is a change in outside temperature. Many would accept that living in a caravan can be uncomfortable because it heats up quickly on hot days and cools down quickly on cold days, and we tend to perceive that temperature variation as being uncomfortable. On the other hand, a stone building that stays at roughly the same temperature no matter what happens outside (within reason) is often seen as being more comfortable. The stone building isn't more thermally efficient than the caravan, it may well be a lot less thermally efficient, but it has a high heat capacity and that tends to even out variations in temperature, even though it may need a greater heat input to stay comfortable.

Where will the batteries be? In or adjacent to the house? Normally off-grid PV arrays are run at significantly lower voltages than on-grid ones - the maximum input voltage to an MPPT charge controller is typical 150 or 250 volts whereas grid-connected ones usually work around 600 volts or so. This means you usually want the PV array quite close to the battery otherwise you need a lot of copper wire; low voltage means higher current so thicker wire for a given amount of power transferred. Alternatively, you can AC-couple your system. You have a normal on-grid style inverter by the PV array then connect it to the house and battery via 230 volt AC lines, typically SWA buried in the ground for this sort of system. At the battery you then have an inverter/charger which establishes the 50 Hz mains frequency for your mini-grid and can even tweak the frequency up and down to control the amount of generation the PV's inverter puts out depending on the loads the house is taking and the state of charge of the batteries. There are not a lot of AC-coupled systems around. Paul at the end of the road has one.

I have scoured my various boxes of plumbing fittings and come up with a collection of fittings that will get me from my female BSP to 15mm copper, with a bit of stretching and a jubilee clip the hose should go on that. At the other end the hose fits properly to the outside tap at full mains pressure. I will give that a go tomorrow and see if I can flush this thing through. Using my hole in my top pipe as a guide. I will be happy if I can get a fountain spurting from that.

@Tennentslager I thought it looked like an old carpet from 70s, hopefully it will be warm. It was very itchy and scratchy to handle. @Redoctober UFH is an option for a suspended timber floor. I think @ProDave has done this on his I believe you use a dry screed mix on top of the subfloor, don't know whether the system differs. At the moment our heating is going to be electric and our stove. I want to utilise the firewood on our croft and hopefully next year make a peat stack. The house is classed as a crofter's cottage, so looking to use the croft to heat the house where possible. I want to use the electric radiators really just as a quick boost early in the morning. Hopefully the amount of south facing will provide sufficient solar gains for most of the day. Although it can be windy here, generally the temperatures are fairly mild through the winter and the recent snow was fairly rare. The house is well sheltered from the prevailing wind coming off those mountains behind the gable end and from those cold north winds behind the house. Here is a couple more that my wife took when I was working overtime in the office ?

Drain rods or Cobra rod must be easier than digging and then making holes in the pipe.

Drain rods without fittings (you may need to borrow some extra sets) will let you establish where the blockage is.

It’s not that it does not exist, people just use the wrong name/terminology .

John, have you reviewed the wealth of information on BH about thermal mass? It took me at least a year to get it..... Here's a shortened reading list.

Me too! I won’t be scraping mine out afterwards though. It will have to do.

I am a long way behind @Onoff in the silicone skills dept..... I am following his masterclass so I can learn this very difficult art

I think @Onoff should resilicone it everyday . It would be good practice.

Big ones yes, micro ones no. I saw inside an AP Micro and most of the back of it was anodised black aluminum as a huge heatsink as they are designed to sit behind the panel on the roof. Last time I checked they had one on test for something like 4 years 24x7 at 200% load and it was still going strong. As @JSHarris will attest to, this is more about decent components such as capacitors and removing any superfluous moving parts as that is what breaks first ....

Some do, yes. Our IP65 rated one doesn't, as it's designed to be fitted outside, so just has a large finned heat sink with a cover over it, but inverters intended for use indoors can have cooling fans. I think there's probably an advantage in having passive cooling, as fans can and do fail. The disadvantage of passive cooling is that the unit tends to be a bit larger.

You can get outdoor rated PV inverters, we have one bolted to the back wall of our house. I believe that having the inverter mounted in a shaded location outside is likely to result in longer inverter life, as the most common cause of inverter failure is failure of the internal commutation capacitors. These have a life that is highly dependent on temperature, and running them a few degrees cooler can have a big impact on making them last much longer (I believe that it's something like a 10°C temperature reduction to almost double the working life).

It's so common I'm beginning to wonder why SI haven't yet invented a new unit for it. I've given up pointing out that mass has sod all to do with the thermal time constant of the building, and that it's the combination of heat capacity and thermal conductivity (both of which have units and can be measured and so quantified) of the structure that are the dominant factors. Easy enough to build a net zero energy/carbon home, ours is actually net negative energy/carbon, in that it both generates more energy than it uses and is, in effect, a CO2 sink (the EPC reports the CO2 "emissions" as being -0.9 tonnes per year). Given that the structure of our house is an off-the-shelf build system, then there's no real reason for more houses not to be built to a similar standard.

?They mention thermal mass !!!!!! (Don’t tell Jeremy?).

Scraping the old silicone out.